Purpose - The purpose of this paper is to assess the suitability of various methods for the reduction of a large finite element model (FEM) of satellites to produce models to be used for correlation of the FEM with test results. The robustness of the cross-orthogonality checks (COC) for the correlation process carried out utilizing the reduced model is investigated, showing its dependence on the number of mode shapes used in the reduction process. Finally the paper investigates the improvement in the robustness of the COC that can be achieved utilizing optimality criteria for the selection of the degrees of freedom (DOF) used for the correlation process. Design/methodology/approach - A Monte Carlo approach has been used to simulate inaccuracies in the mode shapes (analysis and experimental) of a satellite FEM that are compared during the COC. The sensitivity of the COC to the parameters utilized during the reduction process, i.e. mode shapes and DOFs, is then assessed for different levels of inaccuracy in the mode shapes. Findings - The System Equivalent Expansion Reduction Process (SEREP) has been identified as a particularly suitable method, with the advantage that a SEREP reduced model has the same eigenvalues and eigenvector of the whole system therefore automatically meeting the criteria on the quality of the reduced model. The inclusion of a high number of mode shapes in the reduction process makes the check very sensitive to minor experimental or modelling inaccuracies. Finally it was shown that utilizing optimality criteria in the selection of the DOFs to carry out the correlation can significantly improve the probability of meeting the COC criteria. Research limitations/implications - This work is based on the FEM of the satellite IT>Aeolus/IT>, and therefore the numerical values obtained in this study are specific for this application. However, this model represents a typical satellite FEM and therefore the trends identified in this work are expected to be generally valid for this type of structure. Practical implications - The correlation of satellite FEM with test results involves a substantial effort, and it is crucial to avoid failures of the COC due to numerical issues rather than real model inaccuracies. This work shows also how an inappropriate choice of reduction parameters can lead to failure of the COC in cases when there are only very minor differences (e.g. due to minor amount of noise in the results) between analytical and test results. Vice versa, the work also shows how the robustness of the reduced model can be improved. Originality/value - The paper shows how the robustness of the correlation process for a satellite FEM carried out utilising a SEREP reduced model needed to be investigated, to demonstrate the suitability of this method to reduce large FEM of satellites. Copyright © 2012 Emerald Group Publishing Limited. All rights reserved
Aluminium composite sandwich panels are widely used to enhance the design of structures subjected to dynamic mechanical loading in thermally harsh environments. Spacecraft structures fall into this category because typical environmental conditions include combined and variable mechanical and thermal loading. Usually mechanical loadings arise as a consequence of localised structural dynamics and the thermal loadings are attributable principally to the effects of solar irradiation and eclipse during the vehicle's orbit. Together these have the potential to influence satellite de-point in particular. Therefore, building a combined physics model which is representative of the thermal and mechanical loadings has emerged as an interesting and useful aim, which can be thought of as defining an important thermoelastic deformation problem in this application. The performance of such a structure loaded in this way could obviously be considered in the context of separate thermodynamic and mechanical interpretations. However, multiphysics modelling is currently in hand based on the premise that the pseudo-static thermal loadings and the mechanical loadings encountered in various operating environments are not necessarily decoupled processes, and this will be the subject of a separate publication. The analytical modelling fully represents both static and dynamic mechanical and thermal loading conditions.It has become clear that predictive accuracy may be compromised by separation of the phenomena, at least without the introduction of a judicious correction factor. Therefore, in this paper an attempt has been made to identify experimentally the presence, and then to understand the attendant effects, of the coupling between the thermal and mechanical effects in an aluminium composite sandwich panel under test. The authors have performed a series of experiments on an aluminium honeycomb composite panel under three-point mechanical bending and controlled environmental temperature. The panel was subjected to a controllable, centrally located, very slowly increasing mechanical load in conjunction with thermal loading in the form of precisely controlled lowered and elevated environmental temperature. The tests were performed on a computer controlled Instron 8801 100 kN test machine for which the rate of change of applied mechanical load was automatically linked through feedback control to the rate of change of displacement. This ensured that the exact load-deflection profile can be obtained, even for materials with highly nonlinear characteristics.Both forms of loading have been shown to influence the displacement of the panel in significant ways, thereby confirming the importance of a combined physics approach.
Abstract. It is common for Finite Element Model (FEM) validation activities to be carried
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