• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.635-640
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• 2004

The present paper provides the design specifications and working principle of flow controlling vortex valve which will be adopted in a Korean next generation reactor (APR1400). The vortex valve is installed inside the pressurized safety injection tank of APR1400, and it passively controls the water discharge flowrate from the tank. In the present study, the performance of the vortex valve have been evaluated throughout the repeated experiments in the full-scale test facility called VAPER(VAlve Performance Evaluation Rig). Based on the experimental results, it is confirmed that the currently developed vortex valve satisfies the major performance requirements of APR1400 plant design in view of the peak discharge flowrate, pressure loss coefficient, and total discharge duration time. To achieve the highest quality of the experimental results, a quality assurance program for vortex valve tests has been strictly applied.

• 한국추진공학회지
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• 제15권4호
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• pp.1-10
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• 2011

본 논문에서는 가스터빈 유로의 열유동 환경을 개선하기 위해 끝벽면의 형상에 대한 최적화를 수행하였으며, 비축대칭 끝벽면을 이용한 방법을 적용하였다. 터빈 유로를 모사하기 위해 $90^{\circ}$ 곡관을 이용하였다. 터빈 유로에서의 전압력 손실과 유로 끝벽면에서의 열전달 계수를 최소화하는 비축대칭 끝벽면형상 도출을 연구의 목적으로 하였으며, 최적화 과정의 효율성을 위해 근사 최적화 기법을 적용하였다. 연구결과를 통해, 최적화된 비축대칭 끝벽면에 의한 상당한 공력열환경 개선을 확인할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권4호
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• pp.447-459
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• 2012

The present study numerically investigates the effect of the wavy leading edge on hydrodynamic characteristics for the flow of rectangular wings with the low aspect ratio of 1.5. Five different wave lengths at fixed wavy amplitude have been considered. Numerical simulations are performed at a wide range of the angle of attack ($0^{\circ}{\leq}{\alpha}{\leq}40^{\circ}$) at one Reynolds number of $10^6$. The wavy wings considered in this study did not experience enough lift drop to be defined as the stall, comparing with the smooth wing. However, in the pre-stall region, the wavy wings reveal the considerable loss of the lift, compared to the smooth wing. In the post-stall, the lift coefficients of the smooth wing and the wavy wings are not much different. The pressure coefficient, limiting streamlines and the iso-surface of the spanwise vorticity are also highlighted to examine the effect of the wave length on the flow structures.

• 설비공학논문집
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• 제22권8호
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• pp.573-578
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• 2010

Topological matrix which reflects characteristics of network connectivity has been widely used in efficient solving for complicated flow network. Using topological matrix, one can easily define continuity at each node of flow network and make algorithm to automatically generate continuity equation of matrix form. In order to analyze flow network completely it is required to satisfy energy conservation in closed loops of flow network. Fundamental cycle retrieving algorithm based on graph theory automatically constructs energy conservation equation in closed loops. However, it is often accompanied by NP-complete problem. In addition, it always needs fundamental cycle retrieving procedure for every structural change of flow network. This paper proposes alternative mathematical method to analyze flow network without fundamental cycle retrieving algorithm. Consequently, the new mathematical method is expected to reduce solving time and prevent error occurrence by means of simplifying flow network analysis procedure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.307-310
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• 2000

Recently, the demand for the Floating, Production Storage, and Offloading facility(FPSO) which has some economic and technical advantages, has increased in offshore oil production areas. The basic characteristics of a 343,000 DWT class FPSO which is being built in Hyundai Heavy Industries and shall be installed in offshore Angola, is almost same as that of oil carriers. However, she do not have self-propulsion system, but has additional facilities for oil production and positioning system. Main noise source contributing to the cabin noise of the accommodation, are classified into the machine in the engine room and the deckhouse, HVAC system, and the topside equipments. In general, the noise regulation for the offshore structure is much severer than that of the common commercial ships and the maximum acceptable sound pressure level of cabins is specified in 45dB(A). This paper describes the procedure of noise analysis along with its results. Noise analysis has been carried out for the case of emergency diesel generator running condition and the case of normal production condition and the results has been compared with the measurement results of the first case. Based on the results, proper countermeasures to reduce excessive noise level has been applied considering the characteristics of sources and receiver spaces and can be satisfied the specifications at all spaces.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3196-3206
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• 2021

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.1-8
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• 2018

본 연구는 Siphon Breaker Simulation Program(SBSP)을 이용하여 소규모 사이펀 차단기 실험장치를 설계 및 제작하고, 실험 수행 후 그 결과를 이용하여 다양한 규모의 사이펀 차단기에 대한 SBSP의 적용 가능성을 평가하기 위해 진행되었다. 실험장치 설계를 위하여 C factor와 Chisholm B 계수, Undershooting Height(UH)에 대한 시뮬레이션 결과값을 SBSP로 도출하였다. 실험장치의 중요파트는 upper tank, lower tank, downcomer, Siphon Breaker Line(SBL) 등이며, upper tank는 넓이 $0.09-m^2$, 높이 0.65-m의 크기로 제작되었고, downcomer 높이는 1.6-m로 제작되었다. 실험결과 분석을 위하여 압력계, 차압계, 전자저울이 사용되어 압력과 차압, 유량에 대한 정보를 도출하였다. 실험에서 사용된 실험변수는 Loss Of Coolant Accident(LOCA) 크기와 SBL 크기이며, LOCA는 30-mm와 38-mm에 대해서, SBL은 6/16-inch와 8/16-inch에 대해서 실험이 진행되었다. 실험의 결과로 유량과 압력, 그리고 UH를 도출하였으며, 실험결과를 SBSP의 시뮬레이션 결과와 비교, 분석하였다. UH 측면에서 SBSP가 수조의 총 높이 대비 2.5 %의 오차로 실험결과를 잘 예측하는 것을 관찰하였다. 그러므로 SBSP를 이용한 다양한 규모의 사이펀 차단기 설계가 가능한 것을 확인하였다.

• 한국세라믹학회지
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• 제52권6호
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• pp.429-434
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• 2015

This study investigates the macroscopic wear behaviors of C/C and C/C-SiC composites coated with hafnium carbide (HfC). To improve the wear resistance of C/C composites, low-pressure chemical vapor deposition (LPCVD) was used to obtain HfC coating. The CVD coatings were deposited at various deposition temperatures of 1300, 1400, and $1500^{\circ}C$. The effect of the substrate material (the C/C substrate, the C/C-CVR substrate, or the C/C-SiC substrate deposited by LSI) was also studied to improve the wear resistance. The experiment used the ball-on-disk method, with a tungsten carbide (WC) ball utilized as an indenter to evaluate the wear behavior. The HfC coatings were found to effectively improve the wear resistance of C/C and C/C-SiC composites, compared with the case of a non-coated C/C composite. The former showed lower friction coefficients and almost no wear loss during the wear test because of the presence of hard coatings. The wear scar width was relatively narrower for the C/C and C/C-SiC composites with hafnium coatings. Wear behavior was found to critically depend on the deposition temperature and the material. Thus, the HfC-coated C/C-SiC composites fabricated at deposition temperatures of $1500^{\circ}C$ showed the best wear resistance, a lower friction coefficient, and almost no loss during the wear test.

• 한국항공우주학회지
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• 제35권11호
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• pp.1013-1021
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• 2007

스마트무인기 연료공급시스템에 사용되는 연료이송 제트펌프의 1차원 유동해석을 통한 설계가 이루어졌으며 성능 검증 및 설계 개선점을 찾고자 상용코드를 이용하여 전산해석이 수행되었다. 해석적 연구 결과로부터 제트펌프는 스마트무인기 연료공급시스템에서 요구하는 유량비 2.23을 만족하는 설계가 이루어졌음이 확인되었다. 구동노즐에 작용하는 압력은 낮게 예측된 손실계수로 인하여 전산해석의 경우가 1차원 유동해석을 통한 설계값보다 더 높은 값을 나타냈다. 결과적으로 제트펌프 구성 요소의 정확한 크기 결정을 위해서는 각 주요부에서의 손실계수에 대한 정확한 데이터가 필요하며, 데이터는 측정위치 및 측정대상의 기하학적 형상 정보와 함께 제공되어져야 한다.

• Structural Engineering and Mechanics
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• 제20권5호
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• pp.543-558
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• 2005

The natural frequencies of a long span bridge vary during its construction and it is thus difficult to apply traditional tuned liquid column dampers (TLCD) with a fixed configuration to reduce bridge vibration. The restriction of TLCD imposed by frequency tuning requirement also make it difficult to be applied to structure with either very low or high natural frequency. A semi-active tuned liquid column damper (SATLCD), whose natural frequency can be altered by active control of liquid column pressure, is studied in this paper. The principle of SATLCD with adaptive tuning capacity is first introduced. The analytical models are then developed for lateral vibration of a structure with SATLCD and torsional vibration of a structure with SATLCD, respectively, under either harmonic or white noise excitation. The non-linear damping property of SATLCD is linearized by an equivalent linearization technique. Extensive parametric studies are finally carried out in the frequency domain to find the beneficial parameters by which the maximum vibration reduction can be achieved. The key parameters investigated include the distance from the centre line of SATLCD to the rotational axis of a structure, the ratio of horizontal length to the total length of liquid column, head loss coefficient, and frequency offset ratio. The investigations demonstrate that SATLCD can provide a greater flexibility for its application in practice and achieve a high degree of vibration reduction. The sensitivity of SATLCD to the frequency offset between the damper and structure can be improved by adapting its frequency precisely to the measured structural frequency.