Estimation of transmitted loads using experimental substructuring (original) (raw)
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The technique has been presented for time-dependence identification of several independent beetwen each other loads distributed over a given area of a structure with arbitrary topology by using quantity values more convenient for measurements. In the assumption that the structure's response linearly depends on the loads, the considered problem, which belongs to the class of boundary inverse problems in the mechanics of solids, is reduced to a system of linear algebraic equations for coefficients that approximate the sought-for influences. The system is solved using a regularizing algorithm providing stability of results to random errors in initial data and calculation errors. Concrete calculations, substantiating the efficiency of the presented technique, have been performed as with theoretical data to identify two non-stationary loads applied to a wheel carrier of a race car as with experimental data to restore an impact force applied to a round plate with fixed boundary. To calculate values of a system's elements corresponding to values of measured quantities under unit loads, the finite element method was used. The suggested technique can be used for designing structures with complex geometry based on criterias of their dynamic (fatigue) strength, etc.
Mechanical Systems and Signal Processing, 2015
Substructure-decoupling techniques are used to identify a substructure as a stand-alone system while it is coupled to a complex structure (an assembly of substructures). These recently introduced techniques can be used for various applications, e.g., when the substructure cannot be measured separately from the complex structure, when modal testing methods are not appropriate due to the limits of the measurement equipment and for vibration-control techniques. The complex structure consists of the unknown substructure and the remaining structure. A drawback of the available substructure-decoupling techniques is that they require a model of the remaining substructure. However, when the model cannot be calculated or (experimentally) identified, the substructure-decoupling techniques cannot be used. In this article a new approach is presented that does not require a model of the remaining substructure, but is based on an experimental identification of the interface forces. As an illustration, the subsystem identification is introduced on a generalized massspring-damper system. To research the application possibilities for real situations, complex structures with beam-like coupling elements are investigated. The sensitivity of the approach to experimental errors was researched using an uncertainty propagation analysis. The article includes numerical and experimental test cases.
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Structural =dentffmation is a technique for restricting uncertainties in structural modelhng by making use of available experimental data. For large and complicated systems these data are frequently very bruited, thus interpretative models which retain most of the a priori information, such as finite element models, are preferable. Those aspects of identification procedures which use FE models in the frequency domain and a Bayesmn context are examined. Attention is given to the optimal choice of parameters and observed quant=ties, =dentffiability, expected accuracy and to features of the numerical procedure. A quantitatwe evaluat=on of these aspects ~s undertaken to =dent=fy a FE model of a spat=al framed structure using pseudoexperimental data.
A methodology for identification of dynamic parameters in assembled aircraft structures
2013
Finite Element Models (FEM) are widely used in order to study and predict the dynamic properties of structures. Comparing dynamic experimental data and analytical results, respectively, of the real and modelled structure, shows that the prediction of the dynamic response can be obtained with much more accuracy in the case of a single component than in the case of assemblies. Generally speaking, as the number of components in the assembly increases the calculation quality declines because the connection mechanisms among components are not represented sufficiently. Specifically for aircrafts, it is quite common that Frequency Response Functions (FRF) obtained via Ground Vibration Test (GVT) show a certain degree of discrepancy from the FRF calculated with the FEM, particularly across the sections where joining is discontinued. When this happens it is necessary to tune up the values of the dynamic parameters of the joints, to allow the numerical FRF to match the results of the experimental FRF. From a modelling and computational point of view, these types of joints can be seen as localized sources of stiffness and damping and can be modelled as lumped spring/damper elements. In this paper this is done by formulating an optimization problem. The approach has been applied to a FEM that mimics the rear fuselage of a commercial aircraft and the numerical results shows that the procedure is very efficient and promising.
Hybrid Experimental/Analytical Models of Structural Dynamics: Creation and Use for Predictions
34th Structures, Structural Dynamics and Materials Conference, 1993
An original complete methodology for the construction of predictive models of damped structural vibrations is introduced. A consistent definition of normal and to an original method to accurately identify nom-proportional1 new method to create predictive hyb trodnced, and the ability of hybrid is discussed. Finally a critical revie C interferometer testbed. omenclature Frequency Response Function matrix input, output shape matrices correction matrix for high frequency modes correction matrix for low frequency modes system mass, damping, and stiffness matrices states of the physical coordinate model states of the normal mode model residue matrix of the jth pole NxN matrix of normal modes normal mode damping matrix diagonal matrix of the 2N poles of the system 1'' order scaled complex modeshape matrix k'h singular value of a residue matrix kth left , right singular vectors of a residue matrix normal mode stiffness matrix NxZN matrix of complex modeshapes jth pole damping ratio jth pole frequency ntroduction ECAUSE of stringent accuracy needs related to Control
A methodology for identification of dynamic parameters in
2016
Finite Element Models (FEM) are widely used in order to study and predict the dynamic properties of structures. Comparing dynamic experimental data and analytical results, respectively, of the real and modelled structure, shows that the prediction of the dynamic response can be obtained with much more accuracy in the case of a single component than in the case of assemblies. Generally speaking, as the number of components in the assembly increases the calculation quality declines because the connection mechanisms among components are not represented sufficiently. Specifically for aircrafts, it is quite common that Frequency Response Functions (FRF) obtained via Ground Vibration Test (GVT) show a certain degree of discrepancy from the FRF calculated with the FEM, particularly across the sections where joining is discontinued. When this happens it is necessary to tune up the values of the dynamic parameters of the joints, to allow the numerical FRF to match the results of the experimental FRF. From a modelling and computational point of view, these types of joints can be seen as localized sources of stiffness and damping and can be modelled as lumped spring/damper elements. In this paper this is done by formulating an optimization problem. The approach has been applied to a FEM that mimics the rear fuselage of a commercial aircraft and the numerical results shows that the procedure is very efficient and promising.
Computational Techniques for Simulation of Monolithic and Heterogeneous Structural Dynamic Systems
CISM International Centre for Mechanical Sciences, 2008
The prediction of the transient dynamic response of monolithic structural systems, as well as of heterogeneous (numerical/ physical) subsystems, decomposed by computational or physical considerations typical of hardware-in-the-loop and pseudo-dynamic tests using numerical integration, has become an accepted practice almost to the extent that such solutions in non-linear problems often are considered to be exact solutions. It is for this reason that this chapter is placed immediately at the beginning of the book. In light of the large body of literature on computational methods developed for both testing and control techniques applied to linear and non-linear systems, no attempt is made to cover this subject in greater depth. Rather the concepts upon which ad hoc computational methods rely are presented in a common framework along with a few applications.
Parameter estimation and investigation of a bolted joint model
Journal of Sound and Vibration, 2007
Mechanical joints are a primary source of variability in the dynamics of built-up structures. Physical phenomena in the joint are quite complex and therefore too impractical to model at the micro-scale. This motivates the development of lumped parameter joint models with discrete interfaces so that they can be easily implemented in finite element codes. Among the most important considerations in choosing a model for dynamically excited systems is its ability to model energy dissipation. This translates into the need for accurate and reliable methods to measure model parameters and estimate their inherent variability from experiments. The adjusted Iwan model was identified as a promising candidate for representing joint dynamics. Recent research focused on this model has exclusively employed impulse excitation in conjunction with neural networks to identify the model parameters. This paper presents an investigation of an alternative parameter estimation approach for the adjusted Iwan model, which employs data from oscillatory forcing. This approach is shown to produce parameter estimates with precision similar to the impulse excitation method for a range of model parameters. (O.V. Shiryayev).