• Structural Engineering and Mechanics
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• 제47권5호
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• pp.713-727
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• 2013

In current study, natural frequency response of fiber metal laminated (FML) fibrous composite panels is optimized under different combination of the three classical boundary conditions using particle swarm optimization (PSO) algorithm and finite strip method (FSM). The ply angles, numbers of layers, panel length/width ratios, edge conditions and thickness of metal sheets are chosen as design variables. The formulation of the panel is based on the classical laminated plate theory (CLPT), and numerical results are obtained by the semi-analytical finite strip method. The superiority of the PSO algorithm is demonstrated by comparing with the simple genetic algorithm.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.61-62
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• 2010

본 연구에서는 1995년부터~2007년까지 한국시설안전공단에서 시행한 정밀안전보고서를 데이터 베이스화한 자료를 이용하여 통계적 방법으로 분석하였다. 대상교량은 총 36개소의 충격계수를 지간장별, 상부구조별, 고유진동수별로 분류하였다. 철도교 설계기준과 외국의 교량 설계시방서의 충격계수 산정식을 비교 검토하고 국가별 설계기준과 조사된 대상교량의 고유진동수와 충격계수를 분석하였다.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.445-468
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• 2014

In this paper a new particle swarm ray optimization algorithm is proposed for truss shape and size optimization with natural frequency constraints. These problems are believed to represent nonlinear and non-convex search spaces with several local optima and therefore are suitable for examining the capabilities of new algorithms. The proposed algorithm can be viewed as a hybridization of Particle Swarm Optimization (PSO) and the recently proposed Ray Optimization (RO) algorithms. In fact the exploration capabilities of the PSO are tried to be promoted using some concepts of the RO. Five numerical examples are examined in order to inspect the viability of the proposed algorithm. The results are compared with those of the PSO and some other existing algorithms. It is shown that the proposed algorithm obtains lighter structures in comparison to other methods most of the time. As will be discussed, the algorithm's performance can be attributed to its appropriate exploration/exploitation balance.

• 한국정밀공학회지
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• 제6권3호
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• pp.46-59
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• 1989

The purpose of test fixture is to mechanically couple energy from a shaker into a test specimen. And then it is necessary to design a fixture of shich the fundamental natural frequency is over than one half times as high as the highest frequency of interest. But the dynamic behavior of vibration test fixture is usually different from, often far different from, what has been calculated. In this paper, the optimal dimensionless frequency parameter, ${lambda}$'s, are calculated from the test results of a various and complex shaped fixtures.

• Advances in concrete construction
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• 제13권4호
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• pp.327-337
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• 2022

This paper is concerned with the vibration analysis of middle layer cylindrical shell made of functionally graded material. The outer layers and inner layer are composed of functionally graded and isotropic material respectively. The Rayleigh Ritz method is applied to solve the presented shell dynamics equations. Two configurations are constructed with layers distributions. Fundamental natural frequencies of the three layered cylindrical shell is plotted against the circumferential wave number with different power law exponents. The frequency decreases with the increase of power law exponent. The fundamental natural frequencies first decreases and fall down to its minimum value, after frequencies increases with circumferential wave number. This is due to change in the magnitude of extensional and bending energies of the cylindrical shells. The computer software MATLAB has been employed for the computation of presented frequencies and tested the results obtained in order to assess the accuracy and validity of the cylindrical shell model for predicting the vibration frequencies of cylindrical shell.

• Advances in aircraft and spacecraft science
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• 제4권2호
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• pp.169-184
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• 2017

The optimum design of structures with frequency constraints is of great importance in the aeronautical industry. In order to avoid severe vibration, it is necessary to shift the fundamental frequency of the structure away from the frequency range of the dynamic loading. This paper develops a novel topology optimisation method for optimising the fundamental frequencies of structures. The finite element dynamic eigenvalue problem is solved to derive the sensitivity function used for the optimisation criteria. An alternative material interpolation scheme is developed and applied to the optimisation problem. A novel level-set criteria and updating routine for the weighting factors is presented to determine the optimal topology. The optimisation algorithm is applied to a simple two-dimensional plane stress plate to verify the method. Optimisation for maximising a chosen frequency and maximising the gap between two frequencies are presented. This has the application of stiffness maximisation and flutter suppression. The results of the optimisation algorithm are compared with the state of the art in frequency topology optimisation. Test cases have shown that the algorithm produces similar topologies to the state of the art, verifying that the novel technique is suitable for frequency optimisation.

• 정보처리학회논문지B
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• 제15B권6호
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• pp.595-602
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• 2008

각 문장 별 중점단어는 발화음성을 인식하고 그 의미를 이해하는데 도움을 준다. 발화된 음성신호로부터 중점단어를 탐색할 수 있는 방법을 찾기 위한 노력의 일환으로 실험을 통하여 문장 내에서 중점단어와 그 외의 단어들의 기본주파수의 평균과 분산, 그리고 평균 에너지를 분석해 보았다. 한국어로 된 100개의 발화문장의 음성데이터를 가지고 실험을 한 결과 중점단어는 그 외의 단어들에 비해 대부분 상대적으로 높은 기본주파수의 평균값을 나타내거나 상대적으로 높은 기본주파수의 분산 값을 나타냈다. 이 연구 결과를 이용하면 한국어의 구어문장에서 운율적 특성을 알 수 있을 뿐만 아니라, 자연어 처리를 이용한 핵심어를 추출하는 데에도 도움이 될 것이다.

• Structural Engineering and Mechanics
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• 제22권2호
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• pp.185-195
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• 2006

Nowadays it is very necessary to generate artificial accelerograms because of lack of adequate earthquake records and vast usage of time-history dynamic analysis to calculate responses of structures. According to the lack of natural records, the best choice is to use proper artificial earthquake records for the specified design zone. These records should be generated in a way that would contain seismic properties of a vast area and therefore could be applied as design records. The main objective of this paper is to present a new method based on wavelet theory to generate more artificial earthquake records, which are compatible with target spectrum. Wavelets are able to decompose time series to several levels that each level covers a specific range of frequencies. If an accelerogram is transformed by Fourier transform to frequency domain, then wavelets are considered as a transform in time-scale domain which frequency has been changed to scale in the recent domain. Since wavelet theory separates each signal, it is able to generate so many artificial records having the same target spectrum.

• Advances in nano research
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• 제8권3호
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• pp.215-228
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• 2020

In this paper, a new method based on the Sander theory is developed for SWCNTs to predict the vibrational behavior of length and ratio of thickness-to-radius according to various end conditions. The motion equation for this system is developed using Rayleigh-Ritz's method. The proposed model shows the vibration frequencies of armchair (5, 5), (7, 7), (9, 9), zigzag (12, 0), (14, 0), (19, 0) and chiral (8, 3), (10, 2), (14, 5) under different support conditions namely; SS-SS, C-F, C-C, and C-SS. The solutions of frequency equations have been given for different boundary condition, which have been given in several graphs. Several parameters of nanotubes with characteristic frequencies are given and vary continuously in length and ratio of thickness-to-radius. It has been illustrated that an enhancing the length of SWCNTs results in decreasing of the frequency range. It was demonstrated by increasing of the height-to-radius ratio of CNTs, the fundamental natural frequency would increase. Moreover, effects of length and ratio of height-to-radius with different boundary conditions have been investigated in detail. It was found that the fundamental frequencies of C-F are always lower than that of other conditions, respectively. In addition, the existence of boundary conditions has a significant impact on the vibration of SWCNTs. To generate the fundamental natural frequencies of SWCNTs, computer software MATLAB engaged. The numerical results are validated with existing open text. Since the percentage of error is negligible, the model has been concluded as valid.

• Advances in aircraft and spacecraft science
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• 제7권1호
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• pp.79-90
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• 2020

The dynamic coupling between shaker and test-article has been investigated by recent research through the so called Virtual Shaker Testing (VST) approach. Basically a VST model includes the mathematical models of the test-item, of the shaker body, of the seismic mass and the facility vibration control algorithm. The subsequent coupled dynamic simulation even if more complex than the classical hard-mounted sine test-prediction, is a closer representation of the reality and is expected to be more accurate. One of the most remarkable benefits of VST is the accurate quantification of the frequency down-shift (with respect to the hard-mounted value), typically affecting the first lateral resonance of heavy test-items, like medium or large size Spacecraft (S/Cs), once mounted on the shaker. In this work, starting from previous successful VST experiences, the parameters having impact on the frequency shift are identified and discussed one by one. A simplified analytical system is thus defined to propose an efficient and effective way of calculating the lower bound frequency shift through a simple equation. Such equation can be useful to correct the S/C lateral natural frequency measured during the test, in order to remove the contribution attributable to the shaker in use. The so-corrected frequency value becomes relevant when verifying the compliance of the S/C w.r.t. the frequency requirement from the Launcher Authority. Moreover, it allows to perform a consistent post-test correlation of the first lateral natural frequency of S/C FE model.