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Cao H.,Harbin Institute of Technology | Chu Y.,Harbin Institute of Technology | Wang E.,Harbin Institute of Technology | Cao Y.,Harbin Institute of Technology | And 3 more authors.
Journal of Propulsion and Power | Year: 2015

The barrel erosion, one type of accelerator grid erosion in an ion thruster, is important and needs more detailed studies. In this paper, a three-dimensional numerical simulation code is developed using a hybrid immersed-finiteelement particle-in-cell method and Monte Carlo collisions method; the dynamics of a neutral atom is modeled using a direct simulation Monte Carlo method; and a numerical simulation study is run to investigate the mechanism of aperture barrel erosion of an ion thruster accelerator grid. Simulation results indicate that the aperture barrel erosion of ion thruster accelerator grid is entirely caused by the charge-exchange ions under nominal operating condition, and the incident charge-exchange ions in four regions, namely the upstream region, the extraction (center) region, the extraction (edge) region, and downstream of the accelerator grid, are the causes of aperture barrel erosion. Highenergy charge-exchange ions originated from upstream region are not well focused and play an important role in the erosion of the aperture barrel. Charge-exchange ions originated from the extraction (center) region, which play an important role in the whole incident charge-exchange ions, also cause significant erosion on the aperture barrel. It is therefore believed that these findings would facilitate the prediction of aperture barrel erosion of an ion thruster accelerator grid. © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Yu Z.,Shanghai JiaoTong University | Hu Z.,Shanghai JiaoTong University | Hu Z.,State Key Laboratory of Structure Analysis for Industrial Equipment | Wang G.,ABS Greater China Division
Analysis and Design of Marine Structures - Proceedings of the 4th International Conference on Marine Structures, MARSTRUCT 2013 | Year: 2013

A theoretical model is introduced in this paper for structural performances of the stiffeners on the double bottom floor plating in a shoal grounding accidental scenario. It is based on a study of the progressive deformation process of numerical simulation results and the plastic analytical methods. Special emphasis is laid on establishing the characteristic deformation mechanism and identifying the major energy dissipation pattern. When calculating the structural performances of ship bottom during ship grounding accident, a prevailing method is to smear the stiffeners into the plating thickness for simplicity. Thus, the corresponding structural responses of the stiffeners are involved in the smeared plating. However, this method may not provide an accurate prediction of the structural performance characteristics of the stiffeners, and the deformation process of the stiffeners cannot be mastered. Therefore, a theoretical model is proposed in this paper to provide a deep insight into the deformation patterns with reasonable predictive accuracy. Using the plastic analytical method, the expressions of distortion energy composed of the crushing, bending, and membrane stretching effect of stiffeners on the floor plating are formulated, and the formulae of subsequent grounding resistances are obtained. The numerical simulation software LS-DYNA is employed to verify the proposed method. It covers a wide range of slope angles and indentations of shoal grounding scenarios. The results of the proposed simplified analytical method compare favorably with those of the numerical simulations and good predictive accuracy is acquired. Furthermore, the theoretical model proposed can conveniently lend itself for quick assessments of the performances of ship double bottom structures during shoal sliding grounding scenario, and it will benefit the application of accidental limit state design concept in the ship design stage. © 2013 Taylor & Francis Group.

Liu G.R.,National University of Singapore | Wang Z.,National University of Singapore | Wang Z.,Dalian University of Technology | Zhang G.Y.,National University of Singapore | And 3 more authors.
Mechanics of Advanced Materials and Structures | Year: 2012

In this work, the edge-based smoothed point interpolation method (ES-PIM) is extended to treat material discontinuity problems. The PIM shape functions used in the ES-PIM possess the Delta function property, which allows straightforward imposition of point essential boundary conditions and, hence, no additional treatment needs to be applied along the interface to meet the interface condition. By performing the generalized strain smoothing operation within the edge-based smoothing domains, the ES-PIM models possess a number of good features compared with the standard FEM using the same set of linear triangular elements, such as better accuracy, higher convergence rate, and efficiency. Three typical numerical examples, including the benchmark sandwiches cantilever beam, a hollow cylinder with two different materials and an automotive part of complicated shape, have been studied using the present ES-PIM. Analytical solutions for the first two problems have also been derived and presented. Very good agreement between the numerical results and the given analytical reference solutions demonstrate the effectiveness of the present ES-PIM method. © 2012 Copyright Taylor and Francis Group, LLC.

Li L.,Shanghai JiaoTong University | Hu Z.,Shanghai JiaoTong University | Hu Z.,State Key Laboratory of Structure Analysis for Industrial Equipment | Jiang Z.,China National Offshore Oil Corporation
Mathematical Problems in Engineering | Year: 2013

This paper deals with ship-jacket platform collisions. An examination on NORSOK N-004 rule is carried out. Furthermore, elastic and plastic response of jacket platform is studied. This paper also conducts a sensitivity analysis, focusing on collision points. Simulation models of a ductile and a rigid supply vessel were developed, as well as models of two typical jacket platforms. Data such as collision force, kinetic energy, and deformation energy have been obtained. Several conclusions have been drawn: NORSOK rule underestimates the resistance for certain indention, due to inaccurate description of column deformation mode. Elastic response is extremely important in dynamic analysis of ship-platform impacts, by contributing to reducing impact loads and local energy dissipation. Struck members are therefore subjected to impacts to a low extent, which can be regarded as result of a buffering effect. Before a buffering effect works, a time delay exists. This is caused because the topside has to take up adequate kinetic energy. Striking position has an effect on dynamic behavior of platform. High local strength is in favor of buffering an effect. Elastic response is more significant in a flexible platform than in a sticky one. © 2013 Liang Li et al.

Zhou P.,State Key Laboratory of Structure Analysis for Industrial Equipment | Wu C.W.,State Key Laboratory of Structure Analysis for Industrial Equipment
Journal of Power Sources | Year: 2010

We developed an equivalent capillary model of a microscale fiber-fence structure to study the microscale evolution and transport of liquid in a porous media and to reveal the basic principles of water transport in gas diffusion layer (GDL). Analytical solutions using the model show that a positive hydraulic pressure is needed to drive the liquid water to penetrate through the porous GDL even consisting of the hydrophilic fibers. Several possible contributions for the water configuration, such as capillary pressure, gravity, vapor condensation, wettability and microstructures of the GDL, are discussed using the lattice Boltzmann method (LBM). It is found that the distribution manners of the fibers and the spatial mixed-wettability in the GDL also play an important role in the transport of liquid water. © 2009 Elsevier B.V. All rights reserved.

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