Time Response of Linear Elastic Systems Using Mode Superposition Technique

2017 ◽  
pp. 465-495
Author(s):  
Karan S. Surana ◽  
J. N. Reddy
Keyword(s):  
Time Response ◽  
Mode Superposition ◽  
Linear Elastic ◽  
Elastic Systems ◽  
Superposition Technique

Control of Elastic Systems via Passivity-Based Methods

2004 ◽  
Vol 10 (11) ◽  
pp. 1699-1735 ◽  
Author(s):  
A. G. Kelkar ◽  
S. M. Joshi
Keyword(s):  
Flexible Structures ◽  
Robotic Manipulators ◽  
Mathematical Concept ◽  
Controller Synthesis ◽  
Control Laws ◽  
Linear Elastic ◽  
Elastic Systems ◽  
Different Types ◽  
Linear Controllers ◽  
Synthesis Approach

In this paper we present a controller synthesis approach for elastic systems based on the mathematical concept of passivity. For nonlinear and linear elastic systems that are inherently passive, robust control laws are presented that guarantee stability. Examples of such systems include flexible structures with col-located and compatible actuators and sensors, and multibody space-based robotic manipulators. For linear elastic systems that are not inherently passive, methods are presented for rendering them passive by compensation. The “passified” systems can then be robustly controlled by a class of passive linear controllers that guarantee stability despite uncertainties and inaccuracies in the mathematical models. The controller synthesis approach is demonstrated by application to five different types of elastic systems.

Time Response Stress Analysis of Solid and Reinforced Thin-Walled Structures by Component-Wise Models

2020 ◽  
pp. 2043010
Author(s):  
R. Azzara ◽  
E. Carrera ◽  
M. Filippi ◽  
A. Pagani
Keyword(s):  
Stress State ◽  
Complex Stress ◽  
Time Response ◽  
Modeling Technique ◽  
Integration Scheme ◽  
Structural Domain ◽  
Mode Superposition ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
Stress States

This paper deals with the evaluation of time response analyses of typical aerospace metallic structures. Attention is focussed on detailed stress state distributions over time by using the Carrera Unified Formulation (CUF) for modeling thin-walled reinforced shell structures. In detail, the already established component-wise (CW) approach is extended to dynamic time response by mode superposition and Newmark direct integration scheme. CW is a CUF-based modeling technique which allows to model multi-component structures by using the same refined finite element for each structural component, e.g. stringers, panels, ribs. Component coupling is realized by imposing displacement continuity without the need of mathematical artifices in the CW approach, so the stress state is consistent in the entire structural domain. The numerical results discussed include thin-walled open and closed section beams, wing boxes and a benchmark wing subjected to gust loading. They show that the proposed modeling technique is effective. In particular, as CW provides reach modal bases, mode superposition can be significantly efficient, even in the case of complex stress states.

On the Stability of Elastic Systems Subjected to Nonconservative Forces

1964 ◽  
Vol 31 (3) ◽  
pp. 435-440 ◽  
Author(s):  
G. Herrmann ◽  
R. W. Bungay
Keyword(s):  
Critical Loads ◽  
Kinetic Method ◽  
Euler Method ◽  
Parameter Instability ◽  
Linear Elastic ◽  
Elastic Systems ◽  
Nonconservative Loading ◽  
The Stability ◽  
Two Degree Of Freedom ◽  
Increasing Load

Free motions of a linear elastic, nondissipative, two-degree-of-freedom system, subjected to a static nonconservative loading, are analyzed with the aim of studying the connection between the two instability mechanisms (termed divergence and flutter by analogy to aeroelastic phenomena) known to be possible for such systems. An independent parameter is introduced to reflect the ratio of the conservative and nonconservative components of the loading. Depending on the value of this parameter, instability is found to occur for compressive loadings by divergence (static buckling), flutter, or by both (at different loads) with multiple stable and unstable ranges of the load. In the latter case either type of instability may be the first to occur with increasing load. For a range of the parameter, divergence (only) is found to occur for tensile loads. Regardless of the non-conservativeness of the system, the critical loads for divergence can always be determined by the (static) Euler method. The critical loads for flutter (occurring only in nonconservative systems) can be determined, of course, by the kinetic method alone.

On-Board Detection of Derailed Wheel and Wheel Defects

2007 ◽  
Author(s):  
Som P. Singh ◽  
Srinivas Chitti ◽  
S. K. Punwani ◽  
Monique F. Stewart
Keyword(s):  
Ride Quality ◽  
Monitoring Systems ◽  
Vertical Acceleration ◽  
Linear Elastic ◽  
Bearing Defects ◽  
Elastic Systems ◽  
Wheel Model ◽  
Board Monitoring ◽  
Wheel Flat ◽  
Railroad Safety

To improve railroad safety and efficiency, the Office of Research and Development of the Federal Railroad Administration (FRA) is running a project to develop and demonstrate an On-Board Monitoring Systems Concept (OBMSC) for freight trains. The project scope includes onboard detection of hot bearings, bearing defects, vehicle, ride quality, wheel tread defects, and derailed wheels. This paper presents an analytical model to detect derailed wheel conditions. In the model, an idealized wheelset with associated sprung and unsprung vehicle masses running on crossties is simulated using LS-Dyna software. Track structure (i.e., ties) ballast/subgrade, and soil are represented as linear elastic systems. This paper identifies wheelset vertical acceleration magnitude and associated frequencies for a derailed wheel for empty and loaded car conditions at various operating speeds. The research shows that the predicted wheelset acceleration magnitude for a derailed wheel overlap with those resulting from wheel tread defects, such as wheel flat, shells, and built-up tread. To differentiate between a derailed wheel and wheels with tread defects, a set of criteria is formulated based on amplitude and frequency ranges. Based on the analytical results from the derailed wheel model and field-tested results of revenue service wheels with tread defects, it is established that the OBMSC bearing adapter acceleration (BAA) can be used to detect a derailed wheel and conditions communicated to the train crew or other appropriate parties.

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