Resumo em Inglês:

Abstract In this paper, the hybrid differential evolution and symbiotic organism search (HDS), is the first-time developed for general solutions of a piezoelectric stack in ultrasonic transducers. The convergence and reliability of the new algorithm are verified through comparison with corresponding data from similar previous publications and differential evolution (DE) algorithm. This study also presents and discusses the calculation results using HDS for commercial piezoelectric stacks. The Matlab HDS programs for a segmented piezoelectric (PZT) model have advanced features including its applicability to any configurations, thickness and arbitrary layer numbers of PZT. Using the novel proposed technique, there is no requirement for initial data guess, no limitations for piezoelectric stacks and the convergence rate is much faster than DE. Therefore, the HDS is promising for direct evaluation of specific aging or degradation mechanisms of ultrasonic transducers.

Resumo em Inglês:

Abstract Wind-induced loading on buildings may be altered due to presence of upwind structures. These variations are quantified by the interference factors (IFs), which is determined experimentally for each case analyzed, since obtaining this quantification in codes and standards is still impractical due to the complexity of the multi-parameters involved. To understand the influence of some of these parameters on the interference effects, contour plots and power spectra density were presented for IFs corresponding to aerodynamic coefficients of the along-wind and cross-wind force, as well as for torsion. Wind tunnel tests were conducted applying the synchronous pressure measurement technique. Interference arrangements with one and two upstream interfering buildings were investigated for different wind angles, relative positions and terrain roughness. Results indicate that the shielding effect is predominant in most of the studied cases. Nevertheless, the amplification effects are generally present in specific configurations and are usually caused by channeling and buffeting effects, as well as vortex shedding.

Resumo em Inglês:

Abstract In this paper, negative poisson's ratio material is used to fill the interlayer of mine refuge chamber, and its characteristics such as light weight, thermal insulation, vibration isolation and impact resistance are used to improve the impact resistance and thermal insulation ability of mine refuge chamber. The equivalent density, elastic modulus and yield strength of negative poisson's ratio structure of material Q345 were obtained by simulation analysis. The negative poisson's ratio material was filled into the mine refuge chamber, and the impact energy absorption and explosion transient thermal analysis were carried out. The results show that compared with the prototype, the maximum inner skin temperature of the negative poisson's ratio refuge chamber is reduced by 44.86%, the transverse and longitudinal stiffeners temperature is reduced by nearly 46.77%, and the impact deformation is reduced by 35mm, which has better safety performance. The response surface optimization method was used to optimize the whole refuge chamber filled with negative poisson's ratio material, which was more secure than before.

Resumo em Inglês:

Abstract The lightweight design of electric heavy quadricycle (L7e) vehicles has contributed to energy savings and sustainable mobility. This study proposes an optimization methodology to design a monocoque sandwich structure under operating conditions for an L7e using a finite element model via HyperWorks. Woven fiberglass fabrics and high-density PVC foam are assigned as the face and core to construct the sandwich structure, respectively. Free-size optimization based on weight minimization is applied to obtain the suitable initial thickness of face and core structures in all components. Multi-objective size optimization is then performed by minimizing both mass and material cost to determine the optimal thickness of each layer. Finally, shuffle optimization is used to modify the stacking sequence for each component to maximize structural stiffness. The results indicate that the core thickness in the passenger compartment is sufficient to maintain stiffness while maintaining the structure's lightweight. However, shuffle optimization is insignificant for the current monocoque model, as the structural stiffness is only marginally improved after the process. Additionally, this study examines the optimized models for structural stiffness and discusses suitable procedures for designing a lightweight and safe electric vehicle.

Resumo em Inglês:

Abstract In this study, we investigated the mechanical and energy-absorption properties of a star-shaped auxetic honeycomb under combined compression-shear loading. Novel fixtures were designed to conduct quasi-static combined compression-shear loadings. Experimental and numerical results show that the honeycomb undergoes an overall deformation based on cell rotation under quasi-static loading, producing an inclined deformation band. The normal yield stress decreased, and the shear yield stress increased with an increase in the loading angle. The extrusion deformation between meso-structures became more sufficient under dynamic combined loadings. The material deformation mode changed from overall deformation to local deformation accompanied by the formation of a shock wave. The yield criteria were established based on the ellipse equation. With an increase in the loading angle, the energy absorption in the normal and shear directions of the materials showed downward and upward trends, respectively. A theoretical model was proposed based on the 1D shock wave model to predict the energy-absorption behaviour under dynamic loading.