• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.90-100
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• 1993

A finite element formulation of vibration control of a laminated plate with piezoelectric sensor/ actuators is presented. Classical lamination theory with the induced strain actuation and Hamilton's principle are used to formulate the equations of motion of the system. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equations of motion and the total charge are discretized with 4 node, 12 degrees of freedom quadrilateral plate bending elements with one electrical degree of freedom. The mass and stiffness of the piezoelectric layer are introduced by treating them as another layer in laminated plate. Piezoelectric sensor/actuators are distributed, but discrete due to the geometry of electrodes. By defining an i.d. number of electrode for each element, modelling of electrodes with variable geometry can be achieved. The static response of a piezoelectric bimorph beam to electrical loading and sensor voltage to given displacement are calculated. For a laminated plate under the negative velocity feedback control, the direct time response by the Newmark-.betha. method and damped frequencies and modal damping ratios by modal state space analysis are derived.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.44 no.3
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• pp.98-107
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• 2007

For high-dimensional pattern recognition, such as face classification, the small number of training samples leads to the Small Sample Size problem when the number of pattern samples is smaller than the number of dimensionality. Recently, various LDA-extensions have been developed, including LDA, PCA+LDA, and Direct-LDA, to address the problem. This paper proposes a method of improving the classification efficiency by increasing the number of (sub)-classes through pre-clustering a training set prior to the execution of Direct-LDA. In LDA (or Direct-LDA), since the number of classes of the training set puts a limit to the dimensionality to be reduced, it is increased to the number of sub-classes that is obtained through clustering so that the classification performance of LDA-extensions can be improved. In other words, the eigen space of the training set consists of the range space and the null space, and the dimensionality of the range space increases as the number of classes increases. Therefore, when constructing the transformation matrix, through minimizing the null space, the loss of discriminatve information resulted from this space can be minimized. Experimental results for the artificial data of X-OR samples as well as the bench mark face databases of AT&T and Yale demonstrate that the classification efficiency of the proposed method could be improved.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.205-212
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• 2018

In order to overcome shortcomings of commercial analysis program for solving certain geotechnical problems, finite element method adopting isoparametric quadrilateral element was selected as a tool for analyzing soil behavior and calculating process was programmed. Two examples were considered in order to verify reliability of the developed program. One of the two examples is the case of acting isotropic confining pressure on finite element and the other is the case of acting shear stress on the sides of the finite element. Isoparametric quadrilateral element was considered as the finite element and displacements in the element can be expressed by node displacements and shape functions in the considered element. Calculating process for determining strain which is defined by derivatives using global coordinates was coded using the Jacobian and the natural coordinates. Four point Gauss rule was adopted to convert double integral which defines stiffness of the element into numerical integration. As a result of executing analysis of the finite element under isotropic confining pressure, calculated stress corresponding to four Gauss points and center of the element were equal to the confining pressure. In addition, according to the analyzed results for the element under shear stress, horizontal stresses and vertical stresses were varied with positions in the element and the magnitudes and distribution pattern of the stresses were thought to be rational.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.9-18
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• 2015

In this paper, we verify the optimal topology design for heat conduction problems in steady stated which is obtained numerically using the adjoint design sensitivity analysis(DSA) method. In adjoint variable method(AVM), the already factorized system matrix is utilized to obtain the adjoint solution so that its computation cost is trivial for the sensitivity. For the topology optimization, the design variables are parameterized into normalized bulk material densities. The objective function and constraint are the thermal compliance of the structure and the allowable volume, respectively. For the experimental validation of the optimal topology design, we compare the results with those that have identical volume but designed intuitively using a thermal imaging camera. To manufacture the optimal design, we apply a simple numerical method to convert it into point cloud data and perform CAD modeling using commercial reverse engineering software. Based on the CAD model, we manufacture the optimal topology design by CNC.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.1-7
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• 2010

PAPR of the pilot symbols can be reduced down by the CAZAC sequence in the SC-FDMA communication system. However, it is very complicated and takes quite a long time to compute the interpolation between the OFDM information symbols for the channel estimation because the pilot data are trasmitted in the block type. Furthermore, situation will be much more serious in the severe fading channel. Actually the pilot insertion of the comb type is much efficient and convenient for the channel estimation since the calculation of the interpolation can be made in the frequency domain symbol by symbol. But, the PAPR will be regrown when the pilot data are inserted with the information data in the comb type. So, in this paper, we like to study the PAPR reduction and comb type pilot assignment for the efficient channel estimation. Unlike the conventional SLM(selected mapping) method requiring the side information, our improved SLM method is to use the phase rotation sequence into information data without rotating phase of pilot. We use different pilot data according to the different phase rotation sequence. From the simulation result, it can be confirmed that when SLM method of 4 phase rotation sequence is used, PAPR is almost same to the block type method without pilot.

• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.118-125
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• 2014

An approximation of speed of sound in the measurement plane is essential for the inverse estimation of temperature. To this end, an inverse problem relating the measured retarded time data in between set of sensors and actuators array located on the wall is formulated. The involved transfer matrix and its coefficient vectors approximate speed of sound of the measurement plane by using the radial basis function with finite number of interpolation points deployed inside the target field. Then, the temperature field can be reconstructed by using spatial interpolation technique, which can achieve high spatial resolution with proper number of interpolation points. A large number of retarded time data of acoustic paths in between sensors and arrays are needed to obtain accurate reconstruction result. However, the shortage of interpolation points due to practical limitations can cause the decrease of spatial resolution and deterioration of the reconstruction result. In this works, a regeneration for obtaining the additional retarded time data for an arbitrary acoustic path is suggested to overcome the shortage of interpolation points. By applying the regeneration technique, many interpolation points can be deployed inside the field by increasing the number of retarded time data. As a simulation example, two rectangular duct sections having arbitrary temperature distribution are reconstructed by two different data set: measured data only, combination of measured and regenerated data. The result shows a decrease in reconstruction error by 15 % by combining the original and regenerated retarded time data.

• Journal of The Korean Association For Science Education
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• v.37 no.4
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• pp.577-586
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• 2017

The purpose of this study is to try to structuralize the perception of the mothers of science-gifted elementary students using the concept mapping approach. The mothers who participated in this research had children who were 5th and 6th graders selected as science-gifted by a regional education office, a science high school and two national universities in a city. One of the authors interviewed 26 mothers, and extracted 50 general statements of their perceptions about the career path of their children. Ten mothers who participated in interviews sorted a shuffled pack of statement cards. The categorization of the statements into the dissimilarity matrix was carried out by SPSS multidimensional scaling analysis and hierarchical cluster analysis to generate a conceptual diagram. After that 140 mothers rated each statement using a Likert-type response scale from one to five. The result showed six clusters of parental views such as were 'Burden of private education, grades and going to the next grade,' 'Thinking about career guidance in gifted education and school,' 'Parental roles in child career education,' 'Difficulties in career guidance at home,' 'Demand for strengthening the parental capacity for career guidance,' and 'Demand for social support.' 'Demand for social support' obtained the highest sympathy from mothers of elementary science gifted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1992.10a
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• pp.25-30
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• 1992

최근 전자계산기를 이용한 진동해석 방법이 눈부시게 발달하여, 일반 구조물 이나 기계 구조물 등의 동특성을 설계 단계에서 정도 높게 예측하는 것이 가능하게 되었다. 그러나 종래의 구조해석은 주어진 시스템의 동특성을 위한 것으로 얻어진 동특성으로부터 질량, 관성제원 및 스프링상수값 등의 설계상 수값을 규명하는 연구는 미미한 실정이다. 이것에 대한 해결방법으로 크게 해석적인 방법과 실험적인 방법으로의 접근이 있어 왔다. 해석적인 방법으로 유한요소해석에서 얻은 모드좌표를 물리좌표로 변환하는 방법으로 Guyan의 정축소와 같은 절점축소를 행하는 방법이 고찰되었다. 실험적인 방법으로 가 진실험에서 얻은 전달함수나 모드파라미터로부터 [M], [K] 행렬을 결정하는 연구가 있었지만 어떤것도 질량, 스프링상수 등의 설계상수를 완전히 규명하 지는 못하였다. 또한, 설계 단계에서 필요한 질량, 관성제원 또는 스프링상수 등의 최적한 값이나, 원하는 시스템특성을 얻을 수 있는 설계상수의 적정한 폭을 구하는 연구는 설계자의 경험과 반복된 시행착오에 의존하는 실정이다. 감도해석은 이러한 문제점을 개선하는 수단으로 설계변수에 대한 동특성의 변화율을 구하는 것이다. 감도해석을 수행하는 것은 어느 설계변수를 수정하 는 것이 주어진 동특성에 부합되는 지를 알려주고, 어느 것을 수정하는 것이 원하는 방향의 동특성변화에 가장 효과적인지를 알려주는 것이다. 따라서 감 도해석을 이용하여 설계의 최적화 프로그램을 만들수 있고, 이것은 설계자가 요구하는 동특성을 목적함수로 하여 주어진 구조물을 최적화하는 설계상수 값을 얻을 수 있게 한다. 본 논문에서는 강체모델의 동특성으로부터 모델의 설계 상수를 규명하고, 동특성의 개선을 위하여 설계변수의 변경량을 물리좌 표계에서 얻는것을 목적으로 한다. 강체 마운트계의 관성제원 및 마운트강성 의 규명을 위하여 임으로 주어진 설계상수를 모델데이타로 하여 관성제원과 스프링 강성을 구하였다. 관성제원의 규명은 주어진 모델의 관성값을 모르는 것으로 하여 임의의 초기 관성값으로 감도해석에 의해 주어진 계의 관성값 을 물리 좌표계에서 규명하였다. 마운트 강성의 규명도 관성제원의 규명과 같은 방법으로 임의의 강성값으로 감도해석을 하여 강성값을 규명하였다. 또 한 감도해석에 의한 동특성 변경은 특정한 고유진동 수의 변경이 필요할 때, 고유진동수의 이동을 위한 관성제원의 변경 및 마운트 강성변경값을 예측할 수 있다. 본 연구수행의 기본적인 흐름도는 Fig.1.1과 같다. 위와 같은 작업 으로 엔진 마운트와 같은 강체 모델의 시스템 규명을 행하는 경우에 유한요 소해석 및 가진 실험으로 얻은 고유진동수의 정보 또는 원하는 고유진동수 의 특성을 기본으로 실제 설계에서 사용이 가능하도록 물리 좌표계에서 관 성 제원 및 스프링상수를 구할 수 있을 것이다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.2 s.302
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• pp.113-120
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• 2005

3D reconstruction of a scene structure from un-calibrated image sequences has been long one of the central problems in computer vision. For 3D reconstruction in Euclidean space, projective reconstruction, which is classified into the merging method and the factorization, is needed as a preceding step. By calculating all camera projection matrices and structures at the same time, the factorization method suffers less from dia and error accumulation than the merging. However, the factorization is hard to analyze precisely long sequences because it is based on the assumption that all correspondences must remain in all views from the first frame to the last. This paper presents a new projective reconstruction method for recovery of 3D structure over long sequences. We break a full sequence into sub-sequences based on a quantitative measure considering the number of matching points between frames, the homography error, and the distribution of matching points on the frame. All of the projective reconstructions of sub-sequences are registered into the same coordinate frame for a complete description of the scene. no experimental results showed that the proposed method can recover more precise 3D structure than the merging method.