• Structural Engineering and Mechanics
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• 제22권4호
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• pp.401-418
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• 2006

Solutions to the problems of structural parameter estimation from modal response using leastsquares minimization of force or displacement residuals are generally sensitive to noise in the response measurements. The sensitivity of the parameter estimates is governed by the physical characteristics of the structure and certain features of the noisy measurements. It has been shown that the regularization method can be used to reduce effects of the measurement noise on the estimation error through adding a regularization function to the parameter estimation objective function. In this paper, we adopt the regularization function as the Euclidean norm of the difference between the values of the currently estimated parameters and the a priori parameter estimates. The effect of the regularization function on the outcome of parameter estimation is determined by a regularization factor. Based on a singular value decomposition of the sensitivity matrix of the structural response, it is shown that the optimal regularization factor is obtained by using the maximum singular value of the sensitivity matrix. This selection exhibits the condition where the effect of the a priori estimates on the solutions to the parameter estimation problem is minimal. The performance of the proposed algorithm is investigated in comparison with certain algorithms selected from the literature by using a numerical example.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.561-582
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• 2012

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

• Earthquakes and Structures
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• 제2권1호
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• pp.43-64
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• 2011

One-dimensional rod theory is very effective as a simplified analytical approach to large scale or complicated structures such as high-rise buildings, in preliminary design stages. It replaces an original structure by a one-dimensional rod which has an equivalent stiffness in terms of global properties. The mechanical behavior of structures composed of distinct constituents of different stiffness such as coupled walls with opening is significantly governed by the local variation of stiffness. Furthermore, in structures with setback the distribution of the longitudinal stress behaves remarkable nonlinear behavior in the transverse-wise. So, the author proposed the two-dimensional rod theory as an extended version of the rod theory which accounts for the two-dimensional local variation of structural stiffness; viz, variation in the transverse direction as well as longitudinal stiffness distribution. This paper proposes how to deal with the two-dimensional rod theory for structures with setback. Validity of the proposed theory is confirmed by comparison with numerical results of computational tools in the cases of static, free vibration and forced vibration problems for various structures. The transverse-wise nonlinear distribution of the longitudinal stress due to the existence of setback is clarified to originate from the long distance from setback.

• 한국지반공학회논문집
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• 제18권5호
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• pp.237-249
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• 2002

파괴 이전 상태의 낮은 변형률 수준 하에서 정확한 지반 변형 거동 예측을 위해서는 흙의 비선형성과 이방성을 함께 고려해야 한다. 본 연구에서는 Ramberg-Osgood 식을 이용하여 흙의 비선형성을 모사하고 직교이방성을 도입하여 흙의 이방성을 구현한 새로운 모델을 개발하였다. 새롭게 개발한 비선형 이방성 모델을 여러 비교 대상 모델과 함께 간단한 경계치 문제와 원형 기초 문제에 적용하였다. 그 결과 이방성을 나타내는 탄성계수비가 체적 계수, 정지 토압계수, 그리고 유효 응력 경로에 큰 영향을 미치는 사실을 알아내었으며, 원형 기초 해석을 통해 초기 지중 응력 상태를 고려한 흙의 비선형성이 지표 침하에 큰 영향을 줌을 알 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.365-368
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• 2006

RBSN Method, Rigid-Body-Spring Network Method, is a structural analysis method that overcomes the problems faced in FEM analysis of concrete or crack forming structures. In RBSN, irregular lattices are used to model structural components consisting of bulk material, curvilinear reinforcements, and their interfaces. Because reinforcements and their interfaces in the bulk material are freely positioned, meshing is irrespective of the geometry of the representing bulk material. In this paper, RBSN method of 3D is applied in simulating the pull-out test of FRP (Fiber Reinforced Polymer) embedded in concrete. The comparison of analysis results to experimental results shows that RBSN method simulates the shear-slip behavior very precisely. From the analysis results, 3D RBSN method is proven to be an effective and accurate analysis method for concrete structural analysis. Also, the results show that RBSN method can be a potential analysis method for concrete structures that can replace the current FEM analysis.

• 한국환경과학회지
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• 제12권9호
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• pp.957-966
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• 2003

Gunsan coastal area is one of region increasing pollution problems. To improve water quality, the reduction of these nutrients loads should be indispensible. In this study, the three-dimensional numerical hydrodynamic and ecosystem model were applied to analyze the processes affecting the eutrophication. In field survey, the average concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus(DIP) at surface waters were found to be 0.43mg/$\ell$ and 0.03mg/$\ell$ respectively, which were exceeding second grade of water quality criteria. In hydrodynamic modelling, the comparison between the simulated and observed tidal ellipses showed fairly good agreement. The ecosystem model was calibrated with the observed data in study area. The simulated results of DIN were fairly good coincided with the observed values within relative error of 32.39%, correlation coefficient(r) of 0.99. In the case of DIP, the simulated results were fairly good coincided with the observed values within relative error of 24.26%, correlation coefficient(r) of 0.82. The simulations of DIN and DIP concentrations using ecosystem model were performed under the conditions of 20∼80% reductions for pollutant loading. At simulation results, concentration of DIN and DIP were reduced to 20∼80% and under 10% in case of the 80% reduction of pollutant loading, respectively.

• 한국전자파학회논문지
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• 제11권8호
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• pp.1363-1375
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• 2000

접지된 유전체 슬랩 위에 주기적으로 스트립이 놓여 있는 격자구조에 대한 전자파 산란 특성을 TM편파의 경우에 대하여 반사격자(reflection grating)관점과 누설파안테나(leaky wave antenna)관점에서 조사하였다. 수치해석 결과로 Bragg blazing 현상을 두가지 형태(공진형과 비공진형)로 구분하였으며 그 특성(복소전파상수, 산란특성, 전류밀도분포)에 대하여 논의하였다. 특히, 본 연구구조의 TE 및 TM편파 경우에서 확인한 Bragg blazing 현상에 관하여 상세히 기술하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.391-398
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• 2005

In this investigation, turbulent premixed combustion and flame front propagation in a gas turbine combustion chamber is studied. Direct numerical simulation of turbulent reacting flows demands extremely high computational resources, especially in more complicated geometry. The alternative choice may be left for Large Eddy Simulation (LES) by which only large scales are solved directly. In combustion problems, capturing the large scales' behavior without solving the details of small scales is a difficult task. Using a transport equation for description of the flame front propagation and therefore avoiding the calculation of inner flame structure is the basic idea of this study. For this purpose. the so-called G-equation has been used by which any iso-level of the G variable provides the flame location. A comparison with the experiment indicates that the present method can predict a turbulent velocity field and also capture a instantaneous 3-dimensional flame structure.

• 대한기계학회논문집B
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• 제26권2호
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• pp.177-183
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• 2002

The field tests on the waterhammer were carried out in the pump pipeline system with an air chamber. The effects of the input variables and the design parameters for the air chamber were investigated by both the numerical calculations and the experiments. Because the waterhammer problems as a result of the pump power failure were the most important, these situations were carefully studied. Among the input variables used in the waterhammer analysis, the polytropic exponent, the discharge coefficient and the wavespeed had influence on the simulated results in that order, and were calibrated in comparison with the experimental results. As the initial air volume in a vessel increased, the period of waterhammer increased and the pressure variation decreased, resulting from the reduction of the rate of pressure change in the air chamber. Using smaller orifice in the bypass pipe, the pressure rise was suppressed in some degree and the pressure surge was dissipated more rapidly as time passed. The simulations were in fairly good agreement with the measured values until 1∼2 periods of waterhammer. Not only the maximum and minimum pressures in the pipe1ine but also those occurring times were reasonably predicted. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system.

• 한국해양공학회지
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• 제34권5호
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• pp.325-333
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• 2020

As regulations concerning ship vibration and noise are becoming stricter, considerable attention is being drawn to prediction technologies for ship vibration and noise. In particular, the resonance and lock-in phenomena caused by vortex-induced vibration (VIV) have become considerably important with increases in the speed and the size of ships and ocean structures, which are known to cause structural problems. This study extends the fluid-structure interaction (FSI) analysis method to predict resonances and lock-in phenomena of high modes and VIV of ship rudders. Numerical stability is secured in underwater conditions by implementing added mass, added damping, and added stiffness by applying the potential theory to structural analysis. An expanded governing equation is developed by implementing displacements and twist angles of high modes. The lock-in velocity range and resonant frequencies of ship rudders obtained using the developed FSI method agree well with the experimental results and the analytic solution. A comparison with local vibration guidelines published by Lloyd's Register shows that predictions of resonances and lock-in phenomena of high modes are necessary in the shipbuilding industry due to the possible risks like fatigue failure.