• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
• /
• pp.245-251
• /
• 1999

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seem that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stresses.

• 한국유체기계학회 논문집
• /
• 제3권2호
• /
• pp.24-30
• /
• 2000

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seen that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stress predictions.

• 한국추진공학회지
• /
• 제27권1호
• /
• pp.37-48
• /
• 2023

본 연구에서는 정상 상태 및 천이 상태에 따른 항공기용 터보팬 엔진의 성능해석 모델링을 수행하였다. 대상 엔진은 Pratt & Whitney 사의 F100-PW-229으로 선정하여 팬, 고압 압축기, 연소기, 고압터빈, 저압 터빈, Mixer, 수축-확산형 노즐 등의 구성품을 모델링하였다. 또한, 이차 유로를 통한 터빈에서의 냉각 효과를 적용하였다. Simulink를 이용하여 터보팬 엔진 성능해석 프로그램을 자체 개발함에 따라 해석의 자유도가 높으며, 엔진 제어기 설계에 활용이 용이한 구성의 성능해석 프로그램을 개발하였다. 개발된 성능해석 프로그램은 상용 프로그램인 GASTURB 해석 결과와의 비교를 통하여 검증하였다.

• 대한기계학회논문집B
• /
• 제28권4호
• /
• pp.395-405
• /
• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Using the proposed numerical technique, the collapse of a water dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions with respect to time have been compared with the reported experimental results.

• 대한기계학회논문집B
• /
• 제28권11호
• /
• pp.1348-1358
• /
• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation fur flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among seven filling patterns at each tetrahedral control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. The collapse of a water dam and the filling of a fluidity spiral have been analyzed. The numerical results have been in good agreement with the experimental results and the efficiency of the adaptive grid refinement and filling pattern techniques have been verified.

• 한국초전도ㆍ저온공학회논문지
• /
• 제3권1호
• /
• pp.64-68
• /
• 2001

An experimental study on the Joule-Thomson cryocooler with the mixed refrigerant (MR) is described in this paper, J-T refrigeration experiment was performed with a single stage regular air-conditioning compressor The mixed refrigerant in the experiment was composed of 75% mol fraction of $N_2$. 30% moi fraction of CH$_4$. 30% moi fraction of $C_2$H$_{6}$. 10% mot fraction of $C_3$H$_{8}$ and 15% mot fraction of iso-C$_4$H$_{10}$. Oil mist in the MR stream could be eliminated completely by the glass microfiber filter. Since a single stage compressor that had been designed thor R22 is not appropriate for high Pressure ratio of the mixed refrigerant especially during the transient period. two modifications were incorporated to regular J-T refrigeration cycle. First. a Portion of the MR was by-passed at the inlet of the heat exchanger and transferred directly to 7he suction of the compressor in the modified system. Second, a buffer volume was Prepared to change the mass flow rate of refrigerant. The pressure ratio in J-T expansion device was relieved at the beginning of the operation due to the by-Pass scheme. but it gradually decreased during the transient Process as some of the MR component condensed at low temperature. The buffer volume at the suction side was used to increase the MR gas density in the system after the transient cool-down period. Form the experiment with the modified system, the refrigerator could reach the lowest temperature of -152$^{\circ}C$ without cooling load. and about -15$0^{\circ}C$ with 5 W of cooling load . . . .

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2018년도 학술발표회
• /
• pp.293-293
• /
• 2018

관망내 흐름의 수치 모델링은 도시 침수 분석, 하수도 관의 손상 탐지 또는 하수도 시스템 설계와 같은 넓은 분야에 적용되는 매우 중요한 문제 중 하나이다. 관망내 흐름상태는 자유수표면이 존재하는 개수로 흐름과 자유수표면이 관내에 존재하지 않는 관수로 흐름, 그리고 개수로 흐름과 관수로 흐름의 경계지점에 혼합흐름상태가 존재한다. 개수로 흐름과 관수로 흐름의 해석을 위해서는 일반적으로 다른 지배방정식의 적용이 필요하며 이는 관망내 흐름해석을 어렵게 만드는 원인 중 하나가 된다. 이러한 어려움을 극복하기 위해서 관망의 흐름해석에는 일반적으로 Preissmann slot 모델이 널리 사용되고 있다. 그러나 그럼에도 불구하고, Preissmann slot 모델의 수치해석 시 수치진동으로 인한 수치적 불안정이 발생하기 쉬우며, 특히 개수로 흐름에서 관수로 흐름으로 넘어가는 혼합흐름상태에서 이러한 수치진동이 쉽게 발생하는 것으로 알려져 있다. 이러한 수치진동은 수치적 불안정성을 유발할 뿐만 아니라, 해의 정확성을 크게 저하시킬 수 있다. 본 연구에서는 이러한 문제를 극복하기 위해 Preissmann slot 모델의 새로운 수치기법을 제안하였다. Approximate Reimann flux solver와 Centred flux solver를 결합하여 하이브리드 해석기법을 개발하였다. 수지진동 발생하기 쉬운 실험들의 모의를 통하여 수치기법의 성능을 검증하였다.

• Journal of Mechanical Science and Technology
• /
• 제15권6호
• /
• pp.735-742
• /
• 2001

This paper reports on the dynamics and friction characteristics of piston skirt with consideration of mixed lubrication. Piston skirt is an important part of the engine that transforms fuel into mechanical energy. The durability and low friction characteristics are important recent issues in piston skirt design. In this paper, the piston skirt motion is analyzed with consideration of mixed lubrication and piston skirt tilting motion. The entire trajectory of piston motion is obtained by using transient numerical method. Also various parameter studies are performed for piston skirt design and the development of lower frictional engine.

• 한국추진공학회지
• /
• 제19권5호
• /
• pp.52-61
• /
• 2015

본 연구에서는 가변 입구 안내익과 블리드 공기 스케줄에 따른 터보팬 엔진에서의 천이 성능특성을 수치적으로 분석하였다. 대상 엔진으로 저 바이패스비 혼합 흐름 터보팬 엔진을 선정하였다. 압축기 가변 입구 안내익에 따른 성능 변화를 고려하기 위해 평균 반경 해석법을 이용하여 압축기 성능성도를 도출하고 엔진 해석 프로그램에 입력하였다. 정상상태 조건에서 축류 압축기 서지마진 10%를 만족하도록 회전속도에 따른 가변 입구 안내익과 블리드 공기 스케줄을 각각 도출하였다. 도출된 스케줄을 이용하여 엔진 천이 성능해석을 수행하였다. 엔진 천이 성능해석 수행 결과 가변 입구 안내익을 사용하는 경우가 블리드 공기를 사용하는 경우보다 천이과정에서 높은 서지마진과 낮은 터빈 입구 온도를 보였다.

• 대한기계학회논문집B
• /
• 제20권7호
• /
• pp.2397-2408
• /
• 1996

A numerical study was made of the control of transient oscillatory flow modes in Czochralski convection. The reduction of temperature oscillation was achieved by changing the rotation rate of crystal rod, .OMEGA.$_{S}$=.OMEG $A_{S0}$(1+ $A_{S}$sin(2.pi. $f_{S}$/ $t_{p}$t)). The temporal behavior of oscillation flow was scrutinized over broad ranges of two parameters, i.e., the rotation amplitude( $A_{S}$.leq.0.5) and the nondimensional frequency (0.9.leq. $f_{S}$.leq.1.5). The mixed convection parameter was ranged 0.225.leq.Ra/PrR $e^{2}$.leq.0.929, which encompassed the buoyancy-and forced-dominant convection regimes. Computational results revealed that the temperature oscillations could be reduced effectively by a proper adjustment of the control parameters. The uniformity of temperature distribution near the crystal rod was examined. The control of oscillatory flow modes was also made for a realistic, low value of Pr.