• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.9-19
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• 1989

The impact stress and wave propagation of graphite/epoxy and glass/epoxy laminates subjected to the transverse low-velocity impact of steel balls are investigated theoretically. A plate finite element model based on Whitney and Pagano's theory for the analysis of heterogeneous and anisotropic plates taking into account of the transverse shear deformation is used for the theoretical investigation. This model is in conjuction with static contact laws. The basic element is a four-node quadrilateral with the five degrees-of-freedom per node. The reduced integration technique is used for shear locking associated with low-order function in application to thin plates. These two materials are composed of [0.deg./45.deg./0.deg./-45.deg./0.deg.]$_{2S}$ and [90.deg./45.deg./90.deg./-45.deg./90.deg.]$_{2S}$ stacking sequences and have clamped-clamped boundary conditions. Finally, the present results are compared with an existing solution and wave propagation theory and then impact stress and wave propagation phenomena are investigated.gated.

• Explosives and Blasting
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• v.23 no.3
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• pp.27-42
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• 2005

An explosion modeling technique was developed by using the spherical discrete element code, $PFC^{3D}$, which can be used to model the dynamic stress wave propagation phenomenon. The modeling technique is simply based on an idea that the explosion pressure should be applied to a $PFC^{3D}$ particle assembly not in the form of an external force (body force), but in the form of a contact force (surface force). The stress wave propagation modeling was conducted by simulating the experimental approach based on the Hopkinson's effect combined with the spatting phenomenon that had previously been developed to determine the dynamic tensile strength of Inada granite. As a result, the stress wave velocity obtained by the proposed modeling technique was 4167 m/s, which is merely $3\%$ lower than the actual wave velocity of 4300 m/s for an Inada granite.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3369-3376
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• 1994

A finite element program for elastic stress wave propagation is developed in order to investigate the shape of stress field and analysis the magnitude of stress wave intensity at time increment. Accuracy and reliance of the finite element analysis are acquired when the element size is smaller than the product of the stress wave speed and the critical value of increasing time step. In the finite element analysis and theoretical solution, the longitudinal stress wave is propagated to the similar direction of impact load, and the stress wave intensity is expressed in terms of the ratio of propagated area. The direction of shear wave is declined at an angle of 45 degrees compared with longitudinal stress wave and the speed of shear wave is half of the longitudinal stress wave.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.561-564
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• 2011

다양한 공학/산업적 측면에서 동적 취성 파괴 현상은 매우 중요하다. 취성 균열은 다른 균열 전파에 비해 그 전파 속도가 매우 빠르고 전파 범위가 넓기 때문에 대규모의 파괴 현상을 일으킨다. 동적 전파 중인 취성 균열 거동을 모델화하기 위해 오랜 기간 동안 많은 연구가 진행되었지만, 여전히 많은 부분들이 해석되지 못한 채 남아있다. 특히 균열 생성 및 전파를 위해 인위적인 조건들을 도입해야 하는 것은 기존 방법론들이 가지는 공통적인 문제점이다. 본 연구는 peridynamics를 동적 분기 균열 문제 해석에 도입한다. Peridynamics는 전통적인 연속체 이론에 기반한 수치해석 모델화 기법으로 균열과 같은 비연속성이 있는 문제의 모델화에 강점이 있으며, 인위적인 조건 없이 매우 간단한 방법으로 파괴 현상을 해석할 수 있다. 본 연구에서는 peridynamics 모델이 실험적으로 관측된 분기균열 형상과 균열 전파 속도를 매우 잘 예측해 낼 수 있음을 보인다. 또한 균열팁 주변에 높은 응력이 발생할 때 나타나는 연쇄 분기 현상도 해석할 수 있다. 이와 같은 연구를 통해 응력파가 균열 전파 속도를 변화시키고 전파 방향에도 영향을 주는 것을 알 수 있었다. 수치해석 결과도 또한 실험 결과들과 잘 부합함을 확인하였다.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.95-104
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• 2002

The theoretical and analytical studies on dynamic signals(force and acceleration signals) measured at SPT rod are actively made. In this paper, the characteristics of stress wave(force signals) in SPT rod were studied experimentally using model rod system. It was noted that the amplitude ratios of reflected wave over incident wave in different end conditions were well matched with theoretical results. The impedance of soil could be determined if the characteristics of incident and reflected waves could be evaluated quantitatively in situ SPT test. On the other hand, the results of model tests showed that the effect of reflected wave caused by side friction was negligible, and therefore, the analysis model considering only end resistance of sampler could be applicable in dynamic analysis of SPT.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.22 no.2
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• pp.79-85
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• 1989

The generation and propagation of shelf wave-like oscillations induced by local wind at a basin with continental shelf and slope are studied by a numerical experiment. Three types of vortices are generated along western boundary and they propagate along the boundaries in the counter-clockwise direction. The first vortex is generated at the early stage of wind stress and its center is located off the continental slope. The second type centered on the continetal slope is generated at about the terminating time of wind stress and follows the first one. The third, centered on continental shelf, decays so soon that its propagation pattern is hard to be identified. Each of those vortices is probably to be one of free modes of the model basin.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.61-71
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• 1993

The stress waves generated by the mechanical energies by impact or the chemical energies by the explosions are transmitted through medium. The wave propagation process through medium is a very complicated procedure due to the reflections and refractions of the waves at the free surfaces and interfaces. In this study the pressure independent Von-Mises model is employed for the wave propagation analysis in the layered systems. Governing equations of this study are conservation equations of momentum and mass in Lagrangian coordinate system which is fixed to the material. Due to the shock-front which violates the continuity assumptions inherent in the differential equations numerical artificial viscosity is used to spread the shock front over several computational zones. These equations are solved by Finite Difference Method with discretized time and space coordinates. The associate normality flow rule as a plastic theory is implemented to find the plastic strains.

• Computational Structural Engineering
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• v.2 no.3
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• pp.85-95
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• 1989

This paper presents a study of soil-structure interaction problems using infinite elements. The infinite elements are formulated for homogeneous and layered soil media, based on approximate expressions for three components of propagating waves, namely the Rayleigh, compressive and shear waves. The integration scheme which was proposed for problems with single wave component by waves. The integration scheme which was proposed for problems with single wave component by Zenkiewicz is expanded to the multi-waves problem. Verifications are carried out on rigid circular footings which are placed on and embedded in elastic half space. Numerical analysis is performed for a containment structure of a nuclear power plant subjected to a horizontal seismic excitation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.637-643
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• 2011

The bond-based peridynamic model is able to capture many of the essential characteristics of dynamic brittle fracture observed in experiments: crack branching, crack-path instability, asymmetries of crack paths, successive branching, secondary cracking at right angles from existing crack surfaces, etc. In this paper we investigate the influence of the stress waves on the crack branching angle and the velocity profile. We observe that crack branching in peridynamics evolves as the phenomenology proposed by the experimental evidence: when a crack reaches a critical stage(macroscopically identified by its stress intensity factor) it splits into two or more branches, each propagating with the same speed as the parent crack, but with a much reduced process zone.

• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1077-1086
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• 2014

The flood wave generated due to dam break is affected by initial depth upstream since it is related with hydraulic characteristics propagating downstream, and flow resistance stress has influence on the celerity, travel distance, and approaching depth of shock wave in implementing numerical simulation. In this study, a shallow water flow model employing SU/PG scheme was developed and verified by analytic solutions; propagation characteristics of dam break according to flow resistance and initial depth were analyzed. When bottom frictional stress was applied, the flow depth was relatively higher while the travel distance of shock wave was shorter. In the case of Coulomb stress, the flow velocity behind the location of dam break became lower compared with other cases, and showed values between no stress and turbulent stress at the reach of shock wave. The value of Froude number obtained by no frictional stress at the discontinuous boundary was the closest to 1.0 regardless of initial depth. The adaption of Coulomb stress gave more appropriate results compared with turbulent stress at low initial depth. However, as the initial depth became increased, the dominance of flow resistance terms was weakened and the opposite result was observed.