• 대한의용생체공학회:의공학회지
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• 제25권4호
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• pp.301-307
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• 2004

보행 중 각 관절의 모멘트를 계산하기 위한 역동역학 모델을 개발하였다. 모델은 1개의 상체와 3개의 체절로 하지를 구성하였고 3개의 병진 조인트와 12개의 회전조인트로 각 체절을 연결하고 뉴턴-오일러 방법으로 역동역학 해를 구하였다. 입력자료로서의 기구학적 사료는 3차원 동작분석 시스템에서 추출하였고 외력으로서 지면 반발력은 동기화한 힘측정판에서 구했다. 개발된 모델을 이용하여 비대칭 모델이나 질량중심의 이동을 포함한 해석 등 다양한 인체운동 해석이 가능하다.

• Journal of Korean Society for Atmospheric Environment
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• 제19권E2호
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• pp.75-81
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• 2003

Variational data assimilation, which is recently introduced to the air quality modeling, is a promising tool for obtaining optimal estimates of initial conditions and other important parameters such as emission and deposition rates. In this paper. two advanced techniques for variational data assimilation, based on the adjoint and quasi-inverse methods, are tested for a simple air quality problem. The four-dimensional variational assimilation (4D-Var) requires to run an adjoint model to provide the gradient information in an iterative minimization process, whereas the inverse 3D-Var (I3D-Var) seeks for optimal initial conditions directly by running a quasi -inverse model. For a process with small dissipation, I3D-Vu outperforms 4D-Var in both computing time and accuracy. Hybrid application which combines I3D-Var and standard 4D-Var is also suggested for efficient data assimilation in air quality problems.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.539-551
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• 2021

With the continuous increase of computational capacity, more and more complex nonlinear elastoplastic constitutive models were developed to study the mechanical behavior of elastoplastic materials. These constitutive models generally contain a large amount of physical and phenomenological parameters, which often require a large amount of computational costs to determine. In this paper, an inverse parameter determination method is proposed to identify the constitutive parameters of elastoplastic materials, with the consideration of both strain rate effect and temperature effect. To carry out an efficient design, a hybrid optimization algorithm that combines the genetic algorithm and the Nelder-Mead simplex algorithm is proposed and developed. The proposed inverse method was employed to determine the parameters for an elasto-viscoplastic constitutive model and Johnson-cook model, which demonstrates the capability of this method in considering strain rate and temperature effect, simultaneously. This hybrid optimization algorithm shows a better accuracy and efficiency than using a single algorithm. Finally, the predictability analysis using partial experimental data is completed to further demonstrate the feasibility of the proposed method.

• Geomechanics and Engineering
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• 제33권5호
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• pp.427-437
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• 2023

The objective of this work is to study the wave propagation of an FGM plate via a new integral inverse shear model with temperature-dependent material properties. In this contribution, a new model based on a high-order theory field of displacement is included by introducing indeterminate integral variables and inverse co-tangential functions for the presentation of shear stress. The temperature-dependent properties of the FGM plate are assumed mixture of metal and ceramic, and its properties change by the power functions of the thickness of the plate. By applying Hamilton's principle, general formulas of wave propagation were obtained to plot the phase velocity curves and wave modes of the FGM plate with simply supported edges. The effects of the temperature and volume fraction by distributions on wave propagation of the FGM plate are investigated in detail. The results of the dispersion and the phase velocity curves of the propagation wave in the functionally graded plate are compared with previous research.

• 충청수학회지
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• 제20권4호
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• pp.577-585
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• 2007

We introduce the inverse shadowing property of geometric Lorenz flows and prove that the geometric Lorenz flows do not have the inverse shadowing property.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제6권3호
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• pp.190-196
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• 2006

In this paper, the nonlinear damping force model is made to identify the properties of the ER damper using higher order spectrum. The higher order spectral analysis is used to investigate the nonlinear frequency coupling phenomena with the damping force signal according to the sinusoidal excitation of the damper. Also, this paper presents an inverse model of the ER damper, i.e., the model can predict the required voltage so that the ER damper can produce the desired force for the requirement of vibration control of vehicle suspension systems. The inverse model has been constructed by using piecewise linear damping force model. In this paper, the fuzzy logic control based on heuristic knowledge is combined with the skyhook control. And it is simulated for a quarter car model. The acceleration of the sprung mass is included in the premise part of the fuzzy rules to reduce the vertical acceleration RMS value of the sprung mass. Then scaling factors and membership functions are tuned using genetic algorithm to obtain optimal performance.

• 융합신호처리학회논문지
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• 제5권2호
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• pp.151-158
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• 2004

본 논문에서는 디지털 필터 모델에 대한 역 필터링 기법을 제안한다. 이 기법은 안정한 non-causal IIR 역 필터를 안정한 causal 역 필터로 변환(근사)시키는 것이다. 실제로 이 역 필터에 대한 FIR 근사 방법을 제안한다. 전역통과 시스템에 대한 역 필터의 임펄스 응답은 그 시스템에 대한 임펄스 응답의 거울 영상(mirror image) 임을 알 수 있다. 특히 전역통과 시스템에 대한 임펄스 응답이 이러한 대칭성을 갖기 때문에, 제안한 기법은 다른 시스템 보다 전역통과 시스템에 더욱 유용하다. 제안한 역 필터링 기법을 설명하기 위하여, 네 개의 예제를 제시한다. 그들 중 둘은 전역통과 필터에 대한 것이며, 다른 두 개의 예제는 IIR과 FIR 필터에 대한 것이다. 또한 컴퓨터 시뮬레이션을 통하여 제안한 기법이 잘 동작함을 보인다.

• Journal of Advanced Marine Engineering and Technology
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• 제21권4호
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• pp.414-420
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• 1997

An intelligent speed control system for marine diesel engines is presented. The approach adopt¬ed is to use a conventional PID controller for normal operation and a feedforward controller for adaptive control. The feedforward controller is a neural network. The neural network is the inverse dynamics model of the plant, which is being trained on line. The parametric model of the diesel engine is represented in a linear second-order system, with a first-order combustion part and a revolution part each at a normal operating point. The time delay in the control of the com¬bustion part is approximated to the first-order system. The tuned PID parameters are set based on the model for normal operating point. To obtain the inverse dynamics of the diesel engine system, two neural networks are used, one for inverse, the other for forward dynamics. The former is posi¬tioned across the plant to learn its inverse dynamics during operation, and the latter is placed in series with the controlled plant. Simulation results are presented to illustrate the applicability of the proposed scheme to intelligent adaptive control of diesel engines.

• Smart Structures and Systems
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• 제14권6호
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• pp.1081-1103
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• 2014

Real-time hybrid simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.

• 응용통계연구
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• 제10권2호
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• pp.293-308
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• 1997

일변량 분할 역회귀 방법은 일반화 회귀모형에서 효과적인 차원축약방향과 공간을 추정하는 방법이다. 본 논문에서는 두 일반화 회귀모형을 동시에 고려하여 효과적인 차원축약방향과 공간을 추정하는 방법으로 이변량 분할 역회귀를 제안한다. 이러한 이변량 분할 역회귀 방법은 모형식이 선형, 이차형, 삼차형, 비선형 등의 여러 모형식에서 효과적인 차원축약방향을 추정하며, 일변량 분할 역회귀에 비하여 모형에 존재하는 오차에 크게 영향을 받지 않고 효과적인 차원축약방향을 추정한다. 특히 모형식이 대칭의 이차형인 경우에 일변량 분할 역회귀 방법이 효과적인 차원축약방향을 추정하지 못하는 문제를 해결할 수 있다.