• Structural Monitoring and Maintenance
• /
• 제4권1호
• /
• pp.33-52
• /
• 2017

A cantilever beam with a breathing crack is studied to improve the breathing crack identification sensitivity by the parametric optimization of sample entropy and wavelet transformation. Crack breathing is a special bi-linear phenomenon experienced by fatigue cracks which are under dynamic loadings. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a fatigue crack. To improve the sensitivity of entropy measurement for crack identification, wavelet transformation is merged with entropy. The crack identification is studied under different sinusoidal excitation frequencies of the cantilever beam. It is found that, for the excitation frequencies close to the first modal frequency of the beam structure, the method is capable of detecting only 22% of the crack depth percentage ratio with respect to the thickness of the beam. Using parametric optimization of sample entropy and wavelet transformation, this crack identification sensitivity is improved up to 8%. The experimental studies are carried out, and experimental results successfully validate the numerical parametric optimization process.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 춘계학술대회논문집
• /
• pp.651-659
• /
• 2002

Component Mode Synthesis (CMS) is a dynamic substructuring technique to get an approximate eigensolutions of large degree-of-freedom structures divisible into several components. But, In practice. most of large structures are modeled by different teams of engineers. and their respective finite element models often require different mesh resolutions. As a result, the finite element substructure models can be non-conforming and/or incompatible. In this work, A hybrid version of component mode synthesis using a localized lagrange multiplier to treat the non-conforming mesh problem was derived. Evolution Strategies (ESs) is a stochastic numerical optimization technique and has shown a robust performance for solving deterministic problems. An ESs conducts its search by processing a population of solutions for an optimization problem based on principles from natural evolution. An optimization example for raising the first natural frequency of a plate structure using beam stiffeners was presented using hybrid component mode synthesis and robust evolution strategies (RES) optimization technique. In the example. the design variables are the positions and lengths of beam stiffeners.

• 전산구조공학
• /
• 제9권4호
• /
• pp.117-126
• /
• 1996

구조물의 손상추정법은 정적방법과 동적방법으로 나눌 수 있다. 정적방법은 정적하중과 정적변위의 관계를 이용하여 구조물의 손상위치와 손상정도를 추정하는 방법으로 동적방법에 비해 수식이 간단하나, 정적하중과 정적변위의 관계만을 사용하여 구조물의 손상을 추정하므로 정적변위에 대한 오차에 매우 민감하다. 동적방법은 구조물의 고유한 진동특성을 나타내는 고유진동수와 진동모우드를 구하여 구조물의 손상을 추정하는 방법으로, 정적방법에 비해 동일한 측점에서 많은 양의 시간기록자료를 계측할 수 는 있으나, 신뢰성이 높은 많은 수의 고유진동수와 진동모우드를 구하기가 어렵다. 본 연구에서는 구조물의 정적변위, 고유진동수와 진동모우드에 대한 민감도행렬을 사용하여 구조물의 정적 및 동적특성을 동시에 고려할 수 있는 구조물의 손상추정법을 제시하였다. 제시한 방법은 구조물의 손상 전.후의 정적변위와 진동모우드의 변화량을 부등구속조건식으로한 최적화기법을 사용하므로, 제한된 계측절점과 오차를 고려할 수 있으며 정적변위와 모우드 민감도행렬이외의 다양한 구조적 특성에 대한 민감도를 구속조건식으로 사용할 수 있다. 트러스구조물에 대한 모의 수치예제를 통한 제안한 방법의 정확성과 효율성을 수치적으로 검증하였다.

• EDISON SW 활용 경진대회 논문집
• /
• 제6회(2017년)
• /
• pp.290-303
• /
• 2017

This paper aims to build a drone platform based on an optimum design of its single arm. We assumed its single arm as a cantilevered beam with a tip mass. Based on the numerical optimization theory, we conducted validation and optimization of a new design by comparing the results with the similar ones obtained by ANSYS. Finally, this design is reflected in the control simulation, and the requirement of an optimum structural design considering the resonance situation is demonstrated.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
• /
• pp.135-142
• /
• 1999

Plate girder bridges for tile Korean high-speed railway are optimally designed. Static and dynamic constraints are all considered. The design variables are the thicknesses and the lengths of the plates that are used to form I-shaped main girders with variable cross-sections. And the objective function is tile steel weight of a main girder. A C++ based design program is developed; this program interfaces with a FORTRAN based optimization program ADS. From the results of optimal design for various span lengths, it is observed that the deck vertical acceleration is one of the most important constraints in a special range of tile span length. Front a parametric study, sensitivity of the optimal design to static as well as dynamic constraints are presented.

• 한국융합학회논문지
• /
• 제12권9호
• /
• pp.161-168
• /
• 2021

복합가공기 분야에서 고속 및 고정밀화에 대한 요구가 늘어남에 따라 복합가공기의 강성과 진동에 관한 관심이 증가하고 있다. 그러나 경험에 의존한 설계로 인해 개발 시간이 많이 소요되며 적절한 설계에도 어려움이 많아 공작기계 설계에 구조 최적화 FEM의 활용이 많아지고 있다. 그러나, 현재 구조물의 응력 분포를 통한 최적화를 주로 활용하고 있어 구조물의 진동 상태를 고려하여 최적화하기에는 어려움이 있다. 본 논문에서는 5축 복합가공기에서 가공에 가장 많은 영향을 끼치는 헤드 구조물의 최적화를 위하여 유한요소해석을 활용한 정적 구조해석, 모드 해석, 가진 주파수 해석을 진행하였으며, 도출된 응력 분포, 변형, 고유진동수, 가진 주파수 그래프를 활용하고 적절한 목적함수와 설계변수를 설정하여 정강성과 동강성을 모두 고려한 위상 최적화 해석 방법을 제시하고자 한다.

• 한국전산구조공학회논문집
• /
• 제12권4호
• /
• pp.573-581
• /
• 1999

액체 금속로(LMIR) 핵연료교환장치의 기본설계를 위해서는 여러 분야(예를 들면, 기구학, 동역 학, 재료역학 등)의 해석을 동시에 수행해야 한다. 그러나 이와 같은 해석들은 각각 별개로 연속적으로 수행되는 것이 아니라, 상호 유기적인 연관을 갖고 수행되어야 한다. 이와 같은 해석에 적합한 기법이 MDO 기법이다. 본 논문에서는 MDO기법에 의한 핵연료교환장치 구조해석의 한 단계로 핵연료교환장치의 기구 동역 학 해석을 수행하여 핵연료 교환장치 작동에 대한 기구운동학적 특성 및 동역학적 특성을 분석하였다. 분석결과 해석대상 핵연료교환장치는 예상한대로 원활하게 작동됨이 확인되었다. 아울러 이 분석 결과를 토대로 핵연료교환장치의 정적 휨 변형을 구하기 위한 재료역학해석에서 요구되는 정적구조를 결정하였다.

• Earthquakes and Structures
• /
• 제10권1호
• /
• pp.239-260
• /
• 2016

Tuned mass dampers (TMDs) have been frequently proposed to mitigate the detrimental effects of dynamic loadings in structural systems. The effectiveness of this protection strategy has been demonstrated for wind-induced vibrations and, to some extent, for seismic loadings. Within this framework, recent numerical studies have shown that beneficial effects can be achieved by placing a linear TMD on the roof of linear elastic structural systems subjected to pulse-like ground motions. Motivated by these positive outcomes, closed-form design formulations have been also proposed to optimize the device's parameters. For structural systems that undergo a near-fault pulse-like ground motion, however, it is unlikely that their dynamic response be linear elastic. Hence, it is very important to understand whether such strategy is effective for inelastic structural systems. In order to provide new useful insights about this issue, the paper presents statistical results obtained from a numerical study conducted for three shear-type hysteretic (softening-type) systems having 4, 8 and 16 stories equipped with a linear elastic TMD. The effectiveness of two design procedures is discussed by examining the performances of the protected systems subjected to 124 natural pulse-like earthquakes.

• Structural Engineering and Mechanics
• /
• 제60권5호
• /
• pp.761-779
• /
• 2016

Design of safe structures with resistance to progressive collapse is of paramount importance in structural engineering. In this paper, an efficient optimization technique is used for optimal design of steel moment frames subjected to progressive collapse. Seismic design specifications of AISC-LRFD code together with progressive collapse provisions of UFC are considered as the optimization constraints. Linear static, nonlinear static and nonlinear dynamic analysis procedures of alternate path method of UFC are considered in design process. Three design examples are solved and the results are discussed. Results show that frames, which are designed solely considering the AISC-LRFD limitations, cannot resist progressive collapse, in terms of UFC requirements. Moreover, although the linear static analysis procedure needs the least computational cost with compared to the other two procedures, is the most conservative one and results in heaviest frame designs against progressive collapse. By comparing the results of this work with those reported in literature, it is also shown that the optimization technique used in this paper significantly reduces the required computational effort for design. In addition, the effect of the use of connections with high plastic rotational capacity is investigated, whose results show that lighter designs with resistance to progressive collapse can be obtained by using Side Plate connections in steel frames.

• 한국공작기계학회논문집
• /
• 제15권3호
• /
• pp.8-16
• /
• 2006

This paper discusses design sensitivity analysis and its application to a structural dynamics modification. Eigenvalue derivatives are determined with respect to the element parameters, which include intrinsic property parameters such as Young's modulus, density of the material, diameter of a beam element, thickness of a plate element, and shape parameters. Derivatives of stiffness and mass matrices are directly calculated by derivatives of element matrices. The first and the second order derivatives of the eigenvalues are then mathematically derived from a dynamic equation of motion of FEM model. The calculation of the second order eigenvalue derivative requires the sensitivity of its corresponding eigenvector, which are developed by Nelson's direct approach. The modified eigenvalue of the structure is then evaluated by the Taylor series expansion with the first and the second derivatives of eigenvalue. Numerical examples for simple beam and plate are presented. First, eigenvalues of the structural system are numerically calculated. Second, the sensitivities of eigenvalues are then evaluated with respect to the element intrinsic parameters. The most effective parameter is determined by comparing sensitivities. Finally, we predict the modified eigenvalue by Taylor series expansion with the derivatives of eigenvalue for single parameter or multi parameters. The examples illustrate the effectiveness of the eigenvalue sensitivity analysis for the optimization of the structures.