• Jorge Ambr'osio


INTRODUCTJON • Models for the simulation of sports activities with body impact draw many of their features fram the use of multibody dynamics. The efficiency and accuracy of the numerical procedures for the simulation of the human body is of utmost importance. The model mus! describe precisely the relative range of motion of the different segments of the human body, the forces transmilted between them and the impactlcontact that involve biomechanieal components. Based on a general methodology using natural coordinates, a whole body response is presented in this work, The joints between biomeehanical segments are defined by forcing adjaeent bodies to share common points and vectors used in their definition. lmproved efficieney in the integration proeess of the equations of motion is obtained using an augmented Lagrange formulation The realistic relative range of motion for the body segments is obtained introdueing ~ set of penalty forees in the model rather than setting up unilateral eonstraints between system components. These forces are reaction moments between segments of the biomechanical model that prevent it from achieving physically unacceptable positions. The contact between the segments of the biomechanical model and the environment is modeled using a nonlinear force contact model based on the Hertzian eonlact theory This modellakes into account the energy dissipation due to localized effects. RESUlTS • The biomechanical model is finally applied in different situations of human motion where activation of the museie farees do not playa role. The cases of a ear driver during a crash and a player during a unexpected tackle are simulated in order to demonstrate lhe methodology. CONCLUSIONS -The methodology proposed shows a good aptitude to describe the results neeessary to fully analyse the human body motion Among these, the reaction forees between the biomechanical segments are fully available. The contaet between body and surrounding objeets is efficiently modelIed including energy dissipation due to local deformations. REFERENCES Jalon, J.G. (1994). Kinematic and dynamic simulation of multibody systems, Heidelberg: Springer-Verlag. Laananen, D. (1983). Computer Simulation of an aircrafl seat and oecupant in a crash environment -Val. 1: Technieal report, US Dep. of Transportatlon, F.A.A, Technical Report DOT/FAA/CT-82/33-1. CIBA GEIGY, (1979). Folia Rheumatologica, Motilität von Hüfte, Schulter, Hand und Fub, GrubH Wehr/Baden, Lankarani, H. (1995). Impact dynamics of multibody mechanical systems and applieation 10 crash responses of aireraft occupantlstructure. Compulational Dyna-mies in Multibody Systems, (eds. M.Pereira e J.Ambr6sio) Kluwer. 239-265. 49