Radu Serban

Radu Serban
University of Wisconsin–Madison | UW · Department of Mechanical Engineering

About

127
Publications
39,269
Reads
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4,103
Citations
Additional affiliations
March 2013 - September 2018
University of Wisconsin–Madison
Position
  • Senior Researcher
April 2008 - December 2012
Xulu Entertainment
Position
  • Senior Computational Scientist
June 2001 - April 2008
Lawrence Livermore National Laboratory
Position
  • Computational Scientist

Publications

Publications (127)
Conference Paper
Sophisticated modeling and simulation, based on rigid and flexible multibody dynamics, are nowadays a standard procedure in the design and analysis of vehicle systems and are widely adopted for on-road driving. Off-road driving for both terrestrial wheeled and tracked vehicles, as well as wheeled and legged robots and rovers for extra-terrestrial e...
Preprint
Full-text available
The focus of this contribution is on camera simulation as it comes into play in simulating autonomous robots for their virtual prototyping. We propose a camera model validation methodology based on the performance of a perception algorithm and the context in which the performance is measured. This approach is different than traditional validation o...
Preprint
Full-text available
We describe a software framework and a hardware platform used in tandem for the design and analysis of robot autonomy algorithms in simulation and reality. The software, which is open source, containerized, and operating system (OS) independent, has three main components: a ROS 2 interface to a C++ vehicle simulation framework (Chrono), which provi...
Article
Full-text available
We describe an analytical framework implemented in a general-purpose mobility simulation platform for enabling the design of control policies for improved rover mobility in granular terrain environments. We employ a homogenization of the granular material and use an elasto-plastic continuum model to capture the dynamics of the deformable terrain. T...
Article
Full-text available
The Discrete Element Method (DEM) is a suitable approach for modeling and simulating arable soil and tillage processes. In this work, we focus on modeling soil fragmentation which is a vital element of many soil treatments. We present a method for computing the indirect tensile strength of soil aggregates through simulation. DEM aggregates are cons...
Article
Full-text available
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...
Preprint
Full-text available
We seek to develop control policies for optimized rover mobility on deformable granular material terrains using a co-simulation framework implemented in an open-source simulation platform. An elasto-plastic continuum model is employed for the purpose of increasing the simulation speed in capturing the dynamics of the deformable granular material te...
Preprint
Full-text available
We describe a field-robotics relevant, general-purpose framework to characterize machine-ground interaction and demonstrate it for bulldozing and mobility studies in conjunction with a replica of NASA's VIPER rover operating on deformable, granular material-type terrain. The contribution of this work is twofold: the approach proposed for capturing...
Chapter
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...
Article
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...
Article
Full-text available
We report on an open-source, publicly available C++ software module called Chrono::GPU, which uses the Discrete Element Method (DEM) to simulate large granular systems on Graphics Processing Unit (GPU) cards. The solver supports the integration of granular material with geometries defined by triangle meshes, as well as co-simulation with the multi-...
Preprint
Full-text available
We describe an analytical framework implemented in an open-source simulation platform for the purpose of enabling the design of control policies for improved rover mobility in granular terrain environments. In order to speed up the simulation, we employ an elastoplastic continuum model to capture the dynamics of the deformable terrain. The solution...
Preprint
Full-text available
We propose a framework to investigate the mobility of a replica of NASA's VIPER rover while operating on de-formable granular material terrains under different scenarios. In order to speed up the simulation, we employ a continuum model to capture the dynamics of the deformable terrain. Thus, the granular material is modeled as an elasto-plastic con...
Conference Paper
We use the Smoothed Particle Hydrodynamics (SPH) method to determine the dynamics of granular material in its interaction with a four-wheel rover. The goal of the simulation is to investigate the mobility of the rover while operating on granular terrains. In order to speed up the simulation, we employ a continuum model to capture the dynamics of th...
Conference Paper
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...
Chapter
Full-text available
Book Series Editorial Board John Michopoulos, Naval Research Laboratory David Rosen, Georgia Institute of Technology Chris Paredis, Georgia Institute of Technology Judy Vance, Iowa State University This is the second volume in this book series that aims to capture advances in computers and information in engineering research, especially by research...
Article
Computer simulation can be a useful tool when designing robots expected to operate independently in unstructured environments. In this context, one needs to simulate the dynamics of the robot's mechanical system, the environment in which the robot operates, and the sensors which facilitate the robot's perception of the environment. Herein, we focus...
Technical Report
Full-text available
We use the SPH method to determine the dynamics of granular material in its interaction with the eight wheels of a rover. The rover wheel geometry is defined through a mesh. The granular material is modeled as an elasto-plastic continuum that dynamically interacts with the rigid wheels of the rover in a Chrono [1] co-simulation setup. Several param...
Article
Full-text available
This contribution looks at how multibody dynamics and fluid dynamics can be used to understand the dynamics of granular material. The study is motivated by two observations: granular dynamics is an ubiquitous problem, given that granular material is second only to water in how often it is handled in practical applications; and, studying the motion...
Conference Paper
Full-text available
In large, rigid multibody dynamics problems with friction and contact, encountered for instance in granular flows, one can witness distinctly different system-level dynamics. This contribution concentrates on the case of fluid-like behavior of large multibody dynamics systems such as granular materials, when the system experiences large strains. Th...
Article
We present an adjoint sensitivity method for hybrid discrete—continuous systems, extending previously published forward sensitivity methods (FSA). We treat ordinary differential equations (ODEs) and differential-algebraic equations (DAEs) of index up to two (Hessenberg) and provide sufficient solvability conditions for consistent initialization and...
Preprint
Full-text available
We present an adjoint sensitivity method for hybrid discrete -- continuous systems, extending previously published forward sensitivity methods. We treat ordinary differential equations and differential-algebraic equations of index up to two (Hessenberg) and provide sufficient solvability conditions for consistent initialization and state transfer a...
Article
Full-text available
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...
Article
Full-text available
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...
Cover Page
Full-text available
As modeling and simulation of physical phenomena are taking a central role in the design, assessment, and optimization of engineering systems, engineers must often answer questions such as: How well does a mathematical model capture the relevant physical phenomena? What confidence can be placed on simulation results? How far from the nominal design...
Article
A Smoothed Particles Hydrodynamics (SPH) method for fluid dynamics is coupled with a rigid and deformable body dynamics solution to yield a framework for solving fluid–solid interaction (FSI) problems. The two-way, force–displacement, coupling of the fluid and solid phases is captured via boundary condition enforcing (BCE) markers. The partial diff...
Technical Report
Full-text available
This document highlights aspects related to the support and use of unified, or managed, memory in CUDA 6. The discussion provides an opportunity to revisit two other CUDA memory transaction topics: zero-copy memory and unified virtual addressing. The latter two can be regarded as intermediary milestones in a process that has led in CUDA 6 to the re...
Technical Report
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantify the tire-terrain interaction. In this paper, we introduce a high-fidelity ground vehicle mobility simulation framework that uses physics-based models of the vehicle, tires, and terrain to factor in both tire flexibility...
Conference Paper
We present the results of an exploratory investigation of applying a hybrid quantum-classical architecture to an off-road vehicle mobility problem, namely the generation of go/no-go maps posed as a machine learning problem. The premise of this work rests on two observations. First, quantum computing allows in principle for algorithms that provide a...
Technical Report
Full-text available
This technical report details a new hybrid OpenMP-MPI infrastructure for performing large-scale granular simulation in Chrono. This hybrid support is provided in a new module, Chrono::Distributed, which builds on the existing OpenMP-enabled module, Chrono::Parallel.
Technical Report
Full-text available
Chrono [1{3] is an open source multi-physics engine whose development is led by teams at the University of Wisconsin { Madison and the University of Parma, Italy. It supports the simulation of systems of rigid bodies, exible bodies, and uids interacting through traditional multi-body constraints, friction, and contact. To lower the learning curve...
Article
Full-text available
We summarize and numerically compare two approaches for modeling and simulating the dynamics of dry granular matter. The first one, the discrete-element method via penalty (DEM-P), is commonly used in the soft matter physics and geomechanics communities; it can be traced back to the work of Cundall and Strack [P. Cundall, Proc. Symp. ISRM, Nancy, F...
Conference Paper
We present a Lagrangian-Lagrangian method for solving Fluid-Solid Interaction (FSI) problems in which the solid phase is deformable/compliant. The fluid phase is modeled using Smoothed Particles Hydrodynamics (SPH); the deformable bodies are modeled with the Absolute Nodal Coordinate Formulation (ANCF). Each phase is integrated implicitly in time a...
Conference Paper
Full-text available
We discuss an early version of an open-source autonomous vehicle simulation framework whereby piloting control programs (PCPs) and vehicle response can be evaluated and improved in a safe environment. Through the interaction of hundreds of autonomous and avatar agents in a simulated environment, edge cases for self-driving vehicles can be analyzed...
Article
Full-text available
Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantifying the vehicle–terrain interaction. Herein, we concentrate on physics-based methodologies for wheeled vehicle mobility that factor in both tire flexibility and terrain deformation within a fully three-dimensional multibo...
Article
Full-text available
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...
Technical Report
Full-text available
We present several simulations carried out using Chrono::FSI and Chrono::Vehicle that highlight the two way coupling between the dynamics of a vehicle and the dynamics of a fluid that is free to move in a tank rigidly attached to the vehicle; i.e., a vehicle sloshing problem. The simulations are carried out in Chrono [1] using a monolithic solution...
Technical Report
Full-text available
We use a complementarity approach to pose the Coulomb friction model, combine it with a non-penetration condition, and append to a differential algebraic problem to characterize the dynamics of multibody systems with friction and contact. The resulting problem is relaxed to a Cone Complementarity Problem, whose solution is shown to represent the fi...
Technical Report
Full-text available
As part of the validation work for Chrono::Vehicle, a short single vehicle comparison study was executed between similar Chrono::Vehicle and ADAMS/Car automotive vehicle models. These models were compared in straight-line acceleration tests, a fixed speed constant radius turn test, and a double lane change test. The simulation results for the two m...
Technical Report
Full-text available
Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantifying the tire-terrain interaction. Herein, for wheeled vehicles, we concentrate on physics-based methodologies that factor in both the tire flexibility and terrain deformation. We represent the tire using a nonlinear finit...
Technical Report
Full-text available
Chrono [2] is an open source multi-physics engine whose development is led by teams at the University of Wisconsin { Madison and the University of Parma, Italy. It supports the simulation of systems of rigid bodies, exible bodies, and uids interacting through traditional multi-body constraints, friction, and contact. To lower the learning curve f...
Conference Paper
Full-text available
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...