• 한국지진공학회논문집
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• 제23권1호
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• pp.19-29
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• 2019

Recent earthquakes in Korea caused some damages to stone pagodas and thereby awakened the importance of earthquake preparedness. Korean stone pagodas which have been built with very creative style of material use and construction method are worthy of world heritage. Each stone pagoda consists of three parts: top; body; and base. However each tower is uniquely defined by its own features, which makes it more difficult to generalize the seismic assessment method for stone pagodas. This study has focused on qualitative preliminary evaluation of stone pagodas that enables us to compare the relative seismic performance across major aspects among many various Korean pagodas. Specifically an analytical model for multi-block stone pagodas is to be proposed upon the investigation of structural characteristics of stone pagoda and their dynamic behavior. A strategy for seismic evaluation of heritage stone pagodas is to be established and major evaluation factors appropriate for the qualitative evaluation are identified. The evaluation factors for overall seismic resisting behavior of stone pagodas are selected based on the dynamic motions of a rigid block and its limit state. Numerical simulation analysis using discrete element method is performed to analyze the sensitivity of each factor to earthquake and discuss some effects on seismic performance.

• Geomechanics and Engineering
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• 제17권1호
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• pp.19-30
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• 2019

Recent research on the behavior of silty sand tends to advocate the use of equivalent skeleton void ratio to characterize the density state of this type of soil. This paper presents an investigation to explore the physical meaning of the equivalent skeleton void ratio by means of DEM simulations for assemblies of coarse and fine particles under biaxial shear. The simulations reveal that the distribution pattern of fine particles in the soil skeleton plays a crucial role in the overall macroscopic response: The contractive response observed at the macro scale is mainly caused by the movement of fine particles out of the force chains whereas the dilative response is mainly associated with the migration of fine particles into the force chains. In an assembly of coarse and fine particles, neither all of the fine particles nor all of the coarse ones participate in the force chains to carry the external loads, and therefore a more reasonable definition for equivalent skeleton void ratio is put forward in which a new parameter d is introduced to take into account the fraction of coarse particles absent from the force chains.

• Geomechanics and Engineering
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• 제24권1호
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• pp.57-65
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• 2021

The effects of initial soil fabric and aspect ratio (AR) on the small-strain stiffness (G0) of granular soils are studied by employing discrete element method (DEM) numerical analysis. Elongated clumps composed of subspheres were adopted, and the G0 values were obtained by DEM simulations of drained triaxial tests under different densities and initial confining pressure (p0). The DEM simulations indicate that the initial soil fabric has an insignificant effect on G0. The effect of the AR on G0 is related to the initial density. Namely, for dense specimens, G0 first increases with increasing AR, reaching a plateau value when the AR ≥ 1.5. However, for loose specimens, G0 gradually increases as the AR increases. Microscopic examination reveals that G0 uniquely depends on the coordination number of the particles (CN-particle) rather than the subspheres (CN-sphere) at the particulate level for the effects of initial soil fabric and AR. Finally, Poisson's ratio ν0 is also determined by CN-particle. In addition, based on data in literature and this study, ν0 can be fitted as ν0 = 5.920(G0/(p0)1/3)-0.99, which can be used to predict ν0 of granular soils based on the measured G0.

• Geomechanics and Engineering
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• 제28권1호
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• pp.89-105
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• 2022

The behavior of the soil subgrade is complex and irregular against loads. When modeling, the soil is often replaced by a more straightforward system called a subgrade model. The Winkler method of linear elastic springs is a popular method of soil modeling in which the spring constant shows the modulus of subgrade reaction. In this research, the factors affecting the distribution of the modulus of subgrade reaction of elastoplastic subgrades are examined. For this purpose, critical theories about the modulus of subgrade reaction were examined. A square raft foundation on a sandy soil subgrade with was analyzed at different internal friction angles and Young's modulus values using ABAQUS software. To accurately model the actual soil behavior, the elastic, perfectly plastic constitutive model was applied to investigate a foundation on discrete springs. In order to increase the accuracy of soil modeling, equations have been proposed for the distribution of the subgrade reaction modulus. The constitutive model of the springs is elastic, perfectly plastic. It was observed that the modulus of subgrade reaction under an elastic load decreased when moving from the corner to the center of the foundation. For the ultimate load, the modulus of subgrade reaction increased as it moved from the corner to the center of the foundation.

• 한국해양공학회지
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• 제36권3호
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• pp.161-167
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• 2022

Three-dimensional finite element analysis (3D-FEA) models have been used to evaluate the shock-resistance responses of various equipments, including armaments mounted on a warship caused by underwater explosion (UNDEX). This paper aims to check the possibility of using one-dimensional (1D) FEA models for the shock-resistance responses. A frigate was chosen for the evaluation of the shock-resistance responses by the UNDEX. The frigate was divided into the thirteen discrete segments along the length of the ship. The 1D Timoshenko beam elements were used to model the frigate. The explosive charge mass and the stand-off distance were determined based on the ship length and the keel shock factor (KSF), respectively. The UNDEX pressure fields were generated using the Geers-Hunter doubly asymptotic model. The pseudo-velocity shock response spectrum (PVSS) for the 1D-FEA model (1D-PVSS) was calculated using the acceleration history at a concerned equipment position where the digital recursive filtering algorithm was used. The 1D-PVSS was compared with the 3D-PVSS that was taken from a reference, and a relatively good agreement was found. In addition, the 1D-PVSS was compared with the design criteria specified by the German Federal Armed forces, which is called the BV043. The 1D-PVSS was proven to be relatively reasonable, reducing the computing cost dramatically.

• 농업과학연구
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• 제50권3호
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• pp.499-510
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• 2023

The purpose of this study is to develop a high-speed combine harvester. The performance was evaluated by composing a dynamic simulation model of a threshing cylinder and analyzing the amount of threshed rice grain during threshing operations. The rotational speed of the threshing cylinder was set at 10 rpm intervals from 500 rpm until 540 rpm, based on the rated rotational speed of 507 rpm. The rice stem model was developed using the EDEM software using measured rice stem properties. Multibody dynamics software was utilized to model the threshing cylinder and tank comprising five sections below the threshing cylinder, and the threshing performance was evaluated by weighing the grain collected in the threshing tank during threshing simulations. The simulation results showed that section 1 and 2 threshed more grains compared to section 3 and 4. It was also found that when the threshing speed was higher, the larger number of grains were threshed. Only simulation was conducted in this study. Therefore, the validation of the simulation model is required. A comparative analysis to validate the simulation model by field experiment will be conducted in the future.

• Geomechanics and Engineering
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• 제11권1호
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• pp.1-39
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• 2016

The finite element method (FEM), discrete element method (DEM), and Discontinuous deformation analysis (DDA) are among the standard numerical techniques applied in computational geo-mechanics. However, in some cases there no possibility for modelling by traditional finite analytical techniques or other mesh-based techniques. The solution presented in the current study as a completely Lagrangian and mesh-free technique is smoothed particle hydrodynamics (SPH). This method was basically applied for simulation of fluid flow by dividing the fluid into several particles. However, several researchers attempted to simulate soil-water interaction, landslides, and failure of soil by SPH method. In fact, this method is able to deal with behavior and interaction of different states of materials (liquid and solid) and multiphase soil models and their large deformations. Soil indicates different behaviors when interacting with water, structure, instrumentations, or different layers. Thus, study into these interactions using the mesh based grids has been facilitated by mesh-less SPH technique in this work. It has been revealed that the fast development, computational sophistication, and emerge of mesh-less particle modeling techniques offer solutions for problems which are not modeled by the traditional mesh-based techniques. Also it has been found that the smoothed particle hydrodynamic provides advanced techniques for simulation of soil materials as compared to the current traditional numerical methods. Besides, findings indicate that the advantages of applying this method are its high power, simplicity of concept, relative simplicity in combination of modern physics, and particularly its potential in study of large deformations and failures.

• Structural Engineering and Mechanics
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• 제89권2호
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• pp.181-197
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• 2024

A numerical method is presented in this paper, for buckling analysis of thin arbitrary stiffened composite cylindrical shells under axial compression. The stiffeners can be placed inside and outside of the shell. The shell and stiffeners are operated as discrete elements, and their interactions are taking place through the compatibility conditions along their intersecting lines. The governing equations of motion are obtained based on Koiter's theory and solved by utilizing the principle of the minimum potential energy. Then, the buckling load coefficient and the critical buckling load are computed by solving characteristic equations. In this formulation, the elastic and geometric stiffness matrices of a single curved strip of the shell and stiffeners can be located anywhere within the shell element and in any direction are provided. Moreover, five stiffened composite shell specimens are made and tested under axial compression loading. The reliability of the presented method is validated by comparing its numerical results with those of commercial software, experiments, and other published numerical results. In addition, by using the ANSYS code, a 3-D finite element model that takes the exact geometric arrangement and the properties of the stiffeners and the shell into consideration is built. Finally, the effects of Poisson's ratio, shell length-to-radius ratio, shell thickness, cross-sectional area, angle, eccentricity, torsional stiffness, numbers and geometric configuration of stiffeners on the buckling of stiffened composite shells with various end conditions are computed. The results gained can be used as a meaningful benchmark for researchers to validate their analytical and numerical methods.

• 대한전자공학회논문지
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• 제8권3호
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• pp.1-14
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• 1971

본논문은 릴레이 제어기구의 안정도해석과 종합성능판별의 기초가 되는 리미트사이클진동의 주기해를 정확하고도 신속하게 얻을 수 있는 방법을 개발한 것으로서 특히 궤적법은 동종의 릴레이에 대해서는 특서정수의 변화에 대해서 직각대응시킬 수 있고, 주기해를 정확하게, 그리고 신속하게 직속할 수 있는 장점을 지닌다. 이제까지 다루워 왔던 describing 함수해석법과도 비교하여 그의 부정확성과 불편성 동종릴레이 특성정수변화에 대한 비적응성도 검토하여 궤적법의 우월을 명시하였다.

• 콘크리트학회지
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• 제6권1호
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• pp.120-130
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• 1994

본 연구의 목적은 반목하중을 받는 철근콘크리트 부재의 이력거동을 적절히 예측할 수 있는 해석모델을 구축하고 기존 연구자들의 실험결과를 분석하여 부재의 다양한 이력거동을 예측할 수 있는 이력모델을 제안하는데 있다. 이력모델의 구축에는 골조의 동적해석에 정량적으로 사용할 수 없는 변수들을 배제함으로써 6개 자유도를 갖는 평면 프레임의 비선형 동적해석에 적용가능한 해석요소를 개발하였다. 해석모델은 소성힌지부를 단일 스프링으로 치환한 분리선형요소 모델을 사용하였으며 부재의 길이방향 철근 배근상태에 따라 소성힌지부의 이동을 고려할 수 있도록 하였다. 기존 연구자들의 실험결과를 비교$\cdot$분석한 결과, 반복하중에 의해 나타나는 부재의 강성저하는 기본 핀칭계수, 부재의 연성비 및 항복강도비의 함수로 적절히 예측할 수 있었으며, 부재의 강도저하에 대해서는 횡보강근 간격비, 단면형상비를 고려한 새로운 개념의 강도감소계수를 제안하였다. 본 해석모델에 의해 계산한 부재의 에너지 소산능력을 실험결과와 약 10%~20% 내외의 오차를 나타냄으로써 본 해석결과의 타당성을 입증하고 있다. 따라서 본 연구에서 제안하는 해석모델은 반복하중을 받는 철근콘크리트 보-기둥 접합부의 이력거동 해석에 사용 가능하다고 판단된다.