• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집A
• /
• pp.643-648
• /
• 2000

It is well known that natural frequencies increase when a cantilever beam rotates about the axis perpendicular to its longitudinal axis. Such phenomena that are caused by centrifugal inertia forces are often referred to as the stiffening effects. Occasionally it is necessary to control the variation of a natural frequency of a rotating beam. By changing the thickness of the rotating beam, the modal characteristics can be changed. The thickness of the rotating beam is assumed to be a cubic spline function in the present work. An optimization method is employed to find the optimal thickness shape of the rotating beam. This method can be utilized usefully for the design of rotating structures such as turbine blades and aircraft rotary wings.

• 대한기계학회논문집A
• /
• 제25권10호
• /
• pp.1613-1620
• /
• 2001

This study is focused on the application of the homogenization design method (HDM) to reduce the vibration level of a structure excited by magnetic harmonic farces. This is accomplished by obtaining the optimal material distribution in a design domain to minimize the frequency response caused by the magnetic harmonic excitation. The Maxwell stress method is used to compute the magnetic force and the HDM is applied leer the optimization. The developed method is applied to a simple pole model that is excited by the harmonic bending farce caused by the current around an adjacent stator. Results shows that the HDM is valid to minimize the frequency response.

• 한국경영과학회지
• /
• 제30권1호
• /
• pp.187-198
• /
• 2005

The structure of a Web site can prevent the search robots or crawling agents from confusion in the midst of huge forest of the Web pages. We formalize the view on the World Wide Web and generalize it as a hierarchy of Web objects such as the Web as a set of Web sites, and a Web site as a directed graph with Web nodes and Web edges. Our approach results in the optimal hierarchical structure that can maximize the weight, tf-idf (term frequency and inverse document frequency), that is one of the most widely accepted content centric measures in the information retrieval community, so that the measure can be used to embody the semantics of search query. The experimental results represent that the optimization model is an effective alternative in the dynamically changing Web environment by replacing conventional heuristic approaches.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2003년도 추계학술대회논문집
• /
• pp.220-225
• /
• 2003

Recent issue of optical actuator is applying to mobile device. It leads actuator to become smaller than conventional type. This paper proposes the design of micro actuator plate spring and analysis of its vibration characteristic. Considering natural frequency of spindle motor, 1st and 2nd eigenfrequency of micro actuator must avoid its natural frequency. First, magnetic circuit is designed by using fine pattern coil and magnetic force is acquired by simulation program. Then, concept design is achieved by topology optimization. From concept design, micro actuator plate spring is embodied through DOE(design of experiment). Finally, considering vibration characteristic simultaneously, optimal plate spring design is determined by RSM(response surface method).

• 한국경영과학회지
• /
• 제32권3호
• /
• pp.33-46
• /
• 2007

This study deals with the adaptive multiuser OFDM (Orthogonal Frequency Division Multiplexing) system which adjusts the resource allocation according to the environmental changes in such as wireless and quality of service required by users. The resource allocation includes subcarrier assignment to users, modulation method and power used for subcarriers. We first develop a general optimization model which maximizes data throughput while satisfying data rates required by users and total power constraints. Based on the property that this problem has the 0 duality gap, we apply the subgradient dual optimization method which obtains the solution of the dual problem by iteration of simple calculations. Extensive experiments with realistic data have shown that the subgradient dual method is applicable to the real world system, and can be used as a dynamic resource allocation mechanism.

• 정보저장시스템학회논문집
• /
• 제1권2호
• /
• pp.161-168
• /
• 2005

This paper optimizes the optical flying head(OFH) suspension using the integrated optimization frame, which automatically integrates the analysis with the optimization and effectively implements the repetitive works between them. The problem formulation for the optimization is suggested to improve the dynamic compliance of OFH and to shift the resonant frequencies caused tracking errors to high frequency domain. Furthermore, the minimization of the effective suspension mass that leads to decrease the so-called 'lift-off' as the disk-head separation acceleration divided by the suspension load is taken into consideration. In particular, this study is carried out the optimal design considering the process of modes tracking through the entire optimization processes. The advanced suspension that reduces the effective mass of the suspension and increases the resonant frequencies of sway and $2^{nd}$ torsion over 10kHz is achieved by using the integrated optimization frame.

• Steel and Composite Structures
• /
• 제28권4호
• /
• pp.509-516
• /
• 2018

The differential quadrature (DQ) and teaching-learning based optimization (TLBO) methods are coupled to introduce a hybrid numerical method for maximizing fundamental natural frequency of laminated composite skew plates. The fiber(s) orientations are selected as design variable(s). The first-order shear deformation theory (FSDT) is used to obtain the governing equations of the plate. The equations of motion and the related boundary conditions are discretized in space domain by employing the DQ method. The discretized equations are transferred from the time domain into the frequency domain to obtain the fundamental natural frequency. Then, the DQ solution is coupled with the TLBO method to find the maximum frequency of the plate and its related optimum stacking sequences of the laminate. Convergence and applicability of the proposed method are shown and the optimum fundamental frequency parameter of the plates with different skew angle, boundary conditions, number of layers and aspect ratio are obtained. The obtained results can be used as a benchmark for further studies.

• Journal of Communications and Networks
• /
• 제17권1호
• /
• pp.1-11
• /
• 2015

In this paper, the transmission of an improper-complex second-order stationary data sequence is considered over a strictly band-limited frequency-selective channel. It is assumed that the transmitter employs linear modulation and that the channel output is corrupted by additive proper-complex cyclostationary noise. Under the average transmit power constraint, the problem of minimizing the mean-squared error at the output of a widely linear receiver is formulated in the time domain to find the optimal transmit and receive waveforms. The optimization problem is converted into a frequency-domain problem by using the vectorized Fourier transform technique and put into the form of a double minimization. First, the widely linear receiver is optimized that requires, unlike the linear receiver design with only one waveform, the design of two receive waveforms. Then, the optimal transmit waveform for the linear modulator is derived by introducing the notion of the impropriety frequency function of a discrete-time random process and by performing a line search combined with an iterative algorithm. The optimal solution shows that both the periodic spectral correlation due to the cyclostationarity and the symmetric spectral correlation about the origin due to the impropriety are well exploited.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 추계학술대회논문집
• /
• pp.694-698
• /
• 2006

This paper presents an optimal design process using beads on a body panel to improve interior noise of a passenger vehicle. Except modification of structural members, it is difficult to find effective countermeasures that can work for the intermediate frequency range from 100 Hz to 300 Hz which lies between the booming and low medium frequency. In this study, it is a major goal to find additional counter-measures for this intermediate frequency range by performing optimal design of beads on body panels. The proposed method for design optimization consists of 4 sub-steps, that is, a) problem definition, b) cause analysis, c) countermeasure development and d) validation. The objective function is minimization of interior noise level. The major design variables are the geometrical shape of a bead and combination of beads on the critical panels. Sensitivity analysis and optimization are performed according to the predefined process for an optimal design. It is verified that the proposed design decreases the level of noise transfer function above 5 dB.

• 한국소음진동공학회논문집
• /
• 제12권10호
• /
• pp.792-798
• /
• 2002

The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function (FRF) of the structure. However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer are transient and have damping, they are undoubtedly non-periodic. It is inevitable that the signals be acquired for limited recording time, which causes the finite record length error and the leakage error. In this paper, the errors in the frequency response function of multi degree of freedom system are formulated theoretically. And the method to remove these errors is also suggested. This method is based on the optimization technique. A numerical example of 3-dof model shows the validity of the proposed method.