Abstract The floor pan is an important component that connects the front and rear segments of the automotive underbody structure. Global stiffness and NVH characteristics of BIW are highly dependent to shape, thickness and mass of the body panels and could be evaluated by modal characteristics of these panels. The feeling of solidness and comfort of passengers in an automotive is also dependent to the modal behavior of the underbody components as well as the floor pan. On the other hand, it is desired to reduce the total mass of the floor pan, in order to have a lighter vehicle with better fuel economy and emission standards. In this paper, the effect of geometrical parameters on natural frequency and total mass of the floor pan of a conventional B-Segment automotive body is investigated using finite element simulation. The finite element model is verified using an experimental test on the floor pan. Taguchi L 16 orthogonal array is used to design the numerical experiments. Subsequently, S/N ratio analysis is performed to evaluate the effect of each design variable on the output functions. The panel's thickness is determined to have the most contribution in affecting the natural frequency and weight using Analysis of Variance (ANOVA). The best combination of geometrical variables which leads to the trade-off results is then figured out by a new multi-criteria decision making (MCDM) method developed in this study. Accuracy of this method is verified by comparing the trade-off results with TOPSIS, as a conventional MCDM method.

Abstract In this study a newly developed thin-walled structure with the combination of circular and square sections is investigated in term of crashworthiness. The results of the experimental tests are utilized to validate the Abaqus/ExplicitTM finite element simulations and analysis of the crush phenomenon. Three polynomial meta-models based on the evolved group method of data handling (GMDH) neural networks are employed to simply represent the specific energy absorption (SEA), the initial peak crushing load (P1) and the secondary peak crushing load (P2) with respect to the geometrical variables. The training and testing data are extracted from the finite element analysis. The modified genetic algorithm NSGA-II, is used in multi-objective optimisation of the specific energy absorption, primary and secondary peak crushing load according to the geometrical variables. Finally, in each optimisation process, the optimal section energy absorptions are compared with the results of the finite element analysis. The nearest to ideal point and TOPSIS optimisation methods are applied to choose the optimal points.

Abstract At conceptual phases of designing a vehicle, engineers need simplified models to examine the structural and functional characteristics and apply custom modifications for achieving the best vehicle design. Using detailed finite-element (FE) model of the vehicle at early steps can be very conducive; however, the drawbacks of being excessively time-consuming and expensive are encountered. This leads engineers to utilize trade-off simplified models of body-in-white (BIW), composed of only the most decisive structural elements that do not employ extensive prior knowledge of the vehicle dimensions and constitutive materials. However, the extent and type of simplification remain ambiguous. In fact during the procedure of simplification, one will be in the quandary over which kind of approach and what body elements should be regarded for simplification to optimize costs and time, while providing acceptable accuracy. Although different approaches for optimization of timeframe and achieving optimal designs of the BIW are proposed in the literature, a comparison between different simplification methods and accordingly introducing the best models, which is the main focus of this research, have not yet been done. In this paper, an industrial sedan vehicle has been simplified through four different simplified FE models, each of which examines the validity of the extent of simplification from different points of views. Bending and torsional stiffness are obtained for all models considering boundary conditions similar to experimental tests. The acquired values are then compared to that of target values from experimental tests for validation of the FE-modeling. Finally, the results are examined and taking efficacy and accuracy into account, the best trade-off simplified model is presented.

A study on the acoustic behavior of double-walled panels, with sandwiched layer of porous materials is presented within Classical Laminated Plate Theory (CLPT) for laminated composite panels. For this purpose, equations of wave propagation are firstly extracted based on Biot's theory for porous materials, then the transmission loss (TL) of the structure is estimated in a broadband frequency. Secondly, TL coefficient of the structure is determined using Statistical Energy Analysis (SEA). In the next step, accuracy of the solution is shown with comparing the data obtained from these two presented models as well as the experimental results available in literature. Finally, the effects of parameters on sound transmission loss of double porous composite panels, especially at a high frequency range, are discussed. In addition, the results show that maximum sound energy is transferred through the waves frame (structure born) due to the porous layer bonded between the two composite panels. Therefore, material parameters that are principally related to solid phase of the foam such as Poisson's ratio, bulk density and bulk Young's modulus, have the most significant effects on the transmission loss. Meanwhile, the impacts of composite material panels and composite plies arrangement on sound transmission loss structures have been addressed in this paper.