• 대한전자공학회논문지SP
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• 제42권5호
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• pp.47-54
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• 2005

일반적으로 웨이블릿 계수는 적은 수의 크기가 큰 계수와 많은 수의 작은 크기의 계수로 구성되어 있다. 따라서 본 논문에서는 웨이블릿 계수의 성긴 특성에 근거한 베르누이-가우스 혼합 모델을 이용한 잡음 제거 방법을 제안한다. 베르누이-가우스 혼합 모델은 베르누이 랜덤 변수와 가우스 혼합 랜덤 변수의 곱으로 구성되며, 이에 대한 베이지안 추정법으로 잡음 제거를 수행한다. 본 논문에서는 국부 자승 오차의 기대값를 이용하여 통한 베르누이 랜덤 변수에 대한 간략화된 파라메터의 추정을 통하여 효율적인 잡음 제거 방법을 제시한다. 모의실험 결과를 통하여 본 논문의 방법이 직교 웨이블릿 변환을 사용한 최신의 잡음 제거 방법보다 우수한 성능을 나타낸다는 것을 보여준다.

• Journal of Power Electronics
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• 제14권5호
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• pp.1008-1027
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• 2014

An electric scooter with a V-belt continuously variable transmission (CVT) driven by a permanent magnet synchronous motor (PMSM) has a lot of nonlinear and time-varying characteristics, and accurate dynamic models are difficult to establish for linear controller designs. A PMSM servo-drive electric scooter controlled by a novel hybrid modified recurrent Legendre neural network (NN) control system is proposed to solve difficulties of linear controllers under the occurrence of nonlinear load disturbances and parameters variations. Firstly, the system structure of a V-belt CVT driven electric scooter using a PMSM servo drive is established. Secondly, the novel hybrid modified recurrent Legendre NN control system, which consists of an inspector control, a modified recurrent Legendre NN control with an adaptation law, and a recouped control with an estimation law, is proposed to improve its performance. Moreover, the on-line parameter tuning method of the modified recurrent Legendre NN is derived according to the Lyapunov stability theorem and the gradient descent method. Furthermore, two optimal learning rates for the modified recurrent Legendre NN are derived to speed up the parameter convergence. Finally, comparative studies are carried out to show the effectiveness of the proposed control scheme through experimental results.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.749-765
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• 2008

Free axisymmetric vibrations of layered cylindrical shells of variable thickness are studied using spline function approximation techniques. Three different types of thickness variations are considered namely linear, exponential and sinusoidal. The equations of axisymmetric motion of layered cylindrical shells, on the longitudinal and transverse displacement components are obtained using Love's first approximation theory. A system of coupled differential equations on displacement functions are obtained by assuming the displacements in a separable form. Then the displacements are approximated using Bickley-spline approximation. The vibrations of two-layered cylindrical shells, made up of several types of layered materials and different boundary conditions are considered. Parametric studies have been made on the variation of frequency parameter with respect to the relative layer thickness, length ratio and type of thickness variation parameter.

• Advances in nano research
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• 제17권3호
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• pp.235-248
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• 2024

This study explores the transmission of waves through polymer composite nanoplates situated on varying elastic foundations. The reinforcement of these nanoplates is assured by graphene nanoplatelets (GNP). Furthermore, the material's behavior is assessed using the Halpin-Tsai model, while the precise representations of stress and strain effects are ensured by the four variables higher order shear deformation theory. The equations of motion are obtained and resolved through the application of Hamilton's principle and the trial function. The study examines how different factors, like the nonlocal parameter, strain gradient parameter, weight fraction, and variable elastic foundations affect the outcomes of wave propagation in nanoplates. This thorough investigation offers valuable insights into the difficult behavior of wave dynamics in nanoplates, this has led to substantial advancements in engineering applications for the future.

• Steel and Composite Structures
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• 제50권5호
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• pp.563-581
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• 2024

This paper presents a novel finite element model for the free vibration analysis of variable-thickness functionally graded porous (FGP) microplates resting on Pasternak's medium in the hygro-thermal environment. The governing equations are established according to refined higher-order shear deformation plate theory (RPT) in construction with the modified couple stress theory. For the first time, three-node triangular elements with twelve degrees of freedom for each node are developed based on Hermitian interpolation functions to describe the in-plane displacements and transverse displacements of microplates. Two laws of variable thickness of FGP microplates, including the linear law and the nonlinear law in the x-direction are investigated. Effects of thermal and moisture changes on microplates are assumed to vary continuously from the bottom surface to the top surface and only cause tension loads in the plane, which does not change the material's mechanical properties. The numerical results of this work are compared with those of published data to verify the accuracy and reliability of the proposed method. In addition, the parameter study is conducted to explore the effects of geometrical and material properties such as the changing law of the thickness, length-scale parameter, and the parameters of the porosity, temperature, and humidity on the free vibration response of variable thickness FGP microplates. These results can be applied to design of microelectromechanical structures in practice.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권1호
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• pp.81-98
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• 2013

Since Probabilistic Latent Semantic Analysis (PLSA) and Latent Dirichlet Allocation (LDA) were introduced, many revised or extended topic models have appeared. Due to the intractable likelihood of these models, training any topic model requires to use some approximation algorithm such as variational approximation, Laplace approximation, or Markov chain Monte Carlo (MCMC). Although these approximation algorithms perform well, training a topic model is still computationally expensive given the large amount of data it requires. In this paper, we propose a new method, called non-simultaneous sampling deactivation, for efficient approximation of parameters in a topic model. While each random variable is normally sampled or obtained by a single predefined burn-in period in the traditional approximation algorithms, our new method is based on the observation that the random variable nodes in one topic model have all different periods of convergence. During the iterative approximation process, the proposed method allows each random variable node to be terminated or deactivated when it is converged. Therefore, compared to the traditional approximation ways in which usually every node is deactivated concurrently, the proposed method achieves the inference efficiency in terms of time and memory. We do not propose a new approximation algorithm, but a new process applicable to the existing approximation algorithms. Through experiments, we show the time and memory efficiency of the method, and discuss about the tradeoff between the efficiency of the approximation process and the parameter consistency.

• Steel and Composite Structures
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• 제34권4호
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• pp.511-524
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• 2020

In this research, a simple four-variable trigonometric integral shear deformation model is proposed for the static behavior of advanced functionally graded (AFG) ceramic-metal plates supported by a two-parameter elastic foundation and subjected to a nonlinear hygro-thermo-mechanical load. The elastic properties, including both the thermal expansion and moisture coefficients of the plate, are also supposed to be varied within thickness direction by following a power law distribution in terms of volume fractions of the components of the material. The interest of the current theory is seen in its kinematics that use only four independent unknowns, while first-order plate theory and other higher-order plate theories require at least five unknowns. The "in-plane displacement field" of the proposed theory utilizes cosine functions in terms of thickness coordinates to calculate out-of-plane shear deformations. The vertical displacement includes flexural and shear components. The elastic foundation is introduced in mathematical modeling as a two-parameter Winkler-Pasternak foundation. The virtual displacement principle is applied to obtain the basic equations and a Navier solution technique is used to determine an analytical solution. The numerical results predicted by the proposed formulation are compared with results already published in the literature to demonstrate the accuracy and efficiency of the proposed theory. The influences of "moisture concentration", temperature, stiffness of foundation, shear deformation, geometric ratios and volume fraction variation on the mechanical behavior of AFG plates are examined and discussed in detail.

• Nuclear Engineering and Technology
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• 제17권4호
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• pp.247-255
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• 1985

본 논문은 가변구조모델추종제어(VSMFC)계 설계의 새로운 방법을 고찰한 것이다. 설계 개념은 가변구조계(VSS)와 슬라이드모드 이론을 사용하여 비선형 시변다변수계가 파라미터 변동이 있을지라도 모델추종을 정확히 하게끔 제어측이 가변구조를 갖게 하는 것이다. 본 논문의 방법을 실제 물리계에 적용할 때 컴퓨터 계산시간의 감소와 파라미터변동에 무관한 동적응답을 기대할 수 있다. 이론의 유효성을 밝히기 위해 VSMPC를 1000MWe의 불등경수형 원자로(BWE)에 적용하였다. 즉 원자로의 출력요구가 정격출력의 85∼90% 범위에서 변할 때 부하추종출력제어가 원활히 이루어지는가를 컴퓨터 시뮬레이션하였다. 12개의 비선형미분방정식으로 동특성이 주어지는 원자로에서 6차계 선형모델을 85% 정격치에서 구하고 여러범위에 걸쳐서 부하변동이 있을 때 파라미터변동을 극복하면서도 출력제어를 원활히 하는가를 연구하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.227-230
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• 1990

In this paper we present a variable structure systeme-model following adaptive control (VSS-MFAC) method for an uncertain turbo-generator system which is apt to suffer from the unmodeled parameter uncertainties and the external disturbances. The simulation results for the power system stabilizer(PSS) exhibit robust adaptive model-following properties well in the PSS designed by the proposed VSS-MFAC methodology when a step change in the mechanical torque and a parameter variation is applied.

• Journal of the Korean Data and Information Science Society
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• 제12권2호
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• pp.57-64
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• 2001

In the Taguchi parameter design, the product-array approach using orthogonal arrays is mainly used. However, it often requires an excessive number of experiments. An alternative approach, which is called the combined-array approach, was suggested by Welch et al (1990) and studied by Vining and Myers (1990) and others. In these studies, only single respouse variable was considered. We propose how to simultaneously optimize multiple responses when there are correlations among responses.