Efficient Loads Analyses of Shuttle-Payloads Using Dynamic Models With Linear Or Nonlinear Interfaces

1990 ◽  
Vol 112 (3) ◽  
pp. 366-373 ◽  
Author(s):  
P. D. Spanos ◽  
T. T. Cao ◽  
D. A. R. Nelson ◽  
D. A. Hamilton
Keyword(s):  
Dynamic Model ◽  
Dry Friction ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Space Shuttle ◽  
Equations Of Motion ◽  
Combined System ◽  
Time Step ◽  
Upper Stage ◽  
Loads Analysis

A technique is presented for conducting efficient loads analyses of Shuttle-payloads systems with linear or nonlinear attachment interfaces. The technique relies on representing the Space Shuttle and the payloads with physical and modal coordinates. Further, by invoking a standard algorithm of numerical integration of equations of motion, the kinematics of the interface degrees of freedom at a given time are determined without calculating the modes of the combined system involving the Space Shuttle and the payload. If the Shuttle-payloads interface coupling induces a linear dynamic model for the loads analysis, the equations of motion of the Shuttle and the payload are integrated separately step-by-step in time. If the dynamic model is nonlinear, the equations of motion of the Shuttle and the payload are again integrated separately. However, in the latter case an iterative procedure is used within a time step to converge to reliable values of the nonlinear terms of the equations of motion. The usefulness of the proposed technique is demonstrated by conducting a loads analysis for the Shuttle abort landing event with the Inertia Upper Stage (IUS) booster carrying a Tracking and Data Relay Satellite (TDRS) in the payload bay. This combined system has at its interface dry friction and hydraulic nonlinear dampers. For the analysis of this system, the discontinuous signum function used traditionally in modeling dry friction is replaced by an expeditious continuous approximation. Because of its efficiency and versatility, the new technique deserves serious consideration for becoming a standard tool for linear or nonlinear analysis of combined systems, in general, and of Shuttle-payloads systems, in particular.

Vibration analysis of multiple degrees of freedom mechanical system with dry friction

2012 ◽  
Vol 227 (7) ◽  
pp. 1505-1514 ◽  
Author(s):  
SD Yu ◽  
BC Wen
Keyword(s):  
Mechanical System ◽  
Dry Friction ◽  
Degrees Of Freedom ◽  
Simple Procedure ◽  
Mathematical Problem ◽  
Equations Of Motion ◽  
Inequality Constraints ◽  
Integration Scheme ◽  
Time Step ◽  
Multiple Degrees Of Freedom

This article presents a simple procedure for predicting time-domain vibrational behaviors of a multiple degrees of freedom mechanical system with dry friction. The system equations of motion are discretized by means of the implicit Bozzak–Newmark integration scheme. At each time step, the discontinuous frictional force problem involving both the equality and inequality constraints is successfully reduced to a quadratic mathematical problem or the linear complementary problem with the introduction of non-negative and complementary variable pairs (supremum velocities and slack forces). The so-obtained complementary equations in the complementary pairs can be solved efficiently using the Lemke algorithm. Results for several single degree of freedom and multiple degrees of freedom problems with one-dimensional frictional constraints and the classical Coulomb frictional model are obtained using the proposed procedure and compared with those obtained using other approaches. The proposed procedure is found to be accurate, efficient, and robust in solving non-smooth vibration problems of multiple degrees of freedom systems with dry friction. The proposed procedure can also be applied to systems with two-dimensional frictional constraints and more sophisticated frictional models.

Development of a reduced dynamic model for comfort evaluation of rail vehicle systems

2016 ◽  
Vol 230 (4) ◽  
pp. 489-504 ◽  
Author(s):  
Mortadha Graa ◽  
Mohamed Nejlaoui ◽  
Ajmi Houidi ◽  
Zouhaier Affi ◽  
Lotfi Romdhane
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Railway Vehicle ◽  
Passenger Comfort ◽  
Rail Vehicle ◽  
Vehicle System ◽  
Comfort Evaluation ◽  
Complex Models ◽  
Reduced Dynamic

In this paper, an analytical reduced dynamic model of a rail vehicle system is developed. This model considers only 38 degrees of freedom of the rail vehicle system. This reduced model can predict the dynamic behaviour of the rail vehicle while being simpler than existing dynamic models. The developed model is validated using experimental results found in the bibliography and its results are compared with existing more complex models from the literature. The developed model is used for the passenger comfort evaluation, which is based on the value of the weighted root mean square acceleration according to the ISO 2631 standard. Several parameters of the system, i.e., passenger position, loading of the railway vehicle and its speed, and their effect on the passenger comfort are investigated. It was shown that the level of comfort is mostly affected by the speed of the railway vehicle and the position of the seat. The load, however, did not have a significant effect on the level of comfort of the passenger.

scholarly journals Computational Modeling: Human Dynamic Model

2021 ◽  
Vol 15 ◽  
Author(s):  
Lijia Liu ◽  
Joseph L. Cooper ◽  
Dana H. Ballard
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Movement Analysis ◽  
Human Movement ◽  
Uncontrolled Manifold ◽  
Human In The Loop ◽  
Joint Forces ◽  
Internal Joint ◽  
Movement Function

Improvements in quantitative measurements of human physical activity are proving extraordinarily useful for studying the underlying musculoskeletal system. Dynamic models of human movement support clinical efforts to analyze, rehabilitate injuries. They are also used in biomechanics to understand and diagnose motor pathologies, find new motor strategies that decrease the risk of injury, and predict potential problems from a particular procedure. In addition, they provide valuable constraints for understanding neural circuits. This paper describes a physics-based movement analysis method for analyzing and simulating bipedal humanoid movements. The model includes the major body segments and joints to report human movements' energetic components. Its 48 degrees of freedom strike a balance between very detailed models that include muscle models and straightforward two-dimensional models. It has sufficient accuracy to analyze and synthesize movements captured in real-time interactive applications, such as psychophysics experiments using virtual reality or human-in-the-loop teleoperation of a simulated robotic system. The dynamic model is fast and robust while still providing results sufficiently accurate to be used to animate a humanoid character. It can also estimate internal joint forces used during a movement to create effort-contingent stimuli and support controlled experiments to measure the dynamics generating human behaviors systematically. The paper describes the innovative features that allow the model to integrate its dynamic equations accurately and illustrates its performance and accuracy with demonstrations. The model has a two-foot stance ability, capable of generating results comparable with an experiment done with subjects, and illustrates the uncontrolled manifold concept. Additionally, the model's facility to capture large energetic databases opens new possibilities for theorizing as to human movement function. The model is freely available.

Toward a Minimal Dynamic Model of a 6-DOF Parallel Robot

1997 ◽  
Author(s):  
L. Beji ◽  
M. Pascal ◽  
P. Joli
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Computational Cost ◽  
Closed Form Solution ◽  
Parallel Robot ◽  
Form Solution ◽  
Lagrangian Formalism ◽  
Inverse Kinematic Problem ◽  
Geometrical Properties

Abstract In this paper, an architecture of a six degrees of freedom (dof) parallel robot and three limbs is described. The robot is called Space Manipulator (SM). In a first step, the inverse kinematic problem for the robot is solved in closed form solution. Further, we need to inverse only a 3 × 3 passive jacobian matrix to solve the direct kinematic problem. In a second step, the dynamic equations are derived by using the Lagrangian formalism where the coordinates are the passive and active joint coordinates. Based on geometrical properties of the robot, the equations of motion are derived in terms of only 9 coordinates related by 3 kinematic constraints. The computational cost of the obtained dynamic model is reduced by using a minimum set of base inertial parameters.

A Study on Sensitivity of Maneuverability Performance on the Hydrodynamic Coefficients for Submerged Bodies

2000 ◽  
Vol 44 (03) ◽  
pp. 186-196
Author(s):  
Debabrata Sen
Keyword(s):  
Dynamic Model ◽  
Dynamic Models ◽  
Equations Of Motion ◽  
Inertial Force ◽  
Axisymmetric Body ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Simulated Trajectory ◽  
Linear Damping

Based on a constant-coefficient dynamic model, a study was made to determine the influence of various hydrodynamic coefficients on the predicted maneuverability quality of submerged bodies. Two types of geometries were considered, a submarine and an axisymmetric slender geometry. For the submarine, the equations of motion used were the revised standard submarine equations (Feldman 1979) while for the latter geometry a dynamic model was developed. From computer simulation of a few selected definitive maneuvers based on these two different dynamic models for the two geometries, the sensitivity of the simulated trajectory on changes in different coefficients was found. The results quantified in form of sensitivity values are presented. It is found that the typical measures from the maneuvers do not depend significantly on most of the nonlinear coefficients. The coefficients having significant effects on the trajectories are found to be the linear damping coefficients for the submarine and the linear inertial force coefficients for the axisymmetric body.

On the Efficiency of Some Recently Developed Integration Algorithms for Offshore Problems

1983 ◽  
Vol 105 (1) ◽  
pp. 73-77 ◽  
Author(s):  
T. K. Datta ◽  
A. M. Sood
Keyword(s):  
Degrees Of Freedom ◽  
Large Time ◽  
Equations Of Motion ◽  
Iterative Solution ◽  
Response Analysis ◽  
Time Step ◽  
Beam Elements ◽  
Integration Schemes ◽  
Large Time Step ◽  
Integration Algorithms

The efficiency of some recently developed integration schemes, namely, Hilber’s ∝-method, collocation schemes and large time step integration schemes developed by Argyris, is evaluated by applying them to the response analysis of an idealized offshore tower. The tower is fixed at the base, having an additional mass at the top. For the analysis the tower has been modeled as an assemblage of 2-D beam elements. The dynamic degrees of freedom at each node are taken as those corresponding to the rotational and sway degrees of freedom. Using the normal mode theory the equations of motion have been decoupled except for the generalized loading vector which appear nonlinearly coupled, thus requiring iterative solution at every time step. The results of the study show that the large time step integration schemes developed by Argyris are more efficient than other integration methods considered here.

A Three-Dimensional Dynamic Model for Determining the Equilibrium Configurations of Buoyantly Unstable Icebergs

1990 ◽  
Vol 112 (3) ◽  
pp. 253-262
Author(s):  
R. G. Jessup ◽  
S. Venkatesh
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Static Potential ◽  
Initial State ◽  
Model Simulations ◽  
Six Degrees Of Freedom ◽  
Equilibrium Configurations ◽  
Variation Range

This paper describes a dynamic model developed for the purpose of determining the final equilibrium configurations of buoyantly unstable icebergs. The model places no restrictions on the size, shape, or dimensionality of the iceberg, or on the variation range of the configuration coordinates. Furthermore, it includes all six degrees of freedom and is based on a Lagrangian formulation of the dynamic equations of motion. It can be used to advantage in those situations in which the iceberg has a complicated potential function and can acquire enough momentum and kinetic energy in the initial phase of its motion to make its final configuration uncertain on the basis of a static potential analysis. The behavior of the model is examined through several model simulations. The sensitivity of the final equilibrium position to the initial orientation and shape of the iceberg is clearly evident in the model simulations. Model simulations also show that when an iceberg is released from a nonequilibrium initial state, the time taken for it to settle down varies from about 40 s for a growler to nearly 400 s for a large iceberg. While these absolute times may change with better parameterization of the forces, the relative variations with iceberg size are likely to be preserved.

A New Approach to Modeling Surface Defects in Bearing Dynamics Simulations

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Ankur Ashtekar ◽  
Farshid Sadeghi ◽  
Lars-Erik Stacke
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Surface Defects ◽  
Equations Of Motion ◽  
Infinite Domain ◽  
Step Size ◽  
Deep Groove ◽  
Dynamics Simulations ◽  
Bearing Dynamics

A dynamic model for deep groove and angular contact ball bearings was developed to investigate the influence of race defects on the motions of bearing components (i.e., inner and outer races, cage, and balls). In order to determine the effects of dents on the bearing dynamics, a model was developed to determine the force-deflection relationship between an ellipsoid and a dented semi-infinite domain. The force-deflection relationship for dented surfaces was then incorporated in the bearing dynamic model by replacing the well-known Hertzian force-deflection relationship whenever a ball/dent interaction occurs. In this investigation, all bearing components have six degrees-of-freedom. Newton’s laws are used to determine the motions of all bearing elements, and an explicit fourth-order Runge–Kutta algorithm with a variable or constant step size was used to integrate the equations of motion. A model was used to study the effect of dent size, dent location, and inner race speed on bearing components. The results indicate that surface defects and irregularities like dent have a severe effect on bearing motion and forces. Furthermore, these effects are even more severe for high-speed applications. The results also demonstrate that a single dent can affect the forces and motion throughout the entire bearing and on all bearing components. However, the location of the dent dictates the magnitude of its influence on each bearing component.

Static and Vibration Analyses of a Three-Dimensional Snake-Like Micropositioning Stage

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Nicola Scuor ◽  
Paolo Gallina ◽  
Marco Giovagnoni
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Natural Frequencies ◽  
Three Dimensional ◽  
Dynamic Tests ◽  
Lumped Mass ◽  
Simulation Data ◽  
End Effector ◽  
Three Degrees Of Freedom

This paper presets three degrees of freedom (DOF) piezoelectric micropositioning stage. The stage is composed of a stack of piezodisk bender actuators actuated in such a way to prevent the end-effector from rotating; this way the end-effector can only translate along the x, y, and z axes. Thanks to its snake-like configuration, the system is capable of large displacements (of the order of 50 μm) with low driving voltages (of the order of 100 V). Several lumped-mass static and dynamic models of the device have been implemented. Static experimental results, which are in agreement with simulation data, confirmed the performances of the device. A dynamic model showed the natural frequencies of the mechanism. Also dynamic tests have been conducted in order to validate the dynamic model.

Numerical Solution of Vehicle-Bridge Coupling Vibration

2013 ◽  
Vol 859 ◽  
pp. 76-79
Author(s):  
Ze Peng Wen
Keyword(s):  
Numerical Solution ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Reliability And Validity ◽  
Element Model ◽  
Interaction Force ◽  
Integration Scheme ◽  
Coupled Vibration ◽  
Time Step ◽  
Coupling Vibration

The bridge simplified two-dimensional plane beam element model, Simplified to two degrees of freedom quarter vehicle model, The entire bridge system is divided into two subsystems vehicle and bridge, Using separate equations of motion of vehicles and bridges, Proposed bridge systems numerical solution of coupled vibration analysis, The law at the wheel in contact with the deck displacement compatibility conditions for a balanced relationship with the interaction force associated, At each time step using the Newmark-β integration scheme, Through this paper the numerical solution results do comparison with the literature, the results show that the proposed method is reliability and validity.

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