An Efficient Solution Method for Multibody Systems with Loops Using Multiple Processors

This paper describes a multibody dynamics algorithm formulated for parallel implementation on multiprocessor computing platforms using the divide-and-conquer approach. The system of interest is a general topology of rigid and elastic articulated bodies with or without loops. The algorithm divides the multibody system into a number of smaller sets of bodies in chain or tree structures, called "branches" at convenient joints called "connection points", and uses an Order-N (O (N)) approach to formulate the dynamics of each branch in terms of the unknown spatial connection forces. The equations of motion for the branches, leaving the connection forces as unknowns, are implemented in separate processors in parallel for computational efficiency, and the equations for all the unknown connection forces are synthesized and solved in one or several processors. The performances of two implementations of this divide-and-conquer algorithm in multiple processors are compared with an existing method implemented on a single processor

Integration of Heterogeneous Simulation Models for Network-Distributed Simulation.

Distributed simulation is close to reaching its potential to fulfill the demands of industrial CAE by harnessing nearly unlimited computing power across network environments and by efficiently reusing and integrating already constructed simulation models. A distributed simulation platform, denoted as D-Sim, has been under development in our research group since 2001. The present work focuses on the integration of heterogeneous subsystem models, including multibody dynamics (MBD) and finite element (FEM) subsystem models, and conducting seamlessly integrated simulation for design tasks in a distributed computing environment. Under the guise of a gluing algorithm, the Partitioned Iteration Method (PIM) was developed, which can be used to integrate distributed deformable bodies while allowing large rigid body motions among the bodies or subsystems. The PIM is based upon a floating frame of reference, in which the global motion of the flexible body can be expressed with linearized elastic deformations by assumption of infinitesimal strains and reference frame as large overall motion. When embedded in D-Sim, it also enables using independent simulation servers, in which each server can run commercially available or research-based MBD and/or FEM codes to minimize the information exchange across the different platforms yet still obtain results within engineering accuracy. Examples are provided which integrate FEM and MBD models and which demonstrate the performance of the PIM. The examples also highlight how to decouple and integrate rigid body motion and elastic deformation using the enhanced gluing algorithm. A gluing algorithm plays a critical role in integrating the distributed subsystems and components. It is one of the research objectives to apply the gluing algorithm to general simulation models, which may be assembled by diverse connecting methods, including spot welds, bolts, bushings, and other physical connections. The gluing algorithm concept has been extended by creating flexible gluing joints, which can deal with various connections between subsystems, and can account for linear and non-linear flexibility at these connections. This not only improves the accuracy of the simulation to represent the real physical system, but also can improve the convergence of multibody dynamics simulation.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64747/1/gsryu_1.pd

On the Numerical Stability of Co-Simulation Methods

To couple two or more subsystem solvers in time domain, co-simulation methods are used in many fields of application. In the framework of mechanical systems, there exist mainly two ways to couple different subsystems, namely coupling either by constitutive laws or by algebraic constraint equations. In this work, the numerical stability and the convergence behavior of co-simulation methods is analyzed. For the stability analysis, a test model has to be defined. Following the stability definition for numerical time integration schemes, namely Dahlquist’s stability theory, a linear test model is used. The co-simulation test model applied here is a two-mass oscillator, where the two masses are connected by a spring-damper element or by a rigid link. Discretizing the test model with a co-simulation method, recurrence equations can be derived, which describe the time discrete co-simulation solution. Applying an applied-force coupling approach, the stability behavior of the linear two-mass oscillator is characterized by 7 independent parameters. In order to compare different co-simulation approaches, 2D stability plots are convenient. Therefore, 5 of the 7 parameters are fixed so that the spectral radius can be depicted as a function of the remaining 2 parameters. The results presented show that implicit coupling schemes exhibit a significantly better numerical stability behavior than explicit schemes. Furthermore, enhanced stability behavior can be achieved by extending the coupling conditions, i.e., by taking into account derivatives and integrals of the constitutive equations. Especially, a very good stability behavior may be obtained with the D-extended force/force-coupling approach in combination with quadratic approximation functions. The analysis of the numerical stability of co-simulation methods with algebraic constraints is the second subject of this work. 5 independent parameters have to be introduced for the corresponding test model. The dimensionless real and imaginary part of the eigenvalue of subsystem 1 are used as axes in 2D stability plots; the other 3 parameters are held constant. Three classical methods for constraint stabilization, namely the Baumgarte stabilization technique, the weighted multiplier approach and the projection technique, are discussed for different approximation orders. Alternatively, co-simulation approaches on index-2 and on index-1 level are discussed, where the Lagrange multiplier is discretized between the macro-time points (extended multiplier approach). As a result, the coupling conditions and their time derivatives can simultaneously be fulfilled at the macro-time points. Different multibody models are used in order to demonstrate the application of the above mentioned co-simulation techniques

Algorithmes adaptatifs pour la simulation moléculaire

Les simulations moléculaires sont devenues un outil essentiel en biologie, chimie et physique. Malheureusement, elles restent très couteuses. Dans cette thèse, nous proposons des algorithmes qui accélèrent les simulations moléculaires en regroupant des particules en plusieurs objets rigides. Nous étudions d'abord plusieurs algorithmes de recherche de voisins dans le cas des grands objets rigides, et démontrons que les algorithmes hiérarchiques permettent d'obtenir des accélérations importantes. En conséquence, nous proposons une technique pour construire une représentation hiérarchique d'un graphe moléculaire arbitraire. Nous démontrons l'usage de cette technique pour la mécanique adaptative en angles de torsion, une méthode de simulation qui décrit les molécules comme des objets rigides articulés. Enfin, nous introduisons ARPS - Adaptively Restrained Particle Simulations ("Simulations de particules restreintes de façon adaptative") - une méthode mathématiquement fondée capable d'activer et de désactiver les degrés de liberté en position. Nous proposons deux stratégies d'adaptation, et illustrons les avantages de ARPS sur plusieurs exemples. En particulier, nous démontrons comment ARPS permet de choisir finement le compromis entre précision et vitesse, ainsi que d'obtenir rapidement des statistiques non biaisées sur les systèmes moléculaires.Molecular simulations have become an essential tool in biology, chemistry and physics. Unfortunately, they still remain computationally challenging. In this dissertation, we propose algorithms that accelerate molecular simulations by clustering particles into rigid bodies. We first study several neighbor-search algorithms for large rigid bodies, and show that hierarchy-based algorithms may provide significant speedups. Accordingly, we propose a technique to build a hierarchical representation of an arbitrary molecular graph. We show how this technique can be used in adaptive torsion-angle mechanics, a simulation method that describes molecules as articulated rigid bodies. Finally, we introduce ARPS - Adaptively Restrained Particle Simulations - a mathematically-grounded method able to switch positional degrees of freedom on and off. We propose two switching strategies, and illustrate the advantages of ARPS on various examples. In particular, we show how ARPS allow us to smoothly trade between precision and speed, and efficiently collect unbiased statistics on molecular systems.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version

Multibody dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: Formulations and Numerical Methods, Efficient Methods and Real-Time Applications, Flexible Multibody Dynamics, Contact Dynamics and Constraints, Multiphysics and Coupled Problems, Control and Optimization, Software Development and Computer Technology, Aerospace and Maritime Applications, Biomechanics, Railroad Vehicle Dynamics, Road Vehicle Dynamics, Robotics, Benchmark Problems. The conference is organized by the Department of Mechanical Engineering of the Universitat Politècnica de Catalunya (UPC) in Barcelona. The organizers would like to thank the authors for submitting their contributions, the keynote lecturers for accepting the invitation and for the quality of their talks, the awards and scientific committees for their support to the organization of the conference, and finally the topic organizers for reviewing all extended abstracts and selecting the awards nominees.Postprint (published version