Input Force Identification in Time Domain Using Optimally Placed Accelerometers

2012 ◽  
Author(s):  
Deepak K. Gupta ◽  
Anoop K. Dhingra
Keyword(s):  
Finite Number ◽  
Time Domain ◽  
Equilibrium Equation ◽  
Dynamic Loads ◽  
Acceleration Response ◽  
Acceleration Time ◽  
Input Force ◽  
Stiffness Matrices ◽  
Load Transducer ◽  
Selection Of

A technique in time domain is presented that aims at identifying dynamic loads acting on a structure from acceleration time response measured experimentally at finite number of locations on the structure. The structure essentially gets transformed into its own load transducer. The approach is based on the standard equilibrium equation in dynamics in time domain. For measurement of the acceleration response, there can be a large number of combinations of locations on the structure where the accelerometers can be mounted and the recovered loads may be quite sensitive to the locations selected for accelerometer placements. In fact, the precision with which the applied loads are estimated from measured acceleration response depends on the number of accelerometers utilized and their locations on the component. Implementation of a methodology to determine the optimum set of accelerometer locations, based on the sparse nature of the mass, damping and stiffness matrices, is presented to guide the selection of number and locations of accelerometers that will provide the most precise load estimates. A numerical validation that helps understand the main characteristics of the proposed approach is also presented. The numerical results reveal the effectiveness and utility of the proposed technique.

An Inverse Approach on Load Identification From Optimally Placed Accelerometers

2013 ◽  
Author(s):  
Deepak K. Gupta ◽  
Anoop K. Dhingra
Keyword(s):  
Natural Frequencies ◽  
Mode Shapes ◽  
Load Identification ◽  
Acceleration Response ◽  
Inverse Approach ◽  
Modal Damping ◽  
Modal Model ◽  
Load Transducer ◽  
Modal Coordinates ◽  
Selection Of

This paper presents an inverse approach for estimating dynamic loads acting on a structure from acceleration time response measured experimentally at finite number of optimally placed accelerometers on the structure. The structure acts as its own load transducer. The approach is based on the standard equilibrium equation of motion in modal coordinates. Modal model of a system is defined by its modal parameters — natural frequencies, corresponding mode shapes and modal damping factors. These parameters can be estimated experimentally from measured data, analytically for simple problems, or from finite element method. For measurement of the acceleration response, there can be a large number of combinations of locations on the structure where the accelerometers can be mounted and the results may be quite sensitive to the locations selected for accelerometer placements. In fact, the precision with which the applied loads are estimated from measured acceleration response depends on the number of accelerometers utilized and their location on the component. Implementation of a methodology to determine the optimum set of accelerometer locations, based on the construction of D-optimal design, is presented to guide the selection of number and locations of accelerometers that will provide the most precise load estimates. A technique based on model reduction is proposed to reconstruct the input forces accurately. A numerical validation that helps to understand the main characteristics of the proposed approach is also presented. The numerical results reveal the effectiveness and utility of the technique.

Physical Realization of Generic-Element Parameters in Model Updating

2002 ◽  
Vol 124 (4) ◽  
pp. 628-633 ◽  
Author(s):  
H. Ahmadian ◽  
J. E. Mottershead ◽  
M. I. Friswell
Keyword(s):  
Model Updating ◽  
Finite Element Models ◽  
Physical Realization ◽  
Governing Equations ◽  
Stiffness Matrices ◽  
Model Predictions ◽  
Physical Effects ◽  
Realization Process ◽  
Physical Phenomena ◽  
Selection Of

The selection of parameters is most important to successful updating of finite element models. When the parameters are chosen on the basis of engineering understanding the model predictions are brought into agreement with experimental observations, and the behavior of the structure, even when differently configured, can be determined with confidence. Physical phenomena may be misrepresented in the original model, or may be absent altogether. In any case the updated model should represent an improved physical understanding of the structure and not simply consist of unrepresentative numbers which happen to cause the results of the model to agree with particular test data. The present paper introduces a systematic approach for the selection and physical realization of updated terms. In the realization process, the discrete equilibrium equation formed by mass, and stiffness matrices is converted to a continuous form at each node. By comparing the resulting differential equation with governing equations known to represent physical phenomena, the updated terms and their physical effects can be recognized. The approach is demonstrated by an experimental example.

Dynamic Response of 3D Surface/Embedded Rigid Foundations of Arbitrary Shapes on Multi-Layered Soils in Time Domain

2019 ◽  
Vol 19 (09) ◽  
pp. 1950106 ◽  
Author(s):  
Zejun Han ◽  
Mi Zhou ◽  
Xiaowen Zhou ◽  
Linqing Yang
Keyword(s):  
Dynamic Response ◽  
Frequency Domain ◽  
Time Domain ◽  
Dynamic Stiffness ◽  
Dynamic Responses ◽  
Rigid Foundation ◽  
Layered Soils ◽  
Stiffness Matrices ◽  
The Time Domain ◽  
Arbitrary Shapes

Significant differences between the predicted and measured dynamic response of 3D rigid foundations on multi-layered soils in the time domain were identified due to the existence of uncertainties, which makes the issue a complicated one. In this study, a numerical method was developed to determine the dynamic responses of 3D rigid surfaces and embedded foundations of arbitrary shapes that are bonded to a multi-layered soil in the time domain. First, the dynamic stiffness matrices of the rigid foundations in the frequency domain are calculated via integral domain transformation. Secondly, a dynamic stiffness equation for rigid foundations in the time domain is established via the mixed variables formulation, which is based on the discrete dynamic stiffness matrices in the frequency domain. The proposed method can be applied to the treatment of systems with multiple degrees of freedom without losing the true information that concerns the coupling characteristics. Numerical examples are presented to demonstrate the accuracy of the proposed method for predicting the horizontal, vertical, rocking, and torsional vibrations. Further, a parametric study was carried out to provide insight into the dynamic behavior of the soil–foundation interaction (SFI) while considering soil nonhomogeneity. The results indicate that the elastic modulus of the soil has a significant impact on the dynamic responses of the rigid foundation. Finally, a numerical example of a rigid foundation resting on a six-layered, semi-infinite soil demonstrates that the proposed method can be used to deal with multi-layered media in the time domain in a relatively easy way.

Analysis of Brief Tension Loss in TLP Tethers

1988 ◽  
Vol 110 (1) ◽  
pp. 43-47 ◽  
Author(s):  
J. N. Brekke ◽  
T. N. Gardner
Keyword(s):  
Time Domain ◽  
Large Diameter ◽  
Nonlinear Effects ◽  
Response Analysis ◽  
Bending Stress ◽  
Large Wave ◽  
Wave Trough ◽  
Design Selection ◽  
The Time Domain ◽  
Selection Of

The avoidance of “slack” tethers is one of the factors which may establish the required tether pretension in a tension leg platform (TLP) design. Selection of an appropriate safety factor on loss of tension depends on how severe the consequences may be. It is sometimes argued that if tethers go slack, the result may be excessive platform pitch or roll motions, tether buckling, or “snap” or “snatch” loading of the tether. The results reported here show that a four-legged TLP would not be susceptible to larger angular motions until two adjacent legs lose tension simultaneously. Even then, this analysis shows that a brief period of tether tension loss (during the passage of a large wave trough) does not lead to excessive platform motion. Similarly, momentary tension loss does not cause large bending stress in the tether or significant tension amplification as the tether undergoes retensioning. This paper presents TLP platform and tether response analysis results for a representative deepwater Gulf of Mexico TLP with large-diameter, self-buoyant tethers. The time-domain, dynamic computer analysis included nonlinear effects and platform/tether coupling.

scholarly journals DYNAMIC LOAD REDUCTION DEVICE IN MACHINE DRIVE WITH SPRING AND SELECTION OF ITS PARAMETERS

2021 ◽  
Vol 297 (3) ◽  
pp. 87-93
Author(s):  
Yuri Kovalyov ◽  
◽  
Sergey Pleshko ◽  
Evgeny Lopukhov ◽  
◽  
...  
Keyword(s):  
Dynamic Loads ◽  
Practical Significance ◽  
Process Equipment ◽  
Technological Equipment ◽  
Light Industry ◽  
Torsion Spring ◽  
Operating Modes ◽  
Start Up ◽  
Dynamic Loadings ◽  
Selection Of

The peculiarity of the technological equipment of light industry is the significant dynamic loads that occur during unstable operating modes and is one of the main reasons for reducing the reliability and durability of its operation. The problem of increasing the reliability and durability of their work by reducing the dynamic loads is relevant, because the known means of reducing the dynamic loads in the drive of machines can not always be used in light industry machines. Therefore, when designing light industry equipment, first of all, attention should be paid to reducing the dynamic loads in the drive and preventing accidents. The paper considers the feasibility of using a device with a torsion spring to reduce the dynamic loads in the drive of process equipment, check its performance and develop a method for selecting rational parameters. In the course of work modern methods of researches of mechanical systems are used for the purpose of an estimation of expediency of use of the device with a torsion spring for reduction of starting dynamic loadings in the drive of machine. On the basis of the analysis of features of work of the technological equipment of light industry the expediency of use in the drive of cars of the gear safety coupling with a torsion spring is established. A new design of the device is proposed to reduce the dynamic loads that occur during machine start-up. Unlike the known devices, the proposed device is made in the form of a toothed safety clutch with a torsion spring, which simplifies its design and increases efficiency. The use of a cylindrical torsion spring as an elastic element, which connects the half-clutch to the flange on which the satellite gears are mounted, prevents overloading of the drive and the choice of rational rigidity of the device depending on the change of operation, which increases its durability and expands performance. The method of checking the efficiency of the device for reducing dynamic loads and selecting its rational parameters is presented. The scientific novelty is the development of scientific bases and engineering methods of designing devices to reduce dynamic loads in the drive of technological equipment. The practical significance lies in the development of a new design of the device to reduce the dynamic loads in the drive of machines and the engineering method of choosing its rational parameters.

Identification of Loads on Suspenders in Bridges Based on Measured Response Data in Time Domain

2012 ◽  
Vol 226-228 ◽  
pp. 1640-1644
Author(s):  
Li Tao Zhang ◽  
Yu Feng Zhang
Keyword(s):  
Differential Equation ◽  
Time Domain ◽  
Simulated Data ◽  
Measured Data ◽  
Superposition Method ◽  
Acceleration Response ◽  
Regularization Technique ◽  
Response Data ◽  
Tied Arch Bridge ◽  
Measured Response

The purpose of this paper is to deal with identification of loads on suspenders. Values of the load at every moment were chose as identification parameters, and the objective function was established using measured data of responses and corresponding simulated ones. The vibration differential equation of suspenders was adopted to obtain the formula of relationship between the load and acceleration responses with superposition method. Furthermore, a regularization technique was applied in identification calculations to improve ill-posedness of the problem to be solved. With a tied arch bridge as the real example, the load on one of its suspenders was identified. Results of identification showed that the simulated data of acceleration response were almost identical to measured ones, which indicated validity of the proposed method.

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