• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1235-1242
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• 2006

Viscoelastic damping materials are widely used to reduce noise and vibration because of its low cost and easy implementation, for examples, on the body structure of passenger cars, air planes, electric appliances and ships. To design the damped structures, the material property such as elastic modulus and loss factor is essential information. The four-parameter fractional derivative model well describes the nonlinear dynamic characteristics of the viscoelastic damping materials with respect to both frequency and temperature with fewer parameters than conventional spring-dashpot models. However the identification procedure of the four-parameter is very time-consuming one. An efficient identification procedure of the four-parameters is proposed by using an FE model and a gradient-based numerical search algorithm. The identification procedure goes two sequential steps to make measured FRFs coincident with simulated FRFs: the first one is a peak alignment step and the second one is an amplitude adjustment. A numerical example shows that the proposed method is efficient and robust in identifying the viscoelastic material parameters of fractional derivative model.

• International Journal of CAD/CAM
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• 제9권1호
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• pp.37-46
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• 2010

Existing methods for the registration of blurred images are efficient for the artificially blurred images or a planar registration, but not suitable for the naturally blurred images existing in the real image mosaic process. In this paper, we attempt to resolve this problem and propose a method for a distortion-free stitching of naturally blurred images for image mosaic. It adopts a multi-resolution and robust feature based inter-layer mosaic together. In each layer, Harris corner detector is chosen to effectively detect features and RANSAC is used to find reliable matches for further calibration as well as an initial homography as the initial motion of next layer. Simplex and subspace trust region methods are used consequently to estimate the stable focal length and rotation matrix through the transformation property of feature matches. In order to stitch multiple images together, an iterative registration strategy is also adopted to estimate the focal length of each image. Experimental results demonstrate the performance of the proposed method.

• Structural Engineering and Mechanics
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• 제29권5호
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• pp.489-504
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• 2008

In piezoelectric flexible structures, the contribution of vibration modes to the dynamic response of system may change with the location of piezoelectric actuator patches, which means that the ability of actuators to control vibration modes should be taken into account in the development of modal reduction model. The spatial $H_2$ norm of modes, which serves as a measure of the intensity of modes to system dynamical response, is used to pick up the modes included in the reduction model. Based on the reduction model, the paper develops the state-space representation for uncertain flexible tructures with piezoelectric material as non-collocated actuators/sensors in the modal space, taking into account uncertainties due to modal parameters variation and unmodeled residual modes. In order to suppress the vibration of the structure, a dynamic output feedback control law is designed by imultaneously considering the conflicting performance specifications, such as robust stability, transient response requirement, disturbance rejection, actuator saturation constraints. Based on linear matrix inequality, the vibration control design is converted into a linear convex optimization problem. The simulation results show how the influence of vibration modes on the dynamical response of structure varies with the location of piezoelectric actuators, why the uncertainties should be considered in the reductiom model to avoid exciting high-frequency modes in the non-collcated vibration control, and the possiblity that the conflicting performance specifications are dealt with simultaneously.

• 대한기계학회논문집A
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• 제28권5호
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• pp.503-510
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• 2004

In this paper, the well-conditioned observer for a stochastic system is designed so that the observer is less sensitive to the ill-conditioning factors in transient and steady-state observer performance. These factors include not only deterministic uncertainties such as unknown initial estimation error, round-off error, modeling error and sensing bias, but also stochastic uncertainties such as disturbance and sensor noise. In deterministic perspectives, a small value in the L$_{2}$ norm condition number of the observer eigenvector matrix guarantees robust estimation performance to the deterministic uncertainties. In stochastic viewpoints, the estimation variance represents the robustness to the stochastic uncertainties and its upper bound can be minimized by reducing the observer gain and increasing the decay rate. Both deterministic and stochastic issues are considered as a weighted sum with a LMI (Linear Matrix Inequality) formulation. The gain in the well-conditioned observer is optimally chosen by the optimization technique. Simulation examples are given to evaluate the estimation performance of the proposed observer.

• International Journal of Control, Automation, and Systems
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• 제6권1호
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• pp.24-34
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• 2008

A novel neural network model, termed the standard neural network model (SNNM), similar to the nominal model in linear robust control theory, is suggested to facilitate the synthesis of controllers for delayed (or non-delayed) nonlinear systems composed of neural networks. The model is composed of a linear dynamic system and a bounded static delayed (or non-delayed) nonlinear operator. Based on the global asymptotic stability analysis of SNNMs, Static state-feedback controller and dynamic output feedback controller are designed for the SNNMs to stabilize the closed-loop systems, respectively. The control design equations are shown to be a set of linear matrix inequalities (LMIs) which can be easily solved by various convex optimization algorithms to determine the control signals. Most neural-network-based nonlinear systems with time delays or without time delays can be transformed into the SNNMs for controller synthesis in a unified way. Two application examples are given where the SNNMs are employed to synthesize the feedback stabilizing controllers for an SISO nonlinear system modeled by the neural network, and for a chaotic neural network, respectively. Through these examples, it is demonstrated that the SNNM not only makes controller synthesis of neural-network-based systems much easier, but also provides a new approach to the synthesis of the controllers for the other type of nonlinear systems.

• 한국정밀공학회지
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• 제11권4호
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• pp.58-68
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• 1994

An equilibrium approach is suggested as an effective tool for the analysis of sheet metal forming processes on the basis of force balance together with geometric relations and plasticity theroy. In computing a force balance equation, it is required to define a geometric curve approximating the shape of the sheet metal at any step of deformation from the geometric interaction between the die and the deforming sheet. Then the geometic informations for contacting and non-contacting sections of the sheet metal such as the number and length of both non-contact region, contact angle, and die radius of contact section are known from the geometric forming curve and utilized for optimization by force balance equation. In computation, the sheet material is assumed to be of normal amisotropy and rigid-phastic workhardening. It has been shown that there are good agreements between the equilibrium approach and FEM computation for the benchmark test example and auto-body panels whose sections can be assumed in plane-strain state. The proposed equilibrium approach can thus be used as a robust computational method in estimating the forming defects and forming severity rather quickly in the die design stage.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 춘계학술대회논문집; 부산수산대학교, 10 May 1996
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• pp.263-270
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• 1996

본 연구에서는 여러개의 원판형 압전소자가 부착된 판구조물의 소음제어를 다루었다. 판재의 아래에는 소음원이 위치하고 이 소음원은 판재를 가진한다. 구조물 및 압전소자는 3차원 요소, 구조물 요소 및 천이요소의 조화로 이루어지는 유한요소로 모델링 되었다. 최적화 과정의 목적함수는 구조물로부터 복사되는 소음 에너지이고 설계변수는 원판형 압전소자의 위치, 크기 및 인가되는 전압이 사용되었다. 최적설계과정에서 요구되는 자동격자형성이 언급되었다. 구조물의 공진 및 비공진 주파수에서 최적설계가 행해졌으며 괄목할 만한 소음감소를 얻었다. 이 결고는 음향 하중의 형태가 다르게 변하더라도 크게 변하지 않는 것이 밝혀졌다. 또한 한 주파수 뿐 아니라 넓은 주파수 영역에서도 압전가진기의 전압을 조정함으로써 좋은감소를 얻을 수 있다.

• 정보처리학회논문지B
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• 제18B권4호
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• pp.193-200
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• 2011

본 논문은인간-컴퓨터 인터페이스, 가상현실의 의학 응용, 환자의 원격 모니터링과 같은 실시간 응용 분야에 적합한 인체 운동의 시각적 해석 알고리즘 (visual analyzer algorithm)을 제안한다. 본 알고리즘을 사용할 때의 비용을 줄이기 위해서, 단수의 카메라를 사용하도록 설계한다. 그리고 제안한 알고리즘을 좀 더 편리하게 사용할 수 있도록 하기 위해서 광학적 표시자의 사용을 피한다. 제안하는 알고리즘이 실시간 사용에 편리하도록 하기 위해서, 폐쇄적 형태가 되도록 설계한다. 폐쇄적 형태의 알고리즘을 설계하기 위해서, 인체의 각 관절을 기존의 3차원 관절 모델 대신 어떤 형태의 근사화도 사용하지 않고도 2차원 관절 모델로 공식화하는 아이디어를 제안한다. 그리고 이 폐쇄적 형태의 알고리즘이 높은 정확도를 갖게 하기 위해서, 계산 알고리즘을 최적화 문제로 공식화한다. 이렇게 해서 설계된 알고리즘을 인체의 각 관절에 차례대로 적용한다.

• 한국정보통신학회논문지
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• 제24권3호
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• pp.398-404
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• 2020

본 논문에서는 변형 경사하강검색법을 이용한 새로운 나선 직교진폭변조 신호성상도와 이를 위한 이진사상규칙을 제시한다. 기존 방법과는 달리 새로운 검색법은 반복설계를 위한 파라미터로 최대 반복 횟수와 함께 성상도 최적화 알고리즘을 사용하여 위상잡음에 더욱 강인한 나선 직교진폭변조 성상도를 생성한다. 또한, 제시된 이진사상기법은 신호성상도에서 동일한 경계를 공유하는 필드 수를 조정함으로써 성상도의 평균 해밍거리를 크게 감소시키는 것으로 나타났다. 그 결과, 제안된 나선 직교진폭변조는 매우 심한 수준의 위상잡음 환경에서도 기존 성상도에 비하여 훨씬 향상된 심볼오류성능을 가지는 것으로 확인되었다. 따라서 제안된 나선 직교진폭변조는 위상잡음의 영향이 크게 나타나는 코히어런트 광통신시스템과 직교 주파수분할다중화 시스템에 유용한 변조방법인 것으로 판단된다.

• 한국광물학회지
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• 제23권3호
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• pp.219-225
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• 2010

저등급 석탄인 갈탄(lignite)을 순환 유동층 가스화기(circulating fluidized bed gasifier)의 효과적인 가스화를 위한 공급탄으로 제조하기 위하여 모든 조건들은 동일하고 스크린의 크기만을 변경하여 목적하는 입도분포 특성을 달성하는 최적조건을 찾기 위한 실험을 수행하였다. 가스화기 공급탄은 0.045~1 mm 크기로 85 wt% 이상이 요구되며 이러한 입도분포를 갖는 공급탄을 제조하기 위해서는 경제적이면서도 효과적인 공정 설계가 반드시 필요하다. 따라서 본 연구는 중국산 갈탄을 해머밀로 효과적으로 분쇄하기 위하여 다구치 설계를 사용하였으며, 설계조건에 따른 실험결과 및 통계분석 결과 95% 유의수준에서 1차 스크린의 크기는 3 mm, 2차 스크린의 크기는 1.3 mm인 경우가 최적화된 조건인 것으로 나타났다.