• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.15-28
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• 1998

As an alternative for solving the incompressible Navier-Stokes equations, we present a vorticity-based integro-differential formulation for vorticity, velocity and pressure variables. One of the most difficult problems encountered in the vorticity-based methods is the introduction of the proper value-value of vorticity or vorticity flux at the solid surface. A practical computational technique toward solving this problem is presented in connection with the coupling between the vorticity and the pressure boundary conditions. Numerical schemes based on an iterative procedure are employed to solve the governing equations with the boundary conditions for the three variables. A finite volume method is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition . The velocity field is obtained by using the Biot-Savart integral derived from the mathematical vector identity. Green's scalar identity is used to solve the total pressure in an integral approach similar to the surface panel methods which have been well-established for potential flow analysis. The calculated results with the present mettled for two test problems are compared with data from the literature in order for its validation. The first test problem is one for the two-dimensional square cavity flow driven by shear on the top lid. Two cases are considered here: (i) one driven both by the specified non-uniform shear on the top lid and by the specified body forces acting through the cavity region, for which we find the exact solution, and (ii) one of the classical type (i.e., driven only by uniform shear). Secondly, the present mettled is applied to deal with the early development of the flow around an impulsively started circular cylinder.

• 대한기계학회논문집
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• 제17권1호
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• pp.51-61
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• 1993

본 연구에서는 에너지법으로 축대칭 박판성형 공정을 해석할 때, Lee와 Yang 이 제안한 방법을 적용함에 있어 굽힘효과를 효과적으로 고려할 수 있는 방법을 제안 하고 축대칭 컵드로잉 공정을 해석하여 본 이론의 타당성을 입증하고자 한다. 굽힘 효과는 박판소재를 몇개의 층(layer)으로 나눈 뒤, 각 층에서 소비되는 변형에너지를 합하여 전체 에너지를 최소화시킴으로써 고려하였다. 해석시 펀치 목부분과 다이목 부분에서의 접촉압력은 각각 균일한 분포를 갖는 것으로 가정하였다. 본 이론의 타 당성을 입증하기 위하여 계산결과를 실험치 및 탄소성 유한요소해석 결과와 비교하였 다.

• 한국정밀공학회지
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• 제27권2호
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• pp.130-136
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• 2010

For stability analysis of the lumbar spine, the hypothesis presented is that the disc has stress sensors driving feedback mechanism, which could react to the imposed loads by adjusting the contraction of the muscles. Fusion in the motion segment of the lumbar spinal column is believed to alter the stability of the spinal column. To identify this effect finite element (FE) models combined with optimization technique was applied and quantify the role of each muscle and reaction forces in the spinal column with respect to the fusion level. The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Vertebral body and pelvis were modeled as a rigid body and the rib cage was constructed with rigid truss element for the computational efficiency. Spinal fusion model was applied to L3-L4, L4-L5, L5-S1 (single level) and L3-L5 (two levels) segments. Muscle architecture with 46 local muscles was used as acting directions. Minimization of the nucleus pressure deviation and annulus fiber average axial stress deviation was selected for cost function. As a result, spinal fusion produced reaction changes at each motion segment as well as contribution of each muscle. Longissimus thoracis and psoas major muscle showed dramatic changes for the cases of L5-S1 and L3-L5 level fusion. Muscle force change at each muscle also generated relatively high nucleus pressure not only at the adjacent level but at another level, which can explain disc degeneration pattern observed in clinical study.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.799-801
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• 1988

This paper was studied on the effects of Ca-La-Nb substitution and Zr/Ti ratio variation to Pb(Zr, Ti)$O_3$ system on structural, electrical, optical and sound level characteristics in order to develope the piezoelectric and electrooptic ceramic devices. Also the specimens were prepared by the two stage sintering technique. The molecular formular was X($CaO{\cdot}1/4La_{2}O_{3}{\cdot}1/4Nb_{2}O_{5}){\cdot}(1-X)Pb(Zr_{Y}Ti_{1-Y})O_{3}$(x=100X, y=100Y), and the variation of x was $6{\sim}12$, y was 60${\sim}$49 and second stage sintering time was 20${\sim}$40 hours. The experimental results obtained from this study are as follows : 1. The density was decreased, the grain size was increased according to increase of Ca-La-Nb substitution. 2. The crystal structure was rhombohedral in composition 6/60/40, and the crystal structure was tetragonal and cubic according to increase of Ca-La-Nb substitution. 3. The Ca substitution of PZT system enhanced the sintering property. The Pb site vacancy resulting from the substitution of La-Nb increased the dielectrical constant, the piezoelectric charge constant, the dielectric loss and decreased the coercive field. 4. The resistivity of PZT system which has the P type conduction mechanism increased according to substitution of La-Nb because of the substituent acting as donor. 5. The PZT ceramics varied from ferroelectric substance according to increase of Ca-La-Nb substituent. The coercive field and saturation remanent polarization decreased, and at last straight line according to increase of La-Nb substitution. 6. The amount of Ca-La-Nb substitution to improve the light transmittance of speciment was 10 mol%, the Zr/Ti ratio was 49/51, and the second stage sintering time was 40 hours. 7. According to Ca-La-Nb substitution, the specimens was to be transparent. The 7.5/51/49 specimen was suitable for transparent sound vibrator because it had 58% light transmittance (thick 0.2[mm], wave length 700[mm]) and 48% electromechanical coupling factor.

• Parasites, Hosts and Diseases
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• 제23권2호
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• pp.247-252
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• 1985

In the present study, the effect of primary infection to reinfection with Ascaris suum larvae was experimented in mouse model. Mice were challenged with 1,000 infective stage eggs of Ascaris suum. The embryonated eggs were directly introduced into stomach of mice. Reinfection was performed at 50 days after the primary infection with same method as primary infection. Mice were sacrificed 3, 5, 7, 10, 15 and 20 days after infection in both groups respectively. Larvae collected from livers and lungs with Baermann's apparatus were enumerated and measured after sacrifice. Sera of mice were also collected at same time. The results of the experiment were as follows: With antigen prepared from coelomic fluid of adult Ascaris suum and sera collected from mice before reinfection, the production of antibody in experimental mice was confirmed by the gel-diffusion technique. In the livers of reinfected mice, the larvae were recovered up to 10 days after challenge, otherwhile in the primary infected mice, the larvae were observed up to 7 days. The maximum number of larvae were observed in the lungs of primary infected mice on 10 days after inoculation. In the lungs of reinfected mice, maximum number of larvae were recovered on 7 days after, only few larvae were recovered on 10 days after reinfection. As regards the growth of the larvae, the third stage larvae, over $500{\mu\textrm{m}}$ in length, appeared in livers at 5 days after reinfection, but it couldn't be found on 7 days and 10 days after challenge. The third stage larvae continuously developed were observed in lungs of mice from 5 days after reinfection. In conclusion, it was found that development of larvae in livers of immune mice were probably repressed by the immune mechanisms being rises in livers and defence mechanism is also acting by interfering with the process of larval penetration into the lung from the liver.

• Ocean and Polar Research
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• 제42권1호
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• pp.77-88
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• 2020

This paper presents the coordinate systems used for trawl doors modeling, and provides matrix equations of connection between these systems. The projections of the forces acting on the door into axes of various coordinate systems were obtained, which were used in the door equilibrium equations. Six equilibrium conditions for the door as a solid were obtained: formulas that allow for the door area in plan to be determined; its weight in water; its mass; three moment equations for determining the position of the warp and backstrops fastening points to the door with triangular and quadrangular backstrop arrangements. It was found that the moment equilibrium equations of trawl doors are generally incompatible, which was not found by any of the authors who have previously conducted research into trawl doors. Using the Kronecker-Capelli theorem, the compatibility equation is obtained. This equation includes the coordinates of the backstrop fastening points to the door, which means that these points cannot be randomly selected. The technique of determining the warp and backstrops' fastening points position to the door is described. Conditions of directional (by angle of attack) and roll (in angle of roll) stability of the doors' equilibrium are presented. The equations presented in this paper comprise a mathematical model that allows, when designing the doors, to select optimal parameters, as well as to carry out adjustments for trawling purposes to ensure the stable movement of the doors and the entire trawl system.

• 한국환경과학회지
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• 제14권8호
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• pp.723-737
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• 2005

The effects of pH (5, 7 and 9) and ionic strength of different salts on the flocculation characteristics of humic acid by inorganic (alum, polyaluminum chloride (PAC) with degree of neutralization, r=(OH/Al) of 1.7) and organic (cationic polyelectrolyte) coagulants, have been examined using a simple continuous optical technique, coupled with measurements of zeta potential. The results are compared mainly by the mechanisms of its destabilization and subsequent removal. The destabilization and subsequent removal of humic acid by PAC and cationic polyelectrolyte occur by a simple charge neutralization, regardless of pH of the solution. However, the mechanism of those by alum is greatly dependent on pH and coagulant dosage, i.e., both mechanisms of charge neutralization at lower dosages and sweep flocculation at higher dosages at pH 5, by sweep flocculation mechanism at pH 7, and little flocculation because of electrostatic repulsion between negatively charged humic acid and aluminum species at pH 9. The ionic strength also affects those greatly, mainly based on the charge of salts, and so is more evident for the salts of highly charged cationic species, such as $CaCl_2$ and $MgCI_2.$ However, it is found that the salts have no effect on those at the optimum dosage for alum acting by the mechanism of sweep flocculation at pH 7, regardless of their charge.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.235-240
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• 2010

분출냉각은 높은 압력과 온도의 가혹한 환경에서 운용되는 액체로켓과 공기흡입식 엔진을 위한 가장 효과적인 냉각방법이다. 연소기 라이너와 터빈 베인은 다공질 벽면을 통과하는 냉각재(공기 또는 연료) 뿐만 아니라 차단막으로 작용하는 공기에 의해 냉각된다. 그러나 이의 실용화는 유용한 다공질 재료의 제한에 의해 방해를 받아왔다. 벽면 내에서 내부 열전달을 증가시키는 보다 현실적인 방법을 찾는 노력을 통해 Lamilloy$^{(R)}$ 및 Transply$^{(R)}$와 같은 다층 기공 구조물을 개발하게 되었다. 본 논문은 액체로켓, 가스터빈 및 스크램제트의 추진기관 적용을 위한 분출냉각의 최근 연구동향을 고찰하였다.

• 한국철도학회논문집
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• 제18권1호
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• pp.53-62
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• 2015

동평판재하시험기(LWDT)는 궤도노반 등의 다짐강성 측정을 위하여 개발된 시험기이며 낙하추를 자유낙하시킬 때 가속도계를 이용하여 다짐표면의 처짐량을 측정, 반무한 탄성체로 가정된 노반의 동탄성계수를 결정한다. 본 연구에서는 LWDT시험기의 구성과 구동 메커니즘 및 동탄성계수 추출공식의 유효성을 상세히 분석하였다. 특히, 2층구조 노반 위에서 LWDT 시험시 상부층의 강성평가 유효깊이를 유한요소해석으로부터 결정하였다. 또한, LWDT 시험시 노반의 강성 차이를 고려하여 사용할 수 있는 동탄성계수 추출공식 수정계수를 제시하였다.

• 한국표면공학회지
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• 제50권6호
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• pp.531-535
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• 2017

Enormous amount of waste oyster-shell (OS) has a major disposal problem in coastal regions. OSs have attracted much attention for recycling, because these are mainly composed of calcium carbonate with rare impurities. In this study, we demonstrate the calcareous deposit films on steel plate by using OSs on the basic of cathodic protection technique. The composition of the OSs was analyzed by wavelength dispersive X-ray fluorescence spectrometer. Carbon dioxide gas was pumped into distilled water to make carbonic acid solution for dissolution of OS. The calcareous deposit was characterized by second electron microscope (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction. Corrosion rates were estimated by measurements of anodic polarization and immersion test. It is confirmed that calcareous deposits on steel plate are formed under all condition of cathodic protection by using waste OS from the SEM and EDX results. Calcareous deposits on steel by OS provide good corrosion resistance by acting as a barrier to oxygen supply to the steel surface.