• 한국강구조학회 논문집
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• 제28권4호
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• pp.271-280
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• 2016

근접거리에서의 폭발하중의 정확한 정량화에 대한 요구는 주요기반시설물, 빌딩 및 교량의 안전설계가 근접폭발에 대한 것이라는 점에서 매우 중요하다. 근접폭발에 대한 입사 및 반사압력은 높은 압력과 온도로 인하여 사용가능한 압력변환기로는 직접적인 측정이 매우 힘들며, 이는 근접거리에서의 압력과 충격량에 대한 합당한 예측을 가능하게 하는 확인되고 검증된 전산유체역학코드를 필요로 한다. 본 논문은 입사 및 반사 초과압력 및 충격량의 산정에 대하여 CFD 코드를 확인하고 증명하기 위한 수치해석에 대하여 소개하였다. 연구는 근접거리에 초점을 맞추어 수행되었으며, 근접폭발 시뮬레이션을 최적화하는 메쉬크기에 대에 대해서도 제안하였다.

• 대한기계학회논문집A
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• 제30권2호
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• pp.149-156
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• 2006

A boundary-based design sensitivity analysis(DSA) technique is proposed for addressing shape optimization issues in the elastostatics problems. Sensitivity formula is derived based on the continuum formulation in a boundary integral form, which consists of the boundary solutions and shape variation vectors. Though the boundary element method(BEM) has been mainly used to obtain the boundary solution, the FEM is used in this paper because this is much more popular, and has greatly improved meshing and computing power recently. The advantage of the boundary DSA is that the shape variation vectors, which are also known as design velocity fields, are needed only on the boundary. Then, the step for determining the design velocity field over the whole domain, which was necessary in the domain-based DSA, is eliminated, making the process easy to implement and efficient. Problem of fillet design is chosen to illustrate the efficiency of the proposed method. Accuracy of the sensitivity is good with this method even by employing the free mesh for the FE analysis.

• 한국분말재료학회지
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• 제24권1호
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• pp.29-33
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• 2017

Titanium carbide (TiC) powders are successfully synthesized by carburization of titanium hydride ($TiH_2$) powders. The $TiH_2$ powders with size lower than $45{\mu}m$ (-325 Mesh) are optimally produced by the hydrogenation process, and are mixed with graphite powder by ball milling. The mixtures are then heat-treated in an Ar atmosphere at $800-1200^{\circ}C$ for carburization to occur. It has been experimentally and thermodynamically determined that the de-hydrogenation, "$TiH_2=Ti+H_2$", and carburization, "Ti + C = TiC", occur simultaneously over the reaction temperature range. The unreacted graphite content (free carbon) in each product is precisely measured by acid dissolution and by the filtering method, and it is possible to conclude that the maximal carbon stoichiometry of $TiC_{0.94}$ is accomplished at $1200^{\circ}C$.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 1999년도 Proceedings of Pre-symposium of the 10th ISWPC
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• pp.172-177
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• 1999

Effect of fiber treatment with cellulase (Liftase A40), and with two refining methods (Valley beating and impact refining) on wood fiber and handsheet properties were investigated at three refining levels (300, 400, and 500ml) for two furnishes (NBKP and LBKP). Part of the treated furnishes were classified by 150 mesh screen into fine-free fiber, and fines. Fiber length analysis, WRV, zero-span strength, and other handsheet mechanical properties were compared. The study showed that Liftase A40 lowered the zero-span and the folding endurance of both furnishes (NBKP much more and LBKP much less). Pretreatment with Liftase A 40 followed by refining significantly lowered the fiber length and refining energy to reach to the target freeness. Impact refining, which is done by hitting the fibers vertically with rod at 20% solid content, kept the fiber length increased WRV, and improved handsheet mechanical properties much more than valley beating. Properties of fines from different sources were compared in detail in the study.

• 대한조선학회논문집
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• 제55권2호
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• pp.169-177
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• 2018

Twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin have been developed computationally for 3,000 TEU container ship through parametric study. The objective function is to minimize delivered power in model scale. Design variables are twisted angle, rudder bulb diameter and fin angle. The governing equation is Reynolds averaged Navier-Stokes equations in an unsteady turbulent flow and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. The calculation was carried out in towing and self-propulsion conditions at design speed. The sliding mesh technique was employed to simulate the flow around the propeller. Form factor is obtained from the towing computation. Self-propulsion point is obtained from the self-propelled computations at two propeller rotating speeds. The delivered power due to the designed twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin are reduced by 1.1%, 1.6%, and 2.0%, respectively.

• Journal of Computational Design and Engineering
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• 제2권2호
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• pp.96-104
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• 2015

Aluminum die casting is an important manufacturing process for mechanical components. Die casting is known to be more accurate than other types of casting; however, post-machining is usually necessary to achieve the required accuracy. The goal of this investigation is to develop machining- free aluminum die casting. Improvement of the accuracy of planar and cylindrical parts is expected by correcting metal molds. In the proposed method, the shape of cast aluminum made with the initial metal molds is measured by 3D scanning. The 3D scan data includes information about deformations that occur during casting. Therefore, it is possible to estimate the deformation and correction amounts by comparing 3D scan data with product computer-aided design (CAD) data. We corrected planar and cylindrical parts of the CAD data for the mold. In addition, we corrected the planar part of the metal mold using the corrected mold data. The effectiveness of the proposed method is demonstrated by evaluating the accuracy improvement of the cast aluminum made with the corrected mold.

• 한국컴퓨터그래픽스학회논문지
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• 제13권1호
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• pp.1-6
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• 2007

곡면은 다각형 메쉬에 비해 간결한 표현을 가지고 부드러운 형상을 표현할 수 있지만, 현재 그래픽스 하드웨어는 곡면 렌더링을 지원하고 있지 않다. 최근의 GPU를 이용하여 프로그래밍 가능한 그래픽스 파이프라인은 기존의 다양한 그래픽스 알고리즘들을 가속화시키는 데 이용될 수 있기 때문에, 이 논문에서는 GPU 하드웨어를 이용하여 블렌딩을 기반으로 생성된 임의의 위상을 가진 곡면을 빠르게 렌더링 하는 방법을 제시한다. 제어 메쉬상에서 샘플링된 매개변수와 지역 곡면을 표현하는 정보들을 그래픽스 파이프라인으로 전달하여, 정점 프로세서에서 이러한 정보들을 가지고 블렌딩된 곡면상의 위치 정보와 노말 벡터를 계산한다. 이러한 방법은 CPU에서 블렌딩 곡면을 계산하는 것보다 훨씬 빠르게 수행된다.

• 한국CDE학회논문집
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• 제11권5호
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• pp.335-343
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• 2006

Design changes for an original surface model are frequently required in a manufacturing area: for example, when the physical parts are modified or when the parts are partially manufactured from analogous shapes. In this case, an efficient 3D model updating method by locally adding scan data for the modified area is highly desirable. For this purpose, this paper presents a new procedure to update an initial model that is composed of combinatorial triangular facets based on a set of locally added point data. The initial surface model is first created from the initial point set by Tight Cocone, which is a water-tight surface reconstructor; and then the point cloud data for the updates is locally added onto the initial model maintaining the same coordinate system. In order to update the initial model, the special region on the initial surface that needs to be updated is recognized through the detection of the overlapping area between the initial model and the boundary of the newly added point cloud. After that, the initial surface model is eventually updated to the final output by replacing the recognized region with the newly added point cloud. The proposed method has been implemented and tested with several examples. This algorithm will be practically useful to modify the surface model with physical part changes and free-form surface design.

• Wind and Structures
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• 제15권4호
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• pp.313-329
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• 2012

There have existed for a number of years good practice guidelines for the use of Computational Fluid Dynamics (CFD) in the field of wind engineering. As part of those guidelines, details are given for the size of flow domain that should be used around a building of height, H. For low-rise buildings, the domain sizes produced by following the guidelines are reasonable and produce results that are largely free from blockage effects. However, when high-rise or tall buildings are considered, the domain size based solely on the building height produces very large domains. A large domain, in most cases, leads to a large cell count, with many of the cells in the grid being used up in regions far from the building/wake region. This paper challenges this domain size guidance by looking at the effects of changing the domain size around a tall building. The RNG ${\kappa}-{\varepsilon}$ turbulence model is used in a series of steady-state solutions where the only parameter varied is the domain size, with the mesh resolution in the building/wake region left unchanged. Comparisons between the velocity fields in the near-field of the building and pressure coefficients on the building are used to inform the assessment. The findings of the work for this case suggest that a domain of approximately 10% the volume of that suggested by the existing guidelines could be used with a loss in accuracy of less than 10%.

• 한국식품조리과학회지
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• 제21권6호통권90호
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• pp.936-941
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• 2005

녹차 잎을 건조 분말하여 래디칼 소거기능을 추출하는 공정으로 순환 이산화탄소유체추출기를 활용할 때의 추출 최적조건을 구하였다. 건조한 녹차 잎의 분말사이즈는 80/100 mesh로 하고, 추출 압력과 온도를 각각 125 kgf 및 $25^{\circ}C$로 12시간 추출한 경우 가장 추출효율이 좋았다. 또한 용매를 열수추출과 에탄을 농도 를 달리한 추출 방법으로 나누어 래디칼 소거기능을 추출하였다. 그 결과, 에탄올 $95\%$농도에서 추출한 경우 가장 효율이 높았으며, 온도는 $100^{\circ}C$로 30분 추출이 최적 조건이었다. 각 추출 방법에 따른 추출 수율과 안정성을 비교한 결과, 이산화탄소유체를 이용한 녹차 래디칼 소거기능 추출 공정이 열수나 에탄올에 비하여 각각 2.8배 및 1.87배 수율이 높았으며, 안정성 실험에서도 활성의 소실이 거의 없었다.