scholarly journals Obtaining a Model and Control for a Rigid Body Motion System. 2nd Report. Case of a 2 Degrees of Freedom Link Motion System including Structural Nonliniearity, Nonlinear Driving Characteristics, Gravity and Friction.

2000 ◽  
Vol 66 (649) ◽  
pp. 2988-2995
Author(s):  
Takashi ANDO ◽  
Takuzo IWATSUBO
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Motion System ◽  
And Control

Dynamic Analysis of Flexible Supercavitating Vehicles Using Modal Based Elements

2003 ◽  
Author(s):  
Jou-Young Choi ◽  
Massimo Ruzzene ◽  
Olivier A. Bauchau
Keyword(s):  
Numerical Model ◽  
Rigid Body ◽  
Degrees Of Freedom ◽  
Structural Characteristics ◽  
Rigid Body Motion ◽  
Operating Conditions ◽  
Flight Mechanics ◽  
Body Motion ◽  
Supercavitating Vehicles ◽  
Elastic Modes

This presents a numerical model for the simulation of the flight mechanics behavior of flexible supercavitating vehicles. Supercavitating vehicles exploit supercavitation as a means to reduce drag and increase the underwater speed. In the proposed formulation, the vehicle’s rigid body motion is described by 6 degrees of freedom, which define pitch, yaw and roll motion and the displacement of the center of gravity with respect to a fixed inertial reference system. The forces applied to the vehicle include the control actions at the nose and at the fins, propulsion, gravity and cavity/vehicle periodic interactions associated to typical operating conditions. The elastic displacements are superimposed to the rigid body motion through a modal superposition technique. The mode synthesis is performed using Herting’s Transformation, which provides maximum flexibility in the selection of the elastic modes to be used for the used for the superposition, and the possibility of easily handling free-free modes. The developed numerical model predicts the dynamic response of the considered class of supercavitating vehicles resulting from assigned maneuvers. The analysis is motivated by the need of accurately modeling the structural characteristics of supercavitating vehicles in order to estimate vibrations in the structure and to envision and design systems that improve their guidance and control efficiency.

Calculations of non-linear waves generated by complex body motion

2000 ◽  
Vol 214 (6) ◽  
pp. 771-780 ◽  
Author(s):  
T Chen ◽  
A T Chwang
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Grid Method ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Promising Alternative ◽  
Potential Flows ◽  
Linear Waves ◽  
Non Linear ◽  
Marine Engineering

A structured and unstructured hybrid overlapping grid method is developed for simulating free-surface waves generated by submerged arbitrary bodies undergoing rigid body motion in multi-degrees of freedom. Exact boundary conditions are applied to the transient free and body surfaces. The accuracy, efficiency and generality of the present two-dimensional code for potential flows are validated by comparisons with available theories and experiments. Numerical experiments are reported in this paper to investigate the non-linear behaviour of waves due to the complex rigid body motion, in terms of wave patterns and the pressure distribution. Combining the best features of both grid systems for finite elements and finite differences, the present method provides a promising alternative in computational fluid dynamics for the design and analysis in marine engineering.

Modelling and Control of a Closed Chain Flexible Linkage

2000 ◽  
Author(s):  
R. Caracciolo ◽  
M. Giovagnoni ◽  
A. Rossi ◽  
A. Trevisani
Keyword(s):  
Rigid Body ◽  
Element Model ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Closed Chain ◽  
Control Scheme ◽  
Inertial Nonlinearities ◽  
And Control ◽  
Four Bar Linkage ◽  
Sampling Times

Abstract The objective of this paper is to describe and numerically test a control scheme for a flexible four-bar linkage. The dynamic response of the mechanism is reproduced by means of an accurate finite element model accounting for geometric and inertial nonlinearities. A reduced number of measured variables is selected to control both rigid-body motion and vibration separately without implementing an estimator of the state of the system. Rigid-body motion control is performed by means of a PID-like regulator while proportional controllers are employed to damp link oscillations. Appropriate devices are proposed to avoid coupling effects among variables. Numerical results demonstrate the effectiveness of the control when it operates at different sampling times.

Efficient Strain Based Triangular and Sector Elements for Elasticity Problems

2017 ◽  
Vol 33 ◽  
pp. 1-21
Author(s):  
Messaoud Bourezane
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Exact Representation ◽  
Independent Functions ◽  
Practical Engineering ◽  
Elasticity Problems

Utilising the strain based approach with exact representation of rigid body motion, an efficient way of constructing membrane elements will be proposed. The major problem encountered in practice is generally the compatibility between degrees of freedom of various elements [1-3]. A simple and efficient triangular and sector element are developed by the use of the strain based approach. They are based on the assumed independent functions for the various components of strain insofar as it is allowed by the compatibility equations. Theses elements produce results which are acceptable within practical engineering accuracy even when few elements are employed.

Lagrangian Formulation of the Equations of Motion for Elastic Mechanisms With Mutual Dependence Between Rigid Body and Elastic Motions: Part I—Element Level Equations

1990 ◽  
Vol 112 (2) ◽  
pp. 203-214 ◽  
Author(s):  
S. Nagarajan ◽  
David A. Turcic
Keyword(s):  
Rigid Body ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Nonlinear Differential Equations ◽  
Equations Of Motion ◽  
Realistic Model ◽  
Open Loop ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Elastic Links

Equations of motion are derived using Lagrange’s equation for elastic mechanism systems. The elastic links are modeled using the finite element method. Both rigid body degrees of freedom and the elastic degrees of freedom are considered as generalized coordinates in the derivation. Previous work in the area of analysis of general elastic mechanisms usually involve the assumption that the rigid body motion or the nominal motion of the system is unaffected by the elastic motion. The nonlinear differential equations of motion derived in this work do not make this assumption and thus allow for the rigid body motion and the elastic motion to influence each other. Also the equations obtained are in closed form for the entire mechanism system, in terms of a minimum number of variables, which are the rigid body and the elastic degrees of freedom. These equations represent a more realistic model of light-weight high-speed mechanisms, having closed and open loop multi degree of freedom chains, and geometrically complex elastic links.

Extracting Signatures for Rigid Body Motion and Modes of Coupled Vibration in Elastic Multi-Rod Mechanisms by POD Processing of the Finite Element Dynamics

2003 ◽  
Author(s):  
Ioannis T. Georgiou ◽  
Mohammad A. Bani-Khaled
Keyword(s):  
Rigid Body ◽  
Weak Coupling ◽  
Degrees Of Freedom ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Flexible Rods ◽  
Flexible Mechanism ◽  
Pod Analysis ◽  
Proper Orthogonal ◽  
Crank Mechanism

The method of Proper Orthogonal Decomposition for coupled dynamic fields is applied to systematically analyze the free dynamics, approximated by the method of finite elements, of a set of moving flexible rods and a two-rod flexible mechanism. The POD analysis identifies unique optimum degrees-of-freedom, Proper Orthogonal (PO) modes, for these systems. For moving stiff rods, the single dominant PO mode involves weak coupling of rigid body motion to deformation motion. The shapes of the PO modes for rigid body motion and vibration have invariant characteristic signatures for rigid body motion coupled to deformation motion. These signatures remain almost the same when two stiff rods are connected to form a slider-crank mechanism. The two dominant POMs of the mechanism represent rigid body mode of motion, which are coupled weakly to higher order PO modes. The weak coupling is due to the high rigidity of the rods in the mechanism.

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