Browsing by Author "Marques, F."
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- An optimization approach to generate accurate and efficient lookup tables for engineering applicationsPublication . Magalhães, H.; Marques, F.; Liu, B.; Pombo, João; Flores, P.; Ambrósio, Jorge; Bruni, S.In a wide number of engineering applications, the interpolation of a lookup table (LUT) can substitute expensive calculations. The generation of a LUT consists of pre-calculating a set of quantities from a collection of points that covers the study domain where the interpolation is possible. Nevertheless, the selection of points where the exact calculation is performed is of utmost im-portance for the LUT size and accuracy. Thus, the goal of this paper is to provide a dedicated optimization tool for the generation of accurate and efficient LUT. Here, the domain of the LUT is structured by the so-called layers, in which, the thicknesses of each layer define the distance between pre-calculated points. The optimization problem consists of maximizing the layer thicknesses, that is, min-imizing the LUT size, such that the interpolation errors within the layer domain are kept under specified tolerances. Thus, a sequential design approach is applied to design each layer of the LUT until the layers cover the study domain. To achieve reliable LUT generations, a new optimization algorithm has been imple-mented to reach optimal layers with minimum iterations. The strategy proposed here is applied to generate a LUT to substitute a selected analytical function. The optimization procedures demonstrate not only the performance of the optimiza-tion algorithm, but also its convenience in the generation of multidimensional LUT.
- An optimization approach to generate accurate and efficient lookup tables for engineering applicationsPublication . Magalhães, H.; Marques, F.; Liu, B.; Pombo, João; Flores, P.; Ambrósio, J.; Bruni, S.In a wide number of engineering applications, the interpolation of a lookup table (LUT) can substitute expensive calculations. The generation of a LUT consists of pre-calculating a set of quantities from a collection of points that covers the study domain where the interpolation is possible. Nevertheless, the selection of points where the exact calculation is performed is of utmost importance for the LUT size and accuracy. Thus, the goal of this paper is to provide a dedicated optimization tool for the generation of accurate and eficiente LUT. Here, the domain of the LUT is structured by the so-called layers, in which, the thicknesses of each layer define the distance between pre-calculated points. The optimization problem consists of maximizing the layer thicknesses, that is, minimizing the LUT size, such that the interpolation errors within the layer domain are kept under specified tolerances. Thus, a sequential design approach is applied to design each layer of the LUT until the layers cover the study domain. To achieve reliable LUT generations, a new optimization algorithm has been implemented to reach optimal layers with minimum iterations. The strategy proposed here is applied to generate a LUT to substitute a selected analytical function. The optimization procedures demonstrate not only the performance of the optimization algorithm, but also its convenience in the generation of multidimensional LUT.
- Wheel-rail contact models in the presence of switches and crossingsPublication . Magalhães, H.; Marques, F.; Antunes, P.; Flores, P.; Pombo, João; Ambrósio, J.; Qazi, A.; Sebes, M.; Yin, H.; Bezin, Y.The development and implementation of wheel-rail contact models in multibody codes are two active research topics, aiming at improving the accuracy of numerical results and computational efficiency of the dynamics analysis. However, the realism of numerical results is challenged when considering switches and crossings (S&C), where the most adverse wheel-rail contact conditions occur. This paper presents a benchmark study where the performance of the multibody codes MUBODyn, VOCO and VI-Rail are assessed using three case scenarios that involve typical contact conditions observed in S&C. A focused description of the relevant methods to determine the wheel-rail contact forces is presented for each software. The three scenarios considered in this work have been designed to represent typical challenging contact conditions observed in S&C, i.e. conformal contact, contact with a sharp edge, and impact loads. The scenarios proposed in this work are fully described, making them easily reproducible. The agreement between results is discussed in the framework of the methods implemented in each code. This work highlights the impact of wheel-rail contact methods on the results as well as on the computational efficiency of the multibody codes.