The in-plane dynamic crushing behaviors and energy-absorbed characteristics of honeycombs with negative Poisson’s ratio (NPR) have been studied by means of explicit dynamic finite element analysis (DFEA) using ANSYS/LS-DYNA. First, the honeycomb models filled with different reentrant cells by the variation of micro-cell configuration parameters (cell-wall angle and shape ratio) are established. The respective influences of micro-structure and impact velocities on the deformation behaviors, the dynamic plateau stresses and the absorbed energy of reentrant honeycombs are explored in detail. It is shown that owing to the variation of cell micro-structure, reentrant honeycombs display different macro-/micro- deformation properties during the crushing. For the given impact velocity, the dynamic plateau stresses are related to the shape ratio by a power law and to the cell-wall angle by least-square curves. And they are also proportional to the square of impact velocities for a high impact velocity. Based on the finite element simulated results and one-dimensional shock wave theory, an empirical formula for auxetic honeycomb to predict the dynamic plateau stress is derived in terms of relative density and impact velocity.
This paper presents an analytical study of the in-plane dynamic crushing and energy absorption of hexagonal honeycombs with density gradients under different impact loading. Explicit dynamic finite element method simulations are carried out by using ANSYS/LS-DYNA. Firstly, under the assumption that the cell wall length is the same, a density-graded honeycomb mode is established by the variation of the cell wall thicknesses along the crushing direction. The effects of density gradient and impact velocity on the crushing deformation modes, plateau stresses and energy absorption characteristics of the specimens are explored in detail. Numerical results show that except for the impact velocity, the dynamic crushing performance and energy absorption abilities of honeycombs also rely on the density/strength gradients. The weakest layer is suggested to be placed at the impact end or the output end, and the strongest layer at the intermediate stage to achieve higher energy absorbing efficiency. According to the one-dimensional shock wave theory, the simple empirical formulae for graded honeycombs to predict the plateau stress are given under high-impact velocities. These results will provide some useful guides in the multi-objective optimization dynamic design and shock energy absorbing control of sandwich structures.
The in-plane dynamic crushing behavior and energy absorption capacity of self-similar hierarchical honeycombs under different impact velocities are numerically studied using ANSYS/LS-DYNA. First, the hierarchical honeycomb models with uniform cell-wall thickness are constructed by replacing every three-edge structure nodes of a regular honeycomb with smaller self-similar hexagons of the same orientation. The respective influences of hierarchical parameters, bulk materials, and impact velocities on the macro-/micro-deformation behaviors, the dynamic strength, and the specific absorbed energy of hierarchical honeycombs are explored in detail. The results show that the crushing strengths and energy-absorbing capacities of honeycombs significantly improve when adding the hierarchy into conventional cellular structures. The variation of hierarchical parameter changes the local dynamic evolution of stress waves, which further results in different macro-/micro-deformation properties. Through the proper choice of hierarchical parameters and bulk materials, the optimal crushing strength and the maximum absorbing energy could be obtained.
A plug-in hybrid electric vehicle (PHEV) can improve fuel economy and emission reduction significantly compared to hybrid electric vehicles and conventional internal combustion engine (ICE) vehicles. Currently there lacks an efficient and effective approach to identify the optimal combination of the battery pack size, electric motor, and engine for PHEVs in the presence of multiple design objectives such as fuel economy, operating cost, and emission. This work proposes a design approach for optimal PHEV hybridization. Through integrating the Pareto set pursuing (PSP) multiobjective optimization algorithm and powertrain system analysis toolkit (PSAT) simulator on a Toyota Prius PHEV platform, 4480 possible combinations of design parameters (20 batteries, 14 motors, and 16 engines) were explored for PHEV20 and PHEV40 powertrain configurations. The proposed approach yielded the optimal solution in a small fraction of computational time, as compared to an exhaustive search. This confirms the efficiency and applicability of PSP to problems with discrete variables. In the design context we have found that battery, motor, and engine collectively define the optimal hybridization scheme, which also varies with the drive cycle and all electric range (AER). The proposed method and software platform could be applied to optimize other powertrain designs.
Windage yaw flashovers under strong wind and rain conditions leave a negative impact on the safe operation of transmission lines. However, the mechanism behind this is not well known yet. Therefore, this paper proposes a systematic method, including three basic parts described as simulation of wind and rain loads, calculation of windage yaw, and flashover analysis, to analyze windage yaw flashovers of transmission lines. The YanMeng-particle swarm optimization (YanMeng-PSO) algorithm is proposed to enhance the simulation accuracy. Unlike the conventional approach, the windage yaw status of conductors and insulator strings is dynamically described with key nodes and the breakdown voltage of their clearances rather than windage yaw angle. Furthermore, in the second part, a new method named key-node method (KNM) is proposed to calculate the conductors’ windage yaw. Moreover, the rain effect is also considered in this paper. This paper then presents a case study on a 110 kV double-circuit transmission line section that suffered severe collapse when the typhoon Rammasun landed in Hainan island. Particular focus was placed on the windage yaw flashover before the structural failure of the transmission line. The results validated the significant rain effect and found that conductors/ground suffer more severe windage yaw flashover than insulator strings. Finally, constructive solutions such as interphase spacers, reasonable conductor arrangement in the design phase, and regular measurements and adjustments of conductor sag in the maintenance phase are proposed to improve the design of transmission lines to enhance their capacity against windage yaw flashovers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.