• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2905-2918
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• 2023

The valve assembly used in nuclear power plants is important safety-related equipment. In the new standard, the physical attributes are measured using a valve diagnosis test, which is used in the expansion to other non-tested valves using a quantitative test-basis methodology. With a motor-operated actuator, the state of stem's lubrication is related to physical attributes such as the stem factor and the friction coefficient. This study analyzed the numerical transient of fluid and solid lubrication with a squeeze film effect due to the loading rate on the stem and the stem nut using the experimental data. The differential equation that governs the motion mechanism of the stem and stem nut is established and analyzed. The flow rate, the fluid and the solid contact forces are calculated with the friction coefficient. Finally, we found that a change in the friction coefficient results from a change of the shear force in the solid contact mode during the interchange process between the solid contact mode and the fluid contact mode. The qualitative understanding of the squeeze film effect is expanded quantitatively for forces, thread surface distance, velocity, and acceleration, with consideration of the metal solid contact and fluid contact.

• 소음진동
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• 제6권3호
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• pp.297-303
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• 1996

The general approach using sine series expansions was represented to evaluate the radiation loading from a vibrating surface on a simply supported cylinder. In this paper, the fluid-loading coefficients (radiation impedance) for a submerged finite cylindrical shell with an arbitrary end condition are defined and evaluated. The vibrations of cylindrical shell are expressed by using cosine series expansions to analyze the radiation impedance for a finite cylindrical shell. It is possible to represent the displacements at both ends of cylindrical shell in comparison with sine series. The direct and cross modal components of fluid-loading coefficients are shown and the validity of cosine series expansions are verified from the results of numerical computations. This approach and results are directly applicable in the analysis of sound radiation from subemerged finite cylindrical shell with arbitrary end conditions.

• 한국음향학회지
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• 제19권6호
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• pp.17-22
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• 2000

항공기나 선박과 같은 복잡한 구조물의 광대역 진동, 소음 예측을 위해 통계에너지해석법(SEA)이 널리 이용되고 있다. SEA를 이용해 접수 구조물의 진동, 소음을 정확히 해석하기 위해서는 접수에 의한 각 파라메터의 변화를 알아야만 한다. 본 연구에서는 기본 결합 요소인 'L'형과 'T'형 선결합 구조물에서 접수를 고려한 연성손실계수를 해석하고 공기중 진동시의 해석 결과와 비교하였다. 또한 'L'형, 'T'형 선결합을 가지는 단순한 형상의 steel box가 수중에서 진동하는 경우에, 접수에 의한 연성손실계수 변화가 세부시스템의 진동에 미치는 영향을 살펴보았다. 이를 통해, 구조물이 접수될 때 발생하는 연성손실계수의 변화를 확인하였으며, SEA를 이용한 접수 구조물의 진동 및 소음 해석시 결과의 신뢰성을 높이기 위해서는 접수에 의한 모드밀도, 내부손실계수 변화와 더불어 접수에 의한 연성손실계수 변화를 반드시 고려하여야 함을 확인하였다.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2697-2711
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• 2023

In this study, the validity of reducing the number of gas turbine stages designed for a nitrogen Brayton cycle coupled to a sodium-cooled fast reactor was assessed. The turbine performance was evaluated through computational fluid dynamics (CFD) simulations under different off-design conditions controlled by a reduced flow rate and reduced rotational speed. Two different multistage gas turbines designed to extract almost the same specific work were selected: two- and three-stage turbines (mid-span stage loading coefficient: 1.23 and 1.0, respectively). Real gas properties were considered in the CFD simulation in accordance with the Peng-Robinson's equation of state. According to the CFD results, the off-design performance of the two-stage turbine is comparable to that of the three-stage turbine. Moreover, compared to the three-stage turbine, the two-stage turbine generates less entropy across the shock wave. The results indicate that under both design and off-design conditions, increasing the stage loading coefficient for a fewer number of turbine stages is effective in terms of performance and size. Furthermore, the Ellipse law can be used to assess off-design performance and increasing exponent of the expansion ratio term better predicts the off-design performance with a few stages (two or three).

• 한국항해학회지
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• 제10권2호
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• pp.139-155
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• 1986

In this paper the dynamic effects due to the free water motions in tanks upon the lateral motion of a floating body in regular waves are calculated, in order to obtain the relationship between a motion of a floating body and that of the free water in tanks. Under the assumption that the fluid is ideal and motion amplitudes are small, velocity potential of the fluid in tanks is calculated by the source distribution method and the hydrodynamic forces and moments are calculated by the integration of fluid pressures over the tank surface. Hydrodynamic effects of the fluid on the floating body are expressed in terms of added mass and coupling coefficient obtained from the integration. Computations are carried out for ship with seven wide center tanks and comparisons between the liquid cargo loading case and the rigid cargo loading case are shown.

• 한국소음진동공학회논문집
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• 제24권1호
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• pp.21-27
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• 2014

In this paper, an approximate formula for radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. By assuming an infinite plate, the fluid loading effect is derived in terms of an effective mass. Based on the observation that the fluid loading effect decreases as frequency increases, the radiation efficiency formula at high frequency, which was originally derived for a plate vibrating in the air, is modified as the approximate formula for a submerged plate. The fluid loading effect is taken into account in the wavenumber of the plate. Comparisons of the approximate formula with the numerical results shows that they match well except the mid-frequency range in which numerical results show many oscillations. In numerically solving the fully coupled equations of motion, fourfold integrals of the impedance coefficients are reduced to single nonsingular integrals, which results in substantial reduction in computing time.

• 한국유체기계학회 논문집
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• 제10권5호
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• pp.46-53
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• 2007

Stem friction coefficient and valve factor are very important parameters for the evaluation of valve performance. In this study, the characteristics of stem friction coefficient and valve factor are analyzed, and thor bounding value is determined. The hydraulic testing is performed for many flexible wedge gate valves in the plant and statistical method is applied to the determination of bounding value. According to the results of this study, stem friction coefficient does not change much with differential pressure, and the bounding value of closing stroke is higher than that of opening stroke. The valve factor of valves with high differential pressure is higher than that of valves with medium differential pressure. It means valve factor is more sensitive to the differential pressure than the stem friction coefficient. Valve factor of the closing stroke is higher than that of opening stroke due to piston effect.

• 한국유체기계학회 논문집
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• 제4권4호
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• pp.28-36
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• 2001

Performance analysis is conducted on an axial-type turbine which is used for fire extinction by injecting water or steam into the turbine. Loss models developed by Hacker and Okapuu are applied for predicting the performance of turbine. Pressure loss generated through a turbine is converted to the thermal efficiency, and thermal and gas properties are calculated within a turbine passage. Total-to-total efficiency, total-to-static efficiency, static temperature at the exit of turbine, output power, flow coefficient, blade loading coefficient, and expansion ratio are predicted with changing the amount of injected steam and the rotational speed. The 74 kW class gas turbine developed at KIMM is chosen for performance analysis. The 74 kW class turbine consists of 1 stage like a current developing gas turbine for fire extinction. Water or steam is injected at the end of combustor, and results show that efficiency and output power are dependent on the temperature of injected water or steam and the static temperature at the exit is decreased.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.562-567
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• 2003

This paper presents the method of Rate of Loading(ROL) improvement for the Motor Operated Gate Valve operating in high differential pressure condition. The character of ROL and Stem Factor is analyzed. Static test and dynamic test were performed and acquired the diagnosis signal for the valve closing stroke. The result of this study is the modification of stem factor is very important factor for the ROL improvement. In order to obtain the same value of dynamic test thread friction coefficient stem and stem nut should be combined appropriately.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.97-103
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• 2011

With the aim to increase blade loadings and stable operating range in highly loaded compressors, this article has been conducted to explore, through a numerical parametric study, the potential of passive control using slotted bladings in cascade configurations. The objective of this numerical investigation is to analyze the influence of location, width and slope of the slots and therefore identify the optimal configuration. The approach is based on two dimensional cascade geometry, low speed regime, steady state and turbulent RANS model. The results show the efficiency of this passive technique to delay separation and enhance aerodynamic performances of the compressor cascade. A maximum of 28.3% reduction in loss coefficient have been reached, the flow turning is increased with approximately $5^0$ and high loading over a wide range of angle of attack have been obtained for the optimized control parameter.