• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.80-94
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• 1994

As for axisymmetirc sheet metal forming, a kind of pick-up apparatus for body-wrinkling is deviced. Experiments with both hemispherical and flat headed punches, with various clearances between punch and die, with respect to three kinds of materials each of which has two thicknesses, are performed. Firstly the process of evolution of body-wrinkling is observed. Then the critical blank-holding force (or meridional tensile force) for suppression of body-wrinkling at a specified punch-stroke is measured for all cases mentioned above. An empirical formula for it is proposed. Deformation patterns and stress distributions are analysed by the use of FEM. A simplified critical condition for body-wrinkling is formulated and introduced into the FEM program. And its effectiveness is checked by comparison with the experimental results. Using this FEM system, the governing factors of body-wrinkling are cleared up.

• 대한조선학회논문집
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• 제55권3호
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• pp.252-264
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• 2018

The calculation of steady-state cavitating flows around Supercavitating Underwater Bodies (SUB's), which consist of a circular disk head (cavitator), a conical fore-body, a cylindrical middle-body and either a boat-tail or a flare-tail, are carried out. To calculate the axisymmetric cavitating flow, used is a commercial computational fluid dynamics code based on the finite volume method, Fluent. From the analysis of numerical results, the cavity and drag, affected by the fore-body and tail of the SUB's, are investigated. Firstly, the effect of the fore-body shape is investigated with the same disk cavitator and a cylindrical rear-body of fixed diameter. Then with the same cavitator and a fixed fore-body, the effect of the rear-body shape is investigated. Before the cavity generated by the cavitator covers the slant of fore-bodies sufficiently, the larger the cone angle of the fore-body(i.e., the shorter the slant length), the larger the drag and the slower the development of cavity. After the cavity covers the fore-body completely so that the pressure drag component of the body is vanished, the characteristics of drag-velocity curves are identical. Also, as the tail angle is bigger, the cavity generated by the cavitator is suppressed further and the drag becomes larger. The peak of the drag appears for the flare-tail, i.e., when the tail angle is positive(+). On the contrary, the trough of the drag appears for the boat-tail, i.e., when the tail angle is negative(-). When the tail angle is 5 degrees, the peak of the drag appears at the body speed of 80m/s and the value of the drag is 43% larger than that at the design speed of 100m/s. When the tail angle is -5 degrees, the trough of the total drag appears at 75m/s and that drag is 30% smaller than that of the cavitator, which means the rest of the body has a negative drag.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.929-930
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• 2010

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.957-965
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• 2011

The wakes of a cylindrical body have been investigated. The cylindrical body was attached with a thin film. The film is made of silicon with configurations of 50mm(W) ${\times}$ 150mm(L) ${\times}$ 0.3mm(T). The cylinder wakes have been measured with PIV experiments under the conditions with and without the thin film. The diameter of the installed cylinder body is 30mm and the Reynolds numbers are 2730, 6160 and 9750 with the diameter. The measurement system consists of an Ar-ion laser(6W), a high speed camera(1024 ${\times}$ 992 pixel, 500fps) and a host computer. FFT analyses have been carried out using the velocity vectors obtained by PIV measurements at the point X/D=1.52 and Z/D=0.52. For understanding the three-dimensional flow structures, a new Volumetric PTV(particle tracking velocimetry) has been constructed, in which the same four high-resolution cameras have been used. It has been verified that the flexible film suppresses or damps the vortices separated from the cylinder body, which makes the cylinder's wakes stable. With increase of Re numbers the intensity of the dominant frequency of the wakes become smaller.

• 한국자기학회지
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• 제21권5호
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• pp.174-179
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• 2011

지금까지 자성체에 미치는 전자기력을 계산하기 위해서는, 맥스웰 응력법, 가상변위법, 자하법, 자화전류법등이 널리 사용되어 왔으며, 이들은 자성체 덩어리 전체에 미치는 전자기력을 계산하는 데 있어 모두 정당한 결과를 가져온다고 보고 있다. 그러나 전자기력 밀도식의 완전한 형태에 대해서는 아직 까지도 논란이 있으며, 각 방법에 의한 표면 전자기력 밀도는 식과 수치해석 모두 다른 결과를 보인다. 본 연구는 전자기력밀도를 체적력으로 국한하여 가상공극법을 적용하였을 때, 모두 같은 형태의 식으로 도출이 됨을 해석식이 존재하는 모델을 통하여 보여준다. 즉, 가상공극 개념을 적용할 경우, 체적력 전자기력 밀도식의 통일 가능성을 보여 주는 것이다.

• Journal of Korean Society for Atmospheric Environment
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• 제16권E호
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• pp.59-68
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• 2000

In this paper Various aerosol cyclones that are developed recently form Kwangju Institute of Science and Technology(KJIST) for increasing collection efficiency or for decreasing pressure drop are reviewed. For the first time, new sets of experimental data are reported on the particle collection efficiency of cyclones with modified surface bodies namely, spiral guide body, circumferential groove body, and vertical groove body. Multi-cylinder cyclones by adding one or two additional cylindrical walls into the conventional cyclone are also described. Ad an attempt to increase the collection efficiency of small particles, electrocyclone using an externally applied electric field was designed and operated. In addition, factors affecting the cyclone performance were studied including flowrate, body and outlet sizes, cyclone dust outlet, and gas property.

• 한국군사과학기술학회지
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• 제7권3호
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• pp.69-76
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• 2004

In this paper, an efficient inverse design method for nose shape of submerged body based on the MGM(Modified Garabedian-McFadden) design method has been developed. The MGM design method is a residual-correction technique, in which the residuals are differences between the desired and the computed pressure distributions. 3-D incompressible Wavier-Stokes equation was adopted for obtaining the surface pressure distribution and combined with the MGM design method to perform the inverse design of nose shape of submerged body. The design method was verified by applying to several airfoil shapes. Improved design shapes could be obtained when the method was applied to nose shapes of submerged body.

• 한국유체기계학회 논문집
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• 제6권3호
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• pp.21-27
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• 2003

Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. In order to investigate the effect of blowing ratios on the film cooling of a turbine blade, cylindrical body model is used. Mainstream Reynolds number based on the cylinder diameter is $7.1{\times}10^4$. The effects of coolant flow rates are studied for blowing ratios of 0.7, 1.0, 1.3 and 1.7, respectively. The temperature distribution of the cylindrical model surface is visualized with infrared thermography (IRT). Results show that the film cooling performance could be significantly improved by the shaped injection holes. For higher blowing ratio, the spanwise-diffused injection holes are better due to the lower momentum flux away from the wall plane at the hole exit.

• 대한기계학회논문집
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• 제19권7호
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• pp.1731-1740
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• 1995

Experimental investigations have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution due to heating from below in a rotating cylindrical cavity. The objective is to examine the flow phenomena and the heat transfer characteristics according to the changes in temperature gradient, concentration gradient and rotating velocity of cavity. Thermal and solutal boundary conditions at side wall are adiabatic and impermeable, respectively. The top and bottom plate are maintained each at constant temperature and concentration. The cavity is put into a state of solid body rotation. Like the stationary case, the types of initially-formed flow pattern are classified into three regimes depending on the effective Rayleigh number and Taylor number; stagnant flow regime, single mixed-layer flow regime and successively formed multi-mixed layer flow regime. At the same effective Rayleigh number, the number of initially-formed mixed layer and its growth rate decrease as the effect of rotation increases. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered-flow regime, but look both liner in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1998년도 제17회 KOSCI SYMPOSIUM 논문집
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• pp.23-30
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• 1998

The stabilization characteristics of diffusion flame formed in the wake of a cylindrical flame holder were investigated. Distribution of turbulence intensity, concentration distribution of combustion gas, and ion currents were measured. The turbulence intensity in the wake of cylindrical- game holder is increased with increase of diameter or blockage ratio of grid. If the auxiliary fuel is injected into recirculation zone, the concentration of $C_3H_8$ is high, but the concentration of $CO_2$ is low at the boundary of recirculation zone. The region with highest average value of ion currents in the middle of flame is moved to the upstream side by the turbulent components of main stream. The flame mass with partially active reaction is moved fast for uniform flow and turbulence generator G3, but the flame mass with relatively slow reaction is moved slowly for turbulence generator G1.