• Smart Structures and Systems
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• 제7권2호
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• pp.133-152
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• 2011

System identification is a fundamental step towards the application of structural health monitoring and damage detection techniques. On this respect, the development of evolved identification strategies is a priority for obtaining reliable and repeatable baseline modal parameters of an undamaged structure to be adopted as references for future structural health assessments. The paper presents the identification of the modal parameters of the Guangzhou New Television Tower, China, using a data-driven stochastic subspace identification (SSI-data) approach complemented with an appropriate automatic mode selection strategy which proved to be successful in previous literature studies. This well-known approach is based on a clustering technique which is adopted to discriminate structural modes from spurious noise ones. The method is applied to the acceleration measurements made available within the task I of the ANCRiSST benchmark problem, which cover 24 hours of continuous monitoring of the structural response under ambient excitation. These records are then subdivided into a convenient number of data sets and the variability of modal parameter estimates with ambient temperature and mean wind velocity are pointed out. Both 10 minutes and 1 hour long records are considered for this purpose. A comparison with finite element model predictions is finally carried out, using the structural matrices provided within the benchmark, in order to check that all the structural modes contained in the considered frequency interval are effectively identified via SSI-data.

• 한국항해항만학회지
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• 제43권6호
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• pp.462-468
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• 2019

해양석유 생산은 예기치 못한 유가 하락과 글로벌 석유물류의 변화로 인한 여러 가지 어려움에 직면하고 있다. 이 연구는 불확실성하의 해양석유생산 최적화를 위한 추계적 모형을 제시한다. 제시된 추계적 모형은 강인한 최적화 모형과 리코스 제한 최적화 모형을 사용하고 리코스 이익 변동의 척도로 하위부분평균을 사용한다. 제안된 모형을 바탕으로 불확실성 하의 원유의 가격과 수요에 관한 시나리오 기반의 자료를 사용하여 수행한 계산실험 및 결과를 검토하여 보고하였다. 이 연구는 불학실성 하에서 위험을 고려한 해양석유생산 문제에 대한 의사결정에 유의하게 적용될 수 있을 것이다.

• Smart Structures and Systems
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• 제26권4호
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• pp.419-433
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• 2020

Investigation of structural integrity has been a critical issue in the field of civil engineering for years. Visual inspection is one of the most available methods to explore deteriorative components in structures. Still, this method is not applicable to invisible damage of structures. Alternatively, system identification methods are capable of tracking modal properties of structures over time. The deviation of these dynamic properties can serve as indicators to access structural integrity. In this study, a modal tracking technique using frequency-domain system identification from seismic responses of structures is proposed. The method first segments the measured signals into overlapped sequential portions and then establishes multiple Hankel matrices. Each Hankel matrix is then converted to the frequency domain, and a temporal-average frequency-domain Hankel matrix can be calculated. This study also proposes the frequency band selection that can divide the frequency-domain Hankel matrix into several portions in accordance with referenced natural frequencies. Once these referenced natural frequencies are unavailable, the first few right singular vectors by the singular value decomposition can offer these references. Finally, the frequency-domain stochastic subspace identification tracks the natural frequencies and mode shapes of structures through quick stabilization diagrams. To evaluate performance of the proposed method, a numerical study is carried out. Moreover, the long-term monitoring strong motion records at a specific site are exploited to assess the tracking performance. As seen in results, the proposed method is capable of tracking modal properties through seismic responses of structures.

• 한국전산구조공학회논문집
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• 제20권6호
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• pp.789-799
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• 2007

본 논문에서는 구조의 재료물성치와 기하학적 인수의 공간적 불확실성에 의한 구조 응답변화도 산정을 위한 정식화를 제안하였다. 정식화는 추계론적 유한요소해석의 해석법 중의 하나인 가중적분법을 기본으로 하였다. 해석 대상 구조는 전단변형을 포함하는 평판구조로서, 평판구조에 나타날 수 있는 불확실 인수로는 재료적 측면에서는 재료탄성계수와 포아송비가 있으며, 기하학적 인수로는 평판의 두께를 들 수 있다. 선형탄성 영역에서 선형성을 나타내는 재료탄성계수와는 달리 평판의 두께는 3차함수로 강성에 기여하고, 포아송비의 경우 분수의 형태로 강성에 기여하므로 직접적으로는 이를 추계론적 해석에 고려할 수 없다. 따라서 본 연구에서는 적합행렬내의 포아송비를 Taylor전개하여 사용하였다. 제안된 정식화에 의한 결과는 기존 연구결과는 물론 몬테카를로 해석에 의한 결과와도 비교하여 제안한 정식화를 검증하였다.

• 대한조선학회논문집
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• 제31권1호
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• pp.142-154
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• 1994

본 논문에서는 정하중을 받는 보강 원통형 쉘의 확률론적 초기결함 민감도 해석을 수행하였다. Donnell의 쉘이론, Galerkin 근사법에 의거 좌굴하중 도출을 위한 다중모드 정식화를 수행하고 이에 random한 기하학적 초기결함의 확률장 이론 및 응답면 기법을 결합하였다. 계산된 확률론적 좌굴하중 결과로부터 신뢰도 지수-하중, 신뢰도 지수-안전계수의 관계를 구할 수 있고 이를 이용하면 요구되는 안전계수의 범위, 허용가능 초기결함의 범위 설정이 가능할 것이다.

• 농업과학연구
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• 제48권1호
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• pp.59-71
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• 2021

This study investigated the extent to which rice producers from the Ayeyarwaddy Region of Myanmar could improve their productivity if inputs were used efficiently in rice cultivation. To achieve this objective, simple random sampling was used to collect data from 300 rice growers in the study area. Data were analyzed with the translog stochastic frontier approach to understand the production efficiencies. The study further estimated the influencing factors that affect the efficiency levels of rice farmers. The empirical result reveals that the average technical, allocative, and economic efficiencies were at 76.11, 47.85, and 34.15%, respectively. This suggests that there is considerable room for improving rice production by better utilization of the available resources at the current level of technology. This study suggests that strenthening agricultural training programs and adoption of improved rice varieties may reduce overall inefficiencies among rice farmers in Myanmar. Factors like age, household size, education, farming experience, farm size, rice variety, training, and off-farm income have a significant impact on increasing/decreasing farmer's efficiency. Efficiency can be improved by establishing farmer field school programs to increase the scale of operations. The government should encourage young educated people to participate in paddy production and also intervene to reduce input prices and control the quality of seeds.

• Smart Structures and Systems
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• 제20권2호
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• pp.115-126
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• 2017

The modal identification of large civil structures such as bridges under the ambient vibrational conditions has been widely investigated during the past decade. Many operational modal analysis methods have been proposed and successfully used for identifying the dynamic characteristics of the constructed bridges in service. However, there is very limited research available on reliable criteria for the robustness of these identified modal parameters of the bridge structures. In this study, two time-domain operational modal analysis methods, the data-driven stochastic subspace identification (SSI-DATA) method and the covariance-driven stochastic subspace identification (SSI-COV) method, are employed to identify the modal parameters from field recorded ambient acceleration data. On the basis of the SSI-DATA method, the modal contribution indexes of all identified modes to the measured acceleration data are computed by using the Kalman filter, and their applicability to evaluate the robustness of identified modes is also investigated. Here, the benchmark problem, developed by Hong Kong Polytechnic University with field acceleration measurements under different excitation conditions of a cable-stayed bridge, is adopted to show the effectiveness of the proposed method. The results from the benchmark study show that the robustness of identified modes can be judged by using their modal contributions to the measured vibration data. A critical value of modal contribution index of 2% for a reliable identifiability of modal parameters is roughly suggested for the benchmark problem.

• Structural Engineering and Mechanics
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• 제83권4호
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• pp.537-549
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• 2022

In this paper, a novel multi-feature model predictive control (MPC) framework with real-time and adaptive performances is proposed for intelligent structural control in which some drawbacks of the algorithm including, complex control rule and non-optimality, are alleviated. Hence, Linear Programming (LP) is utilized to simplify the resulted control rule. Afterward, the Whale Optimization Algorithm (WOA) is applied to the optimal and adaptive tuning of the LP weights independently at each time step. The stochastic control rule is also achieved using Kalman Filter (KF) to handle noisy measurements. The Extreme Learning Machine (ELM) is then adopted to develop a data-driven and real-time control algorithm. The efficiency of the developed algorithm is then demonstrated by numerical simulation of a twenty-story high-rise benchmark building subjected to earthquake excitations. The competency of the proposed method is proven from the aspects of optimality, stochasticity, and adaptivity compared to the KF-based MPC (KMPC) and constrained MPC (CMPC) algorithms in vibration suppression of building structures. The average value for performance indices in the near-field and far-field (El earthquakes demonstrates a reduction up to 38.3% and 32.5% compared with KMPC and CMPC, respectively.

• 한국시뮬레이션학회논문지
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• 제18권1호
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• pp.53-62
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• 2009

실 기동 훈련을 기반으로 획득한 데이터는 전투 또는 워게임 모델링 및 시뮬레이션에 중요한 역할을 지니게 된다. 특히 이들 데이터는 무기체계 분석을 위한 중요한 입력자료로 활용하게 된다. 현존하는 분석모델들은 사격시간간격의 평균값을 상수로 지정하여 적용하여 왔으나 사격시간간격은 기존 확률분포 또는 경험분포로 적합하여 사용함이 보다 현실적이라고 할 수 있다. 실제 전장의 데이터를 획득하기 어려운 여건이므로 실기동 훈련으로 획득된 경험 데이터를 활용할 수 있는 방법을 제시한다. 본 연구는 확률과정을 따르는 전투상황을 보다 근접하게 모의할 수 있는 새로운 접근방법 및 기법을 연구하고 비교한다. 이 연구는 다양한 혼합 무기체계, 적정 전투의 규모, 그리고 전술적 측면 등을 포함하는 향후 연구과제의 필요성을 제기하면서 이를 위한 첫 번째 단계에 해당하는 기초연구이다.

• 지질공학
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• 제5권3호
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• pp.301-308
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• 1995

본 연구에서는 지하암반구조물의 해석시 재료특성변이를 확률론적으로 고려할 수 있는 수치해석기법을 제시하였다. 수치해석적 접근은 확률론적 해석분야에서 비교적 널리 사용 되어지고 있으며, 재료특성변수를 확률공간에서 분포특성과 분산형태에 따라 비교적 정확하게 추출할 수 있는 Monte Carlo 기법을 사용하였으며, 생성된 재료변수에 따른 변위와 응력의 계산과정은 유한요소법을 사용하였다.또한 본 연구 결과로부터 작성한 수치해석프로그램을 사용하여 2축응력장치에서의 지하원형암반공동에 대한 수치해석을 수행하였으며, 재료특성값의 분포특성변화에 따른 공동주변의 거동변화를 파악하였다.