• 한국항해학회지
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• 제9권2호
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• pp.43-63
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• 1985

As a circular cylinder has a comparatively simple shape and becomes a basic problem for flows around other various shapes of bodies, the problem of two-dimensional viscous flow around the circular cylinder has been investigated, both theoretically and experimentally. But not a few problems are left unsolved. It is well known that the calculations are successfully made with the approximations of Stokes or Oseen for very low Reynolds numbers, but as Reynolds number is increased, Oseen's approximations as well as Stokes's ones become more and more remote from the exact solution of the Navier-Stokes equations. Therefore, in this paper, the authors transform the Navier-Stokes equations into the finite difference equations in the steady two-dimensional viscous flow at Reynolds number up to 45, and then solve the solution of the Navier-Stokes equations numerically. Also, the authors examine the accuracy of the solution by means of flow visualization with aluminum powder. The main results are as follows; (1) The critical Reynolds number at which twin vortices begin to form in the rear of the circular cylinder is found to be 6 in the experiment and 4 in the numerical solution. (2) As Reynolds number is increased, it is proved that the ratio of the length of the twin vortices to the diameter is grown almost linearly, both experimentally and numerically. (3) Separation angle is also increased according to reynolds number. But it is found that it would converge into 101.3 degrees, both experimentally and numerically.

• 한국추진공학회지
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• 제12권3호
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• pp.68-75
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• 2008

이전에 개발된 병렬 해석 코드를 이용하여 원형 관내에서의 삼차원 데토네이션 파 전파 특성을 관찰 하였다. 일련의 해석을 통하여 직경이 일정한 원형 관에서 반응 속도 상수 값 k에 의존하는 데토네이션 셀 생성 메커니즘을 알 수 있었다. 삼차원 유동에 대한 비정상 유동의 해석 결과는 two-, three-, four-cell 구조의 메커니즘을 잘 보여주었으며, 반응속도 상수 k가 증가함에 따라 생성되는 셀 수가 증가하고 셀의 폭과 길이는 감소하였다. 모든 다중-셀 모드에서 데토네이션 파의 구조와 그을음막 기록은 횡단파의 움직임에 의하여 만들어지며, 데토네이션 파면은 주기적으로 일정한 다각형 및 풍차 형상을 가지게 된다.

• 한국해양환경ㆍ에너지학회지
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• 제8권2호
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• pp.67-73
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• 2005

부방파제의 특성을 간단히 검토하고 수치해법을 이용하여 소파성능을 분석하였다. 비점성 포텐셜 유동의 일반적인 해법인 경계면적분법을 사용하였고, 다양한 형상의 부방파제 2차원 단면특성을 투과율을 중심으로 살펴보았다. 계류계의 강도와 질량관성반경 및 흘수의 영향을 기본적인 폰툰 형태에 대하여 고찰하였고, 사다리꼴, 중절모형상, 탁자 형상 등의 단면에 대하여 형상에 변화를 주며 소파특성을 조사하였다. 각 단면마다 효과적인 소파가 기대되는 입사파의 파장이 달라지지만 입사파의 파장과 부체의 길이비가 10 이상이 되는 경우까지 만족스런 소파가 이루어지는 경우도 있다.

• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.169-187
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• 2019

This work presents a practical detailed finite element (FE) approach for the three-dimensional (3D) free-vibration analysis of actual aircraft and spacecraft-type lightweight and thin honeycomb sandwich panels. It consists of calling successively in $MATLAB^{(R)}$, via a developed user-friendly GUI, a detailed 3D meshing tool, a macrocommands language translator and a commercial FE solver($ABAQUS^{(R)}$ or $ANSYS^{(R)}$). In contrary to the common practice of meshing finely the faces and core cells, the proposed meshing tool represents each wall of the actual hexagonal core cells as a single two-dimensional (2D) 4 nodes quadrangularshell element or two 3 nodes triangular ones, while the faces meshes are obtained simply using the nodes at the core-faces interfaces. Moreover, as the same 2D FE interpolation type is used for meshing the core and faces, this leads to an automatic handling of their required FE compatibility relations. This proposed approach is applied to a sample made of very thin glass fiber reinforced polymer woven composite faces and a thin aluminum alloy hexagonal honeycomb core. The unknown or incomplete geometric and materials properties are first collected through direct measurements, reverse engineering techniques and experimental-FE modal analysis-based inverse identification. Then, the free-vibrations of the actual honeycomb sandwich panel are analyzed experimentally under different boundary conditions and numerically using different mesh basic cell shapes. It is found that this approach is accurate for the first few modes used for pre-design purpose.

• 한국의류학회지
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• 제45권1호
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• pp.46-55
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• 2021

Seam puckering and the seam strength of conductive threads used to produce smart clothing were analyzed according to stitching methods and fabrics. Samples were prepared in a lock stitch and zigzag stitch on plain woven and jersey knit fabric, using one type of polyester sewing thread and three types of commercial conductive threads that consisted of two types of stainless-steel conductive threads (TST and MST) and one type of silver conductive thread (SSV). Seam pucker percentages, shapes, and seam strength were measured. On plain woven fabric as well as jersey knit fabric, three-ply TST and MST showed a higher SP percentage compared to a polyester sewing thread. Meanwhile, single-ply SSV showed the lowest SP percentage. In addition, the SP percentage of the zigzag stitch decreased along the weft and course directions of the fabric, and decreased significantly as the number of fabric layers increased. Moreover, there was a marked tendency for a higher SP percentage in jersey knit fabric compared to plain woven fabric, and the two-dimensional cross-section waveforms of stitches obtained using three-dimensional data that showed increased irregular waveforms and peaks in the zigzag stitch. There were no correlations between seam strength and tensile strength.

• 한국의상디자인학회지
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• 제14권3호
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• pp.37-49
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• 2012

The purpose of this study is to provide basic data of dress design by researching three-dimensional decorative techniques representing flowers, a popular motif in dress design. This study analyzed 44 dresses that were presented in Valentino collection. The result of this study is as follows: First, the detailing expression method can show various patterns and colors through embroidery technique, sub-materials, and bonding techniques in embroidery, beads flower, and ribbon flowers. Second, the fabric flower technique expressed flower image in three-dimension in more various images than do either the ribbon or beads flower technique. Fabric flowers are mostly made from the same material as dresses. The expression technique of fabric flower is classified into the following three classifications: 1) A technique underlying a flower image with one, two and three large flowers, 2) a technique decorating a large area with a number of an identical motif, and 3) a technique highlighting a part of the body or design line by attracting eyes to one point, creating a corsage decorated where a designer wants to emphasize. Third, a silhouette technique realizes a flower image with a silhouette of a dress like sculpted structure and it is thus used less than a detailing expression technique. A flower image is expressed by making use of body lines or emphasizing the face. Finally, flower images on a dress were realized as a full blossomed flower, through visually streamlined shapes and curved lines.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.921-927
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• 2001

Steady flow bench test is a practical, powerful and widely used test in most engine manufacturers to give a design concept of a new engine. In order to use steady data as a performance index, it is necessary to build some database, which can correlate the port characteristics with engine data. However, it is very hard to investigate all port and valve shapes with experimental tools. The steady flow scheme is relatively simple and its results are bulk ones such as flow rate and momentum of flow. Therefore a CFD code can be easily applied to the port evaluation. In this study, the steady flow test was simulated through two and three-dimensional analysis on intake port design for comparing with experimental data and confirming the feasibility of applying analytic method. For this purpose, the effect of valve curvature on flow rate was estimated by a CFD code. There results were compared with those of real steady flow tests. As a result, the 2-D analysis described the phenomena qualitatively well, and also the results of 3-D analysis were almost consistent with experimental data.

• 한국생활과학회지
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• 제14권2호
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• pp.303-312
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• 2005

The purpose of this research is to analyze the lower part of dress forms with different sectional rotation-angles ($e.g.\;9^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ}$) using three-dimensional measurement system and to investigate measurement properties for dress making. The dress forms used in this experiment were size 8 and six types: four from Korea and two from Japan. The instrument and tools for three-dimensional measurement was Whole Body 3D scanner (Exyma-WBS2H). The analysis program used in this experiment was Rapid Form 2004 PP1 (INUS technology, Inc, Korea). The measurement of dress forms was done three times with different sectional rotation-angles and its data were analyzed using SPSS WIN 10.0 Package. The following results were obtained: 1. With mean and standard deviation of each measured part, it was found out that the dress forms from two countries were different in size per each part. For example, the Japanese one was relatively large in middle hip and hip, compared to the Korean one. 2. The 3D analysis of the sectional rotation-angles revealed some differences between the two dress forms in sectional length per each part. 3. With cluster analysis results, it was found that there were definite differences among measurements per each part, especially in $30^{\circ}\;and\;45^{\circ}$ sections. 4. The proportion of the dress forms showed significant differences in the curvature between center and side section of the lower parts. In addition, the shapes on the horizontal section map of the four levels (waist, middle hip, hip, and bottom) were analyzed.

• 대한의용생체공학회:의공학회지
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• 제34권2호
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• pp.73-79
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• 2013

Purpose: The purposes of this study were to measure the dose distribution of Photodynamic therapy(PDT) laser with 635 nm wavelength using GafChromic film. Method & Result: We made each output 300 J by changing mW and sec using the laser beam radiation mode such as C.W(Continuous Wave) mode, Pulse mode and Burst Pulse mode and measured the does at 0 mm and 5 mm of distance from optic fiber catheter end to the film, and at 5 mm distance by changing the angle of the end of the optic fiber catheter as $0^{\circ}$ and $0.5^{\circ}$. The radiated film was scanned and OD(Optical Density) was compared. And two-dimensional isodose curves were obtained and the consistency of shapes was compared. It was confirmed that there was consistency between optic density and the dose radiated on the film when we radiated GafChromic film by changing distance and angle of 300 J output in each radiation mode coordinating mW and sec. Conclusion: In this study, we could identify the stability according to changes in laser beam modes, changes in output according to distance, changes in uniformity according to angle, and beam profiles using GafChromic film, and we could also get two-dimensional isodose curve. It was found that small change in the distance and angle that is made when optic fiber catheter was contacted on the treatment area did not make big effects on the output of beam and the uniformity of dose, and it was also found that GafChromic film could be utilized for the purpose of QA of PDT laser beam.

• Journal of Welding and Joining
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• 제18권1호
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• pp.97-103
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• 2000

Time series analysis results show the SVD is a candidate of on-line monitoring of welding penetration when the covariance matrix of a full penetration is used as a mapping function. As the reconstructed embedding vectors from the chaotic scalar time series are manipulated by the covariance matrix, the mapped tim series lie on a hyper-ellipsoid which the lengths of semi-axes are the squared eigenvalues of the covariance matrix in the case of full penetration. These visualize by two dimensional stroboscope views. The other cases like partial penetration, are different in the sense of sizes and shapes. Here we test two types of time series; the ion current and the X-ray. The ion current is better than the X-ray as an on-line monitoring signal, because the difference of the eigenvalue spectrum of the ion(between the pull penetration and partial penetration) is bigger than those of the X-ray.