• 대한기계학회논문집A
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• 제26권7호
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• pp.1302-1308
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• 2002

Thermo-mechanical and flexural behavior of a wire-bond plastic ball grid array (WB-PBGA) package are characterized by high sensitive moire interferometry. Moire fringe patterns are recorded and analyzed for several bending loads and temperatures. At the temperature higher than $100^{\circ}C$, the inelastic deformation in solder balls become more dominant, so that the bending of the molding compound decreases while temperature increases. The deformation caused by thermally induced bending is compared with that caused by mechanical bending. The strain results show that the solder ball located at the edge of the chip has largest shear strain by the thermal load while the maximum average shear strain by the bending moment occurs in the end solder.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.71-76
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• 2009

The research to predict the resistance performance of the ship using the CFD analysis is increasing. For the CFD numerical analysis the computational mesh, which is proper to computational model, has to be made before the analysis is begun. In the parametric study, even though the deformation of each case is not very sharp, the whole computational mesh should be regenerated according to the conventional way. Hence, lots of effort is needed to repeated mesh generation work. To solve these problems, the automatic mesh generation method using the macro function of commercial CAD program and mesh generation program is introduced in this study. First, in the CAD program, by using the macro function and putting the deformation rate of bow and stern in lengthwise, the repeated modeling work is performed automatically. Next, the generated geometries are read by the mesh generation program and the proper mesh for the geometry is created automatically also using the macro function. The hybrid mesh which has unstructured grid near the bow and stern and structured grid in the remaining part of domain is used. The verification of the developed method is done by applying the method to predict the resistance performance of the podded propulsion cruise ship of the Daewoo Shipbuilding & Marine Engineering (DSME) in the cases of different length of bow and stern and pod set in different position. The author believes that the introduced method can help to make the database to optimize the resistance performance of the ship in various cases can be constructed without difficulty.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.369-383
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• 2022

In this study, an equivalent boundary conditions (BCs) determination method is developed numerically for a panel reinforced concrete (RC) slab to realistically analyze the deformation and fatigue behaviors of a bridge RC slab. For this purpose, a finite element analysis of a bridge RC slab is carried out beforehand to calculate the stiffness of the bridge RC slab, and then the equivalent BCs for the panel RC slab are determined to achieve the same stiffness at the BCs to the obtained stiffness of the bridge RC slab at the corresponding locations of the bridge RC slab. Moreover, for the simulation of fatigue behaviors, fatigue analysis of the panel RC slab is carried out employing a finite element method based on a numerical model that considers the bridging stress degradation. Both the determined equivalent BCs and the BCs that have been typically applied in past studies are employed. The analysis results confirm that, in contrast to the panel RC slab with typically used BCs, the panel RC slab with equivalent BCs simulate the same bending moment distribution and deformation behaviors of the bridge RC slab. Furthermore, the equivalent BCs reproduce the extensive grid crack pattern in the panel RC slab, which is alike the pattern normally witnessed in a bridge RC slab. Conclusively, the panel RC slab with equivalent BCs behaves identical to the bridge RC slab, and, as a result, it shows more realistic fatigue behaviors observed in the bridge RC slab.

• 한국항공우주학회지
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• 제41권1호
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• pp.1-9
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• 2013

이 논문에서는 2 차원 실린더의 와류유발진동에 따른 Lock-in 현상에 대해 수치해석을 수행하였다. 실린더의 운동을 모사하기 위해 변형격자와 고정격자를 이용하였다. 스프링 상사기법을 이용하여 격자를 변형하였다. 격자수 및 시간 간격 등을 조절해 얻은 수렴된 수치해가 비교 및 검증에 사용되었다. 또한, 유체-구조 결합 방법들의 효율성과 정확도를 비교 검토하였다.

• 한국의류학회지
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• 제30권8호
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• pp.1242-1252
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• 2006

Many applications in computer graphics require complex, highly detailed models. However, to control processing time, it is often desirable to use approximations in place of excessively detailed models. Therefore, we have developed the notion of an optimal matrix to simplify the model surface which can then rapidly obtain high quality 2D patterns by flattening the 3D surface. Firstly, the woman's 3D body was modeled based on Size Korea data. Secondly, the 3D model was divided by shell and block for the pattern draft. Thirdly, each block was flattened by the grid and bridge method. Finally, we select the optimal matrix and demonstrate it's efficiency and quality. The proposed approach accommodates surfaces with darts, which are commonly utilized in the clothing industry to reduce the deformation of surface forming and flattening. The resulting optimal matrix could be an initiation of standardization for pattern flattening. This can facilitate much better approximations, in both efficiency and exactness.

• 대한조선학회논문집
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• 제45권4호
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• pp.379-388
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• 2008

A hybrid Cartesian/immersed boundary code is expanded to simulate flow field around a three-dimensional body which undergoes large dynamic deformation. Immersed boundary nodes are automatically distributed based on the edges crossing triangles on body boundary. Velocity vectors are reconstructed at those immersed boundary nodes along local normal lines to the boundary. The reconstruction of pressure is avoided using the hybrid staggered/non-staggered grid method. The developed code is validated through comparisons with other results on laminar flow over a sphere. The code is applied to simulate flow around a foil which is attached to a body of revolution and rotates under periodic deformation. The periodic variation of the tip vortex is observed and the effects of the deformation on hydrodynamic force acting on the body are investigated.

• 소성∙가공
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• 제20권4호
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• pp.316-323
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• 2011

The hot curvature-forming of large aluminum thick plate using a grid-typed hybrid die is a process for the production of a spherical LNG tank. Many variables such as the initial die surface quality, grid size, grid thickness, size of blank plate and cooling line design, control the success of the process. In addition, the plate used in this process is generally larger than $10{\times}10m$ in size. Thus, it is very difficult to predict the surface characteristics of the plate during forming and to measure the different parameters due to the high cost of the experiments. In order to optimize the process design for the grid-type die, the development of an analytical method to predict the surface characteristics of the final product in hot curvature-forming is needed. This paper described the development of the method and procedures for FE simulations of the hot curvature-forming process, including hot forming, air flow, cooling, and thermal deformation analyses. An experiment for a small scale model of the process was conducted to check the validity of the numerical method. The results showed that the curvature of the plate in the analysis agrees well with that of the experiment within 0.037 and 0.016% tolerance margins for its side and corner, respectively.

• 대한조선학회논문집
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• 제39권3호
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• pp.18-27
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• 2002

Eulerian개념을 사용한 격자계 내 임의의 경계면 주위 점성유동 해석에서, 운동하며 변형하는 경계면 근방 해의 정도를 향상시키기 위해서 격자생성시 경계면으로 격자점들을 집중시켜주는 레벨셋법에 바탕을 둔 격자변형법을 도입하였다. 본 연구에서는 격자점들을 경계면 근방으로 집중되는 정도를 용이하게 조절할 수 있도록 새로운 형태의 모니터함수를 제시하였다. 집중격자계를 사용함으로 얻어지는 향상된 해의 정도의 검증을 위하여 바닥에 고정된 반원 실린더 주위 정상유동에 대하여 가상경계법을 함께 사용하여 해석하였다. 수치계산결과는 물체적합 격자계를 사용해서 얻은 결과와 매우 잘 일치하였으며, 집중격자법을 사용하지 않은 해석결과보다 향상된 결과를 보여주었다. 수치계산의 또 다른 예제로서 다수의 고정된 물체주위 유동해석으로 확장 적용하여 공학적 유용성을 검증하였다. 마지막으로 이동 집중격자계의 생성법의 적용을 위해서 움직이면서 변형을 일으키는 2차원 기포상승문제를 해석하였다. 수치해석결과에서 격자점들은 매시간 기포의 변형에 맞추어 적합하게 집중된 형태를 잘 보여주었으며, 고정된 격자계를 사용한 결과와 잘 일치하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.223-226
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• 2009

The plastics are widely utilized in the inside of vehicles. The dynamic tensile characteristics of auto-body plastics are important in a prediction of deformation mode of the plastic component which undergoes the high speed deformation during car crash. This paper is concerned with the dynamic tensile characteristics of the auto-body plastics at intermediate strain rates. Quasi-static tensile tests were carried out at the strain rate ranged from 0.001/sec to 0.01/sec using the static tensile machine(Instron 5583). Dynamic tensile tests were carried out at the strain rate ranged from 0.1/sec to 100/sec using the high speed material testing machine developed. Conventional extensometry method is no longer available for plastics, since the deformation of plastic is accompanied with localized deformation. In this paper, quasi-static and dynamic tensile tests were performed using ASTM IV standard specimens with grids and images from a high speed camera were analyzed for strain measurement. True stress-strain relations and the actual strain rates at each deformation step were obtained by processing load data and deformation images, assuming the plastics to deform uniformly in each grid.

• 한국전산유체공학회지
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• 제12권1호
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• pp.1-8
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• 2007

A code is developed using the hybrid Cartesian/immersed boundary method and it is applied to simulate flows around a three-dimensional deforming body. A new criterion is suggested to distribute the immersed boundary nodes based on edges crossing a body boundary. Velocities are reconstructed at the immersed boundary nodes using the interpolation along a local normal line to the boundary. Reconstruction of the pressure at the immersed boundary node is avoided using the hybrid staggered/non-staggered grid method. The developed code is validated through comparisons with other experimental and numerical results for the velocity profiles around a circular cylinder under the forced in-line oscillation and the pressure coefficient distribution on a sphere. The code is applied to simulate the flow fields around a plate whose tail is periodically flapping under a translation. The effects of the velocity and acceleration due to the deformation on the periodic shedding of pairs of tip vortices are investigated.