力学进展

2013 Vol. 43, No. 6

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A brief survey on discontinuous Galerkin methods in computational fluid dynamics

Chi-Wang Shu

2013, 43(6): 541-554. doi: 10.6052/1000-0992-13-059

Abstract(3901)

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Abstract:
Discontinuous Galerkin (DG) methods combine features in finite element methods(weak formulation, finite dimensional solution and test function spaces) and in finite volume methods (numerical fluxes, nonlinear limiters) and are particularly suitable for simulating convection dominated problems, such as linear and nonlinear waves including shock waves. In this article we will give a brief survey of DG methods, emphasizing their applications in computational fluid dynamics (CFD). We will discuss essential ingredients and properties of DG methods, and will also give a few examples of recent developments of DG methods which have facilitated their applications in CFD.

Load-unload response ratio——An interplay between earthquake prediction and mechanics

YIN Xiangchu, LIU Yue

2013, 43(6): 555-580. doi: 10.6052/1000-0992-13-075

Abstract(1816)

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Abstract:
Earthquake prediction is a scientific challenge to the world's scientists. Being a complex natural phenomenon, earthquake has a quite clear physical nature, that is, a rapid shear fracture in the crust. Accordingly, earthquake preparation is the damage evolution process for the crust media, which eventually leads to catastrophic fracture. This is mainly a mechanical process. Considering this point and grasping the physical nature of seismogenical process, we have put forward a new approach to earthquake prediction in terms of Load-Unload Response Ratio (LURR) (Yin 1987, Yin 2006).
In the present paper, we introduces the basic scientific problems, including how to load and unload the crust block, how to select proper geophysical parameters as response, and how to define LURR. Based on experiments, numerical simulations and damage mechanics analysis, the universal feature of LURR evolution before a strong earthquake has been revealed. More precisely, LURR fluctuates around 1 at the initial stage of preparation process, and then climbs to an anomalously high value (peak-point). Earthquake does not occur at this time. Instead, there is a delay time duration denoted as T₂, which is related to the magnitude of the event. In order to predict earthquake in China，we propose to conduct countrywide spatial-temporal scanning of LURR, then to integrate with dimensional analysis so as to include more geophysical conditions into consideration. In this way, we have drawn up an approach to predict comprehensively the location, magnitude and occurrence time of forthcoming strong earthquakes. Finally, the practice of earthquake prediction with LURR has been retrospected.

Research progress in degradation mechanism of silicon anode materials for lithium-ion batteries

MA Zengsheng, ZHOU Yichun, LIU Jun, XUE Dongfeng, YANG Qingsheng, PAN Yong

2013, 43(6): 581-599. doi: 10.6052/1000-0992-13-066

Abstract(3389)

PDF(4788)

Abstract:
Silicon anode materials have very high theoretical specific capacity, hence become promising replacement for anode material of lithium-ion batteries. However, during charging and discharging, silicon anode materials suffer big volume deformation that may cause destruction and failure of the active material. This seriously affects the electrochemical cycle performance, and restricts wide applications in the field of lithium-ion batteries. In this paper, we introduce silicon anode materials of different structure form, and the degradation mechanism of the electrochemical properties during charging and discharging. We summarize the latest international research progress in mechanical properties evolution of charging and discharging process, the related theoretical analysis, numerical simulations, and prospects for research emphasis of the mechanical failure in silicon anode materials.

2013 Vol. 43, No. 6

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