DEFF Research Database (Denmark)
Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
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...... 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...
Shabana, Ahmed A.
2005-05-01
Dynamics of Multibody Systems introduces multibody dynamics, with an emphasis on flexible body dynamics. Many common mechanisms such as automobiles, space structures, robots, and micro machines have mechanical and structural systems that consist of interconnected rigid and deformable components. The dynamics of these large-scale, multibody systems are highly nonlinear, presenting complex problems that in most cases can only be solved with computer-based techniques. The book begins with a review of the basic ideas of kinematics and the dynamics of rigid and deformable bodies before moving on to more advanced topics and computer implementation. This new edition includes important new developments relating to the problem of large deformations and numerical algorithms as applied to flexible multibody systems. The book's wealth of examples and practical applications will be useful to graduate students, researchers, and practicing engineers working on a wide variety of flexible multibody systems.
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.
Energy Technology Data Exchange (ETDEWEB)
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.
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...
Geometric Mathematical Framework for Multibody System Dynamics
Terze, Zdravko; Vrdoljak, Milan; Zlatar, Dario
2010-09-01
The paper surveys geometric mathematical framework for computational modeling of multibody system dynamics. Starting with the configuration space of rigid body motion and analysis of it's Lie group structure, the elements of respective Lie algebra are addressed and basic relations pertinent to geometrical formulations of multibody system dynamics are surveyed. Dynamical model of multibody system on manifold introduced, along with the outline of geometric characteristics of holonomic and non-holonomic kinematical constraints.
Multibody Dynamics Formulations Based on Variational Principle
Institute of Scientific and Technical Information of China (English)
孙右烈
2003-01-01
The formulation of multibody dynamics was studied based on variational principle. The body coonection matrix was intro-duced to define the connection configuration. The expression for the system kinematics was obtained by using the body connection ma-trix. From variational principle the general dynamical equations for multibody system were derived and the dynamical equations were given for multibody system subjected to the constraints.
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...
Earth system multi-body restriction dynamics model research
Institute of Scientific and Technical Information of China (English)
ZHANG Qingxian; BI Siwen; GONG Huili
2006-01-01
Research provides a theoretical basis for an Earth system multi-body mechanics model and its dynamics, including the Earth system multi-body restriction function and its power, Earth system multi-body restriction under decreasing generalized velocity and decreasing partial palstance, the Earth system multi-body decreasing generalized force, a moving mechanics function, and the Earth system multi-body restriction's wattful and wattless forces.
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...
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.
NONLINEAR DYNAMIC ANALYSIS OF FLEXIBLE MULTIBODY SYSTEM
Institute of Scientific and Technical Information of China (English)
A.Y.T.Leung; WuGuorong; ZhongWeifang
2004-01-01
The nonlinear dynamic equations of a multibody system composed of flexible beams are derived by using the Lagrange multiplier method. The nonlinear Euler beam theory with inclusion of axial deformation effect is employed and its deformation field is described by exact vibration modes. A numerical procedure for solving the dynamic equations is presented based on the Newmark direct integration method combined with Newton-Raphson iterative method. The results of numerical examples prove the correctness and efficiency of the method proposed.
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...
Alternative variable transformation for simulation of multibody dynamic systems
Yang, Li-Farn
1995-03-01
An alternative variable transformation is proposed and analyzed for the simulation of multibody dynamic systems. The developed alternative variable transformation matrix intended to work directly with the multibody equations of motion without altering the inherent dynamic characteristics also eliminates the need for expensive computation of inversion of a large mass matrix required for the simulation of multibody dynamic systems. From the analytical derivation of an articulated multibody model, it was found that the computation can be saved (3n + 1/4)-fold due to the computational merits associated with the band matrix.
Multibody Dynamics of Very Flexible Damped Systems
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
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
Interval modeling of dynamics for multibody systems
Auer, Ekaterina
2007-02-01
Modeling of multibody systems is an important though demanding field of application for interval arithmetic. Interval modeling of dynamics is particularly challenging, not least because of the differential equations which have to be solved in the process. Most modeling tools transform these equations into a (non-autonomous) initial value problem, interval algorithms for solving of which are known. The challenge then consists in finding interfaces between these algorithms and the modeling tools. This includes choosing between "symbolic" and "numerical" modeling environments, transforming the usually non-autonomous resulting system into an autonomous one, ensuring conformity of the new interval version to the old numerical, etc. In this paper, we focus on modeling multibody systems' dynamics with the interval extension of the "numerical" environment MOBILE, discuss the techniques which make the uniform treatment of interval and non-interval modeling easier, comment on the wrapping effect, and give reasons for our choice of MOBILE by comparing the results achieved with its help with those obtained by analogous symbolic tools.
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
Nonlinear dynamic analysis of flexible multibody systems
Bauchau, Olivier A.; Kang, Nam Kook
1991-01-01
Two approaches are developed to analyze the dynamic behavior of flexible multibody systems. In the first approach each body is modeled with a modal methodology in a local non-inertial frame of reference, whereas in the second approach, each body is modeled with a finite element methodology in the inertial frame. In both cases, the interaction among the various elastic bodies is represented by constraint equations. The two approaches were compared for accuracy and efficiency: the first approach is preferable when the nonlinearities are not too strong but it becomes cumbersome and expensive to use when many modes must be used. The second approach is more general and easier to implement but could result in high computation costs for a large system. The constraints should be enforced in a time derivative fashion for better accuracy and stability.
An Earth multi-body system elasticity and plasticity dynamics model
Institute of Scientific and Technical Information of China (English)
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.
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.
Roller-chain Drives Mechanics using Multibody Dynamics Tools
DEFF Research Database (Denmark)
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 ...
Recursive dynamics algorithm for multibody systems with prescribed motion
Jain, Abhinandan; Rodriguez, Guillermo
1993-10-01
This paper uses spatial operator techniques to develop a new algorithm for the dynamics of multibody systems with hinges undergoing prescribed motion. This algorithm is spatially recursive, and its computational complexity grows only linearly with the number of degrees of freedom in the system. Its structure is a hybrid of known recursive forward and inverse dynamics algorithms for regular multibody systems. Changes to the prescribed/nonprescribed nature of hinges can be implemented during run time since they are handled with very low overhead in the algorithm.
Dynamics and nonlinear attitude control of multibody space systems
Rui, Chunlei
In this dissertation, we study dynamics and attitude control problems for a multibody system in space. The key feature of this work is the systematic use of shape changes as three dimensional attitude controls. Control models are identified for a general class of multibody space systems that are controlled by thrusters, reaction wheels, and/or joint actuators. The important role of shape change in attitude maneuvers for a multibody space system is identified and shape change is recognized as a means of attitude control. Formulas that quantify three dimensional attitude changes induced by periodic shape changes, rotation of reaction wheels and nonzero angular momentum are developed. The formulas prove fundamental for development of numerous attitude control algorithms. Explicit construction procedures are developed for shape changes that accomplish a desired three dimensional reconfiguration of a free-floating multibody space system with zero angular momentum with prescribed accuracy. The control computation involves evaluation of certain Lie brackets and solution of a simple system of algebraic equations. Explicit construction procedures are developed for shape changes that accomplish a desired three dimensional reorientation of a free-floating multibody space system with constant nonzero angular momentum with prescribed accuracy. Control algorithms are provided for reorientation of a multibody space system to one of its relative equilibria. Explicit control algorithms are developed for reaction wheel and shape changes that accomplish a desired three dimensional reorientation for a spacecraft system containing a single reaction wheel and a single movable appendage. Characterization of shape changes that enhance effectiveness of reaction wheels and joint actuators is given, and control algorithms are provided for effective simultaneous attitude changes and shape changes. Feedback attitude control laws are developed for three dimensional attitude maneuvers of a
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
Multiport Models for Dynamics of Flexible Multibody Systems
Yoshimura, Hiroaki; Kawase, Takehiko
The paper presents a multiport model of flexible multibody systems by analogy with a connection multiport in electrical circuit theory. First we introduce a concept of a fundamental pair, that is, a pair of a mechanical joint and its adjacent body to recognize the flexible multibody system as an interconnected system of such fundamental pairs. Second we employ a finite element model to describe flexible deformations associated with large overall motions using moving frames and we also model various kinematical and dynamical relations of the fundamental pair such as geometric nonlinear effects associated with the flexible deformations and kinematical constraints due to the mechanical joint by nonenergic multiports together with dual connection matrices. Finally it is shown that the interconnection of the nonenergic multiports with physical elements provides a multiport model of the fundamental pair and also that the equations of motion of the flexible multibody system can be systematically formulated by the present approach.
Non-intrusive parallelization of multibody system dynamic simulations
González, Francisco; Luaces, Alberto; Lugrís, Urbano; González, Manuel
2009-09-01
This paper evaluates two non-intrusive parallelization techniques for multibody system dynamics: parallel sparse linear equation solvers and OpenMP. Both techniques can be applied to existing simulation software with minimal changes in the code structure; this is a major advantage over Message Passing Interface, the standard parallelization method in multibody dynamics. Both techniques have been applied to parallelize a starting sequential implementation of a global index-3 augmented Lagrangian formulation combined with the trapezoidal rule as numerical integrator, in order to solve the forward dynamics of a variable-loop four-bar mechanism. Numerical experiments have been performed to measure the efficiency as a function of problem size and matrix filling. Results show that the best parallel solver (Pardiso) performs better than the best sequential solver (CHOLMOD) for multibody problems of large and medium sizes leading to matrix fillings above 10. OpenMP also proved to be advantageous even for problems of small sizes. Both techniques delivered speedups above 70% of the maximum theoretical values for a wide range of multibody problems.
Isogeometric shell discretizations for flexible multibody dynamics
Energy Technology Data Exchange (ETDEWEB)
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.
Modeling of complex systems using nonlinear, flexible multibody dynamics
Rodriguez, Jesus Diaz
Finite element based multibody dynamics formulations extend the applicability of classical finite element methods to the modeling of flexible mechanisms. A general computer code will include rigid and flexible bodies, such as beams, joints, and active elements. These procedures are designed to overcome the modeling limitations of conventional multibody formulations that are often restricted to the analysis of rigid systems or use a modal representation to model the flexibility of elastic components. As multibody formulations become more widely accepted, the need to model a wider array of phenomena increases. The goal of this work is to present a methodology for the analysis of complex systems that may require the modeling of new joints and elements, or include the effects of clearance, freeplay or friction in the joints. Joints are essential components of multibody systems, rigid or flexible. Usually, joints are modeled as perfect components. In actual joints, clearance, freeplay, friction, lubrication and impact forces will can have a significant effect on the dynamic response of the system. Certain systems require the formulation of new joints for their analysis. Among one of them is the curve sliding joint which enforces the sliding of a body on a rigid curve connected to another body. The curve sliding joint is especially useful when modeling a vibration absorber device mounted on the rotor hub of rotorcraft: the bifilar pendulum. The formulation of a new modal based element is also presented. A modal based element is a model of an elastic substructure that includes a modal representation of elastic effects together with large rigid body motions. The proposed approach makes use of a component mode synthesis technique that allows the analyst to choose any type of modal basis and simplifies the connection to other multibody elements. The formulation is independent of the finite element analysis package used to compute the modes of the elastic component.
Multibody dynamics modelling of the freight train bogie system
Ballew, B.; Chan, B. J.; Sandu, C.
2011-04-01
Previous work in the railway technology laboratory at Virginia Polytechnic Institute and State University (Virginia Tech) focused on better capturing the dynamics of the friction wedge, modelled using three-dimensional rigid body dynamics with unilateral contact conditions. The current study extends the previous work to a half-bogie model treated as an application of multibody dynamics with unilateral contact to model the friction wedge interactions with the bolster and the sideframe. The half-bogie model was derived using MATLAB and functions as a three dimensional, dynamic, and multibody dynamics model comprised of four rigid bodies: a bolster, two friction wedges, and a sideframe assembly. This expanded model allows each wedge four degrees of freedom: vertical displacement, longitudinal displacement (between the bolster and sideframe), pitch (rotation around the lateral axis), and yaw (rotation around the vertical axis). The bolster and the sideframe are constrained to have only the vertical degree of freedom. The geometry of these bodies can be adjusted for various simulation scenarios. The bolster can be initialised with a pre-defined yaw (rotation around the vertical axis) and the sideframe may be initialised with a pre-defined pitch/toe (rotation around the lateral axis). The results of the multibody dynamics in half-bogie model simulation are shown in comparison with results from NUCARS®, an industry standard in train-modelling software, for similar inputs.
A Constrained Multibody System Dynamics Avoiding Kinematic Singularities
Huang, Chih-Fang; Yan, Chang-Dau; Jeng, Shyr-Long; Cheing, Wei-Hua
In the analysis of constrained multibody systems, the constraint reaction forces are normally expressed in terms of the constraint equations and a vector of Lagrange multipliers. Because it fails to incorporate conservation of momentum, the Lagrange multiplier method is deficient when the constraint Jacobian matrix is singular. This paper presents an improved dynamic formulation for the constrained multibody system. In our formulation, the kinematic constraints are still formulated in terms of the joint constraint reaction forces and moments; however, the formulations are based on a second-order Taylor expansion so as to incorporate the rigid body velocities. Conservation of momentum is included explicitly in this method; hence the problems caused by kinematic singularities can be avoided. In addition, the dynamic formulation is general and applicable to most dynamic analyses. Finally the 3-leg Stewart platform is used for the example of analysis.
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.
Dynamics and control of multibody systems in central gravity
Sanyal, Amit K.
This dissertation studies the dynamics and control of multibody systems, and their numerical simulation, in a central gravitational field. Initially, the dynamics of multibody systems moving in a plane in a central gravity is studied. There is a cyclic orbital coordinate, and the corresponding conjugate momentum is conserved. The dynamics is reduced to eliminate this cyclic variable. A general development for analyzing stability of relative equilibria of the full dynamics, corresponding to equilibria of the reduced dynamics, is obtained. This is applied to some examples of multibody spacecraft in planar motion. A control scheme, based on averaging theory, is developed for orbit transfer from one relative equilibrium to another. This scheme is applied to a planar dumbbell-shaped rigid body in central gravity. The dynamics of such systems in three-dimensional motion also has a cyclic coordinate, and the associated conjugate momentum is conserved. The dynamics is reduced to eliminate this degree of freedom. Stability analysis of the relative equilibria of a rigid dumbbell-shaped body is carried out. Potential shaping with attitude feedback is used to stabilize the unstable relative equilibria of the dumbbell body. For numerical simulations of the dynamics of free and controlled multibody systems in central gravity, numerical integration algorithms obtained from discrete variational mechanics are used. These algorithms exactly preserve the symplectic form and conserved momenta of such systems. They also nearly preserve the total energy of conservative systems over long simulation times. These properties are usually not present in other numerical integration algorithms. Variational integration algorithms for the full and reduced dynamics of multibody systems in a potential field are obtained, and applied to the specific examples treated in this dissertation. Comparison with a standard Runge-Kutta fourth order integrator, for an example problem, shows the better
System Reduction in Multibody Dynamics of Wind Turbines
DEFF Research Database (Denmark)
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. Th...... stiffness matrix during a stopped situation or under nominal operational conditions is used to derive the functional basis of the modal expansion....
Dynamics and control of multibody tethered systems
Kalantzis, S.; Modi, V. J.; Pradhan, S.; Misra, A. K.
The equations of motion for a multibody tethered satellite system in a three dimensional Keplerian orbit are derived. The model considers a multi-satellite system connected in series by flexible tethers. Both tethers and subsatellites are free to undergo three dimensional attitude motion, together with longitudinal and transverse vibration for the tether. The elastic deformations of the tethers are discretized using the assumed-mode method. In addition, the tether attachment points to the subsatellites are kept arbitrary and time varying, with deployment and retrieval degrees of freedom. The governing equations of motion are derived using an Order ( N) Lagrangian formulation. Next, two independent controllers, i.e. an attitude and vibration controller, are designed to regulate the rigid and flexible motion present in the system, excited from various maneuvres performed during the course of a mission. The former controller utilizes the thrusters and momentum-wheels located on the rigid satellites with a control algorithm based on the feedback linearization technique. On the other hand, the latter is designed using the robust linear quadratic Gaussian-loop transfer recovery method actuating the variable tether attachment point, or offset position. Both controllers are successful in suppressing unwanted disturbances in the system in a acceptable amount of time.
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.
Nonlinear Dynamic Analysis of Three Dimensional Flexible Multibody Systems
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The nonlinear dynamic problems of three dimensional flexible multibody systems are investigated. The elastic deformation fields of flexible space beams are decomposed into axial deformation and bending deformation, and described by each exact vibration modes in the body coordinate systems. The constrainted nonlinear dynamic equations are derived by using Lagrange multiplier method. A numerical procedure for solving the resulting differential algebraic equations is presented based on Newmark direct integration method combined with the modified Newton-Raphson iterative method. Numerical results verify the effectiveness of the proposed method.
Numerical Solution for Stiff Dynamic Equations of Flexible Multibody System
Institute of Scientific and Technical Information of China (English)
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.
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.
Dynamics of Multibody Systems Near Lagrangian Points
Wong, Brian
This thesis examines the dynamics of a physically connected multi-spacecraft system in the vicinity of the Lagrangian points of a Circular Restricted Three-Body System. The spacecraft system is arranged in a wheel-spoke configuration with smaller and less massive satellites connected to a central hub using truss/beams or tether connectors. The kinematics of the system is first defined, and the kinetic, gravitational potential energy and elastic potential energy of the system are derived. The Assumed Modes Method is used to discretize the continuous variables of the system, and a general set of ordinary differential equations describing the dynamics of the connectors and the central hub are obtained using the Lagrangian method. The flexible body dynamics of the tethered and truss connected systems are examined using numerical simulations. The results show that these systems experienced only small elastic deflections when they are naturally librating or rotating at moderate angular velocities, and these deflections have relatively small effect on the attitude dynamics of the systems. Based on these results, it is determined that the connectors can be modeled as rigid when only the attitude dynamics of the system is of interest. The equations of motion of rigid satellites stationed at the Lagrangian points are linearized, and the stability conditions of the satellite are obtained from the linear equations. The required conditions are shown to be similar to those of geocentric satellites. Study of the linear equations also revealed the resonant conditions of rigid Lagrangian point satellites, when a librational natural frequency of the satellite matches the frequency of its station-keeping orbit leading to large attitude motions. For tethered satellites, the linear analysis shows that the tethers are in stable equilibrium when they lie along a line joining the two primary celestial bodies of the Three-Body System. Numerical simulations are used to study the long term
Dynamics and linear quadratic optimal control of flexible multibody systems
Tung, Chin-Wei
1994-12-01
An efficient algorithm for the modeling, dynamic analysis, and optimal control of flexible multibody systems (FMBS) is presented. The cantilevered Bernoulli-Euler beam model and the assumed mode method are used to represent flexibility of elastic bodies in 3D vibration problems. Centrifugal stiffening effects are introduced to correctly represent the dynamic response. The governing equations of motion are based on Kane's equations, adopting a recursive formulation and strategic positioning of the generalized coordinates. The linear quadratic optimization scheme is employed to formulate the vibration control problem. The solutions to the Riccati equation and the use of Kalman gain as optimal control feedbacks to the control of flexibility are also introduced. Based on the optimal control theory and the property of the built-in redundancy for flexible multibody systems, the performance index measure in the optimization control of such systems can be classified into two manifolds: (1) using the extra degrees of freedom resulting from redundancy as control inputs and choosing an integral-type performance index which results in a global optimization scheme and (2) using the joint forces and torques as control inputs and allowing the system output state to keep close track to a reference state while the performance index is kept minimum. Several numerical examples are presented to demonstrate the effectiveness of the methodologies developed.
Stress stiffening in the dynamics of flexible multibody systems
Wehrli, E.
1993-09-01
The development of new technologies for deployment of structures in space, such as satellite antennas and solar panel arrays, has motivated research work in the field of multibody dynamics. For some of these structures, it may not be possible to realize realistic ground testing, so that increasing needs have appeared for accurate modeling and good numerical simulation of the dynamics. Many computer programs have been developed in order to perform deployment simulations. The accuracy of the results and the computational cost depend on the hypotheses made while developing mechanical model and on the formulation which is used. In this work, a kinematic model and a dynamical model based on a Lagrangian formulation have been developed for an open chain flexible articulated structure. The flexibility is represented by decomposition of the displacements on a modal basis for each body, and stiffening effects are included. Results are presented for a planar articulated structure.
Dynamics of flexible multibody systems with tree topologies
Jiazhen, Hong; Zhenkuan, Pan
1992-08-01
The dynamic equations of flexible multibody systems with tree topological configuration are derived by using the Jourdain's principle. The independent joint coordinates are introduced to describe the large displacements of the bodies, and the modal coordinates are used to describe small deformations of flexible bodies based on the consistent mass finite element method and normal vibration mode analysis. The minimum differential equations are developed, which are compatible with the equations of multi-rigid body systems or structural dynamics. The stiff problem in the numerical integration is thus alleviated effectively. The method used in this paper can be extended to deal with systems with other topological configurations. Finally, the validity and feasibility of the presented mathematical model are demonstrated by a numerical example of a manipulator with two elastic links.
DYNAMIC MODELLING OF BAR-GEAR MIXED MULTIBODY SYSTEMS USING A SPECIFIC FINITE ELEMENT METHOD
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
A new dynamic model for mixed, flexible bar and gear multibody systems is developed based on a specific finite element method, and a new gear-element is proposed. The gear-element can take into account the time variant stiffness, the gear errors and mass unbalance. The model for geared multibody systems can couple the gear meshing and the flexibility of all contained components. The kinematic and dynamic analyses of the geared multibody systems are expounded and illustrated on an example composed of three gears, two bars and one slider.
On the synthesis of dynamics and control for complex multibody systems
Schutte, Aaron Dane
This dissertation develops in a unified manner a new and simple approach for the modeling and control of complex multibody systems. Complex multibody systems are those nonlinear mechanical systems consisting of individual subsystems that are describable by nonlinear differential equations. The interaction of the various subsystems is, in general, governed by nonlinear 'elements.' The nonlinear analysis of general multibody systems presents theoretically challenging problems in both its dynamics and controls aspects. The theoretical developments obtained in this dissertation permit the modeling of multibody systems so that no restrictions are imposed in its formulation, except that its physical model is continuous. The idea of permissible multibody control is developed, and an effective method is provided for generating nonlinear controllers that satisfy a general set of control objectives. The generalized acceleration describing the rotational motion of a rigid body in terms of quaternions is directly obtained thus providing a rotational description for the general motion of multibody systems. Utilizing this formulation, two new control strategies are obtained that explicitly yield the nonlinear control torque required to re-orient a rigid body from an arbitrary rest orientation to another arbitrary rest orientation. The application of this new approach to problems in complex multibody spacecraft systems is carried out for spacecraft precision pointing and to the precise tumbling control of an elastically connected multibody spacecraft system. Numerical examples are provided showing the ease of implementation of the methodology and the accuracy with which the control objectives are satisfied. These results illustrate the capability to easily generate physical models and provide exact control of highly nonlinear, complex multibody systems.
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.
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...
Recursive Dynamic Algorithm of Open-Chain Multibody System
Directory of Open Access Journals (Sweden)
Ming Lu
2014-01-01
Full Text Available Open-chain multibody systems have been extensively studied because of their widespread application. Based on the structural characteristics of such a system, the relationship between its hinged bodies was transformed into recursive constraint relationships among the position, velocity, and acceleration of the bodies. The recursive relationships were used along with the Huston-Kane method to select the appropriate generalized coordinates and determine the partial velocity of each body and to develop an algorithm of the entire system. The algorithm was experimentally validated; it has concise steps and low susceptibility to error. Further, the algorithm can readily solve and analyze open-chain multibody systems.
Multibody Dynamics Formulations Based on Variational Principle%用变分原理研究多刚体系统动力学方程
Institute of Scientific and Technical Information of China (English)
孙右烈
2003-01-01
The formulation of multibody dynamics was studied based on variational principle. The body coonection matrix was intro-duced to define the connection configuration. The expression for the system kinematics was obtained by using the body connection ma-trix. From variational principle the general dynamical equations for multibody system were derived and the dynamical equations weregiven for multibody system subjected to the constraints.
Dynamic Analysis of a Multibody System Including a Very Flexible Beam Element
Seo, Jong-Hwi; Jung, Il-Ho; Park, Tae-Won; Chai, Jang-Bom
In this paper, the dynamic behavior of a multibody system including very flexible beam elements is presented. The very deformable motion of a beam is demonstrated using absolute nodal coordinate formulation, which is based on finite element procedures, and the general continuum mechanics theory to represent the elastic forces. In order to consider the dynamic interaction between flexible beams and a rigid multibody system, a combined system equation of motion is derived using an absolute nodal coordinate and a rigid body coordinate. In particular, a very flexible catenary cable on which a multibody system moves along its length is presented as a numerical example in this study. To do this, formulations for the sliding joint between a very flexible beam and a rigid body were derived using a non-generalized coordinate, which has no inertia or forces associated with it. This sliding joint is very important to many mechanical applications such as cable cars, pulley systems, and pantograph-catenary system for high-speed trains. In addition, a computation method for the dynamic stress in flexible multibody simulation using an absolute nodal coordinate is presented based on Euler-Bernoulli beam theory, and its reliability was verified by commercial program NASTRAN. Numerical examples are shown using the developed analysis program for flexible multibody systems that include a large deformable beam.
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
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
Takahashi, Takashi; Matunaga, Saburo
In order to analyze dynamics of space systems, such as cluster satellite systems and the capturing process of damaged satellites, it is necessary to consider such space systems as reconfigurable multibody systems. In this paper, we discuss the numerical computation of the dynamics of the ground experiment system to simulate the capturing and berthing process of a satellite by a dual-manipulator on the flat floor as an example. We have previously discussed the efficient dynamics algorithm for reconfigurable multibody system with topological changes. However, the contact dynamics, which is one of the most difficult issues on our study, remains to be discussed. We introduce two types of the linear complementarity problem (LCP) concerned with contact dynamics. The difference between two types of the LCP is whether impacts can be considered. Dynamics systems with impacts and friction are non-conservation systems, moreover the LCP is not always solvable. Therefore we must check if the solutions of the numerical computation are correct, or how accurate those are. In this paper, we derive the method of numerical computation with guaranteed accuracy of the LCP for contact dynamics.
Research on the Earth system multi-body force system dynamical model
Institute of Scientific and Technical Information of China (English)
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.
Dynamics of flexible multibody systems using loaded-interface substructure synthesis approach
Lim, S. P.; Liu, A. Q.; Liew, K. M.
1994-12-01
A simple numerical method for dynamic simulation of multibody systems consisting of rigid and flexible bodies is presented. This paper investigates the multibody systems with inertia properties of flexible components that undergo large angular rotations. The equation of motion is derived using the finite element/Lagrange formulation. A substructure synthesis method is employed to reduce the number of elastic coordinates of the multibody system. A modification to the traditional boundary conditions at the free interface has been incorporated. An example is given to demonstrate the accuracy of the computed results which obtained from this new free interface method. This example has been analyzed using the present free interface method and also the finite element method in order to compare the efficient and accuracy of both methods. It was shown that the new free interface substructure synthesis method provides accurate results even with lesser elements.
Recursive Dynamic Algorithm of Open-Chain Multibody System
Ming Lu; Wenbin Gu; Jianqing Liu; Zhenxiong Wang; Zhisheng Jing; Guowei Qin; Shanchao Tu
2014-01-01
Open-chain multibody systems have been extensively studied because of their widespread application. Based on the structural characteristics of such a system, the relationship between its hinged bodies was transformed into recursive constraint relationships among the position, velocity, and acceleration of the bodies. The recursive relationships were used along with the Huston-Kane method to select the appropriate generalized coordinates and determine the partial velocity of each body and to d...
Camera-based noncontact metrology for static/dynamic testing of flexible multibody systems
Pai, P. Frank; Ramanathan, Suresh; Hu, Jiazhu; Chernova, DarYa K.; Qian, Xin; Wu, Genyong
2010-08-01
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.
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.
DEFF Research Database (Denmark)
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...
Energy Technology Data Exchange (ETDEWEB)
Tsai, Fuh-Feng; Haug, E.J. (Iowa University, Iowa City (United States))
1991-03-01
A modified recursive dynamics formulation and a topological analysis method for the formulation are presented in order to achieve the goal of real-time simulation of multibody mechanical systems. A parallel computational algorithm that exploits inherent parallelism in the modified recursive formulation and numerical results is considered. An efficient general-purpose dynamic simulation method is developed for real-time simulation of shared memory parallel processors. 21 refs.
A New Application of Multi-Body System Dynamics in Vehicle-Road Interaction Simulation
Institute of Scientific and Technical Information of China (English)
RenWei-qun; ZhangYun-qing; JinGuo-dong
2003-01-01
In vehicle-road interaction simulation, multibody system (MBS) dynamics as well as the corresponding software ADAMS has been employed to model the nonlinear vehicle in more detail. The simulation method has been validated by the test data, and been compared to the former simple models. This method can be used for estimating the effects of dynamic tire forces and other vehicle features on road damage so that the “road-friendliness” can be assessed in vehicle design process.
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
Articulated Lifting System Modeling Based on Dynamics of Flexible Multi-Body Systems
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In lifting sub-system of deep-sea mining system, spherical joint is used to connect lifting pipes to replace fixed joint. Based on Dynamics of Flexible Multi-body systems, the mechanics model of articulated lifting system is established. Under the four-grade and six-grade oceanic condition, dynamic responses of lifting system are simulated and experiment verified. The simulation results are consistent with experimental ones. The maximum moment of flexion is 322 kN-m on the first pipe under six-grade sea condition. It is seen that the articulated connection can reduce the moment of flexion. The bending deformation of pipe center is researched, and the maximum is 0.000479 m on the first pipe. Deformation has a little effect on the motion of system. It is feasible to analyze articulated lifting system by applying the theory of flexible multi-body dynamics. The articulated lifting system is obviously better than the fixed one.
A computational procedure for multibody systems including flexible beam dynamics
Downer, J. D.; Park, K. C.; Chiou, J. C.
1990-01-01
A computational procedure suitable for the solution of equations of motions for flexible multibody systems has been developed. The flexible beams are modeled using a fully nonlinear theory which accounts for both finite rotations and large deformations. The present formulation incorporates physical measures of conjugate Cauchy stress and covariant strain increments. As a consequence, the beam model can easily be interfaced with real-time strain measurements and feedback control systems. A distinct feature of the present work is the computational preservation of total energy for undamped systems; this is obtained via an objective strain increment/stress update procedure combined with an energy-conserving time integration algorithm which contains an accurate update of angular orientations. The procedure is demonstrated via several example problems.
Deployment analysis of large space antenna using flexible multibody dynamics simulation^1
Mitsugi, Jin; Ando, Kazuhide; Senbokuya, Yumi; Meguro, Akira
2000-07-01
Flexible multibody dynamics is applied to the deployment analysis of a large space antenna composed of a reflective mesh, a cable network and a deployable truss structure. It is clarified that the tension of some of the cables increase when the reflector is stowed. The largest deployment force is observed slightly before the completion of the deployment. A proper allocation of both translational and rotational springs can provide an efficient deployment force. A deployment experiment on a 4.8 m aperture reflector model verifies the computational results. It is concluded that a flexible multibody dynamics simulation is an indispensable design tool for reducing the weight and ensuring the secure deployment of low-cost mesh reflectors.
Time-stepping for multibody dynamics with friction-affected bilateral constraints
Institute of Scientific and Technical Information of China (English)
Li Fu; Qi Wang; Shimin Wang
2009-01-01
The dynamics of multibody systems with friction-affected bilateral constraints is essentially different from those of smooth multibody systems.In this paper,general modeling and numerical methods for this kind of friction-affected system are given.Each friction-affected bilateral constraint is modeled by splitting it into two unilateral constraints opposite to each other.The constraint equalities are replaced with complementarity inequalities to avoid the absolute value terms in the dynamic equations.A linear complementarity problem time-stepping scheme is presented for simulation that does not suffer from the difficulties of enumeration (known as Delassus' problem).The algorithm has the advantage that it needs no detection for stick-slip transition when neglecting the difference between the static and kinetic friction coefficients.Our method is carried out in an example to analyze the nonsmooth nonlinear behavior of a typical mechanism.
Dynamic Analysis of Flexible Multibody Systems for High-Rise Building Window Cleaning Gondola
Institute of Scientific and Technical Information of China (English)
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.
Bustamante, D. A.; Kurdila, A. J.; Menon, R. G.
1993-04-01
The augmented Lagrangian formulation used in the dynamic analysis of multibody systems under holonomic constraints is presently found to exhibit fixed-step convergence, so that the approximate accelerations and Lagrange multipliers at a fixed time interval approach the exact accelerations and multipliers as the number of iterations becomes large. Also noted are a fixed time-interval rate of convergence inequality for the Lagrange multipliers, and corroborating empirical evidence for these analytical developments.
PACE - A test bed for the dynamics and control of flexible multibody systems
Kwak, M. K.; Schlaegel, W. T.; Das, A.
1993-04-01
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 equations of motion are derived by using the Hamilton principle and the assumed mode method. Control techniques for the slewing control and vibration suppression are also discussed.
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...
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
Energy Technology Data Exchange (ETDEWEB)
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.
Outboard body effects on flexible branch body dynamics in articulated multibody systems
Tadikonda, Sivakumar S. K.; Schubele, Harry W.
1994-05-01
Investigations addressing modeling of component flexible bodies in articulated multibody systems have typically been concerned only with the boundary conditions at the inboard end of a body. It is shown here that the boundary conditions at the end (or joint) leading to the outboard bodies of a branch body play an important roles as well, especially in nonplanar multibody systems. An example for such system is uniform flexible beam fixed at one end and with a rotating end mass attached at the other. The end mass is offset from, and rotates in plane perpendicular to, the beam axis. The results in a time-varying boundary condition are presented in the paper, and using these, the associated dynamic equations are derived. The performance of these shape functions is compared to that of three 'traditional' mode sets, using numerical simulations. The results demonstrate the limitation of the latter mode sets.
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.
Rapid maneuvering of multi-body dynamic systems with optimal motion compensation
Bishop, B.; Gargano, R.; Sears, A.; Karpenko, M.
2015-12-01
Rapid maneuvering of multi-body dynamical systems is an important, yet challenging, problem in many applications. Even in the case of rigid bodies, it can be difficult to maintain precise control over nominally stationary links if it is required to move some of the other links quickly because of the various nonlinearities and coupled interactions that occur between the bodies. Typical control concepts treat the multi-body motion control problem in two-stages. First, the nonlinear and coupling terms are treated as disturbances and a trajectory tracking control law is designed in order to attenuate their effects. Next, motion profiles are designed, based on kinematics parameterizations, and these are used as inputs to the closed loop system to move the links. This paper describes an approach for rapid maneuvering of multi-body systems that uses optimal control theory to account for dynamic nonlinearities and coupling as part of the motion trajectory design. Incorporating appropriate operational constraints automatically compensates for these multi-body effects so that motion time can be reduced while simultaneously achieving other objectives such as reducing the excitation of selected links. Since the compensatory effect is embedded within the optimal motion trajectories, the performance improvement can be obtained even when using simple closed-loop architectures for maneuver implementation. Simulation results for minimum time control of a two-axis gimbal system and for rapid maneuvering of a TDRS single-access antenna, wherein it is desired to limit the excitation of the satellite body to which the antenna is attached, are presented to illustrate the concepts.
Partition method for impact dynamics of flexible multibody systems based on contact constraint
Institute of Scientific and Technical Information of China (English)
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 ...
A Component Mode Synthesis Algorithm for Multibody Dynamics of Wind Turbines
DEFF Research Database (Denmark)
Holm-Jørgensen, Kristian; Nielsen, Søren R.K.
2009-01-01
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...... 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...
Cheng, Yen-Ming
Simulation of the dynamics of physical systems is an important aspect of the engineering discipline for approximating the dynamics of real life. The simulation of complex multibody systems to an acceptable degree of accuracy involves the mathematical modeling and computer implementation of systems such as mechanisms and vehicles comprised of multiple parts. In this dissertation, new algorithms are developed for multibody simulation using a rather general mathematical model. Both open-tree and closed-loop topologies are implemented. Constraints, specifically, joint constraints, are investigated. A new algorithm is developed that projects the original configuration space into the unconstrained orthogonal subspace, thereby reducing the dimension of the system equations without resorting to complicated transformations. The reduced set of equations not only increases the simulation speed, but also improves the numerical accuracy of the simulation results by reducing the number of calculations performed. Constraint forces can easily be obtained if required for analyzing the multibody system. Algorithms by themselves are not immediately useful to users. A program was developed to implement the algorithms. The program, which was written in C/C++, incorporated the use of Microsoft Windows Application Programming Interfaces (Windows API), Microsoft Foundation Classes (MFC), and OpenGL graphics language. The system states are integrated by applying standard numerical techniques for integrating a set of first-order differential equations. Accelerations and constraint forces are obtained using direct and/or iterative techniques for solving a set of simultaneous equations. With today's powerful computers, a graphical interface becomes feasible to serve as the communicator between the program and the user. The software therefore includes a graphical user interface. Concurrent graphical animations of the motion of the system simulated are created. These are important to the user
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...
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.
Earthquake dynamic response of large flexible multibody systems
Directory of Open Access Journals (Sweden)
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
Directory of Open Access Journals (Sweden)
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.
Stability analysis of a multibody system model for coupled slosh-vehicle dynamics
Nichkawde, Chetan; Harish, P. M.; Ananthkrishnan, N.
2004-08-01
The coupled slosh-vehicle dynamics of a rigid body in planar atmospheric flight carrying a sloshing liquid is considered as a multibody system with the sloshing motion modelled as a simple pendulum. The coupled, non-linear equations for the four-degree-of-freedom multibody system are derived using the method of Lagrangian dynamics. Careful non-dimensionalization reveals two crucial parameters that determine the extent of coupling between the rigid body and slosh modes, and also two important frequency parameters. Using a two-parameter continuation method, critical combinations of these four parameters for which the coupled slosh-vehicle dynamics can become unstable are computed. Results are displayed in the form of neutral stability curves (stability boundaries) in parameter space, and an analytical expression incorporating the four parameters that represents the neutral stability curves is obtained. Reduced-order linearized models and key transfer functions are derived in an effort to understand the instability phenomenon. Physically, the sloshing motion is seen to induce a static instability, sometimes called tumbling, in the vehicle pitch dynamics, depending on the slosh mass fraction and the location of the slosh pendulum hinge point above the rigid vehicle center of mass.
Large deflection dynamic response analysis of flexible hull beams by the multibody system method
Zhang, Xiaojun; Wu, Guorong
2007-04-01
In this paper the large deflection dynamic problems of Euler beams are investigated. The vibration control equations are derived based on the multibody system method. A numerical procedure for solving the resulting differential algebraic equations is presented on the basis of the Newmark direct integration method combined with the Newton-Raphson iterative method. The sub beams are treated as small deformation in the convected coordinate systems, which can greatly simplify the deformation description. The rigid motions of the sub beams are taken into account through the motions of the convected coordinate systems. Numerical examples are carried out, where results show the effectiveness of the proposed method.
Large Deflection Dynamic Response Analysis of Flexible Hull Beams by the Multibody System Method
Institute of Scientific and Technical Information of China (English)
ZHANG Xiaojun; WU Guorong
2007-01-01
In this paper the large deflection dynamic problems of Euler beams are investigated. The vibration control equations are derived based on the multibody system method. A numerical procedure for solving the resulting differential algebraic equations is presented on the basis of the Newmark direct integration method combined with the Newton-Raphson iterative method. The sub beams are treated as small deformation in the convected coordinate systems, which can greatly simplify the deformation description. The rigid motions of the sub beams are taken into account through the motions of the convected coordinate systems. Numerical examples are carried out, where results show the effectiveness of the proposed method.
DEFF Research Database (Denmark)
Johansen, Per; Rømer, Daniel; Andersen, Torben Ole;
2014-01-01
is a 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...
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.
Application of the Absolute Nodal Co-Ordinate Formulation to Multibody System Dynamics
Escalona, J. L.; Hussien, H. A.; Shabana, A. A.
1998-07-01
The floating frame of reference formulation is currently the most widely used approach in flexible multibody simulations. The use of this approach, however, has been limited to small deformation problems. In this investigation, the computer implementation of the newabsolute nodal co-ordinate formulationand its use in the small and large deformation analysis of flexible multibody systems that consist of interconnected bodies are discussed. While in the floating frame of reference formulation a mixed set of absolute reference and local elastic co-ordinates are used, in the absolute nodal co-ordinate formulation only absolute co-ordinates are used. In the absolute nodal co-ordinate formulation, new interpretation of the nodal co-ordinates of the finite elements is used. No infinitesimal or finite rotations are used as nodal co-ordinates from beams and plates, instead, global slopes are used to define the element nodal co-ordinates. Using this interpretation of the element co-ordinates, beams and plates can be considered as isoparametric elements, and as a result, exact modelling of the rigid body dynamics can be obtained using the element shape function and the absolute nodal co-ordinates. Unlike the floating frame of reference approach, no co-ordinate transformation is required in order to determine the element inertia. The mass matrix of the finite elements is a constant matrix, and therefore, the centrifugal and Coriolis forces are equal to zero when the absolute nodal co-ordinate formulation is used. Another advantage of using the absolute nodal co-ordinate formulation in the dynamic simulation of multibody systems is its simplicity in imposing some of the joint constraints and also its simplicity in formulating the generalized forces due to spring-damper elements. The results obtained in this investigation show an excellent agreement with the results obtained using the floating frame of reference formulation when large rotation-small deformation problems are
Numerical and experimental studies on impact dynamics of a planar flexible multibody system
Dong, Fu-Xiang; Hong, Jia-Zhen; Zhu, Kun; Yu, Zheng-Yue
2010-08-01
In this paper a computational methodology on impact dynamics of the flexible multibody system is presented. First, the floating frame of reference approach and nodal coordinates on the basis of finite element formulation are used to describe the kinematics of planar deformable bodies. According to the kinematic description of contact conditions, the contact constraint equations of planar flexible bodies are derived. Based on the varying topology technique the impact dynamic equations for a planar multibody system are established. Then the initial conditions of the equations in each contact stage are determined according to the discontinuity theory in continuum mechanics. The experiments between the aluminum rods are performed to check the correctness of the proposed method. Through the comparison between the numerical and experimental results the proposed method is validated. Experimental results also show that the impulse momentum method cannot accurately predict the complex impact dynamic phenomena and the continuous model may lead to a serious error when used to simulate the impact problems with significant wave propagation effects.
On the effect of linear algebra implementations in real-time multibody system dynamics
González, Manuel; González, Francisco; Dopico, Daniel; Luaces, Alberto
2008-03-01
This paper compares the efficiency of multibody system (MBS) dynamic simulation codes that rely on different implementations of linear algebra operations. The dynamics of an N-loop four-bar mechanism has been solved with an index-3 augmented Lagrangian formulation combined with the trapezoidal rule as numerical integrator. Different implementations for this method, both dense and sparse, have been developed, using a number of linear algebra software libraries (including sparse linear equation solvers) and optimized sparse matrix computation strategies. Numerical experiments have been performed in order to measure their performance, as a function of problem size and matrix filling. Results show that optimal implementations can increase the simulation efficiency in a factor of 2 3, compared with our starting classical implementations, and in some topics they disagree with widespread beliefs in MBS dynamics. Finally, advices are provided to select the implementation which delivers the best performance for a certain MBS dynamic simulation.
Rui, Xiao-Ting; Kreuzer, Edwin; Rong, Bao; He, Bin
2012-04-01
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 multibody system with flexible beams moving in space. Formulations and numerical example of a rigid-flexible-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 moving 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.
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.
DEFF Research Database (Denmark)
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....
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
Dynamic multibody protein interactions suggest versatile pathways for copper trafficking.
Keller, Aaron M; Benítez, Jaime J; Klarin, Derek; Zhong, Linghao; Goldfogel, Matthew; Yang, Feng; Chen, Tai-Yen; Chen, Peng
2012-05-30
As part of intracellular copper trafficking pathways, the human copper chaperone Hah1 delivers Cu(+) to the Wilson's Disease Protein (WDP) via weak and dynamic protein-protein interactions. WDP contains six homologous metal binding domains (MBDs) connected by flexible linkers, and these MBDs all can receive Cu(+) from Hah1. The functional roles of the MBD multiplicity in Cu(+) trafficking are not well understood. Building on our previous study of the dynamic interactions between Hah1 and the isolated fourth MBD of WDP, here we study how Hah1 interacts with MBD34, a double-domain WDP construct, using single-molecule fluorescence resonance energy transfer (smFRET) combined with vesicle trapping. By alternating the positions of the smFRET donor and acceptor, we systematically probed Hah1-MBD3, Hah1-MBD4, and MBD3-MBD4 interaction dynamics within the multidomain system. We found that the two interconverting interaction geometries were conserved in both intermolecular Hah1-MBD and intramolecular MBD-MBD interactions. The Hah1-MBD interactions within MBD34 are stabilized by an order of magnitude relative to the isolated single-MBDs, and thermodynamic and kinetic evidence suggest that Hah1 can interact with both MBDs simultaneously. The enhanced interaction stability of Hah1 with the multi-MBD system, the dynamic intramolecular MBD-MBD interactions, and the ability of Hah1 to interact with multiple MBDs simultaneously suggest an efficient and versatile mechanism for the Hah1-to-WDP pathway to transport Cu(+).
Modeling and Simulation of Arresting Gear System with Multibody Dynamic Approach
Directory of Open Access Journals (Sweden)
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.
Numerical Simulation of the Spreading Dynamic Responses of the Multibody System with a Floating Base
Institute of Scientific and Technical Information of China (English)
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.
Multi-body dynamic system simulation of carrier-based aircraft ski-jump takeoff
Institute of Scientific and Technical Information of China (English)
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.
A Coupled Helicopter Rotor/Fuselage Dynamics Model Using Finite Element Multi-body
Directory of Open Access Journals (Sweden)
Cheng Qi-you
2016-01-01
Full Text Available To develop a coupled rotor/flexible fuselage model for vibration reduction studies, the equation of coupled rotor-fuselage is set up based on the theory of multi-body dynamics, and the dynamic analysis model is established with the software MSC.ADMAS and MSC.NASTRAN. The frequencies and vibration acceleration responses of the system are calculated with the model of coupled rotor-fuselage, and the results are compared with those of uncoupled modeling method. Analysis results showed that compared with uncoupled model, the dynamic characteristic obtained by the model of coupled rotor-fuselage are some different. The intrinsic frequency of rotor is increased with the increase of rotational velocities. The results also show that the flying speed has obvious influence on the vibration acceleration responses of the fuselage. The vibration acceleration response in the vertical direction is much higher at the low speed and high speed flight conditions.
Dynamics of deformable multibody systems using recursive projection methods
Shabana, A. A.
1992-12-01
In this investigation, generalized Newton-Euler equations are developed for deformable bodies that undergo large translational and rotational displacements. The configuration of the deformable body is identified using coupled sets of reference and elastic variables. The nonlinear generalized Newton-Euler equations are formulated in terms of a set of time invariant scalars and matrices that depend on the spatial coordinates as well as the assumed displacement field. These time-invariant quantities appear in the nonlinear terms that represent the dynamic coupling between the rigid body modes and the elastic deformation. A set of recursive kinematic equations, in which the absolute accelerations are expressed in terms of the joint and elastic accelerations are developed for several joint types. The recursive kinematic equations and the joint reaction relationships are combined with the generalized Newton-Euler equations in order to obtain a system of loosely coupled equations which have sparse matrix structure. Using matrix partitioning and recursive projection techniques based on optimal block factorization an order n solution for the system equations is obtained.
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.
International Nuclear Information System (INIS)
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
The bond graph model of planar flexible multibody mechanical systems and its dynamic principle
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In order to increase the efficiency and reliability of the dynamic analysis for flexible planar linkage containing the coupling of multi-energy domains, a method based on bond graph is introduced. From the viewpoint of power conservation, the peculiar property of bond graph multiport element MTF is discussed. The procedure of modeling planar flexible multibody mechanical systems by bond graphs and its dynamic principle are described. To overcome the algebraic difficulty brought by differential causality and nonlinear junction structure, the constraint forces at joints can be considered as unknown effort sources and added to the corresponding O-junctions of system bond graph model. As a result, the automatic modeling on a computer is realized. The validity of the procedure is illustrated by a practical example.
Directory of Open Access Journals (Sweden)
Hai-gen Yang
2015-09-01
Full Text Available The complex mechanical systems such as high-speed trains, multiple launch rocket system, self-propelled artillery, and industrial robots are becoming increasingly larger in scale and more complicated in structure. Designing these products often requires complex model design, multibody system dynamics calculation, and analysis of large amounts of data repeatedly. In recent 20 years, the transfer matrix method of multibody system has been widely applied in engineering fields and welcomed at home and in abroad for the following features: without global dynamic equations of the system, low orders of involved system matrices, high computational efficiency, and high programming. In order to realize the rapid and visual simulation for complex mechanical system virtual design using transfer matrix method of multibody system, a virtual design software named MSTMMSim is designed and implemented. In the MSTMMSim, the transfer matrix method of multibody system is used as the solver for dynamic modeling and calculation; the Open CASCADE is used for solid geometry modeling. Various auxiliary analytical tools such as curve plot and animation display are provided in the post-processor to analyze and process the simulation results. Two numerical examples are given to verify the validity and accuracy of the software, and a multiple launch rocket system engineering example is given at the end of this article to show that the software provides a powerful platform for complex mechanical systems simulation and virtual design.
Multi-Body Dynamics Analysis and Low Noise Optimization of X6170ZC Diesel
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The multi-body dynamics model of the X6170ZC diesel is established to analyze vibration and acoustic noise. The high quality finite element and simulation models are developed, and nonlinear springs are used to imitate the joints of engine components. The acoustic behavior of the structure is evaluated by the velocity of surface vibration. The noise level is reduced by improving the structure of the engine. The result shows that the surface vibration velocity level is decreased about 3.7 dB (A) at 1 600 Hz after the optimization. Based on the contrast between the two structures, it is concluded that through structure design the combined noise can be reduced, and the virtual design mode of diesel engines is feasible.
Amirouche, F. M. L.; Xie, M.
1993-01-01
The dynamic simulation of complex rigid/flexible multibody systems relies greatly on the presentation and development of the equations of motion. To achieve computational speed in the execution and to further develop the control algorithms, the expressions involved in the kinematics and the subsequent coefficients associated with the equations of motion must be clearly defined. The intention of this paper is to develop a recursive formulation based on finite element method where all terms are presented in a matrix form. The methodology permits one to identify the coupling between rigid and flexible body motion, and build the necessary arrays for the application at hand. The equations of motion are based on Kane's equation and the general matrix representation for n bodies of its partial velocities and partial angular velocities. The algorithm developed is applied to a single two-link robot manipulator and the subsequent explicit equations of motion are presented.
Dynamic modeling and control of multibody mechanical systems which are structurally flexible
Quinn, R. D.; Chen, J.-L.
1992-01-01
This paper concerns the dynamic modeling and control of multibody, open-chained, structurally flexible, mechanical systems where the bodies are connected by revolute joints. The equations of motion are formulated based on a matrix form of Lagrange's equations for inertial quasi-coordinates. Each body is treated as a substructure of the system. For the purposes of simulation and control, the equations of motion are separated into two sets of equations using a perturbation approach: one to describe large rigid-body motions of the articulated system and the other to describe small linear motions of the bodies about the large motions. A biologically natural control strategy is used for vibration suppression and tracking the prescribed motion.
An accelerated iterative method for the dynamics of constrained multibody systems
Lee, Kisu
1993-01-01
An accelerated iterative method is suggested for the dynamic analysis of multibody systems consisting of interconnected rigid bodies. The Lagrange multipliers associated with the kinematic constraints are iteratively computed by the monotone reduction of the constraint error vector, and the resulting equations of motion are easily time-integrated by a well established ODE technique. The velocity and acceleration constraints as well as the position constraints are made to be satisfied at the joints at each time step. Exact solution is obtained without the time demanding procedures such as selection of the independent coordinates, decomposition of the constraint Jacobian matrix, and Newton Raphson iterations. An acceleration technique is employed for the faster convergence of the iterative scheme and the convergence analysis of the proposed iterative method is presented. Numerical solutions for the verification problems are presented to demonstrate the efficiency and accuracy of the suggested technique.
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.
Energy Technology Data Exchange (ETDEWEB)
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.
Tromme, Emmanuel; Bruls, Olivier; Virlez, Geoffrey; Duysinx, Pierre
2013-01-01
This paper is dedicated to a comparative evaluation between two methods of optimization to realize the structural optimization of flexible components in mechanical systems modeled as multibody systems. A nonlinear finite element method based formalism is considered for the dynamic simulation of the flexible multibody system. The first method is the Equivalent Static Load method which enables to transform a dynamic response optimization problem into a set of static response optimization proble...
Discrete time transfer matrix method for dynamics of multibody system with real-time control
Rong, Bao; Rui, Xiaoting; Wang, Guoping; Yang, Fufeng
2010-03-01
By taking the control and feedback parameters into account in state vectors, defining new state vectors and deducing new transfer equations and transfer matrices for actuator, controlled element and feedback element, a new method named as the discrete time transfer matrix method for controlled multibody system (CMS) is developed to study dynamics of CMS with real-time control in this paper. This method does not need the global dynamics equations of system. It has the modeling flexibility, low order of system matrix, high computational efficiency, and is efficient for general CMS. Compared with the ordinary dynamics methods, the proposed method has more advantages for dynamics design and real-time control of a complex CMS. Adopting the PID adaptive controller and modal velocity feedback control on PZT actuators, and applying the proposed method and ordinary dynamics method, respectively, the tip trajectory tracking for a flexible manipulator is carried out. Formulations of the method as well as numerical simulation are given to validate 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
Energy Technology Data Exchange (ETDEWEB)
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.
Newton-Euler Dynamic Equations of Motion for a Multi-body Spacecraft
Stoneking, Eric
2007-01-01
The Magnetospheric MultiScale (MMS) mission employs a formation of spinning spacecraft with several flexible appendages and thruster-based control. To understand the complex dynamic interaction of thruster actuation, appendage motion, and spin dynamics, each spacecraft is modeled as a tree of rigid bodies connected by spherical or gimballed joints. The method presented facilitates assembling by inspection the exact, nonlinear dynamic equations of motion for a multibody spacecraft suitable for solution by numerical integration. The building block equations are derived by applying Newton's and Euler's equations of motion to an "element" consisting of two bodies and one joint (spherical and gimballed joints are considered separately). Patterns in the "mass" and L'force" matrices guide assembly by inspection of a general N-body tree-topology system. Straightforward linear algebra operations are employed to eliminate extraneous constraint equations, resulting in a minimum-dimension system of equations to solve. This method thus combines a straightforward, easily-extendable, easily-mechanized formulation with an efficient computer implementation.
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,...
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.
Directory of Open Access Journals (Sweden)
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
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.
Gomez Cristobal, Jose Antonio
The thesis presents a method for the optimal dimensional synthesis of multibody systems with topological, geometric, position, kinematic and dynamic constraints. The method is based on the minimization of an elastic potential energy objective function whose design variables are natural coordinates and bar lengths of the system with a system modelling similar to that used in the finite elements method. The optimisation is performed by means of a sequential quadratic programming algorithm implemented through routine E04UCF of the mathematical library NAG. The resulting method can be applied to multibody systems composed of rigid bodies, irrespective of the dimension of their movement, geometric configuration and kinematic pairs of the kinematic chain, and allows for the mobility of fixed points. Using previous developments to resolve velocity and acceleration kinematic problems, the equations systems of the multibody system dynamic equilibrium and their partial derivatives with respect to the designing variables are analytically solved. The resolution of these equations systems provides analytical expressions of the dynamic problem parameters that can be imposed as restrictions in the designing phase, and well as their Jacobians. The Hessians, which are also required by the sequential quadratic programming algorithm, are calculated from the analytical expressions of the dynamic parameters and Jacobians following the numerical method of finite differences. The expressions for the dynamic constraints of input and output forces, constraint forces, support reactions, mass of bodies, as well as the main merit indexes---ratio of angular velocities, mechanical advantage and transmission angle---are developed. These expressions are subsequently used to optimise the dynamic behaviour of planar mechanisms. The described method enables the simultaneous optimisation of the kinematic and dynamic behaviour of the system from the very earliest phases of design, thus making design
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
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.
Developments of studies on multibody system dynamics%多体系统动力学研究进展
Institute of Scientific and Technical Information of China (English)
戎保; 芮筱亭; 王国平; 杨富锋
2011-01-01
Multibody system dynamics is an important branch in the field of the modern mechanics. It provides a strong tool for dynamic performance estimation and optimizing design of many mechanical systems in a lot of important engineering fields, such as, weapon, aeronautics, astronautics, vehicle, robot, precision machinery, and so on. The study on dynamic modeling, design and control of complex multibody systems is the urgent demand of modern engineering problems. Here studies on dynamic modeling methods, computational strategies, control design, software exploitations, and experiments of multibody systems in recently years were reviewed. The future directions of this field were indicated.%多体系统动力学是当今力学领域的研究热点和难点之一,为机械、航空、航天、兵器、机器人等领域中大量机械系统的动态性能评估和优化设计提供了强有力的理论工具与技术支撑.复杂多体系统动力学建模、设计和控制研究是当前重大工程领域的迫切需求.对近年来国内外多体系统动力学建模方法、求解策略、控制设计、软件开发、实验研究等方面的研究现状进行了较为全面地概括和总结,并简要展望了多体系统动力学的发展趋势.
Stick-slip algorithm in a tangential contact force model for multi-body system dynamics
International Nuclear Information System (INIS)
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
Rodriguez, G.; Kreutz, K.
1988-01-01
This report advances a linear operator approach for analyzing the dynamics of systems of joint-connected rigid bodies.It is established that the mass matrix M for such a system can be factored as M=(I+H phi L)D(I+H phi L) sup T. This yields an immediate inversion M sup -1=(I-H psi L) sup T D sup -1 (I-H psi L), where H and phi are given by known link geometric parameters, and L, psi and D are obtained recursively by a spatial discrete-step Kalman filter and by the corresponding Riccati equation associated with this filter. The factors (I+H phi L) and (I-H psi L) are lower triangular matrices which are inverses of each other, and D is a diagonal matrix. This factorization and inversion of the mass matrix leads to recursive algortihms for forward dynamics based on spatially recursive filtering and smoothing. The primary motivation for advancing the operator approach is to provide a better means to formulate, analyze and understand spatial recursions in multibody dynamics. This is achieved because the linear operator notation allows manipulation of the equations of motion using a very high-level analytical framework (a spatial operator algebra) that is easy to understand and use. Detailed lower-level recursive algorithms can readily be obtained for inspection from the expressions involving spatial operators. The report consists of two main sections. In Part 1, the problem of serial chain manipulators is analyzed and solved. Extensions to a closed-chain system formed by multiple manipulators moving a common task object are contained in Part 2. To retain ease of exposition in the report, only these two types of multibody systems are considered. However, the same methods can be easily applied to arbitrary multibody systems formed by a collection of joint-connected regid bodies.
FMD系统模型及其计算机仿真%Modeling and Simulation of FMD (Flexible Multibody Dynamics)
Institute of Scientific and Technical Information of China (English)
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
基于MBDyn的多体系统动力学可视化仿真软件%Visual simulation software for multibody system dynamics based on MBDyn
Institute of Scientific and Technical Information of China (English)
杨海根; 芮筱亭; 刘怡昕; 张建书; 何斌
2013-01-01
为实现一般多体系统动力学计算和结果的可视化仿真，在研究开源动力学代码MBDyn的基础上，设计并实现了多体系统可视化仿真软件( MBDynSimCenter)。采用虚拟原型的思想，集成了Open Cascade建模框架，实现了多体系统可视化建模前处理器。设计了MBDyn求解器计算接口模块，自动求解多体系统动力学问题。开发了曲线绘制及动画分析后处理器。用曲柄滑块机构的仿真算例，验证了软件的有效性和正确性。仿真结果表明该软件能够满足一般多体系统动力学可视化计算仿真的要求。%In order to realize the dynamics calculation of general multibody systems and the visual simulation of the results, a multibody system visual simulation software ( MBDynSimCenter ) is designed and implemented based on open source multibody dynamics analysis code MBDyn. Using the idea of virtual prototype,the Open Cascade modeling framework is integrated,and a preprocessor for multibody system visual modeling is realized. A calculation interface model of MBDyn solver is designed to solve multibody dynamics problems automatically. A powerful post-processor for curve drawing and animation analysis is developed. The crank-slider mechanism simulation example verifies the validity and accuracy of the software. Simulation results show that the software meets the requirements of the visual simulation of general multibody system dynamics.
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®.
Ledesma, Ragnar; Bayo, Eduardo
1993-08-01
A technique is presented for solving the inverse dynamics of flexible planar multibody systems. This technique yields the non-causal joint efforts (inverse dynamics) as well as the internal states (inverse kinematics) that produce a prescribed nominal trajectory of the end effector. A non-recursive Lagrangian approach is used in formulating the equations of motion as well as in solving the inverse dynamics equations. Contrary to the recursive method previously presented, the proposed method solves the inverse problem in a systematic and direct manner for both open-chain as well as closed-chain configurations. Numerical simulation shows that the proposed procedure provides an excellent tracking of the desired end effector trajectory.
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.
International Nuclear Information System (INIS)
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
International Nuclear Information System (INIS)
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
Nagata, Takashi; Modi, Vinod J.; Matsuo, Hiroki
2001-12-01
This paper describes a rather general numerical simulation code newly developed for studying dynamics and control of flexible multibody systems. It accounts for an arbitrary level of topological branching, character of the structural members, slewing, deployment, orbital perturbations, etc. The program is based on a recursive order n formulation whose details are given in Part I. Versatility and validity of the code are illustrated through parametric studies of several distinctively different systems. The dynamical analysis indicates that critical situations can lead to an undesirable system response. To establish specified performance, feasibility of a nonlinear control strategy based on the feedback linearization technique (FLT) in conjunction with the order n algorithm is explored. The FLT can control both the rigid and flexible degrees of freedom. The effectiveness of the control is assessed through numerical simulation.
Recuero, Antonio M.; Escalona, José L.
2014-01-01
In this work, we assessed the capabilities of a method that uses a multibody system description of railway vehicles based on a moving coordinate system in combination with moving modes of deformation to include track elastic displacements. Because this approach suppresses the influence of the boundary conditions of track models, track length ceases to be an issue for simulations. This existing procedure is briefly described and extended to a wide range of applications that require accounting for track frequency contents. A variety of phenomena long surveyed in the railway literature can thus be addressed. Several examples of a wheelset and a subway vehicle running on corrugated rails along varying-parameter tracks were simulated. Based on the results, the proposed method can efficiently capture the dynamic phenomena behind low-to-mid track frequency vehicle-track interactions, contact patch elasticity and vehicle dynamics.
Sandu, Corina; Andersen, Erik R.; Southward, Steve
2011-02-01
In this paper, we develop a multibody dynamics model of a quarter-car test-rig equipped with a McPherson strut suspension and we apply a system identification technique on it. Constrained equations of motion in the Lagrange multiplier form are derived and employed to characterise the dynamic behaviour of the test rig modelled once as a linear system and once as a non-linear system. The system of differential algebraic equations is integrated using a Hilber-Hughes-Taylor integrator. The responses of both models (linear and non-linear) to a given displacement input are obtained and compared with the experimental response recorded using the physical quarter-car test rig equipped with a McPherson strut suspension. The system identification is performed for control purposes. The results, as well as the performance and area of applicability of the test rig models derived, are discussed.
Comparison of Selected Formulations for Multibody System Dynamics with Redundant Constraints
Directory of Open Access Journals (Sweden)
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.
ADVANCES IN TRANSFER MATRIX METHOD FOR MULTIBODY SYSTEM DYNAMICS%多体系统传递矩阵法研究进展
Institute of Scientific and Technical Information of China (English)
芮筱亭; 戎保
2012-01-01
作为一种多体系统动力学新方法，多体系统传递矩阵法由于其无需系统总体动力学方程和快速计算的特点，已被广泛用于各种多管火箭、自行火炮、舰炮等复杂大型机械系统动力学分析与设计．本文介绍了该方法的研究进展，包括：线性多体系统传递矩阵法、多体系统离散时间传递矩阵法、二维系统传递矩阵法、受控多体系统传递矩阵法、多体系统传递矩阵法和通常动力学方法的混合方法等，给出了该方法解决自行火炮、多管火箭武器多体系统动力学的重大工程应用实例．%As a new method of multibody system dynamics, the transfer matrix method of multibody system has the following characteristics： without the global dynamics equation of system, low order of matrix involved, high efficiency. It has been widely used in the dynamic design of many complex mechanical systems, such as multiple launch rocket system, self-propelled artillery system, and warship gun system. In this paper, the advances in transfer matrix method of multibody system, including linear transfer matrix method of multibody system, discrete time transfer matrix method of multibody system, transfer matrix method of two-dimension system, transfer matrix method of controlled multibody system, and the mixed method of transfer matrix method of multibody system and ordinary dynamics methods, are presented. Some engineering applications of this method on self-propelled artillery system and multiple launch rocket system are also given.
International Nuclear Information System (INIS)
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
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...
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.
Application of stabilization techniques in the dynamic analysis of multibody systems
Directory of Open Access Journals (Sweden)
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.
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.
Nagata, Takashi; Modi, Vinod J.; Matsuo, Hiroki
2001-12-01
This paper presents a rather general recursive formulation of flexible multibody systems. It accounts for an arbitrary level of topological branching, character of the structural members, slewing, deployment, orbital perturbations, etc. By introducing the concept of equivalent disconnected system, it leads to an efficient order n algorithm. Validity and efficiency of the formulation are assessed through several numerical examples of flexible multibody systems, which show high accuracy in terms of system energy and angular momentum conservation. A simple and unified methodology for extending the formulation to systems in general topology is also given. A companion paper describes a numerical simulation code which has been developed based upon the formulation, and illustrates versatility of the approach through parametric studies of several particular systems.
Institute of Scientific and Technical Information of China (English)
SHEN Qing; LI Yue; CHEN Xu-jun
2003-01-01
Common effect of wave and slip of internal heavy load will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibodies System with a floating base is composed of ro-ro ship and slipping heavy load. This paper takes the rolling angle of the ship and the transverse displacement of the heavy load on desk as two freedoms. Making use of analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By use of dynamic method of multibodies system with a floating base, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the ship and displacement response of the slipping heavy load under common effect of synchro-slipping heavy loads and wave.
Shen, Qing; Li, Yue; Chen, Xu-Jun
2003-12-01
Common effect of wave and slip of internal heavy load will make rolling of the roll-on ship serious. This is one of the important reasons for overturn of ro-ro ships. The multibodies System with a floating base is composed of ro-ro ship and slipping heavy load. This paper takes the rolling angle of the ship and the transverse displacement of the heavy load on desk as two freedoms. Making use of analysis of apparent gravitation and apparent buoyancy, the wave rolling moment is derived. By use of dynamic method of multibodies system with a floating base, dynamic equations of the system are established. Taking a certain channel ferry as an example, a set of numerical calculation have been carried out for rolling response of the ship and displacement response of the slipping heavy load under common effect of synchro-slipping heavy loads and wave.
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.
Analysis for the Deployment of Single-Point Mooring Buoy System Based on Multi-Body Dynamics Method
Institute of Scientific and Technical Information of China (English)
CHANG Zong-yu; TANG Yuan-guang; LI Hua-jun; YANG Jian-ming; WANG Lei
2012-01-01
Deployment of buoy systems is one of the most important procedures for the operation of buoy system.In the present study,a single-point mooring buoy system which contains surface buoy,cable segments with components,anchor and so on is modeled by applying multi-body dynamics method.The motion equations are developed in discrete node description and fully Cartesian coordinates.Then numerical method is used to solve the ordinary differential equations and dynamics simulations are achieved while anchor is casting from board.The trajectories and velocities of different nodes without current and with current in buoy system are obtained.The transient tension force of each part of the cable is analyzed in the process of deployment.Numerical results indicate that the transient payload increases to a peak value when the anchor is touching the seabed and the maximum tension force will vary with different floating configuration.This work is helpful for design and deployment planning of buoy system.
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
Dynamics of multibody systems in space environment; Lagrangian vs. Eulerian approach
Santini, P.; Gasbarri, P.
2004-01-01
The paper describes the motion of a multibody in space environment: by space environment we mean space-varying gravity, gradient forces, control forces, if any. In the Eulerian approach, the motion of each individual member is described through kinematic parameters: (a) position of its CM with respect to the inertial frame; (b) rotation of the members with respect to the inertial frame; amplitude of the elastic modes (free-free). The said parameters are of different order of magnitudes, and therefore an adequate separation of them is highly desirable. Therefore, individual positions are replaced by overall position of the system (of the order of Earth's radius), and by the motion of each bar relative to it (of the order of members dimension), and for modes amplitudes modal equations are used.It should be noted, however, that the above-described motion parameters are redundant, and we must introduce: (a) reactions between members, (b) equations of compatibility of the same number of reactions.In summary, (i) the set of unknowns is: motion parameters, reactions, control forces; (ii) the equations are equilibrium, compatibility, control. Control is introduced by prescribing the motion of some members, produced by control moments of forces. By simple matrix algebra, it is reduced to a system with motion parameters (overall + local) only. In the Lagrangian approach, motion parameters are selected which are already consistent with compatibility conditions. In this case, as customarily, the expression of kinetic, potential, elastic energy is written, and the application of Lagrangian techniques provides directly the solving system. No reactions and compatibility equations appear here, however; for control purpose, prescribed motion law must again be introduced. Comparison of the two approaches shows perfect agreement (as one should have expected), since they are both exact models referring to the same physical system. In general, however, the Eulerian approach lends
Multibody dynamics model of highline cable%高架索的多体动力学模型
Institute of Scientific and Technical Information of China (English)
李楠; 韦灼彬; 何学军; 张世云; 任爱娣
2014-01-01
针对目前海上补给装备研制中尚无可用的高架索模型的现状，从多体动力学角度入手，研究了绳索多体系统动力学模型的建立方法，将绳索均匀划分为若干刚体单元，各单元之间采用球铰连接。用该方法建立了绳索的多刚体系统动力学模型，并在此基础上，应用仿真软件 ADAMS 对海上横向干货补给过程进行仿真计算。结果表明：海上补给高架索多刚体系统动力学模型完全可以模拟实际的高架索，且仿真计算结果与高架索力学振动模型的计算结果相比更贴近实际情况。%As for an overhead cable model for engineering practice,the ways to establish a multi-body system dynamics model of rope are studied.A rope is divided into a number of rigid units and two ad-jacent units are connected with a ball hinge so as to establish a multi-rigid dynamics model of rope. The model is used to simulate the alongside dry cargo replenishment at sea by means of the software ADAMS.The results show that the multi-rigid-body system dynamics model of highline can simulate the actual overhead cable and that the calculation results are closer to the actual situation than the re-sults of the overhead cable mechanical vibration model.
Energy Technology Data Exchange (ETDEWEB)
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.)
Dynamic distance direct ophthalmoscopy, a novel technique to assess accommodation in children
Directory of Open Access Journals (Sweden)
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.
A Modelling Approach to Multibody Dynamics of Fluid Power Machinery with Hydrodynamic Lubrication
DEFF Research Database (Denmark)
Johansen, Per; Rømer, Daniel; Andersen, Torben Ole;
2013-01-01
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...... mechanisms is necessary in order to accommodate this demand. At present fully coupled thermo-elastic models for various tribological interfaces has been presented. However, in order to analyse the interaction between tribological interfaces in fluid power pumps and motors, these interface models needs...
Linking rigid multibody systems via controllable thin fluid films
DEFF Research Database (Denmark)
Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
, this paper gives a theoretical contribution to the combined fields of fluid–structure interaction and vibration control. The methodology is applied to a reciprocating linear compressor, where the dynamics of the mechanical components are described with help of multibody dynamics. The crank is linked...... to the 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...... 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...
A Multibody Slosh Analysis for the Lunar Reconnaissance Orbiter
Shah, Neerav; Hsu, Oscar; Garrick, Joseph
2007-01-01
The Lunar Reconnaissance Orbiter (LRO) undergoes a series of thruster maneuvers to attain lunar orbit. The first of the series of lunar orbit insertion (LOI) maneuvers is crucial to the success of the mission. Therefore, it is important to characterize the disturbances acting on the spacecraft during this phase of the mission. This paper focuses on the internal disturbance force caused by fuel slosh and its impact on attitude control. During the first LOI maneuver (LOI-1), approximately 50% of the total fuel mass is used or roughly 25% of the spacecraft s wet mass, during the 38-minute burn. The forces imparted on the spacecraft from the fuel are dependent on the fill level of the two fuel tanks. During LOI-1, the fill level in both tanks varies greatly and thus so does the disturbance level caused by the fuel. It is therefore necessary to account for the time-varying mass properties of the spacecraft and the effects of the varying fuel levels during the entire 38-minute maneuver. Two simulations are developed in Mathworks s Simulink to analyze the fuel slosh effect. The first model, a baseline model, is a rigid body dynamics model where the fuel slosh is not modeled. The second is a multibody model, developed using a multibody dynamics toolbox, where each of the two fuel tanks and the remaining spacecraft body are treated as separate rigid bodies. The simulations are executed in a piece-wise fashion to account for the time-varying mass properties, and to accommodate the multibody toolbox. Disturbances caused by fuel slosh during both lunar and mission orbit insertions will be analyzed through simulation of different dynamics models. Results of the analysis will show the effects of the slosh disturbance on the spacecraft s attitude.
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
Institute of Scientific and Technical Information of China (English)
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.
An efficient approach to dynamics and control of flexible multibody systems
Modi, V. J.; Ng, A. C.; Suleman, A.
A relatively general formulation for studying the dynamics and control of an arbitrary spacecraft, with interconnected flexible, deployable and articulating structural members, is reviewed which accounts for thermal deflection, transient system properties, shift in the center of mass, shear deformations, rotary inertias and geometric nonlinearities. A rather self-contained, comprehensive, numerical algorithm using system as well as component modes follows which is applicable to a large class of spacecraft configurations of contemporary and future interests. Versatility of the general formulation has been assessed so far through its application to Japan's Space Flyer Unit (SFU); Canadian Mobile Servicing System (MSS); and the recently launched (August 1992) Indian communications satellite INSAT-2. Here the focus is on the dynamics and control studies aimed at the evolving Space Station Freedom.
Gain in computational efficiency by vectorization in the dynamic simulation of multi-body systems
Amirouche, F. M. L.; Shareef, N. H.
1991-01-01
An improved technique for the identification and extraction of the exact quantities associated with the degrees of freedom at the element as well as the flexible body level is presented. It is implemented in the dynamic equations of motions based on the recursive formulation of Kane et al. (1987) and presented in a matrix form, integrating the concepts of strain energy, the finite-element approach, modal analysis, and reduction of equations. This technique eliminates the CPU intensive matrix multiplication operations in the code's hot spots for the dynamic simulation of the interconnected rigid and flexible bodies. A study of a simple robot with flexible links is presented by comparing the execution times on a scalar machine and a vector-processor with and without vector options. Performance figures demonstrating the substantial gains achieved by the technique are plotted.
DYNAMIC ANALYSIS OF MULTIBODY SYSTEMS WITH PROBABILISTIC PARAMETERS%含随机参数的多体系统动力学分析
Institute of Scientific and Technical Information of China (English)
赵宽; 陈建军; 阎彬; 马洪波
2012-01-01
基于Lagrange方程建立了含随机参数的多体系统的动力学模型,利用广义坐标分离法将随机微分代数方程转化为随机纯微分方程,利用Newmark法进行数值解算.应用随机因子法求解系统随机响应的数字特征,获得统计意义下的解.以旋转杆滑块系统为例,考虑系统中载荷、物理和几何参数的随机性,通过与MonteCarlo法结果的对比验证了文中方法的正确性和有效性.计算结果表明,部分随机参数的分散性对多体系统动力响应的影响不可忽略,利用随机参数的动力学模型将能客观地反映出系统的动力学行为.%Dynamic analysis of multibody systems with probabilistic parameters was presented. Dynamic modeling of multibody systems was obtained by Lagrange＇s method. The probabilistic differential algebraic equations were transformed into pure probabilistic differential equations by generalized coordinate partitioning method. The Newmark step-by-step integration method was used to calculate the results. Using the method of random factor method, the numerical characteristics of the system response were derived, and the results were expressed in statistic view. As an illustrating example, dynamic modeling of a rotating bar and sliding block system considering the probabilistic of load, geometric and physical parameters was presented. Compared with the result of Monte-Carlo numerical simulation method, the accuracy and efficiency of the method are verified. The results illustrate that the probabilistic parameters affect the dynamic response of the multibody system and the dynamic modeling with probabilistic parameters can objectively reflect the dynamic behavior of the objective systems.
Spatial multibody modeling and vehicle dynamics analysis of advanced vehicle technologies
Letherwood, Michael D.; Gunter, David D.; Gorsich, David J.; Udvare, Thomas B.
2004-08-01
The US Army vision, announced in October of 1999, encompasses people, readiness, and transformation. The goal of the Army vision is to transition the entire Army into a force that is strategically responsive and dominant at every point of the spectrum of operations. The transformation component will be accomplished in three ways: the Objective Force, the Legacy (current) Force, and the Interim Force. The objective force is not platform driven, but rather the focus is on achieving capabilities that will operate as a "system of systems." As part of the Objective Force, the US Army plans to begin production of the Future Combat System (FCS) in FY08 and field the first unit by FY10 as currently defined in the FCS solicitation(1). As part of the FCS program, the Future Tactical Truck System (FTTS) encompasses all US Army tactical wheeled vehicles and its initial efforts will focus only on the heavy class. The National Automotive Center (NAC) is using modeling and simulation to demonstrate the feasibility and operational potential of advanced commercial and military technologies with application to new and existing tactical vehicles and to describe potential future vehicle capabilities. This document will present the results of computer-based, vehicle dynamics performance assessments of FTTS concepts with such features as hybrid power sources, active suspensions, skid steering, and in-hub electric drive motors. Fully three-dimensional FTTS models are being created using commercially available modeling and simulation methodologies such as ADAMS and DADS and limited vehicle dynamics validation studies are will be performed.
Dynamic analysis of multibody systems with mixed clearance%含混合间隙多体系统动力学分析
Institute of Scientific and Technical Information of China (English)
王铁成; 陈国平; 马方; 孙东阳
2016-01-01
研究了混合间隙对多体系统动力学特性的影响。首先建立了同时含旋转副间隙和移动副间隙的多体系统动力学模型，然后以曲柄滑块机构为研究对象，分析了混合间隙对该系统动力学特性的影响。结果表明，混合间隙对滑块速度的影响不明显，对滑块加速度和曲柄力矩的影响比单个间隙的影响更加剧烈。为工程中建立更精确的含间隙机械系统动力学模型提供了理论依据。%Here,the effects of mixed clearance on dynamic characteristics of a multibody system were studied. Firstly,the dynamical model of a multibody system including rotation clearance and translation clearance was established. Then,a slider-crank mechanism was used to analyze the effects of mixed clearance on the dynamic characteristics of the system.The results showed that the effects of mixed clearance on the slider velocity are not obvious,while its effects on the slider acceleration and the crank torque are much stronger than those of a single clearance be.The results laid a theoretical foundation for more accurate dynamic modeling of mechanical systems with clearance in engineering.
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
Analog-to-digital conversion to accommodate the dynamics of live music in hearing instruments.
Hockley, Neil S; Bahlmann, Frauke; Fulton, Bernadette
2012-09-01
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
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.
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
Institute of Scientific and Technical Information of China (English)
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 .
Institute of Scientific and Technical Information of China (English)
王琪; 庄方方; 郭易圆; 章杰; 房杰
2013-01-01
The numerical method for the non-smooth dynamics of multibody systems is one of the hot topics of researches on the dynamics of multibody systems. In this paper, recent advances in the research on numerical methods are presented for the non-smooth dynamics of multibody systems with impact and friction. First, the Coulomb friction model, modified Coulomb friction model and the characteristics of the normal forces of multibody systems with unilateral and bilateral constraints are discussed. Second, recently developed numerical methods for the non-smooth dynamics of multibody systems based on continuous and discontinuous models are reviewed. The Event-driven scheme and time-stepping method for the non-smooth dynamics of multibody systems are described in detail based on the complementarity concept. These numerical methods are then analysed and compared. Finally, the problems in need of further studies are pointed out.%非光滑多体系统动力学数值计算方法是多体系统动力学研究的重要内容之一.本文介绍了近年来含摩擦与碰撞的非光滑多体系统动力学数值算法方面的研究进展.首先,讨论了库仑摩擦模型和修正的库仑摩擦模型,以及具有单边和双边约束的多体系统中法向约束力的特点.其次,回顾了基于连续模型和非连续模型的多体系统动力学方程的数值计算方法,详细介绍了基于互补概念的非光滑多体系统动力学的事件驱动法和时间步进法,分析比较了相关的数值算法.最后,指出了一些需要进一步研究的问题.
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
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...
Institute of Scientific and Technical Information of China (English)
许立新; 李永刚
2013-01-01
In order to deeply reveal the relationship between the external impact effect of multibody system and the variation of the dynamic load of rolling bearing joint, a methodology for modeling of multibody systems with rolling bearing joints is presented based on the theories of multibody dynamics, Hertz contact and continuous contact force model. By using this method, an impact multibody system which consists of a slider-crank mechanism with a deep groove ball bearing and a target rigid body with elastic support was modeled and taken as an analytical example. The dynamic responses of this kind of complicated non-continuous dynamic system were discussed. The results show that the impact effects not only have an influence on dynamic performance of the multibody system, but also lead to drastic changes of the equivalent constraint forces and rolling element loads in bearing joint.%为能深入揭示多体系统外部碰撞作用与关节滚动轴承动态载荷变化规律之间的映射关系,基于多体动力学理论、Hertz接触理论及连续碰撞力模型,提出一种可描述含关节滚动轴承多体系统碰撞动力学行为的建模方法.基于该方法,以含深沟球轴承的曲柄滑块机构及具有弹性支撑的目标刚体组成的碰撞多体系统为分析对象,深入探讨该类复杂非连续动力学系统动态响应.研究表明,碰撞作用不仅对系统宏观动力学性态产生影响,同时导致关节滚动轴承运动副等效约束反力及轴承各滚动体载荷发生突变.
Institute of Scientific and Technical Information of China (English)
魏晓林
2015-01-01
多体—离散体动力学是爆破拆除科技理论发展的新阶段。研究描述了建筑物爆破拆除科技的发展历程，定义了建筑物倒塌动力学及包含的多体—离散体动力学，突出了与传统多体的不同特点，建立了动力学方程，列举出典型拆除动力学方程实例，求取其解析解和近似解，提出动力学方程的相似性及无量纲规整应用，实现了变拓扑多体—离散体动力学的全局仿真，阐明了与方程运算参数有关的破损材料力学和混凝土构件冲击动力学。应用多体动力学，可简便地将拆除模型导出各类建筑结构各种倒塌方式的切口尺寸、爆堆形态、后坐下坐、起爆次序和分段时差等无量纲表达，为高大建（构）筑物选择合理的倒塌方式、拆除措施和切口参数提供了完整理论和简单实用算法，实现了对爆破拆除的精确控制。%The multi-discrete body dynamics was new scientific idea in explosive demolition. The building explo-sive demolition was described. The dynamics behavior of building toppling down and multi-discrete body dynamics was defined. The dynamic characteristic was different from traditional multi-body system. The dynamic equations and the representative equations of demolition were erected and enumerated,finally the approximate solutions were put forward. The dynamic equations comparability and applications of complete dimensionless were given. The complete chessboard emulating of variable topological multi-discrete body dynamics were performed. The parameters of material mechanics and impact dynamics of concrete component concerning the equation computing were clarified. With the multi-body dynamics,the demolition model was simply educed such as the dimensionless expression of cutting size, shape of muck pile,back and down sitting,firing order and delay time of collapse types of different buildings. In order to choose reasonable collapse scheme
Institute of Scientific and Technical Information of China (English)
曹大志; 强洪夫; 任革学
2012-01-01
Parallel algorithms were developed for multibody dynamic systems to accelerate the speed of dynamic simulations of large complex flexible multibody systems. The main computational loads during the numerical solution of the differential algebraic equations (DAEs) were analyzed with OpenMP then used to compute the system tangent matrix and residual vector in parallel and with a parallel sparse linear equation solver, Pardiso, used for the linear equations. Both of the parallel strategies were implemented in an in-house multibody algorithm for parallel analyses of multibody dynamic systems. The parallel speedup and the computational efficiency of the algorithm are quite good so the simulation speeds of multibody dynamic analyses are increased substantially.%为加快大型、复杂柔性多体系统的动力学仿真的速度，对多体系统动力学的并行算法进行研究。首先分析了微分代数方程（differentialalgebraicequations，DAEs）在数值计算求解过程中主要的计算量。据此，提出采用OpenMP并行计算系统的刚度矩阵、右端项和采用并行的稀疏线性方程组求解器Pardiso对线性方程组进行求解的并行策略。将这两种并行策略应用到自主开发的柔性多体系统动力学软件THUS01ver中，实现了对多体系统动力学的并行计算。通过两个工程算例的仿真得到并行的加速比和计算效率，结果表明：采用的两种并行策略都有很高的计算效率，能大幅提高多体系统动力学仿真的速度。
斜齿行星传动多体动力学建模与分析%Multibody dynamic modeling and analysis for a helical planetary gear train
Institute of Scientific and Technical Information of China (English)
张俊; 刘先增
2014-01-01
A multibody dynamic model for a helical planetary gear train (HPGT)was proposed and the dynamic performance of the HPGT system was analyzed.Its free vibration characteristics,steady-state dynamic responses and the effects of design parameters on the system dynamic behavior were investigated with numerical simulations.The free vibration of the HGPT was classified into 3 categories according to modal properties,such as,eigenvalue multiplies, modal coordinates of central components and coordinate ratios of planets.The classified vibration modes were axial translational and torsional mode (AT mode ),radial translational and rotational mode (RR mode )and planet mode (P mode).The characteristics of each category were presented.The simulation results agreed well with those using the previous discretized model neglecting the component flexibilities to validate the correctness of the proposed multibody dynamic model.The steady-state dynamic responses indicated that the dynamic meshing forces fluctuate about the average static values and the time-varying meshing stiffness is the major excitation of the system.The parametric sensitivity analysis showed that the floating sun gear and the reduction of circumferential assembly error of planets are effective to suppress the vibration of the HGPT.%建立了斜齿行星传动的多体动力学模型，对其进行了动态特性仿真，获知了该类系统的自由振动特性、稳态动力响应以及部分设计参数对系统动态特性的影响规律。根据系统特征值的重根数、中心构件的振型坐标及各行星轮间振型坐标的比例，将斜齿行星轮系的自由振动归结为3类典型振动模式，即：轴向平移-扭转振动模式、径向平移-扭摆振动模式和行星轮振动模式，并进一步给出了各类模式的特点。当不考虑构件自身柔性时，基于多体动力学模型的自由振动特性与前人的集中参数模型的仿真结果完全一致，表明了本文
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...
Determination of the Accommodation Coefficient Using Vapor/gas Bubble Dynamics in an Acoustic Field
Gumerov, Nail A.; Hsiao, Chao-Tsung; Goumilevski, Alexei G.; Allen, Jeff (Technical Monitor)
2001-01-01
Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as in evaporation in a vacuum. The rate at which such a phase transformation occurs depends on the "condensation" or "accommodation" coefficient, Beta, which is a property of the interface. Existing measurement techniques for Beta are complex and expensive. The development of a relatively inexpensive and reliable technique for measurement of Beta for a wide range of substances and temperatures is of great practical importance. The dynamics of a bubble in an acoustic field strongly depends on the value of Beta. It is known that near the saturation temperature, small vapor bubbles grow under the action of an acoustic field due to "rectified heat transfer." This finding can be used as the basis for an effective measurement technique of Beta. We developed a theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave. A numerical code was developed which enables simulation of a variety of experimental situations and accurately takes into account slowly evolving temperature. A parametric study showed that the measurement of Beta can be made over a broad range of frequencies and bubble sizes. We found several interesting regimes and conditions which can be efficiently used for measurements of Beta. Measurements of Beta can be performed in both reduced and normal gravity environments.
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...
Simulation of Flexible Multibody Dynamics for Deep-Sea Lifting System%深海扬矿系统的柔性多体系统动力学仿真
Institute of Scientific and Technical Information of China (English)
陈宇翔; 阳宁; 金星
2014-01-01
In order to study dynamics of the lifting system in deep⁃sea mining, simulation of flexible multibody dynamics ( MFBD ) for the deep⁃sea lifting system was conducted. Based on dynamics theory of flexible multibody system, a modeling method was proposed for the flexible multibody in the deep⁃sea lifting system. The dynamic simulation of vibration of a beam under force compared with analytical solutions, verified the accuracy of this modeling method. Based on the laboratory simulation, a dynamic model was created for flexible multibody in deep⁃sea lifting system for studying dynamic simulation. It was found that the results of pipeline configuration and stress obtained from simulation tests were all in good accordance with the experimental results, indicating its reference for future research on dynamics of deep⁃sea lifting system.%为研究深海扬矿系统动力学特征，开展了扬矿系统柔性多体系统动力学仿真研究。基于柔性多体系统动力学理论，提出了深海扬矿管道柔性多体建模方法。对经典的梁受迫振动问题进行了动力学仿真并与解析解进行了对比，验证了方法的正确性。针对实验室模拟系统建立了深海扬矿系统柔性多体系统动力学模型并进行了动力学仿真研究，结果表明管道形态、应力等仿真结果与实验结果符合较好。本研究可为深海扬矿系统动力学研究提供参考和依据。
全井钻柱系统多体动力学模型%A multibody dynamical model of full-hole drillstring system
Institute of Scientific and Technical Information of China (English)
程载斌; 姜伟; 任革学; 周建良; 蒋世全; 杨蔡进; 何保生
2013-01-01
采用绝对节点坐标法建立了三维井眼全井钻柱系统多体动力学模型,将大长细比全井钻柱离散为绝对节点坐标梁单元,讨论了梁单元格式,并研究了井口、钻头处边界以及钻柱与井壁的接触/摩擦模型,给出了包含绝对节点坐标梁单元的钻柱系统运动方程.采用向后差分法求解微分-代数方程组,全面计算分析了全井钻柱系统的受力变形、摩阻扭矩、耦合振动、涡动、动力屈曲等力学特性,可在钻柱动力学研究和工程应用中发挥作用.%It is necessary for improving drilling efficiency and safety to investigate drillstring dynamics.A multibody dynamical model for 3D full-hole drillstring system was proposed based on the absolute nodal coordinate formulation (ANCF).The large fineness ratio of full-hole drillstring could be discretized into ANCF beam elements with the model and the format of beam elements was discussed.The absolute nodal coordinate formulation of beam elements and boundary conditions at wellhead and bit,as well as a contact/friction model between drillstring and wellbore were also investigated.A dynamic governing equation set for the full-hole drillstring system that contain ANCF was given and solved with the backward differentiation formulation (BDF) for differential algebraic equations (DAEs).The analysis of deformation,drag and torque,coupled vibration,whirling and dynamic buckling of the full-hole drillstring system was carried out,and the results showed that it can play an active role in drillstring dynamics researches and engineering applications.
Institute of Scientific and Technical Information of China (English)
洪嘉振; 刘铸永
2013-01-01
There is an increasing number of discontinuous dynamics problems,such as contact and impact,in the engineering field.The known modelling theories and methods,which are used to solve the continuous dynamics of flexible multibody systems,are not able to solve those problems or to solve those problems perfectly.In this paper,an appending constraint method was proposed to solve the contact/impact dynamics of flexible multibody system based on the idea of topology variable.The impact experiment of flexible bars was designed to verify the validity of the proposed method.At last,a multi-variable method was proposed to solve the multi-scale problems of time and space when the global simulation of the discontinuous dynamics of flexible multibody systems was carried out,and the computational efficiency of the global simulation of the discontinuous dynamics of flexible multibody systems was improved by using this method.%在实际工程领域中存在着大量接触碰撞等非连续动力学问题,现有的解决柔性多体系统连续动力学过程的建模理论与方法,已经无法解决或无法很好解决这些问题.本文基于变拓扑思想,提出了附加接触约束的柔性多体系统碰撞动力学建模理论；通过设计柔性圆柱杆接触碰撞实验,验证了所提出附加约束接触碰撞模型的有效性；针对柔性多体系统全局动力学仿真面临时间和空间的多尺度问题,提出多变量的离散方法,从而提高了柔性多体系统非连续动力学的仿真效率.
Dynamic modeling of a viscoelastic body in a multibody system%粘弹性体的多体系统动力学建模
Institute of Scientific and Technical Information of China (English)
曹大志; 赵治华; 任革学; 强洪夫
2012-01-01
The properties of viscoelastic materials described by the fractional derivative constitutive were analyzed using the isotropic hypothesis and the Grtinwald definition for the approximation of the fractional derivative. The dynamics equations of the multibody system including the fractional constitutive are derived based on the virtual work principle and the continuum mechanics theory. The total nonlinear finite element method is used to solve the motion equations, so large deformations and arbitrary rigid body movement of the flexible solid body can be accurately predicted. The implicit BDF （backwards differentiation formulation） time integration scheme is used with the Newton-Raphson algorithm to solve the equations of motion. Several numerical examples are presented to analyze the effects of the time step, the fractional order and the truncation number of the Griinwald series on the system＇s dynamic behavior. The results show that the integration step should not be too large for a multibody system with visoelatic dissipation and that thematerial damping increases with increasing fractional index and decreasing relaxation time. The truncated series should be reasonably selected to reflect the material＇s property and reduce the calculating time.%根据材料各向同性假设和分数阶导数的Grtinwald定义，分析和研究了三维分数阶导数本构方程描述的粘弹性体的特性。基于虚功原理和连续介质力学理论推导了含分数阶导数本构的粘弹性体的多体系统动力学方程。由于在推导过程中采用完全非线性有限元法，因此该动力学方程能准确描述多体系统中柔性体的大变形和任意的刚体运动。采用隐式的BDF（backwards differentiation formulation）积分格式和Newton-Raphson迭代算法对动力学方程进行求解。最后通过数值算例对比研究了数值积分步长、分数阶导数的指数与截断级数等参数对系统动力学行为的影
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.
多体系统的集中动载荷识别技术研究%Study on Identification of Concentrated Dynamic Load for Multibody System
Institute of Scientific and Technical Information of China (English)
李欣; 张方; 邓军; 陈国平
2012-01-01
采用考虑刚柔耦合的混合坐标系法和传统的运动弹性动力学（KED）方法,对由悬臂梁和旋转梁组成的简单多体系统进行正问题建模,求旋转梁在集中动载荷作用下的正响应。基于这两种不同的建模方法,在时域内,采用一维切比雪夫正交多项式拟合,推导出多体系统的动态标定矩阵,对作用于旋转梁上的载荷进行识别。通过一仿真算例,对基于不同正问题建模方法的识别结果进行对比,分析出刚柔耦合对识别结果的影响,以及正交多项式拟合法,对此非线性系统进行动态识别的局限性。并且,对于变速工况,给出了滤除驱动力矩影响的方法,识别结果得到改善。%In the paper, we describe the multibody system consist of cantilever beam and rotating beam base on two different methods. One is hybird coordinate method which takes the rigid-flexible coupled into account. The other is traditional Kineto-Elasto-Dynamic （KED） method. The dynamic calibration matrix is derive in time domain by in- troducing chebyshev polynominal to identify the concentrated dynamic load exerted on the rotating beam. The iden- tification results are compare base on different modeling methods through a simulation example. We can analyse the limitation of this identificaion way for nonlinear system and the effect of rigid-flexible coupling on the load identifi- cation caused by nonlinear factors. And we propose a new method to remove the response caused by driving moment to improve the identification accuracy.
Downer, Janice Diane
1990-01-01
The dynamic analysis of three dimensional elastic beams which experience large rotational and large deformational motions are examined. The beam motion is modeled using an inertial reference for the translational displacements and a body-fixed reference for the rotational quantities. Finite strain rod theories are then defined in conjunction with the beam kinematic description which accounts for the effects of stretching, bending, torsion, and transverse shear deformations. A convected coordinate representation of the Cauchy stress tensor and a conjugate strain definition is introduced to model the beam deformation. To treat the beam dynamics, a two-stage modification of the central difference algorithm is presented to integrate the translational coordinates and the angular velocity vector. The angular orientation is then obtained from the application of an implicit integration algorithm to the Euler parameter/angular velocity kinematical relation. The combined developments of the objective internal force computation with the dynamic solution procedures result in the computational preservation of total energy for undamped systems. The present methodology is also extended to model the dynamics of deployment/retrieval of the flexible members. A moving spatial grid corresponding to the configuration of a deployed rigid beam is employed as a reference for the dynamic variables. A transient integration scheme which accurately accounts for the deforming spatial grid is derived from a space-time finite element discretization of a Hamiltonian variational statement. The computational results of this general deforming finite element beam formulation are compared to reported results for a planar inverse-spaghetti problem.
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.
DAE-LCP MIXED METHOD FOR MULTIBODY SYSTEM DYNAMICS WITH FRICTIONAL CONTACTS%多体系统摩擦接触问题的DAE-LCP方法
Institute of Scientific and Technical Information of China (English)
富立; 岳凤桐
2011-01-01
当多体系统的约束全部是摩擦接触时,其动力学问题可归结为一个常微分方程(ordinary differential equation,ODE)与线性互补问题(linear complementarity problem,LCP)的混合动力学问题.如果除了摩擦接触之外还增加了光滑的双边约束,则需要将ODE-LCP混合动力学模型推广为微分代数方程(differential algebra equation,DAE)与LCP的混合动力学模型.该文采用DAE与LCP混合动力学方法求解不考虑碰撞但同时含有持续摩擦接触及光滑等式约束的多体系统动力学问题.在建立系统动力学模型时,首先将含摩擦的约束从系统中移去得到基本动力学系统.由于基本系统中带有等式约束,所以基本系统的动力学方程为一组DAE.结合基本系统的DAE与约束的互补条件便可以得到DAE-LCP混合动力学模型.数值计算采用基于DAE与LCP的步进(time-stepping)算法,将系统动力学方程及其约束离散化并转化为一个混合LCP进行求解.该算法无需进行滞-滑状态检测,避免了事件检测导致的繁复计算.利用所提方法对典型机构的非光滑非线性特征进行了数值分析,验证了该文方法的正确有效性.%Presently, dynamics of nonsmooth multibody systems is a hot research topic. The usual approach in treating such systems is to derive basic system from the original system by removing the nonsmooth constraints firstly. The Lagrange equations of the second kind of basic system combine with the complementarity condition of the nonsmooth constraints to set up at each discrete moment in time a Linear Complementarity Problem (LCP).This article focuses on the problem of dynamic modeling and numerical simulating of multibody systems with friction contacts. By neglecting the clearance and the effect of impact between rigid bodies and constraints,the state variables in the differential equations are continuous. Due to the set-value mapping characteristic of dry friction forces, the
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...
Institute of Scientific and Technical Information of China (English)
王良明
2001-01-01
The concepts of generalized multibody systems and velocity transform matrix and a new form of acceleration transform are presented in the paper. Based on the Lagrange multiplier method, a new method for dynamic analysis of complicated systems is developed, that is, the velocity transform matrix synthesis method for generalized multibody systems. The resulting dynamic equations do not include the Lagrange multipliers and constraint forces. With the aid of the dynamic matrixes of each uncoupled generalized body and the velocity transform matrix for a generalized multibody system, the dynamic equations of the coupled system are obtained by matrix operations. The method is computer-oriented and easy to be coded. An example is provided to illustrate the proposed method.%文中提出了广义多体系统和速度变换矩阵的概念，提出了一种新的加速度变换关系，以带不定乘子的拉格朗日方程为基础推导得到了求解复杂系统动力学问题的一种新方法，即广义多体系统的速度变换矩阵综合法。利用该方法，可根据无耦合广义体的动力学参数和系统的速度变换矩阵直接获得广义多体系统的动力学方程，其中不含拉格朗日不定乘子和约束反力，且方程中逆矩阵求解的维数等于系统的自由度数，因而有利于提高计算效率。该方法主要面向计算机实现程式化的算法，系统的动力方程可以由计算机自动完成运算，从而避免了繁琐的解析推导工作。
Institute of Scientific and Technical Information of China (English)
丁洁玉; 潘振宽
2013-01-01
An efficient and stable numerical method of differential-algebraic equations (DAEs) is one of the key problems in multi-body dynamics. For index 3 DAEs with a general mass matrix, a generalized-a-S method is presented after the deep study of implicit time-stepping methods introduced into multi-body dynamics. Based on the projection method of constraints, the generalized-a-S projection method is developed, which can keep the total energy of the system, the displacement constraints, as well as the velocity and acceleration constraints in higher degree of accuracy. With a longer time step, the method shows good stability to obtain higher computation efficiency.%高效、稳定的微分-代数方程数值求解方法是多体系统动力学领域的关键问题之一.该文针对多体系统动力学指标3微分-代数方程,对目前多体系统动力学中引入的隐式时域逐步积分方法进行了深入研究,提出了适用于一般质量矩阵的广义-α-S法,并结合约束投影方法,构造了广义-α-S投影法.该方法既能较好地保持系统总能量,又能较高程度地同时满足位移约束、速度级约束和加速度级约束,并且在步长较大时可稳定求解,计算效率较高.
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.
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...
Active vibration control of spatial flexible multibody systems
Energy Technology Data Exchange (ETDEWEB)
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.
Flexible Multibody Systems Models Using Composite Materials Components
International Nuclear Information System (INIS)
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
Flexible Multibody Systems Models Using Composite Materials Components
Energy Technology Data Exchange (ETDEWEB)
Neto, Maria Augusta [Faculdade de Ciencia e Tecnologia da Universidade de Coimbra (Polo II), Departamento de Engenharia Mecanica (Portugal); Ambr' osio, Jorge A. C. [Instituto Superior Tecnico, Instituto de Engenharia Mecanica (Portugal)], E-mail: jorge@dem.ist.utl.pt; Leal, Rog' erio Pereira [Faculdade de Ciencia e Tecnologia da Universidade de Coimbra (Polo II), Departamento de Engenharia Mecanica (Portugal)
2004-12-15
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.
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.
Nonlinear formulation for flexible multibody system with large deformation
Institute of Scientific and Technical Information of China (English)
Jinyang Liu; Jiazhen Hong
2007-01-01
In this paper,nonlinear modeling forflexible multibody system with large deformation isinvestigated.Absolute nodal coordinates are employedto describe the displacement,and variational motionequations of a flexible body are derived on the basisof the geometric nonlinear theory,in which both theshear strain and the transverse normal strain are takeninto account.By separating the inner and the bound-ary nodal coordinates,the motion equations of a flexi-ble multibody system are assembled.The advantage ofsuch formulation is that the constraint equations and theforward recursive equations become linear because theabsolute nodal coordinates are used.A spatial doublependulum connected to the ground with a spherical jointis simulated to investigate the dynamic performance offlexible beams with large deformation.Finally,the resul-tant constant total energy validates the present formu-lation.
Rigid elements and their application in dynamics of multibody systems%刚体单元及其在多体系统动力学中的应用
Institute of Scientific and Technical Information of China (English)
齐朝晖; 方慧青
2011-01-01
In many multi-body software based on the traditional theories of dynamics of multibody systems,parameters such as the mass,the center of mass and the moments of inertia of a body usually have to be given artificially,which results in many difficulties in practice applications,because these parameters are not easy to obtain especially when bodies are complicated in shape.This paper presented a methodology enables to overcome these difficulties.The main idea is to divide a body into many pieces with regular shape called rigid elements.Two kinds of element,the rigid beam element and the rigid tetrahedron element are constructed in this paper,with the consideration of their ability to represent any solid body.Based on the new methodology,a software with mesh generator was developed,which can obtain the inertia parameters of bodies with any shape automatically.The correctness of present rigid elements was verified by numerical examples.%多体系统动力学分析软件要求人工输入形状复杂物体的质量、质心位置和转动惯量,而实际上这些参量并不容易获得。本文探索了一种以组成物体的刚体单元为基本要素的新方法,并结合实际需要具体构造了刚性四面体和刚性梁单元。以刚体单元为基础并内嵌网格剖分模块的分析软件能够自动获得这些参数,从而具备处理任何复杂系统的能力。仿真结果的对比分析验证了单元构造的正确性。
DEFF Research Database (Denmark)
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...... of ordinary diffferential equations is employed to avoid the instabilities associated with the direct integrations of differential-algebraic equations. To extend the unconditional stability of the implicit Newmark method to nonlinear dynamic systems, a discrete energy balance is enforced. This constraint...... the kinmatics of the system, and a choice of time integrations algorithms. The current approach uses a non-dissipative implict Newmark method to integrate the equations of motion defined in terms of the independent joint coordinates of the system. The reduction of the equations of motion to a minimal set...
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.
多体系统动力学Kane方法的改进%AN IMPROVED KANE＇S METHOD FOR MULTIBODY DYNAMICS
Institute of Scientific and Technical Information of China (English)
胡权; 贾英宏; 徐世杰
2011-01-01
基于Kane方法，针对约束多体系统，建立了一种新型的自动组集系统动力学方程的方法．首先提出偏速度矩阵和偏角速度矩阵的概念，将各体对系统广义惯性力的贡献用简洁、统一的数学形式表达．然后引入各个运动学变量的递推关系以提高建模效率．最后对新型的Kane方程进行扩展，用于处理多体系统中的运动约束．该算法适用于任意多体系统，建立的动力学模型不含待定乘子，维数与系统广义速率相同，利于控制系统设计．对带有闭环约束的空间多机械臂系统的数值仿真验证了方法的正确性．%This paper presents an improved Kane＇s method for automatically generating the equations of motion of arbitrary multibody systems. The notions of partial velocity matrix and partial angular velocity matrix are introduced. Each body＇s contribution to the system＇s generalized inertial force is expressed in a similar manner, which makes it amenable to computer solutions. All the kinematic quantities＇ recursive relations are developed to improve the modeling efficiency. The motion constraints are handled by the new form of Kane＇s equation. The final mathematical model is of the same dimensions with the generalized speeds and involves no Lagrange multipliers; therefore, it＇s useful for control system design. The simulation of a space platform with two manipulators is compared between the proposed method and recursive algorithm. The results validate the algorithm＇s accuracy.
含分数阻尼特性元件的多体系统动力学研究%DYNAMICS RESEARCH ON THE MULTIBODY SYSTEM WITH FRACTIONAL-DERIVATIVE-DAMPER
Institute of Scientific and Technical Information of China (English)
田强; 张云清; 陈立平; 覃刚
2009-01-01
Based on the absolute nodal coordinate (ANC) framework, the dynamics modeling and solution strategy for the multibody system with fractional derivative damper is investigated. The flexible parts are discretized by the ANC-based locking-free shear deformable beam element. The system equations of motion with constant mass matrix are also obtained and solved by the numerical dissipation controllable generalized-a method. The effects of the algorithm parameter and the fractional index on the dynamics responses are also studied by solving the numerical examples. The presented procedures can also be used to solve many other practical engineering problems.%在绝对节点坐标体系下研究了具有分数导数阻尼特性元件的多体系统动力学建模、求解问题.采用基于绝对节点坐标的无闭锁效应剪变梁单元离散柔性构件,建立了含常数质量矩阵的系统动力学方程,并采用数值耗散可控的广义α方法求解.通过数值算例计算,对比研究了算法参数与阻尼项的分数指数对系统动力学响应的影响规律.该方法可以进一步扩展到众多工程实际问题研究中.
Institute of Scientific and Technical Information of China (English)
TANG Hua-ping; PENG Ya-qing
2005-01-01
A kind of active vibration control method was presented through optimal design of driving load of multi-body system with quick startup and brake. Dynamical equation of multi-body system with quick startup and brake was built, and mathematical model of representing vibration control was also set up according to the moving process from startup to brake. Then optimization vibration control model of system driving load was founded by applying theory of optimization control, which takes rigid body moving variable of braking moment as the known condition, and vibration control equation of multi-body system with quick startup and brake was converted into boundary value problem of differential equation. The transient control algorithm of vibration was put forward, which is the analysis basis for the further research. Theoretical analysis and calculation of numerical examples show that the optimal design method for the multi-body system driving load can decrease the vibration of system with duplication.
DEFF Research Database (Denmark)
Hansen, Michael R.; Hansen, John Michael
1998-01-01
A point contact joint has been developed and implemented in a joint coordinate based planar multibody dynamics analysis program that also supports revolute and translational joints. Further, a segment library for the definition of the contours of the point contact joints has been integrated...... in the 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...
Institute of Scientific and Technical Information of China (English)
Shihui Fu; Qi Wang
2006-01-01
Using the properties of chaos synchronization. the method for estimating the largest Lyapunov exponent in a multibody system with dry friction is presented in this paper. The Lagrange equations with multipliers of the systems are given in matrix form. which is adequate for numerical calculation. The approach for calculating the generalized velocity and acceleration of the slider is given to determine slipping or sticking of the slider in the systems. For slip-slip and stick-slip multibody systems, their largest Lyapunov exponents are calculated to characterize their dynamics.
Planning and executing motions for multibody systems in free-fall. Ph.D. Thesis
Cameron, Jonathan M.
1991-01-01
The purpose of this research is to develop an end-to-end system that can be applied to a multibody system in free-fall to analyze its possible motions, save those motions in a database, and design a controller that can execute those motions. A goal is for the process to be highly automated and involve little human intervention. Ideally, the output of the system would be data and algorithms that could be put in ROM to control the multibody system in free-fall. The research applies to more than just robots in space. It applies to any multibody system in free-fall. Mathematical techniques from nonlinear control theory were used to study the nature of the system dynamics and its possible motions. Optimization techniques were applied to plan motions. Image compression techniques were proposed to compress the precomputed motion data for storage. A linearized controller was derived to control the system while it executes preplanned trajectories.
大变形复合材料薄板多体系统动力学建模%Dynamic modeling of composite thin-plate multibody systems with large deformation
Institute of Scientific and Technical Information of China (English)
张炜华; 刘锦阳
2016-01-01
Dynamic modeling theory of composite thin-plate multibody systems with large deformation was investigated.Based on Kirchhoff's assumption that the normal vector is always perpendicular to the central surface,the relation among in-plane strains,curvatures,absolute nodal coordinates and absolute gradients were derived according to the definition of Green strain,and the generalized elastic-force vector and its differentiation with respect to the generalized coordinates were derived.Equations of motion of the composite thin-plate multibody systems with large deformation were derived based on absolute nodal-coordinate formulation.Generalized method and the Newton-Raphson method were used to solve the differential-algebraic equations.Simulation of a composite thin plate applied with an external force was conducted.Comparison of the present simulation results with those obtained by ANSYS software verifies the accuracy and effectiveness of the formulation.Finally,the proposed formulation is used for numerical simulation of composite solar-array deployment mechanisms.The vibration characteristics of the driving force and constraint forces are analyzed in case of different panel layers.%对大变形复合材料薄板的多体系统动力学建模方法进行研究。基于 Kirchhoff 假设，法线与中面保持垂直，从格林应变的表达式出发，建立了面内应变和曲率与绝对位置坐标和斜率的关系，在此基础上推导了广义弹性力阵和弹性力阵对广义坐标的导数阵，用绝对节点坐标方法建立了大变形复合材料薄板多体系统的动力学方程，用广义α法和和牛顿迭代法求解微分－代数混合方程。对外载荷作用下的复合材料薄板进行数值仿真，通过与 ANSYS 的仿真结果进行对比，验证了该建模方法的准确性和快速收敛性。最后，将建模方法应用于复合材料太阳帆板展开机构的数值仿真，分析了不同铺层情况下驱动力和约束力的振动特性。
Institute of Scientific and Technical Information of China (English)
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.
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
NUMERICAL METHOD OF MULTIBODY DYNAMICS BASED ON θ1 METHOD%基于θ1方法的多体动力学数值算法研究
Institute of Scientific and Technical Information of China (English)
马秀腾; 翟彦博; 罗书强
2011-01-01
In the numerical integration of ordinary differential equations （ODEs） in structural dynamics community, θ1 method has characteristics of controlled numerical dissipation and second-order accuracy for systems with or without physical damping. Based on these characteristics, θ1 method is extended to the numerical integration of motion equations in multibody system dynamics. The solved motion equations are index-3 differential-algebraic equations （DAEs） and index-2 over-determined DAEs （ODAEs）. Numerical experiments validate the θ1 method, experiments also show the relationship of numerical dissipation with parameter 01. As for the integration of index-3 DAEs by θ1 method, it has violation of velocity constraint, while for index-2 ODAEs, there are no violation of position and velocity constraint in the view of computer precision. In addition, experiments illustrate that, for non-conservative system motion equations in the form of index-3 DAEs and index-20DAEs, θ1 method has second-order accuracy. In the end, θ1 methods for motion equations are compared with other direct-time integrations from the CPU time point of view.%将结构动力学领域的θ1方法拓展到数值求解多体系统运动方程——微分-代数方程（DAEs），分别求解指标-3DAEs形式的运动方程和指标-2超定DAEs（ODAEs）形式的运动方程．通过数值算例验证了方法的有效性，并得到θ方法中参数θ的选取与数值耗散量之间的关系．数值算例还说明对于同一个多体系统，采用指标-3的DAEs描述时存在速度违约，用指标-2的ODAEs描述时，从计算机精度上讲，位置和速度约束方程同时满足，并且θ方法在求解非保守系统DAEs和ODAEs形式的运动方程时都具有2阶精度．最后θ方法与其仙盲播积分法求解DAEs和ODAEs形式话动方程的CPI时间进行了比较。
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...
基于弹塑性接触的柔性多体系统碰撞动力学%Flexible Multibody System Impact Dynamics Based on Elastic-plastic Contact
Institute of Scientific and Technical Information of China (English)
段玥晨; 章定国
2012-01-01
To study the impact dynamics of the radially rotating flexible beam and the fixed rigid mass,based on the rigid-flexible coupling dynamic theory of the flexible multibody system,the rigid-flexible coupling dynamic equations with the impact force are established by using the assumed mode method and Lagrange equations. These equations contain the nonlinear coupling deformation item and the impact force potential energy, and can deal with the global dynamics of the impact system and no impact system. The impact process is divided into three stages of the elastic loading, the plastic loading and the elastic unloading by the uniaxial compression elastic-plastic contact model,and the describing method of the impact process and the contact judging condition are given. The dynamic characteristics including the impact force, the deformation and the angular displacement of the impact process are described by an impact dynamic simulation example. The comparation of the elastic-plastic model and the spring-damper model show that the impact forces of the two models are different due to the different descriptions on the impact stages and the impact energy loss, and the elastic-plastic contact model is more practical and applicable.%为了研究作大范围回转运动的柔性梁与固定刚性质量发生正碰撞的动力学问题,该文以柔性多体系统刚柔耦合动力学理论为基础,考虑非线性耦合变形项和碰撞力势能概念,利用假设模态法和Lagrange方程建立了含碰撞力的系统刚柔耦合动力学方程.该方程可以处理系统无碰撞和有碰撞的全局动力学问题.基于单轴压缩弹塑性接触模型将接触碰撞过程分为弹性加载、塑性加载和弹性卸载3个阶段,给出了描述碰撞过程的方法和接触判定条件.碰撞动力学仿真算例描述了碰撞过程中的碰撞力、变形、角位移等动力学特性.弹塑性接触模型与非线性弹簧阻尼模型的仿真结果对比发现,两种接
Institute of Scientific and Technical Information of China (English)
谢州凯; 王秋成; 刘卫国; 宁晓斌
2012-01-01
汽车与行人碰撞是我国道路交通事故的主要类型之一,该类事故在所有事故中致死率最高且与人们的安全出行密切相关,受到民众的广泛关注.然而传统的事故分析方法在此类事故的处理上存在较大困难.文章以多体动力学理论为基础,以PC-CRASH为平台,建立了多刚体数字化行人模型,通过设定代表身体各部分的属性(外形、质量、刚度、摩擦系数等)来定义行人特征.并将模型与国外某实车碰撞试验对比验证其可靠性.通过对仿真结果的回归分析得出了车速-抛距模型,为该类交通事故处理提供了数据参考.%Vehicle-pedestrian collision is a major type traffic accident in China. Because of its high fatality rate and closely related with people's travelling, people pay close attention to this type of accident. However, it is difficult to handle such kind of accident with common use "accident analyzing method". Based on multi-body dynamic theory, the paper built a numerical multi-rigid-body pedestrian model as a platform for PC-CRASH to simulate the collision between vehicle and pedestrian. Through setting rigid-body characters of different parts of the pedestrian (appearance , mass, rigid, friction factor) , the characters of pedestrian can be defined. The model was validated by comparing with a real car collision experiment abroad. The speed throwing distance was obtained through the regression analysis of simulation results. It provides numerical reference for such vehicle-pedestrian traffic accident. [Ch,5 fig. 3 tab. 13 ref.
Institute of Scientific and Technical Information of China (English)
张丰豪; 何榕
2014-01-01
The horizontal axis wind turbine has a tendency of being larger and more flexible, which results in the linear dynamic models based on small deflection assumption inappropriate. The coupled vibration of flexible blades and tower become more important in large wind turbine. Hence, it is necessary to analyze the stability of wind turbine using a global model. Based on the theory of flexible multi-body dynamics, a global structural dynamic model of wind turbine was developed using the rigid finite element method. The model could be used in both small and large deflection situations and could be used to analyze the vibration of wind turbine in different cases. Results of the model were compared with other programs, and it was approved that our model was more accurate than other models based on modal method. Natural frequencies of wind turbine were studied under the coupled and uncoupled vibration conditions of blades and tower. Results show that some higher natural frequencies of blades and tower in the whole system have changed and there are some new frequencies created in coupled vibration. The results mean that it is not reliable to analyze the wind turbine vibration using the natural frequencies of the separate tower or blades. The global model should be used for the large wind turbine.%水平轴风力发电机大型化、柔性化的发展趋势使得基于小变形假设的线性分析方法不再合理。大型风力机柔性叶片和塔架的耦合振动加剧，需采用整机模型对其进行分析。基于柔性多体动力学理论，采用刚体有限元方法建立了风力发电机的整机结构动力学模型，该模型不受几何变形量大小限制，能够对风力机在各种情况下的整机振动进行分析。模型结果与其他程序进行了对比，证实该文模型的精度比模态方法更高。研究了叶片和塔架在耦合与非耦合状态下整机的固有振动频率，结果表明：在整机状态下塔架和叶片的部
Accommodation in mild traumatic brain injury
Directory of Open Access Journals (Sweden)
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.
Active vibration control of multibody system with quick startup and brake based on active damping
Institute of Scientific and Technical Information of China (English)
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.
Research on Modal Parameters Identification of Parallel Manipulator with Flexible Multi-Body System
Directory of Open Access Journals (Sweden)
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.
KEY TECHNIQUES OF MULTI-BODY MODELING OF OCCUPANT RESTRAINT SYSTEM OF VEHICLE SIDE IMPACT
Institute of Scientific and Technical Information of China (English)
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.
Engine Multi-Body with Flexible Crankshaft Modeling and Numerical Simulation
Institute of Scientific and Technical Information of China (English)
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.
Nonlinear Multibody Dynamics of Wind Turbines
DEFF Research Database (Denmark)
Holm-Jørgensen, Kristian
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 neces......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...... each substructure e.g. a part of the blade is modelled by use of Bernoulli-Euler beam elements with St. Venant torsion. For each substructure a belonging moving frame is present, where to the displacements of the substructure must be relative small, in order for the linear displacement assumption...... to define the motion of the moving frames are regularly updated so the relative motion of the substructure from the belonging moving frame is reduced. The update algorithm of these parameters is based on the motion of the belonging beam element substructure. Based on a number of static analyses for a wind...
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.
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
Institute of Scientific and Technical Information of China (English)
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.
Accommodating Translational Research
Giles, Howard
2008-01-01
This is an article in a series illustrating the way scholars in communication have pursued translating their research into practice. The translational nature of communication accommodation theory and examples of its application are the focus of this contribution.
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
Directory of Open Access Journals (Sweden)
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.
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)...
Institute of Scientific and Technical Information of China (English)
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。
Intraocular lens with accommodation capacity
Dorronsoro, Carlos; Alejandre, Nicolás; Bekesi, Nandor; Marcos, Susana
2014-01-01
Intraocular lens with accommodation capacity comprising a first optical member (1) having a dynamic optical power, to which a second optical member (2) with a fixed optical power is affixed, in such a manner that at least a central part of each of one of one of the curved surfaces (2a, 2b) of the second optical member (2) and of at least one of the surfaces (1a, 1b) of the first optical member (1) are in contact with each other, the second optical member (2) and the first optical member (1) p...
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…
Reduced accommodation in children with cerebral palsy.
Leat, S J
1996-09-01
Accommodation in 43 subjects with cerebral palsy was measured objectively using a dynamic retinoscopy technique, which has already been shown to be reliable and repeatable. The subject's ages ranged from 3 to 35 years. Of these, 42% were found to have an accommodative response pattern which was different from the normal control group for his/her age. Nearly 29% had an estimated amplitude of accommodation of 4 D or less. The presence of reduced accommodation was found to be associated with reduced visual acuity, but was not associated with cognitive or communication ability, refractive error or age. The prevalence of other ocular disorders in this group is also high. These findings have developmental and educational implications.
ROBOTRAN: a powerful symbolic gnerator of multibody models
Directory of Open Access Journals (Sweden)
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
Accommodating Different Learning Styles
DEFF Research Database (Denmark)
Ovesen, Nis
2014-01-01
of 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....
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In the first five months, retail sales of the accommodation and catering sector reached 412.77 billion yuan, contributing 13.6 percent to total retail sales of consumer goods, said the Ministry of Commerce. Their year-on-year growth of 15 percent, or 53.78 billion yuan, was 1.78 percentage points higher than the overall increase of retail sales of consumer goods.
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.
Model updating in flexible-link multibody systems
Belotti, R.; Caneva, G.; Palomba, I.; Richiedei, D.; Trevisani, A.
2016-09-01
The dynamic response of flexible-link multibody systems (FLMSs) can be predicted through nonlinear models based on finite elements, to describe the coupling between rigid- body and elastic behaviour. Their accuracy should be as high as possible to synthesize controllers and observers. Model updating based on experimental measurements is hence necessary. By taking advantage of the experimental modal analysis, this work proposes a model updating procedure for FLMSs and applies it experimentally to a planar robot. Indeed, several peculiarities of the model of FLMS should be carefully tackled. On the one hand, nonlinear models of a FLMS should be linearized about static equilibrium configurations. On the other, the experimental mode shapes should be corrected to be consistent with the elastic displacements represented in the model, which are defined with respect to a fictitious moving reference (the equivalent rigid link system). Then, since rotational degrees of freedom are also represented in the model, interpolation of the experimental data should be performed to match the model displacement vector. Model updating has been finally cast as an optimization problem in the presence of bounds on the feasible values, by also adopting methods to improve the numerical conditioning and to compute meaningful updated inertial and elastic parameters.
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...
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...
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.
Directory of Open Access Journals (Sweden)
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
Optimal Disturbance Accommodation with Limited Model Information
Farokhi, F; Johansson, K H
2011-01-01
The design of optimal dynamic disturbance-accommodation controller with limited model information is considered. We adapt the family of limited model information control design strategies, defined earlier by the authors, to handle dynamic-controllers. This family of limited model information design strategies construct subcontrollers distributively by accessing only local plant model information. The closed-loop performance of the dynamic-controllers that they can produce are studied using a performance metric called the competitive ratio which is the worst case ratio of the cost a control design strategy to the cost of the optimal control design with full model information.
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
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
Multiphysics modelling of multibody systems: application to car semi-active suspensions
Docquier, N.; Poncelet, A.; Delannoy, M.; Fisette, P.
2010-12-01
The goal of the present article is to analyse the performances of a modern vehicle equipped with a novel suspension system linking front, rear, right and left cylinders via a semi-active hydraulic circuit, developed by the Tenneco Automotive company. In addition to improving the vehicle's vertical performances (in terms of comfort), both the stiff roll motion of the carbody and the soft wrap motion of the rear/front wheel-axle units can be obtained and tuned via eight electrovalves. The proposed system avoids the use of classical anti-roll bars, which would be incompatible with the wrap performance. A major problem of the project is to produce a realistic and efficient 3D multibody dynamic model of an Audi A6 coupled, at the equational level, with an hydraulic model of the suspension including cylinders, accumulators, valve characteristics, oil compressibility and pipe dynamics. As regards the hydraulic submodel, a particular attention is paid to assemble resistive components properly without resorting to the use of artificial volumes, as proposed by some software dealing with the dynamics of hydraulic systems. According to Tenneco Automotive requirements, this model must be produced in a Matlab/Simulink form, in particular for control purposes. Thanks to the symbolic approach underlying our multibody program; a unified hybrid model can be obtained as a unique plant dynamic block to be real-time integrated in the Simulink environment on a standard computer. Simulation results highlight the advantages of this new suspension system, in particular regarding the behaviour of the car which can remain stiff in roll for curve negotiation, while maintaining a soft wrap behaviour on uneven surfaces.
多柔体系统动力学模型的特征值降阶方法%Eigenvalue Reduced-order Method for Dynamic Model of Flexible Multibody System
Institute of Scientific and Technical Information of China (English)
管红根; 冯金富; 何永; 高树滋
2001-01-01
This paper expounds the problem on eigenvalue reduced-order forflexible umltibody system model, and derives the eigenvalue modal reduced-order oriterion and calculation steps based on Riccati iteration algorithm in accordance with attitude dynamics of flexible spacecraft system.Analysis results indicate that it can reflect better the basic characteristics of the original system than usually eigenvalue truncation criterion and exactly preserve the lower frequencies and mode shapes of the original system.Dynamic response curves of reduced-order model accord better with original system.%详细研究了多柔体系统动力学模型的特征值降阶问题，针对挠性空间飞行器系统的姿态动力学方程，推导出基于Riccati迭代算法的特征值模态截断准则和计算步骤。分析结果表明，它较一般特征值截断准则更能精确地反映原系统特性，并且能准确地保留原系统低阶模态频率和振型。其模态截断后动力响应曲线与原系统吻合较好。
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
浮基多体系统在静水中展开过程的运动响应%Dynamics of multibody system with floating base expanded on water surface
Institute of Scientific and Technical Information of China (English)
袁辉; 陈徐均; 江召兵; 赵红亮
2012-01-01
To investigate the mechanical behaviours of the assembled compound periphery structure under dynamic loads, their scale models were loaded in the nuclear explosion pressure simulation hole. There were two types of scale models with different joint styles. Results of the four test models were presented. The shape of shock wave and the strain histories on the surfaces of steel plate (counterfort column) or concrete are obtained, which agrees with the one-way thick plate theory analysis results. Dynamical characteristics and failure modes of different test models were observed and analysed. It is validated that both the steel plate joints and the counterfort column joints are feasible under the designed shock wave load. It is also proved that the steel plate joints are more ductile than the counterfort column joints as well as better dynamic performance subjected to blast wave.%为模拟浮基多体系统上部结构在展开时的顺序与快慢对浮基运动响应的影响,介绍了建立在齐次矩阵方法基础上的浮基多体系统运动时域求解方法,并对一个由4刚体组成的浮基多体系统进行了建模和数值计算,模拟了上部机构以一定规律依次展开或同时展开时系统的运动响应,得到了浮基在各工况下横摇、横荡和垂荡的时间历程曲线.数值模拟结果表明:对于这2种展开形式,浮基的横荡几乎不随展开时间和形式变化,影响比较明显的是垂荡和横摇.总的来说,该浮基多体系统同时展开的方式要优于依次展开的方式.
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 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.
MULTIBODY DYNAMIC ANALYSIS AND SIMULATION OF ENGINE MODEL
Directory of Open Access Journals (Sweden)
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?
System Reduction in Nonlinear Multibody Dynamics of Wind Turbines
DEFF Research Database (Denmark)
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 eigenmodes...
Accommodating Law Faculty with Disabilities.
Tucker, Bonnie Poitras; Smith, Joseph F., Jr.
1996-01-01
The obligations of law schools, under federal law, to accommodate faculty with disabilities are examined. Employment provisions of the 1990 Americans with Disabilities Act and the Rehabilitation Act of 1973 and the definition of a disabled individual are reviewed, and real and hypothetical scenarios in hiring and employing law teachers are…
Reasonable Accommodation in Training Safety.
Sandoz, Jeff
A pictograph and icon-driven training program has been specifically designed for educators who are responsible for teaching the developmentally disabled regarding the safe use of hazardous chemicals. In alignment with the Americans with Disabilities Act, it offers "reasonable accommodation" by those who educate and train this special population in…
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.
Institute of Scientific and Technical Information of China (English)
刘同众; 朱林; 程曦; 彭双双; 戚银银; 秦义先; 尹成龙; 章文峰; 朱德泉
2015-01-01
In order to better understand the effects of triple-jump movement on jumpers,impact behaviors of left knee joint of a healthy man athlete were studied.Based on CT and MRI scanning pictures of the jumper’s knee joint,a three-dimensional model was built,including complete femur,tibia,fibular,patellar,cartilages and main ligaments of the knee joint.Then,a method combining finite element analysis (FEA)and multi-body dynamic analysis (MDA)was used to simulate a real human triple-jump.Finally,the loading data,such as,muscle force and joint reaction obtained from an MDA were impulted into a finite element model to compute stress,strain and displacement variations of the knee joint under impact conditions.The numerical simulation results showed that the stress,stain and the displacement of medical cartilage are larger than those of lateral cartilage;the contact force and contact areas increase with increase in load,consequently,this can incur severer wear contours of the knee joint and badly injure the jumper.The computation results matched reasonably the research results in the published literatures.The results demonstrated the importance of performing MDA as a preliminary step to FEA in biomechanical fields,and the proposed method had a potential to generate a better understanding of injury mechanisms of jumpers.%为了研究三级跳训练、竞赛对运动员膝关节冲击损伤影响程度，以1名健康男性运动员左膝关节为研究对象，利用膝部 CT 扫描和磁共振（MRI）相结合的方法，建立了包括股骨、胫骨、腓骨、髌骨以及膝部各主要软骨、韧带在内完整的三维膝关节立体模型；采用多体动力学（MDA）与有限元分析（FEA）相结合的方法，计算出三级跳起跑、跳跃、落地全过程运动员膝关节处冲击状态下的应力、应变及位移变化状况。计算显示：在三级跳运动过程中，膝关节胫骨外侧接触区域受到的载荷，
Acri, Antonio; Offner, Guenter; Nijman, Eugene; Rejlek, Jan
2016-10-01
Noise legislations and the increasing customer demands determine the Noise Vibration and Harshness (NVH) development of modern commercial vehicles. In order to meet the stringent legislative requirements for the vehicle noise emission, exact knowledge of all vehicle noise sources and their acoustic behavior is required. Transfer path analysis (TPA) is a fairly well established technique for estimating and ranking individual low-frequency noise or vibration contributions via the different transmission paths. Transmission paths from different sources to target points of interest and their contributions can be analyzed by applying TPA. This technique is applied on test measurements, which can only be available on prototypes, at the end of the designing process. In order to overcome the limits of TPA, a numerical transfer path analysis methodology based on the substructuring of a multibody system is proposed in this paper. Being based on numerical simulation, this methodology can be performed starting from the first steps of the designing process. The main target of the proposed methodology is to get information of noise sources contributions of a dynamic system considering the possibility to have multiple forces contemporary acting on the system. The contributions of these forces are investigated with particular focus on distribute or moving forces. In this paper, the mathematical basics of the proposed methodology and its advantages in comparison with TPA will be discussed. Then, a dynamic system is investigated with a combination of two methods. Being based on the dynamic substructuring (DS) of the investigated model, the methodology proposed requires the evaluation of the contact forces at interfaces, which are computed with a flexible multi-body dynamic (FMBD) simulation. Then, the structure-borne noise paths are computed with the wave based method (WBM). As an example application a 4-cylinder engine is investigated and the proposed methodology is applied on the
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.
Institute of Scientific and Technical Information of China (English)
熊瑛; 万修华; 余翔; 薛丽霞; 李靖; 李树宁; 卿国平; 凌宁; 王宁利
2011-01-01
Objective To investigate the dynamic characteristics of ocular wavefront aberrations and discuss the relationship between aberrations and pupil size, as well as the relationships between aberrations and accommodation under simulated physiological conditions. Design Prospective comperative study. Participants Normal eyes (21 cases) and the simulated eye. Methods The condition of ocular accommodation was controlled by the moving visual target when the value of the wavefront aberrations was collected by Hart-mann-Shark aberrometry. The simulated eye was used as the control. Main Outcome Measures The root mean square of total wave- front aberration (t-RMS) and high-order aberration (h-RMS) from normal eyes and the simulated eye and their coefficient of variance. Results In normal eye, the mean t-RMS was 0.46±0.18μm; the mean h-RMS was 0.27±0.14μm, the coefficient of variance was 40.37% and 36.34%, respectively. As a control, the mean t-RMS and coefficient of variance of the simulated eye' s was 0.39±0.00μm and 0.47% respectively. The h-RMS of normal eyes was correlated with pupil sizes and accommodation. The regression equation could be expressed as: h-RMS= 0.111 x pupil diameter (mm) -0.015 x dioptre (D) - 0.313(P<0.001 ,R2=0.458). Conclusion The ocular wavefront aberrations could change significantly under physiological conditions. The pupil size is the main factor.%目的 模拟生理调节状态下随着眼调节和瞳孔直径的变化人眼高阶像差的波动特点.设计 前瞻性比较性研究.研究对象 21例正常人眼与模拟眼.方法 通过控制视路上移动视标的位置诱发人眼调节,在调节过程中,不人为控制瞳孔直径,使其处于自然收缩舒张状态,实时用哈特曼波前传感器(Hartman-Shark)采集人眼波前像差.模拟眼作为对照.主要指标 人眼与模拟眼的总波前像差的均方根(t-RMS)和高阶像差的均方根(h-RMS)及其变异系数.结果 生理调节状态下,人眼的t-RMS为(0.46±0
A Study on the Dynamic Analysis of A Tracked Vehicle for Ocean Mining on the Deep Seabed
Institute of Scientific and Technical Information of China (English)
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.
Mutual Orbits of Transneptunian Multibody Systems
Grundy, William
2014-08-01
We propose to use LGS AO with NIRC2 during stellar appulses to measure relative astrometry of the large sample of transneptunian binaries for which mutual orbits remain unknown. Our long-term goal is to determine as many of their orbits as possible. These orbits provide a crucial constraint on dynamical conditions in outer parts of the protoplanetary nebula, as well as subsequent outer solar system history. They provide system masses and thus bulk densities, as well as enabling constraint of tidal dissipation parameters, scheduling of mutual event seasons, and revealing possible unresolved n>2 systems.
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...
Institute of Scientific and Technical Information of China (English)
王琪; 陆启韶
2001-01-01
The Lagrange's method is one of the general methods to derive thedynamic equations for multibody systems, which are in the form ofordinary differential equations or differential-algebraic equations.Numerical analysisis an important way to investigate the behaviors of the dynamicsof multibody systems. In this paper, the firstkind and the second kind of Lagrange's equations and the modifiedLagrange's equations for multibody systems with their canonical formsare introduced, together with the characteristics of their numericalsolutions. The advances are reviewed in the followingnumerical methods, symplectic algorithms and the implicit algorithms forthe dynamic equations of multibody systems, as well as other algorithmsfor dynamic behaviors of multibody systems, such asPoincar'e maps and Lyapunov exponents.%Lagrange方法是建立多体系统动力学方程的普遍方法之一,其方程的形式为常微分方程组或微分 - 代数方程组,数值计算与数值分析是研究多体系统动力学特性的重要方法.本文简要介绍了多体系统动力学方程的第一、二类Lagrange方程和修正的Lagrange方程的基本形式及这些方程的正则形式,着重介绍了正则方程在数值计算中的特点,就多体系统Lagrange方程的隐式算法、辛算法和多体系统动力学特性的数值分析方法(包括数值仿真、Poincar'e映射和Lyapunov指数的计算方法)的研究现状进行了综述.
ACCOMMODATION PREFERENCES OF FOREIGN TOURISTS IN ROMANIA
Directory of Open Access Journals (Sweden)
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.
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 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)...
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...
Effect of oculomotor rehabilitation on accommodative responsivity in mild traumatic brain injury
Directory of Open Access Journals (Sweden)
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.
On the Formulation of Flexible Multibody Systems with Constant Mass Matrix
DEFF Research Database (Denmark)
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...... of this formulation is that neither thecentrifugal nor the Coriolis forces appear in theequations due to the description of the flexible body....
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
Directory of Open Access Journals (Sweden)
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.
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.
Study of the railway vehicle suspension using the multibody method
Directory of Open Access Journals (Sweden)
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.
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...
Extra Time as an Accommodation
Directory of Open Access Journals (Sweden)
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 ...
DEFF Research Database (Denmark)
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...
Decentralized Disturbance Accommodation with Limited Plant Model Information
Farokhi, F; Johansson, K H
2011-01-01
The design of optimal disturbance accommodation and servomechanism controllers with limited plant model information is considered in this paper. Their closed-loop performance are compared using a performance metric called competitive ratio which is the worst-case ratio of the cost of a given control design strategy to the cost of the optimal control design with full model information. It was recently shown that when it comes to designing optimal centralized or partially structured decentralized state-feedback controllers with limited model information, the best control design strategy in terms of competitive ratio is a static one. This is true even though the optimal structured decentralized state-feedback controller with full model information is dynamic. In this paper, we show that, in contrast, the best limited model information control design strategy for the disturbance accommodation problem gives a dynamic controller. We find an explicit minimizer of the competitive ratio and we show that it is undomina...
FATIGUE LIFE EVALUATION OF SUSPENSION KNUCKLE USING MULTIBODY SIMULATION TECHNIQUE
Directory of Open Access Journals (Sweden)
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.
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....
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.
BRANDING ORIENTATION IN THE ACCOMMODATION INDUSTRY
Directory of Open Access Journals (Sweden)
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.
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.
Accommodation response for integral photography still images
Yano, Sumio; Park, Min-Chul
2015-05-01
In this paper the accommodation responses for integral photography still images were measured. The experimental results showed that the accommodation responses for integral photography images showed a linear change with images showing the depth position of integral photography, even if the integral photography images were located out of the depth of the field. Furthermore, the discrimination of depth perception, which relates to a blur effect in integral photography images, was subjectively evaluated for the examination of its influence on the accommodation response. As a result, the range of the discrimination of depth perception was narrow in comparison to the range of the rectilinear accommodation response. However, these results were consistent according to the propensity of statistical significance for the discrimination of depth perception in the out range of subjectively effective discriminations.
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.
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...
Institute of Scientific and Technical Information of China (English)
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.
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.
A non-linear two-node superelement for use in flexible multibody systems
Boer, S.E.; Aarts, R.G.K.M.; Meijaard, J.P.; Brouwer, D.M.; Jonker, J.B.
2014-01-01
A nonlinear two-node superelement is proposed for the modeling of flexible complex-shaped links for use in multibody simulations. Assuming that the elastic deformations with respect to a corotational reference frame remain small, substructuring methods may be used to obtain reduced mass and stiffnes
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.
The Influence of Rotor Unbalance on Turbocharger Rotor Dynamics
Directory of Open Access Journals (Sweden)
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.
Dynamics Modeling of Heavy Special Driving Simulator
Institute of Scientific and Technical Information of China (English)
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.
Complex treatment of accommodation disturbances in students
Directory of Open Access Journals (Sweden)
O. G. Pozdeeva
2013-01-01
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.
Complex treatment of accommodation disturbances in students
Directory of Open Access Journals (Sweden)
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.
Directory of Open Access Journals (Sweden)
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.
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...
Accommodating Faculty Members Who Have Disabilities. Report
American Association of University Professors, 2012
2012-01-01
In recent years the rights and responsibilities of students who have disabilities have received considerable attention. Professors routinely accommodate students with a front-row seat in class or extended time on an examination. Faculty members who have disabilities have received far less attention. This report from a subcommittee of Committee A…
22 CFR 142.12 - Reasonable accommodation.
2010-04-01
..., acquisition or modification of equipment or devices, the provision of readers or interpreters, and other... facilities, and size of budget; (2) Job restructuring, part-time or modified work schedules, acquisition and... sign language, when appropriate. (3) The nature and cost of the accommodation needed. (d) A...
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.
Robot response behaviors to accommodate hearing problems
Vroon, Jered; Kim, Jaebok; Koster, Raphaël
2015-01-01
One requirement that arises for a social (semi-autonomous telepresence) robot aimed at conversations with the elderly, is to accommodate hearing problems. In this paper we compare two approaches to this requirement; (1) moving closer, mimicking the leaning behavior commonly observed in elderly with
Is accommodation colorblind? Focusing chromatic contours.
Wolfe, J M; Owens, D A
1981-01-01
Two adjacent regions define an edge if they differ in either color or luminance. If the difference is purely chromatic, the edge is said to be isoluminant. Isoluminant contours are often perceptually unstable. Perhaps some of this instability could be explained if isoluminant contours were difficult to bring into focus. To test this hypothesis, a vernier optometer was used to measure the accuracy of steady-state accommodation for the vertical boundary of a red-green bipartite field. This edge was presented at optical distances of 0, 1.5, 3.0, and 4.5 diopters, with brightness contrasts between the two hemifields of 0% (isoluminant), 15%, 58%, and 100%. Accommodation was essentially unresponsiveness to the isoluminant edge and exhibited increasing focusing accuracy with increased brightness contrast. Control experiments replicated this finding for red-orange, green-blue, and white-white fields. These results imply that luminance contrast is a necessary stimulus for monocular accommodation. Inappropriate accommodation may be a factor contributing to the perceptual instability of isoluminant patterns. PMID:7255083
Institute of Scientific and Technical Information of China (English)
江召兵; 杜乃娟; 陈徐均; 洪娟
2011-01-01
浮基多体系统在波浪中展开过程的顺序与快慢对系统的运动响应和连接处的力矩有较大影响.介绍了建立在齐次矩阵方法基础上的浮基多体系统时域运动求解,并对一具体浮基系统进行了建模和数值模拟,分析了上部机构以一定规律快速展开和慢速展开时系统的运动响应.结果表明,把齐次矩阵方法引入浮基多体系统的求解领域,其符号推导方便,运动学和动力学方程表达式变得相当简洁,而且编制程序也相对简便快捷.在相同波浪周期的情况下,多体系统的最大横摇角响应与波高正相关；在相同波高情况下,长周期的最大横摇响应要比短周期小；相对于波周期,波高对系统横摇响应的影响要大的多.%The dynamics and the joint torque of the floating-base multibody system on wave greatly influence the expanding sequence and speed of upper parts. The homogeneous matrix method is introduced to solve the dynamics of floating-base multibody system at time domain. The result shows that by use of the method, the symbolic derivation becomes convenient, the expressions of kinematics and dynamics of the multibody system are succinct and the coding for computational simulation becomes simple and convenient. A four-body floating-base system is modeled and simulated using this method. And the dynamic responses are analyzed when the upper parts are expanded with fast or slow angular velocity according to a certain rule. The maximum rolling angle of floating-base is directly correlative with the wave height under the same wave period, the maximum polling angle of floating-base excited by wave with long period is smaller than that excited by wave with short period under the same wave height, and the dynamic response of floating-base multibody system is more affected by wave height compared with wave period.
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...
Directory of Open Access Journals (Sweden)
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
Concurrent multibody and Finite Element analysis of the lower-limb during amputee running.
Rigney, Stacey M; Simmons, Anne; Kark, Lauren
2015-01-01
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.
Institute of Scientific and Technical Information of China (English)
Hai-Ping Gao; Qi Wang; Shi-Min Wang; Li Fu
2011-01-01
The Lagrange-I equations and measure differential equations for multibody systems with unilateral and bilateral constraints are constructed. For bilateral constraints,frictional forces and their impulses contain the products of the filled-in relay function induced by Coulomb friction and the absolute values of normal constraint reactions. With the time-stepping impulse-velocity scheme,the measure differential equations are discretized. The equations of horizontal linear complementarity problems(HLCPs),which are used to compute the impulses,are constructed by decomposing the absolute function and the filled-in relay function. These HLCP equations degenerate into equations of LCPs for frictional unilateral constraints,or HLCPs for frictional bilateral constraints. Finally,a numerical simulation for multibody systems with both unilateral and bilateral constraints is presented.
A Large-Scale Multibody Manipulator Soft Sensor Model and Experiment Validation
Directory of Open Access Journals (Sweden)
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.
An exact nonlinear hybrid-coordinate formulation for flexible multibody systems
Institute of Scientific and Technical Information of China (English)
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.
DEFF Research Database (Denmark)
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...
Dynamic deployment analysis of a mesh antenna reflector
Groeger, B.
1991-10-01
Dynamic deployment analyses were performed on a reflector unfurlable mesh antenna using the multibody dynamic program DADS under three conditions: 0 g condition, 1 g condition with gravity compensation, and damage case under 0 g condition. Special restart techniques are applied to prevent excessive long computation times.
Modeling and simulation of wear in revolute clearance joints in multibody systems
Flores, Paulo
2009-01-01
The main goal of this work is to develop a methodology for studying and quantifying the wear phenomenon in revolute clearance joints. In the process, a simple model for a revolute joint in the framework of multibody systems formulation is presented. The evaluation of the contact forces developed is based on a continuous contact force model that accounts for the geometrical and materials properties of the colliding bodies. The friction effects due to the contact in the joints are also represen...
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).
Institute of Scientific and Technical Information of China (English)
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.
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...
Dynamic Analysis of Offshore Oil Pipe Installation Using the Absolute Nodal Coordinate Formulation
DEFF Research Database (Denmark)
Nielsen, Jimmy D; Madsen, Søren B; Hyldahl, Per Christian;
2013-01-01
centrifugal and Coriolis forces [12]. This makes the method attractive for multibody dynamics implementation. The focus in this paper is the application of ANCF beam elements and their performance on large deformation dynamic analysis. Large dynamic deformation is characteristic for the installation process...
Moving beyond misperceptions: the provision of workplace accommodations.
Hernandez, Brigida; McDonald, Katherine; Lepera, Nicole; Shahna, Monna; Wang, T Arthur; Levy, Joel M
2009-01-01
This mixed-methods study examined the provision of workplace accommodations in the health care, hospitality, and retail sectors. First, focus groups with administrators from each sector revealed that accommodations costs were viewed as minimal (although frontline managers were perceived as having misperceptions). Second, the provision of accommodations as documented through human resources records for health care and hospitality indicated that accommodations were infrequent, not costly, and provided to employees with disabilities. Finally, retail employees (irrespective of disability status) reported many more accommodations than health care and hospitality workers. To dispel misperceptions related to accommodations, education is critical and social workers are well-positioned for this role.
Directory of Open Access Journals (Sweden)
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
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.
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
THE IMPACTS OF PRIVATE ACCOMMODATION ATTRIBUTES ON TOURISM DEMAND
Portolan, Ana
2013-01-01
The private tourism accommodation concept has not been largely represented in the scientific research. It started appearing on the margins of the actual research in the past ten years, namely with a hotel as the most analyzed form of tourism accommodation. In the structure of tourism accommodation in Croatia in 2011 private accommodation participated with 465 000 beds which represents 49,8 percent of the total capacity and therefore demands more attention. Using the main marketing postulate w...
Directory of Open Access Journals (Sweden)
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
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.
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.
Multibody Model for Planetary Gearbox of 500 kW Wind Turbine
DEFF Research Database (Denmark)
Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær
The aim of the work is to simulate the loadings in a planetary gearbox of a wind turbine using a multibody program. A realistic wind turbine gearbox of a 500 kW wind turbine is examined using turbulent inflow data. An aeroelastic model of the wind turbine has been set up using the FLEX5-code...... the gearbox fatigue loads, the effect of wind turbulence on the power production/output torque on the highspeed shaft and for calibration and verification of the gearbox model....
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.
Near-unity mass accommodation coefficient of organic molecules of varying structure.
Julin, Jan; Winkler, Paul M; Donahue, Neil M; Wagner, Paul E; Riipinen, Ilona
2014-10-21
Atmospheric aerosol particles have a significant effect on global climate, air quality, and consequently human health. Condensation of organic vapors is a key process in the growth of nanometer-sized particles to climate relevant sizes. This growth is very sensitive to the mass accommodation coefficient α, a quantity describing the vapor uptake ability of the particles, but knowledge on α of atmospheric organics is lacking. In this work, we have determined α for four organic molecules with diverse structural properties: adipic acid, succinic acid, naphthalene, and nonane. The coefficients are studied using molecular dynamics simulations, complemented with expansion chamber measurements. Our results are consistent with α = 1 (indicating nearly perfect accommodation), regardless of the molecular structural properties, the phase state of the bulk condensed phase, or surface curvature. The results highlight the need for experimental techniques capable of resolving the internal structure of nanoparticles to better constrain the accommodation of atmospheric organics.
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.
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.
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.
Simulation of Moving Loads in Elastic Multibody Systems With Parametric Model Reduction Techniques
Directory of Open Access Journals (Sweden)
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.
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.
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...
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...
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...
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 ...
Can Partial Structures Accommodate Inconsistent Science?
Directory of Open Access Journals (Sweden)
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.
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...
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
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.
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.
On the modeling of the intervertebral joint in multibody models for the spine
Energy Technology Data Exchange (ETDEWEB)
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.
A multi-body vehicle for moving inside cluttered nuclear environment
International Nuclear Information System (INIS)
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
Application of Runge-Kutta-Rosenbrock Methods to the Analysis of Flexible Multibody Systems
International Nuclear Information System (INIS)
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
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...
A dynamic model with substructures for contact-impact analysis of flexible multibody systems
Institute of Scientific and Technical Information of China (English)
GUO; Anping(郭安萍); HONG; Jiazhen(洪嘉振); YANG; Hui(杨辉)
2003-01-01
Using a substructure synthesis method this paper studies the longitudinal compressive impact of a flexible bar with a rigid body. The crucial variable affecting the validity of the method is derived theoretically. By computational simulation tests, excellent agreement has been found between the solution of this model and the exact solution when the variable is chosen suitably. Considering both the computational efficiency and the accuracy of solutions obtained on the model in different engineering problems, several optimum values of the variable are suggested.
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
Real-time multibody system dynamic simulation. II - A parallel algorithm and numerical results
Energy Technology Data Exchange (ETDEWEB)
Tsai, Fuh-Feng; Haug, E.J. (Iowa, University, Iowa City (United States))
1991-06-01
In designing a parallel algorithm, an essential requirement is to distribute tasks evenly among all processors. The velocity state recursive Newton-Euler formulation, however, has embedded recurrence relations that must be executed in forward and backward computational path sequences. Here, an algorithm is developed which reduces the critical path time by extracting some operations from the forward and backward computational paths and distributing them evenly among the processors. Numerical examples are presented to show that real-time simulation can be achieved for moderately complex mechanical systems using a shared memory multiprocessor. 6 refs.
Constraint and Dynamic Analysis of Compliant Mechanisms with a Flexible Multibody Modelling Approach
Aarts, R.G.K.M.; Gattringer, H.; Gerstmayr, J.
2013-01-01
The models used in the conceptual phase of the mechatronic design should not be too complicated, yet they should capture the dominant system behaviour. Firstly, the awareness and possibly the avoidance of an overconstrained condition is important. Secondly, the models should reveal the system’s natu
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...
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,…
The Evolution of the Number of Tourists accommodated in Arad
Directory of Open Access Journals (Sweden)
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.
Semicommunication and Accommodation: Observations from the Linguistic Situation in Scandinavia.
Braunmuller, Kurt
2002-01-01
Focuses on semicommunication and accommodation and discusses two longer extracts from a large corpus of authentic communication from Scandinavia. Various aspects of a comprehensive model of semicommunication are presented and discussed, showing code switching and accommodation are not considered antagonistic but rather as scalar phenomena covering…
Privately Provided Accommodation Service Quality and Customer Satisfaction
Directory of Open Access Journals (Sweden)
Joshua Mugambwa
2016-04-01
Full Text Available Privately provided accommodation is a growing service in Uganda’s higher education sector due to education liberalization and demand for education. This research took a case study of Nsamizi Training Institute of Social Development (NTISD to determine the relationship between privately provided accommodation service quality and customer satisfaction. Specifically, the objectives of the study were (a to find out the relationship between security and NTISD students’ satisfaction with privately provided accommodation, and (b to find out the hierarchical level of importance of NTISD student satisfaction of the three service quality dimensions (reliability, security, and tangibles with privately provided accommodation. Using quantitative and qualitative modes of data analysis and a sample of 300 students from 20 private hostels, this study established a strong positive significant relationship between security and satisfaction regarding privately provided accommodation. This implies that accommodation service providers should increase the quality of security so as to increase the satisfaction of students regarding privately provided accommodation. The study established the hierarchical order of importance from the most important service quality dimension, respectively, as follows: reliability, security, and tangibles. Therefore, private accommodation service managers should pay extra attention to the dimensions in the same order.
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
Kundin, J.; Raabe, D.; Emmerich, H.
2011-10-01
If alloys undergo an incoherent martensitic transformation, then plastic accommodation and relaxation accompany the transformation. To capture these mechanisms we develop an improved 3D microelastic-plastic phase-field model. It is based on the classical concepts of phase-field modeling of microelastic problems (Chen, L.Q., Wang Y., Khachaturyan, A.G., 1992. Philos. Mag. Lett. 65, 15-23). In addition to these it takes into account the incoherent formation of accommodation dislocations in the austenitic matrix, as well as their inheritance into the martensitic plates based on the crystallography of the martensitic transformation. We apply this new phase-field approach to the butterfly-type martensitic transformation in a Fe-30 wt%Ni alloy in direct comparison to recent experimental data (Sato, H., Zaefferer, S., 2009. Acta Mater. 57, 1931-1937). It is shown that the therein proposed mechanisms of plastic accommodation during the transformation can indeed explain the experimentally observed morphology of the martensitic plates as well as the orientation between martensitic plates and the austenitic matrix. The developed phase-field model constitutes a general simulations approach for different kinds of phase transformation phenomena that inherently include dislocation based accommodation processes. The approach does not only predict the final equilibrium topology, misfit, size, crystallography, and aspect ratio of martensite-austenite ensembles resulting from a transformation, but it also resolves the associated dislocation dynamics and the distribution, and the size of the crystals itself.
Feasibility of Applying Controllable Lubrication to Dynamically Loaded Journal Bearings
DEFF Research Database (Denmark)
Estupinan, Edgar Alberto; Santos, Ilmar
2009-01-01
A multibody dynamic model of the main mechanical components of a hermetic reciprocating compressor is presented in this work. Considering that some of the mechanical elements are interconnected via thin fluid films, the multibody dynamic model is coupled to the equations from the dynamics...... of the fluid films, based on fluid film theory. For a dynamically loaded journal bearing, the fluid film pressure distribution can be computed by numerically solving the Reynolds equation, by means of finite-difference method. Particularly, in this study the main focus is on the lubrication behavior...... and reaction forces in a reciprocating compressor have a cyclic behavior, periodic oil pressure injection rules based on the instantaneous crank angle and load bearing condition can be established. In this paper, several bearing configurations working under different oil pressure injection rules conditions...
Directory of Open Access Journals (Sweden)
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.
Directory of Open Access Journals (Sweden)
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.
Research on Rigid - elastic Model of Gear in Multibody Systems%刚—弹耦合齿轮多体动力学模型研究
Institute of Scientific and Technical Information of China (English)
黄祝庆; 刘雷
2012-01-01
Based on ADAMS, the rigid - elastic model of gear is built and the relevant parameters of this model are discussed. By fitting the data which are calculated using Ishikawa gears stiffness formulae, the rotary stiffness calculation formula in the model is obtained. Based on the ADAMS secondary development technology, the corresponding gear module is developed to simplify the modeling process. A simulation experiment is used to testify the advancement of rigid - elastic model of gear, which indicates that more accurate results can be obtained in multibody dynamics analysis using the rigid - elastic model of gear.%基于ADAMS建立了刚—弹耦合齿轮多体动力学模型,并论述了相关参数的选取方法.对基于石川公式的相关计算数据进行拟合,得到了模型中转动刚度的计算公式.利用ADAMS二次开发技术,开发了相应的齿轮模块,解决了模型建模过程过于繁杂的问题.通过实例仿真验证了刚—弹耦合齿轮多体动力学模型的先进性.分析表明:在多体动力学中运用此齿轮模型可获得比传统方法更为精确的结果.
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...
Accommodative and Vergence Dysfunctions in mTBI: Treatment Effects and Systems Correlations
Directory of Open Access Journals (Sweden)
Preethi Thiagarajan, MS, PhD
2014-12-01
Full Text Available Background: Traumatic brain injury (TBI is a global, diffuse type of injury, which results in a constellation of visual dysfunctions. The extensive neural network of the oculomotor system makes it highly vulnerable following a TBI, hence the high prevalence of signs and symptoms related to accommodative and vergence dysfunctions. Methods: The present study evaluated the therapeutic effects on clinical (subjective and laboratory (objective measures, as well as their correlated improvements, following an equal dosage of six weeks of vergence and accommodation training in mild TBI (n=12. Results: With only three hours of training for each system, significant improvements in both static and dynamic parameters of both systems were found. Maximum amplitude of both systems increased markedly, along with faster dynamics demonstrating speedy responsivity, following training. Several key parameters between the two systems showed significant correlation (p<0.01, such as amplitudes (r = -0.87 and facilities (r = 0.88 of accommodation and vergence. Conclusions: The present findings demonstrate efficacy of oculomotor rehabilitation in TBI, with the improvements being suggestive of intact neuroplasticity in the compromised adult brain following mTBI.
Amplitude of Accommodation and its Relation to Refractive Errors
Directory of Open Access Journals (Sweden)
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
Opto-mechanical artificial eye with accommodative ability.
Esteve-Taboada, José J; Del Águila-Carrasco, Antonio J; Marín-Franch, Iván; Bernal-Molina, Paula; Montés-Micó, Robert; López-Gil, Norberto
2015-07-27
The purpose of this study was to describe the design and characterization of a new opto-mechanical artificial eye (OMAE) with accommodative ability. The OMAE design is based on a second-pass configuration where a small source of light is used at the artificial retina plane. A lens whose focal length can be changed electronically was used to add the accommodation capability. The changes in the OMAE's aberrations with the lens focal length, which effectively changes the accommodative state of the OMAE, were measured with a commercial aberrometer. Changes in power and aberrations with room temperature were also measured. The OMAE's higher-order aberrations (HOAs) were similar to the ones of the human eye, including the rate at which fourth-order spherical aberration decreased with accommodation. The OMAE design proposed here is simple, and it can be implemented in an optical system to mimic the optics of the human eye.
On cloud modelling and the mass accommodation coefficient of water
Directory of Open Access Journals (Sweden)
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.
Occlusal accommodation and mouthguards for prevention of orofacial trauma.
LENUS (Irish Health Repository)
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.
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.
Towards electricity markets accommodating uncertain offers
DEFF Research Database (Denmark)
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...
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...
Directory of Open Access Journals (Sweden)
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.
Quasi-variational principles of single flexible body dynamics and their applications
Institute of Scientific and Technical Information of China (English)
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.
Quasi-variational principles of single flexible body dynamics and their applications
Institute of Scientific and Technical Information of China (English)
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.
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.
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
Interaction between Accommodation and Vergence on Distance Perception
Directory of Open Access Journals (Sweden)
Tomoyuki Daijogo
2011-05-01
Full Text Available Fisher and Ciuffreda (1988 and Mon-Williams and Tresilian (1999 reported that, without vergence cue, diopter change in accommodation induced change in apparent distance. Meanwhile, there is conflicting evidence about the relative roles of accommodation and vergence in distance perception (Richards & Miller, 1969; von Holst, 1973. In the current study, we investigated interaction between accommodation and vergence on distance perception. The perceived distance from integration of vergence evoked by a fixation target and accommodation by a pair of concave or convex lenses in front of eyes is measured with a mirror stereoscope. The stimulus was a white square with a black cross-shaped fixation on a black background. In dark surroundings, subjects were asked to commit the apparent distance of the target to memory, and then without the lenses, re-create the distance by changing distance of another fixation target. The apparent size of the target through lenses were equivalent to the size without lenses. The results showed that not only vergence but accommodation affect the apparent distance, and they were summed linearly.
A model of job activity description for workplace accommodation assessment.
Sevilla, Joaquin; Sanford, Jon A
2013-01-01
Workplace accommodations to enable employees with disabilities to perform essential job tasks are an important strategy ways for increasing the presence of people with disabilities in the labor market. However, assessments, which are crucial to identifying necessary accommodations, are typically conducted using a variety of methods that lack consistent procedures and comprehensiveness of information. This can lead to the rediscovery of the same solutions over and over, inability to replicate assessments and a failure to effectively meet all of an individual's accommodation needs. To address standardize assessment tools and processes, a taxonomy of demand-producing activity factors is needed to complement the taxonomies of demand-producing person and environment factors already available in the International Classification of Functioning, Disability and Health (ICF). The purpose of this article is to propose a hierarchical model of accommodation assessment based on level of specificity of job activity. While the proposed model is neither a taxonomy nor an assessment process, the seven-level hierarchical model provides a conceptual framework of job activity that is the first step toward such a taxonomy as well as providing a common language that can bridge the many approaches to assessment. The model was designed and refined through testing against various job examples. Different levels of activity are defined to be easily linked to different accommodation strategies. Finally, the levels can be cross-walked to the ICF, which enhances its acceptability, utility and universality.
Relative Importance of Student Accommodation Quality in Higher Education
Directory of Open Access Journals (Sweden)
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.
Energy Technology Data Exchange (ETDEWEB)
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.
Perturbation Dynamics and Its Application for Parachute-Munition System
Institute of Scientific and Technical Information of China (English)
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.
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
Transient free molecular flow with partial accommodation through a tube
Pack, D. C.; Yamamoto, Kyoji
The paper presents the analysis for the distribution of molecules along the walls of a tube of circular cross-section and for the flux of gas through the tube, when there is transient free molecular flow with partial accommodation, from a reservoir to a vacuum, following the opening of a valve at the entrance to the tube. Numerical solutions are presented for various values of the ratio of length to diameter of the tube and of the accommodation coefficient, showing the development of density distribution and flux with time towards the steady state. Finally, there is some discussion of the trends exhibited by the results.
EVALUATION OF SERVICES’ QUALITY IN UPPER SILESIA ACCOMMODATION FACILITIES
Directory of Open Access Journals (Sweden)
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.
Technology needs for the development of the accommodative intraocular lens
Nishi, Okihiro
2010-02-01
Refilling the lens capsule while preserving capsular integrity offers the potential to restore ocular accommodation. There are two persisting problems in capsular bag refilling for possible clinical application: Leakage of the injectable material through the capsular opening and capsular opacification. Numerous attempts for solving these cardinal problems have not been proven to be clinically applicable. Recently, we developed a novel capsular bag refilling procedure using a novel accommodative intraocular lens that serves as an optic as well as a plug for sealing the capsular opening. The procedure and the results of monkey experiments will be presented.
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
DEFF Research Database (Denmark)
Bottasso, C. L.; Campagnolo, F.; Croce, A.;
2014-01-01
model fully-populated cross sectional stiffness matrices. Next, a "fine"-level 3D FEM model is used for the refinement of the coarse-level solution. Improved results obtained at the level of the 3D model are utilized at the following coarse-level iteration through a heuristic modification of the design...... level. At first, a "coarse"-level constrained design optimization is performed by using a 1D spatial geometrically exact beam model for aero-servo-elastic multibody analysis and load calculation, integrated with a 2D FEM cross sectional model for stress/strain analysis, and the evaluation of the 1D...
Fijany, Amir
1993-01-01
In this paper, parallel O(log n) algorithms for computation of rigid multibody dynamics are developed. These parallel algorithms are derived by parallelization of new O(n) algorithms for the problem. The underlying feature of these O(n) algorithms is a drastically different strategy for decomposition of interbody force which leads to a new factorization of the mass matrix (M). Specifically, it is shown that a factorization of the inverse of the mass matrix in the form of the Schur Complement is derived as M(exp -1) = C - B(exp *)A(exp -1)B, wherein matrices C, A, and B are block tridiagonal matrices. The new O(n) algorithm is then derived as a recursive implementation of this factorization of M(exp -1). For the closed-chain systems, similar factorizations and O(n) algorithms for computation of Operational Space Mass Matrix lambda and its inverse lambda(exp -1) are also derived. It is shown that these O(n) algorithms are strictly parallel, that is, they are less efficient than other algorithms for serial computation of the problem. But, to our knowledge, they are the only known algorithms that can be parallelized and that lead to both time- and processor-optimal parallel algorithms for the problem, i.e., parallel O(log n) algorithms with O(n) processors. The developed parallel algorithms, in addition to their theoretical significance, are also practical from an implementation point of view due to their simple architectural requirements.
Knowledge Transfer and Accommodation Effects in Multinational Corporations
DEFF Research Database (Denmark)
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...
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.…
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…
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…
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…
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…
Solutions to Efficient Provision of Accommodations for Universities in China
Institute of Scientific and Technical Information of China (English)
ZHANGSiping
2002-01-01
Chinese universities are facing a series of challenges in their accommodations,of which a pr\\edominant one is how to provide both students and staff with enough accommodations of a large scope and good quality in good time and with limited budgets,In order to find applicable approaches to solve this problem,the current situations of the Chinese higher education reform and the resulted rapid growth of student numbers whereby the requirement of lodgings is greatly incresed are discussed.It is elucidated that in providing enough accommodations for staff and students,Chinese universities are confronted with difficulties including demand too big,lack of funding support,time limitation and incapability in both project management and facilities management.Industrialized building approach is demonstrated to be a desirable access to build large quantities of accommodations of good quality in limited time.and Private Fuinancial Initiative(PFI) appears to be a prosperous solution to the fund shortage,Regarding project and facilities management,qualified professionals are available by either employing exterior consultants or training related staff of universities for such occupations.
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...
Development of a ciliary muscle-driven accommodating intraocular lens
Hermans, Erik A.; Terwee, Thom T.; Koopmans, Steven A.; Dubbelman, Michiel; van der Heijde, Rob G. L.; Heethaar, Rob M.
2008-01-01
PURPOSE: To develop a ciliary muscle-driven accommodating intraocular lens (IOL) that has a large and predictable range of variable power as a step toward spectacle independence. SETTING: Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, The Netherlands. METHODS:
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.…
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
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…
Reasonable accommodation in EU equality law in a broader perspective
Goldschmidt, J.E.
2007-01-01
The Framework Directive on equal treatment in employment and occupation of 2000 introduces the obligation to provide reasonable accommodations to people with disabilities. The author deals with the impact and meaning of this obligation from a human rights perspective. Adopting a substantive approach
Hydrogels for an accommodating intraocular lens. An explorative study
de Groot, JH; Spaans, CJ; van Calck, RV; van Beijma, FJ; Norrby, S; Pennings, AJ
2003-01-01
In this study it was investigated whether hydrogels could be used for an accommodating lens. The requirements of such a hydrogels are a low modulus, high refractive index, transparency, and strength. Since conventional hydrogels do not possess this combination of properties, a novel preparation meth
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…
Thurlow, Martha L.; Lazarus, Sheryl S.; Hodgson, Jennifer R.
2012-01-01
The read-aloud accommodation is one of the most frequently used accommodations. Many educators need training to more confidently select, implement, and evaluate the use of the read-aloud accommodation. Planning by special education leaders can help ensure that test day goes smoothly for students who need the read-aloud accommodation.
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...
Roberts, Barbara L.
2012-01-01
Students with learning disabilities obtain a wide range of recommended accommodations in secondary school, which they anticipate will continue into postsecondary education. Although the student's specific learning disability (SLD) contributes to the accommodation planning process, it is not the sole determinant of appropriate accommodation.…
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.
Dynamic Analysis of The Intelligent Sprayer Boom
DEFF Research Database (Denmark)
Wiggers, Sine Leergaard; Maagaard, Jørgen; Terp, Christian Istjord;
As part of the 3 year project “The intelligent Sprayer Boom”, financed by The Danish National Advanced Technology Foundation, the dynamics of the sprayer boom is to be analysed. In order to minimize the amount of herbicides used to kill the weeds in agriculture a new sprayer boom is being developed...... in Matlab. The model is made in order to analyse the boom movements. The purpose of the model is to support the development of the patented active damping system for the sprayer boom. The Multibody Dynamics model has been made based on data retrieved from a CAD model and a Finite Element model...
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.
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.
DEFF Research Database (Denmark)
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 ...
Institute of Scientific and Technical Information of China (English)
金俐; 王琪; 陆启韶
2001-01-01
A numerical algorithm for calculating Lyapunov exponents of Hamiltonian multibody systems with topological tree configuration is studied. The algorithms for Lyapunov exponents of Hamiltonian multibody systems using the canonical equations of the system and symplectic algorithm for ordinary differential equations are presented, which are used to study the stability of the Hamiltonian multibody systems. An example is given to analyze the stability of a typical Hamiltonian multibody system, including periodic solution and chaos.%研究了树形多体Hamilton系统Lyapunov指数的数值方法.利用多体Hamilton系统的正则方程和辛算法, 给出了多体Hamilton系统Lyapunov指数的计算方法,该算法具有较好的计算精度和通用性.利用该算法可对系统的运动稳定性进行分析.最后用算例说明了该算法的有效性.
CHOA concussion consensus: establishing a uniform policy for academic accommodations.
Popoli, David Michael; Burns, Thomas G; Meehan, William P; Reisner, Andrew
2014-03-01
Concussion research generally centers on physical challenges, though aspects such as social functioning and returning to school also warrant attention in pediatric populations. Restoring academic performance postconcussion remains a challenge. Here we provide recommendations addressing a uniform policy for pediatric concussion patients in academic institutions. Tools that may minimize difficulty with academic re-entry include independent educational evaluations, individualized educational programs (IEPs), student support teams (SSTs), letters of academic accommodation, time off, and 504 Plans. Recognition and treatment is crucial for symptom relief and prevention of functional disruption, as is specialist referral during the acute window. We recommend early intervention with a letter of academic accommodation and SST and suggest that 504 Plans and IEPs be reserved for protracted or medically complicated cases. Students with concussion should be observed for anxiety and depression because these symptoms can lead to prolonged recovery, decreased quality of life, and other social challenges. PMID:23960266
LIFE QUALITY OF FAMILIES STAYING IN ACCOMMODATIONAL INSTITUTIONS
Directory of Open Access Journals (Sweden)
Agah TEKİNDAL
2012-08-01
Full Text Available The present research aims to determine the quality of life and factors affecting the quality of life of families who stay in accommodational institutions. Simple random sampling method was used in the research; and 12 accommodational institutions in Antalya were researched as a cluster. The sample group comprised a total of 200 families with children. The "World Health Organization Brief Form ofQuality of Life Assessment Questionnaire" was used in the study. The research data were analyzed using the SPSS 17 program. T test and variance analysis were used in the assessment of data. A Tukey test was used in the multiple comparison of groups. Significant differences were found between scale sub-dimensions, age, educationalstatus, profession and income level of families who participated in the research (p<.05.
Analysis of marketing communications in the selected accommodation facilities
Uhrová, Pavlína
2010-01-01
The aim of this thesis is an analysis of marketing communication in selected accommodation and suggest possible changes. For this purpose I chose the hotel U Sladka. Estimation of marketing communication was made on the basis of information supplied by directors, employees and the hotel's own observations. An analysis of the present situation results that the hotel uses these elements of promotion: advertising, sales promotion, public relations, sponsorship, trade fairs and personal selling.D...
Union Militancy, External Shocks, and the Accommodation Dilemma
Tson Söderström, Hans
1985-01-01
Stabilization policy under centralized wage-setting is represnted as a non-cooperative game between an encompassing union and the government. The dilemma of the government is whether or not to accommodate supply disturbances when it cannot tell if they are due an intentionally militant wage policy or to unforeseen external price shocks. In a single round of wage setting, there is no government strategy which can both guarantee full employment and prevent union militancy. In a repeated game, h...
Operational-Marketing Study of an Accommodation Estabilishment
Pertilová, Klára
2012-01-01
The study is focused on the operation of a four star hotel in Prague. The main goal is to analyse the hotel operations, use of it's potential and the connection to the managing company. The first - theoretical part consists of the description and evolution of the accommodation services, definition of a hotel, characteristics of marketing in hotel services and marketing mix. In the second part the theoretical knowledge is applied to a particular hotel and the full analyse is created. It includ...
Bimatoprost (0.03%)-induced accommodative spasm and pseudomyopia.
Padhy, Debananda; Rao, Aparna
2015-11-23
Bimatoprost is a prostaglandin analogue used topically in the treatment of glaucoma. Commonly known side effects include eyelash growth, iris pigmentation and conjunctival hyperemia. While pseudomyopia is reported to be caused by parasympathomimetics, such an effect precipitated by bimatoprost has not yet been reported. We report a case demonstrating pseudomyopia and accommodative spasm caused after starting bimatoprost 0.03% in a young patient with glaucoma.
Evaluation, Analysis, and Enhancement of INDOT's Utility Accommodation Policy
Arboleda, Carlos A.; Jeong, Hyung Seok; Abraham, Dulcy M.; Gokhale, Sanjiv B.
2004-01-01
The Utility Accommodation Policy (UAP) is a collection of the regulations and practices to control the utility occupancy of all public highway rights-of-way under jurisdiction of the different States. UAPs not only help to regulate the installation of new utilities and the renovation of the currently installed by construction companies, subcontractors, and utilities companies, but also provide a framework to develop and preserve a safe roadside and to minimize possible interferences and impai...
Digital electronic engine control fault detection and accommodation flight evaluation
Baer-Ruedhart, J. L.
1984-01-01
The capabilities and performance of various fault detection and accommodation (FDA) schemes in existing and projected engine control systems were investigated. Flight tests of the digital electronic engine control (DEEC) in an F-15 aircraft show discrepancies between flight results and predictions based on simulation and altitude testing. The FDA methodology and logic in the DEEC system, and the results of the flight failures which occurred to date are described.
Kinematic and ground reaction force accommodation during weighted walking.
James, C Roger; Atkins, Lee T; Yang, Hyung Suk; Dufek, Janet S; Bates, Barry T
2015-12-01
Weighted walking is a functional activity common in daily life and can influence risks for musculoskeletal loading, injury and falling. Much information exists about weighted walking during military, occupational and recreational tasks, but less is known about strategies used to accommodate to weight carriage typical in daily life. The purposes of the study were to examine the effects of weight carriage on kinematics and peak ground reaction force (GRF) during walking, and explore relationships between these variables. Twenty subjects walked on a treadmill while carrying 0, 44.5 and 89 N weights in front of the body. Peak GRF, sagittal plane joint/segment angular kinematics, stride length and center of mass (COM) vertical displacement were measured. Changes in peak GRF and displacement variables between weight conditions represented accommodation. Effects of weight carriage were tested using analysis of variance. Relationships between peak GRF and kinematic accommodation variables were examined using correlation and regression. Subjects were classified into sub-groups based on peak GRF responses and the correlation analysis was repeated. Weight carriage increased peak GRF by an amount greater than the weight carried, decreased stride length, increased vertical COM displacement, and resulted in a more extended and upright posture, with less hip and trunk displacement during weight acceptance. A GRF increase was associated with decreases in hip extension (|r|=.53, p=.020) and thigh anterior rotation (|r|=.57, p=.009) displacements, and an increase in foot anterior rotation displacement (|r|=.58, p=.008). Sub-group analysis revealed that greater GRF increases were associated with changes at multiple sites, while lesser GRF increases were associated with changes in foot and trunk displacement. Weight carriage affected walking kinematics and revealed different accommodation strategies that could have implications for loading and stability.
Dynamic Modeling of Wind Turbine Gearboxes and Experimental Validation
DEFF Research Database (Denmark)
Pedersen, Rune
in a Fourier series and combined with a simple, torsional multibody model. Under the assumption of constant angular velocity of the gears, the methods of time-varying modal analysis are applied to this system. This investigation is carried out in order to evaluate the potential of the time-varying modal...... analysis in relation to gear dynamics. A multibody model of two complete 2.3MWwind turbine gearboxes mounted back-to-back in a test rig is built. The mean values of the proposed gear mesh stiffnesses are included. The model is validated by comparing with calculated and measured eigenfrequencies and mode...... shapes. The measured eigenfrequencies have been identified in accelerometer signals obtained during run-up tests. Since the calculated eigenfrequencies do not match the measured eigenfrequencies with sufficient accuracy, a model updating technique is applied to ensure a better match by adjusting...
ABOUT GENERAL INFRASTRUCTURE AND ACCOMMODATION SYSTEM IN ROMANIAN BALNEOLOGY
Directory of Open Access Journals (Sweden)
ILIE ROTARIU
2013-12-01
Full Text Available A strong infrastructure is a precondition for the development of balneology. On this base new tourism might build the modern services that supply the experiences. The key factor is the labor force: an EU project about labor force in Romania and Bulgaria in balneology allow us to present the preliminary findings focusing on general infrastructure and accommodation which allow the development of the balneology as well as the additional conditions as the existence of a social pact, easy access facilities etc. Our paper gives more details about the accommodation facilities in Romania insisting about the results of the transition and privatization of the former socialist facilities and the transformation of the property into private ones and the consequences of this. It also present the capability of new developed accommodation units built after 1990 and how they might compete in an international competition. The findings force us to conclude that the actual facilities do not allow the balneology resorts to compete in the international competition and might fill only a poor and low demanding tourists
Banu Yıldız
2013-01-01
The aim of this study is to determine the effect of branding on the purchasing preferences of tourists at accommodation enterprises. Towards this end questionnaire technique was used and 398 questionnaires were considered to be evaluated. The data, gathered, analyzed by using statistical methods. As a result it is revealed that branding (brad awareness, perceived quality, brand image, brand trust, brand attitude and brand loyalty parameters) has a positive effect on purchasing preferences ...
Dynamics of Flexible Wind Power Generator with Unbalanced Rotor
Directory of Open Access Journals (Sweden)
Venelin Jivkov
2016-08-01
Full Text Available The paper deals with dynamic analysis of a wind power generator as a large flexible structure with high speed rotating machines and considerable masses. The dynamic model is considered as a multibody system of rigid and flexible bodies. Nonstationary and transitional processes caused because of eccentricity of the high speed rotating machines, as well as, of the propeller vibrations are simulated and analyzed. Analytical method is applied for dynamic simulation. The results are verified by numerical procedures. Example of wind power generator with three propellers is presented.
Refractive state, ocular anatomy, and accommodative range of the sea otter (Enhydra lutris).
Murphy, C J; Bellhorn, R W; Williams, T; Burns, M S; Schaeffel, F; Howland, H C
1990-01-01
Sea otters are carnivorous, amphibious mammals that are active both above and under water. Accordingly, it might be expected that their eyes are adapted for both aerial and aqueous vision. We examined the anatomy and physiological optics of the sea otter eye with a view towards describing and explaining its amphibious visual characteristics. We employed photokeratoscopy to measure the refractive power of the sea otter cornea, which we found to be 59 D. Using video dynamic photorefraction, we found that sea otters can focus targets clearly both in air and water, relying on accommodation to compensate for the refractive loss of their corneas upon immersion in water. Our anatomical investigations revealed that the anterior epithelium of the cornea is extensively developed, as is the iris musculature, meridional ciliary muscle, and the corneoscleral venous plexus. The first feature is most likely an adaptation to the salinity of the marine environment. We believe the latter features are part of a novel, well-developed lenticular accommodative mechanism. PMID:2321364
Vailionis, A.; Boschker, H.; Liao, Z.; Smit, J. R. A.; Rijnders, G.; Huijben, M.; Koster, G.
2014-09-01
Distinct MnO6 octahedral distortions near and away from the La0.67Sr0.33MnO3/SrTiO3(001) (LSMO/STO) interface are quantified using synchrotron x-ray diffraction and dynamical x-ray diffraction simulations. Three structural regions of stress accommodation throughout the film thickness were resolved: near the LSMO/STO interface, intermediate region farther from the interface, and the main layer away from the interface. The results show that within the first two unit cells stress is accommodated by the suppression of octahedral rotations in the film, leading to the expansion of the c-axis lattice parameter. Farther from the interface film structure acquires octahedral tilts similar to thicker perovskite films under tensile stress, leading to a reduced c-axis parameter. We demonstrate that these regions are related to two different strain coupling mechanisms: symmetry mismatch at the interface and lattice mismatch in the rest of the film. The findings suggest new routes for strain engineering in correlated perovskite heterostructures.
Energy Technology Data Exchange (ETDEWEB)
Vailionis, A. [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305 (United States); Boschker, H. [MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands); Max Planck Institute for Solid State Research, 70569 Stuttgart (Germany); Liao, Z.; Smit, J. R. A.; Rijnders, G.; Huijben, M.; Koster, G. [MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)
2014-09-29
Distinct MnO{sub 6} octahedral distortions near and away from the La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3}(001) (LSMO/STO) interface are quantified using synchrotron x-ray diffraction and dynamical x-ray diffraction simulations. Three structural regions of stress accommodation throughout the film thickness were resolved: near the LSMO/STO interface, intermediate region farther from the interface, and the main layer away from the interface. The results show that within the first two unit cells stress is accommodated by the suppression of octahedral rotations in the film, leading to the expansion of the c-axis lattice parameter. Farther from the interface film structure acquires octahedral tilts similar to thicker perovskite films under tensile stress, leading to a reduced c-axis parameter. We demonstrate that these regions are related to two different strain coupling mechanisms: symmetry mismatch at the interface and lattice mismatch in the rest of the film. The findings suggest new routes for strain engineering in correlated perovskite heterostructures.
Kia, Mohammad; Schafer, Kevin; Lipman, Joseph; Cross, Michael; Mayman, David; Pearle, Andrew; Wickiewicz, Thomas; Imhauser, Carl
2016-05-01
A multibody model of the knee was developed and the predicted ligament forces and kinematics during passive flexion corroborated subject-specific measurements obtained from a human cadaveric knee that was tested using a robotic manipulator. The model incorporated a novel strategy to estimate the slack length of ligament fibers based on experimentally measured ligament forces at full extension and included multifiber representations for the cruciates. The model captured experimentally measured ligament forces (≤ 5.7 N root mean square (RMS) difference), coupled internal rotation (≤ 1.6 deg RMS difference), and coupled anterior translation (≤ 0.4 mm RMS difference) through 130 deg of passive flexion. This integrated framework of model and experiment improves our understanding of how passive structures, such as ligaments and articular geometries, interact to generate knee kinematics and ligament forces. PMID:26926010
Comparison on the rigid and flexible model of attitude maneuvering of a simple multi-body satellite
Directory of Open Access Journals (Sweden)
Teoh Vil Cherd
2014-12-01
Full Text Available 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 done to illustrate the significance of the flexible behaviour that inherited in the satellite system. With the negligence of flexible interference in the rigid model, it is likely to execute an exact attitude motion while the flexible model would yield a harmonic motion that is due to the vibratory motion of the solar panels.
Weis, Robert; Dean, Emily L; Osborne, Karen J
2016-09-01
Clinicians uniformly recommend accommodations for college students with learning disabilities; however, we know very little about which accommodations they select and the validity of their recommendations. We examined the assessment documentation of a large sample of community college students receiving academic accommodations for learning disabilities to determine (a) which accommodations their clinicians recommended and (b) whether clinicians' recommendations were supported by objective data gathered during the assessment process. In addition to test and instructional accommodations, many clinicians recommended that students with learning disabilities should have different educational expectations, standards, and methods of evaluation (i.e., grading) than their nondisabled classmates. Many of their recommendations for accommodations were not supported by objective evidence from students' history, diagnosis, test data, and current functioning. Furthermore, clinicians often recommended accommodations that were not specific to the student's diagnosis or area of disability. Our findings highlight the need for individually selected accommodations matched to students' needs and academic contexts. PMID:25395372
Accommodative load from handheld game consoles in kindergarten children
Sakata, Toshihiro; Miyao, Masaru; Ishigaki, Hisao; Shiraiwa, Yoshio; Ishihara, Shin'ya; Furuta, Masashi; Kondo, Takaaki; Toyoshima, Hideaki
2001-01-01
We analyzed and compared the visual accommodation of kindergarten children who were gazing fixedly at images from three different sources: Nintendo Game Boy DMG-01TM (non-backlit type game console: NBGC), NEC PC EnginePI-TG6TM (color backlit-type game console: CBGC) and a cartoon drawing (drawing). Subjects for the experiment were 13 4- to 5-year-old kindergarten children. The contrast ratios were, in the order, 1.1 (NBGC), 3.1 (drawing), and 3.4 (CBGC). These values show that the contrast of...
ACCOMMODATING WORLD ENGLISHES IN DEVELOPING EFL LEARNERS’ ORAL COMMUNICATION
Directory of Open Access Journals (Sweden)
Nur Mukminatien
2012-07-01
Full Text Available This article aims to discuss issues of World Englishes (WEs and the implications in ELT. It explores the extent to which WEs are taken into account as emerging English varieties different from inner circle varieties, how WEs should be accomodated by English teachers, and which standard to adopt to accommodate learner’s linguistic needs for international communication. It would help ELT practitioners adjust their current practices through the inclusion of varieties of WEs in developing learners’ oral communication. This offers relevant pedagogical movement to argue that changes should be made about the way English is valued and taught.
Treatment of Accommodative Dysfunction in Children: Results from an Random Clinical Trial
Scheiman, Mitchell; Cotter, Susan; Kulp, Marjean Taylor; Mitchell, G. Lynn; Cooper, Jeffrey; Gallaway, Michael; Hopkins, Kristine B.; Bartuccio, Mary; Chung, Ida
2011-01-01
Purpose To report the effectiveness of various forms of vision therapy/orthoptics in improving accommodative amplitude and facility in children with symptomatic convergence insufficiency (CI) and co-existing accommodative dysfunction. Methods In a randomized clinical trial, 221 children 9 to 17 years with symptomatic CI were assigned to one of four treatments. Of the enrolled children, 164 (74%) had accommodative dysfunction; 63 (29%) had a decreased amplitude of accommodation with respect to age, 43 (19%) had decreased accommodative facility, and 58 (26%) had both. Analysis of variance models were used to compare mean accommodative amplitude and accommodative facility for each treatment group after 4, 8, and 12 weeks of treatment. Results After 12 weeks of treatment, the increases in amplitude of accommodation [office-based vergence/accommodative therapy with home reinforcement group (OBVAT) 9.9D, home-based computer vergence/accommodative therapy group (HBCVAT+) 6.7D, home-based pencil push-up therapy group (HBPP) 5.8D] were significantly greater than in the office-based placebo therapy group (2.2D) (p-values ≤ 0.010). Significant increases in accommodative facility were found in all groups (OBVAT: 9cpm, HBCVAT+: 7cpm, HBPP: 5cpm, OBPT: 5.5cpm); only the improvement in the OBVAT group was significantly greater than that found in the OBPT group (p = 0.016). One year after completion of therapy, reoccurrence of decreased accommodative amplitude was present in only 12.5% and accommodative facility in only 11%. Conclusions Vision therapy/orthoptics is effective in improving accommodative amplitude and accommodative facility in school-age children with symptomatic CI and accommodative dysfunction. PMID:21873922
Progressive Fault Accommodation for Time-delay Systems with Parametric Faults
Institute of Scientific and Technical Information of China (English)
WU Jun-sheng; WENG Zheng-xin; TIAN Zuo-hua
2009-01-01
The fault accommodation problem for time-delay system is studied in this paper. The progressive accommodation strategy based on the Newton-Raphson scheme is proposed to solve this problem. This accommodation scheme can significantly reduces the loss of performance and risk associated with system instability which results from the time-delay needed by fault accommodation aigorithms to provide a solution. Simulation results are given to illustrate the efficiency of the provided method.
Cao, Xuebing
2014-01-01
The article evaluates submerged discontent among Chinese public hospital doctors (Note1) regarding their pay and patterns of accommodation, including doctors' responses through formal and informal actions in the context of health service marketization. On the basis of a case study of two public hospitals, the article illustrates the dynamical impact of marketization on Chinese doctors' pay-related dissatisfaction and health service employment relationship. Because of the authoritarian management and compliant trade unions, the conflict between doctors and hospitals is unable to be accommodated through collective methods. Instead, doctors' discontent is often channelled through informal, individual and subtle activities. Meanwhile, doctors' professional society is gradually influential, showing its potential of developing doctors' group identity and protecting members' interests in future. PMID:23737394
Predictive Validity of Accommodated LSAT Scores. Technical Report. LSAC Research Report Series.
Thornton, Andrea E.; Reese, Lynda M.; Pashley, Peter J.; Dalessandro, Susan P.
This study was undertaken to evaluate the predictive validity of the Law School Admission Test (LSAT) earned under accommodated testing conditions. Of special interest was the validity of scores obtained by test takers who were accommodated under nonstandard time conditions (i.e., accommodations that included extra testing time). Separate…
Teaching Adolescent Students with Learning Disabilities to Self-Advocate for Accommodations
Prater, Mary Anne; Redman, Ashleigh Smith; Anderson, Darlene; Gibb, Gordon S.
2014-01-01
In the general education classroom students with learning disabilities (LD) often need academic accommodations to be successful. These accommodations are typically selected and implemented by their general education teachers, not by the students themselves. High school students with LD were taught to recognize when an accommodation was needed,…
41 CFR 301-10.160 - What classes of train accommodations are available?
2010-07-01
... business-class. (1) First-class—Includes bedrooms, roomettes, club service, parlor car accommodations or other premium accommodations. (2) Business-class—A class of extra fare train service that is offered... only has two classes of accommodations available, i.e., first and business class, then the...
46 CFR 30.10-2 - Accommodation space-TB/ALL.
2010-10-01
... 46 Shipping 1 2010-10-01 2010-10-01 false Accommodation space-TB/ALL. 30.10-2 Section 30.10-2... Accommodation space—TB/ALL. The term accommodation space means any public space such as a hall, dining room... that contains no cooking appliances, and a similar space open to the passengers and crew....
Science Language Accommodation in Elementary School Read-Alouds
Glass, Rory; Oliveira, Alandeom W.
2014-03-01
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, open up an alternate channel of communication, namely oral discussion. By doing so, teachers grant students access to a simplified linguistic input, a strategy designed to promote student comprehension of the textual contents of children's science books. It was found that nearly half (46%) of the read-aloud time was allotted to discussions with an increased percentage of less sophisticated words and reduced use of more sophisticated vocabulary than found in the books through communicative strategies such as simplified rewording, simplified definition, and simplified questioning. Further, aloud reading of more linguistically complex books required longer periods of discussion and an increased degree of teacher oral input and accommodation. We also found evidence of reversed simplification (i.e. sophistication), leading to student uptake of scientific language. The main significance of this study is that it reveals that teacher talk serves two often competing pedagogical functions (accessible communication of scientific information to students and promotion of student acquisition of the specialized language of science). It also underscores the importance of giving analytical consideration to the simplification-sophistication dimension of science classroom discourse as well as the potential of computer-based analysis of classroom discourse to inform science teaching.
An experimental assembly for precise measurement of thermal accommodation coefficients.
Trott, Wayne M; Castañeda, Jaime N; Torczynski, John R; Gallis, Michael A; Rader, Daniel J
2011-03-01
An experimental apparatus has been developed to determine thermal accommodation coefficients for a variety of gas-surface combinations. Results are obtained primarily through measurement of the pressure dependence of the conductive heat flux between parallel plates separated by a gas-filled gap. Measured heat-flux data are used in a formula based on Direct Simulation Monte Carlo (DSMC) simulations to determine the coefficients. The assembly also features a complementary capability for measuring the variation in gas density between the plates using electron-beam fluorescence. Surface materials examined include 304 stainless steel, gold, aluminum, platinum, silicon, silicon nitride, and polysilicon. Effects of gas composition, surface roughness, and surface contamination have been investigated with this system; the behavior of gas mixtures has also been explored. Without special cleaning procedures, thermal accommodation coefficients for most materials and surface finishes were determined to be near 0.95, 0.85, and 0.45 for argon, nitrogen, and helium, respectively. Surface cleaning by in situ argon-plasma treatment reduced coefficient values by up to 0.10 for helium and by ∼0.05 for nitrogen and argon. Results for both single-species and gas-mixture experiments compare favorably to DSMC simulations. PMID:21456801
Evidence for neural accommodation to a writing system following learning.
Liu, Ying; Dunlap, Susan; Fiez, Julie; Perfetti, Charles
2007-11-01
Native English speakers with no knowledge of Chinese were trained on 60 Chinese characters according to one of three mapping conditions: orthography to pronunciation and meaning (P + M), orthography to pronunciation (P), and orthography to meaning (M). Following the training, fMRI scans taken during passive viewing of Chinese characters showed activation in brain regions that partially overlap the regions found in studies of skilled Chinese readers, but typically not found in alphabetic readers. Areas include bilateral middle frontal (BA 9), right occipital (BA 18/19), and fusiform (BA 37) regions. The activation pattern of Chinese characters was similar across the three groups. However, peak location was different in the left middle frontal region between groups. Direct contrasts between the groups also revealed stronger activation of left middle frontal in the P + M group. The results suggest that learners acquired skill in reading Chinese characters using a brain network similar to that used by Chinese native speakers. The results are consistent with the system accommodation hypothesis: The brain's reading network accommodates to features of an acquired writing system. PMID:17274024
Scaling and Accommodation of Jaw Adductor Muscles in Canidae.
Penrose, Fay; Kemp, Graham J; Jeffery, Nathan
2016-07-01
The masticatory apparatus amongst closely related carnivoran species raises intriguing questions about the interplay between allometry, function, and phylogeny in defining interspecific variations of cranial morphology. Here we describe the gross structure of the jaw adductor muscles of several species of canid, and then examine how the muscles are scaled across the range of body sizes, phylogenies, and trophic groups. We also consider how the muscles are accommodated on the skull, and how this is influenced by differences of endocranial size. Data were collected for a suite of morphological metrics, including body mass, endocranial volume, and muscle masses and we used geometric morphometric shape analysis to reveal associated form changes. We find that all jaw adductor muscles scale isometrically against body mass, regardless of phylogeny or trophic group, but that endocranial volume scales with negative allometry against body mass. These findings suggest that head shape is partly influenced by the need to house isometrically scaling muscles on a neurocranium scaling with negative allometry. Principal component analysis suggests that skull shape changes, such as the relatively wide zygomatic arches and large sagittal crests seen in species with higher body masses, allow the skull to accommodate a relative enlargement of the jaw adductors compared with the endocranium. Anat Rec, 299:951-966, 2016. © 2016 The Authors The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology Published by Wiley Periodicals, Inc. PMID:27103346
Can mergers-in-progress be unmerged in speech accommodation?
Directory of Open Access Journals (Sweden)
Molly eBabel
2013-09-01
Full Text Available This study examines spontaneous phonetic accommodation of a dialect with distinct categories by speakers who are in the process of merging those categories. We focus on the merger of the NEAR and SQUARE lexical sets in New Zealand English, presenting New Zealand participants with an unmerged speaker of Australian English. Mergers-in-progress are a uniquely interesting sound change as they showcase the asymmetry between speech perception and production. Yet, we examine mergers using spontaneous phonetic imitation, which is phenomenon that is necessarily a behavior where perceptual input influences speech production. Phonetic imitation is quantified by a perceptual measure and an acoustic calculation of mergedness using a Pillai-Bartlett trace. The results from both analyses indicate spontaneous phonetic imitation is moderated by extra-linguistic factors such as the valence of assigned conditions and social bias. We also find evidence for a decrease in the degree of mergedness in post-exposure productions. Taken together, our results suggest that under the appropriate conditions New Zealanders phonetically accommodate to Australian English and that in the process of speech imitation, mergers-in-progress can, but do not consistently, become less merged.
Accommodation coefficient of HOBr on deliquescent sodium bromide aerosol particles
Directory of Open Access Journals (Sweden)
M. Wachsmuth
2002-01-01
Full Text Available Uptake of HOBr on sea salt aerosol, sea salt brine or ice is believed to be a key process providing a source of photolabile bromine (Br2 and sustaining ozone depletion cycles in the Arctic troposphere. In the present study, uptake of HOBr on sodium bromide (NaBr aerosol particles was investigated at an extremely low HOBr concentration of 300 cm-3 using the short-lived radioactive isotopes 83-86Br. Under these conditions, at maximum one HOBr molecule was taken up per particle. The rate of uptake was clearly limited by the mass accommodation coefficient, which was calculated to be 0.6 ± 0.2. This value is a factor of 10 larger than estimates used in earlier models. The atmospheric implications are discussed using the box model "MOCCA'', showing that the increase of the accommodation coefficient of HOBr by a factor of 10 only slightly affects net ozone loss, but significantly increases chlorine release.
Factors shaping physicians' willingness to accommodate medication requests.
Arney, Jennifer; Street, Richard L; Naik, Aanand D
2014-09-01
Medical decisions, including physicians' prescribing behaviors, are shaped by a complex interplay of clinical and nonclinical factors. We aim to determine how physician, patient, and relationship characteristics influence physicians' decisions to accommodate brand-name prescription drug requests. We applied multivariate logistic regression to data from the Attitudinal and Behavioral Effects of Direct-to-Consumer Promotion of Prescription Drugs physician survey. We used a national probability sample of 500 primary care and specialty physicians reporting on a clinical encounter that involved a prescription drug request. Independent variables include physician's assessment of the patient's understanding of risks and benefits of a requested medication, whether the patient had the condition the drug treats, duration of the clinical relationship, and physician's age, area of practice, years of experience, and gender. These variables were used to predict whether the physician prescribed the requested drug. Physicians were more willing to accommodate requests when they believed that patients had a clear understanding of the drug's risks and when patients had the condition the drug treats. Primary care practitioners, compared to specialists, had higher odds of prescribing a requested drug. We conclude that clinical and communicative factors shape physicians' decisions to prescribe requested brand-name drugs. Findings offer insight into the influence that direct-to-consumer advertising can have in medical encounters, and may guide efforts to enhance physician-patient communication and shared decision making. PMID:23232050
H2S, a novel gasotransmitter, involves in gastric accommodation.
Xiao, Ailin; Wang, Hongjuan; Lu, Xin; Zhu, Jianchun; Huang, Di; Xu, Tonghui; Guo, Jianqiang; Liu, Chuanyong; Li, Jingxin
2015-11-04
H2S is produced mainly by two enzymes:cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), using L-cysteine (L-Cys) as the substrate. In this study, we investigated the role of H2S in gastric accommodation using CBS(+/-) mice, immunohistochemistry, immunoblot, methylene blue assay, intragastric pressure (IGP) recording and electrical field stimulation (EFS). Mouse gastric fundus expressed H2S-generating enzymes (CBS and CSE) and generated detectable amounts of H2S. The H2S donor, NaHS or L-Cys, caused a relaxation in either gastric fundus or body. The gastric compliance was significantly increased in the presence of L-Cys (1 mM). On the contrary, AOAA, an inhibitor for CBS, largely inhibited gastric compliance. Consistently, CBS(+/-) mice shows a lower gastric compliance. However, PAG, a CSE inhibitor, had no effect on gastric compliances. L-Cys enhances the non-adrenergic, non-cholinergic (NANC) relaxation of fundus strips, but AOAA reduces the magnitude of relaxations to EFS. Notably, the expression level of CBS but not CSE protein was elevated after feeding. Consistently, the production of H2S was also increased after feeding in mice gastric fundus. In addition, AOAA largely reduced food intake and body weight in mice. Furthermore, a metabolic aberration of H2S was found in patients with functional dyspepsia (FD). In conclusion, endogenous H2S, a novel gasotransmitter, involves in gastric accommodation.
Analysis of internal drive train dynamics in a wind turbine
Peeters, Joris L. M.; Vandepitte, Dirk; Sas, Paul
2006-01-01
Three types of multibody models are presented for the investigation of the internal dynamics of a drive train in a wind turbine. The first approach is limited to the analysis of torsional vibrations only. Then a rigid multibody model is presented with special focus on the representation of the bearings and gears in the drive train. The generic model implementation can be used for parallel as well as planetary gear stages with both helical and spur gears. Examples for different gear stages describe the use of the presented formulations. Furthermore, the influence of the helix angle and the flexibility of the bearings on the results of eigenmode calculations are discussed. The eigenmodes of a planetary stage are classified as rotational, translational or out-of-plane modes. Thirdly, the extension to a flexible multibody model is presented as a method to include directly the drive train components' flexibilities. Finally, a comparison of two different modelling techniques is discussed for a wind turbine's drive train with a helical parallel gear stage and two planetary gear stages. In addition, the response calculation for a torque input at the generator demonstrates which eigenmodes can be excited through this path. Copyright
Directory of Open Access Journals (Sweden)
Banu Yıldız
2013-09-01
Full Text Available The aim of this study is to determine the effect of branding on the purchasing preferences of tourists at accommodation enterprises. Towards this end questionnaire technique was used and 398 questionnaires were considered to be evaluated. The data, gathered, analyzed by using statistical methods. As a result it is revealed that branding (brad awareness, perceived quality, brand image, brand trust, brand attitude and brand loyalty parameters has a positive effect on purchasing preferences of tourists and a negative effect on the volume of perceived risk. Factors contributing to more on purchasing preferences of tourists, respectively, brand attitude, brand loyalty and brand awareness.
A Numerical Method of Large-Scale Concrete Displacing Boom Dynamic and Experimental Validation
Wu Ren; Yun-xin Wu; Zhao-wei Zhang; Wen-ze Shi
2014-01-01
Concrete displacing boom is large-scale motion manipulator. During the long distance pouring the postures needs to frequently change. This makes the real-time dynamic analysis and health monitoring difficult. Virtual spring-damper method is adopted to establish the equivalent hydraulic actuator model. Besides boom cylinder joint clearance is taken into account. Then transfer matrix method is used to build the multibody concrete placing boom model by dividing the system into two substructures....
Bansal, Artee; Cox, Kenneth R; Chapman, Walter G
2016-01-01
A mixture of solvent particles with short-range, directional interactions and solute particles with short-range, isotropic interactions that can bond multiple times is of fundamental interest in understanding liquids and colloidal mixtures. Because of multi-body correlations predicting the structure and thermodynamics of such systems remains a challenge. Earlier Marshall and Chapman developed a theory wherein association effects due to interactions multiply the partition function for clustering of particles in a reference hard-sphere system. The multi-body effects are incorporated in the clustering process, which in their work was obtained in the absence of the bulk medium. The bulk solvent effects were then modeled approximately within a second order perturbation approach. However, their approach is inadequate at high densities and for large association strengths. Based on the idea that the clustering of solvent in a defined coordination volume around the solute is related to occupancy statistics in that def...
Goodman, Lawrence E
2001-01-01
Beginning text presents complete theoretical treatment of mechanical model systems and deals with technological applications. Topics include introduction to calculus of vectors, particle motion, dynamics of particle systems and plane rigid bodies, technical applications in plane motions, theory of mechanical vibrations, and more. Exercises and answers appear in each chapter.
Directory of Open Access Journals (Sweden)
Tobias Strenger
2013-10-01
Full Text Available 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 derived based on a physical context. The numerical results obtained with the Multi-body System approach are compared with experimental results by Laser Doppler measurements of the stapes footplate velocities of five different specimens. Although slightly differing anatomical structures were used for the calculation and the measurement, a high correspondence with respect to the course of stapes footplate displacement along the frequency was found. Notably, a notch at frequencies just below 1 kHz occurred. Additionally, phase courses of stapes footplate displacements were determined computationally if possible and compared with experimental results. The examinations were undertaken to quantify stapes footplate displacements in the clinical practice of middle ear implants and, also, to develop fitting strategies on a physical basis for hearing impaired patients aided with middle ear implants.
Parental accommodation of child anxiety and related symptoms: range, impact, and correlates.
Thompson-Hollands, Johanna; Kerns, Caroline E; Pincus, Donna B; Comer, Jonathan S
2014-12-01
Parental accommodation--i.e., changes in parents' behavior in attempts to prevent or reduce child distress--has been most studied in relation to OCD. Although recent work suggests parents of children with non-OCD anxiety diagnoses also engage in accommodation, little is known about the specific forms, correlates, and associated interference of such accommodation. The present study examined the range and associated interference of parental accommodation behaviors using the newly developed Family Accommodation Checklist and Interference Scale (FACLIS) in a sample of the parents of 71 clinic-referred children with anxiety disorders (NMothers-68; NFathers-51). The FACLIS demonstrated good reliability and validity. Ninety-seven percent of mothers and 88% of fathers reported engaging in at least one type of accommodation in the previous two weeks, with parents reporting an average of roughly 4 interfering parental accommodation behaviors. Greater parental accommodation and associated interference were associated with higher maternal distress. Among the anxiety disorders, accommodation was most strongly associated with generalized and separation anxiety disorder, as well as specific phobias. Findings (a) offer psychometric support for the FACLIS as a reliable and valid tool for the assessment of accommodation range and impact, and (b) help clarify the considerable scope and interference associated with parental accommodation of childhood anxiety. PMID:25261837
Parental accommodation of child anxiety and related symptoms: range, impact, and correlates.
Thompson-Hollands, Johanna; Kerns, Caroline E; Pincus, Donna B; Comer, Jonathan S
2014-12-01
Parental accommodation--i.e., changes in parents' behavior in attempts to prevent or reduce child distress--has been most studied in relation to OCD. Although recent work suggests parents of children with non-OCD anxiety diagnoses also engage in accommodation, little is known about the specific forms, correlates, and associated interference of such accommodation. The present study examined the range and associated interference of parental accommodation behaviors using the newly developed Family Accommodation Checklist and Interference Scale (FACLIS) in a sample of the parents of 71 clinic-referred children with anxiety disorders (NMothers-68; NFathers-51). The FACLIS demonstrated good reliability and validity. Ninety-seven percent of mothers and 88% of fathers reported engaging in at least one type of accommodation in the previous two weeks, with parents reporting an average of roughly 4 interfering parental accommodation behaviors. Greater parental accommodation and associated interference were associated with higher maternal distress. Among the anxiety disorders, accommodation was most strongly associated with generalized and separation anxiety disorder, as well as specific phobias. Findings (a) offer psychometric support for the FACLIS as a reliable and valid tool for the assessment of accommodation range and impact, and (b) help clarify the considerable scope and interference associated with parental accommodation of childhood anxiety.
Intraocular electro-optic lens with ciliary muscle controlled accommodation.
Doornaert, Dries; Glorieux, Christ; De Gersem, Herbert; Puers, Robert; Spileers, Werner; Blanckaert, Johan
2013-01-01
In this paper a concept is proposed of an intraocular lens implant with electro-optic accommodation of a variable-focus hybrid liquid-crystal-based lens. The dioptric strength of the lens is electronically controlled by a signal that is derived from the change of inductance of a sensing coil due to a marker implanted in the nearby contracting or decontracting ciliary muscle. Analytical, numerical and experimental results are reported on the dependency of the frequency of a Colpitts oscillator circuit on the location of a nearby conductive marker. A concept is also reported on the use as an electro-optic lens of a device based on a liquid crystal in planar alignment, which is held between a flat and a curved window coated with optically transparent and electrically conductive layers. PMID:24110406
Disturbance Accommodating Adaptive Control with Application to Wind Turbines
Frost, Susan
2012-01-01
Adaptive control techniques are well suited to applications that have unknown modeling parameters and poorly known operating conditions. Many physical systems experience external disturbances that are persistent or continually recurring. Flexible structures and systems with compliance between components often form a class of systems that fail to meet standard requirements for adaptive control. For these classes of systems, a residual mode filter can restore the ability of the adaptive controller to perform in a stable manner. New theory will be presented that enables adaptive control with accommodation of persistent disturbances using residual mode filters. After a short introduction to some of the control challenges of large utility-scale wind turbines, this theory will be applied to a high-fidelity simulation of a wind turbine.
Method for compensating bellows pressure loads while accommodating thermal deformations
International Nuclear Information System (INIS)
Many metal bellows are used on storage ring vacuum chambers. They allow the ring to accommodate deformations associated with alignment, mechanical assembly and thermal expansion. The NSLS has two such electron storage rings, the VUV ring and the X-Ray ring. Both rings utilize a number of welded metal bellows within the ring and at every beam port. There are provisions for 16 beam ports on the VUV and 28 ports of the X-Ray ring. At each of these locations the bellows are acted on by an external pressure of 1 atmosphere, which causes a 520 lb. reaction at the vacuum chamber beam port and at the beamline flange downstream of the bellows. The use of rigid tie rods across the bellows flanges to support the load is troublesome because most storage ring vacuum chambers are baked in situ to achieve high internal vacuum. Significant forces can develop on components if thermal deformation is restrained and damage could occur
Method for compensating bellows pressure loads while accommodating thermal deformations
Energy Technology Data Exchange (ETDEWEB)
Woodle, M.H.
1985-01-01
Many metal bellows are used on storage ring vacuum chambers. They allow the ring to accommodate deformations associated with alignment, mechanical assembly and thermal expansion. The NSLS has two such electron storage rings, the vuv ring and the x-ray ring. Both rings utilize a number of welded metal bellows within the ring and at every beam port. There are provisions for 16 beam ports on the vuv and 28 ports in the x-ray ring. At each of these locations the bellows are acted on by an external pressure of 1 atmosphere, which causes a 520 lb reaction at the vacuum chamber beam port and at the beamline flange downstream of the bellows. The use of rigid tie rods across the bellows flanges to support this load is troublesome because most storage ring vacuum chambers are baked in situ to achieve high internal vacuum. Significant forces can develop on components if thermal deformation is restrained and damage could occur.
Automation for Accommodating Fuel-Efficient Descents in Constrained Airspace
Coopenbarger, Richard A.
2010-01-01
Continuous descents at low engine power are desired to reduce fuel consumption, emissions and noise during arrival operations. The challenge is to allow airplanes to fly these types of efficient descents without interruption during busy traffic conditions. During busy conditions today, airplanes are commonly forced to fly inefficient, step-down descents as airtraffic controllers work to ensure separation and maximize throughput. NASA in collaboration with government and industry partners is developing new automation to help controllers accommodate continuous descents in the presence of complex traffic and airspace constraints. This automation relies on accurate trajectory predictions to compute strategic maneuver advisories. The talk will describe the concept behind this new automation and provide an overview of the simulations and flight testing used to develop and refine its underlying technology.
Driving time modulates accommodative response and intraocular pressure.
Vera, Jesús; Diaz-Piedra, Carolina; Jiménez, Raimundo; Morales, José M; Catena, Andrés; Cardenas, David; Di Stasi, Leandro L
2016-10-01
Driving is a task mainly reliant on the visual system. Most of the time, while driving, our eyes are constantly focusing and refocusing between the road and the dashboard or near and far traffic. Thus, prolonged driving time should produce visual fatigue. Here, for the first time, we investigated the effects of driving time, a common inducer of driver fatigue, on two ocular parameters: the accommodative response (AR) and the intraocular pressure (IOP). A pre/post-test design has been used to assess the impact of driving time on both indices. Twelve participants (out of 17 recruited) completed the study (5 women, 24.42±2.84years old). The participants were healthy and active drivers with no visual impairment or pathology. They drove for 2h in a virtual driving environment. We assessed AR and IOP before and after the driving session, and also collected subjective measures of arousal and fatigue. We found that IOP and AR decreased (i.e., the accommodative lag increased) after the driving session (p=0.03 and p<0.001, respectively). Moreover, the nearest distances tested (20cm, 25cm, and 33cm) induced the highest decreases in AR (corrected p-values<0.05). Consistent with these findings, the subjective levels of arousal decreased and levels of fatigue increased after the driving session (all p-values<0.001). These results represent an innovative step towards an objective, valid, and reliable assessment of fatigue-impaired driving based on visual fatigue signs. PMID:27235337
Structural Dynamics Modeling of Multibody System%多体系统结构动力学建模
Institute of Scientific and Technical Information of China (English)
赵强; 吴洪涛; 朱剑英
2006-01-01
在多体系统结构动力学建模方法研究中引入了柔性多体系统动力学空间算子代数和子结构综合分析方法,将多体系统划分为由铰链连接的部件或单一零件组成的子件,用有限元分析和模态分析方法求解各子件的模态广义质量矩阵和模态刚度矩阵.再通过动力学空间算子代数,将各子件模态广义质量矩阵和模态刚度矩阵递推到基础坐标下,构成整个系统的模态广义质量矩阵和模态刚度矩阵,以此建立整个多体系统结构动力学模型.同时,由于动力学空间算子代数运用了Kalman滤波和Bryson-Frazier平滑波技巧,在一定程度上消除了白噪声,在结构动力学运算过程中也避免了大量的重复计算,提高了数值精度.此建模方法是一种高效、高精度建模方法,它为多体系统结构动力学研究提供了一种新的建模方法.
Numerical Algorithms of Multibody System Dynamics%多体系统动力学数值解法
Institute of Scientific and Technical Information of China (English)
王国平
2006-01-01
多体系统动力学研究的主要内容动力学建模与数值解法是多体系统动力学研究的主要内容之一.对多体系统动力学方程及其动力学数值解法的研究成果进行了较为全面的阐述.多体系统动力学及动力学方程进行了简单的归纳和总结,多体系统动力学数值求解,特别是刚柔耦合多体系统微分/代数方程的数值解法等研究热点进行了详细的阐述,并简要展望了多体系统动力学数值解法今后的发展趋势,为多体系统动力学计算机仿真奠定了基础.
Institute of Scientific and Technical Information of China (English)
季日臣; 许涛; 苏小凤; 唐艳
2012-01-01
为分析水体晃动对多槽式渡槽结构动力特性的影响,基于流固耦合理论,以南水北调中线工程某双槽式渡槽为例进行研究.应用Westerguard水体附加质量法模拟水体与结构的动力相互作用,采用MIDAS/CIVIL计算软件对该双槽式渡槽的自振特性和地震反应进行有限元计算,分析水体对渡槽动力特性的影响.并选用具有隔震和耗能双重功能的摩擦摆支座对大型渡槽结构进行隔震研究.计算结果表明,摩擦摆支座纵横向隔震能够大幅减小墩顶位移和墩底内力,从而满足结构的抗震需求.%In order to analyse the effects of water sloshing on multi-body aqueduct dynamic characteristics , based on the fluid-structure coupling theory, the double-body aqueduct of South to North Water Diversion Project was studied. The added mass method was used to simulate the dynamic interaction between water and aqueduct structure. The free vibration characteristics and seismic response of the aqueduct were calculated by the MIDAS/CIVIL software. The effects of water sloshing on aqueduct dynamic characteristics were analyzed. Friction Pendulum Bearings ( FPB) with double function of seismic isolation and energy dissipation were adopted to study the seismic isolation of large aqueduct. The results show that the longitudinal and lateral isolation of FPB can reduce signtificantly the top displacement and bottom internal forces of piers satisfying the requirement of seismic resistance.
Kassemi, Mohammad; Kartuzova, Olga
2016-03-01
Pressurization and pressure control in cryogenic storage tanks are to a large extent affected by heat and mass transport across the liquid-vapor interface. These mechanisms are, in turn, controlled by the kinetics of the phase change process and the dynamics of the turbulent recirculating flows in the liquid and vapor phases. In this paper, the effects of accommodation coefficient and interfacial turbulence on tank pressurization and pressure control simulations are examined. Comparison between numerical predictions and ground-based measurements in two large liquid hydrogen tank experiments, performed in the K-site facility at NASA Glenn Research Center (GRC) and the Multi-purpose Hydrogen Test Bed (MHTB) facility at NASA Marshall Space Flight Center (MSFC), are used to show the impact of accommodation coefficient and interfacial and vapor phase turbulence on evolution of pressure and temperatures in the cryogenic storage tanks. In particular, the self-pressurization comparisons indicate that: (1) numerical predictions are essentially independent of the magnitude of the accommodation coefficient; and (2) surprisingly, laminar models sometimes provide results that are in better agreement with experimental self-pressurization rates, even in parametric ranges where the bulk flow is deemed fully turbulent. In this light, shortcomings of the present CFD models, especially, numerical treatments of interfacial mass transfer and turbulence, as coupled to the Volume-of-Fluid (VOF) interface capturing scheme, are underscored and discussed.
The Assessment of Accommodation and Convergence System in the Bank Employees
Directory of Open Access Journals (Sweden)
Monireh Mahjoob
2013-02-01
Full Text Available Background: Regarding the high outbreak rate of the eye disorders and problems particularly accommodation disorders and convergence insufficiency in computer users, the study tries to determine the convergence, accommodation system, condition, fusion reserves and vision dimension in bank employees (who work with computers and the control group (who are not computer users and then to compare the mentioned parameters in the two groups. Materials and Methods: In this cross-sectional and observational study a total of 44 bank employees and 44 people as the control group members were selected randomly. Initially, refractive problems were reformed, and then accommodation, convergence and vision dimension evaluative tests were conducted. The test included measuring the near point of convergence, jump convergence, phoria, accommodation range (one eye, both eyes, ease of accommodation (one eye, both eyes, positive and negative related accommodation, near fusion versions and TNO.Results: Our results showed that there was a not significant difference among the near point of convergence, jump convergence, near phoria, accommodation range (one eye and both eyes, ease of accommodation (one eye, both eyes, positive and negative related accommodation in bank employees and control group.Conclusion: Regarding the studies, the outbreak rate of accommodation and convergence disorders is higher in bank employees than the control group which would be due to over working with computer within a fixed interval.
Optimal secondary coil design for inductive powering of the Artificial Accommodation System.
Nagel, J A; Krug, M; Gengenbach, U; Guth, H; Bretthauer, G; Guthoff, R F
2011-01-01
Age-related ailments like presbyopia and cataract are increasing concerns in the aging society. Both go along with a loss of ability to accommodate. A new approach to restore the patients' ability to accommodate is the Artificial Accommodation System. This micro mechatronic system will be implanted into the capsular bag to replace the human crystalline lens. Depending on the patients' actual need for accommodation, the Artificial Accommodation System autonomously adapts the refractive power of its integrated optical element in a way that the projection on the patients' retina results in a sharp image. As the Artificial Accommodation System is an active implant, its subsystems have to be supplied with electrical energy. Evolving technologies, like energy harvesting, which can potentially be used to power an implant like the Artificial Accommodation System are at the current state of art not sufficient to power the Artificial Accommodation System autonomously [1]. In the near future, therefore an inductive power supply system will be developed which includes an energy storage to power the Artificial Accommodation System autonomously over a period of 24 h and can be recharged wirelessly. This Paper describes a new possibility to optimize the secondary coil design in a solely analytical way, based on a new figure of merit. Within this paper the developed figure of merit is applied to optimize the secondary coil design for the Artificial Accommodation System.