• Journal of Korea Water Resources Association
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• v.40 no.9
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• pp.735-742
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• 2007

In this study, a methodology which is based on segments and minimum outsets to estimate the reliability of a real water distribution system efficiently and accurately is suggested. The current reliability assessment models based on minimum cutset consider a pipe as only area impacted by a pipe failure which incurs underestimation of pipe failure impact. In contrary, the suggested methodology adopts "segment" and "unintended isolation" with the hydraulic pressure failure area to define the actual service interruption area in a water distribution system due to a pipe failure, which is different from the Previous reliability estimating methodologies. In addition, a minimum cutset is defined as a single segment incurring abnormal operating conditions and the success mode approach is used to account for the probability of multiple failure combinations of minimum outsets. The model considers numbers and locations of on-off valves when the service interruption area is defined. Once the methodology is applied to a real water distribution system, it is possible to define actual service interruption areas and using the defined areas, the reliability of the water distribution system is estimated reliably, compared with the previous reliability assessment methodologies.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.19-26
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• 2021

The seismic isolation system have been applied in order to protect the collapse of bridge by seismic load and the vertical load transmitted from the superstructure. However, the failure and damages of non-shrinkage mortar, isolator and wedge in total 12 bridge were reported by Pohang Earthquake. In this study, the damage mechanism and behavior characteristics of elastomeric bearing by an earthquake were evaluated to consider the seismic isolation system including non-shrinkage mortar and the seat concrete of pier. To discuss the effect of installed wedge and damage mode of elastomeric bearing, the compressive-shear tests were carried out. Also, the mechanical behaviors and damage mechanism for each component of elastomeric bearing were evaluated by using finite element analysis. From the test results, the cracks were created at boundary between non-shrinkage mortar and seismic isolator and the shear loads were rapidly increased after bump into wedge. The cause for damage mechanism of seismic isolation system was investigated by comparing stress distribution of anchor socket and non-shrinkage mortar depending on wedge during earthquake.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.451-458
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• 2002

To secure structures from strong earthquakes occurred recently and design economically seismic isolation design is spread rapidly. Specially, frictional isolator has superiority in application to bridge because it has many advantages. however, because isolator lies between pier and girder, responses of pier and superstructure contradict each other and we need to control the two responses to minimize the bridge's failure probability. In this study, frictional coefficient and horizontal stiffness is defined as design parameters of frictional isolator. the optimal design parameters of frictional isolator to minimize the bridge's failure probability are presented according to strength of earthquake and soil conditions. The result says that optimal friction coefficient is higher as the strength of earthquake is increased. And it is also higher as the soils are more flexible. But, optimal horizontal stiffness of rubber spring is insensitive to strength of earthquake and soil condition.

• Korean Journal of Poultry Science
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• v.23 no.2
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• pp.77-84
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• 1996

The purpose of this paper is to introduce the present situation of broiler breeder industry, and to investigate some problems related to it in Korea. The number of broiler breeding farms were 231 in 1990. It peaked to 264 in 1992, but decreased afterward to 232 in 1995. The number of broiler parent stock were over 4 millions since 1992 except in 1993. The number of commercial chicks produced per breeding hen was around 100, which is far below to the suggested values of breeding companies. The number of hatching eggs produced per breeding hen were 168 eggs in US, 156~170 eggs in Thailand, and 160~170 eggs in China. Factors involved in the lowered performances of broiler parent stock in Korea appear to be 1) the poor isolation of breeding farms from commercial broiler farms, causing easy contamination with various diseases, 2) the failure to provide proper environment to the breeder, and 3) the failure to control body weight during laying periods.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1102-1111
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• 2007

The theory for a fault-tolerant control of homopolar magnetic bearings is developed. New coil winding law is utilized such that control fluxes are isolated for an 8-pole homopolar magnetic bearing. Decoupling chokes are not required for the fault tolerant magnetic bearing since C-core fluxes are isolated. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate the theory. Simulations show that very much the same dynamic responses (orbits or displacements) are maintained throughout failure events while currents and fluxes change significantly.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.125.4-125
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• 2001

The problem of recongurable ight control is investigated, focusing on model reference adaptive control(MRAC) through imprecise fault diagnosis. The method integrates the fault detection and isolation(FDI) scheme with the model reference adaptive control, and can be implemented on-line and in real-time. The algorithm can cope with the fast varying parameters. The Simulation results demonstrate the ability of reconguration to maintain the stability and acceptable performance after a failure.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.967-973
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• 2021

In 2011, an earthquake and subsequent tsunami hit the Fukushima Daiichi Nuclear Power Plant, causing simultaneous accidents in several reactors. This accident shows us that if there are several reactors on site, the seismic risk to multiple units is important to consider, in addition to that to single units in isolation. When a seismic event occurs, a seismic-failure correlation exists between the nuclear power plant's structures, systems, and components (SSCs) due to their seismic-response and seismic-capacity correlations. Therefore, it is necessary to evaluate the multi-unit seismic risk by considering the SSCs' seismic-failure-correlation effect. In this study, a methodology is proposed to obtain the seismic-response-correlation coefficient between SSCs to calculate the risk to multi-unit facilities. This coefficient is calculated from a probabilistic multi-unit seismic-response analysis. The seismic-response and seismic-failure-correlation coefficients of the emergency diesel generators installed within the units are successfully derived via the proposed method. In addition, the distribution of the seismic-response-correlation coefficient was observed as a function of the distance between SSCs of various dynamic characteristics. It is demonstrated that the proposed methodology can reasonably derive the seismic-response-correlation coefficient between SSCs, which is the input data for multi-unit seismic probabilistic safety assessment.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.1-13
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• 2010

This paper proposes an optimal design method for the nonlinear seismic isolated bridge. The probabilities of failure at the pier and the seismic isolator are considered as objective functions for optimal design, and a multi-objective optimization technique is employed to efficiently explore a set of multiple solutions optimizing mutually-conflicting objective functions at the same time. In addition, a stochastic linearization method is incorporated into the multi-objective optimization framework in order to effectively estimate the stochastic responses of the bridge without performing numerous nonlinear time history analyses during the optimization process. As a numerical example to demonstrate the efficiency of the proposed method, the Nam-Han river bridge is taken into account, and the proposed method and the existing life-cycle-cost based design method are both applied for the purpose of comparing their seismic performances. The comparative results demonstrate that the proposed method not only shows better seismic performance but also is more economical than the existing cost-based design method. The proposed method is also proven to guarantee improved performance under variations in seismic intensity, in bandwidth and in the predominant frequency of the seismic event.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.1
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• pp.45-51
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• 2004

We have proposed a new shallow trench isolation (STI) process using flowable oxide (F-oxide) chemical vapor deposition (CVD) for DRAM application and it was successfully developed. The combination of F-oxide CVD and HDP CVD is thought to be the superior STI gap-filling process for next generation DRAM fabrication because F-oxide not only improves STI gap-filling capability, but also the reduced local stress by F-oxide in narrow trenches leads to decrease in junction leakage and gate induced drain leakage (GIDL) current. Finally, this process increased data retention time of DRAM compared to HDP STI. However, a serious failure occurred by symphonizing its structural dependency of deposited thickness with poor resistance against HF chemicals. It could be suppressed by reducing the flow time during F-oxide deposition. It was investigated collectively in terms of device yield. In conclusion, the combination of F-oxide and HDP oxide is the very promising technology for STI gap filling process of sub-100nm DRAM technology.

• Smart Structures and Systems
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• v.17 no.6
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• pp.1031-1053
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• 2016

The health conditions of in-service civil infrastructures can be evaluated by employing structural health monitoring technology. A reliable health evaluation result depends heavily on the quality of the data collected from the structural monitoring sensor network. Hence, the problem of sensor fault diagnosis has gained considerable attention in recent years. In this paper, an innovative sensor fault diagnosis method that focuses on fault detection and isolation stages has been proposed. The dynamic or auto-regressive characteristic is firstly utilized to build a multivariable statistical model that measures the correlations of the currently collected structural responses and the future possible ones in combination with the canonical correlation analysis. Two different fault detection statistics are then defined based on the above multivariable statistical model for deciding whether a fault or failure occurred in the sensor network. After that, two corresponding fault isolation indices are deduced through the contribution analysis methodology to identify the faulty sensor. Case studies, using a benchmark structure developed for bridge health monitoring, are considered in the research and demonstrate the superiority of the new proposed sensor fault diagnosis method over the traditional principal component analysis-based and the dynamic principal component analysis-based methods.