• Structural Monitoring and Maintenance
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• 제6권1호
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• pp.33-46
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• 2019

In present study, Operational Modal Analysis (OMA) was employed to carry out the dynamic and vibration analysis of the threshing unit of the combine harvester thresher as a mechanical component. The main study is to find the causes of vibration and to decrease it to enhance the lifetime and efficiency of the threshing unit. By utilizing OMA, structural modal parameters such as mode shapes, natural frequencies, and damping ratio was calculated. The combine harvester was excited by engine to vibrate different parts and accelerometer sensor collected acceleration signals at different speeds, and OMA was utilized by nonparametric and frequency analysis methods to obtain modal parameters while vibrating in real working conditions. Afterwards, finite element model was designed from the thresher and updated using the data obtained from the modal analysis. Using the conducted analyses, it was specified that proximity of the thresher pass frequency to one of the natural frequencies (16.64 Hz) was the most important effect of vibration in the thresher. Modification process of the structure was carried out by increasing mass required for changing the natural frequency location of the first mode to 12.4 Hz in order to reduce resonance and vibration of the thresher.

• Structural Engineering and Mechanics
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• 제68권2호
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• pp.159-170
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• 2018

This paper aims to develop response modification factors for stiffness degrading structures by incorporating soil-structure interaction effects. A comprehensive parametric study is conducted to investigate the effects of key SSI parameters, natural period of vibration, ductility demand and hysteretic behavior on the response modification factor of soil-structure systems. The nonlinear dynamic response of 6300 soil-structure systems are studied under two ensembles of accelograms including 20 recorded and 7 synthetic ground motions. It is concluded that neglecting the stiffness degradation of structures can results in up to 22% underestimation of inelastic strength demands in soil-structure systems, leading to an unexpected high level of ductility demand in the structures located on soft soil. Nonlinear regression analyses are then performed to derive a simplified expression for estimating ductility-dependent response modification factors for stiffness degrading soil-structure systems. The adequacy of the proposed expression is investigated through sensitivity analyses on nonlinear soil-structure systems under seven synthetic spectrum compatible earthquake ground motions. A good agreement is observed between the results of the predicted and the target ductility demands, demonstrating the adequacy of the expression proposed in this study to estimate the inelastic demands of SSI systems with stiffness degrading structures. It is observed that the maximum differences between the target and average target ductility demands was 15%, which is considered acceptable for practical design purposes.

• 한국항해학회지
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• 제25권1호
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• pp.45-52
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• 2001

본 논문은 선체구조에 많이 이용되고 있는 보강판 구조물의 동적 특성을 최적 변경하는데 그 목적이 있다. 유한요소법(FEM), 동적 감도해석법, 최적구조 변경법을 이용하여 보강판의 동적 특성을 최적화한다. 먼저, FEM을 이용하여 보강판 구조물의 동적 특성을 해석한다. 다음으로 설계변수의 변화에 따른 동적 특성의 변화율을 동적 감도해석법으로 해석한다. 감도해석법으로 구한 감도값과 최적구조 변경법을 이용하여 설계변수들의 변경 량을 계산한다. 보강판 구조물의 고유진동수의 변경을 목적함수로 하고, 보강판의 두께와 보강재의 단면2차 모우멘트를 설계 변수로 한다. 본 논문에서 이용한 최적구조 변경법이 보강판 구조물의 동특성을 최적화하는데 유용함을 보여준다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.231-236
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• 1996

Recently to develope an automobile with better properties, much researches and investments are executed in many countries. In this paper, the weight of an engine block intend to minimize without changing the natural frequency. The weight minimization of an engine block is started from much less initial thickness than original thickness of the model and performed by using the sensitive analysis method and the optimum structural modification method. It can be considered that the weight minimization is completed through this process, because the optimum structural modification method includes the constraint of minimum changing quantity.

• 한국구조물진단유지관리공학회 논문집
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• 제17권4호
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• pp.112-118
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• 2013

성능기반 내진설계 및 평가의 정밀도 향상에 있어서 적절한 지반운동 데이터 선정과 이를 합리적으로 수정하는 것에 대한 중요성이 부각되고 있다. 지반운동 데이터를 수정하는 방법으로 단일 진폭수정법 (Amplitude scaling)이 널리 사용되고 있으나, 단일 진폭수정법에서 는 단 하나의 주기, 특히 구조물의 고유주기에서만 그 응답스펙트럼 값이 설계스펙트럼의 값과 일치하도록 수정되므로 특정 지역의 지진 재해도에 대해 일관성 있는 구조 해석 결과를 기대하기 어렵다. 따라서 이에 대해 여러 가지 대안 수정법들이 제시되고 있으나 이들의 타당성을 평가할 수 있는 방안이 마련되어 있지 않다. 본 논문에서는 단일 진폭수정법의 문제점을 설명하고, 대안 수정법과 비교 평가하기 위한 구조 응답에 대한 회귀 모델을 제시하는데 목표를 두었다. 대안 수정법으로써 전체 주기 범위에서 지반운동의 응답스펙트럼이 설계스펙트럼의 값과 일치하도록 수정하는 다중 스펙트럼 수정법을 고려하였다. 설계스펙트럼은 ASCE7-05에 따라 구하였다.

• 한국정밀공학회지
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• 제17권5호
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• pp.93-99
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• 2000

In many dynamic structural optimization problems, the goal is to reduce the total weight of the structure without causing the resonance. Up to now, gradient informations(i.e., design sensitivity) have been used to achieve the goal. For some class of dynamic problems, especially coalescent eigenvalue Problems with multiobjective optimization, the design sensitivity analysis is too much complicated mathematically and numerically. Therefore, this article proposes a new technique fur structural dynamic modification using a mode modification method with Genetic Algorithm(GA). In GA formulation, fitness is defined based on penalty function approach. Design variables are iteratively improved by using genetic algorithm. Two numerical examples are shown, (ⅰ) a cantilevered plate, and (ⅱ) H-shaped structure. The results demonstrate that the proposed method is highly efficient.

• Journal of Advanced Marine Engineering and Technology
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• 제16권3호
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• pp.51-57
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• 1992

Authors had analyzed the Press machine's vibrational characteristics by Substructure Synthesis Method. This paper discribes the structural Dynamic Optimization for the machine using Sensitive Analysis Method. The substructure synthesis method and sensitive analysis methods are used for the vibration analysis and structural modification. The results obtained are as follows ; 1. The tooling precision of the press machine is ruled by the bending vibration of the slide. 2. The structural Modification Method for minimizing impact responses is proposed, and modal analysis and sensitive analysis method are introduced to solve it. 3. The impact responses of running machine were reduced to 40% of the unmodified machine by using the proposed method.

• The Journal of the Acoustical Society of Korea
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• 제19권3E호
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• pp.3-11
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• 2000

A structural modification technique for reducing structure-borne noise of vehicles using a sensitivity analysis is suggested. To estimate the noises generated by the vibration response, a semi structure-acoustic coupling analysis was exploited. As a result of the coupling analysis, severe noise generating positions are identified whose vibrations should be cured through structural modifications. Formulation for the sensitivity analysis of those severe vibration responses with respect to the design changes is derived to enhance the vibration response. Special attention is given in this paper to the use of the experimentally measured vibration responses in the sensitivity analysis. As a result of the proposed method, the structural modifications can be peformed accurately by using experimental data instead of using the finite element method though the higher vibration modes are considered as long as the vibration measurement and acoustic mode calculations are accurate. Effectiveness of this method was examined using an example model by experiments.

• 한국강구조학회 논문집
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• 제22권3호
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• pp.229-239
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• 2010

새롭게 제안된 다이아그리드 구조 시스템은 경사진 기둥을 통해 구조물의 중력하중과 횡력을 모두 저항하는 시스템이다. 하지만 현재 내진설계 기준은 새로운 구조시스템에 대한 적절한 반응수정계수가 없다. 이에 새로운 시스템의 반응수정계수를 포함한 내진설계시 고려되는 내진성능계수들을 산정하기 위해 ATC-63(안)이 새롭게 제안되었다. ATC-63(안)에서는 구조 시스템의 여러 변수에 의해 다른 값을 가지게 되는 반응수정계수를 보완하기 위해 붕괴여유비를 함께 고려하여 건물의 내진성능을 판단한다. 본 논문에서는 4층에서 36층의 서로 다른 높이의 대각가 새 구조물을 설계하여 ATC-63(안)의 방법론에 따라 비선형정적해석과 동적해석을 통해 대각가새 구조의 내진성능계수를 평가하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.641-645
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• 2008

In this paper, vibration sources of the BLOC motor are identified and the motor vibrations are reduced by structural modification. For vibration characteristic identification, vibration signals measured by an accelerometer when the BLOC motor is moving. These signals are presented in a waterfall plot in order to find the dependency of frequency components on the motor speed. It is found that main vibration source is BLOC motor test rig. From finite element analyses and some experiments, it is also found that resonances occur because the natural frequencies of the test rig exist in usual driving speed rang. To shift the natural frequencies outside the driving rang, the test rig is modified increase stiffness. It is verified that considerable amount of vibration are reduced by the structural modification.