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Youcai Xiao,Xiangdong Xiao,Chenyang Fan,Yanyi Xiong,Zhijun Wang,Yi Sun 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.6
Insensitive munitions (IM) assessments are required to carry out the sympathetic detonation (SD) experiments. The impact of blast fragments or strong shock waves is the cause of sympathetic detonation. In this paper, a numerical simulation method is developed to predict the sympathetic detonation behavior of fuze explosive trains under the impact of blast fragments, which includes the ignition and growth (I&G) model, the JonesWilkins-Lee (JWL) equations of state, and a constitutive relationship. The experimental and numerical results were compared and analyzed, and the validity of the numerical simulation method was proven. The sympathetic detonation behavior of a fuze was studied for a single donor and multiple acceptors. The critical distance was obtained with the presence of fragments using numerical simulation. A critical distance model was developed, which provides a theoretical model for relating the detonation sequence and the placement distance of the fuze explosive train. The simulated results agreed with the theoretical calculations, and thus the model can provide the support for sympathetic detonation experiments.
Concrete fragmentation modeling using coupled finite element - meshfree formulations
Wu, Youcai,Choi, Hyung-Jin,Crawford, John E. Techno-Press 2013 Interaction and multiscale mechanics Vol.6 No.2
Meshfree methods are known to have the capability to overcome the strict regularization requirements and numerical instabilities that encumber the finite element method (FEM) in large deformation problems. They are also more naturally suited for problems involving material perforation and fragmentation. To take advantage of the high efficiency of FEM and high accuracy of meshfree methods, a coupled finite element (FE) and reproducing kernel (RK, one of the meshfree approximations) formulation is described in this paper. The coupling of FE and RK approximation is implemented in an evolutionary fashion, where the extent and location of the evolution is dependent on a triggering criteria provided by the material constitutive laws. To enhance computational efficiency, Gauss quadrature is applied to integrate both FE and RK domains so that no state variable transfer is required when mesh conversion is performed. To control the hourglassing that might occur with 1-point integrated hexahedral grids, viscous type hourglass control is implemented. Meanwhile, the FEM version of the K&C concrete (KCC) model was modified to make it applicable in both FE and RK formulations. Results using this code and the KCC model are shown for the modeling of concrete responses under quasi-static, blast and impact loadings. These analyses demonstrate that fragmentation phenomena of the sort commonly observed under blast and impact loadings of concrete structures was able to be realistically captured by the coupled formulation.
An efficient Galerkin meshfree analysis of shear deformable cylindrical panels
Wang, Dongdong,Wu, Youcai Techno-Press 2008 Interaction and multiscale mechanics Vol.1 No.3
A Galerkin meshfree method is presented for analyzing shear deformable cylindrical panels. Based upon the analogy between the cylindrical panel and the curved beam a pure bending mode for cylindrical panel is rationally constructed. The meshfree approximation employed herein is characterized by an enhanced moving least square or reproducing kernel basis function that can exactly represent the pure bending mode and thus meets the requirement of Kirchhoff mode reproducing condition. The variational form is discretized using the efficient stabilized conforming nodal integration with a smoothed nodal gradient based curvature. The resulting meshfree formulation satisfies the integration constraint for bending exactness. Moreover, it is shown here that the smoothed gradient preserves several desired properties which are valid for the standard gradient obtained by direct differentiation, such as partition of nullity and reproduction of a constant strain field. The efficacy of the proposed approach is demonstrated by two benchmark cylindrical panel examples.
Hyung-Jin Choi,John Crawford,Youcai Wu 사단법인 한국계산역학회 2010 Computers and Concrete, An International Journal Vol.7 No.2
This paper presents results from a study concerning the capability afforded by the RKPM (reproducing kernel particle method) meshfree analysis formulation to predict responses of concrete and UHPC components resulting from projectile impacts and blasts from nearby charges. In this paper, the basic features offered by the RKPM method are described, especially as they are implemented in the analysis code KC-FEMFRE, which was developed by Karagozian & Case (K&C).