RESEARCH CENTRE

Inria Centre
at Université Grenoble Alpes

2023
ACTIVITY REPORT

IN PARTNERSHIP WITH:

CNRS, Université de Grenoble Alpes

Project-Team

TRIPOP

Modeling, Simulation and Control of
Nonsmooth Dynamical Systems

IN COLLABORATION WITH: Laboratoire Jean Kuntzmann (LJK)

DOMAIN

Applied Mathematics, Computation and
Simulation

THEME

Optimization and control of dynamic
systems

Contents

Project-Team TRIPOP

1 Team members, visitors, external collaborators

2 Overall objectives

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 General scope and motivations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 A flavor of nonsmooth dynamical systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Nonsmooth Dynamical systems in the large . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Nonsmooth systems versus hybrid systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 Numerical methods for nonsmooth dynamical systems . . . . . . . . . . . . . . . . . . . . .

3 Research program

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Axis 1: Nonsmooth simulation and numerical modeling for natural gravitational risk in
mountains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Rockfall trajectory modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.2 Modeling and simulation of gravity hazards (debris flows, avalanches and large-scale
rock flows) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.3 Axis 2: Modeling, simulation and control of non-smooth dynamical systems.

9
3.2.3 Data-driven modelling for prediction and mitigation of gravity hazards . . . . . . . . 10
. . . . . . . . 10
3.3.1 Modeling, analysis and numerical methods . . . . . . . . . . . . . . . . . . . . . . . . 10
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.2 Automatic Control

1

2

3
3
3
4
7
7
7

8
8

8
9

4 Application domains

5 Social and environmental responsibility

14

14

6 New software, platforms, open data

14
6.1 New software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.1 SICONOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7 New results

7.1 Numerical Modeling for natural risk in mountains

18
. . . . . . . . . . . . . . . . . . . . . . . . 18

7.1.1 Semi-smooth Newton method for non-associative plasticity using the bi-potential

approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7.1.2 Energy conservation and dissipation properties for elastodynamics with contact

impact and friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.3 Numerical modeling of rockfall trajectory . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.4 Numerical modeling of fracture in solids . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1.5 Variational approach for nonsmooth elasto-plastic dynamics with contact and impacts 19
7.1.6 Bayesian interface based calibration of a novel rockfall protection structure modelled

in the Non-smooth contact dynamics framework . . . . . . . . . . . . . . . . . . . . . 20
7.2 Systemic risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
. . . . . . . . . . . . . . . . . . . . . . . . 20
7.3 Numerical solvers for frictional contact problems.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.4 Analysis and Control of Set-Valued Systems
7.4.1 Discrete-time implicit Euler sliding-mode control
. . . . . . . . . . . . . . . . . . . . 21
7.4.2 Optimal control of Lagrangian complementarity systems . . . . . . . . . . . . . . . . 21
7.4.3 Robot-object underactuated nonsmooth dynamical systems . . . . . . . . . . . . . . 21
7.4.4 Modelling and control of overhead cranes (OC) . . . . . . . . . . . . . . . . . . . . . . 22
7.4.5 Bifurcations of equilibria in LCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.4.6 Nonlinear networks with set-valued coupling . . . . . . . . . . . . . . . . . . . . . . . 22
7.4.7 Passive systems interconnections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.4.8 Tracking control of Linear Complementarity Systems . . . . . . . . . . . . . . . . . . . 22

8 Bilateral contracts and grants with industry

23
8.1 Bilateral grants with industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

9 Partnerships and cooperations

9.2 International research visitors

23
9.1 International initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1.1 Participation in other International Programs . . . . . . . . . . . . . . . . . . . . . . . 23
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.2.1 Visits of international scientists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.3.1 Horizon Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.4 National initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.5 Regional initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

9.3 European initiatives

10 Dissemination

27
10.1 Promoting scientific activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1.1 Scientific events: selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1.2 Journal
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1.3 Invited talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1.4 Leadership within the scientific community . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1.5 Scientific expertise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.2 Teaching - Supervision - Juries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.2.1 Teaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.2.2 Supervision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.2.3 Juries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.3 Popularization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.3.1 Internal or external Inria responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . 29

11 Scientific production

29
11.1 Major publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.2 Publications of the year
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.3 Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
11.4 Cited publications

Project TRIPOP

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Project-Team TRIPOP

Creation of the Project-Team: 2019 June 01

Keywords

Computer sciences and digital sciences

A6.1.1. – Continuous Modeling (PDE, ODE)

A6.1.4. – Multiscale modeling

A6.2.6. – Optimization

A6.4.1. – Deterministic control

A6.4.3. – Observability and Controlability

A6.4.4. – Stability and Stabilization

A6.4.5. – Control of distributed parameter systems

A6.4.6. – Optimal control

A6.5.1. – Solid mechanics

A6.5.4. – Waves

Other research topics and application domains

B3.3.1. – Earth and subsoil

B3.4.1. – Natural risks

B5.2.1. – Road vehicles

B5.2.3. – Aviation

B5.2.4. – Aerospace

B5.4. – Microelectronics

B5.6. – Robotic systems

B7.1.2. – Road traffic

B9.5.2. – Mathematics

B9.5.5. – Mechanics

B9.11.1. – Environmental risks

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Inria Annual Report 2023

1 Team members, visitors, external collaborators

Research Scientists

• Vincent Acary [Team leader, INRIA, Senior Researcher, HDR]

• Franck Bourrier [INRAE, Researcher, Convention w/ UGA, HDR]

• Bernard Brogliato [INRIA, Senior Researcher, HDR]

• Olivier Goury [INRIA, Researcher]

• Felix Miranda Villatoro [INRIA, ISFP]

• Arnaud Tonnelier [INRIA, Researcher, HDR]

Faculty Members

• Paul Armand [UNIV LIMOGES, Professor, In delegation, HDR]

• Guillaume James [GRENOBLE INP, Professor, HDR]

Post-Doctoral Fellows

• Nicholas Anton Collins-Craft [INRIA, Post-Doctoral Fellow]

• Ritesh Gupta [INRIA, Post-Doctoral Fellow, from Dec 2023]

• Emilie Rouzies [INRIA, Post-Doctoral Fellow, from Mar 2023 until May 2023]

PhD Students

• Louis Guillet [INRIA]

• Hoang Minh Nguyen [INRIA]

• Matteo Oziol [GRENOBLE INP, from Oct 2023]

• Quang Hung Pham [GRENOBLE INP]

• Florian Vincent [INRIA, from Oct 2023]

• Aya Younes [UGA]

Technical Staff

• Franck Pérignon [CNRS, Engineer]

Interns and Apprentices

• Mustapha Adiouane [INRIA, Intern, from May 2023 until Sep 2023]

• Johnny Godoy Sanchez [INRIA, Intern, until Apr 2023]

• Pascal Nardi [ENS DE LYON, Intern, from May 2023 until Jun 2023]

Administrative Assistant

• Diane Courtiol [INRIA]

Project TRIPOP

Visiting Scientists

• Fernando Castanos Luna [CINVESTAV-IPN MEXICO, from Sep 2023]

3

• Christophe Prieur [CNRS]

2 Overall objectives

2.1 Introduction

The joint research team, TRIPOP, between INRIA Grenoble Rhône–Alpes, Grenoble INP and CNRS,
part of the Laboratoire Jean Kuntzmann (LJK UMR 5224) is mainly concerned with the modeling, the
mathematical analysis, the simulation and the control of nonsmooth dynamical systems, with a strong
application to modeling natural environmental risks in mountains.

Nonsmooth dynamics concerns the study of the time evolution of systems that are not smooth in the
mathematical sense, i.e. systems that are characterized by a lack of differentiability, either of the mappings
in their formulations, or of their solutions with respect to time. In mechanics, the main instances of
nonsmooth dynamical systems are multibody systems with Signorini unilateral contact, set-valued
(Coulomb-like) friction and impacts. In electronics, examples are found in switched electrical circuits
with ideal components (diodes, switches, transistors). In control, nonsmooth systems arise in the sliding
mode control theory and in optimal control. Many examples can also be found in cyber-physical systems
(hybrid systems), in transportation sciences, in mathematical biology or in finance. For the next four
years, the team is organized along two research axes: 1) nonsmooth simulation and numerical modeling
for natural gravitational risks in mountains and 2) modeling, simulation and control of nonsmooth
dynamical systems. The idea of this restructuring is to put forward a strong application axis for which
there is a strong academic research dynamic in the Grenoble region and a network of socio-economic
actors very interested in an industrial transfer of digital science methods on these subjects. The second
axis takes up the main themes of the former axes of the TRIPOP project by updating them after the first
four years.

2.2 General scope and motivations

Nonsmooth dynamics concerns the study of the time evolution of systems that are not smooth in
the mathematical sense, i.e., systems that are characterized by a lack of differentiability, either of the
mappings in their formulations, or of their solutions with respect to time. The class of nonsmooth
dynamical systems recovers a large variety of dynamical systems that arise in many applications. The
term “nonsmooth”, like the term “nonlinear”, does not precisely define the scope of the systems we are
interested in but, and most importantly, they are characterized by the mathematical and numerical
properties that they share. To give more insight into nonsmooth dynamical systems, we give in the
following a very brief introduction of their salient features. For more details, we refer to [58, 26][2][71, 42,
61].

As we have indicated there are many applications to the methods of nonsmooth dynamics. We
have chosen a strong particular application for this technique of nonsmooth dynamics which is that of
natural gravity risk in the mountains. The choice of this application is particularly motivated by global
climate change which has increased the number of rockfall and landslide events very significantly in
recent decades. Especially, the effects of melting permafrost, increased rainfall and rapid temperature
changes means that alpine regions are particularly at risk [82, 70]. Another important interest is the
strong academic research dynamics in the Grenoble region and a network of socio-economic actors very
interested in an industrial transfer of digital science methods on these subjects. The team will conduct
research on the mechanical modeling and simulation of natural hazards in mountains (floods and debris
flows, block falls, glacial hazards), bringing new software development in a high performance computing
(HPC) framework.

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Inria Annual Report 2023

Figure 1: Complementarity condition 0 ≤ y ⊥ λ ≥ 0.

2.3 A flavor of nonsmooth dynamical systems

As a first illustration, let us consider a linear finite-dimensional system described by its state x(t ) ∈ IR n
over a time-interval t ∈ [0, T ]:

˙x(t ) = Ax(t ) + a, A ∈ IR n×n, a ∈ IR n,

subjected to a set of m inequality (unilateral) constraints:

y(t ) = C x(t ) + c ≥ 0,

C ∈ IR m×n, c ∈ IR m.

(1)

(2)

If the constraints are physical constraints, a standard modeling approach is to augment the dynamics
in (1) by an input vector λ(t ) ∈ IR m that plays the role of a Lagrange multiplier vector. The multiplier
restricts the trajectory of the system in order to respect the constraints. Furthermore, as in the continuous
optimization theory, the multiplier must be signed and must vanish if the constraint is not active. This is
usually formulated as a complementarity condition:

0 ≤ y(t ) ⊥ λ(t ) ≥ 0,

(3)

which models the one-sided effect of the inequality constraints. The notation y ≥ 0 holds component–
wise and y ⊥ λ means y T λ = 0. All together we end up with a Linear Complementarity System (LCS) of
the form,






˙x(t ) = Ax(t ) + a + B λ(t )
y(t ) = C x(t ) + c
0 ≤ y(t ) ⊥ λ(t ) ≥ 0

(4)

where B ∈ IR n×m is the matrix that models the input generated by the constraints. In a more general way,
the constraints may also involve the Lagrange multiplier,

y(t ) = C x(t ) + c + Dλ(t ) ≥ 0,

D ∈ IR m×m,

leading to a general definition of LCS as






˙x(t ) = A x(t ) + a + B λ(t )
y(t ) = C x(t ) + c + D λ(t )
0 ≤ y(t ) ⊥ λ(t ) ≥ 0.

(5)

(6)

The complementarity condition, illustrated in Figure 1 is the archetype of a nonsmooth graph that we
extensively use in nonsmooth dynamics. The mapping y (cid:55)→ λ is a multi-valued (set-valued) mapping,
that is nonsmooth at the origin. It has many interesting mathematical properties and reformulations

Project TRIPOP

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that come mainly from convex analysis and variational inequality theory. Let us introduce the indicator
function of IR + as

Ψ

IR + (x) =

(cid:40)

0 if x ≥ 0,
+∞ if x < 0.

(7)

This function is convex, proper and can be sub-differentiated [64]. The definition of the subdifferential of
a convex function f : IR m → IR is defined as:

∂ f (x) = (cid:169)x

⋆ ∈ IR m | f (z) ≥ f (x) + (z − x)

⊤

x

⋆

, ∀z(cid:170) .

A basic result of convex analysis is

0 ≤ y ⊥ λ ≥ 0 ⇐⇒ −λ ∈ ∂Ψ

IR + (y)

(8)

(9)

that gives a first functional meaning to the set-valued mapping y (cid:55)→ λ. Another interpretation of ∂Ψ
based on the normal cone to a closed and nonempty convex set C :

IR + is

NC (x) = (cid:169)v ∈ IR m|v

⊤

(z − x) ≤ 0 for all z ∈ C (cid:170) .

It is easy to check that ∂Ψ

IR + (x) = NIR + (x) and it follows that

0 ≤ y ⊥ λ ≥ 0 ⇐⇒ −λ ∈ NIR + (y).

Finally, the definition of the normal cone yields a variational inequality:

0 ≤ y ⊥ λ ≥ 0 ⇐⇒ λ⊤

(y − z) ≤ 0, ∀z ≥ 0.

(10)

(11)

(12)

The relations (11) and (12) allow one to formulate the complementarity system with D = 0 as a
differential inclusion based on a normal cone (see (15)) or as a differential variational inequality. By
extending the definition to other types of convex functions, possibly nonsmooth, and using more general
variational inequalities, the same framework applies to the nonsmooth laws depicted in Figure 2 that
includes the case of piecewise smooth systems.

The mathematical concept of solutions depends strongly on the nature of the matrix quadruplet
(A, B,C , D) in (6). If D is a positive definite matrix (or a P -matrix), the Linear Complementarity problem

0 ≤ C x + c + Dλ ⊥ λ ≥ 0,

(13)

admits a unique solution λ(x) which is a Lipschitz continuous mapping. It follows that the Ordinary
Differential Equation (ODE)

˙x(t ) = Ax(t ) + a + B λ(x(t )),

(14)

is a standard ODE with a Lipschitz right-hand side with a C 1 solution for the initial value problem. If
D = 0, the system can be written as a differential inclusion in a normal cone as

− ˙x(t ) + Ax(t ) + a ∈ B NIR + (C x(t )),

(15)

that admits a solution that is absolutely continuous if C B is a definite positive matrix and the initial
condition satisfies the constraints. The time derivative ˙x(t ) and the multiplier λ(t ) may have jumps and
are generally considered as functions of bounded variations. If C B = 0, the order of nonsmoothness
increases and the Lagrange multiplier may contain Dirac atoms and must be considered as a measure.
Higher–order index, or higher relative degree systems yield solutions in terms of distributions and
derivatives of distributions [37].

A lot of variants can be derived from the basic form of linear complementarity systems, by changing
the form of the dynamics including nonlinear terms or by changing the complementarity relation by
other multivalued maps. In particular the nonnegative orthant may be replaced by any convex closed
cone K ⊂ IR m leading to complementarity over cones

⋆ ∋ y ⊥ λ ∈ K ,

K

(16)

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Inria Annual Report 2023

(a) Saturation

(b) Relay

(c) Relay with dead zone

Figure 2: Examples of multivalued piecewise linear models

where K

⋆

its dual cone given by

⋆ = (cid:169)x ∈ IR m | x

⊤

y ≥ 0 for all y ∈ K (cid:170) .

K

(17)

In Figure 2, we illustrate some other basic maps that can be used for defining the relation between λ
and y. The saturation map, depicted in Figure 2(a) is a single valued continuous function which is an
archetype of a piece-wise smooth map. In Figure 2(b), the relay multi-function is illustrated. If the upper
and the lower limits of λ are respectively equal to 1 and −1, we obtain the multivalued sign function
defined as

Sgn(y) =






1,
[ − 1, 1],
−1,

y > 0
y = 0
y < 0.

(18)

Using again convex analysis, the multivalued sign function may be formulated as an inclusion into a
normal cone as

More generally, any system of the type,

λ ∈ Sgn(y) ⇐⇒ y ∈ N[−1,1](λ).






˙x(t ) = Ax(t ) + a + B λ(t )
y(t ) = C x(t ) + a
−λ(t ) ∈ Sgn(y(t )),

can reformulated in terms of the following set-valued system






˙x(t ) = Ax(t ) + a + B λ(t )
y(t ) = C x(t ) + c
−y(t ) ∈ N[−1,1]m (λ(t )).

(19)

(20)

(21)

The system (21) appears in a lot of applications; among them, we can cite the sliding mode control,
electrical circuits with relay and Zener diodes [33], or mechanical systems with friction [26].

Though this class of systems seems to be rather specific, it includes as well more general dynamical
systems such as piecewise smooth systems and discontinuous ordinary differential equations. Indeed,
the system (20) for scalars y and λ can be viewed as a discontinuous differential equation:

˙x(t ) =

(cid:189) Ax + a + B
Ax + a − B

if C x + c > 0
if C x + c < 0.

(22)

One of the most well-known mathematical frameworks to deal with such systems is the Filippov the-
ory [58] that embeds the discontinuous differential equations into a differential inclusion. In the case of a

Project TRIPOP

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single discontinuity surface given in our example by S = {x | C x + c = 0}, the Filippov differential inclusion
based on the convex hull of the vector fields in the neighborhood of S is equivalent to the use of the
multivalued sign function in (20). Conversely, as it has been shown in [38], a piecewise smooth system
can be formulated as a nonsmooth system based on products of multivalued sign functions.

2.4 Nonsmooth Dynamical systems in the large

Generally, the nonsmooth dynamical systems we propose to study mainly concern systems that possess
the following features:

(i) A nonsmooth formulation of the constitutive/behavioral laws that define the system. Examples
of nonsmooth formulations are piecewise smooth functions, multi–valued functions, inequality
constraints, yielding various definitions of dynamical systems such as piecewise smooth systems,
discontinuous ordinary differential equations, complementarity systems, projected dynamical
systems, evolution or differential variational inequalities and differential inclusions (into normal
cones). Fundamental mathematical tools come from convex analysis [83, 63, 64], complementarity
theory [54], and variational inequalities theory [57].

(ii) A concept of solutions that does not require continuously differentiable functions of time. For
instance, absolutely continuous, Lipschitz continuous functions or functions of local bounded
variation are the basis for solution concepts. Measures or distributions are also solutions of interest
for differential inclusions or evolution variational inequalities.

2.5 Nonsmooth systems versus hybrid systems

The nonsmooth dynamical systems we are dealing with, have a nonempty intersection with hybrid sys-
tems and cyber-physical systems, as is briefly discussed in Sect. 3.3.1. Like in hybrid systems, nonsmooth
dynamical systems define continuous-time dynamics that can be identified with modes separated by
guards, defined by the constraints. However, the strong mathematical structure of nonsmooth dynamical
systems allows us to state results on the following points:

(i) Mathematical concept of solutions: well-posedness (existence, and possibly, uniqueness properties,

(dis)continuous dependence on initial conditions).

(ii) Dynamical systems theoretic properties: existence of invariants (equilibria, limit cycles, periodic
solutions,. . . ) and their stability, existence of oscillations, periodic and quasi-periodic solutions
and propagation of waves.

(iii) Control theoretic properties: passivity, controllability, observability, stabilization, robustness.

These latter properties, that are common for smooth nonlinear dynamical systems, distinguish the
nonsmooth dynamical systems from the very general definition of hybrid or cyber-physical systems [40,
62]. Indeed, it is difficult to give a precise mathematical concept of solutions for hybrid systems since the
general definition of hybrid automata is usually too loose.

2.6 Numerical methods for nonsmooth dynamical systems

To conclude this brief exposition of nonsmooth dynamical systems, let us recall an important fact related
to numerical methods. Beyond their intrinsic mathematical interest, and the fact that they model real
physical systems, using nonsmooth dynamical systems as a model is interesting, because there exists a
large set of robust and efficient numerical techniques to simulate them. Without entering into the finer
details, let us give two examples of these techniques:

• Numerical time integration methods: convergence, efficiency (order of consistency, stability, sym-
plectic properties). For the nonsmooth dynamical systems described above, there exist event-
capturing time-stepping schemes with strong mathematical results. These schemes have the ability
to numerically integrate the initial value problem without performing an event location, but by
capturing the event within a time step. We call an event, or a transition, every change into the index

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Inria Annual Report 2023

set of the active constraints in the complementarity formulation or in the normal cone inclusion.
Hence these schemes are able to simulate systems with a huge number of transitions or even with
finite accumulation of events (Zeno behavior). Furthermore, the schemes do not suffer from the
weaknesses of the standard schemes based on a regularization (smoothing) of the multi-valued
mapping resulting in stiff ordinary differential equations. For the time-integration of the initial
value problem (IVP), or Cauchy problem, a lot of improvements of the standard time-stepping
schemes for nonsmooth dynamics (Moreau–Jean time-stepping scheme) have been proposed in
the last decade, in terms of accuracy and dissipation properties [30, 31, 84, 85, 29, 52, 48, 87, 50]. A
significant number of these schemes have been developed by members of the BIPOP team and
have been implemented in the Siconos software.

• Numerical solution procedure for the time–discretized problem, mainly through well-identified
problems studied in the optimization and mathematical programming community. Another very
interesting feature is the fact that the discretized problem that we have to solve at each time–step is
generally a well-known problem in optimization. For instance, for LCSs, we have to solve a linear
complementarity problem [54] for which there exist efficient solvers in the literature. Compared to
the brute force algorithm with exponential complexity that consists of enumerating all the possible
modes, the algorithms for linear complementarity problem have polynomial complexity when the
problem is monotone.

3 Research program

3.1 Introduction

In this section, we develop our scientific program. In the framework of nonsmooth dynamical systems,
the activities of the project–team will be focused on the following research axes:

• Axis 1: Nonsmooth simulation and numerical modeling for natural gravitational risk in mountains.

(detailed in Sect. 3.2).

• Axis 2: Modeling, simulation and control (detailed in Sect. 3.3).

These research axes will be developed with a strong emphasis on the software development and the
industrial transfer.

3.2 Axis 1: Nonsmooth simulation and numerical modeling for natural gravitational

risk in mountains.

In this research axis, we propose, on the one hand, to extend existing methods of simulation in mechanics
of complex flows in a nonsmooth framework, which allows us to simplify the models by decreasing the
physical parameters, and to make more robust the numerical simulations and thus to make possible
the construction of reduced models or meta-models. On the other hand, the so-called "data-driven
modeling" methods will be explored for gravity flows and prevention structures. The aim is to make the
most of laboratory and observational data in order to build and calibrate the models, to evaluate their
sensitivity, to improve their predictive character, i.e. to control and take into account the uncertainties,
thanks to variational, statistical and AI methods.

This work will be conducted in close collaboration with the UR IGE of INRAE as well as other research-
ers from INRIA (AIRSEA, LEMON). More generally, our collaboration with INRAE opens new long term
perspectives on granular flow applications such as debris and mud flows, granular avalanches and the
design of structural protections. The numerical methods that go with these new modeling approaches
will be implemented in our software Siconos).

This research is also part of the more general context of a digital platform on environmental risk in

the mountains, including intensive and cloud computing.

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3.2.1 Rockfall trajectory modeling

Trajectory analysis of falling rocks during rockfall events is limited by the currently unrefined modeling of
the impact phase [45, 44, 72]. The goal of this axis is to improve reliability of simulation techniques.

• Rock fracturing: When a rock falls from a steep cliff, it stores a large amount of kinetic energy that is
partly dissipated though the impact with the ground. If the ground is composed of rocks and the
kinetic energy is sufficiently high, the probability of the fracture of the rock is high and yields an
extra amount of dissipated energy but also an increase of the number of blocks that fall. In this
topic, we want to use the capability of the nonsmooth dynamical framework for modeling cohesion
and fracture [69, 28] to propose new cohesive zone models with contact and friction.

• Rock/forest interaction: To prevent damage and incidents to infrastructure, a smart use of the forest
is one of the ways to control trajectories (decrease of the run-out distance, jump heights and the
energy) of the rocks that fall under gravity [55, 56]. From the modeling point of view and to be
able to improve the protective function of the forest, an accurate modeling of impacts between
rocks and trees is required. Due to the aspect ratio of the trees, they must be considered as flexible
bodies that may be damaged by the impact. This new aspect offers interesting modeling research
perspectives, especially, building rockfall simulation method with mechanical models of trees
including damage, fracture and plasticity.

• Experimental validation: The participation of INRAE with F. Bourrier makes possible the exper-
imental validation of models and simulations through comparisons with real data. INRAE has
extensive experience of lab and in-situ experiments for rockfall trajectory modeling [45, 44]. It is a
unique opportunity to strengthen our model and to prove that nonsmooth modeling of impacts is
reliable for such experiments and forecasting of natural hazards.

3.2.2 Modeling and simulation of gravity hazards (debris flows, avalanches and large-scale rock

flows)

Different modeling approaches are used in the literature depending on the type of hazard.

For rockfalls and dense snow avalanches, methods that explicitly model the particles of granular
materials (notably Discrete Element Methods - DEM) are preferred, whereas for flows (debris flows,
avalanches and large-scale rockfalls), methods that assimilate the large number of individual constituents
to materials with complex rheology are more commonly used (notably Material Point Method - MPM,
Smoothed-Particle Hydrodynamics - SPH, Shallow Water models - SWM). It should be noted that these
methods are most often explicit and regularize the constraints of inequalities and thresholds.

This research item will develop the following points:

• Rethinking DEM, MPM, SPH and SWM methods in the nonsmooth framework. This will allow a
simple and efficient modeling of threshold and inequality phenomena (one-sided contact, impact
with Coulomb friction, threshold behavior laws such as plasticity, damage or fracture, Bingham-
type fluids) in order to develop new, implicit and robust numerical methods, where the most
important physical features of frictional cohesive materials are well-modeled neglecting the second
order phenomena. In a context of data utilization and prediction, these methods seem particu-
larly well suited as our first experiments on block trajectography and rock flows have already shown.

• Couple these methods to integrate the "multi-scale (micro/meso/macro)" character of these problems
or, more simply, to spatially couple at the same scale several physical phenomena better taken
into account by different methods, for example a debris flow containing a material with complex
rheology (MPM or SPH) and large size particles (DEM)

• Use “data-driven mechanics” approaches when behavioral models are not reliable and faithful
to the observed physical phenomena. These techniques can also be used to model “sub-mesh”
phenomena, which are not or only slightly taken into account in large-scale phenomenological
models.

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3.2.3 Data-driven modelling for prediction and mitigation of gravity hazards

The objective is to develop simplified models that can be used extensively for the development of
calibration and uncertainty quantification methods that allow for the joint use of data from various
sources to evaluate and improve the predictive capacity of gravity hazard models.
The following points will be developed:

• Statistical models integrating various types of data and the hazard models developed in the previous
section. The identification of the parameters of these hazard models, in particular using Bayesian
approaches, will also allow the calibration and quantification of the uncertainties associated with
the hazard models.

• Model reduction approaches (POD, PGD,...) or construction of substitution models (Sparse Polyno-

mial Chaos, Gaussian Processes,...) to build simplified models usable in this context.

• Application of different data assimilation techniques (particle filters or variational methods) on the

models described in the first axis and the reduced order models.

3.3 Axis 2: Modeling, simulation and control of non-smooth dynamical systems.

This axis is dedicated to the modeling and the mathematical analysis of nonsmooth dynamical systems. It
consists of two main directions: 1) Modeling, analysis and numerical methods and 2) Automatic control.

3.3.1 Modeling, analysis and numerical methods

Multibody vibro-impact systems

• Multiple impacts with or without friction (short-term): there are many different approaches to
model collisions, especially simultaneous impacts (so-called multiple impacts)[80]. One of our
objectives is on one hand to determine the range of application of the models (for instance, when
can one use “simplified” rigid contact models relying on kinematic, kinetic or energetic coefficients
of restitution?) on typical benchmark examples (chains of aligned beads, rocking block systems).
On the other hand, we will try to take advantage of the new results on nonlinear wave phenomena,
to better understand multiple impacts in 2D and 3D granular systems. The study of multiple
impacts with (unilateral) nonlinear visco-elastic models (Simon–Hunt–Crossley, Kuwabara–Kono),
or visco-elasto-plastic models (assemblies of springs, dashpots and dry friction elements), is also a
topic of interest, since these models are widely used.

• Artificial or manufactured or ordered granular crystals, meta-materials (short-term): Granular
metamaterials (or more general nonlinear mechanical metamaterials) offer many perspectives
for the passive control of waves originating from impacts or vibrations. The analysis of waves in
such systems is delicate due to spatial discreteness, nonlinearity and non-smoothness of contact
laws [81, 67, 68, 73]. We will use a variety of approaches, both theoretical (e.g. bifurcation theory,
modulation equations) and numerical, in order to describe nonlinear waves in such systems, with
special emphasis on energy localization phenomena (excitation of solitary waves, fronts, breathers).

• Systems with clearances, modeling of friction (long-term): joint clearances in kinematic chains
deserve specific analysis, especially concerning friction modeling[39]. Indeed contacts in joints are
often conformal, which involve large contact surfaces between bodies. Lubrication models should
also be investigated.

• Painlevé paradoxes (long-term): the goal is to extend the results in [60], which deal with single-
contact systems, to multi-contact systems. One central difficulty here is the understanding and the
analysis of singularities that may occur in sliding regimes of motion.

As a continuation of the work in the BIPOP team, our software Siconos will be our favored software
platform for the integration of these new modeling results.

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Systemic risk

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• The high consumption of natural resources by our society puts in question its long-term sustain-
ability. The decrease of natural resources results in a deterioration of human welfare with a risk
of society instability. Recently, a simple nature-society interrelations model, called the HANDY
model (Human And Nature DYnamics), has been proposed by Montesharrei et al (2014) to address
this concern with a special emphasis on the role of the stratification of the society. The Handy
model is a four dimensional nonlinear dynamical system that describes the evolution of population,
resources and accumulated wealth. We analyse the dynamics of this model and we explore the
influence of two parameters: the nature depletion rate and the inequality factor. We characterize
the asymptotic states of the system through a bifurcation analysis and we derive several quantit-
ative results on the trajectories. We show that some collapses are irreversible and, depending on
the wealth production factor, a bistability regime between a sustainable equilibrium and cycles
of collapse-and-regeneration can be obtained. We discuss possible policies to avoid dramatic
scenarios.

Cyber-physical systems (hybrid systems) Participants: V. Acary, B. Brogliato, C. Prieur, A. Tonnelier

Nonsmooth systems have a non-empty intersection with hybrid systems and cyber–physical systems.
However, nonsmooth systems enjoy strong mathematical properties (concept of solutions, existence
and uniqueness) and efficient numerical tools. This is often the result of the fact that nonsmooth
dynamical systems are models of physical systems, and so can take advantage of their intrinsic properties
(conservation or dissipation of energy, passivity, stability). A standard example is a circuit with n ideal
diodes. From the hybrid point of view, this circuit is a piecewise smooth dynamical system with 2n
modes, that can be quite cumbersome to enumerate in order to determinate the current mode. As a
nonsmooth system, this circuit can be formulated as a complementarity system for which there exist
efficient time-stepping schemes and polynomial time algorithms for the computation of the current
mode. The key idea of this research action is to benefit from this observation to improve hybrid system
modeling tools.

• Structural analysis of multimode DAE : When a hybrid system is described by a Differential
Algebraic Equation (DAE) with different differential indices in each continuous mode, the structural
analysis has to be completely rethought. In particular, the re-initialization rule, when a switching
occurs from one mode to another, has to be consistently designed. We propose in this action to use
our knowledge in complementarity and (distribution) differential inclusions [37] to design consistent
re-initialization rules for systems with nonuniform relative degree vector (r1, r2, . . . , rm) and ri ̸= r j , i ̸= j .
• Cyber–physical in hybrid systems modeling languages : Nowadays, some hybrid modeling lan-
guages and tools are widely used to describe and to simulate hybrid systems (MODELICA, SIMULINK, and
see [51] for references therein). Nevertheless, the compilers and the simulation engines behind these lan-
guages and tools suffer from several serious weaknesses (failure, nonsensical output or extreme sensitivity
to simulation parameters), especially when some components, that are standard in nonsmooth dynamics,
are introduced (piecewise smooth characteristic, unilateral constraints and complementarity condition,
relay characteristic, saturation, dead zone, . . . ). One of the main reasons is the fact that most of the
compilers reduce the hybrid system to a set of smooth modes modeled by differential algebraic equations
and some guards and reinitialization rules between these modes. Sliding mode and Zeno-type behaviour
are extremely difficult for hybrid systems and relatively simple for nonsmooth systems. With B. Caillaud
(Inria HYCOMES) and M. Pouzet (Inria PARKAS), we propose to improve this situation by implementing a
module able to identify/describe nonsmooth elements and to efficiently handle them with SICONOS as
the simulation engine. They have already carried out a first implementation [49] in Zelus, a synchronous
language for hybrid systems Zelus. Removing the weaknesses related to the nonsmoothness of solutions
should improve hybrid systems towards robustness and certification.

• A general solver for piecewise smooth systems This direction is the continuation of the prom-
ising result on modeling and the simulation of piecewise smooth systems [38]. As for general hybrid
automata, the notion or concept of solutions is not rigorously defined from the mathematical point
of view. For piecewise smooth systems, multiplicity of solutions can happen and sliding solutions are
common. The objective is to recast general piecewise smooth systems in the framework of differential
inclusions with Aizerman–Pyatnitskii extension [38, 58]. This operation provides a precise meaning to

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the concept of solutions. Starting from this point, the goal is to design and study an efficient numerical
solver (time-integration scheme and optimization solver) based on an equivalent formulation as mixed
complementarity systems of differential variational inequalities. We are currently discussing the issues in
the mathematical analysis. The goal is to prove the convergence of the time-stepping scheme to get an
existence theorem. With this work, we should also be able to discuss the general Lyapunov stability of
stationary points of piecewise smooth systems.

Numerical optimization for discrete nonsmooth problems

• Second Order Cone Complementarity Problems (SOCCP) for discrete frictional systems (short-
term): After some extensive comparisons of existing solvers on a large collection of examples [25,
34], the numerical treatment of constraint redundancy by the proximal point technique and the
augmented Lagrangian formulation seems to be a promising path for designing new methods.
From the comparison results, it appears that the redundancy of constraints prevents the use of
second order methods such as semi-smooth Newton methods or interior point methods. With P.
Armand (XLIM, U. de Limoges), we propose to adapt recent advances for regularizing constraints
for the quadratic problem [59] for the second-order cone complementarity problem.

• The other question is the improvement of the efficiency of the algorithms by using accelerated
schemes for the proximal gradient method that come from large-scale machine learning and
image processing problems. Learning from the experience in large-scale machine learning and
image processing problems, the accelerated version of the classical gradient algorithm [77] and
the proximal point algorithm [41], and many of their further extensions, could be of interest for
solving discrete frictional contact problems. Following the visit of Y. Kanno (University of Tokyo)
and his preliminary experience on frictionless problems, we will extend its use to frictional contact
problem. When we face large-scale problems, the main available solvers is based on a Gauss–Seidel
strategy that is intrinsically sequential. Accelerated first-order methods could be a good alternative
to benefit from distributed scientific computing architectures.

3.3.2 Automatic Control

This last item is dedicated to the automatic control of nonsmooth dynamical systems, or the nonsmooth
control of smooth systems. The first research direction concerns the discrete-time sliding mode control
and differentiation. The second research direction concerns multibody systems with unilateral constraint,
impacts and set-valued friction. The third research direction concerns a class of dynamics which is an
extension of linear complementarity systems (or, equivalently, of differential algebraic equations).

Discrete-time Sliding-Mode Control (SMC), State Observers (SMSO) and Differentiators (SMD)

• SMC with output feedback: Output feedback can take different forms, like the use of observ-
ers/differentiators in the loop (specific dynamic output feedback), or the design of static or dynamic
output feedback (without state observation). The time-discretization of such feedback systems and
its analysis remains largely open.

• Unifying algorithm for discrete-time SMC and SMD: maximal monotone operators, proximal al-

gorithms.

Control of nonsmooth discrete Lagrangian systems

• Linear Complementarity Systems (LCS): the PhD thesis of Aya Younes is dedicated to the trajectory
tracking control in LCS. In particular the cases with uncertainties and with state jumps are carefully
analysed. The PhD thesis of Quang-Hung Pham focuses on networks of LCS. In both cases passivity
is a central tool for the analysis.

• Optimal control: the optimal control of mechanical systems with unilateral constraints and impacts,
largely remains an open issue. Through a collaboration with Moritz Diehl (Freiburg University) the
problem has been tackled using a suitable dynamics transformation of Lagrangian complementarity

Project TRIPOP

13

systems into a Filippov "classical" differential inclusion with absolutely continuous solutions. The
results are restricted to a single unilateral frictionless constraint. The global objective is to enlarge
it to multiple unilateral constraints (hence multiple impacts) and friction.

• Cable-driven systems: these systems are typically different from the cable-car systems, and are
closer in their mechanical structure to so-called tensegrity structures. The objective is to actuate
a system via cables supposed in the first instance to be flexible (slack mode) but non-extensible
in their longitudinal direction. This gives rise to complementarity conditions, one big difference
with usual complementarity Lagrangian systems being that the control actions operate directly
in one of the complementary variables (and not in the smooth dynamics as in cable-car systems).
Therefore both the cable models and the control properties are expected to differ a lot from what
we may use for cableway systems (for which guaranteeing a positive cable tension is usually not an
issue, hence avoiding slack modes, but the deformation of the cables due to the nacelles and cables
weights, is an important factor). Tethered systems are a close topic.

• Robot-object underactuated dynamical systems: such systems are made of a controlled part (called
the robot) and an uncontrolled part (called the object). Both are linked by Lagrange multipliers
which represent the contact forces. The object can be controlled only through the multipliers,
which are in turn a function of the system’s state. Examples are bipeds which walk, run, jump,
juggling, tapping, pushing robots, prehensile and non-prehensile tasks, some cable-driven systems,
and some circuits with nonsmooth set-valued components. A global approach consists in a
backstepping-like control strategy. The goal is to derive a unifying framework which can be easily
adapted to all these various systems and tasks.

Switching LCS and DAEs

• We have gained a strong experience in the field of complementarity systems and distribution
differential inclusions [37, 47], that may be seen as some kind of switching DAEs. More recently
we have obtained preliminary results on the analysis of so-called differential-algebraic linear
complementarity systems (DALCS) and descriptor-variable LCS (DVLCS), as well as on switching
DAEs with state-dependent swithing bilateral constraints. These systems can be seen as DAEs with
added complementarity constraints, or as LCS with added equality constraints, or as DAEs with
nonsmooth equality constraints. Their well-posedness (existence and uniqueness of solutions
to the one-step nonsmooth problem of the implicit Euler scheme, existence and uniqueness of
solutions to the continuous-time system) is non-trivial. The case of systems with state-jumps also
requires careful analysis.

• A closely related subject is that of interconnections of LCSs or extensions of these (like differential
inclusions with maximal monotone properties). The stability of the interconnected system is a
topic of interest, as well as, the resulting collective behavior.

Dynamics of complex nonlinear networks, set-valued couplings

• The interconnections of uncertain dynamical systems is a topic of broad interest within the control
community. For the case of nonlinear agents with set-valued coupling laws, many questions remain
open regarding the resulting behavior of the network, as well as, their robustness properties against
parametric uncertainties and external disturbances. The PhD thesis of Quang-Hung Pham focuses
on such issues within the context of robust synchronization of LCSs.

• Recently, novel extensions of the concept of passivity have been studied for the analysis of systems
away from equilibrium [74]. However, their relevance in the context of networks remains largely
unexplored.

• Two-dimensional networks of oscillators with set-valued generalized Coulomb friction laws arise
challenging questions regarding their dynamics (nonlinear oscillations, localized waves, excitabil-
ity), with applications in earthquake dynamics and friction control.

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Inria Annual Report 2023

• G. James has recently introduced in collaboration with F. Karbou (Centre d’Etudes de la Neige,
Grenoble) a nonsmooth dynamical system on a network suitable for segmenting wet snow areas
in SAR (synthetic-aperture radar) satellite images. The network corresponds to a large ensemble
of pixels of a grayscale image, whose evolutions are coupled or uncoupled depending on their
distance and local topography given by a digital elevation model. This yields an excitable dynamical
system that tends to create domain walls surrounding snowy areas. The system provides very good
identification results and arises nontrivial questions regarding its theoretical analysis, optimization
(parameters, complexity) and generalizations.

4 Application domains

Nonsmooth dynamical systems arise in many application fields. We briefly highlight here some applic-
ations that have been treated in the BIPOP team and that we will continue in the TRIPOP team, as a
validation for the research axes and also in terms of transfer.

In mechanics, the main instances of nonsmooth dynamical systems are multibody systems with
Signorini’s unilateral contact, set-valued (Coulomb-like) friction and impacts, or in continuum mechanics,
ideal plasticity, fracture or damage. Some illustrations are given in Figure 3(a-f). Other instances of
nonsmooth dynamical systems can also be found in electrical circuits with ideal components (see
Figure 3(g)) and in control theory, mainly with sliding mode control and variable structure systems (see
Figure 3(h)). More generally, every time a piecewise, possibly set–valued, model of systems is invoked, we
end up with a nonsmooth system. This is the case, for instance, for hybrid systems in nonlinear control
or for piecewise linear modeling of gene regulatory networks in mathematical biology (see Figure 3(i)).
Another common example of nonsmooth dynamics is also found when the vector field of a dynamical
system is defined as a solution of an optimization problem under constraints, or a variational inequality.
Examples of this kind are found in optimal control theory, in dynamic Nash equilibrium or in the theory
of dynamic flows over networks.

5 Social and environmental responsibility

As for the environmental footprint, we have already decided to drastically reduce our air travel and our
participation in international conferences. For instance, trips of less than 10 hours by train should not be
made by plane. International conferences should be coupled with a visit to colleagues or other scientific
events. Concerning the computer equipment, it is not replaced before 5 years and we try to keep the
office machines between 7 and 10 years.

Regarding the social impact, the emergence of the research axis 1 on natural gravitational hazards in
relation to climate change and studies on systemic risk are a way to focus research on the major concerns
of societies. Industrial collaborations are now also evaluated according to the social and environmental
responsibility efforts of the partners.

The question of the social and environmental footprint and impact of our research will be discussed

in more detail at our next team seminar.

6 New software, platforms, open data

6.1 New software

6.1.1 SICONOS

Name: Modeling, simulation and control of nonsmooth dynamical systems

Keywords: NSDS, MEMS, DCDC, SD, Collision, Friction, Mechanical multi-body systems

Scientific Description: The aim of this work is to provide a common platform for the simulation, model-
ing, analysis and control of abstract nonsmooth dynamical systems. Besides usual quality attributes
for scientific computing software, we want to provide a common framework for various scientific

Project TRIPOP

15

(a) Rockfall [45, 44, 56], granular and debris flows

(b) Frictional interface and solitary waves in the Burridge-Knopoff model [76]

(c) Circuit breakers mechanisms [39] and Robots (ESA ExoMars Rover [24])

Figure 3: Application fields of nonsmooth dynamics (mechanics)

Vkpkcm16

Inria Annual Report 2023

(d) Switched electrical circuits (delta-sigma converter) [33]

(e) Sliding mode control [36, 27, 66, 65, 75]

(f) Gene regulatory networks [38]

Figure 3: Application fields of nonsmooth dynamics (continued)

OPA−1+1−1+1OPA−1+1−1+1Experimentalsetup:electropneumaticactuatorSchematicDatagateDS 1105ControlControlPID ControllerServodistributorsPressure sensorsPosition sensorForce sensorMain actuatorPerturbation actuatorChamber PChamber NMoving mass -1-0.5 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1x2x1-1-0.5 0 0.5 1 1.5 2 2.5-0.2 0 0.2 0.4 0.6 0.8 1x2x1Gal4GAL4Swi5SWI5Gal80GAL80ASH1CBF1ASH1CBF1Galactose024681012024681012x2x1θ12θ22θ11θ2100.20.40.60.811.21.41.61.8200.20.40.60.811.21.41.61.8200.20.40.60.811.21.41.61.82x3(cI)x1(LacI)x2(TetR)x3(cI)Project TRIPOP

17

fields, to be able to rely on the existing developments (numerical algorithms, description and mod-
eling software), to support exchanges and comparisons of methods, to disseminate the know-how
to other fields of research and industry, and to take into account the diversity of users (end-users,
algorithm developers, framework builders) in building expert interface in Python. After the require-
ments elicitation phase, the Siconos Software project has been divided into 5 work packages which
are identified to software products:

• SICONOS/NUMERICS This library contains a set of numerical algorithms, already well identified,
to solve non smooth dynamical systems. This library is written in low-level languages (C,F77) in
order to ensure numerical efficiency and the use of standard libraries (Blas, Lapack, . . . )

• SICONOS/KERNEL This module is an object-oriented structure (C++) for the modeling and the
simulation of abstract dynamical systems. It provides the users with a set of classes to describe
their nonsmooth dynamical system (dynamical systems, interactions, nonsmooth laws, . . . ) and
to perform a numerical time integration and solving.

• SICONOS/FRONT-END. This module is mainly an auto-generated wrapper in Python which
provides a user-friendly interface to the Siconos libraries. A scilab interface is also provided in the
Front-End module.

• SICONOS/CONTROL This part is devoted to the implementation of control strategies of non
smooth dynamical systems.

• SICONOS/MECHANICS. This part is dedicated to the modeling and the simulation of multi-body
systems with 3D contacts, impacts and Coulomb’s friction. It uses the Siconos/Kernel as simulation
engine but relies on a industrial CAD library (OpenCascade and pythonOCC) to deal with complex
body geometries and to compute the contact locations and distances between B-Rep description
and on Bullet for contact detection between meshes.

Functional Description: Siconos is an open-source scientific software primarily targeted at modeling

and simulating nonsmooth dynamical systems in C++ and in Python:

- Mechanical systems (rigid or solid) with unilateral contact and Coulomb friction and impact
(nonsmooth mechanics, contact dynamics, multibody systems dynamics or granular materials).

- Switched Electrical Circuit such as electrical circuits with ideal and piecewise linear components:
power converter, rectifier, Phase-Locked Loop (PLL) or Analog-to-Digital converter.

- Sliding mode control systems.

- Biology (Gene regulatory network). Other applications are found in Systems and Control (hybrid
systems, differential inclusions, optimal control with state constraints), Optimization (Comple-
mentarity systems and Variational inequalities), Fluid Mechanics, and Computer Graphics.

Release Contributions: Main changes:

[numerics] add sparse linear solver with a sparse rhs based on csparse [numerics] new implement-
ation of NM_LU_solve and NM_Cholesky_solve [kernel] new implementation of linear solvers
in SimpleMatrix The class SimpleMatrix owns a internal NumericsMatrix thats is used for linear
system solving, based on Siconos/Numerics [numerics] add balancing matrice framework [nu-
merics] add freezing contacts in Gauss seidel solvers [externals] add LDL support [mechanics]
modify broadphase for Bullet [numerics] render the truncation in NM_entry [numerics] add matrix
versioning [misc] automates the generation of docker end-user images ’siconos-ready’ [misc] build
with ninja

URL: https://nonsmooth.gricad-pages.univ-grenoble-alpes.fr/siconos/

Contact: Vincent Acary

Participants: Franck Pérignon, Maurice Bremond, Vincent Acary

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7 New results

7.1 Numerical Modeling for natural risk in mountains

7.1.1 Semi-smooth Newton method for non-associative plasticity using the bi-potential approach

Participants:

Louis Guillet, Vincent Acary, Franck Bourrier, Olivier Goury.

A contribution submitted to CSMA 2024 presents an implicit solver for non-associative plasticity
problems based on the semi-smooth Newton method. The method is derived from the Implicit Standard
Material and is easily compatible with various space discretization techniques, particularly the Mater-
ial Point Method and the Finite Element Method. The solver converges quadratically, even for large
time steps, although we have only demonstrated theoretical results for restricted cases. The method is
demonstrated through a footing simulation.

7.1.2 Energy conservation and dissipation properties for elastodynamics with contact impact and

friction

Participants:

Vincent Acary, Nicholas Collins-Craft.

It has long been known that the standard implementation of impact and Coulomb friction leads to
the creation of energy in cases where the sliding direction changes over the impact. The paper [16] (to be
submitted to JTCAM) proposes a time integration scheme for nonsmooth mechanical systems involving
unilateral contact, impact and Coulomb friction, that respects the principles of discrete-time energy
balance with positive dissipation. To obtain energetic consistency in the continuous time model, we work
with an impact law inspired by the work of M. Frémond, which ensures that dissipation is positive, i.e.
that the Clausius–Duhem inequality is satisfied. On this basis, we propose a time integration method
based on the Moreau–Jean scheme with a discrete version of the Frémond impact law, and show that this
method has the correct dissipation properties, i.e. no energy is created.

7.1.3 Numerical modeling of rockfall trajectory

Participants:

Vincent Acary, Franck Bourrier.

Rockfall propagation models are routinely used for the quantitative assessment of rockfall hazard.
Their capacities and limitations remain difficult to assess due to the limited amount of exhaustive
experimental data at the slope scale.

The article [46] presents experiments of block propagation performed in a quarry located in Authume
(France). A total of more than one hundred blocks were released on two propagation paths. The propaga-
tion of the blocks was assessed by measuring the block stopping points as well as their kinematics at
specific locations of the paths, called evaluation screens. Significant variability of the stopping points and
of the block kinematics at the evaluation screens was observed and preferential transit and deposit zones
were highlighted. The analysis of the results showed predominant effect of topography, in particular that
related to topographical discontinuities. Significant influence of local and small scale parameters (e.g.
block orientation, local topography) was also highlighted. These conclusions are of particular interest
for researchers or practitioners who would like to assess the relevance of propagation modelling tools
considering this complex study site. In this configuration, the quality of block propagation simulations
should notably rely on the accuracy of digital terrain models, and on the integration of local conditions
effects using physically based approaches.

Complementary with the research held in [46], the predictive capabilities of block propagation models
after a preliminary calibration phase is investigated. It is focused on models integrating the shape of

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blocks since, despite their sound physical bases, they remain less used than lumped-mass approaches
due to their more recent popularisation. We first performed an expert-based calibration based on the
use of the 2D model and, second, evaluated the predictive capabilities of the calibrated model in 2D and
in 3D using the remaining part of the experimental results. The calibrated model simulations predict
the main characteristics of the propagation : after a calibration phase on sufficient amount of soil types,
the model may be used in a predictive manner. The adequacy between 2D and 3D simulations also
favors applicability of the model since easier and faster calibrations based on 2D simulations only can be
envisaged. As classically observed for block propagation models, the model is not sufficient to predict the
details of the velocity and stopping points but provides accurate prediction of the global ranges of these
quantities, in particular of the extreme values. To lift these limitations in terms of predictive capabilities,
more advanced calibration procedures based on optimization techniques can constitute a promising
perspective as it is studied in [43].

7.1.4 Numerical modeling of fracture in solids

Participants:

Vincent Acary, Franck Bourrier, Nicholas Collins-Craft.

In [53], a new extrinsic cohesive model is developed together with a consistent time–stepping scheme
to simulate fracture in quasi-brittle material like rock or concrete. An extrinsic cohesive zone model
with a novel unload-reload behaviour is developed in the framework of non-smooth mechanics. The
model is extended to include the effects of dynamics with impact, and is discretised in such a way that it
can be written as a Linear Complementarity Problem (LCP). This LCP is proved to be well-posed, and
to respect the discrete energy balance of the system. Finally, the LCP system is validated numerically,
in both statics and dynamics, by simple test cases, and more involved finite element simulations that
correspond to standard test geometries in the literature. The results correspond well with those of other
authors, while also demonstrating the simulations’ ability to resolve with relatively large time steps while
respecting the energetic balance. We are now working on the development of a model taking into account
the tangential cohesion coupled with the Coulomb friction. The objective is to propose a model coupled
with hydro-thermal freezing and thawing phenomena in rock interfaces, which will be used to simulate
the stability of cliffs in connection with the thawing of permafrost. This is still on-going work.

7.1.5 Variational approach for nonsmooth elasto-plastic dynamics with contact and impacts

Participants:

Vincent Acary, Franck Bourrier, Benoit Viano.

The objective of this work [4] is the modelling and the numerical simulation of the response of
elastoplastic structures to impacts. To this end, a numerical method is proposed that takes into account
one-sided contact (Signorini condition) and impact phenomena together with plasticity in a monolithic
solver, while accounting for the non-smooth character of the dynamics. The formulation of the plasticity
and the contact laws are based on inclusions into normal cones of convex sets, or equivalently, variational
inequalities following the pioneering work of Moreau (1974) and Halphen and Nguyen (1975), who
introduced the assumptions of normal dissipation and of generalised standard materials (GSM) in
the framework of associated plasticity with strain hardening. The proposed time-stepping method is
an extension of the Jean and Moreau (1987) scheme for nonsmooth dynamics. The discrete energy
balance shows that spurious numerical damping can be suppressed and that the scheme is in practice
unconditionally stable. Furthermore, the finite-dimensional variational inequality at each time-step
is well-posed and can be solved by optimization methods for convex quadratic programs, providing
an interesting alternative to the return mapping algorithm coupled with a dedicated frictional contact
method.

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7.1.6 Bayesian interface based calibration of a novel rockfall protection structure modelled in the

Non-smooth contact dynamics framework

Participants:

Vincent Acary, Franck Bourrier.

The work in [7] is intended to the development and calibration of a numerical model simulating the
response of a novel rockfall protection structure subjected to localised dynamic loading. This structure is
made of piled-up concrete blocks interconnected via metallic components whose dynamics response
under projectile impact is examined via real-scale experiments. The corresponding numerical model is
developed in a python based open source software Siconos which implements the Non-Smooth Contact
Dynamics (NSCD) method. The geometrical features and mechanical properties are incorporated in the
model via specific developments pertinent to the modelling requirements in Siconos. Some parameters
peculiar to the numerical model are calibrated against the spatial-temporal measurements from two
full-scale impact experiments. The Bayesian interface statistical learning method aided by the polynomial
chaos expansion based meta-model of the NSCD model is deployed for the calibration. The additional
understanding of the model dynamics through the byproducts of the meta-model is highlighted. In the
end, the NSCD model is successfully calibrated against the spatial-temporal response of the experimental
structure with more than 90% accuracy for impact energies up to 1 MJ.

7.2 Systemic risk

Participants:

Arnaud Tonnelier, Vincent Acary.

The overexploitation of natural resources questions the long-term sustainability of our society. A
simple nature-society interrelations model, called the HANDY model (Human And Nature DYnamics), has
been proposed by Montesharrei et al (2014) to address this concern with a special emphasis on the role of
the stratification of the society. We analyze the dynamics of this model and we explore the influence of
two parameters: the nature depletion rate and the inequality factor. Results have been detailed in [14].
Recently, we have focused on a more realistic but more complex model, the World3 model. The model
describes the interactions between the world population, industrial and agricultural productions and
pollution. Preliminary results on the dynamics of the resource-capital subsystem have been obtained
with, in particular, an approximation of the resource half-life. We extended the model to integrate the
dynamics of renewable resources and we showed that a cyclic activity is possible.

A critical question in the study of the dynamics of interconnected elements is linked to the existence
of cascading failure. The failure of one subsystem when a critical threshold is reached can trigger a
breakdown that can propagate through the system yielding to a full collapse. A generic propagation
mechanism in a network made of threshold elements has been studied in [13] and we extend this
approach to more realistic cases in the context of system dynamics modelling.

7.3 Numerical solvers for frictional contact problems.

Participants:

Vincent Acary, Maurice Brémond, Paul Armand.

In [35], we review several formulations of the discrete frictional contact problem that arises in space
and time discretized mechanical systems with unilateral contact and three-dimensional Coulomb’s
friction. Most of these formulations are well–known concepts in the optimization community, or more
generally, in the mathematical programming community. To cite a few, the discrete frictional contact prob-
lem can be formulated as variational inequalities, generalized or semi–smooth equations, second–order
cone complementarity problems, or as optimization problems such as quadratic programming problems

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over second-order cones. Thanks to these multiple formulations, various numerical methods emerge
naturally for solving the problem. We review the main numerical techniques that are well-known in the
literature and we also propose new applications of methods such as the fixed point and extra-gradient
methods with self-adaptive step rules for variational inequalities or the proximal point algorithm for
generalized equations. All these numerical techniques are compared over a large set of test examples
using performance profiles. One of the main conclusion is that there is no universal solver. Nevertheless,
we are able to give some hints to choose a solver with respect to the main characteristics of the set of tests.
Recently, new developments have been carried out on applications of well-known numerical methods
in optimization. With the visit of Paul Armand, Université de Limoges, we co-supervise a M2 internship,
Maksym Shpakovych on the application of interior point methods for quadratic problem with second-
order cone constraints. The results are encouraging [86],[78], [79]. A first publication on rolling friction
has been published [32] and another publication [3] in Optimization Methods ans Software.

7.4 Analysis and Control of Set-Valued Systems

Participants:

Bernard Brogliato, Christophe Prieur, Vincent Acary, Mohammad Ra-
sool Mojallizadeh, Félix Miranda-Villatoro.

7.4.1 Discrete-time implicit Euler sliding-mode control

In [5] it is shown that some discrete-time algorithms, which have the property of finite-time stability
and are written in an explicit form, are in fact the implicit (backward) Euler discretization of suitable
set-valued systems. In other words, they can be written in the form of proximal-point algorithms using
resolvents of maximal operators. This paves the way towards a unified framework for the calculation of
sliding-mode controllers and differentiators when an implicit discretization is used.

The work [21] provides a fresh perspective on sliding mode techniques for control, observation, and
differentiation via its discrete-time implementation with backward terms. In such context, the maximal
monotonicity of the backward terms plays a central role for the well-posedness of the closed-loop, as
well as, for its stability analysis. With such approach, the strong connections between sliding-mode
control and optimization are shown via proximal-point algorithms. The manuscript also underscores
the significance of passivity in the resulting closed-loop system, an aspect that has been overlooked
within the broader community of sliding mode control. As a side-result a novel robust version of the
proximal-point algorithm is presented and later employed to study the finite-time stability of the closed-
loop system for the case of conventional (first-order) sliding-mode control. The manuscript delves into
optimization and maximal monotone operators, underscoring the impact of set-valued control maps
and appropriate selection schemes leading to control strategies that do not suffer the common issue of
numerical chattering.

7.4.2 Optimal control of Lagrangian complementarity systems

In [12] we study the optimal control of Lagrangian complementarity systems. Such systems are nonsmooth
(with impacts and set-valued friction) and undergo varying dimensions (due to the unilateral constraints
and the complementarity constraints). The analysis is based on the transformation of the system with
impacts, into a system without impacts, using an equivalent Filippov’s differential inclusion with ab-
solutely continuous solutions. The difficulty is in the correct design of the sliding surface so that the
post-impact velocity is computed correctly. A specific numerical scheme developed by Nurkanovic and
Diehl at Frieburg university is used for the numerical simulations on a jumping robot.

7.4.3 Robot-object underactuated nonsmooth dynamical systems

In [6] we propose a tutorial survey about an important class of Lagrangian complementarity systems
(hence with impacts and set-valued friction) which possess a specific structure that can be split into two
main parts: a controlled part (named the "robot") and an uncontrolled part (named the "object") which
can be acted upon only through the Lagrange multipliers associated with the constraints (bilateral or/and

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Inria Annual Report 2023

unilateral) and the friction. This class comprises many well-known robotic systems like bipeds which
walk, jump, run, juggling, tapping, hopping, pushing robots, prehensile of non-prehensile manipulation
systems, some cable-driven systems, and some electrical circuits with nonsmooth set-valued components.
The main message is that a backstepping-like control strategy should be followed to get a unified approach
for the feedback control of all these underactuated systems.

7.4.4 Modelling and control of overhead cranes (OC)

This is a subject that we studied in the framework of the IRT project Levage, in collaboration with
Schneider Electric. In [11, 17] we have reviewed different modeling approaches for OCs in 2D and 3D, with
detailed dynamical equations for single and double-pendulums. Many controllers have been reviewed,
and a toolbox has been developed which allows to test numerically the controllers. A comparative
work has been performed over typical open-loop and closed-loop controllers, including passivity-based,
sliding-mode, feedback linearization, etc, for regulation and for trajectory tracking.

7.4.5 Bifurcations of equilibria in LCS

It is well-known that linear complementarity systems (LCSs) can undergo bifurcations at which multiple
equilibria, limit cycle, or chaotic solutions might appear, dissappear or change stability. From a control
viewpoint, it is important to know the range of parameters for which such changes take place. The work
[20] addresses this issue by proposing a novel notion of equivalence between LCPs (linear complement-
arity problems) that permits to make a classification of steady-state bifurcations in dynamic LCS. The
proposed approach takes advantage of the geometric structure of the problem and allows to closely
mimic the bifurcation theory of smooth maps. This type of results allows us, for instance, to design LCSs
with asymptotic behaviors showing multiple steady states, as is the case in negative resistance circuits, as
well as, quantify the structural stability of a given LCP via structural stability margins. In addition, a full
classification of stable and unstable LCPs is provided for the planar case.

7.4.6 Nonlinear networks with set-valued coupling

The work [9]explores the use of maximal monotone set-valued couplings for achieving robust synchron-
ization in networks of agents with external disturbances and/or model uncertainties. It is shown that
perfect synchronization is achievable with bounded set-valued coupling laws under the affections of
persistent disturbances. Moreover, if the coupling is done via the full-state, then finite-time synchroniza-
tion is guaranteed. The work also proposes practical ways of realizing the set-valued coupling law via
electrical circuits. Such regularized coupling law can be simulated in a digital computer using implicit
methods [33] and it is detached from the dynamics of the individual agents. Moreover an estimation of
the ultimate bound is given in function of the regularization index of the implemented coupling.

7.4.7 Passive systems interconnections

The generic interconnection of two passive linear complementarity systems (LCS) is analysed in [19].
The difficulty lies in the fact that the interconnection variables are not the passivity inputs and outputs,
contrarily to the classical passivity theorem. Various cases are analysed in details (interconnection of
passive, strictly state passive, strongly passive, LCS). The stability is also tackled.

7.4.8 Tracking control of Linear Complementarity Systems

The work [22] is largely concerned with trajectory tracking in linear complementarity systems (LCS) where
passivity plays a central role for the analysis and design of the closed-loop. Such approach allows to rely
on linear matrix inequalities (LMIs) for the computation of the control gains. Cases with and without
state-jumps, with and without parametric uncertainties, are analyzed. Theoretical findings are illustrated
with examples from circuits with set-valued, nonsmooth electronic components, and networks with
unilateral interactions.

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8 Bilateral contracts and grants with industry

Participants:

Vincent Acary, Bernard Brogliato, Christophe Prieur.

8.1 Bilateral grants with industry

Schneider Electric

This action started in 2001 with the post-doc of V. Acary co–supported by Schneider Electric and CNRS.
With some brief interruptions, this action is still active and should further continue. It concerns mainly the
simulation and modeling of multi–body systems with contact, friction and impacts with the application
for the virtual prototyping of electrical circuit breakers.

During these years, various forms of collaborations have been held. Two PhD thesis have been granted
by Schneider Electric (D.E. Taha and N. Akhakdar) accompanied with research contracts between INRIA
and Schneider Electric. Schneider Electric participated also the ANR project Saladyn as a main partner.
Without going into deep details of the various actions over the years, the major success of this
collaboration is the statistical tolerance analysis of the functional requirements of the circuit breakers
with respect to clearance in joints and geometrical tolerances on the parts. Starting from the geometrical
descriptions (CAD files) of a mechanism with prescribed tolerances on the manufacturing process, we
perform worst-case analysis and Monte–Carlo simulations of the circuit breaker with Siconos and we
record the variations in the functional requirements. The difficulty in such simulations are the modeling
of contact with friction that models the joints with clearances. The results of these analysis enable
Schneider Electric to define the manufacturing precision that has a huge impact of the production cost
(Schneider Electric produces several millions of C60-type circuit breaker per year). Note that it is not
possible to perform such simulations with the existing software codes of the market.

At the beginning, our interlocutor at Schneider Electric was the innovation (R&D) department.
Now, we are working and discussing with the business unit, Division Power and Dinnov (M. Abadie,
E. Boumediene, X. Herreros) in charge of designing and producing the circuit–breakers. The targeted
users are the R&D engineers of Schneider Electric that use simulation tools for designing new models or
improving existing circuit breakers. This collaboration continues with new modeling and simulation chal-
lenges (flexible parts, multiple impact laws) a collaboration launched in October 2023 with Dr Emmanuel
Frangin, a master student should be recruited in 2024.

STRMTG. Service Technique des remontées mécaniques et des transports guidés.

We have started with STRMTG a research contract about modelling, simulation and control of cable-
transport systems. In such systems, the question of the coupling between the nonlinear dynamics of
cables and their supports with unilateral contact and friction appears now to be determinant in order to
increase the performances of the cableway systems, especially for urban transportation systems.

9 Partnerships and cooperations

9.1 International initiatives

9.1.1 Participation in other International Programs

Programme Samuel-De Champlain:

Participants: Olivier Goury.

In collaboration with Ecole Polytechnique de Montreal, MacGill University and DEFROST Team at
Inria. This fund has two objectives: research and teaching. The research topic is about Soft Robot design

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Inria Annual Report 2023

and simulation using AI. The project also implies phd Student exchanges between the partners to develop
new skills.

9.2 International research visitors

9.2.1 Visits of international scientists

Other international visits to the team

Visitor: Fernando Castaños Luna

Status: Researcher

Institution of origin: CINVESTAV-IPN

Country: Mexico

Dates: September 2023-January 2024

Context of the visit:

Mobility program: Sabbatical internhship

9.3 European initiatives

9.3.1 Horizon Europe

LEMMA LEMMA project on cordis.europa.eu

Title: Landslide and avalanchE Mechanics with Multiphysical datA

Duration: From September 1, 2022 to August 31, 2024

Partners:

• Institut National de Recherche en Informatique et Automatique (INRIA), France

• École Polytechnique Fédérale de Lausane (EPFL), Switzerland

• Université Grenoble Alpes (UGA), France

Inria contact: Vincent Acary

Coordinator:

Summary: Landslides and avalanches jointly cause approximately 150 deaths and €4.9 billion economic
losses each year, with the impacts predicted to become more severe due to climate change. Mitig-
ation and prevention of disasters requires accurate predictions of these phenomena, which due
to their scale is only achievable via modelling and simulation. Accurate models of landslides in
permafrost or avalanches must account for micro-scale (<1mm) processes such as cracks and shear
bands that also involve thermal and hydrological effects that will be exacerbated by climate change.
Such models do not currently exist. Further, this level of refinement is not computationally viable
when modelling an entire mountainside, and so a new approach must be adopted.

This project will: 1) Develop new models for permafrost and snow subject to climate-change-
induced loadings; 2) Use the new data-driven mechanics framework to transfer information from
these models to the scale of the mountainside; and 3) Simulate the effects of climate change on
the Mont-Blanc massif at Chamonix. This will combine the researcher’s experience with shear
band models with the supervisor’s expertise in crack models and optimisation techniques. A
secondment at a group specialising in simulating landslides and avalanches will provide the
expertise to implement the simulation on a real mountainside.

This interdisciplinary project will ideally set the researcher for a career in academia in Europe,
while benefiting the community at Chamonix, in particular the guide’s association, as they will be

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able to plan adaptations and mitigations for the effects of climate change, ensuring their tourism
industry remains viable. Specialised multiphysical models that are adapted to permafrost and snow
will advance the state-of-the-art significantly, and the implementation of optimisation techniques
in data-driven mechanics has wide applicability throughout civil and mechanical engineering,
geology and environmental science.

9.4 National initiatives

Project SsONDS LabEx PERSIVAL ANR-15-IDEX-02 and ANR-11-LABX-0025-01

Self-sustained Oscillations in Nonsmooth Dynamical Systems. October 2021 - September 2024. INRIA
Grenoble TRIPOP team (F. Miranda-Villatoro, B. Brogliato) and Gipsa-Lab UGA (F. Ferrante). Coordinated
by F. Miranda-Villatoro. The SsONDS project aims at developing theoretical methods for the analysis,
design, and control of systems with robust self-sustained oscillations in environments with uncertainties
(as for instance, lack of knowledge of certain parameters of the model, or the presence of external
disturbances). Potential applications include the design of central pattern generators (CPGs) for motion
control, and mathematical analysis of models from computational biology. Total fundings for TRIPOP =
99 keuros.

ANR SPECULAR

Participants: Olivier Goury.

Simulation of Percutaneous Liver tumor Ablation in virtual Reality. The goal of this project is to develop
an immersive simulation of needle-based procedures. Olivier Goury is responsible of Work Package 2 in
collaboration with DEFROST at Inria Lille where the focus will be to speed up the numerical simulation
using reduced-order modeling techniques and parallel programming. This project is coordinated by
Stéphane Cotin at Inria Nancy and Hadrien Courtecuisse at Strasbourg University.

ANR MODEMSEA

Participants: Olivier Goury, Vincent Acary, Franck Bourrier, Franck Perignon,

Maurice Bremond.

Numerical modeling of coastal defense structures using a fully coupled SPH-DEM-FEM model. This
project was submitted to the ANR and we are awaiting the reviews. In collaboration with Ngoc-Son
NGUYEN from GeM, University of Nantes.

PEPR IRIMA

Participants: Olivier Goury, Vincent Acary, Franck Bourrier.

The IRiMa PEPR (integrated risk management for more resilient societies in an era of global change)
is co-piloted by BRGM, CNRS and Grenoble-Alpes University. This exploratory PEPR, with a budget of
€51.9 million over 8 years, brings together more than 30 partner institutions and laboratories. Within this
PEPR, we are actively involved in the "Mountain" targeted project (PC) with the ANR IRIMONT funding
application entitled "Assessment and mitigation of risks related to natural hazards in mountain territories
in the global change context". The IRIMONT project looks at all the physical and social dimensions
of natural hazards in mountain areas, from the characterisation of processes to decision-making and
adaptation in a context of climate change and socio-environmental dynamics.

The project is structures in 3 work packges. Guillaume Chambon (INRAE/IGE), Marc Peruzetto
(BRGM) and Vincent Acary are responsible for WP1 - Analysis and understanding of mountain risks

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Inria Annual Report 2023

and their components. This work package targets the gaps in knowledge and the scientific barriers
concerning mountain risks and their components (hazards, vulnerability, exposure). To this end, it
includes the acquisition and analysis of new data (instrumental, historical, etc.) and the development
of new predictive models (mechanical, stochastic, decisional). This work package thus constitutes the
"toolbox" of the IRIMONT project. However, as in the IRIMONT project as a whole, we are favouring an
approach in which the questions are linked to the mountain terrain and its specific features, rather than
a more disciplinary/methodological approach, and we are focusing on developments that can be best
integrated with the expectations of the other work packages.

PEPR MAth Vives - Mathematics for Life, Environment and Society

Participants:

Vincent Acary, Franck Bourrier.

Within this PEPR, we are actively involved in the targeted project on mass movement modeling in
mountains coordinated by Didier Bresch and Farang Radjai.

9.5 Regional initiatives

Smart Protect

The project aims to develop and test an innovative structure for protection against natural hazards.
It is funded by the Auvergne Rhône-Alpes region as part of the R&D operation BOOSTER 2019. The
partnerships (GEOLITHE INNOV, GEOLITHE, MYOTIS, INRIA and INRAE) and the operational solutions
and tools developed as part of the "Smart-Protect" project will constitute major advances in the methods
and means for the natural risk management, both nationally and internationally. GEOLITHE INNOV is
leader of the SMART-PROTECT collaborative project. The financial support for INRIA is devoted to the
post-doc of Nicholas Collins Craft for the study and the development of cohesive zone model for fracture
mechanics simulation.

OCIRN

The OCIRN Project is supported and accompanied by the Auvergne Rhône-Alpes Region. The partners
of the project are Géolithe, CAN, INRIA, department of Isère, Halias Technologies and INDURA cluster.
The general ambition of the OCIRN project is to support the development of the natural gravity hazards
sector in the development and integration of new digital practices. Natural gravity hazards are a growing
concern in the context of global warming generating an increase in the frequency and intensity of events,
combined with the reduction of societal and economic tolerance of these risks. A functional ambition of
the project is to contribute to the integrated and reasoned management of natural gravitational risks,
coordinated with the projects of development of the territories, in order to allow important progress
in the reduction of the risks, the continuity of service of the installations and the optimization of the
operations of mitigation and protection. The OCIRN project aims at 3 major objectives:

1. The capitalization of data and the improvement of information flows between the actors of natural

risks via the digital platform.

2. The sharing of the uses of innovative software of simulation and modeling via the software bricks

of simulation and modeling on digital platform.

3. The homogenization and standardization of practices through the application of methods chosen

by the sector (C2ROP) via the methodological software bricks on the digital platform.

These three objectives are addressed through access to shared tools on a scalable and collaborative
digital platform made available to the sector. In addition, related training, data collection and processing
services will be set up.

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10 Dissemination

10.1 Promoting scientific activities

10.1.1 Scientific events: selection

Member of the conference program committees

• Vincent Acary is a member of the CMIS 2024 program committee The Contact Mechanics Interna-

tional Symposium (CMIS)

• Vincent Acary was a member of the ICCCM 2023 program committee

Reviewer

• Olivier Goury is a regular reviewer of the conferences IEEE International Conference on Robotics
and Automation (ICRA) and Robosoft. He was also reviewer for Robotics: Science and Systems (RSS
2023).

10.1.2 Journal

Member of the editorial boards

• Vincent Acary is editor and co-founder of the Journal of Theoretical, Computational ans Applied
Mechanics (JTCAM) one of the few diamond open access journals, and the only overlay journal in
Mechanics.

• Bernard Brogliato was Guest Managing Editor for Nonlinear Analysis: Hybrid Systems, for the

special issue Nonsmooth Dynamical Systems: Analysis, Control and Optimization.

• Franck Bourrier is member of the Editorial Board of the Journal Landslides.

Reviewer - reviewing activities

• Olivier Goury was reviewer for the following journals: IEEE Robotics and Automation Letters (RA-L)

and Applied Mathematical Modeling.

• Arnaud Tonnelier was reviewer for the following journals: Nonlinear Analysis: Real World Applica-
tion, Physica D: Nonlinear Phenomena, and Journal of Mathematical Analysis and Applications.

• Félix Miranda Villatoro was a reviewer for the following journals: Systems & Control Letters, Auto-
matica, IEEE Control Systems Letters, IEEE Transactions on Automatic Control, and Nonlinear
Analysis:Hybrid Systems.

• Vincent Acary was reviewer for Computer Methods in Applied Mechanics and Engineering (CMAME),
International Journal for Numerical Methods in Engineering(IJNME), Numericsche Mathematik
(NM), IEEE Transactions on Robotics (IEEE-TRO), Nonlinear Analysis: Hybrid Systems (NA-HS),
Mechanical Systems and Signal Processing (MSSP)

• Franck Bourrier was reviewer for the following journals: Landslides, International Journal of
Rock Mechanics and Mining Sciences, Rock Mechanics and Rock Engineering, Plant and Soil,
International Journal for numerical and analytical methods in geomechanics

10.1.3 Invited talks

• Bernard Brogliato was keynote speaker at the 7th IEEE ICCAD conference, Rome,Italy, May 10-12,

2023.

• Bernard Brogliato was keynote speaker at the ICACAR conference, Beijing, China, April 14-16 2023.

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Inria Annual Report 2023

• Bernard Brogliato gave a seminar at IMTEK, University of Freiburg, 30 November 2023, on the

analysis of differential algebraic linear complementarity systems.

• Bernard Brogliato gave a seminar at Université d’Avignon, Laboratoire de Mathématiques, on the
analysis of descriptor variable linear complementarity systems, on Thursday 12 October 2023.

10.1.4 Leadership within the scientific community

• Vincent Acary is the coordinator with R. Leine of the European Network for Nonsmooth Dynamics

(ENNSD).

• Vincent Acary is a member of the Comité National Francais de Mécanique (CNFM) that is the
national instance member of IUTAM, the International Union of Theoretical and Applied Mechanics
(IUTAM).

10.1.5 Scientific expertise

• Vincent Acary was a reviewer for a research proposal for the Dutch Research Council (NWO).

10.2 Teaching - Supervision - Juries

10.2.1 Teaching

• Master : Franck Bourrier, 5H éq TD Modélisation des chutes de blocs, Master GAIA, Université

Savoie Mont-Blanc.

• Master : Franck Bourrier, 30H éq TD Slope Stabilitiy, Polytech’ Grenoble 4th year, Université

Grenoble Alpes.

• Mster : Franck Bourrier, 30H éq TD, Calcul des Structures, Polytech Grenoble, 4th year, Université

Grenoble Alpes.

• Master : Félix Miranda-Villatoro, 32 H TD, Numerical Optimization, 1st year, Grenoble INP, Uni-

versité Grenoble Alpes.

• Licence : Louis Guillet, 31.5H éq TD Analyse réelle, DLST PCMM 1st year, Université Grenoble

Alpes.

• Licence : Nicholas Collins-Craft, 53H éq CTD & TP Analyse élémentaire et introduction au calcul

scientifique, DLST IMA 1st year, Université Grenoble Alpes.

10.2.2 Supervision

• Bernard Brogliato and Félix Miranda Villatoro supervise the PhD thesis of Quang Hung Pham

(analysis and control of nonsmooth networks).

• Bernard Brogliato and Félix Miranda Villatoro supervise the PhD thesis of Aya Younès (tracking

control in linear complementarity systems).

• Vincent Acary, Franck Bourrier and Olivier Goury supervise the Ph.D. thesis of Louis Guillet (start

01/01/2023).

• Olivier Goury and Christian Duriez supervise the Ph.D. thesis of Tanguy Navez (Embodied Intelli-

gence and Mechanical modelling of soft robots using AI, start 01/10/2021).

• Arnaud Tonnelier surpervised the research internship of Pascal Nardi (L3, ENS Lyon) (Dynamics

and bifurcation in a reduced world3 model).

• Vincent Acary and Paul Armand supervise the Ph.D. thesis of Hoang Minh Nguyen (start 01/10/2021).

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• Vincent Acary, Franck Bourrier and Thierry Faug supervise the Ph.D. thesis of Mattéo Oziol (start

01/11/2023).

• Vincent Acary and Jérome Malick supervise the Ph.D. thesis of Florian Vincent (start 01/11/2023).

• Vincent Acary and Franck Bourrier supervise the post-doc intern of Nicholas Collins-Craft, Emilie

Rouzies and Ritesh Gupta.

10.2.3 Juries

• Bernard Brogliato was a committee member for the PhD thesis of Armin Nurkanovic, Freiburg

University, Germany, 27 November 2023.

• Olivier Goury was a committee member for the PhD thesis of Simon Le Berre, Université PSL Mines

Paris Tech, CEA Cadarache, 20 November 2023.

• Vincent Acary was member for the HdR jury of David Bertrand (Insa de Lyon, 06/2023), rapporteur.

10.3 Popularization

10.3.1 Internal or external Inria responsibilities

Olivier Goury is an elected member of the CE (Commission d’évaluation) of Inria.

11 Scientific production

11.1 Major publications

[1] V. Acary and B. Brogliato. Numerical methods for nonsmooth dynamical systems. Applications in
mechanics and electronics. English. Lecture Notes in Applied and Computational Mechanics 35.
Berlin: Springer. xxi, 525~p., 2008.

[2] B. Brogliato. Nonsmooth Mechanics: Models, Dynamics and Control. Springer International Publish-
ing Switzerland; Communications and Control Engineering, 2016. DOI: 10.1007/978-3-319-286
64-8. URL: https://inria.hal.science/hal-01236953.

11.2 Publications of the year

International journals

[3] V. Acary, P. Armand, H. Minh Nguyen and M. Shpakovych. ‘Second order cone programming
for frictional contact mechanics using interior point algorithm’. In: Optimization Methods and
Software (16th Jan. 2024), pp. 1–31. DOI: 10.1080/10556788.2023.2296438. URL: https://hal
.science/hal-03913568.

[4] V. Acary, F. Bourrier and B. Viano. ‘Variational approach for nonsmooth elasto-plastic dynamics
with contact and impacts’. In: Computer Methods in Applied Mechanics and Engineering 414
(8th Feb. 2023), p. 116156. DOI: 10.1016/j.cma.2023.116156. URL: https://inria.hal.scie
nce/hal-03978387.

[5] B. Brogliato. ‘Comments on "Finite-time stability of discrete autonomous systems" [Automatica 122
(2020) 109282] ⋆’. In: Automatica 156 (2023), pp. 1–3. DOI: 10.1016/j.automatica.2023.111206.
URL: https://inria.hal.science/hal-04121636.

[6] B. Brogliato. ‘Modeling, analysis and control of robot–object nonsmooth underactuated Lagrangian
systems: A tutorial overview and perspectives’. In: Annual Reviews in Control 55 (2023), pp. 297–337.
DOI: 10.1016/j.arcontrol.2022.12.002. URL: https://inria.hal.science/hal-043447
31.

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Inria Annual Report 2023

[7] R. Gupta, F. Bourrier, V. Acary and S. Lambert. ‘Bayesian interface based calibration of a novel
rockfall protection structure modelled in the Non-smooth contact dynamics framework’. In: Engin-
eering Structures (15th Dec. 2023). DOI: 10.1016/j.engstruct.2023.116936. URL: https://ha
l.science/hal-04039263.

[8]

S. Lambert, F. Bourrier, A.-R. Ceron-Mayo, L. Dugelas, F. Dubois and G. Piton. ‘Small-Scale Modeling
of Flexible Barriers. I: Mechanical Similitude of the Structure’. In: Journal of Hydraulic Engineering
149.3 (Mar. 2023), p. 04022043. DOI: 10.1061/JHEND8.HYENG-13070. URL: https://hal.inrae
.fr/hal-03917623.

[9] F. Miranda-Villatoro. ‘Robust output convergence of heterogeneous networks via nonsmooth hard-
threshold couplings’. In: Nonlinear Analysis: Hybrid Systems (2023), pp. 1–26. URL: https://hal.s
cience/hal-04333265.

[10] M. R. Mojallizadeh, B. Brogliato, A. Polyakov, S. Selvarajan, L. Michel, F. Plestan, M. Ghanes, J.-P.
Barbot and Y. Aoustin. ‘Discrete-time differentiators in closed-loop control systems: experiments
on electro-pneumatic system and rotary inverted pendulum’. In: Control Engineering Practice 136
(2023), pp. 1–28. DOI: 10.1016/j.conengprac.2023.105546. URL: https://inria.hal.scien
ce/hal-03125960.

[11] M. R. Mojallizadeh, B. Brogliato and C. Prieur. ‘Modeling and control of overhead cranes: a tutorial
overview and perspectives’. In: Annual Reviews in Control (23rd Feb. 2023), pp. 1–73. DOI: 10.1016
/j.arcontrol.2023.03.002. URL: https://inria.hal.science/hal-04010839.

[12] A. Nurkanovi´c, S. Albrecht, B. Brogliato and M. Diehl. ‘The Time-Freezing Reformulation for Nu-
merical OptimalControl of Complementarity Lagrangian Systems with StateJumps - Extended
Version’. In: Automatica 158 (2023), p. 111295. DOI: 10.1016/j.automatica.2023.111295. URL:
https://inria.hal.science/hal-03427800.

[13] A. Tonnelier. ‘Exact solutions for signal propagation along an excitable transmission line’. In:
Physical Review E (7th Dec. 2023), pp. 1–7. URL: https://hal.science/hal-04349848.

[14] A. Tonnelier. ‘Sustainability or societal collapse, dynamics and bifurcations of the handy model’.
In: SIAM Journal on Applied Dynamical Systems 22.3 (2023). URL: https://hal.science/hal-03
659720.

International peer-reviewed conferences

[15] E. Ménager, T. Navez, O. Goury and C. Duriez. ‘Direct and inverse modeling of soft robots by learning
a condensed FEM model’. In: 2023 IEEE International Conference on Robotics and Automation
(ICRA). ICRA 2023 - IEEE International Conference on Robotics and Automation. London, United
Kingdom: IEEE, 29th May 2023, pp. 530–536. DOI: 10.1109/ICRA48891.2023.10161537. URL:
https://inria.hal.science/hal-04167863.

Reports & preprints

[16] V. Acary and N. A. Collins-Craft. Energy conservation and dissipation properties for elastodynamics
with contact impact and friction. 6th Oct. 2023. URL: https://inria.hal.science/hal-04230
941.

[17] B. Brogliato. Lagrange dynamics of lumped-mass multibody models of overhead cranes in 2D and
3D operational spaces. INRIA, Feb. 2023, pp. 1–40. URL: https://inria.hal.science/hal-036
74652.

[18] B. Brogliato. Nonsmooth Mechanics. Models, Dynamics and Control : Erratum/Addendum. INRIA
Centre de l’Universite Grenoble - Alpes, 7th Jan. 2024, pp. 1–19. URL: https://inria.hal.scien
ce/hal-01331565.

[19] B. Brogliato and A. Tanwani. Feedback Interconnections of Passive Linear Cone Complementarity

Systems. 22nd June 2023. URL: https://inria.hal.science/hal-04137144.

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[20] F. Miranda-Villatoro, F. Castaños and A. Franci. Equivalence of Linear Complementarity Problems:
Theory and Application to Nonsmooth Bifurcations. 21st Mar. 2023. URL: https://inria.hal.sc
ience/hal-03319638.

[21] F. Miranda-Villatoro, F. Castaños and B. Brogliato. When proximal-point algorithms meet set-valued
systems. An Optimization point of view of discrete-time sliding modes. 22nd Dec. 2023. URL: https:
//inria.hal.science/hal-04362282.

[22] A. Younes, F. Miranda-Villatoro and B. Brogliato. Trajectory Tracking in Linear Complementarity
Systems with and without State-Jumps: A Passivity Approach. 1st June 2023. URL: https://hal.sc
ience/hal-04113986.

11.3 Other

Softwares

[23]

[SW ] V. Acary, M. Bremond, O. Huber, F. Perignon and R. Pissard-Gibollet, Siconos version 4.4.0,
3rd Apr. 2023. LIC: https://spdx.org/licenses/Apache-2.0. HAL: 〈hal-04056972〉, URL:
https : / / hal . science / hal - 04056972, VCS: https : / / github . com / siconos / siconos,
SWHID: 〈swh:1:dir:e4e31bb51de8898376e7dce8206c0e6a7176186e;origin=https://git
hub.com/siconos/siconos;visit=swh:1:snp:d9057646a859f43c1eae31cb4c7d7dd3030a
440d;anchor=swh:1:rev:6ca5eb6134478ab9cf0e4a5f259d602e52e3df3a〉.

11.4 Cited publications

[24] V. Acary, M. Brémond, K. Kapellos, J. Michalczyk and R. Pissard-Gibollet. ‘Mechanical simulation of
the Exomars rover using Siconos in 3DROV’. In: ASTRA 2013 - 12th Symposium on Advanced Space
Technologies in Robotics and Automation. ESA/ESTEC. Noordwijk, Netherlands, 2013.

[25] V. Acary, M. Brémond, T. Koziara and F. Pérignon. FCLIB: a collection of discrete 3D Frictional

Contact problems. Technical Report RT-0444. INRIA, 2014, p. 34.

[26] V. Acary and B. Brogliato. Numerical methods for nonsmooth dynamical systems. Applications in
mechanics and electronics. English. Lecture Notes in Applied and Computational Mechanics 35.
Berlin: Springer. xxi, 525 p., 2008.

[27] V. Acary, B. Brogliato and Y. V. Orlov. ‘Chattering-Free Digital Sliding-Mode Control With State
Observer and Disturbance Rejection’. In: IEEE Transactions on Automatic Control 57.5 (2012),
pp. 1087–1101. ,

[28] V. Acary and Y. Monerie. Nonsmooth fracture dynamics using a cohesive zone approach. Anglais.

Research Report RR-6032. INRIA, 2006, p. 56.

[29] V. Acary. ‘Energy conservation and dissipation properties of time-integration methods for the
nonsmooth elastodynamics with contact’. In: ZAMM - Journal of Applied Mathematics and Mech-
anics / Zeitschrift für Angewandte Mathematik und Mechanik 96.5 (2016), pp. 585–603. ,

[30] V. Acary. ‘Higher order event capturing time–stepping schemes for nonsmooth multibody systems
with unilateral constraints and impacts.’ In: Applied Numerical Mathematics 62.10 (2012), pp. 1259–
1275. ,

[31] V. Acary. ‘Projected event-capturing time-stepping schemes for nonsmooth mechanical systems
with unilateral contact and Coulomb’s friction’. In: Computer Methods in Applied Mechanics and
Engineering 256 (2013), pp. 224–250. ,

[32] V. Acary, P. Armand and H. M. Nguyen. ‘High-accuracy computation of rolling friction contact
problems’. In: 9th NAFOSTED Conference on Information and Computer Science (NICS). Ho Chi
Minh City, Vietnam, Vietnam: IEEE, Oct. 2022. DOI: 10.1109/NICS56915.2022. URL: https://in
ria.hal.science/hal-03741048.

[33] V. Acary, O. Bonnefon and B. Brogliato. Nonsmooth modeling and simulation for switched circuits.

Springer Netherlands, 2011. ,

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Inria Annual Report 2023

[34] V. Acary, M. Brémond and O. Huber. ‘Advanced Topics in Nonsmooth Dynamics.’ In: Advanced
Topics in Nonsmooth Dynamics. To appear. Springer International Publishing, 2018. Chap. On
solving frictional contact problems: formulations and comparisons of numerical methods. Pp. 375–
457. ,

[35] V. Acary, M. Brémond and O. Huber. ‘On solving contact problems with Coulomb friction: formula-
tions and numerical comparisons’. In: Advanced Topics in Nonsmooth Dynamics - Transactions of
the European Network for Nonsmooth Dynamics. Ed. by S. I. Publishing. June 2018, pp. 375–457.
DOI: 10.1007/978-3-319-75972-2\_10. URL: https://hal.inria.fr/hal-01878539.

[36] V. Acary and B. Brogliato. ‘Implicit Euler numerical scheme and chattering-free implementation of

sliding mode systems’. In: Systems &amp; Control Letters 59.5 (2010). doi:10.1016/j.sysconle.2010.03.002,
pp. 284–293. ,

[37] V. Acary, B. Brogliato and D. Goeleven. ‘Higher order Moreau’s sweeping process: mathematical
formulation and numerical simulation’. In: Mathematical Programming 113.1 (2008), pp. 133–217.
,

[38] V. Acary, H. de Jong and B. Brogliato. ‘Numerical Simulation of Piecewise-Linear Models of Gene
Regulatory Networks Using Complementarity Systems Theory’. In: Physica D: Nonlinear Phenom-
ena 269 (2013), pp. 103–119. ,

[39] N. Akhadkar, V. Acary and B. Brogliato. ‘Multibody systems with 3D revolute joint clearance, model-
ling, numerical simulation and experimental validation: an industrial case study’. In: Multibody
System Dynamics 42.3 (2017), pp. 249–282. ,

[40] R. Alur, C. Courcoubetis, N. Halbwachs, T. Henzinger, P.-H. Ho, X. Nicollin, A. Olivero, J. Sifakis
and S. Yovine. ‘The algorithmic analysis of hybrid systems.’ In: Theoretical Computer Science 138.1
(1995), pp. 3–34. ,

[41] A. Beck and M. Teboulle. ‘A Fast Iterative Shrinkage-Thresholding Algorithm for Linear Inverse
Problems’. In: SIAM Journal on Imaging Sciences 2.1 (2009), pp. 183–202. eprint: http://dx.doi
.org/10.1137/080716542.

[42] M. di Bernardo, C. Budd, A. Champneys and P. Kowalczyk. Piecewise-smooth dynamical systems :

theory and applications. Applied mathematical sciences. London: Springer, 2008.

[43] F. Bourrier and V. Acary. ‘Predictive capabilities of 2D and 3D block propagation models integrating
block shape assessed from field experiments’. In: Rock Mechanics and Rock Engineering 55.2 (2022),
pp. 591–609.

[44] F. Bourrier, F. Berger, P. Tardif, L. Dorren and O. Hungr. ‘Rockfall rebound: comparison of detailed
field experiments and alternative modelling approaches’. In: Earth Surface Processes and Landforms
37.6 (2012), pp. 656–665.

[45] F. Bourrier, L. Dorren, F. Nicot, F. Berger and F. Darve. ‘Toward objective rockfall trajectory simulation

using a stochastic impact model’. In: Geomorphology 110.3-4 (2009), pp. 68–79. ,

[46] F. Bourrier, D. Toe, B. Garcia, J. Baroth and S. Lambert. ‘Experimental investigations on complex
block propagation for the assessment of propagation models quality’. In: Landslides 18.2 (Feb.
2021), pp. 639–654. DOI: 10.1007/s10346-020-01469-5. URL: https://hal.archives-ouver
tes.fr/hal-03129220.

[47] B. Brogliato and L. Thibault. ‘Existence and uniqueness of solutions for non-autonomous comple-

mentarity dynamical systems’. In: J. Convex Anal. 17.3-4 (2010), pp. 961–990.

[48] O. Brüls, V. Acary and A. Cardona. ‘Simultaneous enforcement of constraints at position and
velocity levels in the nonsmooth generalized-α scheme’. English. In: Computer Methods in Applied
Mechanics and Engineering 281 (2014), pp. 131–161. ,

[49] B. Caillaud. Hybrid vs. nonsmooth dynamical systems. synchron. http://synchron2014.inria.fr/wp-

content/uploads/sites/13/2014/12/Caillaud-nsds.pdf. 2014.

[50] G. Capobianco and S. R. Eugster. ‘Time finite element based Moreau-type integrators’. In: Interna-
tional Journal for Numerical Methods in Engineering 114.3 (2018), pp. 215–231. eprint: https://o
nlinelibrary.wiley.com/doi/pdf/10.1002/nme.5741.

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[51] L. P. Carloni, R. Passerone, A. Pinto and A. L. Angiovanni-Vincentelli. ‘Languages and tools for
hybrid systems design’. In: Foundations and Trends in Electronic Design Automation 1.1/2 (2006),
pp. 1–193. ,

[52] Q.-z. Chen, V. Acary, G. Virlez and O. Brüls. ‘A nonsmooth generalized-α scheme for flexible
multibody systems with unilateral constraints’. In: International Journal for Numerical Methods in
Engineering 96.8 (2013), pp. 487–511. ,

[53] N. A. Collins-Craft, F. Bourrier and V. Acary. ‘On the formulation and implementation of extrinsic
cohesive zone models with contact’. In: Computer Methods in Applied Mechanics and Engineering
400 (Oct. 2022), p. 115545. DOI: 10.1016/j.cma.2022.115545. URL: https://hal.science/ha
l-03371667.

[54] R. W. Cottle, J. Pang and R. E. Stone. The Linear Complementarity Problem. Boston, MA: Academic

Press, Inc., 1992.

[55] L. Dorren, F. Berger, M. Jonsson, M. Krautblatter, M. Mölk, M. Stoffel and A. Wehrli. ‘State of the art
in rockfall – forest interactions’. In: Schweizerische Zeitschrift fur Forstwesen 158.6 (2007), pp. 128–
141. eprint: https://doi.org/10.3188/szf.2007.0128. ,

[56]

S. Dupire, F. Bourrier, J.-M. Monnet, S. Bigot, L. Borgniet, F. Berger and T. Curt. ‘Novel quantitative
indicators to characterize the protective effect of mountain forests against rockfall’. In: Ecological
Indicators 67 (2016), pp. 98–107. ,

[57] F. Facchinei and J. S. Pang. Finite-dimensional Variational Inequalities and Complementarity

Problems. Vol. I & II. Springer Series in Operations Research. Springer New York, 2003. ,

[58] A. F. Filippov. Differential Equations with Discontinuous Right Hand Sides. Dordrecht, the Nether-

lands: Kluwer, 1988.

[59] M. P. Friedlander and D. Orban. ‘A primal–dual regularized interior-point method for convex
quadratic programs’. In: Mathematical Programming Computation 4.1 (2012), pp. 71–107.

[60] F. Génot and B. Brogliato. ‘New results on Painlevé Paradoxes’. In: European Journal of Mechanics -

A/Solids 18.4 (1999), pp. 653–677. ,

[61] D. Goeleven. Complementarity and Variational Inequalities in Electronics. Academic Press, 2017.

[62] T. A. Henzinger. ‘The Theory of Hybrid Automata’. In: Verification of Digital and Hybrid Systems.

Springer Berlin Heidelberg, 1996, pp. 265–292.

[63]

[64]

J.-B. Hiriart-Urruty and C. Lemaréchal. Convex Analysis and Minimization Algorithms. Vol. I and II.
Springer Berlin Heidelberg, 1993. ,

J.-B. Hiriart-Urruty and C. Lemaréchal. Fundamentals of Convex Analysis. Springer Berlin Heidel-
berg, 2001. ,

[65] O. Huber, B. Brogliato, V. Acary, A. Boubakir, F. Plestan and W. B. ‘Experimental results on implicit
and explicit time-discretization of equivalent-control-based sliding-mode control’. In: Recent
Trends in Sliding Mode Control. Ed. by L. Fridman, J. Barbot and F. Plestan. Institution of Engineering
and Technology, 2016, pp. 207–235. ,

[66] O. Huber, V. Acary, B. Brogliato and F. Plestan. ‘Implicit discrete-time twisting controller without
numerical chattering: analysis and experimental results’. In: Control Engineering Practice 46 (2016),
pp. 129–141. ,

[67] G. James. ‘Periodic travelling waves and compactons in granular chains’. In: Journal of Nonlinear

Science 22.5 (2012), pp. 813–848. ,

[68] G. James, P. G. Kevrekidis and J. Cuevas. ‘Breathers in oscillator chains with Hertzian interactions’.

In: Physica D: Nonlinear Phenomena 251 (2013), pp. 39–59. ,

[69] M. Jean, V. Acary and Y. Monerie. ‘Non Smooth Contact dynamics approach of cohesive materials’.
In: Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and
Engineering Sciences 359.1789 (2001), pp. 2497–2518. ,

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[70] M. Keiler, J. Knight and S. Harrison. ‘Climate change and geomorphological hazards in the eastern
European Alps’. In: Philosophical Transactions of the Royal Society A: Mathematical, Physical and
Engineering Sciences 368.1919 (2010), pp. 2461–2479.

[71] R. Leine and N. van de Wouw. Stability and Convergence of Mechanical Systems with Unilateral
Constraints. Vol. 36. Lecture Notes in Applied and Computational Mechanics. Springer Verlag, 2008.

[72] R. I. Leine, A. Schweizer, M. Christen, J. Glover, P. Bartelt and W. Gerber. ‘Simulation of rockfall
trajectories with consideration of rock shape’. In: Multibody System Dynamics 32.2 (2014), pp. 241–
271. ,

[73] L. Liu, G. James, P. Kevrekidis and A. Vainchtein. ‘Nonlinear waves in a strongly resonant granular

chain’. In: Nonlinearity 29.11 (2016), pp. 3496–3527. ,

[74] F. A. Miranda-Villatoro, F. Forni and R. J. Sepulchre. ‘Dissipativity analysis of negative resistance

circuits’. In: Automatica 136 (2022), p. 110011.

[75] F. A. Miranda-Villatoro, B. Brogliato and F. Castanos. ‘Multivalued Robust Tracking Control of
Lagrange Systems: Continuous and Discrete–Time Algorithms’. In: IEEE Transactions on Automatic
Control 62.9 (2017), pp. 4436–4450. ,

[76]

J. Morales, G. James and A. Tonnelier. Solitary waves in the excitable Burridge-Knopoff model.
Research Report RR-8996. To appear in Wave Motion. INRIA Grenoble - Rhône-Alpes, 2016, pp. 103–
121. ,

[77] Y. Nesterov. ‘A method of solving a convex programming problem with convergence rate O(1/k2)’.

In: Soviet Mathematics Doklady 27.2 (1983), pp. 372–376.

[78] M. H. Nguyen. ‘Numerical optimization for rolling frictional contact problems’. MA thesis. Uni-

versité de Limoges, Sept. 2021. URL: https://hal.inria.fr/hal-03483150.

[79] M.-H. Nguyen, V. Acary and P. Armand. ‘Second-order cone programming for rolling friction contact

mechanics’. In: SMAI MODE 2022. 2022.

[80] N. Nguyen and B. Brogliato. Multiple Impacts in Dissipative Granular Chains. Vol. 72. Lecture Notes

in Applied and Computational Mechanics. XXII, 234 p. 109 illus. Springer Verlag, 2014.

[81] M. A. Porter, P. G. Kevrekidis and C. Daraio. ‘Granular crystals: Nonlinear dynamics meets materials

engineering’. In: Physics Today 68.11 (2015), pp. 44–50. ,

[82] A. Rist. ‘Hydrothermal processes within the active layer above alpine permafrost in steep scree

slopes and their influence on slope stability’. PhD thesis. University of Zurich, 2007.

[83] R. T. Rockafellar. Convex Analysis. Princeton University Press, 1970.

[84] T. Schindler and V. Acary. ‘Timestepping schemes for nonsmooth dynamics based on discontinuous
Galerkin methods: Definition and outlook’. In: Mathematics and Computers in Simulation 95 (2013),
pp. 180–199. ,

[85] T. Schindler, S. Rezaei, J. Kursawe and V. Acary. ‘Half-explicit timestepping schemes on velocity
level based on time-discontinuous Galerkin methods’. In: Computer Methods in Applied Mechanics
and Engineering 290.15 (2015), pp. 250–276. ,

[86] M. Shpakovych. ‘Numerical optimization for frictional contact problems’. MA thesis. Université de

Limoges, Sept. 2019. URL: https://hal.inria.fr/hal-03483159.

[87] C. Studer. Numerics of Unilateral Contacts and Friction. – Modeling and Numerical Time Integra-
tion in Non-Smooth Dynamics. Vol. 47. Lecture Notes in Applied and Computational Mechanics.
Springer Verlag, 2009.
<scratchpad>
- Main topic: Research Centre TRIPOP (INRIA Grenoble Rhône-Alpes)
- Key points:
  - Focus on modeling, simulation, and control of nonsmooth dynamical systems
  - Two research axes: (1) nonsmooth simulation and numerical modeling for natural gravitational risk in mountains and (2) modeling, simulation, and control of nonsmooth dynamical systems
  - Collaboration with other research centers and industries
  - Emphasis on software development and industrial transfer
- Structure: The document is divided into several sections, including research program, application domains, social and environmental responsibility, new software, and scientific production.
- Potential artifacts to ignore: Unnecessary web-related elements, such as links, HTML tags, and other web-related elements.
</scratchpad>

<final_summary>
The TRIPOP research centre, located at INRIA Grenoble Rhône-Alpes, focuses on modeling, simulation, and control of nonsmooth dynamical systems. The centre is divided into two research axes: (1) nonsmooth simulation and numerical modeling for natural gravitational risk in mountains and (2) modeling, simulation, and control of nonsmooth dynamical systems. The centre collaborates with other research centers and industries, with an emphasis on software development and industrial transfer. The research centre has produced several notable publications and has been involved in various projects, including the development of new software and the analysis of nonsmooth dynamical systems. Overall, the TRIPOP research centre is dedicated to advancing the field of nonsmooth dynamical systems and their applications in various fields.
The TRIPOP research centre, located at INRIA Grenoble Rhône-Alpes, focuses on modeling, simulation, and control of nonsmooth dynamical systems. The centre is divided into two research axes: (1) nonsmooth simulation and numerical modeling for natural gravitational risk in mountains and (2) modeling, simulation, and control of nonsmooth dynamical systems. The centre collaborates with other research centers and industries, with an emphasis on software development and industrial transfer. The research centre has produced several notable publications and has been involved in various projects, including the development of new software and the analysis of nonsmooth dynamical systems. Overall, the TRIPOP research centre is dedicated to advancing the field of nonsmooth dynamical systems and their applications in various fields.