Alessandro Tasora

University of Parma | UNIPR · Department of Engineering and Architecture

title>ABSTRACT We describe a simulation environment that enables the design and testing of control policies for off-road mobility of autonomous agents. The environment is demonstrated in conjunction with the design and assessment of a reinforcement learning policy that uses sensor fusion and inter-agent communication to enable the movement of mixe...

While an accurate computation of the tangent stiffness matrix of multibody systems is usually of critical importance in various numerical analyses, one contribution often neglected in dynamics is represented by the tangent stiffness matrix of constraints. This term, resulting from the change of joints reactions with respect to the coordinates of th...

The eigenvalues of the free rotation mode of multi-bladed rotor systems are of crucial importance when designing controllers. An unstable free rotation mode of the rotor is unfavorable. In this paper, the Differential Algebraic Equations (DAEs) of the multi-flexible-body system are linearized after having introduced a corotational formulation with...

In this work, we discuss the numerical challenges involved in the computation of the complex eigenvalues of damped multi-flexible-body problems. Aiming at the highest generality, the candidate method must be able to deal with arbitrary rigid body modes (free–free mechanisms), arbitrary algebraic constraints, and must be able to exploit the sparsity...

In this work we discuss the numerical challenges involved in the computation of the complex eigenvalues of damped multi-flexible-body problems. Aiming at the highest generality, the candidate method must be able to deal with arbitrary rigid body modes (free-free mechanisms), arbitrary algebraic constraints, and must be able to exploit the sparsity...

An explicit cosimulation scheme is developed to study the coupling of smooth and nonsmooth systems using kinematic constraints. Using the force-displacement decomposition, the coupling constraints are formulated at the velocity level, to preserve consistency with the impulse-momentum equations for frictional contacts in the nonsmooth solver, which...

Masonry structures

This contribution (i) describes an open-source, physics-based simulation infrastructure that can be used to learn and test control policies in off-road navigation; and (ii) demonstrates the use of the simulation platform in an end-to-end learning exercise that relies on simulated sensor data fusion (camera, GPS and IMU). For (i), the 0.5 million li...

gym-chrono is a set of simulated environments for Deep Reinforcement Learning (DRL) extending OpenAI Gym (Brockman et al., Openai gym, 2016) with robotics and autonomous driving tasks. The physics of these environments is simulated thanks to Project Chrono (Tasora et al., Chrono: An open source multi-physics dynamics engine, 2016), an open-source m...

We propose to use the alternating direction method of multipliers (ADMMs) for solving the variational inequality that arises in non-smooth contact problems in multibody simulations. The ADMM method is based on simple computational primitives and offers good convergence properties especially for scenarios where loose tolerance on the precision can b...

We describe a simulation environment that enables the design and testing of control policies for off-road mobility of autonomous agents. The environment is demonstrated in conjunction with the training and assessment of a reinforcement learning policy that uses sensor fusion and inter-agent communication to enable the movement of mixed convoys of h...

We describe a simulation environment that enables the development and testing of control policies for off-road mobility of autonomous agents. The environment is demonstrated in conjunction with the design and assessment of a reinforcement learning policy that uses sensor fusion and inter-agent communication to enable the movement of mixed convoys o...

This paper proposes a new methodology for the interpolation of a given set of 3D rotation poses that have to be reached in successive times by preserving continuity in orientation, angular velocity and angular acceleration. The discussed algorithm ensures the generation of smooth angular trajectories without singularities. The distinctive features...

This work presents a numerical method for the solution of variational inequalities arising in non‐smooth flexible multi‐body problems that involve set‐valued forces. For the special case of hard frictional contacts, the method solves a second order cone complementarity problem. We ground our algorithm on the Alternating Direction Method of Multipli...

To tackle coupled problems between smooth multibody systems and particle dampers, co-simulation between two general-purpose multibody codes is carried out, where the coupled system is decomposed by the force/displacement technique, and integrated by a loose coupling scheme or a tight one with iterative process. The stability properties of the coupl...

In this paper we use the Proximal Policy Optimization (PPO) deep reinforcement learning algorithm to train a Neural Network to control a four-legged robot in simulation. Reinforcement learning in general can learn complex behavior policies from simple state-reward tuples datasets and PPO in particular has proved its effectiveness in solving complex...

The increasing complexity of dynamic simulations involving unilateral constraints, such as contacts, is pushing for new solvers that may address the problem of handling non-smooth impact events in a more efficient and accurate manner, especially in mixed rigid and flexible-bodies simulations. For this purpose, a new implementation of an interior-po...

This work discusses an efficient formulation of a geometrically exact three-dimensional beam which can be used in dynamical simulations involving large displacements, collisions and non-linear materials. To this end, we base our model on the shear-flexible Cosserat rod theory and we implement it in the context of Isogeometric Analysis (IGA). Accord...

In this work we focus on the role of Multibody Simulation in creating Reinforcement Learning virtual environments for robotic manipulation, showing a versatile, efficient and open source toolchain to create directly from CAD models. Using the Chrono::Solidworks plugin we are able to create robotic environments in the 3D CAD software Solidworks® and...

The Conservation of Historical Architectural Heritage Cannot Be Limited only to a Series of Isolated Interventions on Materials and Structures, but must Include Also the Maintenance or Insertion of Compatible Uses, which can Guarantee a Continuous Upkeep. the Exploitation of Heritage, nevertheless, is a Wedge Issue, as it Involves New Loads, more W...

The cupola (dome) of Santa Maria del Fiore in Florence was ingeniously constructed by Brunelleschi using a conical bricklaying, radial-oriented toward a focus point on the central axis. Therefore, the dome is built as a surface of revolution but with parts cut away to leave the octagonal cluster vault form. This circular arrangement is compared wit...

Materials recycling is a key process to close the loop of materials in the direction of circular economy. However, the variability of waste and the high volatility of the price of recovered materials are posing serious challenges to the current rigid design of mechanical recycling systems. This is particularly true for Waste Electric and Electronic...

Chrono::Vehicle is a module of the open-source multi-physics simulation package Chrono, aimed at modeling, simulation, and visualization of wheeled and tracked ground vehicle multi-body systems. Its software architecture and design was dictated by the desire to provide an expeditious and user-friendly mechanism for assembling complex vehicle models...

This paper describes a model for deformable soil based on triangular meshes with vertical deformation. Such soil model can be used in a multi-body simulation environment to study the performance of wheeled or tracked vehicles. The formulation is inspired by the soil contact model (SCM), but unlike the original idea, our implementation uses triangul...

Chrono::Vehicle is a module of the open-source multi-physics simulation package Chrono, aimed at modeling, simulation, and visualization of wheeled and tracked ground vehicle multi- body systems. Its software architecture and design was dictated by the desire to provide an expeditious and user-friendly mechanism for assembling complex vehicle model...

This document contains details of the SCM deformable soil model implemented in Chrono. The soft soil model discussed herein is an extended version of the classical SCM Soil Contact Model used at DLR for predicting rover mobility. The model, which is based on a fast semi-empirical expeditious approach that requires few parameters, is ideal for scena...

This paper describes a model for deformable soil based on triangular meshes with vertical deformation. Such soil model can be used in a multi-body simulation environment to study the performance of wheeled or tracked vehicles. The formulation is inspired by the the Soil Contact Model (SCM), but unlike the original idea, our implementation uses tria...

The effect of shear sliding on the failure load and collapse mode of segmental arches is studied with a Non-Smooth Contact Dynamics (NSCD) approach, which allows a full 3D dynamic analysis of complex systems of rigid blocks in frictional contact à la Coulomb. The numerical solution at each time-step relies upon an associative frictional model, but...

The observation of old construction works confirms that masonry domes can withstand tensile hoop stresses, at least up to a certain level. Here, such tensile resistance, rather than a priori assumed as a property of the bulk material, is attributed to the contact forces that are developed at the interfaces between interlocked blocks under normal pr...

This paper presents a new mechanical regulator for wrist watches, highlighting the methodology used to set up a comprehensive model of the device. The mechanical regulator, which is characterized by a high frequency monolithic oscillator made of monocrystalline silicon coupled to a deadbeat escapement, has been designed to provide a high quality fa...

Time-stepping methods for non-smooth dynamics are based on the solution of multiple complementarity problems: solving this class of problems represents a major numerical bottleneck, especially when dealing with near-singular and ill-posed systems such as those which feature large mass ratios between mechanical parts. To overcome these difficulties,...

This technical brief revisits the method outlined in Tasora and Anitescu 2011 ["A Matrix-Free Cone Complementarity Approach for Solving Large-Scale, Nonsmooth, Rigid Body Dynamics," Comput. Methods Appl. Mech. Eng., 200(5-8), pp. 439-453], which was introduced to solve the rigid multibody dynamics problem in the presence of friction and contact. Th...

Abstract A Non-Smooth Contact Dynamic (NSCD) formulation is used to analyze complex assemblies of rigid blocks, representative of real masonry structures. A model of associative friction sliding is proposed, expressed through a Differential Variational Inequality (DVI) formulation, relying upon the theory of Measure Differential Inclusion (MDI). A...

The development of dedicated numerical codes has recently pushed forward the study of N -body gravitational dynamics, leading to a better and wider understanding of processes involving the formation of natural bodies in the Solar System. A major branch includes the study of asteroid formation: evidence from recent studies and observations support t...

Abstract The goal of the present paper is to numerically investigate the effects produced by a vertical barrier located inside the ground, when the soil is subjected to seismic waves coming from a seismic source with a planar wave front. Firstly, the acceleration field on the ground surface is computed by varying both geometrical and mechanical pro...

This work presents an efficient way to perform coordinate transformations by computing position, rotation, velocities and accelerations at once, thanks to a custom algebra that maps to synthetic C++ expressions. To this end we took advantage of advanced concepts in object oriented programming, with special emphasis on operator overloading.

Rigid unilateral contacts in multibody problems lead to non-smooth dynamics: this requires the development of new types of time integrators that draw on the solution of a vari-ational inequality at each time step. In most settings, this variational inequality is a comple-mentarity problem. In the context of non-smooth multibody dynamics, projected...

Differential Variational Inequalities (DVI) are generalizations of Differential Algebraic Equations (DAEs) to the case where discontinuities and inequalities are present in the system; as such, they can provide a formulation for the dynamics of non-smooth mechanical problems [1]. A numerical discretization of DVIs lead to the solution of multiple c...

We provide an overview of a multi-physics dynamics engine called Chrono. Its forte is the handling of complex and large dynamic systems containing millions of rigid bodies that interact through frictional contact. Chrono has been recently augmented to support the modeling of fluid-solid interaction (FSI) problems and linear and nonlinear finite ele...

This study deals with the dynamical evolutions exhibited by a simple mechanical model of building, comprising a parallelepiped standing on a horizontal plane. The main goal is the introduction of a pendulum in order to reduce oscillations. The theoretical part of the work consists of a Lagrange formulation and Galerkin approximation method, and dry...

Interactions between buildings and earthquakes have been studied for a long time, and there is much literature about them. This research deals with the dynamical evolutions exhibited by a simple mechanical model of building, comprising a parallelepiped standing on a horizontal plane. The main goal is the introduction of a pendulum in order to contr...

The increasing complexity of multibody dynamic systems demands for efficient linear solvers that could take advantage not only of computational resources of sequential machine, but also of parallel and distributed systems. As high performance computing is becoming an affordable commodity for engineering applications, the development of efficient sp...

Recently, the development of dedicated numerical codes has pushed forward the study of N-body gravitational dynamics leading to better and wider understanding of processes involving the formation of natural bodies in the Solar System. A major branch includes the study of asteroid formation: evidence from recent studies and observations support the...

This work illustrates the application of general-purpose multibody formulations to the analysis of rotating systems dynamics. Various benchmark problems encompassing multiple deformable components are presented and analyzed. The suitability of the approach is assessed and conclusions are drawn on the basis of correlating the numerical simulations w...

We present a solution method that, compared to the traditional Gauss-Seidel approach, reduces the time required to simulate the dynamics of large systems of rigid bodies interacting through frictional contact by one to two orders of magnitude. Unlike Gauss-Seidel, it can be easily parallelized, which allows for the physics-based simulation of syste...

This paper discusses a scalable collision detection algorithm. The algorithm, implemented using software executed on ubiquitous Graphics Processing Unit (GPU) cards, demonstrates two orders of magnitude speedup over state-of-the art sequential implementations when handling multi-million object collision detection tasks. GPUs are composed of many (o...

In this work (also, preprint ANL/MCS-P3020-0812, Argonne National Laboratory) we introduce a complementarity-based rolling friction model to characterize dissipative phenomena at the interface between moving parts. Since the formulation is based on differential inclusions, the model fits well in the context of nonsmooth dynamics, and it does not re...

Many-body dynamics problems are expected to handle millions of unknowns when, for instance, investigating the three-dimensional flow of granular material. Unfortunately, the size of the problems tractable by existing numerical solution techniques is severely limited on convergence grounds. This is typically the case when the equations of motion emb...

The efficiency of parallel solvers for large multibody systems is affected by the topology of the network of constraints. In the most general setting, that is the case of problems involving contacts between large numbers of parts, the mechanical topology cannot be predicted a priori and also changes during the simulation. Depending on the strategy...

This contribution discusses a multi-physics simulation engine, called Chrono, that relies heavily on parallel computing. Chrono aims at simulating the dynamics of systems containing rigid bodies, flexible (compliant) bodies, and fluid-rigid body interaction. To this end, it relies on five modules: equation formulation (modeling), equation solution...

This work describes an approach to simulate contacts between three-dimensional shapes with compliance and damping using the framework of the differential variational inequality theory. Within the context of non-smooth dynamics, we introduce an extension to the classical set-valued model for frictional contacts between rigid bodies, allowing contact...

In the context of this work we present static experimental tests on nitrile-based elastomeric radial lip seals under different radial loads and with different temperatures. The outcomes of these experiments have been used to calibrate a three-dimensional finite element model for performing static analyses of a radial lip seal. Experimental results...

This paper proposes an iterative method that can simulate mechanical systems featuring a large number of contacts and joints between rigid bodies. The numerical method behaves as a contractive mapping that converges to the solution of a cone complementarity problem by means of iterated fixed-point steps with separable projections onto convex manifo...

Aiming at the simulation of dense granular flows, we propose and test a numerical method based on successive convex complementarity problems. This approach origi-nates from a multibody description of the granular flow: all the particles are simulated as rigid bodies with arbitrary shapes and frictional contacts. Unlike the discrete ele-ment method...

The last decade witnessed a manifest shift in the microprocessor industry towards chip designs that promote parallel computing. Until recently the privilege of a select group of large research centers, Teraflop computing is becoming a commodity owing to inexpensive GPU cards and multi to many-core x86 processors. This paradigm shift towards large s...

This contribution is concerned with the modeling and simulation of many-body dynamics problems. In such problems, the solution method has to routinely handle millions of unknowns when, for instance, investigating granular dynamics related phenomena. Given the size of these problems, the scope of tractable applications may be limited by computationa...

Many-body dynamics problems are expected to handle millions of unknowns when, for instance, investigating the three-dimensional flow of granular material. Unfortunately , the size of the problems tractable by existing numerical solution techniques is severely limited on convergence grounds. This is typically the case when the equations of motion em...

At a time when sequential computing is limited to marginal year-to-year gains in speed, multi- and many-core architecture provide teraflop-grade performance to cost-conscious users. The ongoing shift to parallel computing spurs new research into solution methods that emphasize algorithmic concurrency. It also provides an opportunity to revisit comp...

Operator overloading is a powerful feature of modern object-oriented programming languages; it can be used to customize the default algebraic operators to a point where the programming syntax can accommodate new algebras acting on complex objects. The present work introduces a custom T (T,) algebra which can be used to express kinematic transformat...

This paper describes a software infrastructure made up of tools and libraries designed to assist developers in implementing computational dynamics applications running on heterogeneous and distributed computing environments. Together, these tools and libraries compose a so called Heterogeneous Computing Template (HCT). The heterogeneous and distrib...

This paper describes an approach for the dynamic simulation of computer-aided engineering models where large collections of rigid bodies interacting through millions of frictional contacts and bilateral mechanical constraints. Thanks to the massive parallelism available on modern GPUs, we are able to simulate sand, granular materials, and other com...

This paper describes an approach for the dynamic simulation of complex computer-aided engineering models where large collections of rigid bodies interact mutually through millions of frictional contacts and bilateral me-chanical constraints. Thanks to the massive parallelism available on to-day's GPU boards, we are able to simulate sand, granular m...

This work reports on advances in large-scale multibody dynamics simulation facilitated by the use of the Graphics Processing Unit (GPU). A description of the GPU execution model along with its memory spaces is provided to illustrate its potential parallel scientific computing. The equations of motion associated with the dynamics of large system of...

Aiming at a fast and robust simulation of large multibody systems with contacts and friction, this work presents a novel method for solving large cone complementarity problems by means of a fixed-point iteration. The method is an extension of the Gauss-Seidel and Gauss-Jacobi method with overrelaxation for symmetric convex linear complementarity pr...

This paper discusses a scalable collision detection algorithm. The algorithm, implemented using software executed on ubiquitous Graphics Processing Unit (GPU) cards, demonstrates two orders of magnitude speedup over state-of-the art sequential implementations when handling multi-million object collision detection tasks. GPUs are composed of many (o...

Engineers are increasingly relying on simulation to augment and, in some cases, replace large amounts of experimental work. However, current simulation capabilities are sometimes inadequate to capture phenomena of interest. In tracked vehicle analysis, for example, the interaction of the track with granular terrain has been difficult to characteriz...

Engineers are increasingly relying on simulation to augment and, in some cases, replace large amounts of experimental work. However, current simulation capabilities are sometimes inadequate to capture phenomena of interest. In tracked vehicle analysis, for example, the interaction of the track with granular terrain has been difficult to characteriz...

We describe an efficient method for the simulation of complex scenarios with millions of frictional contacts and mechanical constraints. To this end, the GPU processors of the modern graphic boards are used to solve the differential inclusion problem that represents the most challenging part of the multi-rigid-body problem. Thank to the massive par...

This study illustrates the effectiveness of an advanced incisal table surface, featuring adjustable curvature, in the sake of more accurate articulator kinematics in anterior teeth reconstruction. Prosthetic articulators, used by dental technicians in reconstructive dentistry, are adjustable instruments that simulate the motion of mastication betwe...

This paper describes a numerical method for the parallel solution of the differential measure inclusion problem posed by mechanical multibody systems containing bilateral and unilateral frictional constraints. The method proposed has been implemented as a set of parallel algorithms leveraging NVIDIA's Compute Unified Device Architecture (CUDA) libr...

Abstract In the context of simulating the frictional contact dynamics of large systems of rigid bodies, this paper reviews a novel method,for solving large cone complementarity,problems by means,of a fixed-point iteration algorithm. The method is an extension of the Gauss-Seidel and Gauss-Jacobi methods,with overrelaxation for symmetric convex line...

In the context of simulating the frictional contact dynam-ics of large systems of rigid bodies, this paper reviews a novel method for solving large cone complementarity problems by means of a fixed-point iteration algorithm. The method is an extension of the Gauss-Seidel and Gauss-Jacobi methods with overrelaxation for symmetric convex linear compl...