• 한국통신학회논문지
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• 제32권3C호
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• pp.331-337
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• 2007

본 논문에서는 MIMO-OFDM 시스템에서 월쉬 부호화된 훈련신호를 이용하는 새로운 채널 추정 방식을 제안하였다. 월쉬 부호화된 훈련신호는 시간 영역에서 서로 직교하도록 설계된다. 이러한 직교성을 이용하여 월쉬 디코딩을 수행하면 시간 영역에서 원하는 훈련 신호를 분리할 수 있고 채널 추정이 가능하다. 컴퓨터 시뮬레이션 결과 제안된 방법은 계산량 감소에도 불구하고 최적 훈련 신호를 사용하는Li의 원래 방법[4]과 비교했을 때 거의 동일한 mean square error (MSE) 성능을 보였다.

• Transactions on Control, Automation and Systems Engineering
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• 제1권2호
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• pp.94-98
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• 1999

Optical scanning systems use glavanometers to point the laser beam to the desired position on the workpiece. The angular speed of a galvanometer is typically controlled using Proportional+Integral+Derivative(PID) control algorithms. However, natural variations in the dynamics of different galvanometers due to manufacturing, aging, and environmental factors(i.e., process uncertainty) impose a hard limit on the bandwidth of the galvanometer control system. In general, the control bandwidth translates directly into efficiency of the system response. Since the optical scanning system must have rapid response, the higher control bandwidth is required. Auto-tuning PID algorithms have been accepted in this area since they could overcome some of the problems related to process uncertainty. However, when the galvanometer is attached to a larger mechanical system, the combined dynamics often exhibit resonances. It is well understood that PId algorithms may not have the capacity to increase the control bandwidth in the face of such resonances. This paper compares the achieable performance and robustness of a galvanometer control system using a PID controller tuned by the Ziegler-Nichols method and a controller designed by the Quantitative Feedback Theory(QFT) method. The results clearly indicate that-in contrast to PID designs-QFT can deliver a single, fixed controller which will supply high bandwidth design even when the dynamics is uncertain and includes mechanical resonances.

• 한국지진공학회논문집
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• 제22권5호
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• pp.299-309
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• 2018

Now that problems with force-based seismic design have been clearly identified, design is inclined toward displacement-based methods. One such widely used method is Direct-Displacement-Based Design (DDBD). Yet, one of the shortcomings of DDBD is considering higher-mode amplification of story shear, moments, and displacements using equations obtained from limited parametric studies of regular planar frames. In this paper, a different approach to account for higher-mode effects is proposed. This approach determines the lateral secant stiffness of the building frames that fulfill the allowable inter-story drift without exceeding the desired story displacements. Using the stiffness, an elastic response spectrum analysis is carried out to determine elastic higher-mode force effects. These force effects are then combined with DDBD-obtained first-mode force effects using the appropriate modal superposition method so that design can be performed. The proposed design procedure is verified using Nonlinear Time History Analysis (NTHA) of twelve planar frames in four categories accounting for mass and stiffness irregularity along the height. In general, the NTHA response outputs compared well with the allowable limits of the performance objective. Thus, it fulfills the aim of minimizing the use of NTHA for planar frame buildings, thereby saving computational resources and effort.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.513-520
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• 2005

An active modal-fuzzy control method using hydraulic actuators is presented for seismic response reduction. In the proposed control system, a new fuzzy controller designed in the modal space produces the desired active control force. This type controller has all advantages of the fuzzy control algorithm and modal approach. Since it is very difficult to select input variables used in fuzzy controller among an amount of state variables in the active fuzzy control system, the presented algorithm adopts the modal control algorithm which is able to consider more easily information of all state variables in civil structures that are usually dominated by first few modes. In other words, all information of the whole structure can be considered in the control algorithm evaluated to reduce seismic responses and it can be efficient for especially civil structures. In addition, the presented algorithm is expected to magnify utility and performance caused by efficiency that the fuzzy algorithm can handle complex model more easily. An active modal-fuzzy control scheme is applied together with a Kalman filter and a low-pass filter to be applicable to real civil structures. A Kalman filter is considered to estimate modal states and a low-pass filter was used to eliminate spillover problem. The results of the numerical simulations for a wide amplitude range of loading conditions show that the proposed active modal-fuzzy control system can be beneficial in reducing seismic responses of civil structures.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.301-310
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• 2018

In this paper, a multi-objective multiparameter optimization procedure is developed by combining rigorously developed metamodels with an evolutionary search algorithm-Genetic Algorithm (GA). Response surface methodology (RSM) is used for developing the metamodels to replace the tedious finite element analyses. A nine-node isoparametric plate bending element is used for conducting the finite element simulations. Highly accurate numerical data from an author compiled FORTRAN finite element program is first used by the RSM to develop second-order mathematical relations. Four material parameters-${\frac{E_1}{E_2}}$, ${\frac{G_{12}}{E_2}}$, ${\frac{G_{23}}{E_2}}$ and ${\upsilon}_{12}$ are considered as the independent variables while simultaneously maximizing fundamental frequency, ${\lambda}_1$ and frequency separation between the $1^{st}$ two natural modes, ${\lambda}_{21}$. The optimal material combination for maximizing ${\lambda}_1$ and ${\lambda}_{21}$ is predicted by using a multi-objective GA. A general sensitivity analysis is conducted to understand the effect of each parameter on the desired response parameters.

• Advances in aircraft and spacecraft science
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• 제6권6호
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• pp.497-513
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• 2019

A wind tunnel test was conducted that measured surface fluctuating pressures aft of a ramp at transonic speeds. Dynamic pressure test data was used to perform a study to determine best locations for streamwise sensor pairs for shocked and unshocked runs based on minimizing the error in root-mean-square acceleration response of the panel. For unshocked conditions, the upstream sensor is best placed at least 6.5 ramp heights downstream of the ramp, and the downstream sensor should be within 2 ramp heights from the upstream sensor. For shocked conditions, the upstream sensor should be between 1 and 7 ramp heights downstream of the shock, with the downstream sensor 2 to 3 ramp heights of the upstream sensor. The shock was found to prevent the passage coherent flow structures; therefore, it may be desired to use the shock to define the boundary of subzones for the purpose of loads definition. These recommendations should be generally applicable to a range of expansion corner geometries in transonic flow provided similar flow structures exist. The recommendations for shocked runs is more limited, relying on data from a single dataset with the shock located near the forward end of the region of interest.

• 한국지능시스템학회논문지
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• 제9권6호
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• pp.598-604
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• 1999

본 논문에서는 능동형자기베어링(Active Magnetic Bearing AMB)시스템의 제어를 위한 새로운 퍼지제어 알고리즘을 제안한다. 이 방법은 AMB 시스템의 비선형 특성을 효과적으로 다루기 위하여 Joh등[4,5]이 제안한 LMI에 근거한 PDC 알고리즘과 퍼지 싱글톤을 사용하는 Mamdani형의 퍼지제어기를 복합한다. 이들은 각각 fine mode control과 coarse mode control이라고 구분하였다. coarse mode control은 회전축의 위치에러가 큰 경우 빠른 중심복귀 응답특성을 보이며 fine mode control은 회전축의 위치에러가 작을 때 요구되는 과도응답특성을 제공한다. 본 논에서 제안된 방법은 그성능을 입증하기 위하여 AMB 시스템의 제어에 적용되었으며 선형제어기와 일반적인 PDC 알고리즘으로 제어된 결과와의 비교를 통해 제안된 방법의 우수성을 보인다.

• 대한조선학회논문집
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• 제29권2호
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• pp.60-65
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• 1992

불규칙 해상에서 횡파중 선체의 횡요 운동 응답을 threshold crossing 과정의 관점에서 연구하였다. 비 백색 잡음 기진력은 응답의 crossing 성질이 유지되는 크기의 백색 잡음 기진력으로 대치할 수 있다는 가정하에 등가의 백색 잡음 기 진력으로 모델링 하였고 원래의 비선형 감쇄 함수를 복원하였다. 등가의 백색 잡음 기진력을 가지고 복원된 운동방정식으로부터 결합 확률 밀도 함수를 얻기 위해 등가 비선형화법(equivalent non-linearization method)을 사용하였다. 제시된 방법을 각종 계수들의 값을 변화시키면서 예측하고 이를 다른 논문의 결과와 비교하였다.

• Computational Structural Engineering : An International Journal
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• 제2권1호
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• pp.33-42
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• 2002

A computationally efficient stiffness design method for building structures is proposed in which dynamic soil-structure interaction based on the wave-propagation theory is taken into account. A sway-rocking shear building model with appropriate ground impedances derived from the cone models due to Meek and Wolf (1994) is used as a simplified design model. Two representative models, i.e. a structure on a homogeneous half-space ground and a structure on a soil layer on rigid rock, are considered. Super-structure stiffness satisfying a desired stiffness performance condition are determined via an inverse problem formulation for a prescribed ground-surface response spectrum. It is shown through a simple yet reasonably accurate model that the ground conditions, e.g. homogeneous half-space or soil layer on rigid rock (frequency-dependence of impedance functions), ground properties (shear wave velocity), depth of surface ground, have extensive influence on the super-structure design.

• JSTS:Journal of Semiconductor Technology and Science
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• 제8권3호
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• pp.251-263
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• 2008

In this paper, we report an analytical modeling and 2-D Synopsys Sentaurus TCAD simulation of ion implanted silicon carbide MESFETs. The model has been developed to obtain the threshold voltage, drain-source current, intrinsic parameters such as, gate capacitance, drain-source resistance and transconductance considering different fabrication parameters such as ion dose, ion energy, ion range and annealing effect parameters. The model is useful in determining the ion implantation fabrication parameters from the optimization of the active implanted channel thickness for different ion doses resulting in the desired pinch off voltage needed for high drain current and high breakdown voltage. The drain current of approximately 10 A obtained from the analytical model agrees well with that of the Synopsys Sentaurus TCAD simulation and the breakdown voltage approximately 85 V obtained from the TCAD simulation agrees well with published experimental results. The gate-to-source capacitance and gate-to-drain capacitance, drain-source resistance and trans-conductance were studied to understand the device frequency response. Cut off and maximum frequencies of approximately 10 GHz and 29 GHz respectively were obtained from Sentaurus TCAD and verified by the Smith's chart.