Manuel S. Pereira

Biomechanical Model with Joint Resistance for Impact Simulation

Based on a general methodology using naturalco-ordinates, a three-dimensional whole body responsemodel for the articulated human body is presented inthis paper. The joints between biomechanical segmentsare defined by forcing adjacent bodies to share commonpoints and vectors that are used in their definition.A realistic relative range of motion for the bodysegments is obtained introducing a set of penaltyforces in the model rather than setting up newunilateral constraints between the system components.These forces, representing the reaction momentsbetween segments of the human body model when thebiomechanical joints reach the limit of their range ofmotion, prevent the biomechanical model from achievingphysically unacceptable positions. Improved efficiencyin the integration process of the equations of motionis obtained using the augmented Lagrange formulation.The biomechanical model is finally applied indifferent situations of passive human motion such asthat observed in vehicle occupants during a crash orin an athlete during impact.

Sensitivity Analysis of Rigid-Flexible Multibody Systems

An important step in the application of automated design techniques to rigid-flexible multibody systems is the calculation of the sensitivities with respect to design variables. Thispaper presents a general formulation for thecalculation of the first order analytical designsensitivities based on the direct differentiationmethod. The analytical sensitivities are comparedwith the numerical results obtained by the finitedifferences method and the accuracy and validity ofboth methods is discussed. Cartesian co-ordinates areused for the dynamic analysis of rigid-flexiblemultibody systems. To reduce the number ofco-ordinates associated with the flexible bodies, thecomponent mode synthesis method is used. Theequations of the sensitivities are obtainedsymbolically and integrated in time simultaneouslywith the dynamic equations. Examples of 2Dsensitivity analysis of the transient response of aslider-crank and of a vehicle with a flexible chassisare presented, and the accuracy and characteristics ofthe sensitivities are analyzed and discussed.

CRASHWORTHINESS ANALYSIS AND DESIGN USING RIGID–FLEXIBLE MULTIBODY DYNAMICS WITH APPLICATION TO TRAIN VEHICLES

SUMMARY Di⁄erent formulations based on multibody dynamics are shown to be suitable for the development of a methodology for the impact simulation and crashworthiness design of railway vehicles. The proposed design methodology comprises di⁄erent computer-aided tools of increasing complexity and accuracy which can be used with greater advantage and eƒciency in the di⁄erent design stages of railway stock. In general, the crashworthiness design methods and associated multibody dynamic tools which are presented in this paper require information to be obtained from numerical or experimental crush tests of specific structural components, subassemblies and critical energy absorption devices normally located in car extremities. This hybrid feature lends to the present design process various eƒciency gains as a result of a better understanding of the crash and di⁄erent collapse mechanisms and ease of use. To access the merits of the present methodologies some new designs are discussed and the application of the proposed numerical tools is illustrated for di⁄erent structural configurations of car extremities. A formulation for the sensitivity analysis and optimization of planar constrained mechanical systems is also presented. An example of crashworthiness design of an end underframe model of a railway car is solved to demonstrate the use of the methodology. The interest in railway transportation has significantly increased for economical and environmental reasons. In fact, with the advent of high-speed trains, the railway has become a very promising and attractive means of transportation for mass transit and commuter and longdistance travelling. There is now an increasing awareness of the costs of railway accidents, in terms of human su⁄ering in general and property damage. This situation has encouraged operators, manufacturers and research institutions to join e⁄orts in the development of new design capabilities taking into account impact conditions with the aim to significantly reduce damage costs and human injuries and fatalities. This involves an e⁄ort towards a better understanding of the mechanics of railway collisions including more accurate evaluation of impact loads which, in turn, allows the development of new crashworthy railway car extremities with reduced uncertainty margins and with maximal energy absorption characteristics. During the last twenty-five years, computer-aided analysis of crashworthiness and structural impact has received considerable attention and is now emerging as a powerful methodology

Crashworthiness of transportation systems : structural impact and occupant protection

Part I: Impact Biomechanics. Occupant Kinematics and Impact Biomechanics A.I. King. Injury Mechanisms and Biofidelity of Dummies D.C. Viano, A.I. King. Biomechanics of Impact Traumatic Brain Injury F.A. Bandak. Forensic Analysis and Data for Road Users I.R. Hill. Part II: Road Data, Compatibility Issues and Testing. A Review of the Biomechanics of Impacts in Road Accidents M. Mackay. Compatibility Issues and Vulnerable Users C.H.E. Tarriere. Advanced Restraint Systems for Occupant Protection D. Cesari. Car Crash and Safety Testing P.L. Ardoino. Part III: Occupant Simulation Models. Occupant Simulation Models: Experiment and Practice P. Prasad. Models in Injury Biomechanics for Improved Passive Vehicle Safety J. Wismans. Biomechanical Models in Vehicle Accident Simulation E. Haug. Part V: Structural Impact. Dynamic Inelastic Structural Response N. Jones. The Macro Element Approach in Crash Calculations W. Abramowicz. Crashworthiness of Bus Structures and Rollover Protection M. Matolcsy. Part V: Finite Element Modelling in Crashworthiness. Vehicle Crashworthiness and Occupant Protection in Frontal Impact by F.E. Analysis -- An Integrated Approach T.B. Khalil, M.Y. Sheh. Recent Trends and Advances in Crash Simulation and Design of Vehicles E. Haug, et al. Part VI: Multibody Dynamics Approaches. Rigid Flexible Multibody Equations of Motion Suitable for Vehicle Dynamics and Crash Analysis P.F. Nikravesh. Contact/Impact Dynamics Applied to Crash Analysis H.M. Lankarani. Multibody Dynamic Tools for Crashworthiness and Impact J.A.C. Ambrosio, M.S. Pereira. Part VII: Aircraft Crash Protection. Aircraft and Helicopter Crashworthiness: Design and Simulation C.M. Kindervater. Current Issues Regarding Aircraft Crash Injury Protection H.M. Lankarani. Part VIII: Conclusions and Future Trends. Crashworthiness of Transportation Systems: Current Issues and Future Trends J.A.C. Ambrosio, et al.

VALIDATED MULTIBODY MODEL FOR TRAIN CRASH ANALYSIS

The development of numerical simulation tools for train crashworthiness design requires their validation with reference crash scenarios similar, in nature, to the eventual collision conditions in which the new train designs have to be used. The modeling assumptions and the suitability of these tools can be verified using data feedback from experimental testing. In this work, a validated multibody-based model is presented for the design of train crashworthy components. In the proposed methodology, the moving components of a vehicle are described as sets of rigid bodies, with their relative motion constrained by kinematic joints. Rigid bodies connected by nonlinear force elements, which represent the lumped flexibility of the structural components, model the sub-structures that deform as a result of the train collisions. The characteristics of these nonlinear force elements represent the force-deformation curves of individual car-bodies extremities, couplers between car-bodies and stiffness of the suspensions springs. The wheel-rail contact is also represented by a model in which the normal and friction forces are present. The friction forces are described by Coulomb friction, which includes their dependency on static and dynamic friction coefficients. The contact forces between the end extremities of the colliding car-bodies, that model the longitudinal impact, include the action of anti-climber devices, which are designed to prevent sliding between the contacting buffers. The validated model is applied to the collision of two different trains, which have distinct specifications for the nonlinear force elements that represent the end extremities of the colliding car-bodies and their couplers. These two force-deformation curves correspond to the design specifications and to the experimental data acquired in a crash test. The validation of the model is discussed considering the deviations between the results of the test and the numerical tool with both design and experimental specifications. It is shown that the simulation of the model with the design specifications, characterized by elastic-perfectly plastic deformation curves for the structural elements, leads to results similar to those observed in the experimental test. When the force-deformation curves obtained experimentally are used to represent the structural elements the correlation between simulation and experimental test results increases significantly.

Distributed and discrete nonlinear deformations on multibody dynamics

Two different multibody dynamics formulations for the simulation of systems experiencing material and geometric nonlinear deformations while undergoing gross motion are presented in this paper. In the first, an updated Lagrangean formulation is used to derive the equilibrium equations of the flexible body while the finite element method is subsequently applied to obtain a numerical description for the equations of motion. The computational efficiency of the formulation is increased by using a lumped mass description of the flexible body mass matrix and referring the nodal accelerations to the inertial frame. In the resulting equations of motion the flexible body mass matrix is constant and diagonal while the full nonlinear deformations and the inertia coupling description are still preserved. In some cases the flexible components present zones of concentrated deformations resulting from local instabilities. The remaining structure of the system behaves either as rigid bodies or as linear elastic bodies. The second formulation presents a discrete model where all the nonlinear deformations are concentrated in the plastic hinges assuming the multibody components are as being either rigid or flexible with linear elastodynamics. The characteristics of the plastic hinges are obtained from numerical or experimental crush tests of specific structural components. The structural impact of a train carbody against a rigid wall and the performance of its end underframe in a collision situation is studied with the objective of assessing the relative merits of the formulations presented herein. The results are compared with those obtained by experimental testing of a full scale train and conclusions on the application of these methodologies to large size models are drawn.

Treatment of Impact with Friction in Planar Multibody Mechanical Systems

Frictional impact analysis ofmultibody mechanical systems has traditionally reliedon the use of Newtons hypothesis for the definitionof the coefficient of restitution. This approach hasin some cases shown energy gains inherent in the useof Newtons hypothesis. This paper presents a generalformulation, consistent with energy conservationprinciples, for the analysis of impact problems withfriction in any planar multibody mechanical system.Poissons hypothesis is instead utilized for thedefinition of the coefficient of restitution. Acanonical form of Cartesian momentum/impulse-balanceequations are assembled and solved for the changes inthe momenta using an extension of Rouths graphicalmethod for the normal and tangential impulses. Impulse process diagrams are numerically generated,and the Cartesian velocity or momenta jumps arecalculated by balancing the accumulated system momentaduring the contact period. This formulation recognizesthe correct mode of impact, i.e., sliding, sticking,and reverse sliding. Impact problems are classifiedinto seven cases, based on these three modes and theconditions during the compression and restitutionphases of impact. Expressions are derived for thenormal and tangential impulses corresponding to eachimpact case. The developed formulation is shown to bean effective tool in analyzing some frictional impactproblems including frictional impact in a two-bodysystem, an open-loop system, and a closed-loopsystem.

Design of train crash experimental tests by optimization procedures

Abstract Advanced train crashworthiness design requires not only numerical simulation tools capable of describing the dynamic response of train sets during general crash scenarios, but also, optimization procedures that can be used efficiently in the earlier design stages. A multibody dynamics based methodology that combines optimization with efficient analysis techniques is proposed in this work, for the design of train crashworthy components. In this methodology, the components of the trains are described as rigid bodies that have their relative motion constrained by kinematic joints and among which there are nonlinear spring-damper type elements that represent the structures of the trains that deform under normal operating conditions or during the train crash. Interaction between the colliding trains components are described by contact detection and contact force models. A planar dynamics formulation is used to access out-of-direction dynamics of the train cars. Through the use of an optimization algorithm, a general design framework is developed for single objective optimization problems, applied to the design of train crashworthy components. The selection of any optimization function is allowed, particularly, the ones related with train crashworthiness such as train car accelerations, deformations of train car structures or energy absorbed during train impact. Design variables related to the characteristics of the train car structures or components are used, such as train car mass or material behavior of train car structures defined by force-displacement curves. This methodology is applied to optimize the characteristics of complete train sets to design full-scale experimental crash tests. The results are compared with those obtained in simplified unidimensional multibody train models, using optimization algorithms that do not use analytical sensitivity information.

A multibody methodology for the design of anti-climber devices for train crashworthiness simulation

Abstract The impact of train sets is characterized by a very high potential for the longitudinal instability of the train resulting in overriding of the individual car-bodies. Consequently, the end-underframe structural mechanisms for crash energy management are not loaded and the train kinetic energy has to be dissipated by structural components not designed for that purpose. In this work, a multibody-based methodology is presented for the study of train crashworthiness including the anti-climber devices. The simulation of train impact requires models for the structures of the individual train car-bodies, contact forces between train components, systems and mechanisms responsible for the connections between vehicles. The most important motions of the train set are developed in the vertical plane, therefore, the methodology now developed uses a planar dynamics formulation. The vehicles are described by a set of rigid bodies with their relative motions constrained by kinematic joints. The forces that develop during contact, except for the joint reactions are modelled by nonlinear deformable elements. The mechanical characteristics of such elements represent the force-deformation structural response of each train car-body end, obtained by experimental testing or through detailed finite element models. The nonlinear characteristics of the suspension systems, the structural behaviour of the couplers and the friction forces between wheel-sets and rail arc also represented in these models. The anti-climber mechanical devices are modelled using the description of the contact between the train car-bodies ends. This is represented by a continuous contact force model, which accounts for the relative geometry between the car-body ends and material characteristics of the structural devices. The formulation is finally applied to train impacts in various crash scenarios, which are characterized by the collision of complete train sets with different velocities against stopped trains. The modelling assumptions and the suitability of the numerical tools developed are discussed in the framework of their application to the design of train crashworthy components.

Computational Dynamics in Multibody Systems

Preface. Dynamics of Constrained Systems Based on Mass-Orthogonal Projections M. Sofer, D. Bach, H. Brauchli. An Efficient Implementation of the Velocity Transformation Method for Real Time Dynamics with Illustrative Examples J.M. Jimenez, A.N. Avello, J. Garcia de Jalon, A.L. Avello. Efficient Object Oriented Programming of Multibody Dynamics Formalisms U. Rein. A Relational Data Base for General Mechanical Systems C. Hardell, A. Stensson, P. Jeppsson. A Method for Linearization of the Dynamic Equations of Flexible Multibody Systems Y. Li, C. Gontier. Efficient Modelling of General Multibody Dynamic Systems with Flexible Components K.S. Anderson. Elimination of Constraint Equations from Flexible Mechanical Systems D.M. Russel, K.D. Willmer. Eigenvalue Analysis in Flexible Multibody Dynamics Using the Non-Symmetric Lanczos Algorithm D.B. Doan, M. Geradin, N. Kill. Optimal Design and Location of Manipulators M. Ceccarelli. Identification of Minimum Set Parameters of Flexible Robots P. Chedmail, F. Bennis, P. Depince. Safety and Survivability Analysis of Wall-Climbing Robot B. Bahr, G. Li. Synthesis of Spatial Mechanisms Using Optimization and Continuation Methods J.M. Hansen. Modelling of Automotive Vehicles for Motion Control Studies A. Costa, R.P. Jones. Numerical Investigation of the Influence of the Shock Absorber on the Vertical Force Transmissibility of a McPherson Suspension E. Pisino, J. Giacomin, P. Campanile. Impact Dynamics of Multibody Mechanical Systems and Application to Crash Responses of Aircraft Occupant/Structure H.M. Lankarani, D. Ma, R. Menon. Data Fitting Methodology for Frontal Crash Victim Simulation C. Goualou, E. Vittecoq, J.P. Faidy. Quasi-Static Modelling of the Multibody System Dynamics Taking into Accountthe Friction Forces E.V. Zakhariev. Application of Multibody Dynamics to the Crashworthiness Optimization of Vehicle Structures J. Dias, M.S. Pereira. Index.