• 드라이브 ㆍ 컨트롤
• /
• 제16권4호
• /
• pp.93-100
• /
• 2019

Nuclear and thermal power plants must provide the turbines with an appropriate degree of high temperature and high pressure steam, to produce the optimum electricity. Additionally, in the event of system and power system failure during electrical production, the steam is immediately disabled, to protect the turbines and generators rotating at high speed. The plant thus uses a special steam control valve system for turbine control, which is opened by force of the hydraulic servo actuator and closed by a large steel spring force. In this study, the causes of failure of the turbine control valve system, a key device of the power plants, were analyzed, and the causes of failure were improved relative to reliability of the equipment.

• Nuclear Engineering and Technology
• /
• 제54권8호
• /
• pp.2915-2923
• /
• 2022

There is an increasing interest in passive safety systems to minimize the need for operator intervention or external power sources in nuclear power plants. Because a passive system has a weak driving force, there is greater uncertainty in the performance compared with an active system. In previous studies, several methods have been suggested to evaluate passive system reliability, and many of them estimated the failure probability using thermal-hydraulic analyses and the Monte Carlo method. However, if the functional failure of a passive system is rare, it is difficult to estimate the failure probability using conventional methods owing to their high computational time. In this paper, a procedure for the application of the Chernoff bound to the evaluation of passive system reliability is proposed. A feasibility study of the procedure was conducted on a passive decay heat removal system of a micro modular reactor in its conceptual design phase, and it was demonstrated that the passive system reliability can be evaluated without performing a large number of thermal-hydraulic analyses or Monte Carlo simulations when the system has a small failure probability. Accordingly, the advantages and constraints of applying the Chernoff bound for passive system reliability evaluation are discussed in this paper.

• 대한기계학회논문집B
• /
• 제24권11호
• /
• pp.1506-1512
• /
• 2000

Control of shock may be important in the hydraulic system and necessary to avoid failure and to improve the efficiency of operation. This study addresses the design and use of an orifice to provide the desired control of the hydraulic actuator system. The experimental apparatus is an idealization of an automobile shift system. Control is accomplished by installing three different types of orifices at appropriate locations in the system. Experimental results show that the orifice can be used to obtain the control of shock and control level depends on the orifice size, orifice type, operating pressure and flow rate.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.621-626
• /
• 2000

Reduction in pressure transients may be important in the hydraulic system and necessary to avoid failure and to improve the efficiency of operation. This study addresses the design and use of an orifice to provide the desired control of the hydraulic actuator system. The experimental apparatus is a model of an automobile shift system. Control is accomplished by installing four different diameter ratio of orifices at appropriate locations in the system. Experimental results show that the orifice can be used to obtain the control of shock and the control level depends on the orifice size, orifice type, operating conditions.

• 한국지반공학회논문집
• /
• 제22권10호
• /
• pp.69-76
• /
• 2006

지하수흐름에 대한 신뢰성 해석을 실시하였으며, 흐름에 관여하는 매개변수들이 목표 값의 파괴확률을 초과하는데 미치는 영향을 알아보았다. 본 연구를 위하여 2차원 지하수흐름 프로그램을 3-D 프로그램 DGU-FLOW로 확장하여 제작하고, 이를 1계 및 2계 신뢰성 프로그램에 연계하였다. 3차원 흐름 프로그램의 검증은 지하굴착지반의 지하수 흐름 해석 문제를 풀고 이를 MODFLOW 프로그램과 비교하여 수행하였다. 신뢰성부분 또한 몬테칼로 해석을 수행하여 나타난 파괴확률을 비교함으로써 검증하였으며 지하수 흐름에 대한 1계 및 2계 신뢰성해석을 수행하여 산정된 파괴확률 값은 몬테칼로 해석을 통하여 나온 값과 매우 근접하였다. 토질층의 투수계수에 대한 매개변수 해석결과 투수계수의 평균과 분산의 증가는 목표 수량을 초과하는 파괴확률의 증가를 가져오는 것으로 나타났다. 또한 파괴확률의 민감도는 여러흐름 변수중에서 흐름영역 경계부의 일정 수두에 가장 민감한 것으로 나타났다.

• 터널과지하공간
• /
• 제7권1호
• /
• pp.31-38
• /
• 1997

Residual shear strength should be taken into consideration as well as peak one when analysing stability of slopes constituted by weathered rock or overconsolidated soils since such materials could be subjected to progressive failure mechanism. When landslide of a slope is related to progressive failure phenomenon, the failure might occur even though shear strength of the slope materials does not reach their residual shear strength over the whole slip surface. Therefore, stability of the slope concerned may be overstimated or underestimated when using only its peak or residual shear srength parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In this study, his theory has been extended to estimate the distance of failed zone for a plane slope and the results calculated by this extended equatio has been compared with that obtained by numerical modelling using FLAC. In addition, stress state on the slip surface has been, in detail, analysed to understand failure mechanism when a limited progressive failure occurs. Effects of mechanical and hydraulic factors on progressive failure have also been analysed.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.120-126
• /
• 2004

The failure modes analysis by the real process method at the head section of rubble mound breakwaters is more important than other failure modes analysis. because this initial failure modes and failure process will lead to the destruction of the structure. The three-dimensional failure modes are discussed using the experimental data with directional waves considering the failure modes. It was processed step by step failure around the head of rubble mound breakwaters. The spacial characteristics of failure mode by real process analysis was well descript at the rubble mound structures.

• 드라이브 ㆍ 컨트롤
• /
• 제15권2호
• /
• pp.32-37
• /
• 2018

The power plants use turbine output control devices to supply or shut off steam to high pressure and low-pressure steam turbines connected to generators. This turbine output control device is driven by a hydraulic servo actuator. The gas flows into the hydraulic servo actuator during periodic inspection or normal operation, and the resulting adiabatic compression of the gas raises the internal temperature of the actuator to $500^{\circ}C$. This temperature increase causes the seals to burn and show wear and tear, resulting in failure. In this study, an air vent valve was installed to allow gas inside the hydraulic servo actuator to flow large quantities of air at the beginning of the operation and after the periodic inspection. Gas was passed through for only minute flow during normal operation of the power plant. By applying the air vent valve, it improves the reliability of the hydraulic servo actuator by discharge the gas appropriately to improve the life of the seal.

• Geomechanics and Engineering
• /
• 제13권6호
• /
• pp.947-961
• /
• 2017

An innovative spiral variable-section capillary model is established for piping critical hydraulic gradient of cohesion-less soils causing water/mud inrush in tunnels. The relationship between the actual winding seepage channel and grain-size distribution, porosity, and permeability is established in the model. Soils are classified into coarse particles and fine particles according to the grain-size distribution. The piping critical hydraulic gradient is obtained by analyzing starting modes of fine particles and solving corresponding moment equilibrium equations. Gravities, drag forces, uplift forces and frictions are analyzed in moment equilibrium equations. The influence of drag force and uplift force on incipient motion is generally expounded based on the mechanical analysis. Two cases are studied with the innovative capillary model. The critical hydraulic gradient of each kind of sandy gravels with a bimodal grain-size-distribution is obtained in case one, and results have a good agreement with previous experimental observations. The relationships between the content of fine particles and the critical hydraulic gradient of seepage failure are analyzed in case two, and the changing tendency of the critical hydraulic gradient is accordant with results of experiments.

• 한국습지학회지
• /
• 제18권1호
• /
• pp.45-57
• /
• 2016

실무에서 사용되고 있는 제방의 안전도 평가는 여러 가지 붕괴원인 중 하나의 요인에 대해서만 평가를 하거나 주로 제방의 물리적인 특성을 이용한 1차원 수리분석을 통한 평가에 국한되어 왔다. 하지만 이러한 평가기법들은 제방의 다양한 붕괴원인을 동시에 고려할 수 없으며, 정확한 지형정보를 필요로 하는 곳에서 신뢰도가 떨어지는 문제점을 안고 있다. 따라서 본 논문에서는 정확한 지형정보를 반영한 2차원 수리해석을 결과를 이용하여 제방의 다양한 붕괴원인인 월류, 침투, 침식위험도를 동시에 고려한 제방 위험도 지수를 제안하였다. 낙동강 유역의 주요 합류부에 대해 하천준설사업 전 후의 지형 변화를 고려하여 2차원 수리모형을 이용한 수리해석을 실시하고 그 결과를 통해 제방 위험도를 평가하였다. 본 연구는 정확한 하천의 형상을 반영한 수리해석 결과를 이용한 객관적이고 신뢰도 높은 제방위험도 평가에 기여할 수 있을 것으로 기대된다.