• 한국항공우주학회지
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• 제45권3호
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• pp.212-216
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• 2017

두께비 18% 익형(KARI-11-180)에 대한 공력특성 분석이 전산해석기법을 활용해 수행되었다. 익형주위의 격자는 벽면에서 수직으로 투영하여 경계층 격자를 형성하였고 익형 후방에는 정밀한 후류 예측을 위해 조밀한 격자를 위치하였다. 원방경계까지의 거리는 익형 코드의 100배로 정하였고 익형시험결과와의 비교를 위해 자유류 속도, 익형 코드 및 Reynolds수를 풍동시험과 동일하게 정하였다. 또한 난류 모델은 천이지점 예측이 우수한 transition SST 및 DES 모델을 사용하였다. 3차원 전산해석은 세장비가 2와 5인 익형모델에 대해 수행되었는데 양력은 풍동시험결과보다 높은 값을 항력은 낮은 값을 예측하였다.

• Design & Manufacturing
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• 제16권2호
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• pp.46-52
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• 2022

As the consumer market in the eco-friendly vehicle industry grows, the demand for water pump in a electric car parts market. This study intend to propose a mathematical model that can verify the effect of improving thermal properties when a non-conductive cooling filler liquid is introduced into an electric vehicle water pump. Also, the pros and cons of the immersion cooling method and future development way were suggested by analyzing the cooling characteristics using on the derived analysis solution. Thermal characteristics analysis of electric water pump applied with non-conductive filler liquid was carried out, and the diffusion boundary condition in the motor body and the boundary condition the inside pump were expressed as a geometric model. As a result of analyzing the temperature change for the heat source of the natural convection method and the heat conduction method, the natural convection method has difficulty in dissipating heat because no decrease in temperature due to heat release was found even after 300 sec. Also, it can be seen that the heat dissipation effect was obtained even though the non-conductive filling liquid was applied at the 120 sec and 180 sec in the heat conduction method. It has proposed to minimize thermal embrittlement and lower motor torque by injecting a non-conductive filler liquid into the motor body and designing a partition wall thickness of 2.5 mm or less.

• 대한기계학회논문집
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• 제19권7호
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• pp.1675-1683
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• 1995

A numerical study of the fluid flow and heat transfer characteristics of the two-dimensional impingement jet with a confinement plate has been carried out. The fluid flow was calculated by solving the full Navier-Stokes equation. In doing that, the well known SIMPLER algorithm was used and the trouble making convection term was discretized according to QUICKER scheme. The energy equation was simply solved by using the SOR method. For the Reynolds number of 10000, two channel heights, say 1.5 and 3.0 times the jet exit width, and two thermal boundary conditions constant wall temperature and constant wall heat flux were considered. Discrete heat sources were flush mounted along the impingement plate at a distance of 0, 2, 3, 4, 5, 6, 10, 12, times the jet exit width from the stagnation point. The length of each heat source is 4 times the jet exit width long. The Nusselt number averaged over each heat source was compared with experiment. Comparison shows that both calculations and experiment have the secondary peak of Nusselt number at downstream of stagnation point, even though there is a little quantitative difference in between. The difference is believed due to abscure thermal boundary condition in experiment and also accuracy of turbulence model used. The secondary peak is shown to be caused by rigorous turbulent flow motion generated as the wall jet flow is retarded and developes into the channel flow without flow reversal.

• 한국전산유체공학회지
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• 제18권2호
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• pp.85-92
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• 2013

In this study, we consider heat transfer enhancement in laminar channel flow by means of an infinite streamwise array of equispaced identical circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall. An immersed boundary method was employed to facilitate to implement the cylinders on a Cartesian grid system. No-slip condition is employed at all solid boundaries including the cylinders, and the flow is assumed to be periodic in the streamwise direction. Also, the Prandtl number is fixed as 0.7. For thermal boundary conditions on the solid surfaces, it is assumed that heat flux is constant on the channel walls, while the cylinder surfaces remain adiabatic. The presence of the circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to heat transfer enhancement on the channel walls. The Nusselt number averaged on the channel wall is presented for the wide ranges of Reynolds number and the gap. A significant heat transfer enhancement is noticed when the gap is larger than 0.8, while the opposite is the case for smaller gaps. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of varying the gap to enhance heat transfer from the channel walls.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.775-782
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• 2004

Recently, the cases which are constructed close by neighboring structure or underground structure are on the increase to get the utmost out of the land exploitation of underground space in the downtown area. As the building becomes larger, the excavation depth is getting deep, and the excavation area is getting, wide too. These are frequent occasions that the application of Strut or Anchor method is difficult, because of site boundary, civil application and the ground condition. Therefore, to solve these problem, we analyze and compare design with measuring data, change the design factor and show the improvement of course through the application of self-supported diaphragm wall using counterfort technique which is a new method. It is expected to be a contribution to the suitable exploitation method of construction.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.315-322
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• 2016

Room acoustic properties of coupled rooms connected by an aperture has been analyzed using statistical acoustic model based on the diffused sound field assumption, which has limitation in dealing with the parameters such an room geometries and non uniform absorptivity of the boundary surfaces. In order to overcome these difficulties the acoustic diffusion model has been introduced, by which distribution of the acoustic energy density can be analyzed for various shapes and wall absorptivity. In this study acoustic properties of coupled rooms connected by an aperture(e.g. door) is analyzed using acoustic diffusion equation, which is solved numerically. The mean energy densities of two rooms obtained by the diffusion model are compared with those from the statistical model. The results show good agreement for various coupling aperture sizes and absorption coefficients. For a limiting case when the partition wall is substituted by an aperture and the two rooms eventually forms a single room, results of coupled room analysis using diffusion model show good agreement with those of a single room.

• Restorative Dentistry and Endodontics
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• 제23권2호
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• pp.639-646
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• 1998

To evaluate the effect of interface conditions and retention grooves in the Class V composite resin restoration of the maxillary first premolar, the distribution of the values of stress and displacement was analyzed with the two-dimensional finite element method. The results were obtained as follows : 1. Boundary elements and Stiffness values could be used as the interface parameters in the, finite element method. 2. The amount of restriction of the displacement at the cervical margin by placing a retention groove at the cervical wall was about three times as high as that by placing a retention groove at the occlusal wall. 3. Because of the relative amount of tensile components of the stress values in the bucco-lingual direction, the possibility of dislocation of the restoration was much higher at the cervical margin than at the occlusal margin. 4. It might be recommended that both occlusal and cervical retention grooves be used routinely, but if one, it be placed at the cervical wall.

• 반도체디스플레이기술학회지
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• 제21권2호
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• pp.38-44
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• 2022

Plasma density in semiconductor fabrication equipment becomes higher to achieve the improved the throughput of the process, but the increase of surface corrosion of the ceramic coated chamber wall has been observed by the increased plasma density. Plasma chamber wall coating with aerosol deposition prefer to be firm and uniform to prevent the potential creation of particle inside the chamber from the deformation of the coating materials, and the aerosol discharge nozzle is a good control factor for the deposited coating condition. In this paper, we investigated the design of the nozzle of the aerosol deposition to form a high-quality coating film. Computational fluid dynamics (CFD) study was employed to minimize boundary layer effect and shock wave. The degree of expansion, and design of simulation approach was applied to found out the relationship between the divergence angle and nozzle length as the key parameter for the nozzle design. We found that the trade-off tendency between divergence angle and nozzle length through simulation and quantitative analysis, and present the direction of nozzle design that can improve the uniformity of chamber wall coating.

• 대한조선학회논문집
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• 제49권4호
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• pp.304-311
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• 2012

One of the main features of Drillship or FPSO is a moonpool structure. The moonpool structures have various accuracy tolerances according to their functions and targets. This study is mainly interested in roundness of a circular moonpool structure in FPSO. Because this structure needs abrasion-resistance at which bearing of machine touches on inner wall of moonpool, we should do over-lay welding widely and deeply by using Inconel weld material. But a general over-lay can cause a severe distortion at ship block structure. If we can analyze the roundness by thermal distortion under Inconel over-lay, we can establish a special erection policy by the results. In this study, we designed stress-strain curve for strain-boundary condition analysis by an elasto-plastic material property. The results made us to decide an appropriate ship-block size and policy of crane manipulation will follow for its capacity. If a structure that needs over-lay is not large, solid elements also are not a bad choice for FEM modeling. Therefore we also developed a standard of using strain-boundary method that shell elements are used as over-lay on solid element modeling.

• 에너지공학
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• 제11권3호
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• pp.262-268
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• 2002

The present paper investigated the effect of ultrasonic vibrations on the melting process of phase-change materials (PCM). Furthermore, the present study considered constant heat-flux boundary condition, whereas many of the previous researches had adopted constant wall-temperature condition. The results of the present study revealed that ultrasonic vibrations accompanied the effects like acoustic streaming, cavitation, and thermally-oscillating flow. Such effects are a prime mechanism in the overall melting process when ultrasonic vibrations are applied. They speed up the melting process as much as 2.5 times, compared with the result of natural melting. Also, energy can be saved by applying ultrasonic vibrations to the natural melting. In addition, temperature and Nusselt numbers over time provided a conclusive evidence of the important role of ultrasonic vibrations on the melting phenomena.