Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
elements are supported by fluid film bearings, where the hydrodynamic interaction forces are described by the Reynolds equation. The system of nonlinear equations is numerically solved for three different restrictive conditions of the motion of the crank, where the third case takes into account lateral and......In this work, the steps involved for the modelling of a reciprocating linear compressor are described in detail. The dynamics of the mechanical components are described with the help of multibody dynamics (rigid components) and finite elements method (flexible components). Some of the mechanical...
Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
elements are supported by fluid film bearings, where the hydrodynamic interaction forces are described by the Reynolds equation. The system of nonlinear equations is numerically solved for three different restrictive conditions of the motion of the crank, where the third case takes into account lateral and...... tilting oscillations of the extremity of the crankshaft. The numerical results of the behaviour of the journal bearings for each case are presented giving some insights into design parameters such as, maximum oil film pressure, minimum oil film thickness, maximum vibration levels and dynamic reaction...... forces among machine components, looking for the optimization and application of active lubrication towards vibration reduction....
Conference on Multibody Dynamics
Multibody Dynamics : Computational Methods and Applications
2014-01-01
By having its origin in analytical and continuum mechanics, as well as in computer science and applied mathematics, multibody dynamics provides a basis for analysis and virtual prototyping of innovative applications in many fields of contemporary engineering. With the utilization of computational models and algorithms that classically belonged to different fields of applied science, multibody dynamics delivers reliable simulation platforms for diverse highly-developed industrial products such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, smart structures, biomechanical applications and nano-technologies. The chapters of this volume are based on the revised and extended versions of the selected scientific papers from amongst 255 original contributions that have been accepted to be presented within the program of the distinguished international ECCOMAS conference. It reflects state-of-the-art in the advances of multibody dynamics, providing excellent insight in the recen...
Substructured multibody molecular dynamics.
Grest, Gary Stephen; Stevens, Mark Jackson; Plimpton, Steven James; Woolf, Thomas B. (Johns Hopkins University, Baltimore, MD); Lehoucq, Richard B.; Crozier, Paul Stewart; Ismail, Ahmed E.; Mukherjee, Rudranarayan M. (Rensselaer Polytechnic Institute, Troy, NY); Draganescu, Andrei I.
2006-11-01
We have enhanced our parallel molecular dynamics (MD) simulation software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator, lammps.sandia.gov) to include many new features for accelerated simulation including articulated rigid body dynamics via coupling to the Rensselaer Polytechnic Institute code POEMS (Parallelizable Open-source Efficient Multibody Software). We use new features of the LAMMPS software package to investigate rhodopsin photoisomerization, and water model surface tension and capillary waves at the vapor-liquid interface. Finally, we motivate the recipes of MD for practitioners and researchers in numerical analysis and computational mechanics.
Reduced gravity multibody dynamics testing
Sillanpaa, Meija
1993-01-01
The Final Report on reduced gravity multibody dynamics testing is presented. Tests were conducted on board the NASA KC-135 RGA in Houston, Texas. The objective was to analyze the effects of large angle rotations on flexible, multi-segmented structures. The flight experiment was conducted to provide data which will be compared to the data gathered from ground tests of the same configurations. The flight and ground tested data will be used to validate the TREETOPS software, software which models dynamic multibody systems, and other multibody codes. The flight experiment consisted of seven complete flights on board the KC-135 RGA during two one-week periods. The first period of testing was 4-9 Apr. 1993. The second period of testing was 13-18 Jun. 1993.
Computational Workbench for Multibody Dynamics
Edmonds, Karina
2007-01-01
PyCraft is a computer program that provides an interactive, workbenchlike computing environment for developing and testing algorithms for multibody dynamics. Examples of multibody dynamic systems amenable to analysis with the help of PyCraft include land vehicles, spacecraft, robots, and molecular models. PyCraft is based on the Spatial-Operator- Algebra (SOA) formulation for multibody dynamics. The SOA operators enable construction of simple and compact representations of complex multibody dynamical equations. Within the Py-Craft computational workbench, users can, essentially, use the high-level SOA operator notation to represent the variety of dynamical quantities and algorithms and to perform computations interactively. PyCraft provides a Python-language interface to underlying C++ code. Working with SOA concepts, a user can create and manipulate Python-level operator classes in order to implement and evaluate new dynamical quantities and algorithms. During use of PyCraft, virtually all SOA-based algorithms are available for computational experiments.
Multibody system dynamics, robotics and control
Gerstmayr, Johannes
2013-01-01
The volume contains 19 contributions by international experts in the field of multibody system dynamics, robotics and control. The book aims to bridge the gap between the modeling of mechanical systems by means of multibody dynamics formulations and robotics. In the classical approach, a multibody dynamics model contains a very high level of detail, however, the application of such models to robotics or control is usually limited. The papers aim to connect the different scientific communities in multibody dynamics, robotics and control. Main topics are flexible multibody systems, humanoid robots, elastic robots, nonlinear control, optimal path planning, and identification.
Solving Equations of Multibody Dynamics
Jain, Abhinandan; Lim, Christopher
2007-01-01
Darts++ is a computer program for solving the equations of motion of a multibody system or of a multibody model of a dynamic system. It is intended especially for use in dynamical simulations performed in designing and analyzing, and developing software for the control of, complex mechanical systems. Darts++ is based on the Spatial-Operator- Algebra formulation for multibody dynamics. This software reads a description of a multibody system from a model data file, then constructs and implements an efficient algorithm that solves the dynamical equations of the system. The efficiency and, hence, the computational speed is sufficient to make Darts++ suitable for use in realtime closed-loop simulations. Darts++ features an object-oriented software architecture that enables reconfiguration of system topology at run time; in contrast, in related prior software, system topology is fixed during initialization. Darts++ provides an interface to scripting languages, including Tcl and Python, that enable the user to configure and interact with simulation objects at run time.
Numerical methods in multibody dynamics
Eich-Soellner, Edda
1998-01-01
Today computers play an important role in the development of complex mechanical systems, such as cars, railway vehicles or machines. Efficient simulation of these systems is only possible when based on methods that explore the strong link between numerics and computational mechanics. This book gives insight into modern techniques of numerical mathematics in the light of an interesting field of applications: multibody dynamics. The important interaction between modeling and solution techniques is demonstrated by using a simplified multibody model of a truck. Different versions of this mechanical model illustrate all key concepts in static and dynamic analysis as well as in parameter identification. The book focuses in particular on constrained mechanical systems. Their formulation in terms of differential-algebraic equations is the backbone of nearly all chapters. The book is written for students and teachers in numerical analysis and mechanical engineering as well as for engineers in industrial research labor...
Concepts and formulations for spatial multibody dynamics
Flores, Paulo
2015-01-01
This book will be particularly useful to those interested in multibody simulation (MBS) and the formulation for the dynamics of spatial multibody systems. The main types of coordinates that can be used in the formulation of the equations of motion of constrained multibody systems are described. The multibody system, made of interconnected bodies that undergo large displacements and rotations, is fully defined. Readers will discover how Cartesian coordinates and Euler parameters are utilized and are the supporting structure for all methodologies and dynamic analysis, developed within the multibody systems methodologies. The work also covers the constraint equations associated with the basic kinematic joints, as well as those related to the constraints between two vectors. The formulation of multibody systems adopted here uses the generalized coordinates and the Newton-Euler approach to derive the equations of motion. This formulation results in the establishment of a mixed set of differential and algebraic equ...
Spatial Operator Algebra for multibody system dynamics
Rodriguez, G.; Jain, A.; Kreutz-Delgado, K.
1992-01-01
The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.
ECCOMAS Thematic Conference on Multibody Dynamics
Multibody Dynamics : Computational Methods and Applications
2016-01-01
This book includes selected papers from the ECCOMAS Thematic Conference on Multibody Dynamics, that took place in Barcelona, Spain, from June 29 to July 2, 2015. By having its origin in analytical and continuum mechanics, as well as in computer science and applied mathematics, multibody dynamics provides a basis for analysis and virtual prototyping of innovative applications in many fields of contemporary engineering. With the utilization of computational models and algorithms that classically belonged to different fields of applied science, multibody dynamics delivers reliable simulation platforms for diverse highly-developed industrial products such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, smart structures, biomechanical systems,and nanotechnologies.
Contact force models for multibody dynamics
Flores, Paulo
2016-01-01
This book analyzes several compliant contact force models within the context of multibody dynamics, while also revisiting the main issues associated with fundamental contact mechanics. In particular, it presents various contact force models, from linear to nonlinear, from purely elastic to dissipative, and describes their parameters. Addressing the different numerical methods and algorithms for contact problems in multibody systems, the book describes the gross motion of multibody systems by using a two-dimensional formulation based on the absolute coordinates and employs different contact models to represent contact-impact events. Results for selected planar multibody mechanical systems are presented and utilized to discuss the main assumptions and procedures adopted throughout this work. The material provided here indicates that the prediction of the dynamic behavior of mechanical systems involving contact-impact strongly depends on the choice of contact force model. In short, the book provides a comprehens...
A Unifying Multibody Dynamics Algorithm Development Workbench
Ziegler, John L.
2005-01-01
The development of new and efficient algorithms for multibody dynamics has been an important research area. These algorithms are used for modeling, simulation, and control of systems such as spacecraft, robotic systems, automotive applications, the human body, manufacturing operations, and micro-electromechanical systems (MEMS). At JPL's Dynamics and Real Time Simulation (DARTS) Laboratory we have developed software that serves as a computational workbench for these algorithms. This software utilizes the mathematical perspective of the spatial operator algebra, which allows the development of dynamics algorithms and new insights into multibody dynamics.
A DAE Approach to Flexible Multibody Dynamics
The present work deals with the dynamics of multibody systems consisting of rigid bodies and beams. Nonlinear finite element methods are used to devise a frame-indifferent spaced is cretization of the underlying geometrically exact beam theory. Both rigid bodies and semi-discrete beams are viewed as finite-dimensional dynamical systems with holonomic constraints. The equations of motion pertaining to the constrained mechanical systems under consideration take the form of Differential Algebraic Equations (DAEs).The DAEs are discretized directly by applying a Galerkin-based method. It is shown that the proposed DAE approach provides a unified framework for the integration of flexible multibody dynamics
Assumed modes method and flexible multibody dynamics
Tadikonda, S. S. K.; Mordfin, T. G.; Hu, T. G.
1993-01-01
The use of assumed modes in flexible multibody dynamics algorithms requires the evaluation of several domain dependent integrals that are affected by the type of modes used. The implications of these integrals - often called zeroth, first and second order terms - are investigated in this paper, for arbitrarily shaped bodies. Guidelines are developed for the use of appropriate boundary conditions while generating the component modal models. The issue of whether and which higher order terms must be retained is also addressed. Analytical results, and numerical results using the Shuttle Remote Manipulator System as the multibody system, are presented to qualitatively and quantitatively address these issues.
ECCOMAS Thematic Conference on Multibody Dynamics
Fisette, Paul; Multibody Dynamics : Computational Methods and Applications
2013-01-01
This volume provides the international multibody dynamics community with an up-to-date view on the state of the art in this rapidly growing field of research which now plays a central role in the modeling, analysis, simulation and optimization of mechanical systems in a variety of fields and for a wide range of industrial applications. This book contains selected contributions delivered at the ECCOMAS Thematic Conference on Multibody Dynamics, which was held in Brussels, Belgium and organized by the Université catholique de Louvain, from 4th to 7th July 2011. Each paper reflects the State-of-Art in the application of Multibody Dynamics to different areas of engineering. They are enlarged and revised versions of the communications, which were enhanced in terms of self-containment and tutorial quality by the authors. The result is a comprehensive text that constitutes a valuable reference for researchers and design engineers which helps to appraise the potential for the application of multibody dynamics meth...
Investigation of Boundary Conditions for Flexible Multibody Spacecraft Dynamics
MacLean, John R.; Huynh, An; Quiocho, Leslie J.
2007-01-01
In support of both the Space Shuttle and International Space Station programs, a set of generic multibody dynamics algorithms integrated within the Trick simulation environment have addressed the variety of on-orbit manipulator simulation requirements for engineering analysis, procedures development and crew familiarization/training at the NASA Johnson Space Center (JSC). Enhancements to these dynamics algorithms are now being driven by a new set of Constellation program requirements for flexible multibody spacecraft simulation. One particular issue that has been discussed within the NASA community is the assumption of cantilever-type flexible body boundary conditions. This assumption has been commonly utilized within manipulator multibody dynamics formulations as it simplifies the computation of relative motion for articulated flexible topologies. Moreover, its use for modeling of space-based manipulators such as the Shuttle Remote Manipulator System (SRMS) and Space Station Remote Manipulator System (SSRMS) has been extensively validated against flight data. For more general flexible spacecraft applications, however, the assumption of cantilever-type boundary conditions may not be sufficient. This paper describes the boundary condition assumptions that were used in the original formulation, demonstrates that this formulation can be augmented to accommodate systems in which the assumption of cantilever boundary conditions no longer applies, and verifies the approach through comparison with an independent model previously validated against experimental hardware test data from a spacecraft flexible dynamics emulator.
Spatial operator algebra for flexible multibody dynamics
Jain, A.; Rodriguez, G.
1993-01-01
This paper presents an approach to modeling the dynamics of flexible multibody systems such as flexible spacecraft and limber space robotic systems. A large number of degrees of freedom and complex dynamic interactions are typical in these systems. This paper uses spatial operators to develop efficient recursive algorithms for the dynamics of these systems. This approach very efficiently manages complexity by means of a hierarchy of mathematical operations.
Planar multibody dynamics formulation, programming and applications
Nikravesh, Parviz E
2007-01-01
Introduction Multibody Mechanical Systems Types of Analyses Methods of Formulation Computer Programming Application Examples Unit System Remarks Preliminaries Reference Axes Scalars and Vectors Matrices Vector, Array, and Matrix Differentiation Equations and Expressions Remarks Problems Fundamentals of Kinematics A Particle Kinematics of a Rigid Body Definitions Remarks Problems Fundamentals of Dynamics Newton's Laws of Motion Dynamics of a Body Force Elements Applied Forces Reaction Force Remarks Problems Point-Coordinates: Kinematics Multipoint
Fast Parallel Computation Of Multibody Dynamics
Fijany, Amir; Kwan, Gregory L.; Bagherzadeh, Nader
1996-01-01
Constraint-force algorithm fast, efficient, parallel-computation algorithm for solving forward dynamics problem of multibody system like robot arm or vehicle. Solves problem in minimum time proportional to log(N) by use of optimal number of processors proportional to N, where N is number of dynamical degrees of freedom: in this sense, constraint-force algorithm both time-optimal and processor-optimal parallel-processing algorithm.
A residual flexibility approach to multibody dynamics
Blelloch, Paul A.; Antal, Gregory W.
1993-01-01
Many complex systems can be modeled as a collection of interacting bodies, where the relative motion of the bodies may be large. The dynamics of such systems are simulated using multibody dynamic formulations. Many of these treat each body as a rigid component, but recently the flexibility of the components has been incorporated. This paper presents a residual flexibility formulation of the multibody dynamics problem. The formulation is very simple and offers great computational efficiency since it treats each body as a free structure in space, interacting with other bodies only through interface forces. Each body's accelerations can be solved independently, as can each set of interface forces. We have applied the technique successfully to several special applications, and the initial implementation in a general mechanisms code has given excellent results in comparison to a direct finite element representation of flexibility.
Simbody: multibody dynamics for biomedical research
Sherman, Michael A.; Seth, Ajay; Delp, Scott L.
2011-01-01
Multibody software designed for mechanical engineering has been successfully employed in biomedical research for many years. For real time operation some biomedical researchers have also adapted game physics engines. However, these tools were built for other purposes and do not fully address the needs of biomedical researchers using them to analyze the dynamics of biological structures and make clinically meaningful recommendations. We are addressing this problem through the development of an...
Elastic Multibody Dynamics A Direct Ritz Approach
Bremer, H
2008-01-01
This textbook is an introduction to and exploration of a number of core topics in the field of applied mechanics: On the basis of Lagrange's Principle, a Central Equation of Dynamics is presented which yields a unified view on existing methods. From these, the Projection Equation is selected for the derivation of the motion equations of holonomic and of non-holonomic systems. The method is applied to rigid multibody systems where the rigid body is defined such that, by relaxation of the rigidity constraints, one can directly proceed to elastic bodies. A decomposition into subsystems leads to a minimal representation and to a recursive representation, respectively, of the equations of motion. Applied to elastic multibody systems one obtains, along with the use of spatial operators, a straight-on procedure for the interconnected partial and ordinary differential equations and the corresponding boundary conditions. The spatial operators are eventually applied to a RITZ series for approximation. The resulting equ...
Graph Theoretic Foundations of Multibody Dynamics Part I: Structural Properties
Jain, Abhinandan
2011-01-01
This is the first part of two papers that use concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The key contribution is the development of a unifying framework that shows that key analytical results and computational algorithms in multibody dynamics are a direct consequence of structural properties and require minimal assumptions about the specific nature of the underlying multibody system. This first part focuses on identifying...
Developments of multibody system dynamics: computer simulations and experiments
It is an exceptional success when multibody dynamics researchers Multibody System Dynamics journal one of the most highly ranked journals in the last 10 years. In the inaugural issue, Professor Schiehlen wrote an interesting article explaining the roots and perspectives of multibody system dynamics. Professor Shabana also wrote an interesting article to review developments in flexible multibody dynamics. The application possibilities of multibody system dynamics have grown wider and deeper, with many application examples being introduced with multibody techniques in the past 10 years. In this paper, the development of multibody dynamics is briefly reviewed and several applications of multibody dynamics are described according to the author's research results. Simulation examples are compared to physical experiments, which show reasonableness and accuracy of the multibody formulation applied to real problems. Computer simulations using the absolute nodal coordinate formulation (ANCF) were also compared to physical experiments; therefore, the validity of ANCF for large-displacement and large-deformation problems was shown. Physical experiments for large deformation problems include beam, plate, chain, and strip. Other research topics currently being carried out in the author's laboratory are also briefly explained
G-DYN Multibody Dynamics Engine
Acikmese, Behcet; Blackmore, James C.; Broderick, Daniel
2011-01-01
G-DYN is a multi-body dynamic simulation software engine that automatically assembles and integrates equations of motion for arbitrarily connected multibody dynamic systems. The algorithm behind G-DYN is based on a primal-dual formulation of the dynamics that captures the position and velocity vectors (primal variables) of each body and the interaction forces (dual variables) between bodies, which are particularly useful for control and estimation analysis and synthesis. It also takes full advantage of the spare matrix structure resulting from the system dynamics to numerically integrate the equations of motion efficiently. Furthermore, the dynamic model for each body can easily be replaced without re-deriving the overall equations of motion, and the assembly of the equations of motion is done automatically. G-DYN proved an essential software tool in the simulation of spacecraft systems used for small celestial body surface sampling, specifically in simulating touch-and-go (TAG) maneuvers of a robotic sampling system from a comet and asteroid. It is used extensively in validating mission concepts for small body sample return, such as Comet Odyssey and Galahad New Frontiers proposals.
Multibody Dynamics of Very Flexible Damped Systems
An efficient multibody dynamics formulation is presented for simulating the forward dynamics of open and closed loop mechanical systems comprised of rigid and flexible bodies interconnected by revolute, prismatic, free, and fixed joints. Geometrically nonlinear deformation of flexible bodies is included and the formulation does not impose restrictions on the representation of material damping within flexible bodies. The approach is based on Kane's equation without multipliers and the resulting formulation generates 2ndof+m first order ordinary differential equations directly where 2nd of is the smallest number of system degrees of freedom that can completely describe the system configuration and m is the number of loop closure velocity constraint equations. The equations are integrated numerically in the time domain to propagate the solution. Flexible bodies are discretized using a finite element approach. The mass and stiffness matrices for a six-degree-of-freedom planar beam element are developed including mass coupling terms, rotary inertia, centripetal and Coriolis forces, and geometric stiffening terms. The formulation is implemented in the general purpose multibody dynamics computer program 'flxdyn'. Extensive validation of the formulation and corresponding computer program is accomplished by comparing results with analytically derived equations, alternative approximate solutions, and benchmark problems selected from the literature. The formulation is found to perform well in terms of accuracy and solution efficiency. This article develops the formulation and presents a set of validation problems including a sliding pendulum, seven link mechanism, flexible beam spin-up problem, and flexible slider crank mechanism
Multibody Dynamics of Very Flexible Damped Systems
Langlois, R.G.; Anderson, R.J. [Queen' s University at Kingston, Department of Mechanical Engineering (Canada)
1999-05-15
An efficient multibody dynamics formulation is presented for simulating the forward dynamics of open and closed loop mechanical systems comprised of rigid and flexible bodies interconnected by revolute, prismatic, free, and fixed joints. Geometrically nonlinear deformation of flexible bodies is included and the formulation does not impose restrictions on the representation of material damping within flexible bodies. The approach is based on Kane's equation without multipliers and the resulting formulation generates 2ndof+m first order ordinary differential equations directly where 2nd of is the smallest number of system degrees of freedom that can completely describe the system configuration and m is the number of loop closure velocity constraint equations. The equations are integrated numerically in the time domain to propagate the solution. Flexible bodies are discretized using a finite element approach. The mass and stiffness matrices for a six-degree-of-freedom planar beam element are developed including mass coupling terms, rotary inertia, centripetal and Coriolis forces, and geometric stiffening terms. The formulation is implemented in the general purpose multibody dynamics computer program 'flxdyn'. Extensive validation of the formulation and corresponding computer program is accomplished by comparing results with analytically derived equations, alternative approximate solutions, and benchmark problems selected from the literature. The formulation is found to perform well in terms of accuracy and solution efficiency. This article develops the formulation and presents a set of validation problems including a sliding pendulum, seven link mechanism, flexible beam spin-up problem, and flexible slider crank mechanism.
Constraint Embedding Technique for Multibody System Dynamics
Woo, Simon S.; Cheng, Michael K.
2011-01-01
Multibody dynamics play a critical role in simulation testbeds for space missions. There has been a considerable interest in the development of efficient computational algorithms for solving the dynamics of multibody systems. Mass matrix factorization and inversion techniques and the O(N) class of forward dynamics algorithms developed using a spatial operator algebra stand out as important breakthrough on this front. Techniques such as these provide the efficient algorithms and methods for the application and implementation of such multibody dynamics models. However, these methods are limited only to tree-topology multibody systems. Closed-chain topology systems require different techniques that are not as efficient or as broad as those for tree-topology systems. The closed-chain forward dynamics approach consists of treating the closed-chain topology as a tree-topology system subject to additional closure constraints. The resulting forward dynamics solution consists of: (a) ignoring the closure constraints and using the O(N) algorithm to solve for the free unconstrained accelerations for the system; (b) using the tree-topology solution to compute a correction force to enforce the closure constraints; and (c) correcting the unconstrained accelerations with correction accelerations resulting from the correction forces. This constraint-embedding technique shows how to use direct embedding to eliminate local closure-loops in the system and effectively convert the system back to a tree-topology system. At this point, standard tree-topology techniques can be brought to bear on the problem. The approach uses a spatial operator algebra approach to formulating the equations of motion. The operators are block-partitioned around the local body subgroups to convert them into aggregate bodies. Mass matrix operator factorization and inversion techniques are applied to the reformulated tree-topology system. Thus in essence, the new technique allows conversion of a system with
Geometric stiffening in multibody dynamics formulations
Sharf, Inna
1993-01-01
In this paper we discuss the issue of geometric stiffening as it arises in the context of multibody dynamics. This topic has been treated in a number of previous publications in this journal and appears to be a debated subject. The controversy revolves primarily around the 'correct' methodology for incorporating the stiffening effect into dynamics formulations. The main goal of this work is to present the different approaches that have been developed for this problem through an in-depth review of several publications dealing with this subject. This is done with the goal of contributing to a precise understanding of the existing methodologies for modelling the stiffening effects in multibody systems. Thus, in presenting the material we attempt to illuminate the key characteristics of the various methods as well as show how they relate to each other. In addition, we offer a number of novel insights and clarifying interpretations of these schemes. The paper is completed with a general classification and comparison of the different approaches.
Constraint Embedding for Multibody System Dynamics
Jain, Abhinandan
2009-01-01
This paper describes a constraint embedding approach for the handling of local closure constraints in multibody system dynamics. The approach uses spatial operator techniques to eliminate local-loop constraints from the system and effectively convert the system into tree-topology systems. This approach allows the direct derivation of recursive O(N) techniques for solving the system dynamics and avoiding the expensive steps that would otherwise be required for handling the closedchain dynamics. The approach is very effective for systems where the constraints are confined to small-subgraphs within the system topology. The paper provides background on the spatial operator O(N) algorithms, the extensions for handling embedded constraints, and concludes with some examples of such constraints.
Spatial operator algebra framework for multibody system dynamics
Rodriguez, G.; Jain, Abhinandan; Kreutz, K.
1989-01-01
The Spatial Operator Algebra framework for the dynamics of general multibody systems is described. The use of a spatial operator-based methodology permits the formulation of the dynamical equations of motion of multibody systems in a concise and systematic way. The dynamical equations of progressively more complex grid multibody systems are developed in an evolutionary manner beginning with a serial chain system, followed by a tree topology system and finally, systems with arbitrary closed loops. Operator factorizations and identities are used to develop novel recursive algorithms for the forward dynamics of systems with closed loops. Extensions required to deal with flexible elements are also discussed.
Recursive dynamics for flexible multibody systems using spatial operators
Jain, A.; Rodriguez, G.
1990-01-01
Due to their structural flexibility, spacecraft and space manipulators are multibody systems with complex dynamics and possess a large number of degrees of freedom. Here the spatial operator algebra methodology is used to develop a new dynamics formulation and spatially recursive algorithms for such flexible multibody systems. A key feature of the formulation is that the operator description of the flexible system dynamics is identical in form to the corresponding operator description of the dynamics of rigid multibody systems. A significant advantage of this unifying approach is that it allows ideas and techniques for rigid multibody systems to be easily applied to flexible multibody systems. The algorithms use standard finite-element and assumed modes models for the individual body deformation. A Newton-Euler Operator Factorization of the mass matrix of the multibody system is first developed. It forms the basis for recursive algorithms such as for the inverse dynamics, the computation of the mass matrix, and the composite body forward dynamics for the system. Subsequently, an alternative Innovations Operator Factorization of the mass matrix, each of whose factors is invertible, is developed. It leads to an operator expression for the inverse of the mass matrix, and forms the basis for the recursive articulated body forward dynamics algorithm for the flexible multibody system. For simplicity, most of the development here focuses on serial chain multibody systems. However, extensions of the algorithms to general topology flexible multibody systems are described. While the computational cost of the algorithms depends on factors such as the topology and the amount of flexibility in the multibody system, in general, it appears that in contrast to the rigid multibody case, the articulated body forward dynamics algorithm is the more efficient algorithm for flexible multibody systems containing even a small number of flexible bodies. The variety of algorithms described
An Earth multi-body system elasticity and plasticity dynamics model
ZHANG Qingxian; BI Siwen; GONG Huili
2006-01-01
Research on the elasticity and plasticity dynamics of the Earth multi-body system, including the Earth multi-body system stratum-block's equivalent inertia force system and generalized inertia force, the Earth multi-body system stratum-block's equivalent inertia force system expressed with partial velocity and partial palstance, and Earth multi-body system generalized inertia force expressed with partial velocity and partial palstance. This research provides a theoretical foundation for further investigation of Earth multi-body dynamics.
Simulation studies using multibody dynamics code DART
Keat, James E.
1989-01-01
DART is a multibody dynamics code developed by Photon Research Associates for the Air Force Astronautics Laboratory (AFAL). The code is intended primarily to simulate the dynamics of large space structures, particularly during the deployment phase of their missions. DART integrates nonlinear equations of motion numerically. The number of bodies in the system being simulated is arbitrary. The bodies' interconnection joints can have an arbitrary number of degrees of freedom between 0 and 6. Motions across the joints can be large. Provision for simulating on-board control systems is provided. Conservation of energy and momentum, when applicable, are used to evaluate DART's performance. After a brief description of DART, studies made to test the program prior to its delivery to AFAL are described. The first is a large angle reorientating of a flexible spacecraft consisting of a rigid central hub and four flexible booms. Reorientation was accomplished by a single-cycle sine wave shape torque input. In the second study, an appendage, mounted on a spacecraft, was slewed through a large angle. Four closed-loop control systems provided control of this appendage and of the spacecraft's attitude. The third study simulated the deployment of the rim of a bicycle wheel configuration large space structure. This system contained 18 bodies. An interesting and unexpected feature of the dynamics was a pulsing phenomena experienced by the stays whole playout was used to control the deployment. A short description of the current status of DART is given.
Recursive flexible multibody system dynamics using spatial operators
Jain, A.; Rodriguez, G.
1992-01-01
This paper uses spatial operators to develop new spatially recursive dynamics algorithms for flexible multibody systems. The operator description of the dynamics is identical to that for rigid multibody systems. Assumed-mode models are used for the deformation of each individual body. The algorithms are based on two spatial operator factorizations of the system mass matrix. The first (Newton-Euler) factorization of the mass matrix leads to recursive algorithms for the inverse dynamics, mass matrix evaluation, and composite-body forward dynamics for the systems. The second (innovations) factorization of the mass matrix, leads to an operator expression for the mass matrix inverse and to a recursive articulated-body forward dynamics algorithm. The primary focus is on serial chains, but extensions to general topologies are also described. A comparison of computational costs shows that the articulated-body, forward dynamics algorithm is much more efficient than the composite-body algorithm for most flexible multibody systems.
Flexible joints in structural and multibody dynamics
O. A. Bauchau
2013-02-01
Full Text Available Flexible joints, sometimes called bushing elements or force elements, are found in all structural and multibody dynamics codes. In their simplest form, flexible joints simply consist of sets of three linear and three torsional springs placed between two nodes of the model. For infinitesimal deformations, the selection of the lumped spring constants is an easy task, which can be based on a numerical simulation of the joint or on experimental measurements. If the joint undergoes finite deformations, identification of its stiffness characteristics is not so simple, specially if the joint is itself a complex system. When finite deformations occur, the definition of deformation measures becomes a critical issue. This paper proposes a family of tensorial deformation measures suitable for elastic bodies of finite dimension. These families are generated by two parameters that can be used to modify the constitutive behavior of the joint, while maintaining the tensorial nature of the deformation measures. Numerical results demonstrate the objectivity of the deformations measures, a feature that is not shared by the deformations measures presently used in the literature. The impact of the choice of the two parameters on the constitutive behavior of the flexible joint is also investigated.
Dynamic modeling of flexible multibody systems with parameter uncertainty
Dynamic models of practical multibody systems may have inaccuracies which are due to parameter uncertainties. These parameter uncertainties are caused by factors such as joint clearances, friction, lubrication, material non-uniformities and manufacturing and assembly errors. In this paper, a model for the determination of the impact of the stochastic behavior of model parameters on the dynamic response of a system is developed. In the method presented, it is assumed that deformations remain small, so that linearized equations for the dynamics of the flexible multibody systems with 'dynamic stiffening terms' could be obtained. The Monte-Carlo method and the perturbation method are successfully used to simulate multibody systems with parameter uncertainties using the governing equations developed. An example of a flexible beam is used to demonstrate the method
Roller-chain Drives Mechanics using Multibody Dynamics Tools
Ambrosio, Jorge A. C.; Hansen, John Michael
1999-01-01
An integrated model for the simulation of roller-chain drives based on a multibody dynamics methodology is presented here in order to describeits complex dynamic behavior. The chain is modeled by masses lumped at the roller locations and connected by translational spring-damper elements in order ...
Graph Theoretic Foundations of Multibody Dynamics Part I: Structural Properties.
Jain, Abhinandan
2011-06-21
This is the first part of two papers that use concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The key contribution is the development of a unifying framework that shows that key analytical results and computational algorithms in multibody dynamics are a direct consequence of structural properties and require minimal assumptions about the specific nature of the underlying multibody system. This first part focuses on identifying the abstract graph theoretic structural properties of spatial operator techniques in multibody dynamics. The second part paper exploits these structural properties to develop a broad spectrum of analytical results and computational algorithms.Towards this, we begin with the notion of graph adjacency matrices and generalize it to define block-weighted adjacency (BWA) matrices and their 1-resolvents. Previously developed spatial operators are shown to be special cases of such BWA matrices and their 1-resolvents. These properties are shown to hold broadly for serial and tree topology multibody systems. Specializations of the BWA and 1-resolvent matrices are referred to as spatial kernel operators (SKO) and spatial propagation operators (SPO). These operators and their special properties provide the foundation for the analytical and algorithmic techniques developed in the companion paper.We also use the graph theory concepts to study the topology induced sparsity structure of these operators and the system mass matrix. Similarity transformations of these operators are also studied. While the detailed development is done for the case of rigid-link multibody systems, the extension of these techniques to a broader class of systems (e.g. deformable links) are illustrated. PMID:22102790
System Reduction in Multibody Dynamics of Wind Turbines
Holm-Jørgensen, Kristian; Nielsen, Søren R.K.
2009-01-01
Abstract A system reduction scheme is devised related to a multibody formulation from which the dynamic response of a wind turbine is determined. In this formulation each substructure is described in its own frame of reference, which is moving freely in the vicinity of the moving substructure. The...
Dynamic Response Calculation of Spatial Elastic Multibody Systems with High-Frequency Excitation
The objective of this paper is to establish a computational scheme for dynamic response calculations of a three-dimensional multibody mechanical system with impulsive forces, which give rise to high-frequency excitations. The finite-element method is employed to represent the local deformations of three-dimensional beam-like elastic components by either a finite set of nodal coordinates or a truncated set of modal coordinates. A reduced-order model is obtained by invoking a modal transformation. Both planar and complex modal reduction schemes are established. The developed formulation is implemented into a multibody simulation program that assembles the equations of motion and proceeds with its solution. The computational scheme permits a change in the basis of the modal space in order to regulate the admittance of higher frequencies and to accommodate any change in the kinematic configuration. Numerical examples are presented to demonstrate the applicability of the developed computational scheme
Isogeometric shell discretizations for flexible multibody dynamics
Goyal, Anmol, E-mail: goyal@mathematik.uni-kl.de; Doerfel, Michael R., E-mail: michael.doerfel@web.de; Simeon, Bernd, E-mail: simeon@mathematik.uni-kl.de; Vuong, Anh-Vu, E-mail: vuong@mathematik.uni-kl.de [Technische Universitaet Kaiserslautern, Felix Klein Zentrum fuer Mathematik, FB Mathematik (Germany)
2013-08-01
This work aims at including nonlinear elastic shell models in a multibody framework. We focus our attention to Kirchhoff-Love shells and explore the benefits of an isogeometric approach, the latest development in finite element methods, within a multibody system. Isogeometric analysis extends isoparameteric finite elements to more general functions such as B-splines and NURBS (Non-Uniform Rational B-Splines) and works on exact geometry representations even at the coarsest level of discretizations. Using NURBS as basis functions, high regularity requirements of the shell model, which are difficult to achieve with standard finite elements, are easily fulfilled. A particular advantage is the promise of simplifying the mesh generation step, and mesh refinement is easily performed by eliminating the need for communication with the geometry representation in a CAD (Computer-Aided Design) tool. Target applications are wind turbine blades and twist beam rear suspensions. First numerical examples demonstrate an impressive convergence behavior of the isogeometric approach even for a coarse mesh, while offering substantial savings with respect to the number of degrees of freedom.
Isogeometric shell discretizations for flexible multibody dynamics
This work aims at including nonlinear elastic shell models in a multibody framework. We focus our attention to Kirchhoff–Love shells and explore the benefits of an isogeometric approach, the latest development in finite element methods, within a multibody system. Isogeometric analysis extends isoparameteric finite elements to more general functions such as B-splines and NURBS (Non-Uniform Rational B-Splines) and works on exact geometry representations even at the coarsest level of discretizations. Using NURBS as basis functions, high regularity requirements of the shell model, which are difficult to achieve with standard finite elements, are easily fulfilled. A particular advantage is the promise of simplifying the mesh generation step, and mesh refinement is easily performed by eliminating the need for communication with the geometry representation in a CAD (Computer-Aided Design) tool. Target applications are wind turbine blades and twist beam rear suspensions. First numerical examples demonstrate an impressive convergence behavior of the isogeometric approach even for a coarse mesh, while offering substantial savings with respect to the number of degrees of freedom
Absolute nodal coordinate plane beam formulation for multibody systems dynamics
A new plane beam dynamic formulation for constrained multibody system dynamics is developed. Flexible multibody system dynamics includes rigid body dynamics and superimposed vibratory motions. The complexity of mechanical system dynamics originates from rotational kinematics, but the natural coordinate formulation does not use rotational coordinates, so that simple dynamic formulation is possible. These methods use only translational coordinates and simple algebraic constraints. A new formulation for plane flexible multibody systems are developed utilizing the curvature of a beam and point masses. Using absolute nodal coordinates, a constant mass matrix is obtained and the elastic force becomes a nonlinear function of the nodal coordinates. In this formulation, no infinitesimal or finite rotation assumptions are used and no assumption on the magnitude of the element rotations is made. The distributed body mass and applied forces are lumped to the point masses. Closed loop mechanical systems consisting of elastic beams can be modeled without constraints since the loop closure constraints can be substituted as beam longitudinal elasticity. A curved beam is modeled automatically. Several numerical examples are presented to show the effectiveness of this method.
Absolute nodal coordinate plane beam formulation for multibody systems dynamics
Souh, Byungyil, E-mail: bysouh@dyu.ac.kr [Dongyang University (Korea, Republic of)
2013-06-15
A new plane beam dynamic formulation for constrained multibody system dynamics is developed. Flexible multibody system dynamics includes rigid body dynamics and superimposed vibratory motions. The complexity of mechanical system dynamics originates from rotational kinematics, but the natural coordinate formulation does not use rotational coordinates, so that simple dynamic formulation is possible. These methods use only translational coordinates and simple algebraic constraints. A new formulation for plane flexible multibody systems are developed utilizing the curvature of a beam and point masses. Using absolute nodal coordinates, a constant mass matrix is obtained and the elastic force becomes a nonlinear function of the nodal coordinates. In this formulation, no infinitesimal or finite rotation assumptions are used and no assumption on the magnitude of the element rotations is made. The distributed body mass and applied forces are lumped to the point masses. Closed loop mechanical systems consisting of elastic beams can be modeled without constraints since the loop closure constraints can be substituted as beam longitudinal elasticity. A curved beam is modeled automatically. Several numerical examples are presented to show the effectiveness of this method.
Nonlinear Multibody Dynamics of Wind Turbines
Holm-Jørgensen, Kristian
elastic eigenmodes. The second method is based on a Component Mode Synthesis method with constraint modes and fixed interface normal modes. Hereby, the coupling degrees of freedom between adjacent substructures are preserved for use in setting op the kinematical constraints which secure compatibility at......The continuing development of wind turbines aim at higher effect production and reducing the purchase and maintenance costs for the customers. This demands that the components in the wind turbine are optimized closer to the limit than previously. In order to determine the design loads it is...... necessary with a numericalmodel, which represents the reality as good as possible. For this purpose a flexible multibody formulation is suitable because large nonlinear geometric deformations of e.g. the blades can be accounted for while still having the possibility of modelling the remaining components...
Reduced order component models for flexible multibody dynamics simulations
Tsuha, Walter S.; Spanos, John T.
1990-01-01
Many flexible multibody dynamics simulation codes require some form of component description that properly characterizes the dynamic behavior of the system. A model reduction procedure for producing low order component models for flexible multibody simulation is described. Referred to as projection and assembly, the method is a Rayleigh-Ritz approach that uses partitions of the system modal matrix as component Ritz transformation matrices. It is shown that the projection and assembly method yields a reduced system model that preserves a specified set of the full order system modes. Unlike classical component mode synthesis methods, the exactness of the method described is obtained at the expense of having to compute the full order system modes. The paper provides a comprehensive description of the method, a proof of exactness, and numerical results demonstrating the method's effectiveness.
Rigid multibody system dynamics with uncertain rigid bodies
This paper is devoted to the construction of a probabilistic model of uncertain rigid bodies for multibody system dynamics. We first construct a stochastic model of an uncertain rigid body by replacing the mass, the center of mass, and the tensor of inertia by random variables. The prior probability distributions of the stochastic model are constructed using the maximum entropy principle under the constraints defined by the available information. The generators of independent realizations corresponding to the prior probability distribution of these random quantities are further developed. Then several uncertain rigid bodies can be linked to each other in order to calculate the random response of a multibody dynamical system. An application is proposed to illustrate the theoretical development.
Dynamic analysis of multibody system immersed in a fluid medium
This paper is concerned primarily with the development and evaluation of an analysis method for the response prediction of immersed multibody systems to seismic and other dynamic excitations. For immersed multibody systems to seismic and other dynamic excitations. For immersed multibody systems, the hydrodynamic interaction causes coupled motion among the solid bodies. Also, under intense external excitations, impact between bodies may occur. The complex character of such systems inhibit the use of conventional analytical solutions in closed form. Therefore, approximate numerical schemes have been devised. For an incompressible, inviscid fluid, the hydrodynamic forces exerted by the fluid on solid bodies are determined to be linearly proportional to the acceleration of the vibrating solid bodies; i.e., the presence of the fluid only affects the inertia of the solid body system. A finite element computer program has been developed for computing this hydrodynamic (or added) mass effect. This program can be used to determine the hydrodynamic mass of a two-dimensional fluid field with solid bodies of arbitrary geometry. Triangular elements and linear pressure interpolation function are used to discretize the fluid region. The component element method is used to determine the dynamic response of the multibody system to externally applied mechanical loading or support excitation. In the component element method, each structural body is modeled by component elements of conceptual spring-damper type. This method is particularly advantageous for systems having nonlinearities. Direct timewise numerical integration scheme is used to solve the governing dynamic equation of the system. Analytical study is carried out and compared with an experimental result for the forced vibration of 4 simply supported beams in water. Also studied is a case of 25 (5x5) beams within a square fluid-filled container by using two different approaches
Nonrecursive formulations of multibody dynamics and concurrent multiprocessing
Kurdila, Andrew J.; Menon, Ramesh
1993-01-01
Since the late 1980's, research in recursive formulations of multibody dynamics has flourished. Historically, much of this research can be traced to applications of low dimensionality in mechanism and vehicle dynamics. Indeed, there is little doubt that recursive order N methods are the method of choice for this class of systems. This approach has the advantage that a minimal number of coordinates are utilized, parallelism can be induced for certain system topologies, and the method is of order N computational cost for systems of N rigid bodies. Despite the fact that many authors have dismissed redundant coordinate formulations as being of order N(exp 3), and hence less attractive than recursive formulations, we present recent research that demonstrates that at least three distinct classes of redundant, nonrecursive multibody formulations consistently achieve order N computational cost for systems of rigid and/or flexible bodies. These formulations are as follows: (1) the preconditioned range space formulation; (2) penalty methods; and (3) augmented Lagrangian methods for nonlinear multibody dynamics. The first method can be traced to its foundation in equality constrained quadratic optimization, while the last two methods have been studied extensively in the context of coercive variational boundary value problems in computational mechanics. Until recently, however, they have not been investigated in the context of multibody simulation, and present theoretical questions unique to nonlinear dynamics. All of these nonrecursive methods have additional advantages with respect to recursive order N methods: (1) the formalisms retain the highly desirable order N computational cost; (2) the techniques are amenable to concurrent simulation strategies; (3) the approaches do not depend upon system topology to induce concurrency; and (4) the methods can be derived to balance the computational load automatically on concurrent multiprocessors. In addition to the presentation of
Dynamic analysis of multibody system immersed in a fluid medium
This paper is concerned primarily with the development and evaluation of an analysis method for the reponse prediction of immersed systems to seismic and other dynamic excitations. For immersed multibody systems, the hydrodynamic interaction causes coupled motion among the solid bodies. Also, under intense external excitations, impact between bodies may occur. The complex character of such systems inhibit the use of conventional analytical solutions in closed form. Therefore, approximate numerical schemes have been devised. For an incompressible, inviscid fluid, the hydrodynamic forces exerted by the fluid on solid bodies are determined to be linearly proportional to the acceleration of the vibrating solid bodies; i.e., the presence of the fluid only affects the inertia of the solid body system. A finite element computer program has been developed for computing this hydrodynamic (or added) mass effect. This program can be used to determine the hydrodynamic mass of a two-dimensional fluid field with solid bodies of arbitrary geometry. Triangular elements and linear pressure interpolation function are used to discretize the fluid region. The component element method is used to determine the dynamic response of the multibody system to externally applied mechanical loading or support excitation. The present analysis method for predicting the dynamic response of submerged multibody system is quite general and pertains to any number of solid bodies. However in this paper, its application is demonstrated only for 4 and 25 body systems. (Auth.)
Linked-List-Based Multibody Dynamics (MBDyn) Engine
MacLean, John; Brain, Thomas; Wuiocho, Leslie; Huynh, An; Ghosh, Tushar
2012-01-01
This new release of MBDyn is a software engine that calculates the dynamics states of kinematic, rigid, or flexible multibody systems. An MBDyn multibody system may consist of multiple groups of articulated chains, trees, or closed-loop topologies. Transient topologies are handled through conservation of energy and momentum. The solution for rigid-body systems is exact, and several configurable levels of nonlinear term fidelity are available for flexible dynamics systems. The algorithms have been optimized for efficiency and can be used for both non-real-time (NRT) and real-time (RT) simulations. Interfaces are currently compatible with NASA's Trick Simulation Environment. This new release represents a significant advance in capability and ease of use. The two most significant new additions are an application programming interface (API) that clarifies and simplifies use of MBDyn, and a link-list infrastructure that allows a single MBDyn instance to propagate an arbitrary number of interacting groups of multibody top ologies. MBDyn calculates state and state derivative vectors for integration using an external integration routine. A Trickcompatible interface is provided for initialization, data logging, integration, and input/output.
A decoupled recursive approach for constrained flexible multibody system dynamics
Lai, Hao-Jan; Kim, Sung-Soo; Haug, Edward J.; Bae, Dae-Sung
1989-01-01
A variational-vector calculus approach is employed to derive a recursive formulation for dynamic analysis of flexible multibody systems. Kinematic relationships for adjacent flexible bodies are derived in a companion paper, using a state vector notation that represents translational and rotational components simultaneously. Cartesian generalized coordinates are assigned for all body and joint reference frames, to explicitly formulate deformation kinematics under small deformation kinematics and an efficient flexible dynamics recursive algorithm is developed. Dynamic analysis of a closed loop robot is performed to illustrate efficiency of the algorithm.
System Reduction in Nonlinear Multibody Dynamics of Wind Turbines
Holm-Jørgensen, Kristian; Nielsen, Søren R.K.; Rubak, Rune
2007-01-01
. In the other case, the stiff body motion is defined as the chord line connecting the end points of the beam, and the elastic deformations are simply supported at the end points. The system reduction is performed by discretizing the spatial motion into a set of rigid body modes and linear elastic......In this paper the system reduction in nonlinear multibody dynamics of wind turbines is investigated for various updating schemes of the moving frame of reference. In one case, the moving frame of reference is updated to a stiff body, relative to which the elastic deformations are fixed at one end...
Spatial operator approach to flexible multibody system dynamics and control
Rodriguez, G.
1991-01-01
The inverse and forward dynamics problems for flexible multibody systems were solved using the techniques of spatially recursive Kalman filtering and smoothing. These algorithms are easily developed using a set of identities associated with mass matrix factorization and inversion. These identities are easily derived using the spatial operator algebra developed by the author. Current work is aimed at computational experiments with the described algorithms and at modelling for control design of limber manipulator systems. It is also aimed at handling and manipulation of flexible objects.
General background and approach to multibody dynamics for space applications
Santini, Paolo; Gasbarri, Paolo
2009-06-01
Multibody dynamics for space applications is dictated by space environment such as space-varying gravity forces, orbital and attitude perturbations, control forces if any. Several methods and formulations devoted to the modeling of flexible bodies undergoing large overall motions were developed in recent years. Most of these different formulations were aimed to face one of the main problems concerning the analysis of spacecraft dynamics namely the reduction of computer simulation time. By virtue of this, the use of symbolic manipulation, recursive formulation and parallel processing algorithms were proposed. All these approaches fall into two categories, the one based on Newton/Euler methods and the one based on Lagrangian methods; both of them have their advantages and disadvantages although in general, Newtonian approaches lend to a better understanding of the physics of problems and in particular of the magnitude of the reactions and of the corresponding structural stresses. Another important issue which must be addressed carefully in multibody space dynamics is relevant to a correct choice of kinematics variables. In fact, when dealing with flexible multibody system the resulting equations include two different types of state variables, the ones associated with large (rigid) displacements and the ones associated with elastic deformations. These two sets of variables have generally two different time scales if we think of the attitude motion of a satellite whose period of oscillation, due to the gravity gradient effects, is of the same order of magnitude as the orbital period, which is much bigger than the one associated with the structural vibration of the satellite itself. Therefore, the numerical integration of the equations of the system represents a challenging problem. This was the abstract and some of the arguments that Professor Paolo Santini intended to present for the Breakwell Lecture; unfortunately a deadly disease attacked him and shortly took him
Numerical Solution for Stiff Dynamic Equations of Flexible Multibody System
L(U) Yan-ping; WU Guo-rong
2008-01-01
A nonlinear numerical integration method, based on forward and backward Euler integration methods, is proposed for solving the stiff dynamic equations of a flexible multibody system, which are transformed from the second order to the first order by adop- ring state variables. This method is of A0 stability and infinity stability. The numerical solutions violating the constraint equations are corrected by Blajer's modification approach. Simulation results of a slider-crank mechanism by the proposed method are in good a- greement with ones from other literature.
Decoupling Kinematic Loops for Real-Time Multibody Dynamic Simulations
Omar Mohamed
2016-01-01
Full Text Available Earth moving equipment are typically equipped with hydraulic cylinder actuators to perform the designated tasks. Multibody modelling of such systems results in models with kinematic loops that couples the motion variables of the loop bodies. Iterative solutions will be needed to satisfy the loop constraints and the applied constraints, which require evaluation of the constraint Jacobean matrix. The size of the Jacobean matrix and the associated projections depends on the number of motion variables in each kinematic loop. Consequently, the computational cost significantly increases as the number of variables in the kinematic loop increases. Real-time control and hybrid hardware-in-the-loop systems both require efficient and fast computational algorithms. Eliminating the kinematic loops can improve the computational efficiency and effectiveness of the control algorithms. This paper presents an efficient approach to eliminate the coupling due to the cylinder-rod connections and consequently the kinematic loops in the multibody models leading to efficient simulation. The proposed approach calculates the spatial accelerations and inertia forces of the actuator bodies and the interaction forces with other components. The actuator forces are then projected onto the connecting bodies leading to exact dynamics of the system.
Dynamics of underactuated multibody systems modeling, control and optimal design
Seifried, Robert
2014-01-01
Underactuated multibody systems are intriguing mechatronic systems, as they possess fewer control inputs than degrees of freedom. Some examples are modern light-weight flexible robots and articulated manipulators with passive joints. This book investigates such underactuated multibody systems from an integrated perspective. This includes all major steps from the modeling of rigid and flexible multibody systems, through nonlinear control theory, to optimal system design. The underlying theories and techniques from these different fields are presented using a self-contained and unified approach and notation system. Subsequently, the book focuses on applications to large multibody systems with multiple degrees of freedom, which require a combination of symbolical and numerical procedures. Finally, an integrated, optimization-based design procedure is proposed, whereby both structural and control design are considered concurrently. Each chapter is supplemented by illustrated examples.
Positional FEM formulation for flexible multi-body dynamic analysis
Greco, M.; Coda, H. B.
2006-03-01
This paper presents a simple formulation to deal with flexible multi-body dynamic systems by the finite element method. The proposed methodology is based on the minimum potential energy theorem written regarding nodal positions. Velocity, acceleration and strain are achieved directly from positions, not displacements. A non-dimensional space is created and the relative curvature and fibers length are calculated for both reference and deformed configurations and used to calculate the strain energy at general points. The classical Newmark equations are used to integrate time. Damping is introduced into the mechanical system by a rheonomic energy functional. The final formulation has the advantage of being simple and easy to teach, when compared to classical counterparts. The behavior of a bench-mark problem (spin-up maneuver) is studied regarding the influence of mass representation on its overall transient and steady-state behavior. Three other examples are presented to show the applicability of the technique, namely, a flexible slider-crank mechanism, a flexible beam flight and a Peaucellier-type mechanism. The results are compared with other authors' numerical solutions.
Sheong, Fu Kit; Silva, Daniel-Adriano; Meng, Luming; Zhao, Yutong; Huang, Xuhui
2015-01-13
The conformational dynamics of multibody systems plays crucial roles in many important problems. Markov state models (MSMs) are powerful kinetic network models that can predict long-time-scale dynamics using many short molecular dynamics simulations. Although MSMs have been successfully applied to conformational changes of individual proteins, the analysis of multibody systems is still a challenge because of the complexity of the dynamics that occur on a mixture of drastically different time scales. In this work, we have developed a new algorithm, automatic state partitioning for multibody systems (APM), for constructing MSMs to elucidate the conformational dynamics of multibody systems. The APM algorithm effectively addresses different time scales in the multibody systems by directly incorporating dynamics into geometric clustering when identifying the metastable conformational states. We have applied the APM algorithm to a 2D potential that can mimic a protein-ligand binding system and the aggregation of two hydrophobic particles in water and have shown that it can yield tremendous enhancements in the computational efficiency of MSM construction and the accuracy of the models. PMID:26574199
Structure-preserving integrators in nonlinear structural dynamics and flexible multibody dynamics
2016-01-01
This book focuses on structure-preserving numerical methods for flexible multibody dynamics, including nonlinear elastodynamics and geometrically exact models for beams and shells. It also deals with the newly emerging class of variational integrators as well as Lie-group integrators. It discusses two alternative approaches to the discretization in space of nonlinear beams and shells. Firstly, geometrically exact formulations, which are typically used in the finite element community and, secondly, the absolute nodal coordinate formulation, which is popular in the multibody dynamics community. Concerning the discretization in time, the energy-momentum method and its energy-decaying variants are discussed. It also addresses a number of issues that have arisen in the wake of the structure-preserving discretization in space. Among them are the parameterization of finite rotations, the incorporation of algebraic constraints and the computer implementation of the various numerical methods. The practical application...
Nonlinear three-dimensional beam theory for flexible multibody dynamics
In flexible multibody systems, it is convenient to approximate many structural components as beams or shells. Classical beam theories, such as Euler–Bernoulli beam theory, often form the basis of the analytical development for beam dynamics. The advantage of this approach is that it leads to a very simple kinematic representation of the problem: the beam’s section is assumed to remain plane and its displacement field is fully defined by three displacement and three rotation components. While such an approach is capable of capturing the kinetic energy of the system accurately, it cannot represent the strain energy adequately. This paper presents a different approach to the problem. Based on a finite element discretization of the cross-section, an exact solution of the theory of three-dimensional elasticity is developed. The proposed approach is based on the Hamiltonian formalism and leads to an expansion of the solution in terms of extremity and central solutions. Kinematically, the problem is decomposed into an arbitrarily large rigid-section motion and a warping field. The sectional strains associated with the rigid-section motion and the warping field are assumed to remain small. As a consequence of this kinematic decomposition, the governing equations of the problem fall into two distinct categories: the equations describing geometrically exact beams and those describing local deformations. The governing equations for geometrically exact beams are nonlinear, one-dimensional equations, whereas a linear, two-dimensional analysis provides the detailed distribution of three-dimensional stress and strain fields. Within the stated assumptions, the solutions presented here are the exact solution of three-dimensional elasticity for beams undergoing arbitrarily large motions
Nonlinear three-dimensional beam theory for flexible multibody dynamics
Han, Shilei; Bauchau, Olivier A., E-mail: olivier.bauchau@sjtu.edu.cn [University of Michigan–Shanghai Jiao Tong University Joint Institute (China)
2015-07-15
In flexible multibody systems, it is convenient to approximate many structural components as beams or shells. Classical beam theories, such as Euler–Bernoulli beam theory, often form the basis of the analytical development for beam dynamics. The advantage of this approach is that it leads to a very simple kinematic representation of the problem: the beam’s section is assumed to remain plane and its displacement field is fully defined by three displacement and three rotation components. While such an approach is capable of capturing the kinetic energy of the system accurately, it cannot represent the strain energy adequately. This paper presents a different approach to the problem. Based on a finite element discretization of the cross-section, an exact solution of the theory of three-dimensional elasticity is developed. The proposed approach is based on the Hamiltonian formalism and leads to an expansion of the solution in terms of extremity and central solutions. Kinematically, the problem is decomposed into an arbitrarily large rigid-section motion and a warping field. The sectional strains associated with the rigid-section motion and the warping field are assumed to remain small. As a consequence of this kinematic decomposition, the governing equations of the problem fall into two distinct categories: the equations describing geometrically exact beams and those describing local deformations. The governing equations for geometrically exact beams are nonlinear, one-dimensional equations, whereas a linear, two-dimensional analysis provides the detailed distribution of three-dimensional stress and strain fields. Within the stated assumptions, the solutions presented here are the exact solution of three-dimensional elasticity for beams undergoing arbitrarily large motions.
On geometric dynamics of rigid multi-body systems
Stramigioli, Stefano; Duindam, Vincent
2007-01-01
Standard methods to model multibody systems are aimed at systems with configuration spaces isomorphic to Rn. This limitation leads to singularities and other artifacts in case the configuration space has a different topology, for example in the case of ball joints or a free-floating mechanism. This
PACE: A test bed for the dynamics and control of flexible multibody systems
Kwak, Moon K.; Smith, Monty J.; Das, Alok
1993-01-01
The Phillips Laboratory at Edwards AFB has constructed a test bed for the validation and comparison of modeling and control theories for the dynamics and control of flexible multibody systems. This project is called the Planar Articulating Controls Experiment (PACE). This paper presents the experimental apparatus for PACE and the problem formulation. An in-depth analysis on DC motor dynamics was also performed.
Graph Theoretic Foundations of Multibody Dynamics Part II: Analysis and Algorithms.
Jain, Abhinandan
2011-10-01
This second, of a two part paper, uses concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The first part [7] established the block-weighted adjacency (BWA) matrix structure of spatial operators associated with serial and tree topology multibody system dynamics, and introduced the notions of spatial kernel operators (SKO) and spatial propagation operators (SPO). This paper builds upon these connections to show that key analytical results and computational algorithms are a direct consequence of these structural properties and require minimal assumptions about the specific nature of the underlying multibody system. We formalize this notion by introducing the notion of SKO models for general tree-topology multibody systems. We show that key analytical results, including mass matrix factorization, inversion, and decomposition hold for all SKO models. It is also shown that key low-order scatter/gather recursive computational algorithms follow directly from these abstract-level analytical results. Application examples to illustrate the concrete application of these general results are provided. The paper also describes a general recipe for developing SKO models. The abstract nature of SKO models allows the application of these techniques to a very broad class of multibody systems. PMID:22102791
Evolution of the DeNOC-based dynamic modelling for multibody systems
S. K. Saha
2013-01-01
Full Text Available Dynamic modelling of a multibody system plays very essential role in its analyses. As a result, several methods for dynamic modelling have evolved over the years that allow one to analyse multibody systems in a very efficient manner. One such method of dynamic modelling is based on the concept of the Decoupled Natural Orthogonal Complement (DeNOC matrices. The DeNOC-based methodology for dynamics modelling, since its introduction in 1995, has been applied to a variety of multibody systems such as serial, parallel, general closed-loop, flexible, legged, cam-follower, and space robots. The methodology has also proven useful for modelling of proteins and hyper-degree-of-freedom systems like ropes, chains, etc. This paper captures the evolution of the DeNOC-based dynamic modelling applied to different type of systems, and its benefits over other existing methodologies. It is shown that the DeNOC-based modelling provides deeper understanding of the dynamics of a multibody system. The power of the DeNOC-based modelling has been illustrated using several numerical examples.
Research on the Earth system multi-body force system dynamical model
CHEN; Xiaofei; BI; Siwen; WU; Fei; DONG; Qianlin
2006-01-01
This paper presents an overview of the binding force and freedom force of Earth system, and describes force moment to point and line and force system in the Earth system. It introduces the force theory of the Earth system multi-body force system from special or equivalent force system of Earth system mechanics, general force and no-power force of Earth system. Finally it describes the force and moment of nodes of Earth system and provides basic model for the research of the Earth system multi-body dynamics.
Domain decomposition approach to flexible multibody dynamics simulation
Kwak, JunYoung; Chun, TaeYoung; Shin, SangJoon; Bauchau, Olivier A.
2014-01-01
Finite element based formulations for flexible multibody systems are becoming increasingly popular and as the complexity of the configurations to be treated increases, so does the computational cost. It seems natural to investigate the applicability of parallel processing to this type of problems; domain decomposition techniques have been used extensively for this purpose. In this approach, the computational domain is divided into non-overlapping sub-domains, and the continuity of the displacement field across sub-domain boundaries is enforced via the Lagrange multiplier technique. In the finite element literature, this approach is presented as a mathematical algorithm that enables parallel processing. In this paper, the divided system is viewed as a flexible multibody system, and the sub-domains are connected by kinematic constraints. Consequently, all the techniques applicable to the enforcement of constraints in multibody systems become applicable to the present problem. In particular, it is shown that a combination of the localized Lagrange multiplier technique with the augmented Lagrange formulation leads to interesting solution strategies. The proposed algorithm is compared with the well-known FETI approach with regards to convergence and efficiency characteristics. The present algorithm is relatively simple and leads to improved convergence and efficiency characteristics. Finally, implementation on a parallel computer was conducted for the proposed approach.
Kelkar, Atul G.; Joshi, Suresh M.; Alberts, Thomas E.
1993-01-01
The stability characteristics of dynamic dissipative compensators are investigated for multibody flexible space structures having nonlinear dynamics. The problem addressed is that of proving asymptotic stability of dynamic dissipative compensators. The stability proof uses the Liapunov approach and exploits the inherent passivity of such systems. For such systems these compensators are shown to be robust to parametric uncertainties and unmodeled dynamics. The results are applicable to a large class of structures such as flexible space structures with articulated flexible appendages.
Damkjær, Jesper; Erleben, Kenny
2009-01-01
simultaneous descend in the tandem traversal. The data structure design and traversal are highly specialized for exploiting the parallel threads in the NVIDIA GPUs. As proof-of-concept we demonstrate a GPU implementation for a multibody dynamics simulation, showing an approximate speedup factor of up to 8...
Advances in Chimera Grid Tools for Multi-Body Dynamics Simulations and Script Creation
Chan, William M.
2004-01-01
This viewgraph presentation contains information about (1) Framework for multi-body dynamics - Geometry Manipulation Protocol (GMP), (2) Simulation procedure using Chimera Grid Tools (CGT) and OVERFLOW-2 (3) Further recent developments in Chimera Grid Tools OVERGRID, Grid modules, Script library and (4) Future work.
Camera-based noncontact metrology for static/dynamic testing of flexible multibody systems
Presented here is a camera-based noncontact measurement theory for static/dynamic testing of flexible multibody systems that undergo large rigid, elastic and/or plastic deformations. The procedure and equations for accurate estimation of system parameters (i.e. the location and focal length of each camera and the transformation matrix relating its image and object coordinate systems) using an L-frame with four retroreflective markers are described in detail. Moreover, a method for refinement of estimated system parameters and establishment of a lens distortion model for correcting optical distortions using a T-wand with three markers is described. Dynamically deformed geometries of a multibody system are assumed to be obtained by tracing the three-dimensional instantaneous coordinates of markers adhered to the system's outside surfaces, and cameras and triangulation techniques are used for capturing marker images and identifying markers' coordinates. Furthermore, an EAGLE-500 motion analysis system is used to demonstrate measurements of static/dynamic deformations of six different flexible multibody systems. All numerical simulations and experimental results show that the use of camera-based motion analysis systems is feasible and accurate enough for static/dynamic experiments on flexible multibody systems, especially those that cannot be measured using conventional contact sensors
Zhang, Yong; Wu, Delong
With the fast development of the industry technology especially the applications of spacecraft and weapon systems, a great deal of problems come forth in the dynamics of flexible multibody system and should be settled urgently. Because of the facts of time-varying topologies in these systems, such as impact, friction, stiction, intermittent motion, lock-up and loose of the joint, etc., the topological configuration, the degree of freedom, or the number of constraint equations will be changed during the motion of the system. So the traditional dynamics of flexible multibody system have to face those problems. For example, during launching of the mobile weapon system, the constraint relationship between the launching barrel and the missile must be changed when the adapters slide out in order when the missile was pushed out of the launching barrel. Based on the theory of dynamics of flexible multibody system, started with studying on launching dynamics of mobile launching system, combined with the dynamics characteristics of spacecraft, a model came into being on the dynamics of flexible multibody system with variable topologies, and the detailed simulation were given on the launching process during the aircraft flying away from the barrel in mobile missile system. Used the Lagrange method, a dynamics model of topology-changing flexible multibody system was founded in this paper, which included the motions coupling of orbit, attitude, large displacement of mechanism, and vibration of flexible bodies. Several critical problems were analyzed such as the addition and/or deletion of constraints, compatibility conditions etc. The constraints of the topology-changing system can be divided into two types, base constraints and condition constraints. The base constraints will not change during the motion of the multibody system, however, the condition constraints will be deleted from or added into the system depended on certain conditions. It is the exist of the condition
Boyer, Frédéric; Porez, Mathieu
2015-04-01
This article presents a set of generic tools for multibody system dynamics devoted to the study of bio-inspired locomotion in robotics. First, archetypal examples from the field of bio-inspired robot locomotion are presented to prepare the ground for further discussion. The general problem of locomotion is then stated. In considering this problem, we progressively draw a unified geometric picture of locomotion dynamics. For that purpose, we start from the model of discrete mobile multibody systems (MMSs) that we progressively extend to the case of continuous and finally soft systems. Beyond these theoretical aspects, we address the practical problem of the efficient computation of these models by proposing a Newton-Euler-based approach to efficient locomotion dynamics with a few illustrations of creeping, swimming, and flying. PMID:25811531
On the Modeling of Shells in Multibody Dynamics
Bauchau, Olivier A.; Choi, Jou-Young; Bottasso, Carlo L.
2000-01-01
Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the, constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.
Modeling Multibody Stage Separation Dynamics Using Constraint Force Equation Methodology
Tartabini, Paul V.; Roithmayr, Carlos M.; Toniolo, Matthew D.; Karlgaard, Christopher D.; Pamadi, Bandu N.
2011-01-01
This paper discusses the application of the constraint force equation methodology and its implementation for multibody separation problems using three specially designed test cases. The first test case involves two rigid bodies connected by a fixed joint, the second case involves two rigid bodies connected with a universal joint, and the third test case is that of Mach 7 separation of the X-43A vehicle. For the first two cases, the solutions obtained using the constraint force equation method compare well with those obtained using industry- standard benchmark codes. For the X-43A case, the constraint force equation solutions show reasonable agreement with the flight-test data. Use of the constraint force equation method facilitates the analysis of stage separation in end-to-end simulations of launch vehicle trajectories
Polach P.
2008-11-01
Full Text Available Vertical dynamic properties of the ŠKODA 21 Tr low-floor trolleybus were investigated on an artificial test track when driving with a real vehicle and when simulating driving with a multibody model along a virtual test track. Driving along the artificial test track was aimed to determine vertical dynamic properties of the real trolleybus and on the basis of them to verify computer trolleybus models. Time histories and extreme values of the air springs relative deflections are the monitored quantities. Due to differences of the experiments and the computer simulations results the influences of the characteristics of the spring-damper structural elements of the axles suspension and the radial characteristics of the tires used in the trolleybus multibody model on the extreme values of the monitored quantities are evaluated.
A Simplified Flexible Multibody Dynamics for a Main Landing Gear with Flexible Leaf Spring
Zhi-Peng Xue; Ming Li; Yan-Hui Li; Hong-Guang Jia
2014-01-01
The dynamics of multibody systems with deformable components has been a subject of interest in many different fields such as machine design and aerospace. Traditional rigid-flexible systems often take a lot of computer resources to get accurate results. Accuracy and efficiency of computation have been the focus of this research in satisfying the coupling of rigid body and flex body. The method is based on modal analysis and linear theory of elastodynamics: reduced modal datum was used to desc...
Dynamic Analysis of Flexible Multibody Systems for High-Rise Building Window Cleaning Gondola
无
2005-01-01
A virtual prototype of high-rise building window cleaning gondola based on multibody system dynamics software MSC.ADAMS is presented. The rigid bodies are modeled by CAD software and flexible bodies are modeled by discrete beam method. The whole machine's natural characteristics are analyzed and changed to frequency field. According to the results, the dangerous frequencies are avoided and the design can be optimized and the performance can be improved.
A Modelling Approach to Multibody Dynamics of Fluid Power Machinery with Hydrodynamic Lubrication
Johansen, Per; Rømer, Daniel; Andersen, Torben Ole; Pedersen, Henrik C.
The efficiency potential of the digital displacement technology and the increasing interest in hydraulic transmissions in wind and wave energy applications has created an incentive for development of high efficiency fluid power machinery. Modelling and analysis of fluid power machinery loss mecha...... coupled with multibody dynamics models. The focus of the current paper is an approach where the transient pressure field in hydrodynamic lubricated joint clearances are modelled by a set of control volumes and coupled with the fluid power machinery mechanics....
Online Kinematic and Dynamic-State Estimation for Constrained Multibody Systems Based on IMUs
José Luis Torres-Moreno
2016-03-01
Full Text Available This article addresses the problems of online estimations of kinematic and dynamic states of a mechanism from a sequence of noisy measurements. In particular, we focus on a planar four-bar linkage equipped with inertial measurement units (IMUs. Firstly, we describe how the position, velocity, and acceleration of all parts of the mechanism can be derived from IMU signals by means of multibody kinematics. Next, we propose the novel idea of integrating the generic multibody dynamic equations into two variants of Kalman filtering, i.e., the extended Kalman filter (EKF and the unscented Kalman filter (UKF, in a way that enables us to handle closed-loop, constrained mechanisms, whose state space variables are not independent and would normally prevent the direct use of such estimators. The proposal in this work is to apply those estimators over the manifolds of allowed positions and velocities, by means of estimating a subset of independent coordinates only. The proposed techniques are experimentally validated on a testbed equipped with encoders as a means of establishing the ground-truth. Estimators are run online in real-time, a feature not matched by any previous procedure of those reported in the literature on multibody dynamics.
Online Kinematic and Dynamic-State Estimation for Constrained Multibody Systems Based on IMUs.
Torres-Moreno, José Luis; Blanco-Claraco, José Luis; Giménez-Fernández, Antonio; Sanjurjo, Emilio; Naya, Miguel Ángel
2016-01-01
This article addresses the problems of online estimations of kinematic and dynamic states of a mechanism from a sequence of noisy measurements. In particular, we focus on a planar four-bar linkage equipped with inertial measurement units (IMUs). Firstly, we describe how the position, velocity, and acceleration of all parts of the mechanism can be derived from IMU signals by means of multibody kinematics. Next, we propose the novel idea of integrating the generic multibody dynamic equations into two variants of Kalman filtering, i.e., the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), in a way that enables us to handle closed-loop, constrained mechanisms, whose state space variables are not independent and would normally prevent the direct use of such estimators. The proposal in this work is to apply those estimators over the manifolds of allowed positions and velocities, by means of estimating a subset of independent coordinates only. The proposed techniques are experimentally validated on a testbed equipped with encoders as a means of establishing the ground-truth. Estimators are run online in real-time, a feature not matched by any previous procedure of those reported in the literature on multibody dynamics. PMID:26959027
Online Kinematic and Dynamic-State Estimation for Constrained Multibody Systems Based on IMUs
Torres-Moreno, José Luis; Blanco-Claraco, José Luis; Giménez-Fernández, Antonio; Sanjurjo, Emilio; Naya, Miguel Ángel
2016-01-01
This article addresses the problems of online estimations of kinematic and dynamic states of a mechanism from a sequence of noisy measurements. In particular, we focus on a planar four-bar linkage equipped with inertial measurement units (IMUs). Firstly, we describe how the position, velocity, and acceleration of all parts of the mechanism can be derived from IMU signals by means of multibody kinematics. Next, we propose the novel idea of integrating the generic multibody dynamic equations into two variants of Kalman filtering, i.e., the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), in a way that enables us to handle closed-loop, constrained mechanisms, whose state space variables are not independent and would normally prevent the direct use of such estimators. The proposal in this work is to apply those estimators over the manifolds of allowed positions and velocities, by means of estimating a subset of independent coordinates only. The proposed techniques are experimentally validated on a testbed equipped with encoders as a means of establishing the ground-truth. Estimators are run online in real-time, a feature not matched by any previous procedure of those reported in the literature on multibody dynamics. PMID:26959027
Experimental validation of flexible multibody dynamics beam formulations
Bauchau, Olivier A., E-mail: olivier.bauchau@sjtu.edu.cn; Han, Shilei [University of Michigan-Shanghai Jiao Tong University Joint Institute (China); Mikkola, Aki; Matikainen, Marko K. [Lappeenranta University of Technology, Department of Mechanical Engineering (Finland); Gruber, Peter [Austrian Center of Competence in Mechatronics GmbH (Austria)
2015-08-15
In this paper, the accuracies of the geometrically exact beam and absolute nodal coordinate formulations are studied by comparing their predictions against an experimental data set referred to as the “Princeton beam experiment.” The experiment deals with a cantilevered beam experiencing coupled flap, lag, and twist deformations. In the absolute nodal coordinate formulation, two different beam elements are used. The first is based on a shear deformable approach in which the element kinematics is described using two nodes. The second is based on a recently proposed approach featuring three nodes. The numerical results for the geometrically exact beam formulation and the recently proposed three-node absolute nodal coordinate formulation agree well with the experimental data. The two-node beam element predictions are similar to those of linear beam theory. This study suggests that a careful and thorough evaluation of beam elements must be carried out to assess their ability to deal with the three-dimensional deformations typically found in flexible multibody systems.
Experimental validation of flexible multibody dynamics beam formulations
In this paper, the accuracies of the geometrically exact beam and absolute nodal coordinate formulations are studied by comparing their predictions against an experimental data set referred to as the “Princeton beam experiment.” The experiment deals with a cantilevered beam experiencing coupled flap, lag, and twist deformations. In the absolute nodal coordinate formulation, two different beam elements are used. The first is based on a shear deformable approach in which the element kinematics is described using two nodes. The second is based on a recently proposed approach featuring three nodes. The numerical results for the geometrically exact beam formulation and the recently proposed three-node absolute nodal coordinate formulation agree well with the experimental data. The two-node beam element predictions are similar to those of linear beam theory. This study suggests that a careful and thorough evaluation of beam elements must be carried out to assess their ability to deal with the three-dimensional deformations typically found in flexible multibody systems
Modelling of contact dynamics of two flexible multi-body systems
Kim, S. W.; Misra, A. K.; Modi, V. J.; Cyril, X.
Details of contact dynamics of two flexible multi-body systems (e.g. a spacecraft-mounted manipulator capturing a flexible satellite) are considered in this paper. The components undergoing direct contact (e.g. the end-effector of the manipulator and the grapple surface) are modelled using the finite element method that incorporates large rigid body displacements, while the rest of the system is handled through the usual flexible multi-body formulation. The basic condition of the contact is that no material overlap can occur; this condition is expressed in terms of a set of algebraic constraint equations. Thus, the system dynamics is described by two sets of differential equations (one for the multi-body formulation and the other for the finite element nodal displacements of the contacting surfaces) subjected to a set of algebraic constraint equations. A procedure to solve this system of equations is proposed in the paper. A typical scenario involving capture of a flexible satellite using a manipulator is considered and computer simulation results are presented.
Effect of using composites on the dynamic response of multi-body systems
Shabana, A. A.
1986-08-01
A finite element scheme is presented for studying the dynamic response of multi-body systems with components manufactured from orthotropic materials. The formulation presented is exemplified by using fiber-reinforced cornposite laminates. The multi-body system considered in this investigation consists of interconnected rigid and flexible components, each undergoing large angular rotations. The configuration of the elastic components is identified by using two sets of generalized co-ordinates, reference and elastic co-ordinates. Reference co-ordinates describe the location and orientation of a selected body reference while elastic co-ordinates describe the deformation with respect to the body reference. Component modes of elastic components in the system are used to reduce the number of generalized co-ordinates. The system differential equations of motion and the algebraic constraint equations describing mechanical joints in the system are written in terms of mixed sets of reference and modal co-ordinates. Two numerical examples, for a slider crank mechanism and a Peaucellier mechanism, are presented in order to demonstrate the effect of the use of the composites on the dynamic response of multi-body systems. Numerical results showed that the use of composites represents an effective passive control strategy.
Partition method for impact dynamics of flexible multibody systems based on contact constraint
段玥晨; 章定国; 洪嘉振
2013-01-01
The impact dynamics of a flexible multibody system is investigated. By using a partition method, the system is divided into two parts, the local impact region and the region away from the impact. The two parts are connected by specific boundary conditions, and the system after partition is equivalent to the original system. According to the rigid-flexible coupling dynamic theory of multibody system, system’s rigid-flexible coupling dynamic equations without impact are derived. A local impulse method for establishing the initial impact conditions is proposed. It satisfies the compatibility con-ditions for contact constraints and the actual physical situation of the impact process of flexible bodies. Based on the contact constraint method, system’s impact dynamic equa-tions are derived in a differential-algebraic form. The contact/separation criterion and the algorithm are given. An impact dynamic simulation is given. The results show that system’s dynamic behaviors including the energy, the deformations, the displacements, and the impact force during the impact process change dramatically. The impact makes great effects on the global dynamics of the system during and after impact.
Modeling and Simulation of Arresting Gear System with Multibody Dynamic Approach
Wenhou Shen; Zhihua Zhao; Gexue Ren; Jiapeng Liu
2013-01-01
The arresting dynamics of the aircraft on the aircraft carrier involves both a transient wave propagation process in rope and a smooth decelerating of aircraft. This brings great challenge on simulating the whole process since the former one needs small time-step to guarantee the stability, while the later needs large time-step to reduce calculation time. To solve this problem, this paper proposes a full-scale multibody dynamics model of arresting gear system making use of variable time-step ...
Henry, Alan; Chipman, Richard; Hu, Tsay-Hsin G.
1993-04-01
An efficient simulation has been successfully developed to analyze the dynamics and control of spacecraft comprised of multiple rigid/flexible articulating bodies. The implementation employs a typical order-(N) multi-body dynamic approach coupled with a state-of-the-art symbolic equation optimization algorithm. The simulation has been modified to compute the instantaneous acceleration at any arbitrary location on an orbiting body. Gravity gradient, rotational and aerodynamic accelerations contribute to the total quasi-steady state microgravity environment. The simulation is used to evaluate the microgravity levels within Space Station Freedom to demonstrate the excellent microgravity environment which it can provide for scientific experiments.
Evolution of Flexible Multibody Dynamics for Simulation Applications Supporting Human Spaceflight
Huynh, An; Brain, Thomas A.; MacLean, John R.; Quiocho, Leslie J.
2016-01-01
During the course of transition from the Space Shuttle and International Space Station programs to the Orion and Journey to Mars exploration programs, a generic flexible multibody dynamics formulation and associated software implementation has evolved to meet an ever changing set of requirements at the NASA Johnson Space Center (JSC). Challenging problems related to large transitional topologies and robotic free-flyer vehicle capture/ release, contact dynamics, and exploration missions concept evaluation through simulation (e.g., asteroid surface operations) have driven this continued development. Coupled with this need is the requirement to oftentimes support human spaceflight operations in real-time. Moreover, it has been desirable to allow even more rapid prototyping of on-orbit manipulator and spacecraft systems, to support less complex infrastructure software for massively integrated simulations, to yield further computational efficiencies, and to take advantage of recent advances and availability of multi-core computing platforms. Since engineering analysis, procedures development, and crew familiarity/training for human spaceflight is fundamental to JSC's charter, there is also a strong desire to share and reuse models in both the non-realtime and real-time domains, with the goal of retaining as much multibody dynamics fidelity as possible. Three specific enhancements are reviewed here: (1) linked list organization to address large transitional topologies, (2) body level model order reduction, and (3) parallel formulation/implementation. This paper provides a detailed overview of these primary updates to JSC's flexible multibody dynamics algorithms as well as a comparison of numerical results to previous formulations and associated software.
Pål Johan From
2012-01-01
This paper presents the explicit dynamic equations of multibody mechanical systems. This is the second paper on this topic. In the first paper the dynamics of a single rigid body from the Boltzmann--Hamel equations were derived. In this paper these results are extended to also include multibody systems. We show that when quasi-velocities are used, the part of the dynamic equations that appear from the partial derivatives of the system kinematics are identical to the single rigid body case, bu...
Earthquake dynamic response of large flexible multibody systems
E. V. Zahariev
2013-02-01
Full Text Available In the paper dynamics of large flexible structures imposed on earthquakes and high amplitude vibrations is regarded. Precise dynamic equations of flexible systems are the basis for reliable motion simulation and analysis of loading of the design scheme elements. Generalized Newton–Euler dynamic equations for rigid and flexible bodies are applied. The basement compulsory motion realized because of earthquake or wave propagation is presented in the dynamic equations as reonomic constraints. The dynamic equations, algebraic equations and reonomic constraints compile a system of differential algebraic equations which are transformed to a system of ordinary differential equations with respect to the generalized coordinates and the reactions due to the reonomic constraints. Examples of large flexible structures and wind power generator dynamic analysis are presented.
Multibody Dynamic Stress Simulation of Rigid-Flexible Shovel Crawler Shoes
Samuel Frimpong
2016-06-01
Full Text Available Electric shovels are used in surface mining operations to achieve economic production capacities. The capital investments and operating costs associated with the shovels deployed in the Athabasca oil sands formation are high due to the abrasive conditions. The shovel crawler shoes interact with sharp and abrasive sand particles, and, thus, are subjected to high transient dynamic stresses. These high stresses cause wear and tear leading to crack initiation, propagation and premature fatigue failure. The objective of this paper is to develop a model to characterize the crawler stresses and deformation for the P&H 4100C BOSS during propel and loading using rigid-flexible multi-body dynamic theory. A 3-D virtual prototype model of the rigid-flexible crawler track assembly and its interactions with oil sand formation is simulated to capture the model dynamics within multibody dynamics software MSC ADAMS. The modal and stress shapes and modal loads due to machine weight for each flexible crawler shoes are generated from finite element analysis (FEA. The modal coordinates from the simulation are combined with mode and stress shapes using modal superposition method to calculate real-time stresses and deformation of flexible crawler shoes. The results show a maximum von Mises stress value of 170 MPa occurring in the driving crawler shoe during the propel motion. This study provides a foundation for the subsequent fatigue life analysis of crawler shoes for extending crawler service life.
Modeling the Multi-Body System Dynamics of a Flexible Solar Sail Spacecraft
Kim, Young; Stough, Robert; Whorton, Mark
2005-01-01
Solar sail propulsion systems enable a wide range of space missions that are not feasible with current propulsion technology. Hardware concepts and analytical methods have matured through ground development to the point that a flight validation mission is now realizable. Much attention has been given to modeling the structural dynamics of the constituent elements, but to date an integrated system level dynamics analysis has been lacking. Using a multi-body dynamics and control analysis tool called TREETOPS, the coupled dynamics of the sailcraft bus, sail membranes, flexible booms, and control system sensors and actuators of a representative solar sail spacecraft are investigated to assess system level dynamics and control issues. With this tool, scaling issues and parametric trade studies can be performed to study achievable performance, control authority requirements, and control/structure interaction assessments.
Johansen, Per; Rømer, Daniel; Andersen, Torben Ole; Pedersen, Henrik C.
2014-01-01
multibody dynamics model of a radial piston fluid power motor, which connects the rigid bodies through models of the transient hydrodynamic lubrication pressure in the joint clearance. A finite volume approach is used to model the pressure dynamics of the fluid film lubrication. The model structure and...
Wagner, Falko Jens
1999-01-01
Multibody Systems is one area, in which methods for solving DAEs are of special interst. This chapter is about multibody systems, why they result in DAE systems and what kind of problems that can arise when dealing with multibody systems and formulating their corresponding DAE system....
Dynamics and control of multibody systems: An approach with application
Grewal, A.; Modi, V. J.
1996-09-01
The paper focuses on the study of the dynamics and control of large flexible space structures, comprised of sub-assemblies, a subject of considerable contemporary interest. To begin with, a relatively general Lagrangian formulation of the problem is developed. The governing equations are non-linear, non-autonomous, coupled and extremely lengthy even in matrix notation. Next, an efficient computer code is developed and the versatility of the program illustrated through a study of the dynamics of the First Element Launch (FEL) configuration of the Space Station Freedom, now superseded by the International Space Station Alpha. The response of the FEL is obtained for two critical disturbances: (a) docking of the Space Shuttle; and (b) maneuver of the onboard mobile manipulator system (MSS). The study clearly demonstrates a need for active control. To that end, robust control of the rigid body motion of the FEL configuration using the LQG/LTR procedure is demonstrated. The controller designed using the simplified linear model, proves to be effective in regulating librational disturbances. Such a global approach—formulation, numerical code, dynamics and control—can serve as a powerful tool to gain comprehensive understanding of the interactions of the dynamics and thus aid in the development of effective and efficient control systems.
A multibody approach for 6-DOF flight dynamics and stability analysis of the hawkmoth Manduca sexta
This paper investigates the six degrees of freedom (6-DOF) flight dynamics and stability of the hawkmoth Manduca sexta using a multibody dynamics approach that encompasses the effects of the time varying inertia tensor of all the body segments including two wings. The quasi-steady translational and unsteady rotational aerodynamics of the flapping wings are modeled with the blade element theory with aerodynamic coefficients derived from relevant experimental studies. The aerodynamics is given instantaneously at each integration time step without wingbeat-cycle-averaging. With the multibody dynamic model and the aerodynamic model for the hawkmoth, a direct time integration of the fully coupled 6-DOF nonlinear multibody dynamics equations of motion is performed. First, the passive damping magnitude of each single DOF is quantitatively examined with the measure of the time taken to half the initial velocity (thalf). The results show that the sideslip translation is less damped approximately three times than the other two translational DOFs, and the pitch rotation is less damped approximately five times than the other two rotational DOFs; each DOF has the value of (unit in wingbeat strokes): thalf,forward/backward = 7.10, thalf,sideslip = 17.95, thalf,ascending = 7.13, thalf,descending = 5.77, thalf,roll = 0.68, thalf,pitch = 2.39, and thalf,yaw = 0.25. Second, the natural modes of motion, with the hovering flight as a reference equilibrium condition, are examined by analyzing fully coupled 6-DOF dynamic responses induced by multiple sets of force and moment disturbance combinations. The given disturbance combinations are set to excite the dynamic modes identified in relevant eigenmode analysis studies. The 6-DOF dynamic responses obtained from this study are compared with eigenmode analysis results in the relevant studies. The longitudinal modes of motion showed dynamic modal characteristics similar to the eigenmode analysis results from the relevant literature
A multibody approach for 6-DOF flight dynamics and stability analysis of the hawkmoth Manduca sexta.
Kim, Joong-Kwan; Han, Jae-Hung
2014-03-01
This paper investigates the six degrees of freedom (6-DOF) flight dynamics and stability of the hawkmoth Manduca sexta using a multibody dynamics approach that encompasses the effects of the time varying inertia tensor of all the body segments including two wings. The quasi-steady translational and unsteady rotational aerodynamics of the flapping wings are modeled with the blade element theory with aerodynamic coefficients derived from relevant experimental studies. The aerodynamics is given instantaneously at each integration time step without wingbeat-cycle-averaging. With the multibody dynamic model and the aerodynamic model for the hawkmoth, a direct time integration of the fully coupled 6-DOF nonlinear multibody dynamics equations of motion is performed. First, the passive damping magnitude of each single DOF is quantitatively examined with the measure of the time taken to half the initial velocity (thalf). The results show that the sideslip translation is less damped approximately three times than the other two translational DOFs, and the pitch rotation is less damped approximately five times than the other two rotational DOFs; each DOF has the value of (unit in wingbeat strokes): thalf,forward/backward = 7.10, thalf,sideslip = 17.95, thalf,ascending = 7.13, thalf,descending = 5.77, thalf,roll = 0.68, thalf,pitch = 2.39, and thalf,yaw = 0.25. Second, the natural modes of motion, with the hovering flight as a reference equilibrium condition, are examined by analyzing fully coupled 6-DOF dynamic responses induced by multiple sets of force and moment disturbance combinations. The given disturbance combinations are set to excite the dynamic modes identified in relevant eigenmode analysis studies. The 6-DOF dynamic responses obtained from this study are compared with eigenmode analysis results in the relevant studies. The longitudinal modes of motion showed dynamic modal characteristics similar to the eigenmode analysis results from the relevant literature
Multibody dynamics simulation of geometrically exact Cosserat rods
Lang, H.; Linn, J; Arnold, M.
2009-01-01
In this paper, we present a viscoelastic rod model that is suitable for fast and accurate dynamic simulations. It is based on Cosserat’s geometrically exact theory of rods and is able to represent extension, shearing (‘stiff’ dof), bending and torsion (‘soft’ dof). For inner dissipation, a consistent damping potential proposed by Antman is chosen. We parametrise the rotational dof by unit quaternions and directly use the quaternionic evolution differential equation for the discretisation of t...
Modeling and Simulation of Arresting Gear System with Multibody Dynamic Approach
Wenhou Shen
2013-01-01
Full Text Available The arresting dynamics of the aircraft on the aircraft carrier involves both a transient wave propagation process in rope and a smooth decelerating of aircraft. This brings great challenge on simulating the whole process since the former one needs small time-step to guarantee the stability, while the later needs large time-step to reduce calculation time. To solve this problem, this paper proposes a full-scale multibody dynamics model of arresting gear system making use of variable time-step integration scheme. Especially, a kind of new cable element that is capable of describing the arbitrary large displacement and rotation in three-dimensional space is adopted to mesh the wire cables, and damping force is used to model the effect of hydraulic system. Then, the stress of the wire ropes during the landing process is studied. Results show that propagation, reflection, and superposition of the stress wave between the deck sheaves contribute mainly to the peak value of stress. And the maximum stress in the case of landing deviate from the centerline is a little bit smaller than the case of landing along centerline. The multibody approach and arresting gear system model proposed here also provide an efficient way to design and optimize the whole mechanism.
Multi-body dynamic system simulation of carrier-based aircraft ski-jump takeoff
Wang Yangang; Wang Weijun; Qu Xiangju
2013-01-01
The flight safety is threatened by the special flight conditions and the low speed of carrier-based aircraft ski-jump takeoff.The aircraft carrier motion,aircraft dynamics,landing gears and wind field of sea state are comprehensively considered to dispose this multidiscipline intersection problem.According to the particular naval operating environment of the carrier-based aircraft ski-jump takeoff,the integrated dynamic simulation models of multi-body system are developed,which involves the movement entities of the carrier,the aircraft and the landing gears,and involves takeoff instruction,control system and the deck wind disturbance.Based on Matlab/Simulink environment,the multi-body system simulation is realized.The validity of the model and the rationality of the result are verified by an example simulation of carrier-based aircraft ski-jump takeoff.The simulation model and the software are suitable for the study of the multidiscipline intersection problems which are involved in the performance,flight quality and safety of carrier-based aircraft takeoff,the effects of landing gear loads,parameters of carrier deck,etc.
Numerical Simulation of the Spreading Dynamic Responses of the Multibody System with a Floating Base
Zhaobing Jiang; Luzhong Shao; Fei Shao
2015-01-01
To simulate the dynamic responses of the multibody system with a floating base when the upper parts spread with a certain sequence and relative speed, the homogeneous matrix method is employed to model and simulate a four-body system with a floating base and the motions are analyzed when the upper parts are spread sequentially or synchronously. The rolling, swaying and heaving temporal variations are obtained when the multibody system is under the conditions of the static water along with the wave loads and the mean wind loads or the single pulse wind loads, respectively. The moment variations of each joint under the single pulse wind load are also gained. The numerical results showed that the swaying of the floating base is almost not influenced by the spreading time or form when the upper parts spread sequentially or synchronously, while the rolling and the heaving mainly depend on the spreading time and forms. The swaying and heaving motions are influenced significantly by the mean wind loads. The single pulse wind load also has influences on the dynamic responses. The torque of joint 3 and joint 4 in the single pulse wind environment may be twice that in the windless environment when the system spreads with 60 s duration.
A Non-smooth Newton Method for Multibody Dynamics
In this paper we deal with the simulation of rigid bodies. Rigid body dynamics have become very important for simulating rigid body motion in interactive applications, such as computer games or virtual reality. We present a novel way of computing contact forces using a Newton method. The contact problem is reformulated as a system of non-linear and non-smooth equations, and we solve this system using a non-smooth version of Newton's method. One of the main contribution of this paper is the reformulation of the complementarity problems, used to model impacts, as a system of equations that can be solved using traditional methods.
Stress stiffening and approximate equations in flexible multibody dynamics
Padilla, Carlos E.; Vonflotow, Andreas H.
1993-01-01
A useful model for open chains of flexible bodies undergoing large rigid body motions, but small elastic deformations, is one in which the equations of motion are linearized in the small elastic deformations and deformation rates. For slow rigid body motions, the correctly linearized, or consistent, set of equations can be compared to prematurely linearized, or inconsistent, equations and to 'oversimplified,' or ruthless, equations through the use of open loop dynamic simulations. It has been shown that the inconsistent model should never be used, while the ruthless model should be used whenever possible. The consistent and inconsistent models differ by stress stiffening terms. These are due to zeroth-order stresses effecting virtual work via nonlinear strain-displacement terms. In this paper we examine in detail the nature of these stress stiffening terms and conclude that they are significant only when the associated zeroth-order stresses approach 'buckling' stresses. Finally it is emphasized that when the stress stiffening terms are negligible the ruthlessly linearized equations should be used.
Model Reduction in Co-Rotated Multi-Body Dynamics Based on the Dual Craig-Bampton Method
Weerathunge Kadawathagedara, S.T.; Rixen, D.J.
2011-01-01
A new reduction method for dynamical analsis of multi-body systems is presented in this paper. It fundamentally differs from the ones previously published in the way kinematical constraints are handled. Our approach is based on component mode synthesis, but the specificity of articulated mechanism,
Spanos, John T.; Tsuha, Walter S.
1989-01-01
The assumed-modes method in multibody dynamics allows the elastic deformation of each component in the system to be approximated by a sum of products of spatial and temporal functions commonly known as modes and modal coordinates respectively. The choice of component modes used to model articulating and non-articulating flexible multibody systems is examined. Attention is directed toward three classical Component Mode Synthesis (CMS) methods whereby component normal modes are generated by treating the component interface (I/F) as either fixed, free, or loaded with mass and stiffness contributions from the remaining components. The fixed and free I/F normal modes are augmented by static shape functions termed constraint and residual modes respectively. A mode selection procedure is outlined whereby component modes are selected from the Craig-Bampton (fixed I/F plus constraint), MacNeal-Rubin (free I/F plus residual), or Benfield-Hruda (loaded I/F) mode sets in accordance with a modal ordering scheme derived from balance realization theory. The success of the approach is judged by comparing the actuator-to-sensor frequency response of the reduced order system with that of the full order system over the frequency range of interest. A finite element model of the Galileo spacecraft serves as an example in demonstrating the effectiveness of the proposed mode selection method.
Parametric modeling of NREL 5MW wind turbine was set up for multi-body dynamics simulation by the TurbSim, AeroDyn, FAST (fatigue, aerodynamics, structures, and turbulence) software respectively. According to the analysis of the characteristics of wind in the space discrete point, using TurbSim to establish the steady-state wind and random changes with time and space wind. Based on the AeroDyn software, which can coupled to FAST, we calculated the aerodynamic load. Loading the aerodynamic data which has been calculated, FAST can establish a fully parameterized simulation model. Making a comparison of the results obtained by FAST in 3 different wind conditions, the different of dynamic responses of the structure were obtained. The results obtained by FAST have some meaning in the study of wind turbine under extreme turbulence wind conditions
Structural analysis of floating offshore wind turbine tower based on flexible multibody dynamics
Park, Kwang Phil; Jo, A Ra [Daewoo Shipbuilding and Marine Engineering, Co., Ltd., Seoul (Korea, Republic of); Cha, Ju Hwan [Mokpo Nat' l Univ., Muan (Korea, Republic of)
2012-12-15
In this study, we perform the structural analysis of a floating offshore wind turbine tower by considering the dynamic response of the floating platform. A multibody system consisting of three blades, a hub, a nacelle, the platform, and the tower is used to model the floating wind turbine. The blades and the tower are modeled as flexible bodies using three dimensional beam elements. The aerodynamic force on the blades is calculated by the Blade Element Momentum (BEM) theory with hub rotation. The hydrostatic, hydrodynamic, and mooring forces are considered for the platform. The structural dynamic responses of the tower are simulated by numerically solving the equations of motion. From the simulation results, the time history of the internal forces at the nodes, such as the bending moment and stress, are obtained. In conclusion, the internal forces are compared with those obtained from static analysis to assess the effects of wave loads on the structural stability of the tower.
Wu, P.; Li, C.; Ye, Z.
2013-12-01
Parametric modeling of NREL 5MW wind turbine was set up for multi-body dynamics simulation by the TurbSim, AeroDyn, FAST (fatigue, aerodynamics, structures, and turbulence) software respectively. According to the analysis of the characteristics of wind in the space discrete point, using TurbSim to establish the steady-state wind and random changes with time and space wind. Based on the AeroDyn software, which can coupled to FAST, we calculated the aerodynamic load. Loading the aerodynamic data which has been calculated, FAST can establish a fully parameterized simulation model. Making a comparison of the results obtained by FAST in 3 different wind conditions, the different of dynamic responses of the structure were obtained. The results obtained by FAST have some meaning in the study of wind turbine under extreme turbulence wind conditions.
Structural analysis of floating offshore wind turbine tower based on flexible multibody dynamics
In this study, we perform the structural analysis of a floating offshore wind turbine tower by considering the dynamic response of the floating platform. A multibody system consisting of three blades, a hub, a nacelle, the platform, and the tower is used to model the floating wind turbine. The blades and the tower are modeled as flexible bodies using three dimensional beam elements. The aerodynamic force on the blades is calculated by the Blade Element Momentum (BEM) theory with hub rotation. The hydrostatic, hydrodynamic, and mooring forces are considered for the platform. The structural dynamic responses of the tower are simulated by numerically solving the equations of motion. From the simulation results, the time history of the internal forces at the nodes, such as the bending moment and stress, are obtained. In conclusion, the internal forces are compared with those obtained from static analysis to assess the effects of wave loads on the structural stability of the tower
A fast algorithm for parallel computation of multibody dynamics on MIMD parallel architectures
Fijany, Amir; Kwan, Gregory; Bagherzadeh, Nader
1993-01-01
In this paper the implementation of a parallel O(LogN) algorithm for computation of rigid multibody dynamics on a Hypercube MIMD parallel architecture is presented. To our knowledge, this is the first algorithm that achieves the time lower bound of O(LogN) by using an optimal number of O(N) processors. However, in addition to its theoretical significance, the algorithm is also highly efficient for practical implementation on commercially available MIMD parallel architectures due to its highly coarse grain size and simple communication and synchronization requirements. We present a multilevel parallel computation strategy for implementation of the algorithm on a Hypercube. This strategy allows the exploitation of parallelism at several computational levels as well as maximum overlapping of computation and communication to increase the performance of parallel computation.
Menon, R. G.; Kurdila, A. J.
1992-01-01
This paper presents a concurrent methodology to simulate the dynamics of flexible multibody systems with a large number of degrees of freedom. A general class of open-loop structures is treated and a redundant coordinate formulation is adopted. A range space method is used in which the constraint forces are calculated using a preconditioned conjugate gradient method. By using a preconditioner motivated by the regular ordering of the directed graph of the structures, it is shown that the method is order N in the total number of coordinates of the system. The overall formulation has the advantage that it permits fine parallelization and does not rely on system topology to induce concurrency. It can be efficiently implemented on the present generation of parallel computers with a large number of processors. Validation of the method is presented via numerical simulations of space structures incorporating large number of flexible degrees of freedom.
Dynamic modeling and simulation of multi-body systems using the Udwadia-Kalaba theory
Zhao, Han; Zhen, Shengchao; Chen, Ye-Hwa
2013-09-01
Laboratory experiments were conducted for falling U-chain, but explicit analytic form of the general equations of motion was not presented. Several modeling methods were developed for fish robots, however they just focused on the whole fish’s locomotion which does little favor to understand the detailed swimming behavior of fish. Udwadia-Kalaba theory is used to model these two multi-body systems and obtain explicit analytic equations of motion. For falling U-chain, the mass matrix is non-singular. Second-order constraints are used to get the constraint force and equations of motion and the numerical simulation is conducted. Simulation results show that the chain tip falls faster than the freely falling body. For fish robot, two-joint Carangiform fish robot is focused on. Quasi-steady wing theory is used to approximately calculate fluid lift force acting on the caudal fin. Based on the obtained explicit analytic equations of motion (the mass matrix is singular), propulsive characteristics of each part of the fish robot are obtained. Through these two cases of U chain and fish robot, how to use Udwadia-Kalaba equation to obtain the dynamical model is shown and the modeling methodology for multi-body systems is presented. It is also shown that Udwadia-Kalaba theory is applicable to systems whether or not their mass matrices are singular. In the whole process of applying Udwadia-Kalaba equation, Lagrangian multipliers and quasi-coordinates are not used. Udwadia-Kalaba theory is creatively applied to dynamical modeling of falling U-chain and fish robot problems and explicit analytic equations of motion are obtained.
Leyendecker, Sigrid [University of Kaiserslautern, Chair of Applied Mechanics, Department of Mechanical Engineering (Germany)], E-mail: slauer@rhrk.uni-kl.de; Betsch, Peter [University of Siegen, Chair of Computational Mechanics, Department of Mechanical Engineering (Germany); Steinmann, Paul [University of Kaiserslautern, Chair of Applied Mechanics, Department of Mechanical Engineering (Germany)
2008-02-15
In the present work, the unified framework for the computational treatment of rigid bodies and nonlinear beams developed by Betsch and Steinmann (Multibody Syst. Dyn. 8, 367-391, 2002) is extended to the realm of nonlinear shells. In particular, a specific constrained formulation of shells is proposed which leads to the semi-discrete equations of motion characterized by a set of differential-algebraic equations (DAEs). The DAEs provide a uniform description for rigid bodies, semi-discrete beams and shells and, consequently, flexible multibody systems. The constraints may be divided into two classes: (i) internal constraints which are intimately connected with the assumption of rigidity of the bodies, and (ii) external constraints related to the presence of joints in a multibody framework. The present approach thus circumvents the use of rotational variables throughout the whole time discretization, facilitating the design of energy-momentum methods for flexible multibody dynamics. After the discretization has been completed a size-reduction of the discrete system is performed by eliminating the constraint forces. Numerical examples dealing with a spatial slider-crank mechanism and with intersecting shells illustrate the performance of the proposed method.
In the present work, the unified framework for the computational treatment of rigid bodies and nonlinear beams developed by Betsch and Steinmann (Multibody Syst. Dyn. 8, 367-391, 2002) is extended to the realm of nonlinear shells. In particular, a specific constrained formulation of shells is proposed which leads to the semi-discrete equations of motion characterized by a set of differential-algebraic equations (DAEs). The DAEs provide a uniform description for rigid bodies, semi-discrete beams and shells and, consequently, flexible multibody systems. The constraints may be divided into two classes: (i) internal constraints which are intimately connected with the assumption of rigidity of the bodies, and (ii) external constraints related to the presence of joints in a multibody framework. The present approach thus circumvents the use of rotational variables throughout the whole time discretization, facilitating the design of energy-momentum methods for flexible multibody dynamics. After the discretization has been completed a size-reduction of the discrete system is performed by eliminating the constraint forces. Numerical examples dealing with a spatial slider-crank mechanism and with intersecting shells illustrate the performance of the proposed method
Multibody dynamics driving GNC and system design in tethered nets for active debris removal
Benvenuto, Riccardo; Lavagna, Michèle; Salvi, Samuele
2016-07-01
Debris removal in Earth orbits is an urgent issue to be faced for space exploitation durability. Among different techniques, tethered-nets present appealing benefits and some open points to fix. Former and latter are discussed in the paper, supported by the exploitation of a multibody dynamics tool. With respect to other proposed capture mechanisms, tethered-net solutions are characterised by a safer capturing distance, a passive angular momentum damping effect and the highest flexibility to unknown shape, material and attitude of the target to interface with. They also allow not considering the centre of gravity alignment with thrust axis as a constraint, as it is for any rigid link solution. Furthermore, the introduction of a closing thread around the net perimeter ensures safer and more reliable grasping and holding. In the paper, a six degrees of freedom multibody dynamics simulator is presented: it was developed at Politecnico di Milano - Department of Aerospace Science and Technologies - and it is able to describe the orbital and attitude dynamics of tethered-nets systems and end-bodies during different phases, with great flexibility in dealing with different topologies and configurations. Critical phases as impact and wrapping are analysed by simulation to address the tethered-stack controllability. It is shown how the role of contact modelling is fundamental to describe the coupled dynamics: it is demonstrated, as a major novel contribution, how friction between the net and a tumbling target allows reducing its angular motion, stabilizing the system and allowing safer towing operations. Moreover, the so-called tethered space tug is analysed: after capture, the two objects, one passive and one active, are connected by the tethered-net flexible link, the motion of the system being excited by the active spacecraft thrusters. The critical modes prevention during this phase, by means of a closed-loop control synthesis is shown. Finally, the connection between
Monteiro, Nuno Miguel Barroso, E-mail: nuno.barroso.monteiro@gmail.com; Silva, Miguel Pedro Tavares da, E-mail: MiguelSilva@ist.utl.pt; Folgado, Joao Orlando Marques Gameiro, E-mail: jfolgado@dem.ist.utl.pt [Technical University of Lisbon, IDMEC/IST-Instituto Superior Tecnico (Portugal); Melancia, Joao Pedro Levy, E-mail: levymelancia@netcabo.pt [University of Lisbon, FML-Faculdade de Medicina de Lisboa (Portugal)
2011-02-15
This work describes a methodology for the dynamic and structural analysis of complex (bio)mechanical systems that joins both multibody dynamics and finite element domains, in a synergetic way, through a cosimulation procedure that takes benefit of the advantages of each numerical formulation. To accomplish this goal, a cosimulation module is developed based on the gluing algorithm X-X, which is the key element responsible for the management of the information flux between the two software packages (each using its own mathematical formulation and code). The X-X algorithm uses for each cosimulated structure multiple pairs of reference points whose kinematics are solved by the multibody module and prescribed, as initial data, to the finite element counterpart. The finite element module, by its turn, solves the structural problem imposed by the prescribed kinematics, calculates the resulting generalized loads applied over the reference points and return these loads back to the multibody module that uses them to solve the dynamic problem and to calculate new reference kinematics to prescribe to the finite element module in the next time step. The proposed method is applied to study the cervical spine dynamics in a pathologic situation in which an intersomatic fusion is simulated to confirm its potential advantages. Taking into account the proposed simulation scenario, a cervical spine multibody model that includes the rigid vertebrae, the facet joints' and spinous processes' contacts, ligaments and the finite element models of the intervertebral discs, and their surrogates is developed. The proposed model is simulated for extension in a forward dynamics perspective.
This work describes a methodology for the dynamic and structural analysis of complex (bio)mechanical systems that joins both multibody dynamics and finite element domains, in a synergetic way, through a cosimulation procedure that takes benefit of the advantages of each numerical formulation. To accomplish this goal, a cosimulation module is developed based on the gluing algorithm X-X, which is the key element responsible for the management of the information flux between the two software packages (each using its own mathematical formulation and code). The X-X algorithm uses for each cosimulated structure multiple pairs of reference points whose kinematics are solved by the multibody module and prescribed, as initial data, to the finite element counterpart. The finite element module, by its turn, solves the structural problem imposed by the prescribed kinematics, calculates the resulting generalized loads applied over the reference points and return these loads back to the multibody module that uses them to solve the dynamic problem and to calculate new reference kinematics to prescribe to the finite element module in the next time step. The proposed method is applied to study the cervical spine dynamics in a pathologic situation in which an intersomatic fusion is simulated to confirm its potential advantages. Taking into account the proposed simulation scenario, a cervical spine multibody model that includes the rigid vertebrae, the facet joints’ and spinous processes’ contacts, ligaments and the finite element models of the intervertebral discs, and their surrogates is developed. The proposed model is simulated for extension in a forward dynamics perspective.
Kurtaj, Lavdim; Limani, Ilir; Shatri, Vjosa; Skeja, Avni
2014-01-01
Cerebellum is part of the brain that occupies only 10% of the brain volume, but it contains about 80% of total number of brain neurons. New cerebellar function model is developed that sets cerebellar circuits in context of multibody dynamics model computations, as important step in controlling balance and movement coordination, functions performed by two oldest parts of the cerebellum. Model gives new functional interpretation for granule cells-Golgi cell circuit, including distinct function ...
Model Reduction in Co-Rotated Multi-Body Dynamics Based on the Dual Craig-Bampton Method
Weerathunge Kadawathagedara, S.T.; Rixen, D.J.
2011-01-01
A new reduction method for dynamical analsis of multi-body systems is presented in this paper. It fundamentally differs from the ones previously published in the way kinematical constraints are handled. Our approach is based on component mode synthesis, but the specificity of articulated mechanism, in which components are assembled through connecting forces, is taken into account from the reduction level. This is achieved by using a set of modes that are consistent with this type of assembly,...
Hardy stress definition has been restricted to pair potentials and embedded-atom method potentials due to the basic assumptions in the derivation of a symmetric microscopic stress tensor. Force decomposition required in the Hardy stress expression becomes obscure for multi-body potentials. In this work, we demonstrate the invariance of the Hardy stress expression for a polymer system modeled with multi-body interatomic potentials including up to four atoms interaction, by applying central force decomposition of the atomic force. The balance of momentum has been demonstrated to be valid theoretically and tested under various numerical simulation conditions. The validity of momentum conservation justifies the extension of Hardy stress expression to multi-body potential systems. Computed Hardy stress has been observed to converge to the virial stress of the system with increasing spatial averaging volume. This work provides a feasible and reliable linkage between the atomistic and continuum scales for multi-body potential systems
Glaese, John R.; McDonald, Emmett J.
2000-01-01
Orbiting space solar power systems are currently being investigated for possible flight in the time frame of 2015-2020 and later. Such space solar power (SSP) satellites are required to be extremely large in order to make practical the process of collection, conversion to microwave radiation, and reconversion to electrical power at earth stations or at remote locations in space. These large structures are expected to be very flexible presenting unique problems associated with their dynamics and control. The purpose of this project is to apply the expanded TREETOPS multi-body dynamics analysis computer simulation program (with expanded capabilities developed in the previous activity) to investigate the control problems associated with the integrated symmetrical concentrator (ISC) conceptual SSP system. SSP satellites are, as noted, large orbital systems having many bodies (perhaps hundreds) with flexible arrays operating in an orbiting environment where the non-uniform gravitational forces may be the major load producers on the structure so that a high fidelity gravity model is required. The current activity arises from our NRA8-23 SERT proposal. Funding, as a supplemental selection, has been provided by NASA with reduced scope from that originally proposed.
Otsuka, Keisuke; Makihara, Kanjuro
2016-05-01
Morphing wings have been developed by several organizations for a variety of applications including the changing of flight ability while in the air and reducing the amount of space required to store an aircraft. One such example of morphing wings is the deployable wing that is expected to be used for Mars exploration. When designing wings, aeroelastic simulation is important to prevent the occurrence of destructive phenomena while the wing is in use. Flutter and divergence are typical issues to be addressed. However, it has been difficult to simulate the aeroelastic motion of deployable wings because of the significant differences between these deployable wings and conventional designs. The most apparent difference is the kinematic constraints of deployment, typically a hinge joint. These constraints lead not only to deformation but also to rigid body rotation. This research provides a novel method of overcoming the difficulties associated with handling these kinematic constraints. The proposed method utilizes flexible multibody dynamics and absolute nodal coordinate formulation to describe the dynamic motion of a deployable wing. This paper presents the simulation of the rigid body rotation around the kinematic constraints as induced by the aeroelasticity. The practicality of the proposed method is confirmed.
Pål Johan From
2012-04-01
Full Text Available This paper presents the explicit dynamic equations of multibody mechanical systems. This is the second paper on this topic. In the first paper the dynamics of a single rigid body from the Boltzmann--Hamel equations were derived. In this paper these results are extended to also include multibody systems. We show that when quasi-velocities are used, the part of the dynamic equations that appear from the partial derivatives of the system kinematics are identical to the single rigid body case, but in addition we get terms that come from the partial derivatives of the inertia matrix, which are not present in the single rigid body case. We present for the first time the complete and correct derivation of multibody systems based on the Boltzmann--Hamel formulation of the dynamics in Lagrangian form where local position and velocity variables are used in the derivation to obtain the singularity-free dynamic equations. The final equations are written in global variables for both position and velocity. The main motivation of these papers is to allow practitioners not familiar with differential geometry to implement the dynamic equations of rigid bodies without the presence of singularities. Presenting the explicit dynamic equations also allows for more insight into the dynamic structure of the system. Another motivation is to correct some errors commonly found in the literature. Unfortunately, the formulation of the Boltzmann-Hamel equations used here are presented incorrectly. This has been corrected by the authors, but we present here, for the first time, the detailed mathematical details on how to arrive at the correct equations. We also show through examples that using the equations presented here, the dynamics of a single rigid body is reduced to the standard equations on a Lagrangian form, for example Euler's equations for rotational motion and Euler--Lagrange equations for free motion.
A component mode synthesis algorithm for multibody dynamics of wind turbines
Holm-Jørgensen, K.; Nielsen, S. R. K.
2009-10-01
A system reduction scheme related to a multibody formulation of wind turbine dynamics is devised. Each substructure is described in its own frame of reference, which is moving freely in the vicinity of the moving substructure, in principle without any constraints to the rigid body part of the motion of the substructure. The system reduction is based on a component mode synthesis method, where the response of the internal degrees of freedom of the substructure is described as the quasi-static response induced by the boundary degrees of freedom via the constraint modes superimposed in combination to a dynamic component induced by inertial effects and internal loads. The latter component is modelled by a truncated modal expansion in fixed interface undamped eigenmodes. The selected modal vector base for the internal dynamics ensures that the boundary degrees of freedom account for the rigid-body dynamics of the substructure, and explicitly represent the coupling degrees of freedom at the interface to the adjacent substructures. The method has been demonstrated for a blade structure, which has been modelled as two substructures. Two modelling methods have been examined where the first is by use of fixed-fixed eigenmodes for the innermost substructure and fixed-free eigenmodes for the outermost substructure. The other approach is by use of fixed-free eigenmodes for both substructures. The fixed-fixed method shows good correspondence with the full FE model which is not the case for the fixed-free method due to incompatible displacements and rotations at the interface between the two substructures. Moreover, the results from the reduced model by use of constant constraint modes and constant fixed interface modes over a large operating area for the wind turbine blade are almost identical to the full FE model.
A joint-space numerical model of metabolic energy expenditure for human multibody dynamic system.
Kim, Joo H; Roberts, Dustyn
2015-09-01
Metabolic energy expenditure (MEE) is a critical performance measure of human motion. In this study, a general joint-space numerical model of MEE is derived by integrating the laws of thermodynamics and principles of multibody system dynamics, which can evaluate MEE without the limitations inherent in experimental measurements (phase delays, steady state and task restrictions, and limited range of motion) or muscle-space models (complexities and indeterminacies from excessive DOFs, contacts and wrapping interactions, and reliance on in vitro parameters). Muscle energetic components are mapped to the joint space, in which the MEE model is formulated. A constrained multi-objective optimization algorithm is established to estimate the model parameters from experimental walking data also used for initial validation. The joint-space parameters estimated directly from active subjects provide reliable MEE estimates with a mean absolute error of 3.6 ± 3.6% relative to validation values, which can be used to evaluate MEE for complex non-periodic tasks that may not be experimentally verifiable. This model also enables real-time calculations of instantaneous MEE rate as a function of time for transient evaluations. Although experimental measurements may not be completely replaced by model evaluations, predicted quantities can be used as strong complements to increase reliability of the results and yield unique insights for various applications. PMID:25914404
Rigid multibody simulation of a helix-like structure: the dynamics of bacterial adhesion pili.
Zakrisson, Johan; Wiklund, Krister; Servin, Martin; Axner, Ove; Lacoursière, Claude; Andersson, Magnus
2015-07-01
We present a coarse-grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymer's force-extension response. With building blocks representing individual subunits, the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include the effects of both unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and results in this work give enhanced understanding of how a pilus unwinds under the action of external forces and provide a new perspective of the complex bacterial adhesion processes. PMID:25851543
Computationally efficient multibody simulations
Ramakrishnan, Jayant; Kumar, Manoj
1994-01-01
Computationally efficient approaches to the solution of the dynamics of multibody systems are presented in this work. The computational efficiency is derived from both the algorithmic and implementational standpoint. Order(n) approaches provide a new formulation of the equations of motion eliminating the assembly and numerical inversion of a system mass matrix as required by conventional algorithms. Computational efficiency is also gained in the implementation phase by the symbolic processing and parallel implementation of these equations. Comparison of this algorithm with existing multibody simulation programs illustrates the increased computational efficiency.
The presence of different time scales in a dynamic model significantly hampers the efficiency of its simulation. In multibody systems the fact is particularly relevant, as the mentioned time scales may be very different, due, for example, to the coexistence of mechanical components controled by electronic drive units, and may also appear in conjunction with significant nonlinearities. This paper proposes a systematic technique, based on the principles of dynamic decoupling, to partition a model based on the time scales that are relevant for the particular simulation studies to be performed and as transparently as possible for the user. In accordance with said purpose, peculiar to the technique is its neat separation into two parts: a structural analysis of the model, which is general with respect to any possible simulation scenario, and a subsequent decoupled integration, which can conversely be (easily) tailored to the study at hand. Also, since the technique does not aim at reducing but rather at partitioning the model, the state space and the physical interpretation of the dynamic variables are inherently preserved. Moreover, the proposed analysis allows us to define some novel indices relative to the separability of the system, thereby extending the idea of “stiffness” in a way that is particularly keen to its use for the improvement of simulation efficiency, be the envisaged integration scheme monolithic, parallel, or even based on cosimulation. Finally, thanks to the way the analysis phase is conceived, the technique is naturally applicable to both linear and nonlinear models. The paper contains a methodological presentation of the proposed technique, which is related to alternatives available in the literature so as to evidence the peculiarities just sketched, and some application examples illustrating the achieved advantages and motivating the major design choice from an operational viewpoint
Papadopoulos, Alessandro Vittorio, E-mail: alessandro.papadopoulos@control.lth.se [Lund University, Department of Automatic Control (Sweden); Leva, Alberto, E-mail: alberto.leva@polimi.it [Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria (Italy)
2015-06-15
The presence of different time scales in a dynamic model significantly hampers the efficiency of its simulation. In multibody systems the fact is particularly relevant, as the mentioned time scales may be very different, due, for example, to the coexistence of mechanical components controled by electronic drive units, and may also appear in conjunction with significant nonlinearities. This paper proposes a systematic technique, based on the principles of dynamic decoupling, to partition a model based on the time scales that are relevant for the particular simulation studies to be performed and as transparently as possible for the user. In accordance with said purpose, peculiar to the technique is its neat separation into two parts: a structural analysis of the model, which is general with respect to any possible simulation scenario, and a subsequent decoupled integration, which can conversely be (easily) tailored to the study at hand. Also, since the technique does not aim at reducing but rather at partitioning the model, the state space and the physical interpretation of the dynamic variables are inherently preserved. Moreover, the proposed analysis allows us to define some novel indices relative to the separability of the system, thereby extending the idea of “stiffness” in a way that is particularly keen to its use for the improvement of simulation efficiency, be the envisaged integration scheme monolithic, parallel, or even based on cosimulation. Finally, thanks to the way the analysis phase is conceived, the technique is naturally applicable to both linear and nonlinear models. The paper contains a methodological presentation of the proposed technique, which is related to alternatives available in the literature so as to evidence the peculiarities just sketched, and some application examples illustrating the achieved advantages and motivating the major design choice from an operational viewpoint.
A combined multibody and finite element approach is given to solve the dynamic interaction of a Shinkansen train (high-speed train in Japan) and the railway structure including post-derailment during an earthquake effectively. The motion of the train is expressed in multibody dynamics. Efficient mechanical models to express interactions between wheel and track structure including post-derailment are given. Rail and track elements expressed in multibody dynamics and FEM are given to solve contact problems between wheel and long railway components effectively. The motion of a railway structure is modeled with various finite elements and rail and track elements. The computer program has been developed for the dynamic interaction analysis of a Shinkansen train and railway structure including post derailment during an earthquake. Numerical examples are demonstrated.
Applied mathematics analysis of the multibody systems
Sahin, H.; Kar, A. K.; Tacgin, E.
2012-08-01
A methodology is developed for the analysis of the multibody systems that is applied on the vehicle as a case study. The previous study emphasizes the derivation of the multibody dynamics equations of motion for bogie [2]. In this work, we have developed a guide-way for the analysis of the dynamical behavior of the multibody systems for mainly validation, verification of the realistic mathematical model and partly for the design of the alternative optimum vehicle parameters.
Stick-slip algorithm in a tangential contact force model for multi-body system dynamics
Contact force of Multi-body dynamics (MBD) system can be classified two parts. First is a normal force and the other is a tangential force called friction force. And the friction force can be represented by two states such as stick and slip. The stick-slip phenomenon is simply described as a simple contact model which is a rigid body contacted on a sloped surface. If the calculated friction coefficient between the body and sloped surface is less than the static friction coefficient, the body should be stuck. If the calculated friction coefficient is greater than the static friction coefficient, the body will be sliding along the surface. The phenomenon is called as stick and slip state of friction, respectively. Usually many researchers and commercial MBD software used a coulomb friction force model which is defined with an only function of relative velocity. This kind of friction force model will be called a conventional friction force model in this paper. A big problem of the conventional model can not describe a stick state of friction phenomenon. In the case of conventional friction force model, the body will be sliding even though friction state is stick. Because, the relative velocity must have a non-zero value in order to generate the friction force. To solve this kind of problem, we propose a stick-slip friction force model including a spring like force. In the case of stick-slip friction force model, the body can be stuck on the sloped surface because the friction force will be a non-zero value, even though the relative velocity approaches zero. We defined a relative displacement variable called stiction deformation. In this paper, the stick-slip friction model is proposed and applied in the contact algorithm of MBD system. And then two friction models are compared with numerical examples. With the proposed stick-slip friction model, more realistic results are achieved
FMD系统模型及其计算机仿真%Modeling and Simulation of FMD (Flexible Multibody Dynamics)
于霖冲; 巫喜红
2004-01-01
介绍了多柔体系统动力学FMD(Flexible Multibody Dynamics)的力学模型建立、数值求解和计算机仿真的方法.利用Lagrange方法建立多柔体动力学模型,利用参考文献[10]中的实例进行多柔体假设,将计算机仿真结果进行了比较.
Lagrangian Dynamics of Open Multibody Systems with Generalized Holonomic and Nonholonomic Joints
Duindam, Vincent; Stramigioli, Stefano
2007-01-01
Standard methods to model multibody systems are aimed at systems with configuration spaces isomorphic to Rn. This limitation leads to singularities and other artifacts in case the configuration space has a different topology, for example in the case of ball joints or a free-floating mechanism. This
Mántaras, Daniel A.; Luque, Pablo; Nava, Javier A.; Riva, Paolo; Girón, Pablo; Compadre, Diego; Ferran, Jordi
2013-10-01
A key factor to understand the vehicle dynamic behaviour is to know as accurately as possible the interaction that occurs between the tyre and the road, since it depends on many factors that influence the dynamic response of the vehicle. This paper aims to develop a methodology in order to characterise the tyre-road behaviour, applying it to obtain the tyre-road grip coefficient. This methodology is based on the use of dynamic simulation of a virtual model, integrated into a genetic algorithm that identifies the tyre-road friction coefficient in order to adjust the response obtained by simulation to real data. The numerical model was developed in collaboration with SEAT Technical Centre and it was implemented in multibody dynamic simulation software Adams®, from MSC®.
Jamali, Safa; Boromand, Arman; Khani, Shaghayegh; Wagner, Jacob; Yamanoi, Mikio; Maia, Joao
2015-04-01
In this work, a generalized relation between the fluid compressibility, the Flory-Huggins interaction parameter (χ), and the simulation parameters in multi-body dissipative particle dynamics (MDPD) is established. This required revisiting the MDPD equation of state previously reported in the literature and developing general relationships between the parameters used in the MDPD model. We derive a relationship to the Flory-Huggins χ parameter for incompressible fluids similar to the work previously done in dissipative particle dynamics by Groot and Warren. The accuracy of this relationship is evaluated using phase separation in small molecules and the solubility of polymers in dilute solvent solutions via monitoring the scaling of the radius of gyration (Rg) for different solvent qualities. Finally, the dynamics of the MDPD fluid is studied with respect to the diffusion coefficient and the zero shear viscosity.
We theoretically investigate quantum phases and transport dynamics of ultracold atoms trapped in an optical lattice in the presence of effective multi-body interaction. When a harmonic external potential is added, several interesting phenomena are revealed, such as the broadening and the emergence of a central insulator plateau and the phase transition between superfluid and Mott insulator phase. We also study the transport of the system which runs across the superfluid—insulator transition after ramping up the lattice, and predict a slower relaxation which is attributed to the influence of the multi-body interaction on the mass transport
Parallel Evolutionary Optimization of Multibody Systems with Application to Railway Dynamics
The optimization of multibody systems usually requires many costly criteria computations since the equations of motion must be evaluated by numerical time integration for each considered design. For actively controlled or flexible multibody systems additional difficulties arise as the criteria may contain non-differentiable points or many local minima. Therefore, in this paper a stochastic evolution strategy is used in combination with parallel computing in order to reduce the computation times whilst keeping the inherent robustness. For the parallelization a master-slave approach is used in a heterogeneous workstation/PC cluster. The pool-of-tasks concept is applied in order to deal with the frequently changing workloads of different machines in the cluster. In order to analyze the performance of the parallel optimization method, the suspension of an ICE passenger coach, modeled as an elastic multibody system, is optimized simultaneously with regard to several criteria including vibration damping and a criterion related to safety against derailment. The iterative and interactive nature of a typical optimization process for technical systems is emphasized
Spatial Formulation of Elastic Multibody Systems with Impulsive Constraints
The problem of modeling the transient dynamics of three-dimensional multibody mechanical systems which encounter impulsive excitations during their functional usage is addressed. The dynamic behavior is represented by a nonlinear dynamic model comprising a mixed set of reference and local elastic coordinates. The finite-element method is employed to represent the local deformations of three-dimensional beam-like elastic components by either a finite set of nodal coordinates or a truncated set of modal coordinates. The finite-element formulation will permit beam elements with variable geometry. The governing equations of motion of the three-dimensional multibody configurations will be derived using the Lagrangian constrained formulation. The generalized impulse-momentum-balance method is extended to accommodate the persistent type of the impulsive constraints. The developed formulation is implemented into a multibody simulation program that assembles the equations of motion and proceeds with its solution. Numerical examples are presented to demonstrate the applicability of the developed method and to display its potential in gaining more insight into the dynamic behavior of such systems
Comparison of Selected Formulations for Multibody System Dynamics with Redundant Constraints
Pękal Marcin
2016-03-01
Full Text Available This paper compares selected optimization-based methods for the analysis of multibody systems with redundant constraints. The following numerical schemes are examined: direct integration method, Udwadia-Kalaba formulation, two types of least-squares block solution method and Udwadia-Phohomsiri formulation. In order to compare efficiency of the algorithms, a series of simulations is performed on two exemplary McPherson struts. In the first variant, the mechanism has no redundant constraints whereas the other is overconstrained. Three constraint stabilization schemes are also compared in terms of integration errors.
Using the multi-body Classical Molecular Dynamics simulation of 6Li+209Bi reaction it is shown that: (i) the breakup of a projectile fragment near the barrier leads to substantial increase in the ICF probabilities; (ii) the expected increase in σCF on relaxation of the rigid-body (RB) constraint on the projectile is compensated by reduction in the flux leading to CF, due to ICF events; (iii) the breakup probability increases with ECM and, for given ECM it also increases as b increases and peaks around some b>0, while cross sections σCF and σTF were calculated for b=0 only Therefore, we present the results of σCF (Complete Fusion) and σTF (Total Fusion) calculations which are obtained at critical impact parameter, bcr, where many ICF channels open up and compare with the calculations performed at b=0 only, where only few ICF channels open up
Pamadi, Bandu N.; Toniolo, Matthew D.; Tartabini, Paul V.; Roithmayr, Carlos M.; Albertson, Cindy W.; Karlgaard, Christopher D.
2016-01-01
The objective of this report is to develop and implement a physics based method for analysis and simulation of multi-body dynamics including launch vehicle stage separation. The constraint force equation (CFE) methodology discussed in this report provides such a framework for modeling constraint forces and moments acting at joints when the vehicles are still connected. Several stand-alone test cases involving various types of joints were developed to validate the CFE methodology. The results were compared with ADAMS(Registered Trademark) and Autolev, two different industry standard benchmark codes for multi-body dynamic analysis and simulations. However, these two codes are not designed for aerospace flight trajectory simulations. After this validation exercise, the CFE algorithm was implemented in Program to Optimize Simulated Trajectories II (POST2) to provide a capability to simulate end-to-end trajectories of launch vehicles including stage separation. The POST2/CFE methodology was applied to the STS-1 Space Shuttle solid rocket booster (SRB) separation and Hyper-X Research Vehicle (HXRV) separation from the Pegasus booster as a further test and validation for its application to launch vehicle stage separation problems. Finally, to demonstrate end-to-end simulation capability, POST2/CFE was applied to the ascent, orbit insertion, and booster return of a reusable two-stage-to-orbit (TSTO) vehicle concept. With these validation exercises, POST2/CFE software can be used for performing conceptual level end-to-end simulations, including launch vehicle stage separation, for problems similar to those discussed in this report.
Numerical methods for multibody systems
Glowinski, Roland; Nasser, Mahmoud G.
1994-01-01
This article gives a brief summary of some results obtained by Nasser on modeling and simulation of inequality problems in multibody dynamics. In particular, the augmented Lagrangian method discussed here is applied to a constrained motion problem with impulsive inequality constraints. A fundamental characteristic of the multibody dynamics problem is the lack of global convexity of its Lagrangian. The problem is transformed into a convex analysis problem by localization (piecewise linearization), where the augmented Lagrangian has been successfully used. A model test problem is considered and a set of numerical experiments is presented.
Julin, Jan; Shiraiwa, Manabu; Miles, Rachael E H; Reid, Jonathan P.; Pöschl, Ulrich; Riipinen, Ilona
2013-01-01
The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatib...
Non-linear substructure approach for dynamic analysis of rigid-flexible multibody systems
Liu, A. Q.; Liew, K. M.
1994-04-01
This paper presents a substructure synthesis method (SSM) for nonlinear analysis of multibody systems. The detailed derivation of the equation of motion which takes into account the geometric nonlinear effects of large rotation undergoing small strain elastic deformation is presented. Using the substructure synthesis approach, the equation of motion is condensed through the boundary conditions at the interface between the flexible and rigid substructures. As a result, equations of motion for multi-flexible-body systems including the geometric non-linear effects of large rotation are derived. To demonstrate the applicability and accuracy of the proposed approach, an example of a two-link manipulator was chosen for this presentation. The results using the linear and nonlinear models are presented to highlight the effects of geometric nonlinearities.
Application of stabilization techniques in the dynamic analysis of multibody systems
Hajžman M.
2007-11-01
Full Text Available This paper is intended to the discussion of possible methods for the solution of the motion equations of constrained multibody systems. They can be formulated in the form of differential-algebraic equations and their numerical solution brings the problems of constraint violation and numerical stability. Therefore special methods were proposed to handle these problems. Various approaches for the numerical solution of equations are briefly reviewed and the application of the Baumgarte’s stabilization method on testing examples is shown. The paper was motivated by the effort to find the suitable solution methods for the equations of motion in the form of differentialalgebraic equations using the MATLAB standard computational system.
Massive Parallelization of Multibody System Simulation
Michael Valášek
2012-01-01
Full Text Available This paper deals with the decrease in CPU time necessary for simulating multibody systems by massive parallelization. The direct dynamics of multibody systems has to be solved by a system of linear algebraic equations. This is a bottleneck for the efficient usage of multiple processors. Simultaneous solution of this task means that the excitation is immediately spread into all components of the multibody system. The bottleneck can be avoided by introducing additional dynamics, and this leads to the possibility of massive parallelization. Two approaches are described. One is a heterogeneousmultiscale method, and the other involves solving a system of linear algebraic equations by artificial dynamics.
Rismantab-Sany, J.; Chang, B.; Shabana, A. A.
1989-01-01
A total Lagrangian finite element formulation for the deformable bodies in multibody mechanical systems that undergo finite relative rotations is developed. The deformable bodies are discretized using finite element methods. The shape functions that are used to describe the displacement field are required to include the rigid body modes that describe only large translational displacements. This does not impose any limitations on the technique because most commonly used shape functions satisfy this requirement. The configuration of an element is defined using four sets of coordinate systems: Body, Element, Intermediate element, Global. The body coordinate system serves as a unique standard for the assembly of the elements forming the deformable body. The element coordinate system is rigidly attached to the element and therefore it translates and rotates with the element. The intermediate element coordinate system, whose axes are initially parallel to the element axes, has an origin which is rigidly attached to the origin of the body coordinate system and is used to conveniently describe the configuration of the element in undeformed state with respect to the body coordinate system.
A verification library for multibody simulation software
Kim, Sung-Soo; Haug, Edward J.; Frisch, Harold P.
1989-01-01
A multibody dynamics verification library, that maintains and manages test and validation data is proposed, based on RRC Robot arm and CASE backhoe validation and a comparitive study of DADS, DISCOS, and CONTOPS that are existing public domain and commercial multibody dynamic simulation programs. Using simple representative problems, simulation results from each program are cross checked, and the validation results are presented. Functionalities of the verification library are defined, in order to automate validation procedure.
Bersini, Simone; Sansone, Valerio; Frigo, Carlo A
2016-01-01
Obtaining tibio-femoral (TF) contact forces, ligament deformations and loads during daily life motor tasks would be useful to better understand the aetiopathogenesis of knee joint diseases or the effects of ligament reconstruction and knee arthroplasty. However, methods to obtain this information are either too simplified or too computationally demanding to be used for clinical application. A multibody dynamic model of the lower limb reproducing knee joint contact surfaces and ligaments was developed on the basis of magnetic resonance imaging. Several clinically relevant conditions were simulated, including resistance to hyperextension, varus-valgus stability, anterior-posterior drawer, loaded squat movement. Quadriceps force, ligament deformations and loads, and TF contact forces were computed. During anterior drawer test the anterior cruciate ligament (ACL) was maximally loaded when the knee was extended (392 N) while the posterior cruciate ligament (PCL) was much more stressed during posterior drawer when the knee was flexed (319 N). The simulated loaded squat revealed that the anterior fibres of ACL become inactive after 60° of flexion in conjunction with PCL anterior bundle activation, while most components of the collateral ligaments exhibit limited length changes. Maximum quadriceps and TF forces achieved 3.2 and 4.2 body weight, respectively. The possibility to easily manage model parameters and the low computational cost of each simulation represent key points of the present project. The obtained results are consistent with in vivo measurements, suggesting that the model can be used to simulate complex and clinically relevant exercises. PMID:26057607
Varying parameter models to accommodate dynamic promotion effects
Foekens, E.W.; Leeflang, P.S.H.; Wittink, D.R.
1999-01-01
The purpose of this paper is to examine the dynamic effects of sales promotions. We create dynamic brand sales models (for weekly store-level scanner data) by relating store intercepts and a brand's own price elasticity to a measure of the cumulated previous price discounts - amount and time - for t
Gross, Volker [ZF Friedrichshafen AG, Friedrichshafen (Germany)
2011-07-01
The legal regulations and the customers' requirements as regards vehicle comfort are growing more and more stringent. This also includes the transmission systems, as they are expected not so show any obvious acoustic or dynamic weaknesses. Modern simulation methods permit evaluation and optimization of structure-borne and airborne noise in the early stage of development. Especially the FE method is a well-established technique for the simulation of structure-borne sound. With regard to complex transmissions, multibody simulations (MBS) can provide valuable insights for a realistic evaluation of the dynamic behaviour of a transmission. This is demonstrated using a truck transmission as an example. (orig.)
Chen, Shanshin; Tortorelli, Daniel A.; Hansen, John Michael
1999-01-01
Advances in computer hardware and improved algorithms for multibody dynamics over the past decade have generated widespread interest in real-time simulations of multibody mechanics systems. At the heart of the widely used algorithms for multibody dynamics are a choice of coordinates which define...... tool. To exemplify the methodology, a wheel loader mechanism is designed to minimize energy consumption subject to trajectory constraints....
Dynamic distance direct ophthalmoscopy, a novel technique to assess accommodation in children
Mihir Kothari
2012-01-01
Full Text Available Aim: To describe and compare dynamic distance direct ophthalmoscopy (DDDO with dynamic retinoscopy (DR in assessment of accommodation in children. Materials and Methods: This prospective observational study had four components. Component 1: to understand the characteristic digital images of DDDO. Component 2: to compare DDDO with DR for detection of accommodative defects in children (1-16 years. Component 3: to compare DDDO with DR for the detection of completeness of pharmacologically induced cycloplegia in children (5-16 years and Component 4: to assess which one of the two techniques was more sensitive to detect onset of cycloplegia after instillation of 1% cyclopentolate eye drops. Results: Component 1: image analysis of DDDO on two subjects (7 years and 35 years demonstrated superior pupillary crescent that progressively disappeared with increasing accommodation. Concurrently an inferior crescent appeared that became bigger in size with increasing accommodation. Component 2: the prevalence of defects in accommodation was 3.3% (33/1000 children. Three had unilateral accommodation failure. Sensitivity of DDDO was 94%, specificity 100%, positive predictive value 100%, negative predictive value 99%, and clinical agreement (kappa 0.97. Component 3: in the detection of completeness of pharmacologically induced cycloplegia (n=30, the sensitivity of DDDO was 94%, specificity 96%, positive predictive value 97%, negative predictive value 93% and kappa 0.9. DR had two false positives. DDDO had one false negative. Component 4: DDDO detected onset of pharmacologically induced cycloplegia 5 min earlier than DR (n=5. Conclusion: DDDO is a novel, simple, clinical and reliable method to assess accommodation in young children. This test can assess the accommodative response of both eyes simultaneously.
Electron accommodation dynamics in the DNA base thymine
The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I−T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from −120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I−T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I−T VDE, which suggests that if the dipole-bound anion acts as a “doorway” to the valence-bound anion, it only does so at excitation energies near the VDE of the complex
Xiao-Ting Rui; Edwin Kreuzer; Bao Rong; Bin He
2012-01-01
In this paper,by defining new state vectors and developing new transfer matrices of various elements moving in space,the discrete time transfer matrix method of multi-rigid-flexible-body system is expanded to study the dynamics of muhibody system with flexible beams moving in space.Formulations and numerical example of a rigidflexible-body three pendulums system moving in space are given to validate the method. Using the new method to study the dynamics of multi-rigid-flexible-body system mov ing in space,the global dynamics equations of system are not needed,the orders of involved matrices of the system are very low and the computational speed is high,irrespective of the size of the system.The new method is simple,straightforward,practical,and provides a powerful tool for multi-rigid-flexible-body system dynamics.
Linking rigid multibody systems via controllable thin fluid films
Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
rotor via a thin fluid film, where the hydrodynamic pressure is described by the Reynolds equation, which is modified to accommodate the controllable lubrication conditions. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the reciprocating linear......This work deals with the mathematical modelling of multibody systems interconnected via thin fluid films. The dynamics of the fluid films can be actively controlled by means of different types of actuators, allowing significant vibration reduction of the system components. In this framework, this...... compressor. The system of equations is numerically solved for the case when the system operates with conventional hydrodynamic lubrication and for several cases of the bearing operating under controlled hybrid lubrication conditions. The analysis of the results is carried out with focus on the behaviour of...
Julin, Jan; Shiraiwa, Manabu; Miles, Rachael E H; Reid, Jonathan P; Pöschl, Ulrich; Riipinen, Ilona
2013-01-17
The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatibility of the two. Molecular dynamics simulations were performed for a planar TIP4P-Ew water surface at four temperatures in the range 268-300 K as well as two droplets, with radii of 1.92 and 4.14 nm at T = 273.15 K. The evaporation flux from molecular dynamics was found to be in good qualitative agreement with that predicted by the simple kinetic condensation equations. Water droplet growth was also modeled with the kinetic multilayer model KM-GAP of Shiraiwa et al. [Atmos. Chem. Phys. 2012, 12, 2777]. It was found that, due to the fast transport across the interface, the growth of a pure water droplet is controlled by gas phase diffusion. These facts indicate that the simple kinetic treatment is sufficient in describing pure water condensation and evaporation. The droplet size was found to have minimal effect on the value of the mass accommodation coefficient. The mass accommodation coefficient was found to be unity (within 0.004) for all studied surfaces, which is in agreement with previous simulation work. Additionally, the simulated evaporation fluxes imply that the evaporation coefficient is also unity. Comparing the evaporation rates of the mass accommodation and evaporation simulations indicated that the high collision flux, corresponding to high supersaturation, present in typical molecular dynamics mass accommodation simulations can under certain conditions lead to an increase in the evaporation rate. Consequently, in such situations the mass accommodation coefficient
A Component Mode Synthesis Algorithm for Multibody Dynamics of Wind Turbines
Holm-Jørgensen, Kristian; Nielsen, Søren R.K.
2009-01-01
motion of the substructure. The system reduction is based on a component mode synthesis method, where the response of the internal degrees of freedom of the substructure is described as the quasi-static response induced by the boundary degrees of freedom via the constraint modes superimposed in...... combination to a dynamic component induced by inertial effects and internal loads. The latter component is modelled by a truncated modal expansion in fixed interface undamped eigenmodes. The selected modal vector base for the internal dynamics ensures that the boundary degrees of freedom account for the rigid...... fixed-free method due to incompatible displacements and rotations at the interface between the two substructures. Moreover, the results from the reduced model by use of constant constraint modes and constant fixed interface modes over a large operating areal for the wind turbine blade are almost...
Biometry of the ciliary muscle during dynamic accommodation assessed with OCT
Ruggeri, Marco; Hernandez, Victor; de Freitas, Carolina; Manns, Fabrice; Parel, Jean-Marie
2014-02-01
Little is known about the structural changes of the ciliary muscle with age and how it may contribute to presbyopia. Optical coherence tomography (OCT) has been used to perform ciliary muscle biometry at different age and accommodative states with low resolution and speed. Dynamic imaging and accurate biometry of the ciliary muscle requires high-speed, high-resolution and correction of the OCT image distortions. We integrate an existing custom-made Spectral Domain OCT (SD-OCT) platform working at 840nm for biometry of the human eye with a SD-OCT system working at 1325nm that enables high-speed and high-resolution transscleral imaging of the ciliary muscle dynamically during accommodation and we developed an algorithm to provide corrected thickness measurements of the ciliary muscle.
Wear analysis of revolute joints with clearance in multibody systems
Bai, ZhengFeng; Zhao, Yang; Wang, XingGui
2013-08-01
In this work, the prediction of wear for revolute joint with clearance in multibody systems is investigated using a computational methodology. The contact model in clearance joint is established using a new hybrid nonlinear contact force model and the friction effect is considered by using a modified Coulomb friction model. The dynamics model of multibody system with clearance is established using dynamic segmentation modeling method and the computational process for wear analysis of clearance joint in multibody systems is presented. The main computational process for wear analysis of clearance joint includes two steps, which are dynamics analysis and wear analysis. The dynamics simulation of multibody system with revolute clearance joint is carried out and the contact forces are drawn and used to calculate the wear amount of revolute clearance joint based on the Archard's wear model. Finally, a four-bar multibody mechanical system with revolute clearance joint is used as numerical example application to perform the simulation and show the dynamics responses and wear characteristics of multibody systems with revolute clearance joint. The main results of this work indicate that the contact between the joint elements is wider and more frequent in some specific regions and the wear phenomenon is not regular around the joint surface, which causes the clearance size increase non-regularly after clearance joint wear. This work presents an effective method to predict wear of revolute joint with clearance in multibody systems.
Analog-to-Digital Conversion to Accommodate the Dynamics of Live Music in Hearing Instruments
Bahlmann, Frauke; Fulton, Bernadette
2012-01-01
Hearing instrument design focuses on the amplification of speech to reduce the negative effects of hearing loss. Many amateur and professional musicians, along with music enthusiasts, also require their hearing instruments to perform well when listening to the frequent, high amplitude peaks of live music. One limitation, in most current digital hearing instruments with 16-bit analog-to-digital (A/D) converters, is that the compressor before the A/D conversion is limited to 95 dB (SPL) or less at the input. This is more than adequate for the dynamic range of speech; however, this does not accommodate the amplitude peaks present in live music. The hearing instrument input compression system can be adjusted to accommodate for the amplitudes present in music that would otherwise be compressed before the A/D converter in the hearing instrument. The methodology behind this technological approach will be presented along with measurements to demonstrate its effectiveness. PMID:23258618
刚柔耦合多体系统动力学模型降阶%Model reduction of dynamics for rigid-flexible multi-body systems
孙东阳; 陈国平
2014-01-01
提出了基于模态综合法的刚柔耦合多体系统动力学模型降阶方法。该方法用自然坐标法和绝对节点坐标法分别描述刚柔耦合多体系统中的刚体构件和柔性体构件，同时用Craig-Bampton方法对柔性体模型进行减缩。对于刚体构件与柔性体构件之间只存在线性约束的情况，建立了消除线性约束的刚柔耦合多体系统动力学方程。最后，为了验证的该方法的有效性，对刚柔耦合双摆进行了研究。仿真结果表明：适当选择模态就可以在满足计算精度的同时减少计算时间，提高计算效率。%Based on the component modal synthesis ,a modal reduction method for rigid-flexible multibody systems is presented in the paper .The natural coordinate formulation and the absolute nodal coordinate formulation are used to describe the rigid parts and the flexible parts of rigid-flexible multi-body systems respectively .Craig-Bampton method is used to reduce the modes of the flexible parts .In the case linear constraints exist between the rigid parts and the flexible parts ,the linear con-straints are eliminated and the dynamical equation for rigid-flexible multi-body systems is obtained .Finally ,in order to verify the effectiveness of the method ,a rigid-flexible double pendulum is studied ,which shows that properly selected modes can meet the requirement of calculation accuracy while the computing time is reduced .
Lee, Dongryeol; Gray, Alexander G
2011-01-01
A three-body potential function can account for interactions among triples of particles which are uncaptured by pairwise interaction functions such as Coulombic or Lennard-Jones potentials. Likewise, a multibody potential of order $n$ can account for interactions among $n$-tuples of particles uncaptured by interaction functions of lower orders. To date, the computation of multibody potential functions for a large number of particles has not been possible due to its $O(N^n)$ scaling cost. In this paper we describe a fast tree-code for efficiently approximating multibody potentials. For the first time, we show how to extend the series-expansion-based approach of Fast Multipole Method-like algorithms to handle interactions among more than two particles. Our approach guarantees a user-specified bound on the absolute or relative error in the computed potential. We provide speedup results on a three-body dispersion potential, the Axilrod-Teller potential.
Multibody minimum-energy trajectory with applications to protein folding
Leandro, Carlos; Ambrósio, Jorge
2016-01-01
This work addresses the optimal control of multibody systems being actuated with control forces in order to find a dynamically feasible minimum-energy trajectory of the system. The optimal control problem and its constraints are integrated in a discrete version of the equation of motion allowing the minimization of system energy with respect to a discrete state and control trajectory. The work is centred on a specific type of open-chain multibody system, with strong local propensity, where th...
Flexible Multibody Systems Models Using Composite Materials Components
Neto, Maria Augusta; Ambrósio, Jorge A. C.; Leal, Rogério Pereira
2004-01-01
The use of a multibody methodology to describe the large motion of complex systems that experience structural deformations enables to represent the complete system motion, the relative kinematics between the components involved, the deformation of the structural members and the inertia coupling between the large rigid body motion and the system elastodynamics. In this work, the flexible multibody dynamics formulations of complex models are extended to include elastic components made of compos...
Khurelbaatar, Tsolmonbaatar; Kim, Kyungsoo; Hyuk Kim, Yoon
2015-11-01
Computational musculoskeletal models have been developed to predict mechanical joint loads on the human spine, such as the forces and moments applied to vertebral and facet joints and the forces that act on ligaments and muscles because of difficulties in the direct measurement of joint loads. However, many whole-spine models lack certain elements. For example, the detailed facet joints in the cervical region or the whole spine region may not be implemented. In this study, a detailed cervico-thoraco-lumbar multibody musculoskeletal model with all major ligaments, separated structures of facet contact and intervertebral disk joints, and the rib cage was developed. The model was validated by comparing the intersegmental rotations, ligament tensile forces, facet joint contact forces, compressive and shear forces on disks, and muscle forces were to those reported in previous experimental and computational studies both by region (cervical, thoracic, or lumbar regions) and for the whole model. The comparisons demonstrated that our whole spine model is consistent with in vitro and in vivo experimental studies and with computational studies. The model developed in this study can be used in further studies to better understand spine structures and injury mechanisms of spinal disorders. PMID:26292160
Sun, Yafeng; Peng, Danling; Ding, Guosheng; Qi, Ting; Desroches, Amy S; Liu, Li
2015-10-01
The framework of assimilation and accommodation has been proposed to explain the brain mechanisms supporting second language reading acquisition (Perfetti et al. [2007]: Bilingual Lang Cogn 10:131). Assimilation refers to using the procedures of the native language network in the acquisition of a new writing system, whereas accommodation refers to using second language procedures for reading the newly acquired writing system. We investigated assimilation and accommodation patterns in the brains of bilingual individuals by recruiting a group of Chinese-English bilinguals and a group of English-Chinese bilinguals to perform lexical decision tasks in both English and Chinese. The key question was whether the assimilation/accommodation procedures supporting second language reading in the brains of Chinese-English and English-Chinese bilinguals were dynamic, i.e., modulated by proficiency in the second language and perceptual features of the second language's script. Perceptual features of the scripts were manipulated through orthographic degradation by inserting spaces between the radicals of a Chinese character or between the syllables of an English word. This manipulation disrupts the visual configuration of the orthography but does not change its more fundamental design principles. We found that for English-Chinese bilinguals, higher proficiency was associated with greater accommodation, suggesting that the accommodation procedure in a bilingual individual's brain is modulated by second language proficiency. Most interestingly, we found that the assimilation/accommodation effects vanished or diminished when orthographically degraded scripts were processed by both Chinese-English and English-Chinese bilinguals, suggesting that the assimilation/accommodation procedures in a bilingual individual's brain are modulated by perceptual features of orthography. This work therefore offers a new, dynamic perspective for our understanding of the assimilation/accommodation
Multibody simulation of adhesion pili
Zakrisson, Johan; Servin, Martin; Axner, Ove; Lacoursiere, Claude; Andersson, Magnus
2014-01-01
We present a coarse grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymers force-extension response. With building blocks representing individual subunits the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include both the effects of unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and the results in this work give enhanced understanding of how a pilus unwinds under action of external forces and provide new perspective of th...
Composite materials in flexible multibody systems
Neto, Maria Augusta; Ambrósio, Jorge A. C.; Leal, Rogério P.
2006-01-01
In this work the flexible multibody dynamics formulations of complex models are extended to include elastic components made of laminated composite materials. The only limitation for the deformation of a structural member is that it must be elastic and linear when described in a body fixed frame. A finite element model for each flexible body is obtained such that the nodal coordinates are described with respect to the body fixed frame and the inertia terms involved in the mass matrix and gyros...
Revolute joints with clearance in multibody systems
Flores, Paulo; Ambrósio, Jorge
2004-01-01
A computational methodology for dynamic analysis of multibody mechanical systems with joint clearance is presented in this work. Clearances always exist in real joints in order to ensure the correct relative motion between the connected bodies being the gap associated to them a result of machining tolerance, wear, and local deformations. Clearance at different joints is the source for impact forces, resulting in wear and tear of the joints, and consequently the degradation of the system perfo...
Amengonu, Yawo H.; Kakad, Yogendra P.
2014-07-01
Quasivelocity techniques were applied to derive the dynamics of a Differential Wheeled Mobile Robot (DWMR) in the companion paper. The present paper formulates a control system design for trajectory tracking of this class of robots. The method develops a feedback linearization technique for the nonlinear system using dynamic extension algorithm. The effectiveness of the nonlinear controller is illustrated with simulation example.
Analysis of Nonlinear Multibody Systems with Elastic Couplings
This paper is concerned with the dynamic analysis of nonlinear multibody systems involving elastic members made of laminated, anisotropic composite materials. The analysis methodology can be viewed as a three-step procedure. First, the sectional properties of beams made of composite materials are determined based on an asymptotic procedure that involves a two-dimensional finite element analysis of the cross-section. Second, the dynamic response of nonlinear, flexible multibody systems is simulated within the framework of energy-preserving and energy-decaying time-integration schemes that provide unconditional stability for nonlinear systems. Finally, local three-dimensional stresses in the beams are recovered, based on the stress resultants predicted in the previous step. Numerical examples are presented and focus on the behavior of multibody systems involving members with elastic couplings
Amengonu, Yawo H.; Kakad, Yogendra P.
2014-07-01
Quasivelocity techniques such as Maggi's and Boltzmann-Hamel's equations eliminate Lagrange multipliers from the beginning as opposed to the Euler-Lagrange method where one has to solve for the n configuration variables and the multipliers as functions of time when there are m nonholonomic constraints. Maggi's equation produces n second-order differential equations of which (n-m) are derived using (n-m) independent quasivelocities and the time derivative of the m kinematic constraints which add the remaining m second order differential equations. This technique is applied to derive the dynamics of a differential mobile robot and a controller which takes into account these dynamics is developed.
... effect of the accommodative effort can be excess convergence or crossing of the eyes. Why is accommodative esotropia a concern in children? ... accommodative effort. In turn, this will reduce the convergence or crossing stimulus and the eyes will straighten as they relax. Glasses or contacts ...
An improved method for deriving elastic generalized coordinates is considered. Then Kane's equations of motion for multibody systems consisting of an arbitrary number of rigid and elastic bodies are presented. The equations are in general form and are applicable for any desired holonomic system. Flexibility in choosing generalized speeds interims of generalized coordinate derivatives in Kane's method is used. It is shown that proper choice of a congruency transformation between generalized coordinate derivatives and generalized speeds leads to equations of motion for holonomic multibody systems consisting of an arbitrary number of rigid and elastic bodies. These equations are decoupled in first-order terms. In order to show the use of this method, a simple system consisting of a lumped mass, a spring and clamped-free elastic beam is modeled. Finally, the numerical implementation of decoupling using congruency transformation is discussed and shown via simulation of a two-degrees-of-freedom flexible robot
Olney, Karl L.
The dynamic behavior of granular/porous and laminate reactive materials is of interest due to their practical applications; reactive structural components, reactive fragments, etc. The mesostructural properties control meso- and macro-scale dynamic behavior of these heterogeneous composites including the behavior during the post-critical stage of deformation. They heavily influence mechanisms of fragment generation and the in situ development of local hot spots, which act as sites of ignition in these materials. This dissertation concentrates on understanding the mechanisms of plastic strain accommodation in two representative reactive material systems with different heterogeneous mesostructrues: Aluminum-Tungsten granular/porous and Nickel-Aluminum laminate composites. The main focus is on the interpretation of results of the following dynamic experiments conducted at different strain and strain rates: drop weight tests, explosively expanded ring experiments, and explosively collapsed thick walled cylinder experiments. Due to the natural limitations in the evaluation of the mesoscale behavior of these materials experimentally and the large variation in the size scales between the mesostructural level and the sample, it is extremely difficult, if not impossible, to examine the mesoscale behavior in situ. Therefore, numerical simulations of the corresponding experiments are used as the main tool to explore material behavior at the mesoscale. Numerical models were developed to elucidate the mechanisms of plastic strain accommodation and post critical behavior in these heterogeneous composites subjected to dynamic loading. These simulations were able to reproduce the qualitative and quantitative features that were observable in the experiments and provided insight into the evolution of the mechanisms of plastic strain accommodation and post critical behavior in these materials with complex mesotructure. Additionally, these simulations provided a framework to examine
Tourism in European cities: insights into the dynamics of weekend hotel accommodation
Poater Teixidor, Albert; Garriga Ripoll, Anna
2009-01-01
The rationalization of the cost of accommodation for the most representative night of the weekend (from Saturday to Sunday) was examined using hotel price information from the Internet. The overall data are related to 20 benchmark European cities, but also include brief comparisons with other cities around the world. The tool used to obtain the information was a web searcher with similar characteristics to a travel agency, which allows booking via the Internet. The amount of data thus collect...
Kumar, Rakesh; Li, Zheng; van Duin, Adri; Levin, Deborah
2011-08-14
Using molecular dynamics (MD), we have studied the mechanism of heat accommodation between carbon dioxide clusters and monomers for temperatures and cluster size conditions that exist in homogeneous condensing supersonic expansion plumes. The work was motivated by our meso-scale direct simulation Monte Carlo and Bhatnagar-Gross-Krook based condensation simulations where we found that the heat accommodation model plays a key role in the near-field of the nozzle expansion particularly as the degree of condensation increases [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. The heat released by nucleation and condensation and the heat removed by cluster evaporation can be transferred or removed from either the kinetic or translational modes of the carbon dioxide monomers. The molecular dynamics results show that the time required for gas-cluster interactions to establish an equilibrium from an initial state of non-equilibrium is less than the time step used in meso-scale analyses [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. Therefore, the good agreement obtained between the measured cluster and gas number density and gas temperature profiles with the meso-scale modeling using the second energy exchange mechanism is not fortuitous but is physically based. Our MD simulations also showed that a dynamic equilibrium is established by the gas-cluster interactions in which condensation and evaporation processes take place constantly to and from a cluster. PMID:21842939
Tetraquark state and multibody interaction
The tetraquark states with diquark-anti-diquark configuration have been studied in the flux-tube model, in which the multibody confinement is used. In this model approach, the states Y(2175), f0(600), f0(980), and X(1576) can be assigned as tetraquark states. They are color confinement resonances with three-dimension structure. This study suggests that the multibody confinement should be employed in the quark model study of multiquark states instead of the additive two-body confinement.
Research on Modal Parameters Identification of Parallel Manipulator with Flexible Multi-Body System
Chunxia Zhu; Jiman Luo; Dan Wang; Bing Cai
2013-01-01
In this study, a new method based on simulation is proposed. And the analysis method based on flexible multi-body system of parallel manipulator is provided in the same time. Firstly, modal analysis principle of parallel manipulator was analyzed in theory and the parameters of dynamic characteristic were identified by theoretical analysis. Then vibration model of flexible multi-body for parallel manipulator was built in virtual prototype software and formed vibration system of rigid and flexi...
Flexible Multibody Systems Models Using Composite Materials Components
The use of a multibody methodology to describe the large motion of complex systems that experience structural deformations enables to represent the complete system motion, the relative kinematics between the components involved, the deformation of the structural members and the inertia coupling between the large rigid body motion and the system elastodynamics. In this work, the flexible multibody dynamics formulations of complex models are extended to include elastic components made of composite materials, which may be laminated and anisotropic. The deformation of any structural member must be elastic and linear, when described in a coordinate frame fixed to one or more material points of its domain, regardless of the complexity of its geometry. To achieve the proposed flexible multibody formulation, a finite element model for each flexible body is used. For the beam composite material elements, the sections properties are found using an asymptotic procedure that involves a two-dimensional finite element analysis of their cross-section. The equations of motion of the flexible multibody system are solved using an augmented Lagrangian formulation and the accelerations and velocities are integrated in time using a multi-step multi-order integration algorithm based on the Gear method
Active vibration control of spatial flexible multibody systems
Neto, Maria Augusta, E-mail: augusta.neto@dem.uc.pt [Universidade de Coimbra (Polo II), Departamento de Engenharia Mecanica, Faculdade de Ciencia e Tecnologia (Portugal); Ambrosio, Jorge A. C., E-mail: jorge@dem.ist.utl.pt [Instituto Superior Tecnico, Instituto de Engenharia Mecanica (Portugal); Roseiro, Luis M., E-mail: lroseiro@isec.pt [Instituto Superior de Engenharia de Coimbra, Departamento de Engenharia Mecanica (Portugal); Amaro, A., E-mail: ana.amaro@dem.uc.pt [Universidade de Coimbra (Polo II), Departamento de Engenharia Mecanica, Faculdade de Ciencia e Tecnologia (Portugal); Vasques, C. M. A., E-mail: cvasques@inegi.up.pt [Universidade do Porto, INEGI-Instituto de Engenharia Mecanica e Gestao Industrial (Portugal)
2013-06-15
In this work a flexible multibody dynamics formulation of complex models including elastic components made of composite materials is extended to include piezoelectric sensors and actuators. The only limitation for the deformation of a structural member is that they must remain elastic and linear when described in a coordinate frame fixed to a material point or region of its domain. The flexible finite-element model of each flexible body is obtained referring the flexible body nodal coordinates to the body fixed frame and using a diagonalized mass description of the inertia in the mass matrix and on the gyroscopic force vector. The modal superposition technique is used to reduce the number of generalized coordinates to a reasonable dimension for complex shaped structural models of flexible bodies. The active vibration control of the flexible multibody components is implemented using an asymmetric collocated piezoelectric sensor/actuator pair. An electromechanically coupled model is taken into account to properly consider the surface-bonded piezoelectric transducers and their effects on the time and spatial response of the flexible multibody components. The electromechanical effects are introduced in the flexible multibody equations of motion by the use of beam and plate/shell elements, developed to this purpose. A comparative study between the classical control strategies, constant gain and amplitude velocity feedback, and optimal control strategy, linear quadratic regulator (LQR), is performed in order to investigate their effectiveness to suppress vibrations in structures with piezoelectric sensing and actuating patches.
Active vibration control of spatial flexible multibody systems
In this work a flexible multibody dynamics formulation of complex models including elastic components made of composite materials is extended to include piezoelectric sensors and actuators. The only limitation for the deformation of a structural member is that they must remain elastic and linear when described in a coordinate frame fixed to a material point or region of its domain. The flexible finite-element model of each flexible body is obtained referring the flexible body nodal coordinates to the body fixed frame and using a diagonalized mass description of the inertia in the mass matrix and on the gyroscopic force vector. The modal superposition technique is used to reduce the number of generalized coordinates to a reasonable dimension for complex shaped structural models of flexible bodies. The active vibration control of the flexible multibody components is implemented using an asymmetric collocated piezoelectric sensor/actuator pair. An electromechanically coupled model is taken into account to properly consider the surface-bonded piezoelectric transducers and their effects on the time and spatial response of the flexible multibody components. The electromechanical effects are introduced in the flexible multibody equations of motion by the use of beam and plate/shell elements, developed to this purpose. A comparative study between the classical control strategies, constant gain and amplitude velocity feedback, and optimal control strategy, linear quadratic regulator (LQR), is performed in order to investigate their effectiveness to suppress vibrations in structures with piezoelectric sensing and actuating patches.
Computational Methods for Structural Mechanics and Dynamics
Stroud, W. Jefferson (Editor); Housner, Jerrold M. (Editor); Tanner, John A. (Editor); Hayduk, Robert J. (Editor)
1989-01-01
Topics addressed include: transient dynamics; transient finite element method; transient analysis in impact and crash dynamic studies; multibody computer codes; dynamic analysis of space structures; multibody mechanics and manipulators; spatial and coplanar linkage systems; flexible body simulation; multibody dynamics; dynamical systems; and nonlinear characteristics of joints.
Modeling Multibody Systems with Uncertainties. Part I: Theoretical and Computational Aspects
This study explores the use of generalized polynomial chaos theory for modeling complex nonlinear multibody dynamic systems in the presence of parametric and external uncertainty. The polynomial chaos framework has been chosen because it offers an efficient computational approach for the large, nonlinear multibody models of engineering systems of interest, where the number of uncertain parameters is relatively small, while the magnitude of uncertainties can be very large (e.g., vehicle-soil interaction). The proposed methodology allows the quantification of uncertainty distributions in both time and frequency domains, and enables the simulations of multibody systems to produce results with 'error bars'. The first part of this study presents the theoretical and computational aspects of the polynomial chaos methodology. Both unconstrained and constrained formulations of multibody dynamics are considered. Direct stochastic collocation is proposed as less expensive alternative to the traditional Galerkin approach. It is established that stochastic collocation is equivalent to a stochastic response surface approach. We show that multi-dimensional basis functions are constructed as tensor products of one-dimensional basis functions and discuss the treatment of polynomial and trigonometric nonlinearities. Parametric uncertainties are modeled by finite-support probability densities. Stochastic forcings are discretized using truncated Karhunen-Loeve expansions. The companion paper 'Modeling Multibody Dynamic Systems With Uncertainties. Part II: Numerical Applications' illustrates the use of the proposed methodology on a selected set of test problems. The overall conclusion is that despite its limitations, polynomial chaos is a powerful approach for the simulation of multibody systems with uncertainties
Alternate space station freedom configuration considerations to accommodate solar dynamic power
Deryder, L. J.; Cruz, J. N.; Heck, M. L.; Robertson, B. P.; Troutman, P. A.
1989-01-01
The results of a technical audit of the Space Station Freedom Program conducted by the Program Director was announced in early 1989 and included a proposal to use solar dynamic power generation systems to provide primary electrical energy for orbital flight operations rather than photovoltaic solar array systems. To generate the current program baseline power of 75 kW, two or more solar concentrators approximately 50 feet in diameter would be required to replace four pairs of solar arrays whose rectangular blanket size is approximately 200 feet by 30 feet. The photovoltaic power system concept uses solar arrays to generate electricity that is stored in nickel-hydrogen batteries. The proposed concept uses the solar concentrator dishes to reflect and focus the Sun's energy to heat helium-xenon gas to drive electricity generating turbines. The purpose here is to consider the station configuration issues for incorporation of solar dynamic power system components. Key flight dynamic configuration geometry issues are addressed and an assembly sequence scenario is developed.
Design sensitivity analysis of flexible multibody systems is important in optimizing the performance of mechanical systems. The choice of coordinates to describe the motion of multibody systems has a great influence on the efficiency and accuracy of both the dynamic and sensitivity analysis. In the flexible multibody system dynamics, both the floating frame of reference formulation (FFRF) and absolute nodal coordinate formulation (ANCF) are frequently utilized to describe flexibility, however, only the former has been used in design sensitivity analysis. In this article, ANCF, which has been recently developed and focuses on modeling of beams and plates in large deformation problems, is extended into design sensitivity analysis of flexible multibody systems. The Motion equations of a constrained flexible multibody system are expressed as a set of index-3 differential algebraic equations (DAEs), in which the element elastic forces are defined using nonlinear strain-displacement relations. Both the direct differentiation method and adjoint variable method are performed to do sensitivity analysis and the related dynamic and sensitivity equations are integrated with HHT-I3 algorithm. In this paper, a new method to deduce system sensitivity equations is proposed. With this approach, the system sensitivity equations are constructed by assembling the element sensitivity equations with the help of invariant matrices, which results in the advantage that the complex symbolic differentiation of the dynamic equations is avoided when the flexible multibody system model is changed. Besides that, the dynamic and sensitivity equations formed with the proposed method can be efficiently integrated using HHT-I3 method, which makes the efficiency of the direct differentiation method comparable to that of the adjoint variable method when the number of design variables is not extremely large. All these improvements greatly enhance the application value of the direct differentiation
Modeling multibody systems with uncertainties. Part II: Numerical applications
This study applies generalized polynomial chaos theory to model complex nonlinear multibody dynamic systems operating in the presence of parametric and external uncertainty. Theoretical and computational aspects of this methodology are discussed in the companion paper 'Modeling Multibody Dynamic Systems With Uncertainties. Part I: Theoretical and Computational Aspects .In this paper we illustrate the methodology on selected test cases. The combined effects of parametric and forcing uncertainties are studied for a quarter car model. The uncertainty distributions in the system response in both time and frequency domains are validated against Monte-Carlo simulations. Results indicate that polynomial chaos is more efficient than Monte Carlo and more accurate than statistical linearization. The results of the direct collocation approach are similar to the ones obtained with the Galerkin approach. A stochastic terrain model is constructed using a truncated Karhunen-Loeve expansion. The application of polynomial chaos to differential-algebraic systems is illustrated using the constrained pendulum problem. Limitations of the polynomial chaos approach are studied on two different test problems, one with multiple attractor points, and the second with a chaotic evolution and a nonlinear attractor set. The overall conclusion is that, despite its limitations, generalized polynomial chaos is a powerful approach for the simulation of multibody dynamic systems with uncertainties
Analysis of servo-constraint problems for underactuated multibody systems
R. Seifried
2013-02-01
Full Text Available Underactuated multibody systems have fewer control inputs than degrees of freedom. In trajectory tracking control of such systems an accurate and efficient feedforward control is often necessary. For multibody systems feedforward control by model inversion can be designed using servo-constraints. So far servo-constraints have been mostly applied to differentially flat underactuated mechanical systems. Differentially flat systems can be inverted purely by algebraic manipulations and using a finite number of differentiations of the desired output trajectory. However, such algebraic solutions are often hard to find and therefore the servo-constraint approach provides an efficient and practical solution method. Recently first results on servo-constraint problems of non-flat underactuated multibody systems have been reported. Hereby additional dynamics arise, so-called internal dynamics, yielding a dynamical system as inverse model. In this paper the servo-constraint problem is analyzed for both, differentially flat and non-flat systems. Different arising important phenomena are demonstrated using two illustrative examples. Also strategies for the numerical solution of servo-constraint problems are discussed.
Omar, Mohamed A
2014-01-01
Initial transient oscillations inhibited in the dynamic simulations responses of multibody systems can lead to inaccurate results, unrealistic load prediction, or simulation failure. These transients could result from incompatible initial conditions, initial constraints violation, and inadequate kinematic assembly. Performing static equilibrium analysis before the dynamic simulation can eliminate these transients and lead to stable simulation. Most exiting multibody formulations determine the static equilibrium position by minimizing the system potential energy. This paper presents a new general purpose approach for solving the static equilibrium in large-scale articulated multibody. The proposed approach introduces an energy drainage mechanism based on Baumgarte constraint stabilization approach to determine the static equilibrium position. The spatial algebra operator is used to express the kinematic and dynamic equations of the closed-loop multibody system. The proposed multibody system formulation utilizes the joint coordinates and modal elastic coordinates as the system generalized coordinates. The recursive nonlinear equations of motion are formulated using the Cartesian coordinates and the joint coordinates to form an augmented set of differential algebraic equations. Then system connectivity matrix is derived from the system topological relations and used to project the Cartesian quantities into the joint subspace leading to minimum set of differential equations. PMID:25045732
On the use of the consistent mass matrix in flexible multibody systems
Anthony, Tobin C.; Craig, Roy R., Jr.
1993-01-01
Two different methods are used in finite element structural analysis to define element mass distribution: consistent and lumped mass approximations. The lumped mass method is currently favored in multibody dynamics software packages because of its computational efficiency. This paper, however, presents a multibody dynamics formulation based on the consistent mass approach which should prove to be as computationally efficient as the lumped mass approach. It is shown that when component flexibility is modelled using modal coordinates, the equations of motion, as formulated by these two methods, are very similar in appearance, thereby facilitating their comparison. It is also shown, through simulation of a simple multibody system, that a system formulated with the lumped mass approximation will often require more finite elements and smaller integration step sizes than the corresponding consistent mass system.
Algebraic analysis approach for multibody problems
Here we propose an algebraic analysis approach for multibody Coulomb interactions. The momentum transfer cross section calculated by the algebraic approximation is close to the exact one. The CPU time required for the algebraic approximation is only about 20 min using a personal computer, whereas the exact analysis requires 15 h to integrate the entire set of multibody equations of motion, in which all the field particles are at rest. (author)
Further Results of Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses
Masarati, Pierangelo; Quaranta, Giuseppe; Piatak, David J.; Singleton, Jeffrey D.
2004-01-01
This investigation focuses on the development of multibody analytical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint deadband may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model are examined. A parametric study of the design parameters which may have influence on the aeromechanics of the soft-inplane rotor system are also included in this investigation.
Multibody fusion model to explain experimental results
Worldwide cold fusion experiments have given anomalous results with regard to levels of kilo-electron-volts per atom excess heat, He generation, level of emission of neutrons and tritons with a 10-4 to 10-7 neutron-to-triton yield ratio, and emission of high-energy charged particles, which cannot be explained by the known d+d fusion process. A previously proposed multibody deuteron fusion model in solids is elaborated further to explain these anamalous results. A transient dynamics in metal deuterides is proposed to generate close pairs and clusters of deuterons with time-dependent deep atomic potential inducing a strong screening effect on Coulomb barrier penetration. Very approximate numerical estimations of reaction rates for the competing 2D, 3D, and 4D fusion processes in PdDx and TiDx are obtained with high-levels. Decay channels of virtual compound states, i.e., 4He*, 5Li*, 6Li*, 7Be*, and 8Be* by 2D, H+2D, 3D, H+3D, and 4D fusions, are discussed in detail to know the nuclear products. Major generation of 4He by H+2D, 3D, H+3D, and 4D processes are concluded. Identification of particle types and their specific released kinetic energies is given to explain measured charged-particle spectra by deuteron beam inplantation experiments. 28 refs., 16 figs
A class of stabilizing controllers for flexible multibody systems
Joshi, Suresh M.; Kelkar, Atul G.; Maghami, Peiman G.
1995-01-01
The problem of controlling a class of nonlinear multibody flexible space systems consisting of a flexible central body to which a number of articulated appendages are attached is considered. Collocated actuators and sensors are assumed, and global asymptotic stability of such systems is established under a nonlinear dissipative control law. The stability is shown to be robust to unmodeled dynamics and parametric uncertainties. For a special case in which the attitude motion of the central body is small, the system, although still nonlinear, is shown to be stabilized by linear dissipative control laws. Two types of linear controllers are considered: static dissipative (constant gain) and dynamic dissipative. The static dissipative control law is also shown to provide robust stability in the presence of certain classes of actuator and sensor nonlinearities and actuator dynamics. The results obtained for this special case can also be readily applied for controlling single-body linear flexible space structures. For this case, a synthesis technique for the design of a suboptimal dynamic dissipative controller is also presented. The results obtained in this paper are applicable to a broad class of multibody and single-body systems such as flexible multilink manipulators, multipayload space platforms, and space antennas. The stability proofs use the Lyapunov approach and exploit the inherent passivity of such systems.
A natural partitioning scheme for parallel simulation of multibody systems
Chiou, J. C.; Park, K. C.; Farhat, C.
1993-01-01
A parallel partitioning scheme based on physical-co-ordinate variables is presented to systematically eliminate system constraint forces and yield the equations of motion of multibody dynamics systems in terms of their independent coordinates. Key features of the present scheme include an explicit determination of the independent coordinates, a parallel construction of the null space matrix of the constraint Jacobian matrix, an easy incorporation of the previously developed two-stage staggered solution procedure and a Schur complement based parallel preconditioned conjugate gradient numerical algorithm.
Multibody interactions of actuated magnetic particles used as fluid drivers in microchannels
Derks, R.J.S.; Frijns, A.J.H.; Prins, M.W.J.; Dietzel, A.H.
2010-01-01
The forced motion of superparamagnetic particles and their multibody interactions are studied in view of the application as integrated fluid drivers in microchannel systems. Previous studies on particle manipulation in open fluid volumes serve as our starting point for the analysis of particle dynam
李延春; 刘鸿; 黄旭日; 孙家锺
2011-01-01
利用多体耗散粒子动力学(Multibody Dissipative Particle Dynamics,Multibody DPD)方法研究了在溶剂蒸发条件下,嵌段共聚物在表面自组装形成薄膜的过程,分别考虑了两嵌段共聚物和三嵌段共聚物及不同组成对薄膜形貌的影响.模拟得到了无序状薄膜和层状薄膜,并计算了这些薄膜的序参量和薄膜厚度随时间的演化.结果表明,嵌段共聚物的组成对薄膜厚度几乎没有影响,当某种组分的链段很短时,只能形成序参量较小的无序薄膜,相反,则可以得到序参量较大的层状薄膜.%We use multibody dissipative particle dynamics method to investigate the thin film formed by self-assembly of block copolymer on attractive surface under evaporation condition. We consider the composition effect on the morphology of diblock and triblock copolymer thin film. We obtain disorder and lamellar morphology and give the time evolution of the order parameter and the film thickness. The results reveal that the composition of block copolymer effects on the order parameter rather than the film thickness. If one of the compositions is shorter, it is easily to form disorder morphology with lower order parameter. On the other hand, it is easily to form lamellar morphology with higher order parameter.
On validation of multibody musculoskeletal models
Lund, Morten Enemark; de Zee, Mark; Andersen, Michael Skipper; Rasmussen, John
2012-01-01
This paper reviews the opportunities to validate multibody musculoskeletal models in view of the current transition of musculoskeletal modelling from a research topic to a practical simulation tool in product design, healthcare and other important applications. This transition creates a new need...... practical steps for improvement of the validation of multibody musculoskeletal models are pointed out and directions for future research in the field are proposed. It is our hope that a more structured approach to model validation can help to improve the credibility of musculoskeletal models....
Stein, Michael Ashley; Silvers, Anita; Areheart, Bradley A.; Francis, Leslie P.
2014-01-01
This Article contends that workplace accommodations should be predicated on need or effectiveness instead of group identity status. It proposes that, in principle, “accommodating every body” be achieved by extending Americans with Disabilities Act type reasonable accommodation to all work-capable members of the general population for whom accommodation is necessary to enable their ability to work. Doing so shifts the focus of accommodation disputes from the contentious identity-based contours...
Eliminating Computational Instability In Multibody Simulations
Watts, Gaines L.
1994-01-01
TWOBODY implements improved version of Lagrange multiplier method. Program ultilizes programming technique eliminating computational instability in multibody simulations in which Lagrange multipliers used. In technique, one uses constraint equations, instead of integration, to determine coordinates that are not independent. To illustrate technique, it includes simple mathematical model of solid rocket booster and parachute connected by frictionless swivel. Written in FORTRAN 77.
Multibody quark forces in quantum chromodynamics
A general exposition of multibody quark forces in quantum chromodynamics is given. The low-energy Hamiltonian involves two-, three-, and four-body quark potentials. We compute the short-range three- and four-body potentials to lowest-order terms in v/c and show that the former does not contribute to the mass of baryons
Analysis of floating offshore wind turbine hydrodynamics using coupled CFD and multibody methods
Beyer, Friedemann; Arnold, Matthias; Cheng, Po Wen
2013-01-01
The focus of this study is the application of a higher order hydrodynamic modeling technique for the analysis of Floating Offshore Wind Turbine dynamics. This approach is based on a coupling between Multibody and Computational Fluid Dynamics methods. Results of the translational and rotational platform displacement are presented for a basic free-decay simulation in surge direction in still water. A comparison to linear hydrodynamics is presented. Additional, pressure mapping is demonstrated.
Active vibration control of multibody system with quick startup and brake based on active damping
TANG Hua-ping; TANG Yun-jun; TAO Gong-an
2006-01-01
A kind of active vibration control method was presented based on active damping and optimization design for driving load of multibody system with quick startup and brake. Dynamical equation of multibody system with quick startup and brake and piezoelectric actuators intelligent structure was built. The optimum driving load was calculated by applying the presented method. The self-sensing and self-tuning closed-loop active vibration control in quick startup and brake process was realized. The control algorithm, using local velocity negative feedback, i.e. the output of a sensor only affects the output of the actuator collocated, can induce damping effectively to actively suppress the system vibration. Based on the optimization design for driving load of multibody system with quick startup and bake, the active damping of piezoelectric actuators intelligent structure was used to farther suppress the vibration of system. Theoretical analysis and calculation of numerical show that the proposed method makes the vibration of system decrease more than the optimal design method for driving load of multibody system.
Surrounding rock deformation analysis of underground caverns with multi-body finite element method
Wan-jin LIANG
2009-09-01
Full Text Available Discontinuous deformation problems are common in rock engineering. Numerical analysis methods based on system models of the discrete body can better solve these problems. One of the most effective solutions is discontinuous deformation analysis (DDA method, but the DDA method brings about rock embedding problems when it uses the strain assumption in elastic deformation and adopts virtual springs to simulate the contact problems. The multi-body finite element method (FEM proposed in this paper can solve the problems of contact and deformation of blocks very well because it integrates the FEM and multi-body system dynamics theory. It is therefore a complete method for solving discontinuous deformation problems through balance equations of the contact surface and for simulating the displacement of whole blocks. In this study, this method was successfully used for deformation analysis of underground caverns in stratified rock. The simulation results indicate that the multi-body FEM can show contact forces and the stress states on contact surfaces better than DDA, and that the results calculated with the multi-body FEM are more consistent with engineering practice than those calculated with DDA method.
Symplectic reduction of holonomic open-chain multi-body systems with constant momentum
Chhabra, Robin; Emami, M. Reza
2015-03-01
This paper presents a two-step symplectic geometric approach to the reduction of Hamilton's equation for open-chain, multi-body systems with multi-degree-of-freedom holonomic joints and constant momentum. First, symplectic reduction theorem is revisited for Hamiltonian systems on cotangent bundles. Then, we recall the notion of displacement subgroups, which is the class of multi-degree-of-freedom joints considered in this paper. We briefly study the kinematics of open-chain multi-body systems consisting of such joints. And, we show that the relative configuration manifold corresponding to the first joint is indeed a symmetry group for an open-chain multi-body system with multi-degree-of-freedom holonomic joints. Subsequently using symplectic reduction theorem at a non-zero momentum, we express Hamilton's equation of such a system in the symplectic reduced manifold, which is identified by the cotangent bundle of a quotient manifold. The kinetic energy metric of multi-body systems is further studied, and some sufficient conditions are introduced, under which the kinetic energy metric is invariant under the action of a subgroup of the configuration manifold. As a result, the symplectic reduction procedure for open-chain, multi-body systems is extended to a two-step reduction process for the dynamical equations of such systems. Finally, we explicitly derive the reduced dynamical equations in the local coordinates for an example of a six-degree-of-freedom manipulator mounted on a spacecraft, to demonstrate the results of this paper.
KEY TECHNIQUES OF MULTI-BODY MODELING OF OCCUPANT RESTRAINT SYSTEM OF VEHICLE SIDE IMPACT
ZHANG Junyuan; ZHANG Min; DING Rufang; QIU Shaobo; ZHANG Yu; LI Hongjian
2006-01-01
Based on multi-body dynamics, the simulation models of auto-side structures and occupant's dynamic responses are set up, using the occupant injury simulation software MADYMO3D. These models include auto-body structure, impact barrier, seat and dummy. Definitions of multi-body and joints and dynamics properties of joints based on FE combination models, of model setup are introduced. Kelvin element of MADYMO is introduced to show the force action between non-adjoining rigid bodies, too. Then all examples of the methods mentioned are given. By the comparison of simulation and real test, the contract curves between simulation and real test for main structures and biology mechanics properties of dummy are obtained. The result shows the accuracy and validity of the models.
Research on Modal Parameters Identification of Parallel Manipulator with Flexible Multi-Body System
Chunxia Zhu
2013-03-01
Full Text Available In this study, a new method based on simulation is proposed. And the analysis method based on flexible multi-body system of parallel manipulator is provided in the same time. Firstly, modal analysis principle of parallel manipulator was analyzed in theory and the parameters of dynamic characteristic were identified by theoretical analysis. Then vibration model of flexible multi-body for parallel manipulator was built in virtual prototype software and formed vibration system of rigid and flexible coupling for simulation analysis and from the simulation results got the value of parameters for vibration characteristic of parallel manipulator. And the dynamic characteristic parameters were identified according to the simulation results. The results showed that the simulation method and result dates are validated. So the integration simulation method is feasible, which can provide reference for dynamic optimal design.
Engine Multi-Body with Flexible Crankshaft Modeling and Numerical Simulation
LIU Yong-hong; WANG Hong; GU Hong-liang; ZHANG You-yun
2005-01-01
A multi-body model of engine system with flexible crankshaft was presented in this paper to analyze the dynamic behavior of an internal combustion engine. The flexible crankshaft structural dynamics was coupled with the main bearing hydrodynamic lubrication in this model by a system approach. An application of an I4 engine was given to show this sophisticated simulation model and to predict the loads and the orbit plots in the journal bearings by the dynamic response of the multi-body engine system with flexible crankshaft. The numerical results show the capabilities and significance of the flexible crankshaft in this system. The objective of the research is to provide the scientific guidance for design and maintenance of the internal combustion engine.
Accommodation in mild traumatic brain injury
Wesley Green, MS
2010-05-01
Full Text Available Accommodative dysfunction in individuals with mild traumatic brain injury (mTBI can have a negative impact on quality of life, functional abilities, and rehabilitative progress. In this study, we used a range of dynamic and static objective laboratory and clinical measurements of accommodation to assess 12 adult patients (ages 18-40 years with mTBI. The results were compared with either 10 control subjects with no visual impairment or normative literature values where available. Regarding the dynamic parameters, responses in those with mTBI were slowed and exhibited fatigue effects. With respect to static parameters, reduced accommodative amplitude and abnormal accommodative interactions were found in those with mTBI. These results provide further evidence for the substantial impact of mTBI on accommodative function. These findings suggest that a range of accommodative tests should be included in the comprehensive vision examination of individuals with mTBI.
Verification of component mode techniques for flexible multibody systems
Wiens, Gloria J.
1990-01-01
Investigations were conducted in the modeling aspects of flexible multibodies undergoing large angular displacements. Models were to be generated and analyzed through application of computer simulation packages employing the 'component mode synthesis' techniques. Multibody Modeling, Verification and Control Laboratory (MMVC) plan was implemented, which includes running experimental tests on flexible multibody test articles. From these tests, data was to be collected for later correlation and verification of the theoretical results predicted by the modeling and simulation process.
Transfer matrix method for multibody systems for piezoelectric stack actuators
In order to achieve a large displacement output from a piezoelectric actuator, we realized the piezoelectric stack actuator (PSA) by mechanically layering/stacking multi-chip piezoelectric wafers in a series and electrically connecting the electrodes in parallel. In this paper, in order to accurately model the hysteresis and the dynamic characteristics of a PSA, the transfer matrix method for multibody systems (MSTMM) was adopted to describe the dynamic characteristics, and the Bouc-Wen hysteresis operator was used to represent the hysteresis. The vibration characteristics of a PSA and a piezo-actuated positioning mechanism (PPM) are derived and analyzed by the MSTMM; then, the dynamic responses of the PSA and the PPM are calculated. The experimental results show that the new method can accurately portray the hysteresis and the dynamic characteristics of a PSA and a PPM. On one hand, if we use this method to model the dynamic response of the PSA and the PPM, the PSA can be considered as a flexible body, as opposed to a mass-spring-damper system, which is in better agreement with the actual condition. On the other hand, the global dynamics equation is not needed for the study of system dynamics, and the dynamics equation has a small-sized matrix and a higher computational speed. Therefore, this method gives a broad range of possibilities for model-based controller design. (paper)
Transfer matrix method for multibody systems for piezoelectric stack actuators
Zhu, Wei; Chen, Gangli; Bian, Leixiang; Rui, Xiaoting
2014-09-01
In order to achieve a large displacement output from a piezoelectric actuator, we realized the piezoelectric stack actuator (PSA) by mechanically layering/stacking multi-chip piezoelectric wafers in a series and electrically connecting the electrodes in parallel. In this paper, in order to accurately model the hysteresis and the dynamic characteristics of a PSA, the transfer matrix method for multibody systems (MSTMM) was adopted to describe the dynamic characteristics, and the Bouc-Wen hysteresis operator was used to represent the hysteresis. The vibration characteristics of a PSA and a piezo-actuated positioning mechanism (PPM) are derived and analyzed by the MSTMM; then, the dynamic responses of the PSA and the PPM are calculated. The experimental results show that the new method can accurately portray the hysteresis and the dynamic characteristics of a PSA and a PPM. On one hand, if we use this method to model the dynamic response of the PSA and the PPM, the PSA can be considered as a flexible body, as opposed to a mass-spring-damper system, which is in better agreement with the actual condition. On the other hand, the global dynamics equation is not needed for the study of system dynamics, and the dynamics equation has a small-sized matrix and a higher computational speed. Therefore, this method gives a broad range of possibilities for model-based controller design.
Factorization in Multibody Radiative B Decays
We study the radiative decays B->Kπγ and B->Kπe+e-, including both K* resonant contributions and non-resonant ones. We describe new soft pion theorems with which we compute certain non-resonant multibody amplitudes. We present results for CP asymmetry in B->Kπγ and for the forward-backward asymmetry in B->Kπe+e-
An Efficient Solution Method for Multibody Systems with Loops Using Multiple Processors
Ghosh, Tushar K.; Nguyen, Luong A.; Quiocho, Leslie J.
2015-01-01
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.
Applications of Lie Group Theory to the Modeling and Control of Multibody Systems
This paper reviews our research activities concerning the modeling and control of rigid and elastic joint multibody mechanical systems, including some investigations into nonholonomic systems. Bearing in mind the different parameterizations of the rotation group in three-dimensional space SO(3), and the fact that the properties of the parameterization more or less influence the efficiency of the dynamics model, here the so-called vector parameter is used for parallel considerations of rigid body motion and of rigid and elastic joint multibody mechanical systems. Besides the fundamental role of this study, the vector-parameter approach is efficient in its computational aspect and quite convenient for real time simulation and control. The consideration of the mechanical system on the configuration space of pure vector parameters with a group structure opens the possibilities for the Lie group theory to be applied in problems of dynamics and control
Inverse problem for multi-body interaction of nonlinear waves
Marruzzo, Alessia; Antenucci, Fabrizio; Pagnani, Andrea; Leuzzi, Luca
2016-01-01
The inverse problem is studied in multi-body systems with nonlinear dynamics representing, e.g., phase-locked wave systems, standard multimode and random lasers. Using a general model for four-body interacting complex-valued variables we test two methods based on pseudolikelihood, respectively with regularization and with decimation, to determine the coupling constants from sets of measured configurations. We test statistical inference predictions for increasing number of sampled configurations and for an externally tunable {\\em temperature}-like parameter mimicing real data noise and helping minimization procedures. Analyzed models with phasors and rotors are generalizations of problems of real-valued spherical problems (e.g., density fluctuations), discrete spins (Ising and vectorial Potts) or finite number of states (standard Potts): inference methods presented here can, then, be straightforward applied to a large class of inverse problems.
Optimization of actuator/sensor position of multi-body system with quick startup and brake
无
2007-01-01
A new method was put forward to optimize the position of actuator/sensor of multi-body system with quick startup and brake. Dynamical equation was established for the system with intelligent structure of piezoelectric actuators. According to the property of the modes varying with time, the performance index function was developed based on the optimal configuration principle of energy maximal dissipation, and the relevant optimal model was obtained. According to its characteristic, a float-encoding genetic algorithm, which is efficient, simple and excellent for solving the global-optimal solution of this problem, was adopted. Taking the plane manipulator as an example, the result of numerical calculation shows that, after the actuator/sensor position being optimized,the vibration amplitude of the multi-body system is reduced by 35% compared with that without optimization.
Physical essence of the multibody contact-sliding at atomic scale
Han, Xuesong
2014-01-01
Investigation the multibody contact-sliding occurred at atomic discrete contact spot will play an important role in determine the origin of tribology behavior and evaluates the micro-mechanical property of nanomaterials and thus optimizing the design of surface texture. This paper carries out large scale parallel molecular dynamics simulation on contact-sliding at atomic scale to uncover the special physical essence. The research shows that some kind of force field exists between nanodot pair and the interaction can be expressed by the linear combination of exponential function while the effective interaction distance limited in 1 angstrom for nanodot with several tens of nanometer diameter. The variation tendency about the interaction force between nanodot array is almost the same between nanodot pairs and thus the interaction between two nanodot array can be characterized by parallel mechanical spring. Multibody effect which dominates the interaction between atoms or molecules will gradually diminish with the increasing of length scales.
Three-dimensional formulation of rigid-flexible multibody systems with flexible beam elements
Multibody systems generally contain solids with appreciable deformations and which decisively influence the dynamics of the system. These solids have to be modeled by means of special formulations for flexible solids. At the same time, other solids are of such a high stiffness that they may be considered rigid, which simplifies their modeling. For these reasons, for a rigid-flexible multibody system, two types of formulations coexist in the equations of the system. Among the different possibilities provided in the literature on the material, the formulation in natural coordinates and the formulation in absolute nodal coordinates are utilized in this paper to model the rigid and flexible solids, respectively. This paper contains a mixed formulation based on the possibility of sharing coordinates between a rigid solid and a flexible solid. The global mass matrix of the system is shown to be constant and, in addition, many of the constraint equations obtained upon utilizing these formulations are linear and can be eliminated
DAEs and PDEs in elastic multibody systems
Simeon, B.
1998-12-01
Elastic multibody systems arise in the simulation of vehicles, robots, air- and spacecrafts. They feature a mixed structure with differential-algebraic equations (DAEs) governing the gross motion and partial differential equations (PDEs) describing the elastic deformation of particular bodies. We introduce a general modelling framework for this new application field and discuss numerical simulation techniques from several points of view. Due to different time scales, singular perturbation theory and model reduction play an important role. A slider crank mechanism with a 2D FE grid for the elastic connecting rod illustrates the techniques.
Drop Test Simulation for An Aircraft Landing Gear Via Multi-Body Approach
Leo Romeo Di
2014-08-01
Full Text Available This work deals with the effectiveness of a multi-body approach for the study of the dynamic behavior of a fixed landing gear, especially the research project concerns the drop tests of the AP.68 TP-300 aircraft. First, the Digital Mock-up of the of landing gear system in a C.A.D. software has been created, then the experimental structural stiffness of the leaf spring has been validated using the FEM tools MSC. Patran/Nastran. Finally, the entire model has been imported in MSC.ADAMS environment and, according to the certifying regulations, several multi-body simulations have been performed varying the heights of fall and the weights of the system. The results have shown a good correlation between numerical and experimental tests, thus demonstrating the potential of a multi-body approach. Future development of the present activity will probably be an application of the methodology, herein validated, to other cases for a more extensive validation of its predictive power and development of virtual certification procedures.
A minimum state multibody/FEM approach for modeling flexible orbiting space systems
Pisculli, A.; Gasbarri, P.
2015-05-01
In the past the deployment of space structures has widely been analyzed by using multibody formulations. The two leading approaches are usually based on the Newton-Euler (NE) formulation and Euler-Lagrange (EL) formulation. Both of them present advantages and drawbacks. The ideal approach for describing multi-body systems can be represented by a combination between NE and EL formulations. This can be obtained by considering the NE formulation for assembling the equation of motion and then by defining the ODE governing equations with the use of a minimum set of variables. In this paper the authors present a mixed NE/EL formulation suitable for synthesizing optimal control strategies during the deploying maneuvers of robotic arms or solar arrays. The proposed method has two main characteristics: (i) the reference frame, which all the bodies motions are referred to, is a floating reference frame attached to the orbiting base platform body; (ii) it leads to a more organic formulation which makes a shifting from the NE to the EL formulations possible, through the use of a Jacobian matrix. In the present work this mixed formulation is derived to describe a fully elastic multi-body spacecraft. Furthermore the presented formulation, complemented with gravity, gravity gradient and generalized gravitational modal forces, will be used to study the dynamic behavior of an orbiting manipulator with flexible appendages. Finally a Reaction Null/Jacobian Transpose control strategy will be applied to control and deploy the robotic arms to grasp an orbiting flexible spacecraft.
Integrated Aeromechanics with Three-Dimensional Solid-Multibody Structures
Datta, Anubhav; Johnson, Wayne
2014-01-01
A full three-dimensional finite element-multibody structural dynamic solver is coupled to a three-dimensional Reynolds-averaged Navier-Stokes solver for the prediction of integrated aeromechanical stresses and strains on a rotor blade in forward flight. The objective is to lay the foundations of all major pieces of an integrated three-dimensional rotor dynamic analysis - from model construction to aeromechanical solution to stress/strain calculation. The primary focus is on the aeromechanical solution. Two types of three-dimensional CFD/CSD interfaces are constructed for this purpose with an emphasis on resolving errors from geometry mis-match so that initial-stage approximate structural geometries can also be effectively analyzed. A three-dimensional structural model is constructed as an approximation to a UH-60A-like fully articulated rotor. The aerodynamic model is identical to the UH-60A rotor. For preliminary validation measurements from a UH-60A high speed flight is used where CFD coupling is essential to capture the advancing side tip transonic effects. The key conclusion is that an integrated aeromechanical analysis is indeed possible with three-dimensional structural dynamics but requires a careful description of its geometry and discretization of its parts.
马戎; 周发
2012-01-01
Based on the software of AVL Excite Power Unit, Muhi-body dynamic method is used to calculate the connecting rod small end force of one cycle. Then Abaqus is used to finite element analysis of connecting rod, where three-dimensional stress distribution can be got. Finally import the results of multi-body dynamic calculation and finite-element analysis to MSC.Fatigue software to calculate the fatigue safety factor of connecting-rod. These all may establish a basis to optimize the design of engine connecting-rod.%基于AVL公司的Excite Power Unit软件进行连杆的多体动力学计算，得到连杆小头在发动机一个循环下的一维受力曲线，然后采用Abaqus软件进行连杆的有限元分析，得到连杆的三维应力分布，最后利用MSC.Fatigue软件导入多体动力学计算结果和有限元应力分布结果进行疲劳安全系数计算，得到疲劳安全系数的分布，从而为发动机连杆的优化设计建立基础。
Reasonable Accommodation Information Tracking System
U.S. Environmental Protection Agency — The Reasonable Accommodation Information Tracking System (RAITS) is a case management system that allows the National Reasonable Accommodation Coordinator (NRAC)...
Criteria of benchmark selection for efficient flexible multibody system formalisms
Valášek M.
2007-10-01
Full Text Available The paper deals with the selection process of benchmarks for testing and comparing efficient flexible multibody formalisms. The existing benchmarks are briefly summarized. The purposes for benchmark selection are investigated. The result of this analysis is the formulation of the criteria of benchmark selection for flexible multibody formalisms. Based on them the initial set of suitable benchmarks is described. Besides that the evaluation measures are revised and extended.
ROBOTRAN: a powerful symbolic gnerator of multibody models
N. Docquier
2013-05-01
Full Text Available The computational efficiency of symbolic generation was at the root of the emergence of symbolic multibody programs in the eighties. At present, it remains an attractive feature of it since the exponential increase in modern computer performances naturally provides the opportunity to investigate larger systems and more sophisticated models for which real-time computation is a real asset. Nowadays, in the context of mechatronic multibody systems, another interesting feature of the symbolic approach appears when dealing with enlarged multibody models, i.e. including electrical actuators, hydraulic devices, pneumatic suspensions, etc. and requiring specific analyses like control and optimization. Indeed, since symbolic multibody programs clearly distinguish the modeling phase from the analysis process, extracting the symbolic model, as well as some precious ingredients like analytical sensitivities, in order to export it towards any suitable environment (for control or optimization purposes is quite straightforward. Symbolic multibody model portability is thus very attractive for the analysis of mechatronic applications. In this context, the main features and recent developments of the ROBOTRAN software developed at the Université catholique de Louvain (Belgium are reviewed in this paper and illustrated via three multibody applications which highlight its capabilities for dealing with very large systems and coping with multiphysics issues.
Analysis and design of planar multibody systems with revolute joint wear
Mukras, Saad M.
Wear prediction on the components of a mechanical system without considering the system as a whole will, in most cases, lead to inaccurate predictions. This is because the wear is directly affected by the system dynamics which evolves simultaneously with the wear. In addition, the contact condition (regions of contact for the wearing bodies) also depends on the system dynamics and, in most cases, can only be determined in a multibody dynamics framework. In this work, a procedure to analyze planar multibody systems in which wear is present at one or more revolute joints is presented. The analysis involves modeling multibody systems with revolute joints that consist of clearance. Wear can then be incorporated into the system dynamic analysis by allowing the size and shape of the clearance to evolve as dictated by wear. An iterative wear prediction procedure based on the Archard's wear model is used to compute the wear as a function of the evolving dynamics and tribological data. In this framework, two procedures for the analysis of planar multibody systems with joint wear are developed. In the first procedure contact force at the concerned joint is determined using a contact force law and the wear prediction is based on the finite element method. In the second procedure, contact force determination and the wear prediction are based on the elastic foundation model. The two procedures are validated by comparing the wear predictions with wear on an experimental slider-crank mechanism. The experimental slider-crank is also used as a reference to assess the performance of the two models. It turns out that the procedure based on the finite element method provides reasonably accurate predictions for both wear profile and wear volume/mass whereas the procedure based on the elastic foundation model provides reasonably accurate estimates on the wear volume/mass, is computationally faster but provides progressively poor estimates on the wear profile. Finally an example is
Lum, Lydia
2007-01-01
Healthy gourmet offerings are fast becoming the norm at college dining halls around the country. At a time when the children of Baby Boomers are hitting higher education in record numbers, college officials have scrambled to accommodate their picky palates and their insistence for healthier meals than were served to past generations. At the same…
Drop Test Simulation for An Aircraft Landing Gear Via Multi-Body Approach
Leo Romeo Di; Fenza Angelo De; Barile Marco; Lecce Leonardo
2014-01-01
This work deals with the effectiveness of a multi-body approach for the study of the dynamic behavior of a fixed landing gear, especially the research project concerns the drop tests of the AP.68 TP-300 aircraft. First, the Digital Mock-up of the of landing gear system in a C.A.D. software has been created, then the experimental structural stiffness of the leaf spring has been validated using the FEM tools MSC. Patran/Nastran. Finally, the entire model has been imported in MSC.ADAMS environme...
Heat flux expressions are derived for multibody potential systems by extending the original Hardy's methodology and modifying Admal & Tadmor's formulas. The continuum thermomechanical quantities obtained from these two approaches are easy to compute from molecular dynamics (MD) results, and have been tested for a constant heat flux model in two distinctive systems: crystalline iron and polyethylene (PE) polymer. The convergence criteria and affecting parameters, i.e. spatial and temporal window size, and specific forms of localization function are found to be different between the two systems. The conservation of mass, momentum, and energy are discussed and validated within this atomistic–continuum bridging
Fu, Yao; Song, Jeong-Hoon
2015-08-01
Heat flux expressions are derived for multibody potential systems by extending the original Hardy's methodology and modifying Admal & Tadmor's formulas. The continuum thermomechanical quantities obtained from these two approaches are easy to compute from molecular dynamics (MD) results, and have been tested for a constant heat flux model in two distinctive systems: crystalline iron and polyethylene (PE) polymer. The convergence criteria and affecting parameters, i.e. spatial and temporal window size, and specific forms of localization function are found to be different between the two systems. The conservation of mass, momentum, and energy are discussed and validated within this atomistic-continuum bridging.
Generalized multibody computer simulations of plasma-wall desorption and energy-transfer processes
We present calculations that describe the kinematic factors influencing the recombinant desorption of hydrogen from metal surfaces and a preliminary study of the sputtering and possible recombination of subsurface hydrogen following surface impact of a flux of ions. A new multi-body computer molecular dynamics method used in these studies is discussed. In the first instance we are able to describe both a scattering channel in which backscattering is the dominant result and also a reactive channel leading to molecular formation with the molecules leaving importance of these processes to negative ion formation is discussed
Fu, Yao, E-mail: Yao.Fu@colorado.edu; Song, Jeong-Hoon, E-mail: JH.Song@colorado.edu
2015-08-01
Heat flux expressions are derived for multibody potential systems by extending the original Hardy's methodology and modifying Admal & Tadmor's formulas. The continuum thermomechanical quantities obtained from these two approaches are easy to compute from molecular dynamics (MD) results, and have been tested for a constant heat flux model in two distinctive systems: crystalline iron and polyethylene (PE) polymer. The convergence criteria and affecting parameters, i.e. spatial and temporal window size, and specific forms of localization function are found to be different between the two systems. The conservation of mass, momentum, and energy are discussed and validated within this atomistic–continuum bridging.
Fixation by active accommodation
Pahlavan, Kourosh; Uhlin, Tomas; Eklundh, Jan-Olof
1992-11-01
The field of computer vision has long been interested in disparity as the cue for the correspondence between stereo images. The other cue to correspondence, blur, and the fact that vergence is a combination of the two processes, accommodative vergence and disparity vergence, have not been equally appreciated. Following the methodology of active vision that allows the observer to control all his visual parameters, it is quite natural to take advantage of the powerful combination of these two processes. In this article, we try to elucidate such an integration and briefly analyze the cooperation and competition between accommodative vergence and disparity vergence on one hand and disparity and blur stimuli on the other hand. The human fixation mechanism is used as a guide-line and some virtues of this mechanism are used to implement a model for vergence in isolation. Finally, some experimental results are reported.
Accommodating Different Learning Styles
Ovesen, Nis
2014-01-01
facilitating learning across this diverse group of students. The paper is based on a survey with 99 former participants of the course as respondents. The results of the survey imply that certain types of students benefit from the combination of mathematical theory and practical exercises related to basic...... shapes and form, whereas other types of students do not. The results thereby underpin that learning is typically based on individual preferences and that cross-disciplinary educational programmes have to accommodate this....
Bridging as Coercive Accommodation
Bos, J W; Mineur, A M; Bos, Johan; Buitelaar, Paul; Mineur, Anne-Marie
1995-01-01
In this paper we discuss the notion of "bridging" in Discourse Representation Theory as a tool to account for discourse referents that have only been established implicitly, through the lexical semantics of other referents. In doing so, we use ideas from Generative Lexicon theory, to introduce antecedents for anaphoric expressions that cannot be "linked" to a proper antecedent, but that do not need to be "accommodated" because they have some connection to the network of discourse referents that is already established.
Multibody charmless b-hadron decays
Dujany, Giulio
2016-01-01
Multibody charmless b-hadron decays are a unique laboratory to probe CP violation, to look for effects of new physics and to provide insights into the hadronisation mechanism. The decay modes $\\Lambda_b^0 \\to \\Lambda K^+ K^-$, $\\Lambda_b^0 \\to \\Lambda K^+ \\pi^-$, $\\Lambda_b^0 \\to \\Lambda \\phi$ and $B_s^0 \\to K_{\\rm S}^0 K^*$ are observed for the first time by LHCb and their branching fractions are measured. Evidence is seen for the $\\Lambda_b^0 \\to \\Lambda \\pi^+ \\pi^-$ decay and limits are set for the decays $\\Xi_b^0\\to \\Lambda h^+ h^{(\\prime)-}$ and $B^0 \\to K_{\\rm S}^0 K^*$ . The phase-space integrated CP asymmetry parameters are measured for $\\Lambda_b^0 \\to \\Lambda K^+ K^-$ and $\\Lambda_b^0 \\to \\Lambda K^+ \\pi^-$ while several triple-product asymmetries are measured for $\\Lambda_b^0 \\to \\Lambda \\phi$. All these asymmetries are found to be compatible with zero.
K. Anandhanarayanan
2010-10-01
Full Text Available Grid-free solver has the ability to solve complex multi-body industrial problems with minimal effort. Grid-free Euler solver has been applied to number of multi-body aerospace vehicles using Chimera clouds of points including flight vehicle with fin deflection, nose fairing separation of hypersonic launch vehicle. A preprocessor has been developed to generate connectivity for multi-bodies using overlapped grids. Surface transpiration boundary condition has been implemented to model aerodynamic damping and to impose the relative velocity of moving components. Dynamic derivatives are estimated with reasonable accuracy and less effort using the grid-free Euler solver with the transpiration boundary condition. Further, the grid-free Euler solver has been integrated with six-degrees of freedom (6-DOF equations of motion to form store separation dynamics suite which has been applied to obtain the trajectory of a rail launch air-to-air-missile from a complex fighter aircraft.Defence Science Journal, 2010, 60(6, pp.653-662, DOI:http://dx.doi.org/10.14429/dsj.60.583
Accommodation facilities positioning
Dan PAUNA; Cornelia TUREAC
2014-01-01
This paper is based on the positioning concept as it was established in 1972 by Al Ries and Jack Trout as being a tangible good, a service, a company, an organism or even a person. Positioning does not mean what one does with the product but especially what the product represents according to the conception of the one prospecting the market.In this case the product accommodation, which is in fact a sum of complex services at the customers disposal, makes it impossible to compare on a certain ...
Nonverbal Accommodation in Healthcare Communication
D’Agostino, Thomas A.; Bylund, Carma L.
2013-01-01
This exploratory study examined patterns of nonverbal accommodation within healthcare interactions and investigated the impact of communication skills training and gender concordance on nonverbal accommodation behavior. The Nonverbal Accommodation Analysis System (NAAS) was used to code the nonverbal behavior of physicians and patients within 45 oncology consultations. Cases were then placed in one of seven categories based on patterns of accommodation observed across the interaction. Results...
Oliveira, Sílvia Margarida Gonçalves de; Jorge, Jorge; González-Méijome, José Manuel
2012-01-01
PURPOSE: The aim of the present study was to compare the accommodative response to the same visual content presented in two dimensions (2D) and stereoscopically in three dimensions (3D) while participants were either watching a television (TV) or Nintendo 3DS console. METHODS: Twenty-two university students, with a mean age of 20.3 ± 2.0 years (mean ± S.D.), were recruited to participate in the TV experiment and fifteen, with a mean age of 20.1 ± 1.5 years took part in the Nintendo 3DS co...
Zhuang, Fang-Fang; Wang, Qi
2014-06-01
An approach is proposed for modeling and analyses of rigid multibody systems with frictional translation joints and driving constraints. The geometric constraints of translational joints with small clearance are treated as bilateral constraints by neglecting the impact between sliders and guides. Firstly, the normal forces acting on sliders, the driving constraint forces (or moments) and the constraint forces of smooth revolute joints are all described by complementary conditions. The frictional contacts are characterized by a setvalued force law of Coulomb's dry friction. Combined with the theory of the horizontal linear complementarity problem (HLCP), an event-driven scheme is used to detect the transitions of the contact situation between sliders and guides, and the stick-slip transitions of sliders, respectively. And then, all constraint forces in the system can be computed easily. Secondly, the dynamic equations of multibody systems are written at the acceleration-force level by the Lagrange multiplier technique, and the Baumgarte stabilization method is used to reduce the constraint drift. Finally, a numerical example is given to show some non-smooth dynamical behaviors of the studied system. The obtained results validate the feasibility of algorithm and the effect of constraint stabilization.
Control of satellite imaging arrays in multi-body regimes
Millard, Lindsay Demoore
In the current study, control strategies are investigated for spacecraft imaging formations in multi-body regimes. The specific focus of the analysis is spacecraft motion as modeled in the circular restricted three-body problem, where two large gravitational bodies affect the motion of spacecraft in their vicinity. Five equilibrium points, or libration points, exist as solutions to the differential equations of motion in the circular restricted three-body problem. A specific periodic solution to these equations is an orbit in the vicinity of a libration point, i.e., a halo orbit. Halo orbits are ideal locations for spacecraft imaging arrays as they remain at a nearly fixed distance from the larger, or primary, bodies in the system. For example, if the Sun and Earth are considered the primary bodies, a spacecraft array can be placed near a libration point on the far side of the Earth, protected from the harsh radiation of the Sun at all times. A model of image reconstruction is developed for two common satellite imaging platform designs: an interferometric sparse aperture array and an occulter-telescope formation. The resolution of an image produced by an array is largely determined by the corresponding coverage of the (u, v) plane. The (u, v) plane is not a physical plane, but rather a relationship between frequencies and amplitudes in the Fourier expansion of the electromagnetic signal from the object of interest. Coverage of the (u, v) plane is derived based on several characteristics of the spacecraft configuration and the motion in physical space. Therefore, to determine formation motion history that may be advantageous to imaging, a mathematical model relating spacecraft motion in physical space to coverage of the (u, v) plane, and thus image reconstruction, is necessary. From these models, two control algorithms are developed that increase the resolution of the images produced by the formation while exploiting multi-body dynamics to reduce satellite fuel
Searches for CP violation in multibody D decays
Fu, J
2014-01-01
Multibody charm decays are a good place to search for $CP$ violation. The results of the LHCb collaboration in the decays of $D^+ \\to \\pi^- \\pi^+ \\pi^+$, $D^0 \\to \\pi^+ \\pi^- \\pi^+ \\pi^-$ and $D^0 \\to K^+ K^- \\pi^+ \\pi^-$ are presented.
Analytical and multibody modeling for the power analysis of standing jumps.
Palmieri, G; Callegari, M; Fioretti, S
2015-01-01
Two methods for the power analysis of standing jumps are proposed and compared in this article. The first method is based on a simple analytical formulation which requires as input the coordinates of the center of gravity in three specified instants of the jump. The second method is based on a multibody model that simulates the jumps processing the data obtained by a three-dimensional (3D) motion capture system and the dynamometric measurements obtained by the force platforms. The multibody model is developed with OpenSim, an open-source software which provides tools for the kinematic and dynamic analyses of 3D human body models. The study is focused on two of the typical tests used to evaluate the muscular activity of lower limbs, which are the counter movement jump and the standing long jump. The comparison between the results obtained by the two methods confirms that the proposed analytical formulation is correct and represents a simple tool suitable for a preliminary analysis of total mechanical work and the mean power exerted in standing jumps. PMID:24960184
Analysis of Large Flexible Body Deformation in Multibody Systems Using Absolute Coordinates
To consider large deformation problems in multibody system simulations a finite element approach, called absolute nodal coordinate.formulation,has been proposed. In this formulation absolute nodal coordinates and their material derivatives are applied to represent both deformation and rigid body motion. The choice of nodal variables allows a fully nonlinear representation of rigid body motion and can provide the exact rigid body inertia in the case of large rotations. The methodology is especially suited for but not limited to modeling of beams, cables and shells in multibody dynamics.This paper summarizes the absolute nodal coordinate formulation for a 3D Euler-Bernoulli beam model, in particular the definition of nodal variables, corresponding generalized elastic and inertia forces and equations of motion. The element stiffness matrix is a nonlinear function of the nodal variables even in the case of linearized strain/displacement relations. Nonlinear strain/displacement relations can be calculated from the global displacements using quadrature formulae.Computational examples are given which demonstrate the capabilities of the applied methodology. Consequences of the choice of shape.functions on the representation of internal forces are discussed. Linearized strain/displacement modeling is compared to the nonlinear approach and significant advantages of the latter, when using the absolute nodal coordinate formulation, are outlined
Multibody Parachute Flight Simulations for Planetary Entry Trajectories Using "Equilibrium Points"
Raiszadeh, Ben
2003-01-01
A method has been developed to reduce numerical stiffness and computer CPU requirements of high fidelity multibody flight simulations involving parachutes for planetary entry trajectories. Typical parachute entry configurations consist of entry bodies suspended from a parachute, connected by flexible lines. To accurately calculate line forces and moments, the simulations need to keep track of the point where the flexible lines meet (confluence point). In previous multibody parachute flight simulations, the confluence point has been modeled as a point mass. Using a point mass for the confluence point tends to make the simulation numerically stiff, because its mass is typically much less that than the main rigid body masses. One solution for stiff differential equations is to use a very small integration time step. However, this results in large computer CPU requirements. In the method described in the paper, the need for using a mass as the confluence point has been eliminated. Instead, the confluence point is modeled using an "equilibrium point". This point is calculated at every integration step as the point at which sum of all line forces is zero (static equilibrium). The use of this "equilibrium point" has the advantage of both reducing the numerical stiffness of the simulations, and eliminating the dynamical equations associated with vibration of a lumped mass on a high-tension string.
We report here the experimental results suggesting the occurrence of multibody nuclear reactions in metal deuterides under ion-beam irradiation and electrolysis. A meaningful increase of helium-4 was observed during electrolysis with the Pd-D2O system, while neutron emission was not observed. The D + D + D fusion, 3D → t + 3He + 9.5 MeV, has been observed repeatedly in deuteron-beam irradiation experiments with a TiDχ target. On the other hand, in proton-beam experiments with TiDχ, H + D + D-fusion: H + D + D → p + 4He + 23.8 MeV was observed. Considering this result, it seems that the 3D reaction occurred between two deuterons trapped closely in TiDχ and an incident particle of deuteron. The multibody nuclear reaction model can interpret both the results obtained in electrolysis and ion-beam experiments. It is considered that the lattice dynamics of metal deuteride is of key importance for inducing short-transient and closely packed d-d pairs and, thus, such fusions. (author)
During numerical forward dynamics of constrained multibody systems, a numerical violation of system kinematical constraints is the important issue that has to be properly treated. In this paper, the stabilized time-integration procedure, whose constraint stabilization step is based on the projection of integration results to underlying constraint manifold via post-integration correction of the selected coordinates is discussed. A selection of the coordinates is based on the optimization algorithm for coordinates partitioning. After discussing geometric background of the optimization algorithm, new formulae for optimized partitioning of the generalized coordinates are derived. Beside in the framework of the proposed stabilization algorithm, the new formulae can be used for other integration applications where coordinates partitioning is needed. Holonomic and non-holonomic systems are analyzed and optimal partitioning at the position and velocity level are considered further. By comparing the proposed stabilization method to other projective algorithms reported in the literature, the geometric and stabilization issues of the method are addressed. A numerical example that illustrates application of the method to constraint violation stabilization of non-holonomic multibody system is reported
[Research Progress in Measurement of Human Accommodative Amplitude].
Long, Erping; Lin, Haotian
2015-09-01
Accommodation is an important function of the human eye, which can change the parameters of ocular refractive system and also has a strong correlation with the development of myopia and presbyopia. Several subjective measurements have been applied in accommodation assessment such as push-up test, push-down test and minus-lens procedures. It can be measured objectively by measuring the change in refraction of the eye with dynamic retinoscopy or autorefractor. This article reviews the application of measurement of accommodative amplitude and research progress in accommodation, providing clinical information for further studies. PMID:26930838
Water Accommodation on Bare and Coated Ice
Kong, Xiangrui
2015-04-01
A good understanding of water accommodation on ice surfaces is essential for quantitatively predicting the evolution of clouds, and therefore influences the effectiveness of climate models. However, the accommodation coefficient is poorly constrained within the literature where reported values vary by up to three orders of magnitude. In addition, the complexity of the chemical composition of the atmosphere plays an important role in ice phase behavior and dynamics. We employ an environmental molecular beam (EMB) technique to investigate molecular water interactions with bare and impurity coated ice at temperatures from 170 K to 200 K. In this work, we summarize results of water accommodation experiments on bare ice (Kong et al., 2014) and on ice coated by methanol (Thomson et al., 2013), butanol (Thomson et al., 2013) and acetic acid (Papagiannakopoulos et al., 2014), and compare those results with analogous experiments using hexanol and nitric acid coatings. Hexanol is chosen as a complementary chain alcohol to methanol and butanol, while nitric acid is a common inorganic compound in the atmosphere. The results show a strong negative temperature dependence of water accommodation on bare ice, which can be quantitatively described by a precursor model. Acidic adlayers tend to enhance water uptake indicating that the system kinetics are thoroughly changed compared to bare ice. Adsorbed alcohols influence the temperature dependence of the accommodation coefficient and water molecules generally spend less time on the surfaces before desorbing, although the measured accommodation coefficients remain high and comparable to bare ice for the investigated systems. We conclude that impurities can either enhance or restrict water uptake in ways that are influenced by several factors including temperature and type of adsorbant, with potential implications for the description of ice particle growth in the atmosphere. This work was supported by the Swedish Research Council and
Multi-Body Analysis of the 1/5 Scale Wind Tunnel Model of the V-22 Tiltrotor
Ghiringhelli, G. L.; Masarati, P.; Mantegazza, P.; Nixon, M. W.
1999-01-01
The paper presents a multi-body analysis of the 1/5 scale wind tunnel model of the V-22 tiltrotor, the Wing and Rotor Aeroelastic Testing System (WRATS), currently tested at NASA Langley Research Center. An original multi-body formulation has been developed at the Dipartimento di Ingegneria Aerospaziale of the Politecnico di Milano, Italy. It is based on the direct writing of the equilibrium equations of independent rigid bodies, connected by kinematic constraints that result in the addition of algebraic constraint equations, and by dynamic constraints, that directly contribute to the equilibrium equations. The formulation has been extended to the simultaneous solution of interdisciplinary problems by modeling electric and hydraulic networks, for aeroservoelastic problems. The code has been tailored to the modeling of rotorcrafts while preserving a complete generality. A family of aerodynamic elements has been introduced to model high aspect aerodynamic surfaces, based on the strip theory, with quasi-steady aerodynamic coefficients, compressibility, post-stall interpolation of experimental data, dynamic stall modeling, and radial flow drag. Different models for the induced velocity of the rotor can be used, from uniform velocity to dynamic in flow. A complete dynamic and aeroelastic analysis of the model of the V-22 tiltrotor has been performed, to assess the validity of the formulation and to exploit the unique features of multi-body analysis with respect to conventional comprehensive rotorcraft codes; These are the ability to model the exact kinematics of mechanical systems, and the possibility to simulate unusual maneuvers and unusual flight conditions, that are particular to the tiltrotor, e.g. the conversion maneuver. A complete modal validation of the analytical model has been performed, to assess the ability to reproduce the correct dynamics of the system with a relatively coarse beam model of the semispan wing, pylon and rotor. Particular care has been used
Planar reorientation maneuvers of space multibody systems using internal controls
Reyhanoglu, Mahmut; Mcclamroch, N. H.
1992-01-01
In this paper a reorientation maneuvering strategy for an interconnection of planar rigid bodies in space is developed. It is assumed that there are no exogeneous torques, and torques generated by joint motors are used as means of control so that the total angular momentum of the multibody system is a constant, assumed to be zero in this paper. The maneuver strategy uses the nonintegrability of the expression for the angular momentum. We demonstrate that large-angle maneuvers can be designed to achieve an arbitrary reorientation of the multibody system with respect to an inertial frame. The theoretical background for carrying out the required maneuvers is briefly summarized. Specifications and computer simulations of a specific reorientation maneuver, and the corresponding control strategies, are described.
Multibody Finite Element Method and Application in Hydraulic Structure Analysis
Chao Su; Yebin Zhao; Yusong Jiang
2015-01-01
Multibody finite element method is proposed for analysis of contact problems in hydraulic structure. This method is based on the block theory of discontinuous deformation analysis (DDA) method and combines advantages of finite element method (FEM) and the displacement compatibility equation in classical elastic mechanics. Each single block is analyzed using FEM in corresponding local coordinate system and all contacting blocks need to satisfy the displacement compatibility requirement between...
Nonresonant multibody production by e+e- annihilation
Several aspects of nonresonant multibody production by e+e- annihilation are reviewed. At high energies the ratio of the hadronic cross section to the μ pair production cross section is consistent with being constant; inclusive distributions show approximate Bjorken scaling; and there is strong evidence for jet-like structure. The jets are produced with an angular distribution characteristic of that of pairs of spin 1/2 particles
Multibody model reduction by component mode synthesis and component cost analysis
Spanos, J. T.; Mingori, D. L.
1990-01-01
The classical assumed-modes method is widely used in modeling the dynamics of flexible multibody systems. According to the method, the elastic deformation of each component in the system is expanded in a series of spatial and temporal functions known as modes and modal coordinates, respectively. This paper focuses on the selection of component modes used in the assumed-modes expansion. A two-stage component modal reduction method is proposed combining Component Mode Synthesis (CMS) with Component Cost Analysis (CCA). First, each component model is truncated such that the contribution of the high frequency subsystem to the static response is preserved. Second, a new CMS procedure is employed to assemble the system model and CCA is used to further truncate component modes in accordance with their contribution to a quadratic cost function of the system output. The proposed method is demonstrated with a simple example of a flexible two-body system.
Multibody Modeling and Simulation for the Mars Phoenix Lander Entry, Descent and Landing
Queen, Eric M.; Prince, Jill L.; Desai, Prasun N.
2008-01-01
A multi-body flight simulation for the Phoenix Mars Lander has been developed that includes high fidelity six degree-of-freedom rigid-body models for the parachute and lander system. The simulation provides attitude and rate history predictions of all bodies throughout the flight, as well as loads on each of the connecting lines. In so doing, a realistic behavior of the descending parachute/lander system dynamics can be simulated that allows assessment of the Phoenix descent performance and identification of potential sensitivities for landing. This simulation provides a complete end-to-end capability of modeling the entire entry, descent, and landing sequence for the mission. Time histories of the parachute and lander aerodynamic angles are presented. The response of the lander system to various wind models and wind shears is shown to be acceptable. Monte Carlo simulation results are also presented.
Null Space Integration Method for Constrained Multibody Systems with No Constraint Violation
A method for integrating equations of motion of constrained multibody systems with no constraint violation is presented. A mathematical model, shaped as a differential-algebraic system of index 1, is transformed into a system of ordinary differential equations using the null-space projection method. Equations of motion are set in a non-minimal form. During integration, violations of constraints are corrected by solving constraint equations at the position and velocity level, utilizing the metric of the system's configuration space, and projective criterion to the coordinate partitioning method. The method is applied to dynamic simulation of 3D constrained biomechanical system. The simulation results are evaluated by comparing them to the values of characteristic parameters obtained by kinematics analysis of analyzed motion based unmeasured kinematics data
The systematics of the deexcitation of hot nuclei and the onset of multibody decay
Results from the asymmetric reactions 80 and 100 MeV/uLa + C are presented and compared to earlier work with the same system at 18 and 50 MeV/u. Fragment-fragment correlations, cross sections, and distributions in velocity space indicate the continued dominance of a quasi-binary decay mechanism with increased emission of light charged particles. The distributions in velocity also indicate a progression toward a ''fireball'' type of reaction mechanism. However, the angular distributions of the emitted fragments are incompatible with statistical production mechanisms that have successfully explained the lower energy results, and indicate the dynamical nature of the emission process. Dalitz plots of triple complex fragment coincidences are presented in order to investigate the nature of the multibody decays. 18 refs., 9 figs
Molecular dynamics simulations are used to study energy and momentum transfer of low-energy Ar atoms scattered from the Ni(001) surface. The investigation concentrates on the dependence of these processes on incident energy, angles of incidence and surface temperature. Energy transfer exhibits a strong dependence on the surface temperature, at incident energies below 500 meV, and incident angles close to specular incidence. Above 500 meV, the surface temperature dependence vanishes, and a limiting value in the amount of energy transferred to the surface is attained. Momentum exchange is investigated in terms of tangential and normal components. Both components exhibit a weak surface temperature dependence, but they have opposite behaviours at all incidence angles. In each component, momentum can be lost or gained following the interaction with the surface. (orig.)
Chirita, V.; Pailthorpe, B.A.; Collins, R.E. [Sydney Univ., NSW (Australia). School of Physics
1997-09-01
Molecular dynamics simulations are used to study energy and momentum transfer of low-energy Ar atoms scattered from the Ni(001) surface. The investigation concentrates on the dependence of these processes on incident energy, angles of incidence and surface temperature. Energy transfer exhibits a strong dependence on the surface temperature, at incident energies below 500 meV, and incident angles close to specular incidence. Above 500 meV, the surface temperature dependence vanishes, and a limiting value in the amount of energy transferred to the surface is attained. Momentum exchange is investigated in terms of tangential and normal components. Both components exhibit a weak surface temperature dependence, but they have opposite behaviours at all incidence angles. In each component, momentum can be lost or gained following the interaction with the surface. (orig.). 40 refs.
Developments in Accommodating Intraocular Lenses
Zeki Tunç
2012-07-01
Full Text Available Technical progress in cataract surgery has decreased the incidence of severe complications in this type of surgery. The introduction of micro incision cataract surgery (MICS (sub- 2.0 mm incision allow the surgeon to achieve better postoperative control of astigmatism and higherorder aberration (HOAs with minimum induction of both. It is believed that multifocal lenses provide very successful results, however, there are limitations to these. Implantation of accommodating intraocular lenses (IOLs is an option to treat presbyopia. The IOLs work by using the continued functionality of the ciliary muscle after cataract removal. Accommodating IOLs were designed to avoid the optical side effects of multifocal IOLs. Two main design concepts exist. First, axial shift concepts rely on anterior axial movement of one or two optics creating accommodative ability. Second, curvature change designs are designed to provide significant amplitudes of accommodation with little physical displacement. Accommodative IOLs to correct astigmatism and HOAs in the future are needed. (Turk J Ophthalmol 2012; 42: 288-93
MULTIBODY DYNAMIC ANALYSIS AND SIMULATION OF ENGINE MODEL
Dr. S.C. Jaiswal; Rahul Singh
2011-01-01
An assembly model for the internal combustion engine model has been proposed. The basis for the model is a study of earlier designs. The proposed design will run at a different speed, so the designers want to analyse the components, and in particular the stress in the connecting-rod, at the new speed. The designer's question is: at what speed can the engine be run without the stress in the connecting rodexceeding the permissible stress for the material?
Serial and parallel computation of Kane's equations for multibody dynamics
Fijany, Amir
1991-01-01
The analysis of the efficiency of algorithms resulting from Kane's Equation for serial and parallel computation of mass matrix is examined. The algorithms resulting from Kane's equation and Modified Kane's equations are detailed. An analysis was made of two classes of algorithms for computation of mass matrix: the Newton-Euler based algorithms and the Composite rigid body algorithms. An analysis was also made of the efficiency of different algorithms for serial and parallel computations. Conclusions are drawn and presented.
MULTIBODY DYNAMIC ANALYSIS AND SIMULATION OF ENGINE MODEL
Dr. S.C. Jaiswal
2011-10-01
Full Text Available An assembly model for the internal combustion engine model has been proposed. The basis for the model is a study of earlier designs. The proposed design will run at a different speed, so the designers want to analyse the components, and in particular the stress in the connecting-rod, at the new speed. The designer's question is: at what speed can the engine be run without the stress in the connecting rodexceeding the permissible stress for the material?
A standard-model self-consistent multibody bound-state Higgs scalar near the tt-bar threshold
We consider a simple model in which a non-elementary electroweak neutral Higgs scalar (H) can arise primarily as a multibody bound state which can include large numbers of constituent particles. Only standard-model elementary particles and effects with an energy scale ∼1 TeV have to be introduced explicitly. We do this by working with a non-perturbative analytic tt-bar scattering-amplitude unitarization scheme (basically a relativistic generalization of the usual Schroedinger equation), but with a strong high-energy (multibody) inelastic contribution added in, and with no divergences requiring arbitrary cut-offs or subtraction constants. The H itself is required to be simultaneously consistent in both mass and coupling with the exchange of the same H in the crossed channel when constructing the relativistic generalization of the input potential. The strong energy dependence of our amplitude near the tt-bar threshold then leads to a bound-state H with standard-model coupling and mass calculated to be near that tt-bar threshold, a result which is expected to persist for a broad class of similar models and suggests that alternative solutions may be obtained with H immediately below the ZZ or W+W- thresholds. We also find that our high-energy tt-bar scattering-amplitude multibody inelastic contribution can be constructed explicitly from the exchange of a Regge trajectory passing through the H and generated dynamically in the same way (but for unphysical angular momentum). Finally, we find that we can have massive W± and Z with longitudinal polarizations and approximately correct masses and standard-model couplings. These may be accompanied by higher-mass states with the same quantum numbers. (author)
Effect of geometric elastic non-linearities on the impact response of flexible multi-body systems
Bakr, E. M.; Shabana, A. A.
1987-02-01
The intermittent motion behavior of large scale geometrically non-linear flexible multi-body systems due to impact loading is investigated. Impacts and the associated impulsive forces are incorporated into the dynamic formulation by using a generalized momentum balance. The solution of the momentum equation provides the jump discontinuities in the system velocities and reaction forces. Flexible components in the system are discretized by using the finite element method. Because of the large rotations of the system components, a set of reference co-ordinates are employed to describe the motion of a selected body reference. The rigid body modes of the finite element shape functions are eliminated by using a set of reference conditions and accordingly a unique displacement field is defined. In order to account for the inertia and elastic non-linearities which are, respectively, the results of the large rotations and finite deformations, the system inertia and stiffness characteristics have to be iteratively updated. Two numerical examples of different nature are presented. The first example is a high speed slider crank mechanism with a flexible connecting rod. In the second example, however, the dynamic response of a flexible multi-body aircraft during the touch down impact is predicted.
Sensitivity analysis approach to multibody systems described by natural coordinates
Li, Xiufeng; Wang, Yabin
2014-03-01
The classical natural coordinate modeling method which removes the Euler angles and Euler parameters from the governing equations is particularly suitable for the sensitivity analysis and optimization of multibody systems. However, the formulation has so many principles in choosing the generalized coordinates that it hinders the implementation of modeling automation. A first order direct sensitivity analysis approach to multibody systems formulated with novel natural coordinates is presented. Firstly, a new selection method for natural coordinate is developed. The method introduces 12 coordinates to describe the position and orientation of a spatial object. On the basis of the proposed natural coordinates, rigid constraint conditions, the basic constraint elements as well as the initial conditions for the governing equations are derived. Considering the characteristics of the governing equations, the newly proposed generalized-α integration method is used and the corresponding algorithm flowchart is discussed. The objective function, the detailed analysis process of first order direct sensitivity analysis and related solving strategy are provided based on the previous modeling system. Finally, in order to verify the validity and accuracy of the method presented, the sensitivity analysis of a planar spinner-slider mechanism and a spatial crank-slider mechanism are conducted. The test results agree well with that of the finite difference method, and the maximum absolute deviation of the results is less than 3%. The proposed approach is not only convenient for automatic modeling, but also helpful for the reduction of the complexity of sensitivity analysis, which provides a practical and effective way to obtain sensitivity for the optimization problems of multibody systems.
A Lie group formulation of Kane's equations for multibody systems
We propose a Lie group approach to formulate the Kane's equations of motion for multibody systems. This approach regards the set of rigid body transformations as the special Euclidean group SE(3). By expressing rigid body displacements as exponential maps generated from the Lie algebra se(3), it subsequently manipulates rigid body kinematics as convenient matrix operations. With this approach, all the individual quantities involved in Kane's equations can be computed explicitly in an intrinsic manner, and the motion equations can be obtained systematically and efficiently. An example is presented to illustrate its use and effectiveness
Accommodation Assisting Glasses for Presbyopia
Fujita, Toyomi; Idesawa, Masanori
2002-10-01
We have considered the important functions for developing accommodation-assistance glasses which can assist eye focusing for aged person with presbyopia.We focused on keys to realize small and lightweight variable focusing lens and gaze distance detection. We devised new variable focusing lenses with control and gaze distance detection with a tunnel light path device. A prototype of glasses with devised elements was manufactured experimentally. From the result of trial use of them and experiments for evaluating characteristics,it was confirmed that proposed technologies were useful for realization of accommodation-assistance glasses.
A Generic Multibody Parachute Simulation Model
Neuhaus, Jason Richard; Kenney, Patrick Sean
2006-01-01
Flight simulation of dynamic atmospheric vehicles with parachute systems is a complex task that is not easily modeled in many simulation frameworks. In the past, the performance of vehicles with parachutes was analyzed by simulations dedicated to parachute operations and were generally not used for any other portion of the vehicle flight trajectory. This approach required multiple simulation resources to completely analyze the performance of the vehicle. Recently, improved software engineering practices and increased computational power have allowed a single simulation to model the entire flight profile of a vehicle employing a parachute.
Visual accommodation trainer-tester
Randle, Robert J. (Inventor)
1988-01-01
An apparatus for training the human visual accommodation system is described. Specifically, the apparatus is useful for training personnel to volitionally control focus to the far point (normally infinity) from a position of myopia due to functional causes. The functional causes could be due, for example, to a behavioral accommodative spasm or the effects of an empty field. The device may also be used to measure accommodation, the accommodation resting position and the near and far points of vision. The device comprises a number of optical elements arranged on a single optical axis. Several of the elements are arranged in order on a movable stage in fixed relationship to each other: a light source, a lens, a target, an aperture and/or a second lens. On a base and in fixed relationship to each other are eyepiece and third lens. A stage generates an image of the target and the stage is movable with respect to the base by means of a knob. The device is utilized for the various training and test functions by following a series of procedural steps, and interchanging the apertures as necessary for the selected procedure.
A Study on the Dynamic Analysis of A Tracked Vehicle for Ocean Mining on the Deep Seabed
Hyung-suk HAN
2003-01-01
A study is presented on the dynamic analysis of a tracked vehicle for mining on the deep seabed of very soft soil. Equations for the interaction between the track and extremely soft seabed are employed to develop a track/soil interaction module called TVAS. The vehicle is modeled as a multibody dynamic system by the use of a multibody dynamic analysis program. The module developed is cooperated with the multibody dynamic analysis program with a user-defined subroutine. The dynamic behavior and the conceptual design of the mining vehicle on the deep seabed are investigated.
A 3D Finite Element Method for Flexible Multibody Systems
An efficient finite element (FE) formulation for the simulation of multibody systems is derived from Hamilton's principle. According to the classical assumptions of multibody systems, a large rotation formulation has been chosen, where large rotations and large displacements, but only small deformations of the single bodies are taken into account. The strain tensor is linearized with respect to a co-rotated frame. The present approach uses absolute coordinates for the degrees of freedom and forms an alternative to the floating frame of reference formulation that is based on relative coordinates and describes deformation with respect to a co-rotated frame. Due to the modified strain tensor, the present formulation distinguishes significantly from standard nodal based nonlinear FE methods. Constraints are defined in integral form for every pair of surfaces of two bodies. This leads to a small number of constraint equations and avoids artificial stress singularities. The resulting mass and stiffness matrices are constant apart from a transformation based on a single rotation matrix for each body. The particular structure of this transformation allows to prevent from the usually expensive factorization of the system Jacobian within implicit time--integration methods. The present method has been implemented and tested with the FE-package NGSolve and specific 3D examples are verified with a standard beam formulation
FDI and Accommodation Using NN Based Techniques
Garcia, Ramon Ferreiro; de Miguel Catoira, Alberto; Sanz, Beatriz Ferreiro
Massive application of dynamic backpropagation neural networks is used on closed loop control FDI (fault detection and isolation) tasks. The process dynamics is mapped by means of a trained backpropagation NN to be applied on residual generation. Process supervision is then applied to discriminate faults on process sensors, and process plant parameters. A rule based expert system is used to implement the decision making task and the corresponding solution in terms of faults accommodation and/or reconfiguration. Results show an efficient and robust FDI system which could be used as the core of an SCADA or alternatively as a complement supervision tool operating in parallel with the SCADA when applied on a heat exchanger.
Frequency-Accommodating Manchester Decoder
Vasquez, Mario J.
1988-01-01
No adjustment necessary to cover a 10:1 frequency range. Decoding circuit converts biphase-level pulse-code modulation to nonreturn-to-zero (NRZ)-level pulse-code modulation plus clock signal. Circuit accommodates input data rate of 50 to 500 kb/s. Tracks gradual changes in rate automatically, eliminating need for extra circuits and manual switching to adjust to different rates.
Extra Time as an Accommodation
Ruth Colker
2008-01-01
Although the provision of extra time has become the standard method of accommodating students with various disabilities when they take the Law School Admissions Test (LSAT) or in-class timed exams, this Article suggests that we consider other means of attaining fairness on exams. Through a survey of the psychometric literature, as well as a modest empirical study, this Article argues that the rank order of students is likely to be significantly affected by the type of examination instrument u...
Spherical aberration, accommodation and myopia
Tarrant, Janice
2010-01-01
Myopia is a condition in which the eye grows too long to match its optical focal length and represents a failure in both structure and function. Because of the potential risks of vision loss associated with high myopia, and also with corrective treatments such as refractive surgery and occasionally also with contact lenses, myopia should not be considered a benign condition. The hypothesis that hyperopic defocus from under-accommodation during near work is the driving stimulus in the progress...
On the Formulation of Flexible Multibody Systems with Constant Mass Matrix
Pedersen, Niels Leergaard
1997-01-01
A flexible body in a multibody system isdescribed only by the position of the nodes in theinertial frame. With this description we can formulatethe mass matrix of the flexible multibody as aconstant matrix. This matrix can be inverted in apreprocessing stage which yields a more efficientaccelerat...... this formulation is that neither thecentrifugal nor the Coriolis forces appear in theequations due to the description of the flexible body....
CP violation in multibody decays of beauty baryons
Durieux, Gauthier
2016-01-01
Beauty baryons are being observed in large number in the LHCb detector. The rich kinematics of their multibody decays are therefore becoming accessible and provide us with new opportunities to search for CP violation. We analyse the angular distributions of some three- and four-body decays of spin-$1/2$ baryons using the Jacob-Wick helicity formalism. The asymmetries that provide access to small differences of CP-odd phases between decay amplitudes of identical CP-even phases are notably discussed. The understanding gained on processes featuring specific resonant intermediate states allows us to establish which asymmetries are relevant for what purpose. It is for instance shown that some CP-odd angular asymmetries measured by the LHCb collaboration in the $\\Lambda_b \\to \\Lambda\\,\\varphi \\to p\\,\\pi\\, K^+ K^-$ decay are expected to vanish identically.
A simple probabilistic model of multibody interactions in proteins
Johansson, Kristoffer Enøe; Hamelryck, Thomas
2013-01-01
predictions. Our coarse-grained model is compared to state-of-art methods that use full atomic detail. This article illustrates how the use of simple probabilistic models can lead to new opportunities in the treatment of nonlocal interactions in knowledge-based protein structure prediction and design.......Protein structure prediction methods typically use statistical potentials, which rely on statistics derived from a database of know protein structures. In the vast majority of cases, these potentials involve pairwise distances or contacts between amino acids or atoms. Although some potentials...... beyond pairwise interactions have been described, the formulation of a general multibody potential is seen as intractable due to the perceived limited amount of data. In this article, we show that it is possible to formulate a probabilistic model of higher order interactions in proteins, without...
Study of the railway vehicle suspension using the multibody method
Gheorghe GHITA
2011-12-01
Full Text Available The article presents a mathematical model for the study of a passenger coach hunting motion using the multibody approach. The model comprises the lateral displacement, rolling and yawing motions for the main constitutive elements: axles, bogies and case. The equation system is written applying energetic methods. The forced vibrations determined by the irregular profile of the tracks are considered. The wheel – rail contact forces are expressed using the creepage coefficients established according to Kalker's linear theory. The equations system is solved through numeric methods using specialized calculus programs. The response of the system – passenger coach on a tangent track, the critical speed and the influence of the constructive characteristics of the coach on its performances are determined.
A Multi-Leveled Coordinate for Multibody Mechanics
Shen Fan
2016-01-01
Full Text Available For a proper way of modelling and simulation, as well as the precise and completeness, and a new multi-level method named homogeneous tensor coordinate(HTC was developed by improving the absolute nodal coordinate formulation(ANCF and the homogeneous coordinates(HC. In HTC, a new form of 2×2 matrix was employed instead of angles, when the capacity of expression and calculation was increased at the same time. HTC has good performance in traditional rigid body mechanics, which especially suitable for multibody modelling. Therefore, the robotic engineering may benefit from this finding, and a new formulation for scientific research may also affect the physics although some mathematical problems are raised in matrix theory.
Multibody-plasma interactions - Charging in the wake
Wang, J.; Leung, P.; Murphy, G.; Ruff, B.
1993-01-01
Multibody-plasma interactions refers to two or more charged bodies simultaneously interacting with the surrounding plasma as well as each other. This paper concerns a basic type of such interactions in space: the charging of a free flyer in the wake of a large structure. The conditions for severe charging are discussed quantitatively. Computer particle simulations are carried out to obtain the charging potentials in the wake of both floating and biased plate. It is shown that a severe charging zone exists in the near wake of a floating plate within which a free flyer is charged to the KV range under the sun shadow/auroral electron condition. Whether the plate is biased or floating, a large potential difference always exists between the plate and a docking free flyer in the wake. The effects of wake charging on spacecraft docking operations are discussed.
ACCOMMODATION PREFERENCES OF FOREIGN TOURISTS IN ROMANIA
Ionela Mituko VLAD
2014-04-01
Full Text Available The present work is a study on indicators that define tourism in Romania. Analysis focused on indicators of the number of tourists and tourist arrivals in accommodation establishments in Romania, in total and in agro-touristic boarding houses on four macro-administrative units and by category of comfort in our country. The methodology used to track the preferences of foreign tourists in accommodation establishments in Romania was to analyse the dynamics of the mentioned indicators, the seasonality of arrivals and forecasting the arrivals of foreign tourists. The data used are from the Statistical Yearbook of Romania, covering the period 2010-2013; some of them are quarterly data. The results have indicated a preference of the arrivals especially in Q3 of each year, in macro-regions M3 and M1, for foreigners and in the macro-regions M1 and M2 for the Romanian tourists. Another results designed the preferences of tourists related to the degree of comfort, which has decreased in time with the increasing levels of comfort; over time, the tourist’s number increases on the total from year to year; in particular, in the agro hostels this number is growing slowly.
Prediction of elbow joint contact mechanics in the multibody framework.
Rahman, Munsur; Cil, Akin; Stylianou, Antonis P
2016-03-01
Computational multibody musculoskeletal models of the elbow joint that are capable of simultaneous and accurate predictions of muscle and ligament forces, along with cartilage contact mechanics can be immensely useful in clinical practice. As a step towards producing a musculoskeletal model that includes the interaction between cartilage and muscle loading, the goal of this study was to develop subject-specific multibody models of the elbow joint with discretized humerus cartilage representation interacting with the radius and ulna cartilages through deformable contacts. The contact parameters for the compliant contact law were derived using simplified elastic foundation contact theory. The models were then validated by placing the model in a virtual mechanical tester for flexion-extension motion similar to a cadaver experiment, and the resulting kinematics were compared. Two cadaveric upper limbs were used in this study. The humeral heads were subjected to axial motion in a mechanical tester and the resulting kinematics from three bones were recorded for model validation. The maximum RMS error between the predicted and measured kinematics during the complete testing cycle was 2.7mm medial-lateral translation and 9.7° varus-valgus rotation of radius relative to humerus (for elbow 2). After model validation, a lateral ulnar collateral ligament (LUCL) deficient condition was simulated and, contact pressures and kinematics were compared to the intact elbow model. A noticeable difference in kinematics, contact area, and contact pressure were observed for LUCL deficient condition. LUCL deficiency induced higher internal rotations for both the radius and ulna during flexion and an associated medial shift of the articular contact area. PMID:26832391
K. Anandhanarayanan
2010-01-01
Grid-free solver has the ability to solve complex multi-body industrial problems with minimal effort. Grid-free Euler solver has been applied to number of multi-body aerospace vehicles using Chimera clouds of points including flight vehicle with fin deflection, nose fairing separation of hypersonic launch vehicle. A preprocessor has been developed to generate connectivity for multi-bodies using overlapped grids. Surface transpiration boundary condition has been implemented to model aerodynami...
77 FR 38833 - Job Accommodation Network
2012-06-29
... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF LABOR Job Accommodation Network AGENCY: Office of Disability Employment Policy, Department of Labor. Announcement Type... operate its Job Accommodation Network (JAN), a national technical assistance center that facilitates...
46 CFR 108.143 - Accommodation space.
2010-10-01
... 46 Shipping 4 2010-10-01 2010-10-01 false Accommodation space. 108.143 Section 108.143 Shipping... EQUIPMENT Construction and Arrangement Structural Fire Protection § 108.143 Accommodation space. (a) Each corridor bulkhead in an accommodation space must be an A class or B class bulkhead except if an A...
46 CFR 177.810 - Overnight accommodations.
2010-10-01
... 46 Shipping 7 2010-10-01 2010-10-01 false Overnight accommodations. 177.810 Section 177.810 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SMALL PASSENGER VESSELS (UNDER 100 GROSS TONS) CONSTRUCTION AND ARRANGEMENT Passenger Accommodations § 177.810 Overnight accommodations. (a)...
Soyuz/ACRV accommodation study
Cruz, Jonathan; Gould, Marston J.; Dahlstrom, Eric
1993-11-01
Included is a set of viewgraphs that present the results of a study conducted at the LaRC Space Station Freedom Office at the request of the Space Station Freedom Level 1 Program Office and the JSC ACRV Project Office to determine the implications of accommodating two Soyuz TM spacecraft as Assured Crew Return Vehicles (ACRV) on the Space Station Freedom (SSF) at the Permanently Crewed Capability (PCC) stage. The study examined operational as well as system issues associated with the accommodation of the Soyuz for several potential configuration options. Operational issues considered include physical hardware clearances, worst case Soyuz departure paths, and impacts to baseline operations such as Pressurized Logistics Module (PLM) exchange, Space Station Remote Manipulator System (SSRMS) attachment, Extravehicular Activity (EVA), and automatic rendezvous and docking (AR&D). Systems impact analysis included determining differences between Soyuz interface requirements and SSF capabilities for the Electrical Power System (EPS), Thermal Control System (TCS), Communications and Tracking (C&T), Audio-Video Subsystem (A/V), Data Management System (DMS), and Environmental Control and Life Support System (ECLSS). Significant findings of this study have indicated that the current AV capability of the Soyuz will need to be increased to provide adequate departure clearances for a worst case escape from an uncontrolled SSF and that an interface element will be required to mate the Soyuz vehicles to station, provide for AR&D structural loads, and to house Soyuz-to-SSF system interfaces.
Psychophysiology of Refractive Accommodative Esotropia
Ungsoo Samuel Kim
2014-01-01
Full Text Available Purpose. To investigate the psychophysiologic aspects of refractive accommodative esotropia (RAE. Methods. I prospectively recruited patients aged 3–6 years with more than 3.0 diopters of hyperopia who presented at Kim’s Eye Hospital from January 2011 to March 2013. I compared Korean Child Behavior Checklist (K-CBCL which consists of internalizing factors (social withdrawal, somatic complaints, anxiety, and depression and externalizing factors (social problems, thought problems, attention problems, delinquent behavior, and aggressive behavior between RAE group and control group. Results. Two out of three internalizing indexes were significantly different between groups (somatic complaints: RAE children 50.1±4.6 and controls 46.6±5.8, P=0.026; depression/anxiety: RAE children 48.8±7.9 and controls 43.9±6.8, P=0.024. Although there was no significant difference, RAE children scored slightly higher on the externalizing behavior index. In the RAE group, the far angle of esodeviation showed a moderate correlation with withdrawn behaviors. Conclusion. Hypermetropic children with high scores on the somatic complaint and depression/anxiety subscales of the CBCL could be at high risk for developing RAE. Psychosocial problems might be related to the pathogenesis of refractive accommodative esotropia.
Effect of oculomotor rehabilitation on accommodative responsivity in mild traumatic brain injury
Preethi Thiagarajan, BS Optom, MS, PhD
2014-03-01
Full Text Available Accommodative dysfunction is a common oculomotor sequelae of mild traumatic brain injury (mTBI. This study evaluated a range of dynamic (objective and static (subjective measures of accommodation in 12 nonstrabismic individuals with mTBI and near vision-related symptoms before and after oculomotor training (OMT and placebo (P training (6 wk, two sessions per week, 3 h of training each. Following OMT, the dynamics of accommodation improved markedly. Clinically, there was a significant increase in the maximum accommodative amplitude both monocularly and binocularly. In addition, the near vision symptoms reduced along with improved visual attention. None of the measures were found to change significantly following P training. These results provide evidence for a significant positive effect of the accommodatively based OMT on accommodative responsivity. Such improvement is suggestive of oculomotor learning, demonstrating considerable residual brain-visual system plasticity in the adult compromised brain.
A multibody systems approach to suspension modelling and simulation using suspension derivatives
This paper describes the initial phase of a study where the modelling of the suspension system has been adapted for use with computer simulations of vehicle handling during the early concept stages of vehicle design. This work has been carried out using an industry standard multibody systems analysis program known as ADAMS (Automatic Dynamic Analysis of Mechanical Systems). Work has been carried out using measured characteristics from a McPherson strut suspension system installed in a laboratory based suspension rig. A traditional approach based on modelling the suspension is considerable detail is compared with a method that considers the wheel movement relative to the vehicle body to be controlled by mathematical relationships. Using this method the wheel centre can be constrained by follow a path in three-dimensional space and the orientation of the wheel is defined as a function of the wheel position. At this stage the gradients of curves, obtained at the origin, from plots of suspension characteristics such as chamber angle against bump movement are used to define the change in orientation. These gradients are sometimes referred to as suspension derivatives. The paper concludes by discussing the advantages of a model based on parameters rather than the modelling of physical components and the further work needed to develop a similar approach for the modelling of suspension compliance. (Author)
Ruiz, S. [Idiada Automotive Technology SA (Spain)
2003-09-01
Lateral wind gusts affect the driving characteristics of a vehicle in a complex way. This is why a sophisticated test procedure is employed, i.e. integrated multibody and CFD simulation. For an exact virtual analysis of the dynamic response of a motor car to complex aerodynamic excitations, Idiada Automotive Technology SA, Spain, used the MKS program MSC.Adams by MSC. Software in combination with the CFD program STAR-CD. (orig.) [German] Seitenwindboeen verursachen aerodynamische Seitenkraefte, Gier- und Wankmomente, die das Fahrverhalten und die Querstabilitaet beeinflussen. Die komplexen Fahrverhaeltnisse in Seitenwindtests erfordern deshalb einen anspruchsvollen Ansatz fuer dieses Phaenomen: die Integration von Mehrkoerper- und CFD-Simulation. Fuer eine exakte virtuelle Analyse der Fahrzeugdynamik bei komplexen aerodynamischen Anregungen verwendete Idiada Automotive Technology SA, Spanien, das MKS-Programm MSC.Adams von MSC.Software in Verbindung mit dem CFD-Programm STAR-CD. (orig.)
Extra Time as an Accommodation
Ruth Colker
2008-04-01
Full Text Available Although the provision of extra time has become the standard method of accommodating students with various disabilities when they take the Law School Admissions Test (LSAT or in-class timed exams, this Article suggests that we consider other means of attaining fairness on exams. Through a survey of the psychometric literature, as well as a modest empirical study, this Article argues that the rank order of students is likely to be significantly affected by the type of examination instrument used. This Article places the psychometric literature on examination results in the context of testing of prelaw students as well as law students and suggests that we place less emphasis on timed instruments in ranking students.
Owen-Smith, Norman
2011-07-01
1. There is a pressing need for population models that can reliably predict responses to changing environmental conditions and diagnose the causes of variation in abundance in space as well as through time. In this 'how to' article, it is outlined how standard population models can be modified to accommodate environmental variation in a heuristically conducive way. This approach is based on metaphysiological modelling concepts linking populations within food web contexts and underlying behaviour governing resource selection. Using population biomass as the currency, population changes can be considered at fine temporal scales taking into account seasonal variation. Density feedbacks are generated through the seasonal depression of resources even in the absence of interference competition. 2. Examples described include (i) metaphysiological modifications of Lotka-Volterra equations for coupled consumer-resource dynamics, accommodating seasonal variation in resource quality as well as availability, resource-dependent mortality and additive predation, (ii) spatial variation in habitat suitability evident from the population abundance attained, taking into account resource heterogeneity and consumer choice using empirical data, (iii) accommodating population structure through the variable sensitivity of life-history stages to resource deficiencies, affecting susceptibility to oscillatory dynamics and (iv) expansion of density-dependent equations to accommodate various biomass losses reducing population growth rate below its potential, including reductions in reproductive outputs. Supporting computational code and parameter values are provided. 3. The essential features of metaphysiological population models include (i) the biomass currency enabling within-year dynamics to be represented appropriately, (ii) distinguishing various processes reducing population growth below its potential, (iii) structural consistency in the representation of interacting populations and
An object oriented data model for vehicle dynamics problems
Schiehlen, Werner
1993-01-01
The design of automotive systems using computer codes for vehicle dynamics problems features cost reduction and quality enhancement. This paper presents two basic approaches. The first approach deals with the application of CAD data bases to the evaluation of input data for multibody system formalisms, most adequate for automotive system modelling. An object oriented data model for multibody systems is presented. The second approach covers the development of an integrated simulation tool for ...
Disorders of Accommodative Convergation and Accommodation (AC/A) Relations at Traumatic Brain Injury
Serdarevic, Raif
2015-01-01
Introduction: Accommodative Convergence/Accommodation (AC/A) ratio is constant at one and the same person in the course of life, i.e. the same ratio accommodative convergence monitor any change in accommodation measured in diopters. Such a perfect relationship is possible if there are no refractive anomalies in both eyes and oculomotor imbalance of eye muscles. Material and methods: We are examined 50 patients with close brain injury, and patients which had problems with near vision, accommod...
The child sexual abuse accommodation syndrome.
Summit, R C
1983-01-01
Child victims of sexual abuse face secondary trauma in the crisis of discovery. Their attempts to reconcile their private experiences with the realities of the outer world are assaulted by the disbelief, blame and rejection they experience from adults. The normal coping behavior of the child contradicts the entrenched beliefs and expectations typically held by adults, stigmatizing the child with charges of lying, manipulating or imagining from parents, courts and clinicians. Such abandonment by the very adults most crucial to the child's protection and recovery drives the child deeper into self-blame, self-hate, alienation and revictimization. In contrast, the advocacy of an empathic clinician within a supportive treatment network can provide vital credibility and endorsement for the child. Evaluation of the responses of normal children to sexual assault provides clear evidence that societal definitions of "normal" victim behavior are inappropriate and procrustean, serving adults as mythic insulators against the child's pain. Within this climate of prejudice, the sequential survival options available to the victim further alienate the child from any hope of outside credibility or acceptance. Ironically, the child's inevitable choice of the "wrong" options reinforces and perpetuates the prejudicial myths. The most typical reactions of children are classified in this paper as the child sexual abuse accommodation syndrome. The syndrome is composed of five categories, of which two define basic childhood vulnerability and three are sequentially contingent on sexual assault: (1) secrecy, (2) helplessness, (3) entrapment and accommodation, (4) delayed, unconvincing disclosure, and (5) retraction. The accommodation syndrome is proposed as a simple and logical model for use by clinicians to improve understanding and acceptance of the child's position in the complex and controversial dynamics of sexual victimization. Application of the syndrome tends to challenge entrenched
Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær
2014-01-01
This paper investigates gear tooth fatigue damage in a 500 kW wind turbine using FLEX5 and own multibody code. FLEX5 provides the physical wind eld, rotor and generator torque and the multibody code is used for obtaining gear tooth reaction forces in the planetary gearbox. Dierent turbulence levels...
FATIGUE LIFE EVALUATION OF SUSPENSION KNUCKLE USING MULTIBODY SIMULATION TECHNIQUE
A.G.A. Rahman
2012-12-01
Full Text Available Suspension is part of automotive systems, providing both vehicle control and passenger comfort. The knuckle is an important part within the suspension system, constantly encountering the cyclic loads subjecting it to fatigue failure. This paper presents an evaluation of the fatigue characteristics of a knuckle using multibody simulation (MBS techniques. Load time history extracted from the MBS is used for stress analysis. An actual road profile of road bumps was used as the input to MBS. The stress fluctuations for fatigue simulations are considered with the road profile. The strain-life method is utilized to assess the fatigue life. The instantaneous stress distributions and maximum principal stress are used for fatigue life predictions. Mesh sensitivity analysis has been performed. The results show that the steering link in the knuckle is found to be the most susceptible region for fatigue failure. The number of times the knuckle can manage a road bump at 40 km/hr is determined to be approximately 371 times with a 50% certainty of survival. The proposed method of using the loading time history extracted from MBS simulation for fatigue life estimation is found to be very promising for the accurate evaluation of the performance of suspension system components.
A simple probabilistic model of multibody interactions in proteins.
Johansson, Kristoffer Enøe; Hamelryck, Thomas
2013-08-01
Protein structure prediction methods typically use statistical potentials, which rely on statistics derived from a database of know protein structures. In the vast majority of cases, these potentials involve pairwise distances or contacts between amino acids or atoms. Although some potentials beyond pairwise interactions have been described, the formulation of a general multibody potential is seen as intractable due to the perceived limited amount of data. In this article, we show that it is possible to formulate a probabilistic model of higher order interactions in proteins, without arbitrarily limiting the number of contacts. The success of this approach is based on replacing a naive table-based approach with a simple hierarchical model involving suitable probability distributions and conditional independence assumptions. The model captures the joint probability distribution of an amino acid and its neighbors, local structure and solvent exposure. We show that this model can be used to approximate the conditional probability distribution of an amino acid sequence given a structure using a pseudo-likelihood approach. We verify the model by decoy recognition and site-specific amino acid predictions. Our coarse-grained model is compared to state-of-art methods that use full atomic detail. This article illustrates how the use of simple probabilistic models can lead to new opportunities in the treatment of nonlocal interactions in knowledge-based protein structure prediction and design. PMID:23468247
Toso, Mario; Baldesi, Gianluigi; Moratto, Claudio; De Wilde, Don; Bureo Dacal, Rafael; Castellsaguer, Joaquim
2012-07-01
Even though human exploration of Mars is a distant objective, it is well understood that, for human space voyages of several years duration, crews would be at risk of catastrophic consequences should any of the systems that provide adequate air, water, food, or thermal protection fail. Moreover, crews will face serious health and/or safety risks resulting from severe physiologic deconditioning associated with prolonged weightlessness. The principal ones are related to physical and functional deterioration of the regulation of the blood circulation, decreased aerobic capacity, impaired musculo-skeletal systems, and altered sensory- motor system performance. As the reliance of future space programmes on virtual modelling, simulation and justification has substantially grown together with the proto-flight hardware development approach, a range of simulation capabilities have become increasingly important in the requirements specification, design, verification, testing, launch and operation of new space systems. In this frame, multibody software is a key tool in providing a more coordinated and consistent approach from the preliminary development phases of the most complex systems. From a scientific prospective, an artificial gravity facility, such as the one evaluated in this paper, would be the first in-flight testing of the effectiveness and acceptability of short radius centrifuge as a countermeasure to human deconditioning on orbit. The ISS represents a unique opportunity to perform this research. From an engineering point of view, the preliminary assessment described in this paper, highlights the difficult engineering challenges of such a facility. The outcome proves that a human can be accommodated in the available volume, while respecting the human ergonomic basic requirements and preserving the global structural integrity of the hosting ISS module. In particular, analysis shows that, although the load capacity of the structural interfaces imposes a very low
Evaluating relative accommodations in general binocular dysfunctions
García Muñoz, Ángel; Cacho Martínez, Pilar; Lara Lacarcel, Francisco
2001-01-01
Purpose. To examine the relationship between relative accommodation and general binocular disorders and to establish their importance in the diagnosis of these anomalies. Methods. We analyzed data of negative relative accommodation (NRA) and positive relative accommodation (PRA) in 69 patients with nonstrabismic binocular anomalies. Results. Statistical analysis showed that low values of NRA and PRA were not associated with any particular disorder. High values of PRA (>3.50 D) were related to...
Investigating accommodation using eyes and lenses
Dilek, Ufuk; Sahin, Mehmet
2013-03-01
In this paper, an in-class activity concerned with real image formation by a converging lens in the context of accommodation in human eyes is described. In the first part of the activity, students are encouraged to experience the accommodation of their eyes in a prescribed way using simple materials. In the second part, the accommodation function of the human eye is illustrated by means of a simple demonstration.
Accommodative response and cortical activity during sustained attention.
Poltavski, Dmitri V; Biberdorf, David; Petros, Thomas V
2012-06-15
Greater accommodative lag and vergence deficits have been linked to attentional deficits similar to those observed in Attention Deficit Hyperactivity Disorder (ADHD). The purpose of the present study was to assess the effect of accommodative-vergence stress on a measure of sustained attention (Conners CPT) used in the diagnosis of ADHD. Twenty-seven normal non-ADHD adults completed the Conners CPT twice: wearing -2.00 D lenses and normally (without the -2.00 D lenses) in a counterbalanced order with at least 24 h between the sessions. Simultaneous recording of participants' dynamic accommodative responses was performed from the right eye using the Grand Seiko WAM-5500 auto-refractor and electroencephalographic activity (EEG) in the left prefrontal region using the Neurosky Mindset headset. The results demonstrated a significantly greater accommodative lag in the -2.00 D stress condition and a significantly poorer performance on the Conners CPT as indexed by slower reaction time, greater standard error of hit reaction time, grater response variability, poorer stimulus detectability and a greater number of perseverations. No differences were observed on measures of EEG in the theta (4-7 Hz), alpha (8-12 Hz), and beta (12-20 Hz) bands. Moreover, when directly juxtaposed with each EEG band in multiple linear regression analyses, greater accommodative lag in the stress condition was significantly associated with a greater probability of clinical classification on the Conners CPT, and was also marginally predictive of the number of omissions recorded in the stress condition. The results demonstrated that sustained attention can be influenced by such factors as accommodative-vergence stress and suggest that bottom-up processes can contribute to and potentially exacerbate attentional problems in individuals with ADHD. The study also showed that cortical dysfunction (while sufficient) may not be a necessary condition for attentional deficits. PMID:22580016
Fijany, Amir
1993-01-01
In this paper parallel 0(log N) algorithms for dynamic simulation of single closed-chain rigid multibody system as specialized to the case of a robot manipulatoar in contact with the environment are developed.
Raiszadeh, Behzad; Queen, Eric M.; Hotchko, Nathaniel J.
2009-01-01
A capability to simulate trajectories of multiple interacting rigid bodies has been developed, tested and validated. This capability uses the Program to Optimize Simulated Trajectories II (POST 2). The standard version of POST 2 allows trajectory simulation of multiple bodies without force interaction. In the current implementation, the force interaction between the parachute and the suspended bodies has been modeled using flexible lines, allowing accurate trajectory simulation of the individual bodies in flight. The POST 2 multibody capability is intended to be general purpose and applicable to any parachute entry trajectory simulation. This research paper explains the motivation for multibody parachute simulation, discusses implementation methods, and presents validation of this capability.
A recursive multibody formalism for systems with small mass and inertia terms
M. Arnold
2013-05-01
Full Text Available Complex multibody system models that contain bodies with small mass or nearly singular inertia tensor may suffer from high frequency solution components that deteriorate the solver efficiency in time integration. Singular perturbation theory suggests to neglect these small mass and inertia terms to allow a more efficient computation of the smooth solution components. In the present paper, a recursive multibody formalism is developed to evaluate the equations of motion for a tree structured N body system with O(N complexity even if isolated bodies have a rank-deficient body mass matrix. The approach is illustrated by some academic test problems in 2-D.
Test Accommodations for LEP Students. ERIC Digest.
Stansfield, Charles; Rivera, Charlene
This digest presents an overview of accommodations for students of limited English proficiency (LEP) and an overview of inclusion practices on statewide assessments, with emphasis on the accommodation known as linguistic simplification. The inclusion of LEP students in statewide testing programs over the last decade has been uneven. In the…
46 CFR 177.710 - Overnight accommodations.
2010-10-01
... 46 Shipping 7 2010-10-01 2010-10-01 false Overnight accommodations. 177.710 Section 177.710 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SMALL PASSENGER VESSELS (UNDER 100 GROSS TONS) CONSTRUCTION AND ARRANGEMENT Crew Spaces § 177.710 Overnight accommodations....
BRANDING ORIENTATION IN THE ACCOMMODATION INDUSTRY
Melissa Li Sa Liow
2015-04-01
Full Text Available This paper starts by clarifying the role of branding orientation (BO among academic studies. It shortly introduces the development of the BO concepts. The empirical part consists of a search for and analysing of academic articles using a meta-analysis that consider BO in the accommodation industry. According to the results, significant appraisal of the branding building activities among higher star rating and luxury accommodation businesses are taking place due to the increasingly demanding guests. Thus, there is an upward pressure on small and medium accommodation businesses to survive or perform well. This paper recommends that scholars study the owners-managers, employees, and customer perspectives altogether, to better comprehend how large accommodation businesses displaying BO can generate superior performance. For the small and medium accommodation businesses, the emphasis is the owners-managers perceptions since they are the main decision-makers, and due to infancy of the small and medium enterprise (SME branding application.
Multibody correlations in the hydrophobic solvation of glycine peptides
Protein collapse during folding is often assumed to be driven by a hydrophobic solvation energy (ΔGvdw) that scales linearly with solvent-accessible surface area (A). In a previous study, we argued that ΔGvdw, as well as its attractive (ΔGatt) and repulsive (ΔGrep) components, was not simply a linear function of A. We found that the surface tensions, γrep, γatt, and γvdw, gotten from ΔGrep, ΔGatt, and ΔGvdw against A for four configurations of deca-alanine differed from those obtained for a set of alkanes. In the present study, we extend our analysis to fifty decaglycine structures and atomic decompositions. We find that different configurations of decaglycine generate different estimates of γrep. Additionally, we considered the reconstruction of the solvation free energy from scaling the free energy of solvation of each atom type, free in solution. The free energy of the isolated atoms, scaled by the inverse surface area the atom would expose in the molecule does not reproduce the γrep for the intact decaglycines. Finally, γatt for the decaglycine conformations is much larger in magnitude than those for deca-alanine or the alkanes, leading to large negative values of γvdw (−74 and −56 cal/mol/Å2 for CHARMM27 and AMBER ff12sb force fields, respectively). These findings imply that ΔGvdw favors extended rather than compact structures for decaglycine. We find that ΔGrep and ΔGvdw have complicated dependencies on multibody correlations between solute atoms, on the geometry of the molecular surface, and on the chemical identities of the atoms
Multibody correlations in the hydrophobic solvation of glycine peptides
Harris, Robert C.; Drake, Justin A.; Pettitt, B. Montgomery
2014-12-01
Protein collapse during folding is often assumed to be driven by a hydrophobic solvation energy (ΔGvdw) that scales linearly with solvent-accessible surface area (A). In a previous study, we argued that ΔGvdw, as well as its attractive (ΔGatt) and repulsive (ΔGrep) components, was not simply a linear function of A. We found that the surface tensions, γrep, γatt, and γvdw, gotten from ΔGrep, ΔGatt, and ΔGvdw against A for four configurations of deca-alanine differed from those obtained for a set of alkanes. In the present study, we extend our analysis to fifty decaglycine structures and atomic decompositions. We find that different configurations of decaglycine generate different estimates of γrep. Additionally, we considered the reconstruction of the solvation free energy from scaling the free energy of solvation of each atom type, free in solution. The free energy of the isolated atoms, scaled by the inverse surface area the atom would expose in the molecule does not reproduce the γrep for the intact decaglycines. Finally, γatt for the decaglycine conformations is much larger in magnitude than those for deca-alanine or the alkanes, leading to large negative values of γvdw (-74 and -56 cal/mol/Å2 for CHARMM27 and AMBER ff12sb force fields, respectively). These findings imply that ΔGvdw favors extended rather than compact structures for decaglycine. We find that ΔGrep and ΔGvdw have complicated dependencies on multibody correlations between solute atoms, on the geometry of the molecular surface, and on the chemical identities of the atoms.
Multibody correlations in the hydrophobic solvation of glycine peptides
Harris, Robert C.; Drake, Justin A.; Pettitt, B. Montgomery, E-mail: mpettitt@utmb.edu [Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, 301 University Blvd, Galveston, Texas 77555-0304 (United States)
2014-12-14
Protein collapse during folding is often assumed to be driven by a hydrophobic solvation energy (ΔG{sub vdw}) that scales linearly with solvent-accessible surface area (A). In a previous study, we argued that ΔG{sub vdw}, as well as its attractive (ΔG{sub att}) and repulsive (ΔG{sub rep}) components, was not simply a linear function of A. We found that the surface tensions, γ{sub rep}, γ{sub att}, and γ{sub vdw}, gotten from ΔG{sub rep}, ΔG{sub att}, and ΔG{sub vdw} against A for four configurations of deca-alanine differed from those obtained for a set of alkanes. In the present study, we extend our analysis to fifty decaglycine structures and atomic decompositions. We find that different configurations of decaglycine generate different estimates of γ{sub rep}. Additionally, we considered the reconstruction of the solvation free energy from scaling the free energy of solvation of each atom type, free in solution. The free energy of the isolated atoms, scaled by the inverse surface area the atom would expose in the molecule does not reproduce the γ{sub rep} for the intact decaglycines. Finally, γ{sub att} for the decaglycine conformations is much larger in magnitude than those for deca-alanine or the alkanes, leading to large negative values of γ{sub vdw} (−74 and −56 cal/mol/Å{sup 2} for CHARMM27 and AMBER ff12sb force fields, respectively). These findings imply that ΔG{sub vdw} favors extended rather than compact structures for decaglycine. We find that ΔG{sub rep} and ΔG{sub vdw} have complicated dependencies on multibody correlations between solute atoms, on the geometry of the molecular surface, and on the chemical identities of the atoms.
王海伟; 杨会侠; 刘更; 吴立言
2011-01-01
The concept and application of virtual prototype technology were simply presented here, and the veracity of a complex multi-body system simulation was analyzed. A rigid-flexible coupled virtual prototype model of a complex multi-body system containing impact was built with multi-body dynamics software Virtual Lab, and the correctness of the virtual prototype simulation was evaluated combining with the test data. Some key system parameters were revised by using the sensitivity and perturbation methods, the scattering level of the simulation results had better consistency with that of the test ones, and the reality of the virtual prototype model was improved.%简要阐述虚拟样机技术的概念及应用,分析了复杂多体系统仿真过程中存在的准确性问题.应用多体动力学软件Virtual Lab建立含冲击复杂多体系统的刚柔耦合虚拟样机模型,结合试验数据评估虚拟样机仿真的准确性.采用灵敏度方法和摄动法修正一些关键的系统参数,使散布度的仿真结果和试验结果有更好的一致性,提高了虚拟样机模型的真实度.
Almesallmy, Mohammed
Methodologies are developed for dynamic analysis of mechanical systems with emphasis on inertial propulsion systems. This work adopted the Lagrangian methodology. Lagrangian methodology is the most efficient classical computational technique, which we call Equations of Motion Code (EOMC). The EOMC is applied to several simple dynamic mechanical systems for easier understanding of the method and to aid other investigators in developing equations of motion of any dynamic system. In addition, it is applied to a rigid multibody system, such as Thomson IPS [Thomson 1986]. Furthermore, a simple symbolic algorithm is developed using Maple software, which can be used to convert any nonlinear n-order ordinary differential equation (ODE) systems into 1st-order ODE system in ready format to be used in Matlab software. A side issue, but equally important, we have started corresponding with the U.S. Patent office to persuade them that patent applications, claiming gross linear motion based on inertial propulsion systems should be automatically rejected. The precedent is rejection of patent applications involving perpetual motion machines.
Multibody Model for Planetary Gearbox of 500 kW Wind Turbine
Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær
(industrial standard software). The FLEX5 model as well as the developed multibody code has been verified from strain gauge measurements, giving e.g. the main shaft torque, and met mast wind data measurements. The realistic measurements on both input and output variables form an excellent base for studying...
Summary of the 2015 LHCb workshop on multi-body decays of D and B mesons
Amato, Sandra; Baesso, Clarissa; Haim, Eli Ben; Bigi, Ikaros; Boito, Diogo; Brodzicka, Jolanta; Reis, Alberto Correa dos; Craik, Daniel Charles; Torres, Melissa Maria Cruz; Dalseno, Jeremy; Hickman, Ignacio de Bediaga; Vieira, Daniel Evangelho; Rodrigues, Fernando Luiz Ferreira; Gershon, Timothy; Göbel, Carla; Greenwald, Daniel; Harnew, Samuel Thomas; Henry, Louis; Hicheur, Adlene; Latham, Thomas Edward; Loiseau, Benoit; London, David; Lopes, Helder; Magalhães, Patricia; de Miranda, Jussara Marques; Tostes, Danielle Martins; Rodrigues, Andre Massafferri; Mathad, Abhijit; Meadows, Brian; Carreno, Diego Milanes; Rodriguez, Josue Danilo Molina; Moraes, Danielle; Nasteva, Irina; Nielsen, Marina; Nogueira, Jorge; O'Hanlon, Daniel Patrick; Oset, Eulogio; Rodrigues, Bruno Osorio; Goicochea, Juan Martin Otalora; Paul, Stephan; Polycarpo, Erica; Prouvé, Claire; Quagliani, Renato; Rademacker, Jonas; Robilotta, Manoel; Rodriguez, Jairo Alexis; Coutinho, Rafael Silva; Skwarnicki, Tomasz; Sun, Liang; Szczepaniak, Adam; Aoude, Rafael Tourinho; Wallace, Charlotte; Whitehead, Mark
2016-01-01
This document contains a summary of the LHCb workshop on multi-body decays of D and B mesons, held at CBPF, Rio de Janeiro, in July 2015. The workshop was focused on issues related to amplitude analysis of three- and four-body hadronic decays. In addition to selected LHCb results, contributions from guest theorists are included.
Hansen, Michael R.; Hansen, John Michael
1998-01-01
code and as a result any desired contour shape may be defined. The sensitivities of the basic physical variables of a multibody system, i.e. the positions, velocities, accelerations, and reactions of the system with respect to the automatically identified independent design variables may be determined...
Search for Exclusive Multibody Non-DD Decays at the ψ(3770) Resonance
Using data collected at the ψ(3770) resonance with the CLEO-c detector at the Cornell e+e- storage ring, we present searches for 25 charmless decay modes of the ψ(3770), mostly multibody final states. No evidence for charmless decays is found
Cronskar, Marie; Rasmussen, John; Tinnsten, Mats
2015-01-01
imported into the FE solver where the model was subjected to muscle forces and other boundary conditions from a multibody musculoskeletal model performing a typical activity of daily life. A reconstruction plate and screws were also imported into the model. The combination models returned stresses and...
Accommodative Performance of Children With Unilateral Amblyopia
Manh, Vivian; Chen, Angela M.; Tarczy-Hornoch, Kristina; Cotter, Susan A.; Candy, T. Rowan
2015-01-01
This study of amblyopic children shows an increased accommodative error during monocular viewing of naturalistic targets with the amblyopic eye compared to nonamblyopic and control eyes. These errors could degrade retinal image quality in the amblyopic eye during patching therapy.
The Influence of Rotor Unbalance on Turbocharger Rotor Dynamics
Knotek Jiří
2015-12-01
Full Text Available This paper describes the influence of an unbalance on turbocharger rotor dynamics. The structural model of the turbocharger rotor and the hydrodynamic model of the journal floating ring bearing are described and assembled in multibody dynamics software. Moreover, the paper presents various results describing rotor dynamics where the influence of an unbalance is discussed.
The Influence of Rotor Unbalance on Turbocharger Rotor Dynamics
Knotek Jiří; Novotný Pavel; Maršálek Ondřej; Raffai Peter; Dlugoš Jozef
2015-01-01
This paper describes the influence of an unbalance on turbocharger rotor dynamics. The structural model of the turbocharger rotor and the hydrodynamic model of the journal floating ring bearing are described and assembled in multibody dynamics software. Moreover, the paper presents various results describing rotor dynamics where the influence of an unbalance is discussed.
Adaptability: how to accommodate changing user preferences
Remoy, H.T.; Van der Voordt, D.J.M.
2013-01-01
Purpose: When current accommodation is unsatisfactorily, office organisations consider relocating to new accommodation that optimally facilitate their main processes, supporting image and financial yield. However, due to high vacancy levels, public opinion and governmental awareness oppose new office construction. Reusing existing buildings could be the egg of Columbus. This paper aims at answering the questions: Which property characteristics are important push and pull factors for relocatio...
JAMUS: Java Accommodation of Mobile Untrusted Software
Le Sommer, Nicolas; Guidec, Frédéric
2002-01-01
Security is a major issue for mobile components that roam the Internet. When downloading a software component from the Internet, it is often impossible to decide in advance if this piece of code should be considered as safe or potentially dangerous for the local system. With the JAMUS (Java Accommodation of Mobile Untrusted Software) platform we tackle these problems based on a contractual approach of resource management and access control. JAMUS can accommodate mobile Java components, provid...
Complex treatment of accommodation disturbances in students
Pozdeeva, O. G.; I. P. Kruglyakova
2014-01-01
Purpose: Assessment of the effectiveness of different methods of treatment accommodation disturbances in patients 18‑23 years old.Methods: Determination of refraction and the size of the absolute accommodation and reserves of the relative accommodationbefore and after the treatment with Midrimax and Irifrin 2.5 % in combination with the course of electrostimulation.Results: The clinical effect was obtained in all patients. The maximum improvement of visual functions with a lower degree of myo...
Dynamics Modeling of Heavy Special Driving Simulator
无
2008-01-01
Based on the dynamical characteristic parameters of the real vehicle, the modeling approach and procedure of dynamics of vehicles are expatiated. The layout of vehicle dynamics is proposed, and the sub-models of the diesel engine, drivetrain system and vehicle multi-body dynamics are introduced. Finally, the running characteristic data of the virtual and real vehicles are compared, which shows that the dynamics model is similar closely to the real vehicle system.
Juan J. Arbeláez-Toro
2013-11-01
Full Text Available A computational simulation is Implemented, in order to response to a problem of dynamics associated With The assessment of adherence in suspension systems. The process begins with the lifting of the most representative geometries of a MacPherson system of a Nissan Sentra B13, where each of the devices is created and assembled into a CAD software to give a dynamic solution on a CAE multibody package. Afterwards a mathematical model was created whose differential equations are generated substantiated on Newton's second law and this are resolved using Matlab-Simulink applications. Once the model developing process is over, the variables are fed with accurate information of the studied vehicle to obtain the graphs that give an answer to EuSAMA (European Shock Absorber Manufacturers Association test protocol for the adherence analysis. The results presented show the reliability of the developed models when compared with the experimental test; furthermore, it demonstrates that the decrease of the damping coefficient compromises the vehicle´s adherence on the track, affecting its stability and maneuverability.
Simone Pascuzzi
2015-01-01
This paper proposes the use of the multibody approach to evaluate the severity of the injuries to the driver associated with rollover of an agricultural tractor. A simple rollover accident of a narrow-track wheeled tractor was simulated in the multibody-FEM Madymo environment and the biomechanical damage to the operator with and without 2-point pelvic restraint was analysed. The structure of the tractor was considered to be unbendable, whereas i) infinitely rigid, ii) clay-based and iii) sand...
I. G. Ovechkin; Yudin, V.E.; G. A. Emel’yanov; Mironov, A. V.
2015-01-01
Increased load on the visual analyzer of an operator, increase in everyday visual performance, universal introduction of information displaying on cathode-ray tubes result in temporary and stable visual disturbances. Accommodative refractive apparatus of an eye is one of the key points of application of visually intensive labor. Work associated with permanent eyestrain overloads oculomotor and accommodative apparatus thus provoking myopic shift, increase in dynamic refraction, exophoric or es...
Overview for Attached Payload Accommodations and Environments
Schaffer, Craig; Cook, Gene; Nabizadeh, Rodney; Phillion, James
2007-01-01
External payload accommodations are provided at attach sites on the U.S provided ELC, U.S. Truss, the Japanese Experiment Module Exposed Facility (JEM EF) and the Columbus EPF (External Payload Facilities). The Integrated Truss Segment (ITS) provides the backbone structure for the ISS. It attaches the solar and thermal control arrays to the rest of the complex, and houses cable distribution trays Extravehicular Activity (EVA) support equipment such as handholds and lighting; and providing for Extravehicular Robotic (EVR) accommodations using the Mobile Servicing System (MSS). It also provides logistics and maintenance, and payload attachment sites. The attachment sites accommodate logistics and maintenance and payloads carriers, zenith and nadir. The JEM-EF, a back porch-like attachment to the JEM Pressurized Module, accommodates up to eight payloads, which can be serviced by the crew via the JEM PM's airlock and dedicated robotic arm. The Columbus-EPF is another porch-like platform that can accommodate two zenith and two nadir looking payloads.
Recovery of Accommodative Capabilities of Ocular Pseudophakia
Ivonin K.S.
2012-12-01
Full Text Available There are considered three modern prospective ways to solve the problem of pseudophakic presbyopia: development of induced anisometropia (monovision, and implantation of accommodative and pseudo-accommodative intraocular lens (IOL. According to the findings of numerous studies, pseudophakic monovision enables to achieve good results of close-up and distant acuity of vision without correction. However, monovision use involves such limitations as individual intolerance to anisometropia, and the lack of stereoscopic vision. Despite accommodative IOL have more potential, accommodative effect after the implantation of this type of lens is not always guaranteed. There can be several reasons for that, including inconsistency between IOL diameter and capsular sac diameter, incorrect capsulorrhexis diameter, increased or reduced ciliary muscle contraction, capsular sac fibrosis, synchysis corporis vitrei, posterior vitreous detachment, the change of lens ligament elasticity. Currently, the use of pseudo-accommodative IOL is the most effective way of pseudophakic presbyopia correction, and among them the most effective ones are bifocal refractive and diffractive IOL. But along with the recognized advantages of the lens, they have a number of disadvantages, e.g. low intermediate vision.
Complex treatment of accommodation disturbances in students
O. G. Pozdeeva
2014-07-01
Full Text Available Purpose: Assessment of the effectiveness of different methods of treatment accommodation disturbances in patients 18‑23 years old.Methods: Determination of refraction and the size of the absolute accommodation and reserves of the relative accommodationbefore and after the treatment with Midrimax and Irifrin 2.5 % in combination with the course of electrostimulation.Results: The clinical effect was obtained in all patients. The maximum improvement of visual functions with a lower degree of myopia (1.0‑3.0 D, increase of absolute accommodation (by 2.5‑3,.D and reserves of the relative accommodation (up to age norms were observed in the younger age group of patients, wich had received the treatment with Midrimax, especially when combined with electrostimulation.Conclusion: Instillation of Midrimax in the treatment of violations of accommodation contribute to the effective reduction in the degree of myopia and improve of accomodation in patients 18‑23 years old. The combination of this therapy with functional methods of treatment increase its effectiveness.
Boyer, Frédéric; Belkhiri, Ayman
2013-01-01
Papier en révision International audience This article proposes a general modelling approach for locomotion dynamics of Mobile Multibody Systems (MMS) containing passive internal degrees of freedom (dofs) concentrated into (ideal or not) joints and/or distributed along deformable bodies of the system. The approach embraces the case of non-holonomic mobile multibody systems with passive wheels, the pendular climbers and the locomotion systems bio-inspired by animals that exploit the adva...
Wefstaedt Patrick
2009-11-01
Full Text Available Abstract Background Among other causes the long-term result of hip prostheses in dogs is determined by aseptic loosening. A prevention of prosthesis complications can be achieved by an optimization of the tribological system which finally results in improved implant duration. In this context a computerized model for the calculation of hip joint loadings during different motions would be of benefit. In a first step in the development of such an inverse dynamic multi-body simulation (MBS- model we here present the setup of a canine hind limb model applicable for the calculation of ground reaction forces. Methods The anatomical geometries of the MBS-model have been established using computer tomography- (CT- and magnetic resonance imaging- (MRI- data. The CT-data were collected from the pelvis, femora, tibiae and pads of a mixed-breed adult dog. Geometric information about 22 muscles of the pelvic extremity of 4 mixed-breed adult dogs was determined using MRI. Kinematic and kinetic data obtained by motion analysis of a clinically healthy dog during a gait cycle (1 m/s on an instrumented treadmill were used to drive the model in the multi-body simulation. Results and Discussion As a result the vertical ground reaction forces (z-direction calculated by the MBS-system show a maximum deviation of 1.75%BW for the left and 4.65%BW for the right hind limb from the treadmill measurements. The calculated peak ground reaction forces in z- and y-direction were found to be comparable to the treadmill measurements, whereas the curve characteristics of the forces in y-direction were not in complete alignment. Conclusion In conclusion, it could be demonstrated that the developed MBS-model is suitable for simulating ground reaction forces of dogs during walking. In forthcoming investigations the model will be developed further for the calculation of forces and moments acting on the hip joint during different movements, which can be of help in context with the in
Kim, Taeseong; Hansen, Anders Melchior; Branner, Kim
2013-01-01
parametric study is conducted in order to investigate if the given anisotropic effect of the composite blade, bend-twist coupling effect, is able to be examined by the developed beam element in a multibody system or not. Two different coupled examples of bend-twist coupling for the blade of a 5 MW fictitious......In this paper a new anisotropic beam finite element for composite wind turbine blades is developed and implemented into the aeroelastic nonlinear multibody code, HAWC2, intended to be used to investigate if use of anisotropic material layups in wind turbine blades can be tailored for improved...... wind turbine are considered. The two cases differ in the amount of bend-twist coupling introduced into the blade so that they produce 0.3 and 1 twist at the blade tip (toward feather), respectively, for a 1mflapwise tip deflection toward the tower. It is examined if the current structural model is able...
An exact nonlinear hybrid-coordinate formulation for flexible multibody systems
Jinyang Liu; Jiazhen Hong; Lin Cui
2007-01-01
The previous low-order approximate nonlinear formulations succeeded in capturing the stiffening terms,but failed in simulation of mechanical systems with large deformation due to the neglect of the high-order deforma-tion terms. In this paper, a new hybrid-coordinate formu-lation is proposed, which is suitable for flexible multibody systems with large deformation. On the basis of exact strain-displacement relation, equations of motion for flexible multi-body system are derived by using virtual work principle. A matrix separation method is put forward to improve the efficiency of the calculation. Agreement of the present results with those obtained by absolute nodal coordinate formula-tion (ANCF) verifies the correctness of the proposed formu-lation. Furthermore, the present results are compared with those obtained by use of the linear model and the low-order approximate nonlinear model to show the suitability of the proposed models.
Multibody Simulation Software Testbed for Small-Body Exploration and Sampling
Acikmese, Behcet; Blackmore, James C.; Mandic, Milan
2011-01-01
G-TAG is a software tool for the multibody simulation of a spacecraft with a robotic arm and a sampling mechanism, which performs a touch-and-go (TAG) maneuver for sampling from the surface of a small celestial body. G-TAG utilizes G-DYN, a multi-body simulation engine described in the previous article, and interfaces to controllers, estimators, and environmental forces that affect the spacecraft. G-TAG can easily be adapted for the analysis of the mission stress cases to support the design of a TAG system, as well as for comprehensive Monte Carlo simulations to analyze and evaluate a particular TAG system design. Any future small-body mission will benefit from using G-TAG, which has already been extensively used in Comet Odyssey and Galahad Asteroid New Frontiers proposals.
A linearized input-output representation of flexible multibody systems for control synthesis
In this paper, a linearized input-output representation of flexible multibody systems is proposed in which an arbitrary combination of positions, velocities, accelerations, and forces can be taken as input variables and as output variables. The formulation is based on a nonlinear finite element approach in which a multibody system is modeled as an assembly of rigid body elements interconnected by joint elements such as flexible hinges and beams. The proposed formulation is general in nature and can be applied for prototype modeling and control system analysis of mechatronic systems. Application of the theory is illustrated through a detailed model development of an active vibration isolation system for a metrology frame of a lithography machine
A Large-Scale Multibody Manipulator Soft Sensor Model and Experiment Validation
Wu Ren
2014-01-01
Full Text Available Stress signal is difficult to obtain in the health monitoring of multibody manipulator. In order to solve this problem, a soft sensor method is presented. In the method, stress signal is considered as dominant variable and angle signal is regarded as auxiliary variable. By establishing the mathematical relationship between them, a soft sensor model is proposed. In the model, the stress information can be deduced by angle information which can be easily measured for such structures by experiments. Finally, test of ground and wall working conditions is done on a multibody manipulator test rig. The results show that the stress calculated by the proposed method is closed to the test one. Thus, the stress signal is easier to get than the traditional method. All of these prove that the model is correct and the method is feasible.
Computer aided design environment for the analysis and design of multi-body flexible structures
Ramakrishnan, Jayant V.; Singh, Ramen P.
1989-01-01
A computer aided design environment consisting of the programs NASTRAN, TREETOPS and MATLAB is presented in this paper. With links for data transfer between these programs, the integrated design of multi-body flexible structures is significantly enhanced. The CAD environment is used to model the Space Shuttle/Pinhole Occulater Facility. Then a controller is designed and evaluated in the nonlinear time history sense. Recent enhancements and ongoing research to add more capabilities are also described.
Determining γ using B±→DK± with multibody D decays
We propose a method for determining γ using B±→DK± decays followed by a multibody D decay, such as D→KSπ-π+, D→KSK-K+, and D→KSπ-π+π0. The main advantages of the method are that it uses only Cabibbo allowed D decays, and that large strong phases are expected due to the presence of resonances. Since no knowledge about the resonance structure is needed, γ can be extracted without any hadronic uncertainty
Ke-Qi Pan; Jin-Yang Liu
2012-01-01
The objective of this investigation is to examine the correctness and efficiency of the choice of boundary conditions when using assumed mode approach to simulate flexible multi-body systems.The displacement field due to deformation is approximated by the Rayleigh-Ritz assumed modes in floating frame of reference (FFR) formulation.The deformations obtained by the absolute nodal coordinate (ANC) formulation which are transformed by two sets of reference coordinates are introduced as a criterion to verify the accuracy of the simulation results by using the FFR formulation.The relationship between the deformations obtained from different boundary conditions is revealed.Numerical simulation examples demonstrate that the assumed modes with cantilevered-free,simply-supported and freefree boundary conditions without inclusion of rigid body modes are suitable for simulation of flexible multi-body system with large over all motion,and the same physical deformation can be obtained using those mode functions,differ only by a coordinate transformation.It is also shown that when using mode shapes with statically indeterminate boundary conditions,significant error may occur.Furthermore,the slider crank mechanism with rigid crank is accurate enough for investigating boundary condition problem of flexible multi-body system,which cost significant less simulating time.
Pan, Ke-Qi; Liu, Jin-Yang
2012-02-01
The objective of this investigation is to examine the correctness and efficiency of the choice of boundary conditions when using assumed mode approach to simulate flexible multi-body systems. The displacement field due to deformation is approximated by the Rayleigh-Ritz assumed modes in floating frame of reference (FFR) formulation. The deformations obtained by the absolute nodal coordinate (ANC) formulation which are transformed by two sets of reference coordinates are introduced as a criterion to verify the accuracy of the simulation results by using the FFR formulation. The relationship between the deformations obtained from different boundary conditions is revealed. Numerical simulation examples demonstrate that the assumed modes with cantilevered-free, simply-supported and free-free boundary conditions without inclusion of rigid body modes are suitable for simulation of flexible multi-body system with large over all motion, and the same physical deformation can be obtained using those mode functions, differ only by a coordinate transformation. It is also shown that when using mode shapes with statically indeterminate boundary conditions, significant error may occur. Furthermore, the slider crank mechanism with rigid crank is accurate enough for investigating boundary condition problem of flexible multi-body system, which cost significant less simulating time. The project was supported by the National Natural Science Foundation of China (10872126) and the Research Fund of the Doctoral Program of Higher Education of China (20100073110007).
Multibody operator matrix elements and subduction coefficients in U(n): II
Matrix elements of multibody operators in Gel'fand and similar bases of irreducible representations of U(n) are evaluated algebraically to arbitrary order. It is shown that in all cases the matrix element expressions consist of products of terms, each a matrix factor associated only with subgroup labels at step U(k)contains U(k-1) in the group chain U(n)contains hor-ellipsis contains U(k)contains hor-ellipsis contains (1). Further, the matrices at step k occurring in the product are diagonalizable according to the irreps of SN, which signifies also for N the number of one-body operators contained in the multibody operator at the level. The results extend previous work that was directed at special cases of multibody operators. Attention has been focused recently on such operators in connection with spin-dependent and higher-order multipole spin-independent interactions as arise in the unitary group approach. Explicit phase relations are incorporated throughout the treatment. copyright 1997 American Institute of Physics
Creation of 3D Multi-Body Orthodontic Models by Using Independent Imaging Sensors
Armando Viviano Razionale
2013-02-01
Full Text Available In the field of dental health care, plaster models combined with 2D radiographs are widely used in clinical practice for orthodontic diagnoses. However, complex malocclusions can be better analyzed by exploiting 3D digital dental models, which allow virtual simulations and treatment planning processes. In this paper, dental data captured by independent imaging sensors are fused to create multi-body orthodontic models composed of teeth, oral soft tissues and alveolar bone structures. The methodology is based on integrating Cone-Beam Computed Tomography (CBCT and surface structured light scanning. The optical scanner is used to reconstruct tooth crowns and soft tissues (visible surfaces through the digitalization of both patients’ mouth impressions and plaster casts. These data are also used to guide the segmentation of internal dental tissues by processing CBCT data sets. The 3D individual dental tissues obtained by the optical scanner and the CBCT sensor are fused within multi-body orthodontic models without human supervisions to identify target anatomical structures. The final multi-body models represent valuable virtual platforms to clinical diagnostic and treatment planning.
Adaptive reuse in Dutch care accommodation
de Jong, P.; Remøy, H.T.; van der Voordt, D.J.M.; van der Kuij, R.S.
2014-01-01
Purpose – Identifying opportunities for adaptive reuse in a changing (increasing market driven) context for Dutch care accommodation. Design/methodology/approach – Combination of two student thesis, both based on case study and decision model development. Findings – Due to new courses in the Dutch
Anthropometric Accommodation in Space Suit Design
Rajulu, Sudhakar; Thaxton, Sherry
2007-01-01
Design requirements for next generation hardware are in process at NASA. Anthropometry requirements are given in terms of minimum and maximum sizes for critical dimensions that hardware must accommodate. These dimensions drive vehicle design and suit design, and implicitly have an effect on crew selection and participation. At this stage in the process, stakeholders such as cockpit and suit designers were asked to provide lists of dimensions that will be critical for their design. In addition, they were asked to provide technically feasible minimum and maximum ranges for these dimensions. Using an adjusted 1988 Anthropometric Survey of U.S. Army (ANSUR) database to represent a future astronaut population, the accommodation ranges provided by the suit critical dimensions were calculated. This project involved participation from the Anthropometry and Biomechanics facility (ABF) as well as suit designers, with suit designers providing expertise about feasible hardware dimensions and the ABF providing accommodation analysis. The initial analysis provided the suit design team with the accommodation levels associated with the critical dimensions provided early in the study. Additional outcomes will include a comparison of principal components analysis as an alternate method for anthropometric analysis.
New concepts in accommodation and presbyopia
Edson dos Santos-Neto
2011-10-01
Full Text Available The authors conducted a review of classical and conflicting theories of accommodation and presbyopia. They make a critical comparison with the findings of magnetic resonance imaging (MRI that have been developed in recent decades. Based on these studies, formulates a new approach on the subject, shifting the focus of the discussion of the lens to the posterior pole of the eye.
New concepts in accommodation and presbyopia
Edson dos Santos-Neto; Milton Ruiz Alves
2011-01-01
The authors conducted a review of classical and conflicting theories of accommodation and presbyopia. They make a critical comparison with the findings of magnetic resonance imaging (MRI) that have been developed in recent decades. Based on these studies, formulates a new approach on the subject, shifting the focus of the discussion of the lens to the posterior pole of the eye.
46 CFR 72.20-20 - Sleeping accommodations.
2010-10-01
... 46 Shipping 3 2010-10-01 2010-10-01 false Sleeping accommodations. 72.20-20 Section 72.20-20... ARRANGEMENT Accommodations for Officers and Crew § 72.20-20 Sleeping accommodations. (a) Where practicable, each licensed officer shall be provided with a separate stateroom. (b) Sleeping accommodations for...
46 CFR 92.20-20 - Sleeping accommodations.
2010-10-01
... 46 Shipping 4 2010-10-01 2010-10-01 false Sleeping accommodations. 92.20-20 Section 92.20-20... CONSTRUCTION AND ARRANGEMENT Accommodations for Officers and Crew § 92.20-20 Sleeping accommodations. (a) Where practicable, each licensed officer must be provided with a separate stateroom. (b) Sleeping accommodations...
Grading and price in the accommodation sector of South Africa
Saayman, Melville; 10811281 - Du Plessis, Engelina
2011-01-01
Abstract: Grading and price in the accommodation sector of South Africa This article analyses the relationship between grading and price in the accommodation sector in South Africa. The literature review investigates whether the accommodation grading system is a good indicator of accommodation quality, and whether tourists get what they are paying for. The research was conducted in cooperation with the major role players in the accommodation sector in South Africa, namely the South Africa...
Public housing accommodations for individuals with disabilities.
Little, Samuel B
2002-01-01
The federal Housing Act of 1962 as amended and the subsequent laws of accommodations insure that all groups within American society, including those with disabilities, have access to housing opportunities. In spite of the clear provisions of various laws of accommodations enacted after 1962, it is questionable whether disabled individuals are adequately served by resident programs operated by Public Housing Agencies (PHAs) because rates of poverty, unemployment, domestic violence, and suicide are much higher among people with disabilities than in the nondisabled population. There are approximately 5 million residents living in 2.5 public housing units nationwide. New York, Puerto Rico, Chicago, Philadelphia and Baltimore have the five largest PHAs in the country. In combination, they rent 320,000 of the 1,300,495 inventory of rental properties owned by the country's 3,400 PHAs. Elderly and disabled residents without children account for 43% of all public housing families in the country. PMID:12809381
Accommodation processes during deformation of nanocrystalline palladium
Atomistic simulations of uniaxial tensile and compressive straining of three-dimensional nanocrystalline palladium were performed at room temperature and different strain rates. Detailed analysis revealed that initial plastic deformation is due to grain boundary sliding accommodated by localized bending inside the grains and the formation of dislocation embryos. Intergranular cracking in the absence of dislocation activity was found at later stages of tensile straining. During compressive straining the sample shows a plastic response which is brought about mainly by intergranular accommodation processes. The contribution of extended partial dislocations emitted from the grain boundaries as well as full dislocations and twinning at later stages of deformation to the total strain was found to be insignificant.
Injectable accommodative lenses, a preclinical study
Koopmans, Steven Ate
2006-01-01
Currently, attempts at surgical correction of presbyopia (with or without simultaneous cataract surgery) are receiving considerable attention. Different approaches to presbyopia correction can be chosen. It is generally believed that hardening of the lens substance contributes to the development of presbyopia. In order to restore accommodation, we have chosen an approach in which the hardened lens substance is removed through a small opening in the lens capsule and the lens contents is replac...
Accommodating and promoting multilingualism through blended learning
Olivier, Jak
2011-01-01
Multilingualism is a reality in South African classrooms. The Constitution of South Africa (Act 108 of 1996) and the national language policy recognize language rights and aims at supporting, promoting and developing the official languages. However, despite the advantages of mother tongue education, English is often chosen as language of learning and teaching at the cost of the African official languages. This study proposes the accommodation and promotion of multilingualism through blended l...
de la Fuente Marcos, C.; de la Fuente Marcos, R.
2014-07-01
Uranus has three known co-orbitals: 83982 Crantor (2002 GO9), 2010 EU65 and 2011 QF99. All of them were captured in their current resonant state relatively recently. Here, we perform a comparative analysis of the orbital evolution of these transient co-orbitals to understand better how they got captured in the first place and what makes them dynamically unstable. We also look for additional temporary Uranian co-orbital candidates among known objects. Our N-body simulations show that the long-term stability of 2011 QF99 is controlled by Jupiter and Neptune; it briefly enters the 1:7 mean motion resonance with Jupiter and the 2:1 with Neptune before becoming a Trojan and prior to leaving its tadpole orbit. During these ephemeral two-body mean motion resonance episodes, apsidal corotation resonances are also observed. For known co-orbitals, Saturn is the current source of the main destabilizing force but this is not enough to eject a minor body from the 1:1 commensurability with Uranus. These objects must enter mean motion resonances with Jupiter and Neptune in order to be captured or become passing Centaurs. Asteroid 2010 EU65, a probable visitor from the Oort cloud, may have been stable for several Myr due to its comparatively low eccentricity. Additionally, we propose 2002 VG131 as the first transient quasi-satellite candidate of Uranus. Asteroid 1999 HD12 may signal the edge of Uranus' co-orbital region. Transient Uranian co-orbitals are often submitted to complex multibody ephemeral mean motion resonances that trigger the switching between resonant co-orbital states, making them dynamically unstable. In addition, we show that the orbital properties and discovery circumstances of known objects can be used to outline a practical strategy by which additional Uranus' co-orbitals may be found.
Adaptive Locomotion of Multibody Snake-like Robot
Meister, Eugen; Kernbach, Serge
2011-01-01
This paper represents an adaptive rhythmic control for a snake-like robot with 25 degrees of freedom. The adaptive gait control is implemented in algorithmic way in simulation and on a real robot. We investigated behavioral and energetic properties of this control and a dynamics of different body segments. It turned out that despite using homogeneous generators, physical constraints have an inhomogeneous impact on neighbor body segments. By analytical modeling of such dynamics, it may result in heterogeneous coupling of oscillators for a rhythmic control and impact scalability and synchronization effects of gait pattern generators.
Designing of Multibody Gravity Assist Tours in Jovian System for the Satellite Landing
Grushevskii, Alexey; Koryanov, Victor; Tuchin, Andrey; Golubev, Yury
the other implementation of P2 can be used. They are- “crossed” gravity assists from one small body G(“Ganymede”) to the second small body NG(“Not Ganymede”, generally for a not big TID it is Callisto) and then - in the opposite direction. We can “to outwit” the Tisserand’s criterion like this. It allows us to build special effective “phase beam”(PB) methods of orbit design synthesis for landing space mission in classes of encounter sequences-disjunctions G-NG-G (or modified G-…-G-NG-…-NG-G-…). As the result, the idea of adaptive synthesis of mission design was constructed by authors. Then it was implemented by effective algorithm. The corresponding numerical scheme was developed with using Tisserand-Poincare graph and the simulation of hundreds of thousands of options formation of the calculation. The DeltaV-low cost searching was utilized also for trajectory design with help of multiple rebounds of phase beams modeling. REFERENCES 1. Golubev Yu.F., Grushevskii A.V., Koryanov V.V., Tuchin A.G. A Method of Orbits Designing Using Gravity Assist Maneuvers To The Landing on the Jovian’s Moons // International Colloquium and Workshop Ganymede Lander: scientific goals and experiments, Moscow, March 4-8, 2013. URL: http://glcw2013.cosmos.ru/presentations 2. Campagnola S., Russell R.P. Endgame Problem. Part 2: Multi-Body Technique and TP Graph // Journal of Guidance, Control, and Dynamics, Vol. 33, No. 2, 2010, pp. 476-486, doi:10.2514/1.44290
An efficient 3D approach is proposed for simulating the complicated responses of the multi-body structure in reactor core under seismic loading. By utilizing the rigid-body and connector functions of the software Abaqus, the multi-body structure of the reactor core is simplified as a mass-point system interlinked by spring-dashpot connectors. And reasonable schemes are used for determining various connector coefficients. Furthermore, a scripting program is also complied for the 3D parametric modeling. Numerical examples show that, the proposed method can not only produce the results which satisfy the engineering requirements, but also improve the computational efficiency more than 100 times. (authors)
I. G. Ovechkin
2015-01-01
Full Text Available Increased load on the visual analyzer of an operator, increase in everyday visual performance, universal introduction of information displaying on cathode-ray tubes result in temporary and stable visual disturbances. Accommodative refractive apparatus of an eye is one of the key points of application of visually intensive labor. Work associated with permanent eyestrain overloads oculomotor and accommodative apparatus thus provoking myopic shift, increase in dynamic refraction, exophoric or esophoric shift of initial visual equilibrium. Accommodation disorders are accompanied by changes in ciliary muscle blood supply, abnormalities of vegetative segment regulation, parasympathetic brain vascular dystonia due to the decreased tonus of sympathetic nervous system. Evaluation of certain kind of activity in terms of ergonomics includes examination of visual status and visual working capacity, development of visual professiograms and vision standards for certain professions, justification of methods and tools of visual work optimization. Visual disturbances in operators developing in the course of visually intensive occupational work should be considered from the viewpoint of traditional accommodation and refraction disorders as well as functional manifestations of general fatigue or thoracic cervical spine dysfunction. Symptoms of accommodative asthenopia can be regarded as a functional manifestation of general fatigue syndrome or functional neurosis. Development of multidisciplinary approach to the correction of accommodation refraction disorders in visually intensive labor persons is of scientific urgency and practical reasonability. There is a long-felt need in additional attraction of different specialists who use in their work physical factors for accommodative asthenopia correction. Development of multidisciplinary approach to accommodation refraction disorder correction in visually intensive labor persons is based on syndromic pathogenic
Finite element multibody simulation of a breathing crack in a rotor with a cohesive zone model
Liong, Rugerri Toni; Proppe, Carsten
2014-01-01
The breathing mechanism of a transversely cracked shaft and its influence on a rotor system that appears due to shaft weight and inertia forces is studied. The presence of a crack reduces the stiffness of the rotor system and introduces a stiffness variation during the revolution of the shaft. Here, 3D finite element (FE) model and multibody simulation (MBS) are introduced to predict and to analyse the breathing mechanism on a transverse cracked shaft. It is based on a cohesive zone model (CZ...
Selection of component modes for the simulation of flexible multibody spacecraft
Spanos, John T.; Tsuha, Walter S.
1990-01-01
This paper describes a procedure for the selection of component modes employed in discretization of component deformation in a flexible multibody spacecraft. The emphasis is placed on the selection of modes which adequately represent the interaction of the various on-board control systems with the vehicle structural flexibility. The method combines the component mode synthesis approaches of Craig-Bampton (1968), MacNeal (1971) and Rubin (1975), and Benfield-Hruda (1971) with the modal balancing method of Moore (1981) and Gregory (1984). The procedure, which is applicable to both articulating and nonarticulating systems, was used to develop a low-order model of the three-body articulating Galileo spacecraft.
Measuring $CP$ violation and mixing in charm with inclusive self-conjugate multibody decay modes
Malde, S; Wilkinson, G
2015-01-01
Time-dependent studies of inclusive charm decays to multibody self-conjugate final states can be used to determine the indirect $CP$-violating observable $A_\\Gamma$ and the mixing observable $y_{CP}$, provided that the fractional $CP$-even content of the final state, $F_+$, is known. This approach can yield significantly improved sensitivity compared with the conventional method that relies on decays to $CP$ eigenstates. In particular, $D \\to \\pi^+\\pi^-\\pi^0$ appears to be an especially powerful channel, given its relatively large branching fraction and the high value of $F_+$ that has recently been measured at charm threshold.
Measuring C P violation and mixing in charm with inclusive self-conjugate multibody decay modes
Malde, S.; Thomas, C.; Wilkinson, G.
2015-05-01
Time-dependent studies of inclusive charm decays to multibody self-conjugate final states can be used to determine the indirect C P -violating observable AΓ and the mixing observable yC P , provided that the fractional C P -even content of the final state, F+ , is known. This approach can yield significantly improved sensitivity compared with the conventional method that relies on decays to C P eigenstates. In particular, D →π+π-π0 appears to be an especially powerful channel, given its relatively large branching fraction and the high value of F+ that has recently been measured at charm threshold.
Direct CPV in two-body and multi-body charm decays at LHCb
,
2014-01-01
The Standard Model predicts CP asymmetries in charm decays of $O(10^{-3})$ and the observation of significantly larger CP violation could indicate non-Standard Model physics effects. During 2011 and 2012, the LHCb experiment collected a sample corresponding to 3/fb yielding the world's largest sample of decays of charmed hadrons. This allowed the CP violation in charm to be studied with unprecedented precision in many two- body and multibody decay modes. The most recent LHCb searches for direct CP violation are presented in these proceedings.
Direct $CPV$ in two-body and multi-body charm decays at LHCb
Gersabeck, Evelina
2014-01-01
The Standard Model predics $CP$ asymmetries in charm decays of $O$(10$^{-3}$) and the observation of significantly larger $CP$ violation could indicate non-Standard Model physics effects. During 2011 and 2012, the LHCb experiment collected a sample corresponding to 3$/fb$ yielding the worlds largest sample of decays of charmed hadrons. This allowed the $CP$ violation in charm to be studied with unprecedented precision in many two- body and multibody decay modes. The most recent LHCb searches for direct $CP$ violation are presented in these proceedings.
46 CFR 108.197 - Construction of accommodation spaces.
2010-10-01
... UNITS DESIGN AND EQUIPMENT Construction and Arrangement Accommodation Spaces § 108.197 Construction of accommodation spaces. (a) Each sleeping, mess, recreational, or hospital space that is adjacent to or... readily enter any sleeping, mess, recreational, or hospital space....
Reimbursement of education fees / accommodation fees
2003-01-01
Your attention is drawn to the 20 km distance limit set in Article R A 8.01 of the Staff Regulations, namely, that only accommodation fees of students attending an educational establishment which is more than 20 km from the place of residence and the duty station of the member of the personnel are reimbursed by the Organization, subject to the percentage rate and maximum amounts set out in this article and in Administrative Circular N° 12. Human Resources Division Tel: 72862 / 74474
Reminder : Reimbursement of education fees / accommodation fees
2003-01-01
Your attention is drawn to the 20 km distance limit set in Article R A 8.01 of the Staff Regulations, namely, that only accommodation fees of students attending an educational establishment which is more than 20 km from the place of residence and the duty station of the member of the personnel are reimbursed by the Organization, subject to the percentage rate and maximum amounts set out in this article and in Administrative Circular N° 12. Human Resources Division Tel : 72862 / 74474
Modelling of structural flexiblity in multibody railroad vehicle systems
Escalona, José L.; Sugiyama, Hiroyuki; Shabana, Ahmed A.
2013-07-01
This paper presents a review of recent research investigations on the computer modelling of flexible bodies in railroad vehicle systems. The paper will also discuss the influence of the structural flexibility of various components, including the wheelset, the truck frames, tracks, pantograph/catenary systems, and car bodies, on the dynamics of railroad vehicles. While several formulations and computer techniques for modelling structural flexibility are discussed in this paper, a special attention is paid to the floating frame of reference formulation which is widely used and leads to reduced-order finite-element models for flexible bodies by employing component modes synthesis techniques. Other formulations and numerical methods such as semi-analytical approaches, absolute nodal coordinate formulation, finite-segment method, boundary elements method, and discrete elements method are also discussed. This investigation is motivated by the fact that the structural flexibility can have a significant effect on the overall dynamics of railroad vehicles, ride comfort, vibration suppression and noise level reduction, lateral stability, track response to vehicle forces, stress analysis, wheel-rail contact forces, wear and crashworthiness.
Vehicle dynamics modeling and simulation
Schramm, Dieter; Bardini, Roberto
2014-01-01
The authors examine in detail the fundamentals and mathematical descriptions of the dynamics of automobiles. In this context different levels of complexity will be presented, starting with basic single-track models up to complex three-dimensional multi-body models. A particular focus is on the process of establishing mathematical models on the basis of real cars and the validation of simulation results. The methods presented are explained in detail by means of selected application scenarios.
Implementation of A Geometric Constraint Regularization For Multibody System Models
Müller Andreas
2014-08-01
Full Text Available Redundant constraints in MBS models severely deteriorate the computational performance and accuracy of any numerical MBS dynamics simulation method. Classically this problem has been addressed by means of numerical decompositions of the constraint Jacobian within numerical integration steps. Such decompositions are computationally expensive. In this paper an elimination method is discussed that only requires a single numerical decomposition within the model preprocessing step rather than during the time integration. It is based on the determination of motion spaces making use of Lie group concepts. The method is able to reduce the set of loop constraints for a large class of technical systems. In any case it always retains a sufficient number of constraints. It is derived for single kinematic loops.
Rapid Onboard Trajectory Design for Autonomous Spacecraft in Multibody Systems
Trumbauer, Eric Michael
This research develops automated, on-board trajectory planning algorithms in order to support current and new mission concepts. These include orbiter missions to Phobos or Deimos, Outer Planet Moon orbiters, and robotic and crewed missions to small bodies. The challenges stem from the limited on-board computing resources which restrict full trajectory optimization with guaranteed convergence in complex dynamical environments. The approach taken consists of leveraging pre-mission computations to create a large database of pre-computed orbits and arcs. Such a database is used to generate a discrete representation of the dynamics in the form of a directed graph, which acts to index these arcs. This allows the use of graph search algorithms on-board in order to provide good approximate solutions to the path planning problem. Coupled with robust differential correction and optimization techniques, this enables the determination of an efficient path between any boundary conditions with very little time and computing effort. Furthermore, the optimization methods developed here based on sequential convex programming are shown to have provable convergence properties, as well as generating feasible major iterates in case of a system interrupt -- a key requirement for on-board application. The outcome of this project is thus the development of an algorithmic framework which allows the deployment of this approach in a variety of specific mission contexts. Test cases related to missions of interest to NASA and JPL such as a Phobos orbiter and a Near Earth Asteroid interceptor are demonstrated, including the results of an implementation on the RAD750 flight processor. This method fills a gap in the toolbox being developed to create fully autonomous space exploration systems.
Mitchell Scheiman, OD
2014-01-01
Full Text Available Background: To evaluate objective changes in vergence and accommodation after treatment of symptomatic convergence insufficiency (CI with office-based optometric vision therapy in a pediatric patient. Case Report: A 10-year, 10-month-old child with symptomatic CI was treated with 16 visits of office-based vision therapy with home reinforcement. Pre- and post-therapy testing included both traditional clinical measures and objective laboratory measures of vergence and accommodation. The main clinical outcome measures were the CI Symptom Survey (CISS, near point of convergence (NPC, positive fusional vergence range at near (PFV, accommodative amplitude, and accommodative facility. The objective vergence range outcome measures were peak velocity, time constant, total response time, and steady-state response variability as assessed with the Power Refractor II. The objective accommodative outcome measures were peak velocity, time constant, total response time, steady-state response variability, and steady-state level, as assessed with the Grand Seiko WAM-5500. Most accommodative and vergence objective laboratory parameters improved/normalized following the vision therapy. Gains were greater for vergence than for accommodation. These objective measures confirmed the concurrent improvements in the clinical tests and markedly reduced symptom levels. Conclusions: This is the first study to document, objectively, improvements in laboratory-based dynamic measures of both accommodation and vergence following conventional office-based optometric vision therapy for CI in a child. Objective oculomotor measures can and should be performed in similar future studies in children, as well as in adults
Passive dynamic controllers for non-linear mechanical systems
Juang, Jer-Nan; Wu, Shih-Chin; Phan, Minh; Longman, Richard W.
1992-01-01
The objective is to develop active model-independent controllers for slewing and vibration control of nonlinear multibody flexible systems, including flexible robots. The topics are presented in viewgraph form and include: passive stabilization; work-energy rate principle; Liapunov theory; displacement feedback; dynamic controller; displacement and acceleration feedback; velocity feedback; displacement feedback; physical interaction; a 6-DOF robot; and simulation results.
Multibody Interactions, Phase Behavior and Clustering in Nanoparticle-Polyelectrolyte Mixtures
Ganesan, Venkatraghavan; Pandav, Gunja; Pryamitsyn, Victor; Errington, Jeffrey
We present the results of a computational study of the interactions, phase-behavior and aggregation characteristics of charged nanoparticles (CNPs) suspended in solution of oppositely charged polyelectrolytes (PEs). We used an extension of the mean-field polymer self-consistent field theory (SCFT) model to explicitly characterize the multibody interactions in such systems. For dilute-moderate particle volume fractions, the magnitudes of three and higher multibody interactions were seen to be weak relative to the contributions from pair interactions. We embedded the pair-interaction potentials within a thermodynamic perturbation theory approach to identify the phase behavior of such systems. The results of such a framework suggested that the gas and FCC crystal phases were thermodynamically stable, whereas the fluid-like phase was metastable in such systems. To complement the parameters studied, we used a recently developed simulation approach to study the aggregation and cluster morphologies in CNP-PE mixtures. For low particle charges, such systems mainly exhibited clusters arising from direct contact aggregation between CNPs. However, for higher particle and PE charges and low PE concentrations, large regions of PE-bridged clusters were seen to form.
Simulation of Moving Loads in Elastic Multibody Systems With Parametric Model Reduction Techniques
Fischer Michael
2014-08-01
Full Text Available In elastic multibody systems, one considers large nonlinear rigid body motion and small elastic deformations. In a rising number of applications, e.g. automotive engineering, turning and milling processes, the position of acting forces on the elastic body varies. The necessary model order reduction to enable efficient simulations requires the determination of ansatz functions, which depend on the moving force position. For a large number of possible interaction points, the size of the reduced system would increase drastically in the classical Component Mode Synthesis framework. If many nodes are potentially loaded, or the contact area is not known a-priori and only a small number of nodes is loaded simultaneously, the system is described in this contribution with the parameter-dependent force position. This enables the application of parametric model order reduction methods. Here, two techniques based on matrix interpolation are described which transform individually reduced systems and allow the interpolation of the reduced system matrices to determine reduced systems for any force position. The online-offline decomposition and description of the force distribution onto the reduced elastic body are presented in this contribution. The proposed framework enables the simulation of elastic multibody systems with moving loads efficiently because it solely depends on the size of the reduced system. Results in frequency and time domain for the simulation of a thin-walled cylinder with a moving load illustrate the applicability of the proposed method.
Cronskär, Marie; Rasmussen, John; Tinnsten, Mats
2015-01-01
This paper addresses the evaluation of clavicle fixation devices, by means of computational models. The aim was to develop a method for comparison of stress distribution in various fixation devices, to determine whether the use of multibody musculoskeletal input in such model is applicable and to report the approach. The focus was on realistic loading and the motivation for the work is that the treatment can be enhanced by a better understanding of the loading of the clavicle and fixation device. The method can be used to confirm the strength of customised plates, for optimisation of new plates and to complement experimental studies. A finite element (FE) mesh of the clavicle geometry was created from computed tomography data and imported into the FE solver where the model was subjected to muscle forces and other boundary conditions from a multibody musculoskeletal model performing a typical activity of daily life. A reconstruction plate and screws were also imported into the model. The combination models returned stresses and displacements of plausible magnitudes in all included parts and the result, upon further development and validation, may serve as a design guideline for improved clavicle fixation. PMID:24156391
Concurrent multibody and Finite Element analysis of the lower-limb during amputee running.
Rigney, Stacey M; Simmons, Anne; Kark, Lauren
2015-08-01
Lower-limb amputee athletes use Carbon fiber Energy Storage and Return (ESAR) prostheses during high impact activities such as running. The advantage provided to amputee athletes due to the energy-storing properties of ESAR prostheses is as yet uncertain. Conventional energy analysis methods for prostheses rely upon multibody models with articulating joints. Alternatively, Finite Element (FE) analysis treats bodies as a deforming continuum and can therefore calculate the energy stored without using these rigid-body mechanics assumptions. This paper presents a concurrent multibody and FE model of the femur, tibia, socket and ESAR prosthesis of a transtibial amputee athlete during sprinting. Gait analysis spatial data was used to conduct an offline simulation of the affected leg's stance phase in COMSOL Multiphysics. The calculated peak elastic strain energy of the prosthesis was 80J, with an overall RMSE of simulated marker displacement of 4.19 mm. This concurrent model presents a novel method for analyzing in vivo ESAR prosthesis behavior. PMID:26736785
Holm-Jørgensen, Kristian; Nielsen, Søren R.K.
The paper deals with different updating algorithms of the moving frame of reference parameters in a multibody formulation for flexible structures. The updating algorithms are based on the motion of one or two beam element nodes in the belonging substructure. An example of a clamped wind turbine...
Accommodating profile dynamism in MiFID II
Hübner, Georges; Plunus, Séverine
2013-01-01
The requirements of the MiFID I and II Directives regarding suitability of investor's advice seem a burden to many banks. Such a point of view induces them, in turn, to consider investor profiling with great reluctance, and restrict their view on the administrative side only. In this paper, we claim that a genuine client-centric advisory process could turn the personal information gathering and analysis stage into a real asset for a loyal and mutually profitable relationship. The recognition ...
Schiehlen, Werner
2014-01-01
Applied Dynamics is an important branch of engineering mechanics widely applied to mechanical and automotive engineering, aerospace and biomechanics as well as control engineering and mechatronics. The computational methods presented are based on common fundamentals. For this purpose analytical mechanics turns out to be very useful where D’Alembert’s principle in the Lagrangian formulation proves to be most efficient. The method of multibody systems, finite element systems and continuous systems are treated consistently. Thus, students get a much better understanding of dynamical phenomena, and engineers in design and development departments using computer codes may check the results more easily by choosing models of different complexity for vibration and stress analysis.
The interactive processes of accommodation and vergence.
Semmlow, J L; Bérard, P V; Vercher, J L; Putteman, A; Gauthier, G M
1994-01-01
A near target generates two different, though related stimuli: image disparity and image blur. Fixation of that near target evokes three motor responses: the so-called oculomotor "near triad". It has long been known that both disparity and blur stimuli are each capable of independently generating all three responses, and a recent theory of near triad control (the Dual Interactive Theory) describes how these stimulus components normally work together in the aid of near vision. However, this theory also indicates that when the system becomes unbalanced, as in high AC/A ratios of some accommodative esotropes, the two components will become antagonistic. In this situation, the interaction between the blur and disparity driven components exaggerates the imbalance created in the vergence motor output. Conversely, there is enhanced restoration when the AC/A ratio is effectively reduced surgically. PMID:7633627
Biomimetic accommodating lens with implementation in MEMS
Hogan, Alexander L.; Baker, Brian; Fisher, Charles; Naylor, Stephen; Fettig, Doug; Harvey, Ian R.
2012-03-01
We describe an accommodating lens patterned after the crystalline lens of the eye. Our biomimetic MEMS design calls to mind the zonules of zinn which pull radially to stretch the crystalline lens of the eye to modify the optical path. We present initial characterization of the prototype macro-scale device constructed through traditional machining techniques and using a PDMS polymer lens. Testing of the macro-scale lens indicated a 22% change in focal length through the range of radial stretching, with degradation of the spherical lens shape but no hysteresis after low-cycle testing. We also demonstrate a MEMS implementation of the lens actuator constructed using the Sandia SUMMiT-V ™ surface micromachining process. The optical path of this system is approximately 300 microns in diameter, providing a platform to potential applications improving mobile camera optics and medical imaging.
Accommodating life sciences on the Space Station
Arno, Roger D.
1987-01-01
The NASA Ames Research Center Biological Research Project (BRP) is responsible for identifying and accommodating high priority life science activities, utilizing nonhuman specimens, on the Space Station and is charged to bridge the gap between the science community and the Space Station Program. This paper discusses the approaches taken by the BRP in accomodating these research objectives to constraints imposed by the Space Station System, while maintaining a user-friendly environment. Consideration is given to the particular research disciplines which are given priority, the science objectives in each of these disciplines, the functions and activities required by these objectives, the research equipment, and the equipment suits. Life sciences programs planned by the Space Station participating partners (USA, Europe, Japan, and Canada) are compared.
Helsen, Jan; Marrant, Ben; Vanhollebeke, Frederik; De Coninck, Filip; Berckmans, Dries; Vandepitte, Dirk; Desmet, Wim
2013-10-01
Reliable gearbox design calculations require sufficient insight in gearbox dynamics, which is determined by the interaction between the different excitation mechanisms and the gearbox modal behavior. Both external gearbox excitation originating from the wind turbine drive train and internal gearbox excitation are important. Moreover with regard to the modal behavior the different gearbox structural components: planet carrier, shafts and housing are of influence. The main objective of this article is the experimental investigation of the interaction between the different excitation mechanisms and the gearbox modal behavior. The insights gathered are used to prove the need for accurate gear mesh representation and structural flexibility within the corresponding flexible multibody gearbox simulation model. Experiments are conducted on a dynamic 13.2 MW test facility on which two multi-megawatt wind turbine gearboxes are placed back to back and subjected to a speed run-up. Measurement sensors consist of bearing displacement sensors, torque sensors, encoders and accelerometers distributed over the gearbox. Excitation order amplitudes on different locations in the gearbox are determined by means of a Time Varying Discrete Fourier Transform (TVDFT) order tracking on the measured sensor signals. Moreover the propagation of this excitation throughout the gearbox is assessed. Relating the orders to the corresponding excitation source allows the definition of order influence regions within the gearbox. The interaction between the gear mesh order excitation and structural flexibility is shown.
Modeling and identification of passenger car dynamics using robotics formalism
Venture, Gentiane; Ripert, Pierre-Jean; Khalil, Wisama; Gautier, Maxime; Bodson, Philippe
2006-01-01
This paper deals with the problem of dynamicmodeling and identification of passenger cars. It presents a new method that is based on robotics techniques for modeling and description of tree-structured multibody systems. This method enables us to systematically obtain the dynamic identification model, which is linear with respect to the dynamic parameters. The estimation of the parameters is carried out using a weighted least squares method. The identification is tested using vehicle dynamics ...
Tobias Strenger; Stefan Lehner; Frank Böhnke; Theodor Bretan
2013-01-01
The transfer characteristic of the human middle ear with an applied middle ear implant (floating mass transducer) is examined computationally with a Multi-body System approach and compared with experimental results. For this purpose, the geometry of the middle ear was reconstructed from μ-computer tomography slice data and prepared for a Multi-body System simulation. The transfer function of the floating mass transducer, which is the ratio of the input voltage and the generated force, is deri...
Evaluation of Accommodation Companies Recreation Activities in İstanbul
ALBAYRAK, Aslı
2012-01-01
Recreation activities represent quality of company, image and attractiveness for both staying guests and day use guests. At the same time recreation can be important income source for accommodation companies. This study investigate the web page of 82 five star accommodation company in Istanbul from the side of recreation activities. At the end of the study find that most of accommodation company don't have in place recreation activities, recreation tab and representation about activities in t...
Relative Importance of Student Accommodation Quality in Higher Education
Simon Gyasi Nimako; Francis Kwesi Bondinuba
2013-01-01
This study, which was part of a large study, empirically examinesthe importance students attach to different dimensions of Student Accommodation Quality (SAQ) delivered by Student Accommodation Providers (SAP) in two tertiary (higher education) institutions in Ghana. The study involved a cross-sectional survey that used a structured questionnaire administered to 700 tertiary students in residential and non-residential accommodation. The survey yielded a usable 66.6% response rate for analysis...
Restoration of accommodation: surgical options for correction of presbyopia
Glasser, Adrian
2008-01-01
Accommodation is a dioptric change in the power of the eye to see clearly at near. Ciliary muscle contraction causes a release in zonular tension at the lens equator, which permits the elastic capsule to mould the young lens into an accommodated form. Presbyopia, the gradual age-related loss of accommodation, occurs primarily through a gradual age-related stiffening of the lens. While there are many possible options for relieving the symptoms of presbyopia, only relatively recently has consid...
Marketing of Accommodation services : Case-Hotel Azam Cameroon
Youkam, Germaine
2012-01-01
Cameroon is Africa in miniature with a lot of tourist attractions owing to its geological and cultural diversity. Natural features include beaches, deserts, mountains, rainforests, and savannas. Accommodation services have been a grand phenomenon within the tourism industry in Cameroon. The accommodation sector has developed tremendously within the past decades. The objective of this research work was to find about out the marketing of accommodation services in Cameroon with Hotel Azam as...
Can Partial Structures Accommodate Inconsistent Science?
Peter Vickers
2009-08-01
Full Text Available The semantic approach to scientific representation is now long established as a favourite amongst philosophers of science. One of the foremost strains of this approach—the model-theoretic approach (MTA—is to represent scientific theories as families of models, all of which satisfy or ‘make true’ a given set of constraints. However some authors (Brown 2002, Frisch 2005 have criticised the approach on the grounds that certain scientific theories are logically inconsistent, and there can be no models of an inconsistent set of constraints. Thus it would seem that the MTA fails to represent inconsistent scientific theories at all, and this raises concerns about the way it represents in general. In a series of papers (1990, 1993, 1995 and a recent book (2003 da Costa and French have developed a variant of the MTA approach which they call ‘partial structures’, and which they claim can accommodate inconsistent theories. I assess this claim, looking to two theories which have been called ‘inconsistent’: Bohr’s theory of the atom and classical electrodynamics.
Development of a real-time bogie test rig model based on railway specialised multibody software
Spiryagin, Maksym; Sun, Yan Quan; Cole, Colin; McSweeney, Tim; Simson, Scott; Persson, Ingemar
2013-02-01
The design of mechatronic systems of rail vehicles requires performing verification and validation in the real-time mode. One useful validation instrument is the application of software-in-the-loop, hardware-in-the-loop or processor-in-the-loop simulation approaches. All of these approaches require development of a real-time model of the physical system. In this paper, the investigation of the usage of the model of the locomotive's bogie test rig created in Gensys multibody software has been performed and the calculation time for each time step has been analysed. The verification of the possibility of the usage of such an approach for real-time simulation has been made by means of a simple data transferring process between Gensys and Simulink through the TCP/IP interface. The limitations and further development issues for the proposed approach have been discussed in this paper.
A multi-body vehicle for moving inside cluttered nuclear environment
The paper presents the result of the TALOS (Technologies for Advanced locomotion Systems) programme. The general aim of the TALOS was to prove the feasibility of multi-body articulated vehicles for intervention missions in nuclear plant were high payload volume and mass are required, combined with great geometrical and obstacles constraints. This programme was based on one hand on the TLV (Train Like Vehicle) concept, developed by CEA ( Atomic Energy Commission) and on the other hand on the KfK experience on locomotion. The main difficulties of this programme were to find the mechanical linkage concept and the locomotion concept, and also to build an integrated mockup with linkage and locomotion concepts. (TEC). 4 refs., 5 figs
On the modeling of the intervertebral joint in multibody models for the spine
Christophy, Miguel, E-mail: christophy@gmail.com [University of California at Berkeley, Department of Mechanical Engineering (United States); Curtin, Maurice, E-mail: moecurtin@gmail.com [University College Dublin, School of Electrical, Electronic and Communications Engineering (Ireland); Faruk Senan, Nur Adila, E-mail: adilapapaya@gmail.com [University of California at Berkeley, Department of Mechanical Engineering (United States); Lotz, Jeffrey C., E-mail: lotzj@orthosurg.ucsf.edu [University of California at San Francisco, Department of Orthopaedic Surgery (United States); O’Reilly, Oliver M., E-mail: oreilly@berkeley.edu [University of California at Berkeley, Department of Mechanical Engineering (United States)
2013-12-15
The need to develop feasible computational musculoskeletal models of the spine has led to the development of several multibody models. Central features in these works are models for the ligaments, muscles, and intervertebral joint. The purpose of the present paper is to show how experimental measurements of joint stiffnesses can be properly incorporated using a bushing element. The required refinements to existing bushing force functions in musculoskeletal software platforms are discussed and further implemented using a SpineBushing element specific to the intervertebral joint. Four simple lumbar spine models are then used to illustrate the accompanying improvements. Electronic supplemental material for this article includes a complementary review of formulations of stiffness matrices for the intervertebral joint.
Application of Runge-Kutta-Rosenbrock Methods to the Analysis of Flexible Multibody Systems
Numerical integration methods are discussed for general equations of motion for multibody systems with flexible parts, which are fairly stiff, time-dependent and non-linear. A family of semi-implicit methods, which belong to the class of Runge-Kutta-Rosenbrock methods, with rather weak non-linear stability properties, are developed. These comprise methods of first, second and third order of accuracy that are A-stable and L-stable and hence introduce numerical damping and the filtering of high frequency components. It is shown, both from theory and examples, that it is generally preferable to use deformation mode coordinates to global nodal coordinates as independent variables in the formulation of the equations of motion. The methods are applied to a series of examples consisting of an elastic pendulum, a beam supported by springs, a four-bar mechanism, and a robotic manipulator with collocated control
Kelkar, Atul G.; Joshi, Suresh M.
1994-01-01
Global asymptotic stability of a class of nonlinear multibody flexible space-stnuctures under dissipative compensation is established. Two cases are considered. The first case allows unlimited nonlinear motions of the entire system and uses quaternion feedback. The second case assumes that the central body motion is in the linear range although the other bodies can undergo unrestricted nonlinear motion. The stability is proved to be robust to the inherent modeling nonlinearities and uncertainties. Furthermore for the second case the stability is also shown to be robust to certain actuator and sensor nonlinearities. The stability proofs use the Lyapunov approach and exploit the inherent passivity of such systems. The results are applicable to a wide class of systems including flexible space-structures with articulated flexible appendages.
Heading Control System for a Multi-body Vehicle with a Virtual Test Driver
POSTALCIOGLU OZGEN, S.
2010-08-01
Full Text Available This paper includes a Heading Control (HC system for a multi-body vehicle. HC system helps reducing the required torque from the driver and improves the lane keeping efficiency. HC system is important for safety and driver comfort in traffic. The controller performance is examined on a virtual test drive platform. The optimal control theory is applied to HC system and examined on a curved path and under a side wind disturbance. Different assistance levels are applied to see the characteristics of the controller with different virtual test drivers. The results are analyzed based on three performance indices; lane keeping performance (LKP index, assist torque performance (ATP index and driver torque performance (DTP index. As seen from the results while using HC system the lateral displacement decreases as the lane keeping performance increases and the driver torque performance decreases as the assist torque performance increases.
Kipping, David M; Jasinski, Jamie M; Manthri, Varun P
2011-01-01
We present a novel method to determine eccentricity constraints of extrasolar planets in systems with multiple transiting planets through photometry alone. Our method is highly model independent, making no assumptions about the stellar parameters and requiring no radial velocity, transit timing or occultation events. Our technique exploits the fact the light curve derived stellar density must be the same for all planets transiting a common star. Assuming a circular orbit, the derived stellar density departs from the true value by a predictable factor, Psi, which contains information on the eccentricity of the system. By comparing multiple stellar densities, any differences must be due to eccentricity and thus meaningful constraints can be placed in the absence of any other information. The technique, dubbed "Multibody Asterodensity Profiling" (MAP), is a new observable which can be used alone or in combination with other observables, such as radial velocities and transit timing variations. An eccentricity pri...
On the modeling of the intervertebral joint in multibody models for the spine
The need to develop feasible computational musculoskeletal models of the spine has led to the development of several multibody models. Central features in these works are models for the ligaments, muscles, and intervertebral joint. The purpose of the present paper is to show how experimental measurements of joint stiffnesses can be properly incorporated using a bushing element. The required refinements to existing bushing force functions in musculoskeletal software platforms are discussed and further implemented using a SpineBushing element specific to the intervertebral joint. Four simple lumbar spine models are then used to illustrate the accompanying improvements. Electronic supplemental material for this article includes a complementary review of formulations of stiffness matrices for the intervertebral joint
Sub-discretized surface model with application to contact mechanics in multi-body simulation
Johnson, S; Williams, J
2008-02-28
The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidates assumptions for popular models of contact, such as the Hertzian and its derivatives, for the non-adhesive case, and the JKR and DMT models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.
Take-off and Landing Using Ground Based Power - Landing Simulations Using Multibody Dynamics
P. Wu; Voskuijl, M; van Tooren, M. J. L.
2014-01-01
A novel take-off and landing system using ground based power is proposed in the EUFP7 project GABRIEL. The proposed system has the potential benefit to reduce aircraft weight, emissions and noise. A preliminary investigation of the feasibility of the structural design of the connection mechanism between aircraft and ground system has been performed by simulating the landing procedure on a moving ground system. One of the key challenges is the landing on a moving ground system under high cross...
Take-off and Landing Using Ground Based Power - Landing Simulations Using Multibody Dynamics
Wu, P.; Voskuijl, M.; Van Tooren, M.J.L.
2014-01-01
A novel take-off and landing system using ground based power is proposed in the EUFP7 project GABRIEL. The proposed system has the potential benefit to reduce aircraft weight, emissions and noise. A preliminary investigation of the feasibility of the structural design of the connection mechanism bet
Plantar pressure analysis of accommodative insole in older people with metatarsalgia.
Chang, Bao-Chi; Liu, Ding-Hao; Chang, Jeffrey Liao; Lee, Si-Huei; Wang, Jia-Yi
2014-01-01
Foot pain frequently reduces physical activity and increases the risk of falls in older people. In current orthotic management of forefoot pain, metatarsal padding is the main strategy to reduce metatarsal pressure. However, pressure reductions are usually diverse and limited. The multi-step accommodative insole is fabricated by sequential foam padding on Plastazote under dynamic accommodation in daily walking. The aims of this study were to investigate the effectiveness and mechanisms of accommodative insole on plantar pressure redistribution in older people with metatarsalgia. The study was conducted on 21 old outpatients with moderate to severe metatarsalgia, using the ethylene vinyl acetate control, 9-mm flat Plastazote, and accommodative insoles with and without metatarsal and arch support. Outcome measures included pressure-related variables measured by a Pedar-X system, and pain scores assessed with a 0-10 Visual Analog Scale. The accommodative insole significantly decreased peak pressure under the metatarsal heads by 47.2% (p<0.001) and the pain scores from 8.2 to 1.1 (p<0.001). Plantar pressure analyses indicated that the effects of dynamic metatarsal contouring and cushioning on reducing peak pressure were greater than those of metatarsal padding. The temporo-spatial relationships between the toe and metatarsal head can assist in explaining an elevated metatarsal pressure and higher risk of falls in older people with toe deformities. The multi-step insole is simple in orthotic fabrication and ensures an even distribution of plantar pressure loading in walking. It can effectively relieve metatarsalgia and help to preserve regular walking activity for older people with metatarsalgia. PMID:24119776
Martin Felix Jørgensen
2014-04-01
Full Text Available This paper investigates gear tooth fatigue damage in a 500 kW wind turbine using FLEX5 and own multibody code. FLEX5 provides the physical wind field, rotor and generator torque and the multibody code is used for obtaining gear tooth reaction forces in the planetary gearbox. Different turbulence levels are considered and the accumulated fatigue damage levels are compared. An example where the turbulence/fatigue sensitivity could be important, is in the middle of a big wind farm. Interior wind turbines in large wind farms will always operate in the wake of other wind turbines, causing increased turbulence and therefore increased fatigue damage levels. This article contributes to a better understanding of gear fatigue damage when turbulence is increased (e.g. in the center of large wind farms or at places where turbulence is pronounced.
46 CFR 190.20-20 - Sleeping accommodations.
2010-10-01
... 46 Shipping 7 2010-10-01 2010-10-01 false Sleeping accommodations. 190.20-20 Section 190.20-20... CONSTRUCTION AND ARRANGEMENT Accomodations for Officers, Crew, and Scientific Personnel § 190.20-20 Sleeping...) Sleeping accommodations for the crew must be divided into rooms, no one of which must berth more than...
Testing Accommodations: Theory and Research to Inform Practice
Kettler, Ryan J.
2012-01-01
This article presents a framework for practitioners in education and psychology to select accommodations based on student profiles and testing demands. A brief history of testing accommodations policy in the US and a definition of terms provide context for the discussion. A review of theory and empirical findings related to testing accommodations…
The Evolution of the Number of Tourists accommodated in Arad
Sergiu Rusu
2014-12-01
Full Text Available The paper analyses the evolution of the number of tourists accommodated in Arad between January 2006 and September 2009. For this purpose we have used the statistics data from the official sites. As variables we chose: X – independent variable - Total tourist arrival and accommodated in Arad, Y - dependent variable - Tourists staying in hotels.
46 CFR 127.260 - Ventilation for accommodations.
2010-10-01
... vessel of 100 or more gross tons must be provided with a mechanical ventilation system unless the... 46 Shipping 4 2010-10-01 2010-10-01 false Ventilation for accommodations. 127.260 Section 127.260... ARRANGEMENTS Particular Construction and Arrangements § 127.260 Ventilation for accommodations. (a)...
Regional Sign Language Varieties in Contact: Investigating Patterns of Accommodation
Stamp, Rose; Schembri, Adam; Evans, Bronwen G.; Cormier, Kearsy
2016-01-01
Short-term linguistic accommodation has been observed in a number of spoken language studies. The first of its kind in sign language research, this study aims to investigate the effects of regional varieties in contact and lexical accommodation in British Sign Language (BSL). Twenty-five participants were recruited from Belfast, Glasgow,…
Cultural value orientations, internalized homophobia, and accommodation in romantic relationships.
Gaines, Stanley O; Henderson, Michael C; Kim, Mary; Gilstrap, Samuel; Yi, Jennifer; Rusbult, Caryl E; Hardin, Deletha P; Gaertner, Lowell
2005-01-01
In the present study, we examined the impact of cultural value orientations (i.e., the personally oriented value of individualism, and the socially oriented values of collectivism, familism, romanticism, and spiritualism) on accommodation (i.e., voice and loyalty, rather than exit and neglect, responses to partners' anger or criticism) in heterosexual and gay relationships; and we examined the impact of internalized homophobia (i.e., attitudes toward self, other, and disclosure) on accommodation specifically in gay relationships. A total of 262 heterosexuals (102 men and 162 women) and 857 gays (474 men and 383 women) participated in the present study. Consistent with hypotheses, among heterosexuals and gays, socially oriented values were significantly and positively related to accommodation (whereas the personally oriented value of individualism was unrelated to accommodation); and among gays in particular, internalized homophobia was significantly and negatively related to accommodation. Implications for the study of heterosexual and gay relationships are discussed. PMID:16368666
Comparison on the rigid and flexible model of attitude maneuvering of a simple multi-body satellite
Teoh Vil Cherd; Shahriman Abu Bakar; Norhizam Hamzah; Sazali Yaacob; Ruslizam Daud,; Rakhmad Arief Siregar
2014-01-01
Rigid body assumption of a satellite model has been a common practice in spacecraft attitude manoeuvring. However, with the increasing demand for greater functionality of space activities, requires bigger and wider solar panels to cater the power needs. In this paper, simple rigid and flexible multi-body satellite model is derived using basic Newton’s second law and Assumed Mode Method. The response from both model are then simulated using MATLAB software while comparison is do...
We present a double-mapping method (D-MM), a natural combination of a similarity with F-expansion methods, for obtaining general solvable nonlinear evolution equations. We focus on variable-coefficients complex Ginzburg-Landau equations (VCCGLE) with multi-body interactions. We show that it is easy by this method to find a large class of exact solutions of Gross-Pitaevskii and Gross-Pitaevskii-Ginzburg equations. We apply the D-MM to investigate the dynamics of Bose-Einstein condensation with two- and three-body interactions. As a surprising result, we obtained that it is very easy to use the built D-MM to obtain a large class of exact solutions of VCCGLE with two-body interactions via a generalized VCCGLE with two- and three-body interactions containing cubic-derivative terms. The results show that the proposed method is direct, concise, elementary, and effective, and can be a very effective and powerful mathematical tool for solving many other nonlinear evolution equations in physics.
Trochimczuk R.
2014-11-01
Full Text Available Analytical formulas describing the kinematics and dynamics of a multibody system of a new polar positioning system dedicated to mechatronic laser glass or other transparent dielectrics engraving system will be presented in this work. The analytical results will become in the later stages of the research the basis of numerical simulations. They will optimize the proposed solution of the positioning system.
Trochimczuk, R.
2014-11-01
Analytical formulas describing the kinematics and dynamics of a multibody system of a new polar positioning system dedicated to mechatronic laser glass or other transparent dielectrics engraving system will be presented in this work. The analytical results will become in the later stages of the research the basis of numerical simulations. They will optimize the proposed solution of the positioning system.
Microgravity Flight: Accommodating Non-Human Primates
Dalton, Bonnie P.; Searby, Nancy; Ostrach, Louis
1995-01-01
thermoregulation, muscular, and cardiac responses to weightlessness. In contrast, the five completed Cosmos/Bion flights, lacked the metabolic samples and behavioral task monitoring, but did facilitate studies of the neurovestibular system during several of the flights. The RRF accommodated two adult 8-11 kg rhesus monkeys, while the Russian experiments and hardware were configured for a younger animal in the 44 kg range. Both the American and Russian hardware maintained a controlled environmental system, specifically temperature, humidity, a timed lighting cycle, and had means for providing food and fluids to the animal(s). Crew availability during a Shuttle mission was to be an optimal condition for retrieval and refrigeration of the animal urine samples along with a manual calcein injection which could lead to greater understanding of bone calcium incorporation. A special portable bioisolation glove box was under development to support this aspect of the experiment profile along with the capability of any contingency human intervention. As a result of recent U.S./Russian negotiations, funding for Space Station, and a series of other events, the SLS-3 mission was cancelled and applicable Rhesus Project experiments incorporated into the Russian Bion 11 and 12 missions. A presentation of the RRF and COSMOS/Bion rhesus hardware is presented along with current plans for the hardware.
Private university accommodation: developmentscenarios and critical success factors
Maria Luisa Del Gatto
2012-10-01
Full Text Available The number of students looking for accommodation away from home is increasing significantly. Many countries have demonstrated their ability in responding to this demand with university accommodation initiatives. Italy has taken action a little late and with some discrepancies, on the one hand trying to attract foreign students while on the other neglecting the provision of services and hospitality. This study investigates the elements that contribute to determining the feasibility and economic/financial balance of private investment in the university accommodation sector, illustrating the possible development scenarios in our country and considering previous experience, through the identification of some critical success factors.
Control/structure interactions of Freedom's solar dynamic modules
Quinn, R. D.; Yunis, I.
1990-01-01
The purpose of this paper is to address potential control/structures interaction (CSI) problems of large flexible multibody structures in the presence of pointing and tracking requirements. A control approach is introduced for the simultaneous tracking and vibration control of multibody space structures. The application that is discussed is Space Station Freedom configured with solar dynamic (SD) modules. The SD fine-pointing and tracking requirements may necessitate controller frequencies above the structural natural frequencies of Freedom and the SD modules. It is well known that this can give rise to CSI problems if the controller is designed without due consideration given to the structural dynamics of the system. In this paper, possible CSI problems of Freedom's solar dynamic power systems are demonstrated using a simple lumped mass model. A NASTRAN model of Freedom developed at NASA Lewis is used to demonstrate potential CSI problems and the proposed tracking and vibration control approach.
On cloud modelling and the mass accommodation coefficient of water
A. Laaksonen
2004-11-01
Full Text Available The mass accommodation coefficient of water is a quantity for which different experimental techniques have yielded conflicting values in the range 0.04–1. From the viewpoint of cloud modelling, this is an unfortunate situation, since the value of the mass accommodation coefficient affects the model results, e.g. the number concentration of activated cloud droplets. In this paper we argue that a mass accommodation coefficient of unity should be used in cloud modelling, since this value has been obtained in experimental studies of water droplet growth rates, a quantity which is explicitly described in cloud models. In contrast, mass accommodation coefficient values below unity have been derived from experimental results which are analyzed with different theoretical expressions than those included in cloud models.
Amplitude of Accommodation and its Relation to Refractive Errors
Abraham Lekha
2005-01-01
Full Text Available Aims: To evaluate the relationship between amplitude of accommodation and refractive errors in the peri-presbyopic age group. Materials and Methods: Three hundred and sixteen right eyes of 316 consecutive patients in the age group 35-50 years who attended our outpatient clinic were studied. Emmetropes, hypermetropes and myopes with best-corrected visual acuity of 6/6 J1 in both eyes were included. The amplitude of accommodation (AA was calculated by measuring the near point of accommodation (NPA. In patients with more than ± 2 diopter sphere correction for distance, the NPA was also measured using appropriate soft contact lenses. Results: There was a statistically significant difference in AA between myopes and hypermetropes ( P P P P P P >0.5. Conclusion: Our study showed higher amplitude of accommodation among myopes between 35 and 44 years compared to emmetropes and hypermetropes
Occlusal accommodation and mouthguards for prevention of orofacial trauma.
Geary, Julian Lindsay
2009-01-01
The aim of this study was to investigate the effect of two types of occlusal accommodation on the arch separation in centric and eccentric arch positions and to assess the opposing tooth contacts in professionally made, thermoformed sports mouthguards.
Jungtae Lee
2012-07-01
Full Text Available Background: Human life can be further improved if diseases and disorders can be predicted before they become dangerous, by correctly recognizing signals from the human body, so in order to make disease detection more precise, various body-signals need to be measured simultaneously in a synchronized manner. Object: This research aims at developing an integrated system for measuring four signals (EEG, ECG, respiration, and PPG and simultaneously producing synchronous signals on a Wireless Body Sensor Network. Design: We designed and implemented a platform for multiple bio-signals using Bluetooth communication. Results: First, we developed a prototype board and verified the signals from the sensor platform using frequency responses and quantities. Next, we designed and implemented a lightweight, ultra-compact, low cost, low power-consumption Printed Circuit Board. Conclusion: A synchronous multi-body sensor platform is expected to be very useful in telemedicine and emergency rescue scenarios. Furthermore, this system is expected to be able to analyze the mutual effects among body signals.
Stress and heat flux for arbitrary multi-body potentials: A unified framework
Admal, Nikhil Chandra
2015-01-01
A two-step unified framework for the evaluation of continuum field expressions from molecular simulations for arbitrary interatomic potentials is presented. First, pointwise continuum fields are obtained using a generalization of the Irving-Kirkwood procedure to arbitrary multi-body potentials. Two ambiguities associated with the original Irving-Kirkwood procedure (which was limited to pair potential interactions) are addressed in its generalization. The first ambiguity is due to the non-uniqueness of the decomposition of the force on an atom as a sum of central forces, which is a result of the non-uniqueness of the potential energy representation in terms of distances between the particles. This is in turn related to the shape space of the system. The second ambiguity is due to the non-uniqueness of the energy decomposition between particles. The latter can be completely avoided through an alternate derivation for the energy balance. It is found that the expressions for the specific internal energy and the h...
Efficient methodology for multibody simulations with discontinuous changes in system definition
A new method is presented for accurately and efficiently simulating multi-scale multibody systems with discontinuous changes in system definitions as encountered in adaptive switching between models with different resolutions as well as models with different system topologies. An example of model resolution change is a transition of a system from a discrete particle model to a reduced order articulated multi-rigid body model. The discontinuous changes in system definition may be viewed as an instantaneous change (release or impulsive application of) the system constraints. The method uses a spatial impulse-momentum formulation in a divide and conquer scheme. The approach utilizes a hierarchic assembly-disassembly process by traversing the system topology in a binary tree map to solve for the jumps in the system generalized speeds and the constraint impulsive loads in linear and logarithmic cost in serial and parallel implementations, respectively. The method is applicable for systems in serial chain as well as kinematical loop topologies. The coupling between the unilateral and bilateral constraints is handled efficiently through the use of kinematic joint definitions. The equations of motion for the system are produced in a hierarchic sub-structured form. This has the advantage that changes in sub-structure definitions/models results in a change to the system equations only within the associated sub-structure. This allows for significant changes in model types and definitions without having to reformulate the equations for the whole system
Repeatability intraexaminer and agreement in amplitude of accommodation measurements
Antona Peñalba, Beatriz; Barra Lázaro, Francisco; Barrio de Santos, Ana Rosa; González Díaz-Obregón, Enrique; Sánchez Pérez, Isabel
2009-01-01
Background: Clinical measurement of the amplitude of accommodation (AA) provides an indication of maximum accommodative ability. To determine whether there has been a significant change in the AA, it is important to have a good idea of the repeatability of the measurement method used. The aim of the present study was to compare AA measurements made using three different subjective clinical methods: the push-up, push-down, and minus lens techniques. These methods differ in terms of the apparen...
Single-optic positional accommodating intraocular lenses: a review
Tomás Juan, Javier; Piñero Llorens, David Pablo; Larrañaga Murueta-Goyena, Ane
2014-01-01
Presbyopia is an age-related physiological condition that causes a gradual loss in the ability to focus on near objects, secondary to changes in zonular fibers, ciliary muscle and crystalline lens. Different surgical approaches are being pursued to surgically compensate presbyopia, such as corneal techniques or implantation of multifocal intraocular lenses (IOLs); however, their inability to restore accommodation has led to the development of single-optic positional accommodative IOLs. The ax...
Symptomatology associated with accommodative and binocular vision anomalies
García Muñoz, Ángel; Carbonell-Bonete, Stela; Cacho Martínez, Pilar
2014-01-01
Purpose: To determine the symptoms associated with accommodative and non-strabismic binocular dysfunctions and to assess the methods used to obtain the subjects’ symptoms. Methods: We conducted a scoping review of articles published between 1988 and 2012 that analysed any aspect of the symptomatology associated with accommodative and non-strabismic binocular dysfunctions. The literature search was performed in Medline (PubMed), CINAHL, PsycINFO and FRANCIS. A total of 657 articles were identi...
An application of SODA methodology in student accommodation problems
E. Teimoury; H. Gitinavard; Mousavi, S. M.
2014-01-01
The one of the main problems that students have faced with are the accommodation problems. In this paper, we review problems that may occur in university systems. Also, we use strategic options development and analysis method (SODA) to represent the accommodation problems and to create an agreement between student and staff. This method can help us with achieving goals; because in the same situation, there are different viewpoints for various reasons. By plotting the cognitive maps of involve...
Classical Unemployment, Accommodation Policies and the Adjustment of Real Wages
Calmfors, Lars; Horn, Henrik
1984-01-01
The paper develops a model of wage formation and stabilization policy in economies with centralized wage setting and strong trade unions. The aim is to explain the present stagflation with heavy unemployment and large government deficits. The analysis gives a theoretical underpinning to the assertion that accommodation policies may cause wage inflation and in the end reduce employment. Various methods of accomplishing a real wage adjustment are discussed: (1) a policy of complete non-accommod...
The level of burnout of housekeeping personnel in accommodation facilities
Sibel Erkal; Hande Şahin
2012-01-01
This study aimed to determine the level of burnout of the housekeeping personnel (cleaner, manager, crew chief) working in accommodation facilities and discovering if there was a relationship between their level of burnout and their personal features. In the study a cluster sampling method was used. 12 accommodation facilities in Antalya were handled as cluster and a total of 146 personnel working in these facilities comprised the sample group. A “Burnout Inventory” was used in the study. Th...
Factors influencing pricing in the accommodation sector in South Africa
Saayman, Melville; 10811281 - Du Plessis, Engelina
2011-01-01
Price is a significant factor of competitiveness. Price is a complex issue and is determined by a variety of demand and supply factors. These factors also differ from industry to industry. The purpose of this article is to determine the factors that influence pricing in the South African accommodation sector. In order to generate proper data, a survey was conducted at various South African accommodation establishments that were obtained from the databases of the three major associations in th...
Towards electricity markets accommodating uncertain offers
Papakonstantinou, Athanasios; Pinson, Pierre
2014-01-01
The use of renewable energy sources of energy and in particular wind and solar has been on the rise over the last decades with plans to increase it even more. Such developments introduce significant challenges in existing power systems and can result in high electricity prices and costly infrastr......The use of renewable energy sources of energy and in particular wind and solar has been on the rise over the last decades with plans to increase it even more. Such developments introduce significant challenges in existing power systems and can result in high electricity prices and costly...... infrastructure investments. In this paper we propose a new electricity market mechanism whereby the uncertain and dynamic nature of wind power and other stochastic sources is embedded in the market mechanism itself, by modelling producers’ bids as probabilistic estimates. An extension on the bilevel programming...... formulation of an electricity market, based on the Continuous Ranked Probability Score (CRPS) reduces the impact of poor estimates for both the stochastic producers and the system operator. We introduce a simulation setting which first demonstrates that impact and then proceed to illustrate the main features...
Human walking dynamics: modeling, identification and control
Schiehlen W.
2014-01-01
Full Text Available Human gait simulation is a complex dynamical problem that requires, in addition to the mechanical model, the observance of muscle activations, neural excitations, and energetic and aesthetic considerations. After an short review on the historical development two- and three-dimensional models using multibody system dynamics are presented. The identification of the muscle actuation during human walking is based on data in literature comparing the resultant torques to each other. The control design uses inverse dynamics approaches and an optimization framework minimizing the metabolical energy consumption and improving the aesthetics. Numerical simulation results are shown for planar as well as spatial models.
Quasi-variational principles of single flexible body dynamics and their applications
无
2009-01-01
The reasons for studying single flexible body dynamics are that on one hand,it is the basis of flexible multi-body dynamics.If the theory of the single flexible body dynamics has been deeply studied,the theory of flexible multi-body dynamics will be researched easily.On the other hand,it has its unique and important applications.Quasi-variational principle of non-conservative single flexible body dynamics is established under the cross-link of particle rigid body mechanics and deformable body mechanics.Taking the interceptor as an example,this paper has explained the physical meaning of the quasi-stationary value condition of the quasi-variational principle in non-conservative single flexible body dynamics.Taking the launch of rocket as an example,it has illustrated the features of"one force for two effects"in a single flexible body dynamics.With an example of the extending flexible beam coupled with the spacecraft attitude,it has shown the transition from the single flexible body dynamics to the flexible multi-body dynamics.Finally,a number of related problems are discussed.
Quasi-variational principles of single flexible body dynamics and their applications
LIANG LiFu; LIU ShiQuan; ZHOU JianSheng
2009-01-01
The reasons for studying single flexible body dynamics are that on one hand, it is the basis of flexible multi-body dynamics. If the theory of the single flexible body dynamics has been deeply studied, the theory of flexible multi-body dynamics will be researched easily. On the other hand, it has its unique and important applications. Quasi-variational principle of non-conservative single flexible body dynamics is established under the cross-link of particle rigid body mechanics and deformable body mechanics. Taking the interceptor as an example, this paper has explained the physical meaning of the quasi-stationary value condition of the quasi-variational principle in non-conservative single flexible body dynamics. Taking the launch of rocket as an example, it has illustrated the features of "one force for two effects" in s single flexible body dynamics. With an example of the extending flexible beam coupled with the spacecraft attitude, it has shown the transition from the single flexible body dynamics to the flexible multi-body dynamics. Finally, a number of related problems are discussed.
Tischler, M. B.; Ringland, R. F.; Jex, H. R.
1983-01-01
The basic aerodynamic and dynamic properties of an example heavy-lift airship (HLA) configuration are analyzed using a nonlinear, multibody, 6-degrees-of-freedom digital simulation. The slung-payload model is described, and a preliminary analysis of the coupled vehicle-payload dynamics is presented. Trim calculations show the importance of control mixing selection and suggest performance deficiencies in crosswind stationkeeping for the unloaded example HLA. Numerically linearized dynamics of the unloaded vehicle exhibit a divergent yaw mode and an oscillatory pitch mode whose stability characteristic is sensitive to flight speed. An analysis of the vehicle-payload dynamics shows significant coupling of the payload dynamics with those of the basic HLA. It is shown that significant improvement in the vehicle's dynamic behavior can be achieved with the incorporation of a simple flight controller having proportional, rate, and integral-error feedbacks.
Full text: This paper deals with the modeling of a coupled tool-workpiece system during the forming process. The initial software is based on the finite element method to solve the deformation of the part which can be viscoplastic or elastoviscoplastic. Interaction with the rigid tool are performed through a penalization algorithm for contact, coupled with a friction and a thermal dissipation term. A MINRES method is used to solve the systems and the program is fully parallel. The multi-body algorithm is based on a master slave algorithm with a node to face approach. The nodes of the tool are related to the surface triangle (creating a fictitious tetrahedron) of the part to express the contact and friction term in the mechanical system and the conduction in the thermal one. The fully coupled system is solved with an iterative method. If the thermal coupled problem requires an acceptable computation time, the mechanical coupled problem is 11 times more expensive than the single domain one if the number of nodes of the coupled system is 5 times higher. The parallel algorithm for the multi-body system is based on the domain decomposition of the standard program. The main issue being to partition the whole domains in order to give equivalent computation work to each processor. The simplest is to assign a domain to each processor, leads to unbalanced tasks if the rheologies are of same type and the number of nodes very different. The selected procedure is to assign to each processor one fraction of each domain. The contact analysis is then performed for each processor and the fictitious elements are local to the processor. An optimization would be to re-partition after the definition of these elements to improve the communication. Remeshing step is also to be considered. Another way to improve the computation time of multi-body systems is to alternate multi-body and single-body computations for the mechanical problem. The deformation of the tool can be neglected except
A method to measure φ1 using B-bar 0->D(*)h0 with multibody D decay
We describe a new method to measure the angle φ1 of the CKM Unitarity Triangle using amplitude analysis of the multibody decay of the neutral D meson produced via B-bar ->D(*)h0 colour-suppressed decays. The method employs the interference between D0 and D-bar 0 to directly extract the value of 2φ1, and thus resolve the ambiguity between 2φ1 and π-2φ1 in the measurement of sin(2φ1) using B-bar 0->J/ψKS. We present a feasibility study of this method using Monte Carlo simulation
Perturbation Dynamics and Its Application for Parachute-Munition System
无
2007-01-01
The nine-degree-freedom dynamic model of the parachute-munition system is developed by the theories and the analysis methods of parachute dynamics and multibody dynamics. On the basis of the above model, a linear five-degree-offreedom dynamic model is developed by linearization at the steady state. A new algorithm, which can be fused with submunition kinematics and used in target identification, is developed by the principle of parachute dynamics. The simulation program is developed and used to remove the influence of wind gust on hitting accuracy. The successful airdrop test demonstrates that the new method can be used in the guidance of smart munition.
Theorizing accommodation in supportive home care for older people.
Ceci, Christine; Purkis, Mary Ellen; Björnsdóttir, Kristin
2013-01-01
This paper examines the issue of what thinking is necessary in order to advance a notion of accommodation in the organization and provision of supportive home care for older people. Accommodation in this context is understood as responsiveness to the singularity of older adults, and we consider how this idea might be used to support opportunities for (independent) living for elders as they age and become frailer. To elaborate the question we draw on examples from our empirical work - ethnographic studies of home care practice undertaken in Canada and Iceland - and consider these examples in light of critical philosophical and social theory, particularly Agamben's (1993) work, The Coming Community. This is a relevant frame through which to consider the potential for the accommodation of the unique needs of older adults in home care because it helps us to problematize the systems through which care is accomplished and the current, dominant terms of relations between individuals and collectives. We argue that giving substance to a notion of accommodation contributes an important dimension to aligned ideas, such as patient-centeredness in care, by working to shift the intentionality of these practices. That is, accommodation, as an orientation to care practices, contests the organizational impulse to carry on in the usual way. PMID:23273554
Relative Importance of Student Accommodation Quality in Higher Education
Simon Gyasi Nimako
2013-07-01
Full Text Available This study, which was part of a large study, empirically examinesthe importance students attach to different dimensions of Student Accommodation Quality (SAQ delivered by Student Accommodation Providers (SAP in two tertiary (higher education institutions in Ghana. The study involved a cross-sectional survey that used a structured questionnaire administered to 700 tertiary students in residential and non-residential accommodation. The survey yielded a usable 66.6% response rate for analysis. The findings indicate that utility facility quality is the most important SAQ dimension to the students, followed by the overall impression of hostel, security, physical environment, toilet, distance to lecture, bedroom, bath room, accommodation fee, among others. Moreover, it was found that kitchen facility, access to transport and entertainment facility are less important SAQ items while the least important is garage facility. Few differences were found in the priority for SAQ items between COLTEK and K-Poly respondents and between residential and non-residential respondents. Implications for theory and recommendations to management of the two higher education institutions and SAP have been discussed. The study contributes to the body of knowledge in student affairs and managing student accommodation quality in higher education.
Accommodating Autistics and Treating Autism: Can We Have Both?
Lim, Chong-Ming
2015-10-01
One of the central claims of the neurodiversity movement is that society should accommodate the needs of autistics, rather than try to treat autism. People have variously tried to reject this accommodation thesis as applicable to all autistics. One instance is Pier Jaarsma and Stellan Welin, who argue that the thesis should apply to some but not all autistics. They do so via separating autistics into high- and low-functioning, on the basis of IQ and social effectiveness or functionings. I reject their grounds for separating autistics. IQ is an irrelevant basis for separating autistics. Charitably rendering it as referring to more general capacities still leaves us mistaken about the roles they play in supporting the accommodation thesis. The appeal to social effectiveness or functionings relies on standards that are inapplicable to autistics, and which risks being deaf to the point of their claims. I then consider if their remaining argument concerning autistic culture may succeed independently of the line they draw. I argue that construing autistics' claims as beginning from culture mistakes their status, and may even detract from their aims. Via my discussion of Jaarsma and Welin, I hope to point to why the more general strategy of separating autistics, in response to the accommodation thesis, does not fully succeed. Finally, I sketch some directions for future discussions, arguing that we should instead shift our attention to consider another set of questions concerning the costs and extent of change required to accommodate all autistics. PMID:25689416
Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production—detrimental for high current negative ion systems such as beam sources for fusion—are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared
Sartori, E.; Brescaccin, L.; Serianni, G.
2016-02-01
Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production—detrimental for high current negative ion systems such as beam sources for fusion—are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared.
Sartori, E., E-mail: emanuele.sartori@igi.cnr.it; Serianni, G. [Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), C.so Stati Uniti 4, 35127 Padova (Italy); Brescaccin, L. [Università degli Studi di Padova, Padova PD (Italy)
2016-02-15
Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production—detrimental for high current negative ion systems such as beam sources for fusion—are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared.
Advanced Dynamics Analytical and Numerical Calculations with MATLAB
Marghitu, Dan B
2012-01-01
Advanced Dynamics: Analytical and Numerical Calculations with MATLAB provides a thorough, rigorous presentation of kinematics and dynamics while using MATLAB as an integrated tool to solve problems. Topics presented are explained thoroughly and directly, allowing fundamental principles to emerge through applications from areas such as multibody systems, robotics, spacecraft and design of complex mechanical devices. This book differs from others in that it uses symbolic MATLAB for both theory and applications. Special attention is given to solutions that are solved analytically and numerically using MATLAB. The illustrations and figures generated with MATLAB reinforce visual learning while an abundance of examples offer additional support. This book also: Provides solutions analytically and numerically using MATLAB Illustrations and graphs generated with MATLAB reinforce visual learning for students as they study Covers modern technical advancements in areas like multibody systems, robotics, spacecraft and des...
An application of SODA methodology in student accommodation problems
E. Teimoury
2014-06-01
Full Text Available The one of the main problems that students have faced with are the accommodation problems. In this paper, we review problems that may occur in university systems. Also, we use strategic options development and analysis method (SODA to represent the accommodation problems and to create an agreement between student and staff. This method can help us with achieving goals; because in the same situation, there are different viewpoints for various reasons. By plotting the cognitive maps of involved persons and aggregating all cognitive maps, this methodology reaches us to a consensus. The aggregated cognitive maps are called strategic maps. Finally, with the relational clustering the strategic map, we offer some suggestions to improve the accommodation system in each university.
Mark My Words! Linguistic Style Accommodation in Social Media
Danescu-Niculescu-Mizil, Cristian; Dumais, Susan; 10.1145/1963405.1963509
2011-01-01
The psycholinguistic theory of communication accommodation accounts for the general observation that participants in conversations tend to converge to one another's communicative behavior: they coordinate in a variety of dimensions including choice of words, syntax, utterance length, pitch and gestures. In its almost forty years of existence, this theory has been empirically supported exclusively through small-scale or controlled laboratory studies. Here we address this phenomenon in the context of Twitter conversations. Undoubtedly, this setting is unlike any other in which accommodation was observed and, thus, challenging to the theory. Its novelty comes not only from its size, but also from the non real-time nature of conversations, from the 140 character length restriction, from the wide variety of social relation types, and from a design that was initially not geared towards conversation at all. Given such constraints, it is not clear a priori whether accommodation is robust enough to occur given the con...
The determinants of transitions into sheltered accommodation in later life in England and Wales
Vlachantoni, Athina; Maslovskaya, Olga; Evandrou, Maria; Falkingham, Jane
2016-01-01
Background Population ageing is a global challenge and understanding the dynamics of living arrangements in later life and their implications for the design of appropriate housing and long-term care is a critical policy issue. Existing research has focused on the study of transitions into residential care in the UK. This paper investigates transitions into sheltered accommodation among older people in England and Wales between 1993 and 2008. Methods The study uses longitudinal data constructed from pooled observations across waves 2–18 of the British Household Panel Survey (BHPS) data, focusing on individuals aged 65 and over who lived in private housing at baseline and who were observed for two consecutive time points. A discrete-time logistic regression model was used to examine the association of transitioning into sheltered accommodation with a range of demographic, health and socioeconomic predictors. Results Demographic (age, region), socioeconomic factors (housing tenure, having a washing machine) and contact with health professionals (number of visits to the general practitioner, start in use of health visitor) were significant determinants of an older person's move into sheltered accommodation. Conclusions Transitions into sheltered accommodation are associated with a range of demographic and socioeconomic characteristics as well as service use but not with health. Such results indicate that this type of housing option may be accessible by individuals with relatively good health, but may be limited to those who are referred by gatekeepers. Policymakers could consider making such housing option available to everyone, as well as providing incentives for building lifecourse-sensitive housing in the future. PMID:26896519
Corneal topography, refractive state, and accommodation in harbor seals (Phoca vitulina).
Hanke, Frederike D; Dehnhardt, Guido; Schaeffel, Frank; Hanke, Wolf
2006-03-01
Corneal topography of a harbor seal measured with a Placido's disc shows a central flattened stripe in the vertical meridian. Together with a pupil that can form a vertical slit, the flat vertical meridian can minimize the optical effects caused by the transition from water to air. Using infrared (IR) photoretinoscopy, we analyzed the refractive state of harbor seals and revealed a high degree of myopia and astigmatism in air, but emmetropia or slight hyperopia with little astigmatism underwater. The brightness distribution in the pupils suggest the presence of a multifocal dioptric apparatus in air and underwater. We found a first indication for accommodation by dynamic recordings underwater. PMID:16256164
Du, Dongsheng; Jiang, Bin
2016-05-01
This paper investigates the problems of actuator fault estimation and accommodation for discrete-time switched systems with state delay. By using reduced-order observer method and switched Lyapunov function technique, a fault estimation algorithm is achieved for the discrete-time switched system with actuator fault and state delay. Then based on the obtained online fault estimation information, a switched dynamic output feedback controller is employed to compensate for the effect of faults by stabilizing the closed-loop systems. Finally, an example is proposed to illustrate the obtained results. PMID:26924247
Saccadic lens instability increases with accommodative stimulus in presbyopes
He, Lin; Donnelly, William J.; Stevenson, Scott B.; Glasser, Adrian
2010-01-01
An SRI dual Purkinje image (dPi) eye tracker was used to measure lens wobble following saccades with increasing accommodative effort as an indirect measure of ciliary muscle function in presbyopes. Ten presbyopic subjects executed 32 four-degree saccades at 1-s intervals between targets arranged in a cross on illuminated cards at each of 9 viewing distances ranging from 0.5- to 8-D accommodative demands. Post-saccadic lens wobble artifacts were extracted by subtraction of P1 (H1/V1) position ...
The accommodative ciliary muscle function is preserved in older humans
Tabernero, Juan; Chirre, Emmanuel; Hervella, Lucia; Prieto, Pedro; Artal, Pablo
2016-01-01
Presbyopia, the loss of the eye’s accommodation capability, affects all humans aged above 45–50 years old. The two main reasons for this to happen are a hardening of the crystalline lens and a reduction of the ciliary muscle functionality with age. While there seems to be at least some partial accommodating functionality of the ciliary muscle at early presbyopic ages, it is not yet clear whether the muscle is still active at more advanced ages. Previous techniques used to visualize the accomm...
Adapting your teaching to accommodate the net generation of learners.
Skiba, Diane J; Barton, Amy J
2006-05-01
Educators are faced with the challenge of adapting their teaching styles to accommodate a new generation of learners. The Net Generation or Millennials, who are now entering colleges and universities, have learning expectations, styles, and needs different from past students. This article assists educators in teaching the Net Generation by highlighting the characteristics of the Net Generation and providing examples of how to adapt teaching strategies to accommodate the Net Generation, in light of their preferences for digital literacy, experiential learning, interactivity, and immediacy. PMID:17201579
EVALUATION OF SERVICES’ QUALITY IN UPPER SILESIA ACCOMMODATION FACILITIES
Iwona Cieślik
2013-12-01
Full Text Available This paper presents the results of study about impact of accommodation services’ quality, particularly quality of work and qualifications of staff, on the guests’ opinion, and thus promoting the accommodation facilities, and making a choice of a hotel in the Upper Silesia. The study involved 200 people, taking into account their gender, age, place of residence, education and occupational status. The research tool was a survey questionnaire. The results indicate close correlation between the quality of staff services (individual approach, aesthetics, discretion, understanding and the customer is satisfaction. Particular attention was paid to the quality of service by the guests with high professional status, and higher education.
Dynamic analysis and design of a high voltage circuit breaker with spring operating mechanism
Spring Operating Mechanism (SOM) is a dynamic system to open and close the circuit breaker in a voltage controlling system. For a high-speed action of opening and closing within a few mili-seconds, a SOM consists of many links, joints, chains, and cams. Thus, various dynamic characteristics are occurred, especially large contact forces between the cam and the roller, the shaft and the stopper. To save time and money for a new design of SOM system, analysis of the mechanism is necessary. In this paper, a multibody dynamic analysis and test technique was applied for a SOM to predict, estimate and validate forces occurring during the operation. For the multibody dynamic analysis, the ADAMS program was employed for 145kV circuit breaker with a SOM. For an accurate modeling, several components were sequentially added and the reliability of modeling was validated through the comparison with test data of opening and closing
Chen, Peng; Liu, Jin-Yang; Hong, Jia-Zhen
2016-04-01
In this paper, an efficient formulation based on the Lagrangian method is presented to investigate the contact-impact problems of flexible multi-body systems. Generally, the penalty method and the Hertz contact law are the most commonly used methods in engineering applications. However, these methods are highly dependent on various non-physical parameters, which have great effects on the simulation results. Moreover, a tremendous number of degrees of freedom in the contact-impact problems will influence the numerical efficiency significantly. With the consideration of these two problems, a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact-impact problems in flexible multi-body system numerically. Meanwhile, the finite element meshing laws of the contact bodies will be studied preliminarily. A numerical example with experimental verification will certify the reliability of the presented formulation in contact-impact analysis. Furthermore, a series of numerical investigations explain how great the influence of the finite element meshing has on the simulation results. Finally the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficiency.
Mohrfeld-Halterman, J. A.; Uddin, M.
2016-07-01
We described in this paper the development of a high fidelity vehicle aerodynamic model to fit wind tunnel test data over a wide range of vehicle orientations. We also present a comparison between the effects of this proposed model and a conventional quasi steady-state aerodynamic model on race vehicle simulation results. This is done by implementing both of these models independently in multi-body quasi steady-state simulations to determine the effects of the high fidelity aerodynamic model on race vehicle performance metrics. The quasi steady state vehicle simulation is developed with a multi-body NASCAR Truck vehicle model, and simulations are conducted for three different types of NASCAR race tracks, a short track, a one and a half mile intermediate track, and a higher speed, two mile intermediate race track. For each track simulation, the effects of the aerodynamic model on handling, maximum corner speed, and drive force metrics are analysed. The accuracy of the high-fidelity model is shown to reduce the aerodynamic model error relative to the conventional aerodynamic model, and the increased accuracy of the high fidelity aerodynamic model is found to have realisable effects on the performance metric predictions on the intermediate tracks resulting from the quasi steady-state simulation.
Simone Pascuzzi
2015-10-01
Full Text Available This paper proposes the use of the multibody approach to evaluate the severity of the injuries to the driver associated with rollover of an agricultural tractor. A simple rollover accident of a narrow-track wheeled tractor was simulated in the multibody-FEM Madymo environment and the biomechanical damage to the operator with and without 2-point pelvic restraint was analysed. The structure of the tractor was considered to be unbendable, whereas i infinitely rigid, ii clay-based and iii sand-based soils have been studied. The obtained results highlight the important role played by the seat belt in confining the farm operator within the safety volume maintained by the rollover protective structure (ROPS of the tractor so that the injuries are reduced. The deformation of the soil produces lower acceleration and velocity values than those obtained with a rigid soil. On the other hand, as soil plastic deformations increase, the penetration of ROPS into the soil also increases, thus reducing the safety volume of the tractor and increasing the probability of interactions between the operator and the soil.
Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær;
2014-01-01
The aeroelastic FLEX 5 code and a semi-advanced rigid multibody model has been utilized for simulating drivetrain forces and moments in a real 500 kW wind turbine. Experimental validation is carried out with results based on known physical properties of the blades, tower, hub, gearbox, shaft and ...
Fast Dynamic Model of a Moving-base 6-DOF Parallel Manipulator
Lopes, Antonio M.
2010-01-01
A parallel manipulator is a complex multi-body dynamic system having several closed loops. Typically, it is composed of a (usually) fixed base platform and a moving payload platform, connected by at least two independent open kinematic chains. Dynamic modelling of parallel manipulators presents an inherent difficulty. Despite the intensive study in this topic of robotics, mostly conducted in the last two decades, additional research still has to be done in this area.
Accommodating Black Students on Traditionally White Campuses: Some Considerations.
Henry, Philip N.
This paper concerns the need for colleges to accommodate black students, especially in the area of guidance. The use of standardized tests and other means for predicting the academic success of blacks is discussed. It is suggested that admission personnel include such variables as self concept, leadership potential, ambition, and maturity as means…
Teaching Disability Employment Discrimination Law: Accommodating Physical and Mental Disabilities
Kulow, Marianne DelPo
2012-01-01
Disability employment discrimination is often treated summarily in legal environment courses. This is actually a topic with significant practical application in the workplace since managers are often those who are confronted with accommodation requests. It is therefore desirable to include a class with hands-on exercises for students to begin to…
Can Shneidman's "Ten Commonalities of Suicide" Accommodate Rational Suicide?
Werth, James L., Jr.
1996-01-01
Reviews the concept of rational suicide and compares it with one researcher's list of commonalities of suicide. Claims that the list cannot accommodate rational suicide. Suggests that the list is biased against rational suicide and should be renamed so it cannot be maintained that suicide must be irrational. (RJM)
Accommodating the Special Learner in Secondary General Music Classes
VanWeelden, Kimberly
2011-01-01
It can be challenging to know which accommodations for special learners can be used within the various secondary general music class settings. Fortunately, there have been several recent music education and therapy articles based on special education practices that have addressed techniques for working with students with special needs in music.…
Coworker Informal Work Accommodations to Family: Scale Development and Validation
Mesmer-Magnus, Jessica; Murase, Toshio; DeChurch, Leslie A.; Jimenez, Miliani
2010-01-01
Drawing on research regarding the utility of coworker support in mitigating work/family conflict, the authors developed a scale to measure Coworker-enacted Informal Work Accommodations to Family (C-IWAF). C-IWAF differs from coworker support in that it describes actual behaviors coworkers engage in to help one another deal with incompatible work…
Accommodations in Homeschool Settings for Children with Special Education Needs
Stoudt, Patricia Koelsch
2012-01-01
This qualitative study was designed to examine how homeschooling parents in Pennsylvania make the determination to engage with public school districts to accommodate the special education needs (SEN) of their children. This phenomenological study used direct interviews with 30 Pennsylvania families who are homeschooling children with SEN. Data…
Accommodation, Cafes and Restaurants. Industry Training Monograph No. 8.
Dumbrell, Tom
Australia's accommodation, cafes, and restaurants industry represents more than half of the nation's total tourism and hospitality employment. It accounts for roughly 4.5% of all jobs in Australia (400,000 workers). Since 1987, the number of jobs in the sector has risen from about 257,000 to about 372,000. Approximately 57% of employees are…
Understanding and Accommodating Students with Depression in the Classroom
Crundwell, R. Marc; Killu, Kim
2007-01-01
Depression and mood disorders present a significant challenge in the classroom; resulting symptoms can impact memory, recall, motivation, problem solving, task completion, physical and motor skills, and social interactions. Little information is available on practical instructional accommodations and modifications for use by the classroom teacher.…
Translation Accommodations Framework for Testing English Language Learners in Mathematics
Solano-Flores, Guillermo
2012-01-01
The present framework is developed under contract with the Smarter Balanced Assessment Consortium (SBAC) as a conceptual and methodological tool for guiding the reasonings and actions of contractors in charge of developing and providing test translation accommodations for English language learners. The framework addresses important challenges in…
THE STATE TECHNOLOGICAL ACCOUNTING OF ACCOMMODATIONS: HISTORY AND CONTEMPORARY LEGISLATION
Maslennikova L. V.; Sarosek A. P.
2014-01-01
The authors analyze the changes of legislation in the sphere of state technological accounting of accommodations. They consider the information meaning of technological inventory office for state registration of the estate in land and bargains with it. They investigate the drawbacks of separate normative legal act planed for publishing
The Contribution of University Accommodation to International Student Security
Paltridge, Toby; Mayson, Susan; Schapper, Jan
2010-01-01
In this paper we argue that living in university accommodation is a possible means of improving the security of international students. Our argument is supported by a qualitative case study of a single Hall of Residence on Monash University's Clayton campus. Data were collected primarily from interviews with three groups of participants--six…
Knowledge Transfer and Accommodation Effects in Multinational Corporations
Geisler Asmussen, Christian; Foss, Nicolai J.; Pedersen, Torben
2013-01-01
Foreign subsidiaries in multinational corporations (MNCs) possess knowledge that has different sources (e.g., the firm itself or various sources in the environment). How such sources influence knowledge transfer is not well understood. Drawing on the "accommodation effect" from cognitive psychology...
The accommodative ciliary muscle function is preserved in older humans.
Tabernero, Juan; Chirre, Emmanuel; Hervella, Lucia; Prieto, Pedro; Artal, Pablo
2016-01-01
Presbyopia, the loss of the eye's accommodation capability, affects all humans aged above 45-50 years old. The two main reasons for this to happen are a hardening of the crystalline lens and a reduction of the ciliary muscle functionality with age. While there seems to be at least some partial accommodating functionality of the ciliary muscle at early presbyopic ages, it is not yet clear whether the muscle is still active at more advanced ages. Previous techniques used to visualize the accommodation mechanism of the ciliary muscle are complicated to apply in the older subjects, as they typically require fixation stability during long measurement times and/or to have an ultrasound probe directly in contact with the eye. Instead, we used our own developed method based on high-speed recording of lens wobbling to study the ciliary muscle activity in a small group of pseudophakic subjects (around 80 years old). There was a significant activity of the muscle, clearly able to contract under binocular stimulation of accommodation. This supports a purely lenticular-based theory of presbyopia and it might stimulate the search for new solutions to presbyopia by making use of the remaining contraction force still presented in the aging eye. PMID:27151778
36 CFR 910.34 - Accommodations for the physically handicapped.
2010-07-01
... physically handicapped. 910.34 Section 910.34 Parks, Forests, and Public Property PENNSYLVANIA AVENUE... § 910.34 Accommodations for the physically handicapped. (a) Every development shall incorporate features which will make the development accessible by the physically handicapped. The standards in the...
Disability Accommodations in Online Courses: The Graduate Student Experience
Terras, Katherine; Leggio, Joseph; Phillips, Amy
2015-01-01
Research is beginning to demonstrate that online learning may afford students with disabilities enhanced opportunities for academic success. In this study, the authors interviewed 11 graduate students to determine their experiences with disability accommodations in online courses and their perceptions of the relationship between those…
Science Language Accommodation in Elementary School Read-Alouds
Glass, Rory; Oliveira, Alandeom W.
2014-01-01
This study examines the pedagogical functions of accommodation (i.e. provision of simplified science speech) in science read-aloud sessions facilitated by five elementary teachers. We conceive of read-alouds as communicative events wherein teachers, faced with the task of orally delivering a science text of relatively high linguistic complexity,…
Simplified Language as an Accommodation on Math Tests
Johnson, Evelyn; Monroe, Brandon
2004-01-01
As accountability requirements for determining adequate yearly progress increase, states are working to make standards-based assessments accessible for all students. Providing accommodations on assessments is one of the main ways to allow not only students with disabilities but also students who are English Language Learners to be included in…
Accommodating Students with Disabilities in Soil Science Activities
Langley-Turnbaugh, S. J.; Murphy, Kate; Levin, E.
2004-01-01
Soil science education is lacking in terms of accommodations for persons with disabilities. Individuals with disabilities are often excluded from soil science activities in school, and from soil science careers. GLOBE (Global Learning Observations to Benefit the Environment) is a worldwide, hands-on primary and secondary school-based education and…
Analysis and applications of accommodative lenses for vision corrections.
Lin, Jui-Teng; Jiang, Minshan; Chang, Chun-Lin; Hong, Yu-Ling; Ren, Qiushi
2011-01-01
Analysis and applications of vision correction via accommodating intraocular lens (AIOL) are presented. By Gaussian optics, analytic formulas for the accommodation rate function (M) for two-optics and three-optics systems are derived and compared with the exact numerical results. In a single-optics AIOL, typical value of M is (0.5-1.5) D∕mm, for an IOL power of (10-20) diopter. For a given IOL power, higher M is achieved in positive-IOL than negative-IOL. In the dual-optics AIOL, maximum accommodation is predicted when the front positive-optics moves toward the corneal plan and the back negative-optics moves backward. Our analytic formulas predict that greater accommodative rate may be achieved by using a positive-powered front optics, a general feature when either front or back optics is mobile. The M function is used to find the piggy-back IOL power for customized design based on the individual ocular parameters. Many of the new features demonstrated in this study can be easily realized by our analytic formulas, but not by raytracing method. PMID:21280927
Efficient dynamic models of tensegrity systems
Skelton, Robert
2009-03-01
The multi-body dynamics appear in a new form, as a matrix differential equation, rather than the traditional vector differential equation. The model has a constant mass matrix, and the equations are non-minimal. A specific focus of this paper is tensegrity systems. A tensegrity system requires prestress for stabilization of the configuration of rigid bodies and tensile members. This paper provides an efficient model for both static and dynamic behavior of such systems, specialized for the case when the rigid bodies are axi-symmetric rods.
Nonsmooth fracture dynamics of functionally graded materials
Perales, F.; Monerie, Y.; Chrysochoos, A.
2006-08-01
This paper presents a numerical framework for the simulation of dynamic fracture of heterogeneous material. It consists in a multibody approach based both on the concept of Frictional Cohesive Zone Model and on NonSmooth Contact Dynamics. The heterogeneities of the material are taken into account using a multiscale method. The microscopic scale corresponds to the scale of heterogeneities. The macroscopic scale corresponds to the structure where gradients of properties will be invoked. The ability of the framework is illustrated by the fracture of hydrided Zircaloy-4, constituting nuclear cladding tube, under transient loading.
14 CFR 382.81 - For which passengers must carriers make seating accommodations?
2010-01-01
... seating accommodations? 382.81 Section 382.81 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF... TRAVEL Seating Accommodations § 382.81 For which passengers must carriers make seating accommodations? As a carrier, you must provide the following seating accommodations to the following passengers...
14 CFR 382.83 - Through what mechanisms do carriers make seating accommodations?
2010-01-01
... seating accommodations? 382.83 Section 382.83 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF... TRAVEL Seating Accommodations § 382.83 Through what mechanisms do carriers make seating accommodations... provide the seating accommodations required by § 382.81. (i) You must not assign these seats to...