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Sungsik Yoon,Young-Joo Lee,Hyung-Jo Jung 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.2
Conventional Monte Carlo simulation-based methods for seismic risk assessment of water networks often require excessive computational time costs due to the hydraulic analysis. In this study, an Artificial Neural Network-based surrogate model was proposed to efficiently evaluate the flow-based system reliability of water distribution networks. The surrogate model was constructed with appropriate training parameters through trial-and-error procedures. Furthermore, a deep neural network with hidden layers and neurons was composed for the high-dimensional network. For network training, the input of the neural network was defined as the damage states of the k-dimensional network facilities, and the output was defined as the network system performance. To generate training data, random sampling was performed between earthquake magnitudes of 5.0 and 7.5, and hydraulic analyses were conducted to evaluate network performance. For a hydraulic simulation, EPANET-based MATLAB code was developed, and a pressure-driven analysis approach was adopted to represent an unsteady-state network. To demonstrate the constructed surrogate model, the actual water distribution network of A-city, South Korea, was adopted, and the network map was reconstructed from the geographic information system data. The surrogate model was able to predict network performance within a 3% relative error at trained epicenters in drastically reduced time. In addition, the accuracy of the surrogate model was estimated to within 3% relative error (5% for network performance lower than 0.2) at different epicenters to verify the robustness of the epicenter location. Therefore, it is concluded that ANN-based surrogate model can be utilized as an alternative model for efficient seismic risk assessment to within 5% of relative error.
Flow-based seismic resilience assessment of urban water transmission networks
Sungsik Yoon,Young-Joo Lee,Hyung-Jo Jung 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.4
In this study, a new framework of seismic resilience estimation for urban water transmission networks was developed. The proposed resilience estimation model consists of three phases: input earthquake generation, hydraulic analysis, and recovery of network facilities. In the earthquake generation phase, the uncertainty of the ground motion is determined using the spatially correlated seismic attenuation law. In the hydraulic analysis phase, a hydraulic simulation is performed in conjunction with EPANET analysis. In the recovery phase, network components are restored, and the performance of the recovered network is evaluated through hydraulic analysis. Then, the seismic resilience curve and recovery costs are calculated. For a numerical simulation, a MATLAB-based computer code was developed for pressure-driven analysis in EPANET simulation. To demonstrate the proposed model, an actual water transmission network in South Korea was reconstructed based on geographic information system data. The performance of the network system was evaluated according to two performance indices: system and nodal serviceability. Finally, the cost of repairing the network facilities and water loss are estimated according to earthquake magnitude and interdependency. Numerical results show that the recovery slope of the resilience curve tends to decrease as the earthquake magnitude and interdependency with the power facilities increase.
Seismic fragility analysis of a buried pipeline structure considering uncertainty of soil parameters
Yoon, Sungsik,Lee, Do Hyung,Jung, Hyung-Jo Elsevier 2019 The International journal of pressure vessels and Vol.175 No.-
<P><B>Abstract</B></P> <P>In this study, the seismic fragility analysis for a buried gas pipeline of API 5L X65 was performed considering the uncertainty of soil parameters. For this purpose, nonlinear time history analyses were carried out for the pipeline considering soil-pipeline interaction represented by beam on nonlinear Winkler foundation model. A total of 12 input ground motions were employed and four different analytical cases were considered to evaluate the effect of the uncertainty of soil parameters. The four cases proved that uncertainty of soil parameters needs to be taken into account for the assessment of the pipeline response. Using results of the nonlinear time history analyses, seismic fragility analyses were conducted in accordance with three damage states. Analytical predictions indicated that seismic fragility curves with the uncertainty of soil parameters exhibit higher failure probability than those without the uncertainty. It is thus concluded that the present study is promising for the exploration of the seismic fragility analysis considering the uncertainty of soil parameters.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Seismic fragility analysis has been carried out for a buried gas pipeline considering uncertainty of soil parameters. </LI> <LI> Beam on nonlinear-Winkler foundation model was utilized for soil-pipeline interaction. </LI> <LI> An efficient Monte Carlo Simulation employing Latin Hypercube Sampling was adopted. </LI> <LI> Unit-weight has been identified as dominant factor affecting the behavior of pipeline. </LI> <LI> Seismic fragility curve that takes into account the uncertainty of soil parameters was more vulnerable to earthquakes. </LI> </UL> </P>
Analysis of SCTP Performance by Multi-streaming Feature
SungSik Yoon,SeokJoo Koh,JungSoo Park,HyoungJun Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this paper, we analyze the performance of the Stream Control Transmission Protocol (SCTP) in the viewpoint of its multi-streaming feature. From the experiments, it is shown that there exists an optimal number of SCTP streams in terms of the throughput performance in the lossy networks.
교량 복구 우선순위에 따른 도로망의 내진 복원력 비교 연구
윤성식(Sungsik Yoon) 한국방재학회 2023 한국방재학회논문집 Vol.23 No.2
최근 빈번히 발생하는 지진은 교량 구조물의 손상을 발생시켰고, 그 결과 도로 네트워크의 통행시간 증가에 따른 큰 불편을 초래하였다. 본 연구에서는 도로 네트워크에 지진이 발생하였을 때 교량의 복구 우선순위를 결정하고, 인공신경망을 활용하여 내진 복원력을 비교하고자 한다. 이를 위하여, 교량의 복구순위를 결정하기 위하여 1) 성능기반, 2) 이익-비용에 기반한 복구순위를 도입하였다. 제안된 복구 우선순위에 따른 도로망의 내진 복원력을 비교하기 위하여 실제 포항 도로 네트워크를 재구성하였다. 수치해석 결과 이익-비용에 기반한 복구 우선순위보다 성능에 기반한 복구 우선순위가 더 신속한 복원력 곡선을 나타내었다. Recently, frequent earthquakes have damaged bridge structures, causing great inconvenience owing to the disruption of transportation networks and increasing travel time. In this study, the restoration priority of bridges under seismic conditions was proposed and the seismic resilience curves were compared based on an artificial neural network model. To determine the restoration priority of bridges, 1) performance-based and 2) benefit-cost-based restoration priorities were introduced. For demonstration purposes, the actual Pohang road network was reconstructed and the seismic resilience curves of the transportation network corresponding to the proposed restoration priorities were compared. Numerical analysis showed that the performance-based restoration priority had a more rapid seismic resilience curve than benefit-cost-based restoration priority.
윤성식(Sungsik Yoon) 한국방재학회 2023 한국방재학회논문집 Vol.23 No.3
Recent frequent earthquakes have caused serious damage to water supply structures, significantly affecting the drinking water supply of local residents. In particular, because water supply structures are extensively buried underground, prediction of their deteriorated performance against external disturbances is crucial for maintenance purpose. Therefore, this study aims to evaluate the degraded seismic performance of the water transmission network based on connectivity-based network analysis against seismic conditions. The proposed methodology consists of i) network map reconstruction using a graph theory, ii) ground motion generation considering the uncertainty of seismic motion, and iii) connectivity verification between source and sink nodes. To demonstrate the proposed methodology, the network topology was reconstructed by adopting the water transmission network located in A-city, and the seismic performance of the target network was evaluated considering the epicenter of the historical earthquakes. As a result of numerical analysis, the seismic response of the water transmission network showed the highest network connectivity when the water was supplied from node 62, and water was stably secured at node 107 under different earthquake magnitudes.