Radu Serban

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

About

156
Publications
64,063
Reads
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5,514
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 (156)
Preprint
Recently, the integration of advanced simulation technologies with artificial intelligence (AI) is revolutionizing science and engineering research. ChronoLlama introduces a novel framework that customizes the open-source LLMs, specifically for code generation, paired with PyChrono for multi-physics simulations. This integration aims to automate an...
Conference Paper
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...
Conference Paper
title>ABSTRACT A Model Predictive Control (MPC) LIDAR-based constant speed local obstacle avoidance algorithm has been implemented on rigid terrain and granular terrain in Chrono to examine the robustness of this control method. Provided LIDAR data as well as a target location, a vehicle can route itself around obstacles as it encounters them and...
Conference Paper
title>ABSTRACT Current modeling and simulation capabilities permit tackling complex multi-physics problems, such as those encountered in ground vehicle mobility studies, using high-fidelity physics-based models for all involved subsystems, including the vehicle, tires, and deformable terrain. However, these come at significant computational burden...
Preprint
This contribution reports on a software framework that uses physically-based rendering to simulate camera operation in lunar conditions. The focus is on generating synthetic images qualitatively similar to those produced by an actual camera operating on a vehicle traversing and/or actively interacting with lunar terrain, e.g., for construction oper...
Preprint
We introduce SimBench, a benchmark designed to evaluate the proficiency of student large language models (S-LLMs) in generating digital twins (DTs) that can be used in simulators for virtual testing. Given a collection of S-LLMs, this benchmark enables the ranking of the S-LLMs based on their ability to produce high-quality DTs. We demonstrate this...
Preprint
Full-text available
Recently, there has been a surge of international interest in extraterrestrial exploration targeting the Moon, Mars, the moons of Mars, and various asteroids. This contribution discusses how current state-of-the-art Earth-based testing for designing rovers and landers for these missions currently leads to overly optimistic conclusions about the beh...
Article
Full-text available
This paper introduces DEM-Engine, a new submodule of Project Chrono, that is designed to carry out Discrete Element Method (DEM) simulations. Based on spherical primitive shapes, DEM-Engine can simulate polydisperse granular materials and handle complex shapes generated as assemblies of primitives, referred to as clumps. DEM-Engine has a multi-tier...
Article
Full-text available
This paper discusses the use of the discrete element method (DEM) to simulate the dynamics of granular systems made up of elements with nontrivial geometries. The DEM simulator is GPU accelerated and can handle elements whose shape is defined as the union with overlap of diverse sets of spheres with user-specified radii. The simulator can also hand...
Article
Full-text available
We present a Vehicle Model (VM) that has 17 degrees of freedom and includes nonlinear tire and powertrain subsystems. Implemented as a relatively small piece of C++ code, the model runs vehicle dynamics 2000 times faster than real time at a simulation time step of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3...
Article
This contribution focuses on how the quality of synthetic images can be measured in the context of robotics and autonomous vehicle applications. We propose a validation methodology grounded in the sim-to-real difference exhibited by a perception algorithm that comes into play in the autonomy stack associated with a robot or autonomous vehicle (AV)...
Article
Full-text available
The soil contact model (SCM) is widely used in practice for off‐road wheeled vehicle mobility studies when simulation speed is important and highly accurate results are not a main concern. In practice, the SCM parameters are obtained via a bevameter test, which requires a complex apparatus and experimental procedure. Here, we advance the idea of ru...
Conference Paper
In this contribution, we discuss the pros and cons of using the Smoothed Particle Hydrodynamics (SPH) method in providing support to multiphysics simulations. The Lagrangian SPH method is proposed to address a fluid-structure interaction (FSI) problem in which the response of a flexible baffle with elastic behavior is solved by using three modeling...
Preprint
Full-text available
This paper introduces DEM-Engine, a new submodule of Project Chrono, that is designed to carry out Discrete Element Method (DEM) simulations. Based on spherical primitive shapes, DEM-Engine can simulate polydisperse granular materials and handle complex shapes generated as assemblies of primitives, referred to as clumps. DEM-Engine has a multi-tier...
Article
Modeling cameras for the simulation of autonomous robotics is critical for generating synthetic images with appropriate realism to effectively evaluate a perception algorithm in simulation. In many cases though, simulated images are produced by traditional rendering techniques that exclude or superficially handle processing steps and aspects encoun...
Preprint
Full-text available
We discuss the use of the Discrete Element Method (DEM) to simulate the dynamics of granular systems made up of elements with nontrivial geometries. The DEM simulator is GPU accelerated and can handle elements whose shape is defined as the union with overlap of diverse sets of spheres with user-specified radii. The simulator can also handle complex...
Article
Full-text available
We are delighted to bring to the readers of the ASME Journal of Computational and Nonlinear Dynamics (JCND) a special issue dedicated to select papers from the 18th International Conference on Multibody Systems, Nonlinear Dynamics, and Control (MSNDC), held during the 2022 ASME International Design Engineering Technical Conferences and Computers an...
Preprint
Full-text available
This contribution outlines a high-fidelity simulation framework for Human-in-the-loop (HIL) traffic simulation built upon Project Chrono, an open-source physics simulation engine. The framework is designed to provide the software infrastructure for human factors, traffic, and human-automation interplay research. We conclude this platform overview p...
Preprint
Full-text available
In robotics, simulation has the potential to reduce design time and costs, and lead to a more robust engineered solution and a safer development process. However, the use of simulators is predicated on the availability of good models. This contribution is concerned with improving the quality of these models via calibration, which is cast herein in...
Article
Full-text available
In robotics, simulation has the potential to reduce design time and costs, and lead to a more robust engineered solution and a safer development process. However, the use of simulators is predicated on the availability of good models. This contribution is concerned with improving the quality of these models via calibration, which is cast herein in...
Article
Full-text available
Techniques for modeling deformable terrain span an entire range varying in complexity, representation accuracy, and ensuing computational effort. While formulations such as fully-resolved granular dynamics, continuum representation of granular material, or finite element can provide a high level of accuracy, they do so at a significant cost, even w...
Preprint
Full-text available
The soil contact model (SCM) is widely used in practice for off-road wheeled vehicle mobility studies when simulation speed is important and highly accurate results are not a main concern. In practice, the SCM parameters are obtained via a bevameter test, which requires a complex apparatus and experimental procedure. Here, we advance the idea of ru...
Preprint
Full-text available
Modeling cameras for the simulation of autonomous robotics is critical for generating synthetic images with appropriate realism to effectively evaluate a perception algorithm in simulation. In many cases though, simulated images are produced by traditional rendering techniques that exclude or superficially handle processing steps and aspects encoun...
Preprint
Full-text available
We discuss a platform that has both software and hardware components, and whose purpose is to support research into characterizing and mitigating the sim-to-real gap in robotics and vehicle autonomy engineering. The software is operating-system independent and has three main components: a simulation engine called Chrono, which supports high-fidelit...
Article
Full-text available
For multibody dynamics simulation using the Absolute Nodal Coordinate Formulation, multiple strategies are reported in the linear elastic material literature for calculating the generalized internal force and its Jacobian matrix. When examining the presentation of these strategies, which are all sound, it is difficult to assess which method is more...
Preprint
Full-text available
Given the versatility of generative adversarial networks (GANs), we seek to understand the benefits gained from using an existing GAN to enhance simulated images and reduce the sim-to-real gap. We conduct an analysis in the context of simulating robot performance and image-based perception. Specifically, we quantify the GAN's ability to reduce the...
Conference Paper
Full-text available
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
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...
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...
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
Full-text available
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
Full-text available
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
Full-text available
title>ABSTRACT 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 algori...