• 한국강구조학회 논문집
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• 제15권2호
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• pp.175-185
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• 2003

사장교의 정확한 초기형상을 결정하기 위하여 초기부재력법과 TCUD법을 효과적으로 결합시킨 개선된 해석방법을 제시한다. 먼저 사장재, 주탑 그리고 주형을 모델링하기 위하여 무응력길이의 변화를 고려한 탄성현수선요소, 보-기둥요소의 힘-변형관계식과 접선강성 행렬 산정법을 간략히 제시한다. 이제 케이블의 무응력길이를 변수로 취급하여 교량 전체의 접선강성행렬을 산정하고, 경계조건 이외에 케이블 개수만큼의 절점변위를 설계자의 초기형상에 가깝게 되도록 추가적으로 절점변위를 구속하여 절점변위 및 무응력길이의 증분을 산정하고 이를 토대로 케이블 부재력과 주형 및 주탑의 부재력을 산정한다. 이렇게 계산된 부재력으로부터 불평형하중을 산정하고 수렴이 될 때까지 다시 반복계산이 이루어진다. 수렴이 되었을 때 사장교의 주탑 및 주형의 축방향 변위를 제거하기 위하여 초기부재력법을 적용한다. 결론적으로, 케이블의 무응력길이를 변수로 추가함으로써 사장재 주형정착부의 수직변위와 주탑의 수평변위를 설계목적에 적합하도록 제어하여 휨모멘트를 최소화할 수 있었고, 초기부재력법을 결합시켜 주형, 주탑의 축방향변위가 발생하지 않는 해석결과를 얻었다.

• 대한기계학회논문집A
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• 제29권9호
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• pp.1209-1216
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• 2005

Three methods for design sensitivity such as numerical differentiation, analytical method and semi-analytical method have been developed for the last three decades. Although analytical design sensitivity analysis is exact, it is hard to implement for practical design problems. Therefore, numerical method such as finite difference method is widely used to simply obtain the design sensitivity in most cases. The numerical differentiation is sufficiently accurate and reliable for most linear problems. However, it turns out that the numerical differentiation is inefficient and inaccurate because its computational cost depends on the number of design variables and large numerical errors can be included especially in nonlinear design sensitivity analysis. Thus semi-analytical method is more suitable for complicated design problems. Moreover semi-analytical method is easy to be performed in design procedure, which can be coupled with an analysis solver such as commercial finite element package. In this paper, implementation procedure for the semi-analytical design sensitivity analysis outside of the commercial finite element package is studied and computational technique is proposed, which evaluates the pseudo-load for design sensitivity analysis easily by using the design variation of corresponding internal nodal forces. Errors in semi-analytical design sensitivity analysis are examined and numerical examples are illustrated to confirm the reduction of numerical error considerably.

• 한국전산구조공학회논문집
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• 제27권1호
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• pp.17-26
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• 2014

본 논문은 MLS(Moving Least Squares) 차분법을 바탕으로 동적균열전파 해석을 수행하기 위한 알고리즘을 제시한다. MLS 차분법은 절점만으로 이루어진 수치모델을 사용하며, 이동최소제곱법을 이용하여 전개한 Taylor 다항식을 기초로 미분근사식을 유도하기 때문에, 요소망의 제약에서 완벽하게 벗어난 절점해석이 가능하다. 시간항을 포함하는 동적 평형방정식은 Newmark 방법으로 시간적분 하였다. 동적하중을 받는 균열이 전파할 때, 매 시간단계마다 절점모델을 재구성하지 않고 균열선단 주변에서 국부적인 수정을 통해 해석이 가능하다. 동적균열을 묘사하기 위해 가시한계법(visibility criterion)을 적용하였고, 동적 에너지해방률을 산정하여 균열의 진전유무와 그에 상응하는 진전방향을 결정하였다. 모드 I 상태와 혼합모드 상태에서 균열이 진전하는 현상을 모사하였고, 이론해와 Element-Free Galerkin법으로 계산한 결과와의 비교를 통해 개발된 알고리즘의 정확성과 안정성을 검증하였다.

• 농업과학연구
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• 제30권2호
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• pp.184-190
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• 2003

Finite element method(FEM) was used to obtain an approximate solution, since the mathematical formulations for the problem are complex and cannot be solved analytically. In this study, the fruit as well as the aluminum support on vibrator are discretized into small elements, and the approximate functions are used to describe the displacements in each element in terms of nodal values, and because of the complexity of the problem of viscoelastic materials such as the fruit and vegetables, it was necessary to validate the modeling approach before pear simulations were performed, and the finite element modeling approach was first validated by comparing the results obtained from simulation and experiment for the pear in the frequency range 3 to 150 Hz and acceleration level of 0.25 G-rms. Based on the relatively good agreement between simulated and measured frequencies for the pear, finite element models of tomato and oriental melon were created to study the vibration characteristics of the fruit and vegetables. The resonance frequencies of the pear, tomato and oriental melon using FEM were 62.50, 39.45 and 62.73 Hz and the peak accelerations of them using FEM were 2.21, 1.38 and 1.98 G-rms.

• Structural Engineering and Mechanics
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• 제67권5호
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• pp.439-455
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• 2018

Within a probabilistic framework, this paper addresses the determination of the static structural response of beams and frames with partially restrained (semi-rigid) connections. The flexibility of the nodal connections is incorporated via an idealized linear-elastic behavior of the beam constraints through the use of rotational springs, which are here considered uncertain for taking into account the largely scattered results observed in experimental findings. The analysis is conducted via the Probabilistic Transformation Method, by modelling the spring stiffness terms (or equivalently, the fixity factors of the beam) as uniformly distributed random variables. The limit values of the Eurocode 3 fixity factors for steel semi-rigid connections are assumed. The exact probability density function of a few indicators of the structural response is derived and discussed in order to identify to what extent the uncertainty of the beam constraints affects the resulting beam response. Some design considerations arise which point out the paramount importance of probability-based approaches whenever a comprehensive experimental background regarding the stiffness of the beam connection is lacking, for example in steel frames with semi-rigid connections or in precast reinforced concrete framed structures. Indeed, it is demonstrated that resorting to deterministic approaches may lead to misleading (and in some cases non-conservative) outcomes from a design viewpoint.

• 한국지반공학회지:지반
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• 제4권3호
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• pp.19-26
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• 1988

본 논문에서는 기초지반의 부등침하를 해석하기 위하여 추계론적 수치해석 방법을 사용하였다. 부등침하는 토질탄성계수의 공간적 변화와 밀접한 관계를 갖고 있다. Kriging 이론은 탄성계수의 공간적 변화를 설명하기 위하여 사용되었다. 이 방법은 선형최적불편추정기법으로 제한된 자료로 부터 최소의 분산을 가진 추정값을 구할 수 있다. 추계론적 유한요소법을 이용하여 일차근사 2차모멘트 기법으로 변위의 평균값과 분산값 그리고 공분산값을 구한다. 최종적으로 부등침하의 신뢰도모델이 제시되었다. 해석결과 두 기초사이의 거리와 탄성계수의 수평방향 변동거리가 거의 같을 때 최대부 등침하량이 일어난다는 것과 이 때 부등침하량이 허용간을 넋을 확률이 상당히 크다는 것이 밝혀 졌다.

• 전산구조공학
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• 제3권3호
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• pp.133-140
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• 1990

케이블 구조물은 응력-변형도관계에서 비선형성이 강하고 대변위에 의해 기하학적 비선형이 도입되므로 해석이 복잡하다. 그러므로 케이블 구조물의 평형형태 탐색과 해석에 앞서 기하학적 비선형을 고려해야만 한다. 본 논문에서는 이러한 문제를 해결하기 위해 케이블, 네트, 전선, 현수케이블 지붕등에 적용될 수 있는 수치해석과정이 소개된다. 이 과정은 두 부분으로 나눌 수 있는데, 하나는 유연성반복과정에의해 등분포하중을 받는 케이블 구조물의 응력과 평형형태를 구하는 것이고, 다른 한 부분은 비선형 유한요소법에 의해 절점외력을 받는 평형형태를 해석하는 것이다.

• Journal of Welding and Joining
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• 제27권3호
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• pp.60-66
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• 2009

The structures distorted by welding have to be corrected. Since the correcting work needs a lot of costs and time, it is very important to minimize the buckling distortion due to welding of thin plate structure. Therefore the aim of this study is to investigate the effect of single bead on plate welding and fillet welding on the buckling distortion. In the single bead on plate welding, it was found that the welding speed and welding sequence were the most dominant factors on distortion. In the fillet welding, there were four typical buckling modes observed, and the welding sequence was the most influential factor on the buckling distortion. However typical distortion measuring method is not considered for the distortion correcting process costs of each buckling modes, therefore, in this study, the measuring method is developed to classify the buckling modes for torsion of specimen and buckling distortion depend on nodal point for the bead on plate welding specimen and fillet welds.

• 동력기계공학회지
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• 제17권1호
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• pp.50-57
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• 2013

This describes the formulation for the free vibration of joined conical-cylindrical shells with uniform thickness using the transfer of influence coefficient. This method was developed based on successive transmission of dynamic influence coefficients, which were defined as the relationships between the displacement and the force vectors at arbitrary nodal circles of the system. The two edges of the shell having arbitrary boundary conditions are supported by several elastic springs with meridional/axial, circumferential, radial and rotational stiffness, respectively. The governing equations of vibration of a conical shell, including a cylindrical shell, are written as a coupled set of first order differential equations by using the transfer matrix of the shell. Once the transfer matrix of a single component has been determined, the entire structure matrix is obtained by the product of each component matrix and the joining matrix. The natural frequencies and the modes of vibration were calculated numerically for joined conical-cylindrical shells. The validity of the present method is demonstrated through simple numerical examples, and through comparison with the results of previous researchers.

• 한국소음진동공학회논문집
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• 제20권2호
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• pp.153-159
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• 2010

This work focuses on finding a method to reduce the noise of a hermetic reciprocating compressor during start-up using an acoustical analysis. The noise of compressor during start-up, which is a higher level than that of a normal operating condition, has transient and non-stationary characteristics. The acoustical analysis of compressor cavity is performed to find an effective method to reduce the noise level. In the acoustical analysis, the shape variations of frequency response function in the neighborhood of resonances are tested for three parameters: the height of remained oil, the suction position of refrigerant and the position of driving part. As a conclusion of this result, to reduce the emission noise of compressor during start-up, the height of remained oil should be kept at 16 mm, the refrigerant should be sucked at the cross point of nodal lines of X and Y directional cavity modes, and the driving part should be positioned in the center of cavity.