• Proceedings of the KSME Conference
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• 2001.06c
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• pp.392-397
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• 2001

Topology optimization is applied to determine the layout of a structure whose eigenfrequency coincides with a specified frequency. The topology optimization problem is formulated to minimize the difference between the structural frequency and a given frequency using the homogenization method and the modified optimality criteria method. It turns out that the value of a weighting factor in the updating scheme plays an important role to achieve both a suitable speed and a stable convergence of an algorithm. Unlike a constant weighting factor in previous works, it is suggested that a weight factor is varied during the iteration to control the amount of the frequency change. To substantiate the proposed approach two-dimensional structural design problems are presented and the resulted topology layouts for the specified eigenfrequency are compared to layouts for maximizing the corresponding eigenfrequency.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1118-1127
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• 2008

The position and size of holes in the partition of a double cavity are known to strongly affect the eigenfrequency of the longitudinal eigenmodes of the double cavity. To maximize or minimize the eigenfrequency of the hole-partitioned double cavity, two acoustical topology optimization problems are formulated and solved. While two sub-cavities are filled with air, a partition between them is assumed to consist of sub-partitions of variable acoustical properties. One design variable is assigned to each sub-partition, whose material properties are interpolated as those of an intermediate material between air and a rigid body. The penalty parameter of the used interpolation function is adjusted to obtain a distinct air and rigid body distribution at the converged stage in each acoustical topology optimization problem. A special attention is paid to the selection of initial values of design variables to obtain solutions as close to global optimum and symmetric as possible. To show numerical characteristics of these optimization problems, the formulated problems are first solved for the one-dimensional partition design domain and then for the two-dimensional partition design domain.

• Journal of Computing Science and Engineering
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• v.8 no.3
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• pp.129-136
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• 2014

This paper presents the equivalent circuit modelling and eigenfrequency analysis of a wideband robust capacitive radio frequency (RF) microelectromechanical system (MEMS) switch that was designed using Poly-Si and Au layer membrane for highly reliable switching operation. The circuit characterization includes the extraction of resistance, inductance, on and off state capacitance, and Q-factor. The first six eigenfrequencies are analyzed using a finite element modeler, and the equivalent modes are demonstrated. The switch is optimized for millimeter wave frequencies, which indicate excellent RF performance with isolation of more than 55 dB and a low insertion loss of 0.1 dB in the V-band. The designed switch actuates at 13.2 V. The R, L, C and Q-factor are simulated using Y-matrix data over a frequency sweep of 20-100 GHz. The proposed switch has various applications in satellite communication networks and can also be used for devices that will incorporate the upcoming IEEE Wi-Fi 802.11ad protocol.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1210-1216
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• 2003

Topology optimization is applied to determine the layout of a structural component with a specified frequency by minimizing the difference between the specified structural frequency and a given frequency. The homogenization design method is employed and the topology design problem is solved by the optimality criteria method. The value of a weighting factor in the optimality criteria plays an important role in this topology design problem. The modified optimality criteria method approximated by using the binomial expansion is suggested to determine the suitable value of the weighting factor, which makes convergence stable. If a given frequency is set as an excited frequency, it is possible to avoid resonance by moving away the specified structural frequency from the given frequency. The results of several test problems are compared with previous works and show the validity of the proposed algorithm.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.89-92
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• 2009

본 논문에서는 비선형구조물의 위상최적화를 위하여 개발된 요소 연결 매개법 (Element Connectivity Parameterization Method)을 이용하여 기하비선형 구조물의 고유진동수(Eigenfrequency)를 최적화하는 연구를 소개한다. 기존의 밀도를 기반으로 한 위상최적화기법은 비선형 구조물의 위상최적화를 수행할 때 약한 탄성계수를 가지는 요소가 대변형을 일으켜 전체 강성행렬(Tangent Stiffness Matrix)이 양정정성(Positive definiteness)를 잃어버리는 문제점이 있어서 위상최적화를 수행하기 어렵다. 이 문제점을 해결하기 위하여 최근에 요소 연결 매개법(Element Connectivity Parameterization Method)이 개발되었다. 이 요소 연결 매개법은 요소의 강성을 설계하는 것이 아니라 요소의 연결성을 설계하는 기법으로 이를 이용하여 비선형 구조물의 위상최적화를 효과적으로 수행할 수 있다. 이 연구에서는 요소 연결 매개법을 동적인 문제에 적용하기 위한 연구를 수행하며 이를 이용하여 비선형 구조물의 고유진동수를 최적화 하는 위상최적화 문제에 적용하였다. 비선형 수치 예제를 통하여 기하 비선형 구조물의 고유진동수를 최대화를 통하여 기하 비선형 구조물의 강성최대화 문제와 같은 결과를 얻을 수 있었다.

• New & Renewable Energy
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• v.2 no.4 s.8
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• pp.19-26
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• 2006

Tower shell design is very important because tower takes about 20% of overall wind turbine cost. This paper contains procedure of tower analysis and tower shell thickness optimization concept. Some of requirements like eigenfrequency and buckling evaluated by numerical method. But strength and fatigue can be derived by mathematical method simply. Using this procedure, tower shell thickness can be designed without repetition of complicated calculation.

• Journal of Korean Association for Spatial Structures
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• v.24 no.1
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• pp.57-64
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• 2024

This study numerically compares optimum solutions generated by element- and node-wise topology optimization designs for free vibration structures, where element-and node-wise denote the use of element and nodal densities as design parameters, respectively. For static problems optimal solution comparisons of the two types for topology optimization designs have already been introduced by the author and many other researchers, and the static structural design is very common. In dynamic topology optimization problems the objective is in general related to maximum Eigenfrequency optimization subject to a given material limit since structures with a high fundamental frequency tend to be reasonable stiff for static loads. Numerical applications topologically maximizing the first natural Eigenfrequency verify the difference of solutions between element-and node-wise topology optimum designs.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.20-27
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• 2017

This study investigated the problems in current practice of drive-train resonance analysis procedure and suggested solutions. The first problem is the resonance occurrence at the un-identified resonance point by the current practice, as for a solution the force spectrum analysis for each critical force transmitting component was suggested. The second one is the inaccurate estimation of potential resonance point in eigenfrequency analysis because of the non-consideration about the eigenfrequency dependency on rotor-speed, the fine linearization at each rotor speed point all over operational range was proposed to account for the affection. Lastly the insufficient time for resonance activation under run-up simulation condition was recognized as a problem in resonance load increasing analysis, as an alternative, steady state condition was suggested to estimate the maximum load increasing level.

• Structural Engineering and Mechanics
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• v.36 no.1
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• pp.79-94
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• 2010

This study shows how uncertainties of data like material properties quantitatively have an influence on structural topology optimization results for dynamic problems, here such as both optimal topology and shape. In general, the data uncertainties may result in uncertainties of structural behaviors like deflection or stress in structural analyses. Therefore optimization solutions naturally depend on the uncertainties in structural behaviors, since structural behaviors estimated by the structural analysis method like FEM need to execute optimization procedures. In order to quantitatively estimate the effect of data uncertainties on topology optimization solutions of dynamic problems, a so-called interval analysis is utilized in this study, and it is a well-known non-stochastic approach for uncertainty estimate. Topology optimization is realized by using a typical SIMP method, and for dynamic problems the optimization seeks to maximize the first-order eigenfrequency subject to a given material limit like a volume. Numerical applications topologically optimizing dynamic wall structures with varied supports are studied to verify the non-stochastic interval analysis is also suitable to estimate topology optimization results with dynamic problems.

• The Journal of the Acoustical Society of Korea
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• v.35 no.1
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• pp.16-23
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• 2016

Present study shows three different methods finding the eigenfrequencies of an infinite circular cylinder under free-vibration; Elasticity theory that can be applied to general case, thin-shell theory that can be effectively applied to the cylinders with small thickness, and numerical study using Finite Element Method (FEM). The results obtained from those methods were verified through the cross check among the calculations. Changing the thickness of the cylinder for a fixed outer radius, all the eigenfrequencies below 1 kHz were found and their dependences on the modal index and the thickness were observed.