Dynamic analysis of space structures including elastic, multibody, and control behavior

The problem is to develop analysis methods, modeling stategies, and simulation tools to predict with assurance the on-orbit performance and integrity of large complex space structures that cannot be verified on the ground. The problem must incorporate large reliable structural models, multi-body flexible dynamics, multi-tier controller interaction, environmental models including 1g and atmosphere, various on-board disturbances, and linkage to mission-level performance codes. All areas are in serious need of work, but the weakest link is multi-body flexible dynamics

Masticatory biomechanics in the rabbit : a multi-body dynamics analysis

Acknowledgement We thank Sue Taft (University of Hull) for the µCT-scanning of the rabbit specimen used in this study. We also thank Raphaël Cornette, Jacques Bonnin, Laurent Dufresne, and l'Amicale des Chasseurs Trappistes (ACT) for providing permission and helping us capture the rabbits used for the in vivo bite force measurements at la Réserve Naturelle Nationale de St Quentin en Yvelines, France.Peer reviewedPublisher PD

From multi-body to many-body dynamics

This article provides a brief historical review of multi-body dynamics analysis, initiated by the Newtonian axioms through constrained (removed degrees of freedom) Lagrangian dynamics or restrained (resisted degrees of freedom) Newton–Euler formulation. It provides a generic formulation method, based on system dynamics in a reduced configuration space, which encompasses both the aforementioned methods and is applicable to any cluster of material points. A detailed example is provided to show the integration of other physical phenomena such as flexibility and acoustic wave propagation into multi-body dynamics analysis. It is shown that in the scale of minutiae, when the action potentials deviate from Newtonian laws, the forces are often described by empirical or stochastic functions of separation and the medium of interactions. These make for complex analyses and distinguish a host of many body problems from Newtonian laws of motion. A simple example is provided to demonstrate this. It is suggested that unification of many-body analysis with that of multi-body dynamics is incumbent on the fundamental understanding of interaction potentials at close separations

Influence of Interfacial Dynamics and Multi-Dimensional Coupling from Isolator Brackets on Exhaust Isolation System Performance

An automotive exhaust structure is a primary structure-borne noise path by which vibratory forces from the powertrain are transmitted to the vehicle body. The exhaust structure is typically connected to the vehicle body through a system of brackets containing elastomeric isolators, serving as the principal means of vibration isolation. In exhaust isolator system design, the isolator brackets are often modeled as simple springs. This approach neglects the effects of interfacial dynamics and multi-dimensional coupling, which result from distributed mass and stiffness throughout the isolator brackets. Accordingly, the objective of this research is to better understand how the interfacial dynamics and multi-dimensional coupling of the isolator brackets affect the exhaust isolation system performance in the 0-100 Hz range. Therefore, models with a proper representation of these interfacial dynamics and multi-dimensional coupling are created using finite element analysis (FEA) and then parameterized into multi-dimensional lumped parameter models through correlation of static and modal testing on the components and assembled system. The dynamic responses from the models for the exhaust structure and isolator brackets are then combined into a system-level model through a frequency-response-function-based substructuring method. A design study is conducted on the system-level model by systematically changing component parameters and evaluating the effect on the transmitted vertical body forces. The results show that the inclusion of these interfacial dynamics have nominal influence on isolation performance; however, the coupling terms show an observable influence, typically increasing the force transmitted to the vehicle body. In addition, the study identified additional design modifications that could improve isolation performance, such as an increase in isolator material loss factor and an increase in the isolator fore-aft stiffness. Although the results are specific to this isolation system design, the modeling procedure outlined has the potential to be used early in the vehicle design process to identify improvements to other baseline designs.NSF I/UCRC Smart Vehicle Concepts CenterTenneco, Inc.A three-year embargo was granted for this item.Academic Major: Mechanical Engineerin

Simulation of spacecraft attitude dynamics using TREETOPS and model-specific computer Codes

The simulation of spacecraft attitude dynamics and control using the generic, multi-body code called TREETOPS and other codes written especially to simulate particular systems is discussed. Differences in the methods used to derive equations of motion--Kane's method for TREETOPS and the Lagrangian and Newton-Euler methods, respectively, for the other two codes--are considered. Simulation results from the TREETOPS code are compared with those from the other two codes for two example systems. One system is a chain of rigid bodies; the other consists of two rigid bodies attached to a flexible base body. Since the computer codes were developed independently, consistent results serve as a verification of the correctness of all the programs. Differences in the results are discussed. Results for the two-rigid-body, one-flexible-body system are useful also as information on multi-body, flexible, pointing payload dynamics

Linear dynamic modeling of spacecraft with various flexible appendages and on-board angular momentums

We present here a method and some tools developed to build linear models of multi-body systems for space applications (typically satellites). The multi-body system is composed of a main body (hub) fitted with rigid and flexible appendages (solar panels, antennas, propellant tanks,...) and on-board angular momentums (flywheels, control moment gyros). Each appendage can be connected to the hub by a cantilever joint or a pivot joint. More generally, our method can be applied to any open mechanical chain. In our approach, the rigid six degrees of freedom (d.o.f) (three translational and three rotational) are treated all together. That is very convenient to build linear models of complex multi-body systems. Then, the dynamics model used to design AOCS, i.e. the model between forces and torques (applied on the hub) and angular and linear position and velocity of the hub, can be derived very easily. This model can be interpreted using block diagram representation

Different Scenarios for Critical Glassy Dynamics

We study the role of different terms in the $N$-body potential of glass forming systems on the critical dynamics near the glass transition. Using a simplified spin model with quenched disorder, where the different terms of the real $N$-body potential are mapped into multi-spin interactions, we identified three possible scenarios. For each scenario we introduce a ``minimal'' model representative of the critical glassy dynamics near, both above and below, the critical transition lin e. For each ``minimal'' model we discuss the low temperature equilibrium dynamics.Comment: Completely revised version, 8 pages, 5 figures, typeset using EURO-LaTeX, Europhysics Letters (in press