• Structural Monitoring and Maintenance
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• 제9권2호
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• pp.157-177
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• 2022

In this paper, an innovative finite element updating method is presented based on the variation wavelet transform coefficients of Auto/cross-correlations function (WTCF). The Quasi-linear sensitivity of the wavelet coefficients of the WTCF concerning the structural parameters is evaluated based on incomplete measured structural responses. The proposed algorithm is used to estimate the structural parameters of truss and plate models. By the solution of the sensitivity equation through the least-squares method, the finite element model of the structure is updated for estimation of the location and severity of structural damages simultaneously. Several damage scenarios have been considered for the studied structure. The parameter estimation results prove the high accuracy of the method considering measurement and mass modeling errors.

• International Journal of Ocean System Engineering
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• 제3권2호
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• pp.68-76
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• 2013

In this study, a 3D numerical model was used to predict nonlinear wave forces on a cylindrical pile installed in a shallow water region. The model was based on solving the viscous and incompressible Navier-Stokes equations for a two-phase flow (water and air) model and the volume of fluid method for treating the free surface of water. A new application was developed based on the cut-cell method to allow easy installation of complicated obstacles (e.g., bottom geometry and cylindrical pile) in a computational domain. Free-surface elevation, water particle velocities, and inline wave forces were calculated, and the results show good agreement with experimental data obtained by the Danish Hydraulic Institute. The simulation results revealed that the proposed model can, without the use of empirical formulas (i.e., Morison equation) and additional wave analysis models, reliably predict non-linear wave forces on an offshore wind turbine foundation installed in a shallow water region.

• Steel and Composite Structures
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• 제33권6호
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• pp.865-875
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• 2019

The current article proposed to develop a geometrical model for the analysis and modelling of the uniaxial functionally graded structure using the higher-order displacement kinematics with and without the presence of porosity including the distribution. Additionally, the formulation is capable of modelling three different kinds of grading patterns i.e., Power-law, sigmoid and exponential distribution of the individual constituents through the thickness direction. Also, the model includes the distribution of porosity (even and uneven kind) through the panel thickness. The structural governing equation of the porous graded structure is obtained (Hamilton's principle) and solved mathematically by means of the isoparametric finite element technique. Initially, the linear frequency parameters are obtained for different geometrical configuration via own computer code. The comparison and the corresponding convergence studies are performed for the unidirectional FG structure for the validation purpose. Finally, the impact of different influencing parameters like aspect ratio (O), thickness ratio (S), curvature ratio (R/h), porosity index (λ), type of porosity (even or uneven), power-law exponent (n), boundary condition on the free vibration characteristics are obtained for the FG panel and discussed in details.

• 대한기계학회논문집A
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• 제26권4호
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• pp.602-608
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• 2002

The flexible structure like solar array and antenna in spacecraft shows very sensitive responses to the inner or outer disturbance and noise. And the spacecraft becomes more complex and larger as it has various mission and role. But since the spacecraft need to have the limited mass, the thin and light material should be selected and this necessity induces the decrease d natural frequency and structural stiffness. It reduces the ability of adapting to the disturbance and induces the structural unstability. Certainly, the disturbance does not only make the structural unstability, but also give the bad effect to the precise attitude control. So it is necessary to control the vibration in the space. In this paper, the flexible structure control modeling with piezo sensor and piezo actuator is developed. The model uncertainty of damping ratio is overcome by robust control. The system equation is induced by the finite element method.

• Structural Engineering and Mechanics
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• 제29권1호
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• pp.91-111
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• 2008

This paper outlines the development of a computational model in order to analyze the dynamic behaviour of coupled fluid-structure systems such as a) liquid containers, b) a set of parallel or radial plates. In this work a hybrid fluid-solid element is developed, capable of simulating both membrane and bending effects of the plate. The structural mass and stiffness matrices are determined using exact integration of governing equations which are derived using a combination of classical plate theory and a finite element approach. The Bernoulli equation and velocity potential function are used to describe the liquid pressure applied on the solid-fluid element. An impermeability condition assures a permanent contact at the fluid-structure interface. Applications of this model are presented for both parallel and radial plates as well as fluid-filled rectangular reservoir. The effect of physical parameters on the dynamic behaviour of a coupled fluid-structure system is investigated. The results obtained using the presented approach for dynamic characteristics such as natural frequency are in agreement to those calculated using other theories and experiments.

• 대한토목학회논문집
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• 제35권2호
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• pp.471-480
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• 2015

민간투자사업에 대한 부정적인 시각으로 인해 민간투자사업 시장은 축소되었으나, 최근 국내 재정사업의 축소로 인해 민간투자사업에 대한 필요성이 다시금 제기되고 있다. 민간투자사업은 건설사, special purpose company (SPC), 재무투자자 등 다양한 참여자들 간의 이해관계가 복잡하여 사업의 성과를 판단하기 위해서는 참여자 간 관점 차이에 대한 고려가 필요하나, 기존의 연구는 재무적 관점의 수익성 예측, 또는 리스크 식별을 통한 수익성 예측을 중심으로 수행되었다. 이러한 점을 고려하여 본 연구에서는 민간투자사업 주요 참여자별 특성에 따른 민간투자사업 성과예측 모델을 개발하였다. 이를 위해 첫째, 다양한 분야의 문헌고찰을 통해 민간투자사업의 조직구조를 분석하였으며, 건설사, SPC, 재무투자자의 관점에서 민간투자사업 수익성 영향요인을 도출하였다. 둘째, 도출된 수익성 영향인자들을 바탕으로 민간투자사업 관련 전문가 설문조사 및 인터뷰를 실시하였다. 셋째, 구조방정식 모델(structural equation model)을 통해 민간투자사업의 구성개념들 간에 직접효과와 간접효과를 분석하여 민간투자사업의 수익성 및 수익안정성 측면에서의 성과를 거시적으로 이해할 수 있는 모델을 개발하였다. 넷째, 모델을 통해 도출된 결과를 바탕으로 민간투자사업의 재도약을 위한 발전방안을 제시하였다. 향후 본 모델을 통해 수익성과 수익안정성 측면에서 건설사, 재무투자자, SPC 운영사의 사업성과 예측이 가능하며, 이에 따른 대응전략을 모색하는데 활용 가능할 것으로 기대된다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.172-179
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• 2001

A numelical model has been developed for the permeable coastal structures to simulate hydraulic characteristics on the permeable slopes, which interact with internal flow field of the structures. The model includes hydraulics in the porous medium. Numerical model was calibrated using hydraulic model experiments performed in 2-D wave flume in the Institute of Orean Hydraulics in PKNU. Good agreement were obtained with the model which employed inertia resistance term than with the conventional model, PBREAK.

• Structural Monitoring and Maintenance
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• 제10권2호
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• pp.175-190
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• 2023

This article aims to quantitatively predict the snowmelt in extreme cold regions, considering a combination of grayscale and neural models. The traditional non-equidistant GM(1,1) prediction model is optimized by adjusting the time-distance weight matrix, optimizing the background value of the differential equation and optimizing the initial value of the model, and using the BP neural network for the first. The adjusted ice forecast model has an accuracy of 0.984 and posterior variance and the average forecast error value is 1.46%. Compared with the GM(1,1) and BP network models, the accuracy of the prediction results has been significantly improved, and the quantitative prediction of the ice sheet is more accurate. The monitoring and maintenance of the structure by quantitative prediction model by gray models was clearly demonstrated in the model.

• 한국항만학회지
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• 제8권2호
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• pp.37-56
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• 1994

The effects of wave energy focusing by a submerged berm type of structure is examined. The fundamental idea is based on the phenomenon of refraction by a lens-shaped crescent structure which results in the focusing of wave energy on the center line of the structure. The shape of the submerged structure is a complex curve combining circular with elliptical elements. Based on the design procedure, a special configuration of structure(termed herein as a triple crescent structure) is introduced. Next, some hydraulic model tests are performed to confirm the wave focusing effect in laboratory. In addition, in order to interpret the wave focusing performance behind the structure, a numerical procedure by the hybrid element method is used on the basis of the conventional mild slope equation but modified and extended to allow for steeper bottom slopes and higher curvature. The modified refraction and diffraction provide additional mechanism for wave height amplification and the maximum amplification for triple crescent structure is presented. It also allows for the possibility of wave energy scattering with the change of the incident wave direction. Comparisons with previous theoretical results involving a submerged crescent shape structure are described.

• Nuclear Engineering and Technology
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• 제21권1호
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• pp.40-47
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• 1989

중성입자입사 장치의 효율적인 빔형성 구조를 목적으로 정전기장 내에서 하전 입자의 움직임을 시간의 흐름에 따라 계산해 볼 수 있는 프로그램을 만들어 입자 모사 모형을 찾았다. 가속관 내의 입자의 움직임은 일정 시간 간격으로 계산하였고 전위는 유한차분법에 의해 Poisson 방정식에서 구하였다. 행렬식은 반복해법인 successive overrelaxation법을 사용하였고 전하밀도와 임자에 미치는 전기장의 힘을 구할 때는 cloud-in-cell모델을 사용하였다. 이 전자계산 코드를 사용하여 가속관 내 전극의 여러 조건들을 변화시켜가면서 빔형성 구조의 최적 설계를 수행하였다. 중성자 입사 장치의 가속관에서 가속 감속-전극간의 간격변화, 감속전극의 두께 변화, 가속 전극의 형태변화 등을 통하여 이들이 빔의 모양에 끼치는 영향을 조사하여 몇 가지 경우에 있어서 일정한 시간 간격으로 나타나는 입자들의 움직임을 예시하였다. 이 입자 모사모형을 통하여 가속전극의 형태가 빔 퍼짐에 가장 주요한 역할을 하는 것을 알았다.