• Advances in aircraft and spacecraft science
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• 제4권4호
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• pp.437-448
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• 2017

The problem of flow through the vent is formulated as an unsteady, nonlinear, ordinary differential equation and solved using Runge-Kutta method to obtain pressure inside payload faring. An inverse problem for prediction of the discharge coefficient is presented employing measured internal pressure of the payload fairing during the ascent phase of a satellite launch vehicle. A controlled random search method is used to estimate the discharge coefficient from the measured transient pressure history during the ascent period of the launch vehicle. The algorithm predicts the discharge coefficient stepwise with function of Mach number. The estimated values of the discharge coefficients are in good agreement with differential pressure measured during the flight of typical satellite launch vehicle.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.540-545
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• 2001

In this paper dynamic responses of an engine, which is supported by hydraulic mount, to throttle tip-in/tip out are analyzed. Because the hydraulic mounts have non-linearity which the characteristics of stiffness and damping vary with frequencies, it is difficult to analyze the dynamic behavior of an engine using general integral algorithms. Convolution integrals and relationships between unit impulse response functions and frequency response functions are therefore used to simulate the transient behavior of an engine indirectly. In time domain, impulse response functions are calculated by two-side discrete inverse Fourier transform of frequency response function achieved by Laplace transform of equations of motion. Considering the fact that the shapes of behavior of an engine simulated by the proposed method are in good agreement with test results, it is confirmed that the proposed method is very effective for the analysis of transient response to throttle tip-in/out of an engine with hydraulic mounts.

• 전기학회논문지
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• 제58권10호
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• pp.1936-1941
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• 2009

This paper deals with a new methodology for topology optimization in which the topology of the design domain may change during the shape optimization process. To achieve this, the concept of the topological gradient is introduced to compute the sensitivity of an objective function when a small hole is drilled in the domain. Based on shape and topological sensitivity values, the shape and topology of the design domain may be simultaneously changed during design iterations if necessary. To verify the advantages and also to facilitate understanding of the method itself, two electrostatic design problems have been tested by using 2D finite element analysis: the first is the inverse problem of a simple dielectric model and the second is the rotor design of a MEMS actuator.

• Journal of Multimedia Information System
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• 제1권1호
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• pp.87-93
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• 2014

The aim of microscopic image restoration is to recover the image by applying the inverse process of degradation, and the results facilitate automated and improved analysis of the image. In this work, we consider the problem of image restoration as a minimization problem of convex cost function, which consists of a least-squares fitting term and regularization terms with non-negative constraints. The finite step method is proposed to solve this constrained convex optimization problem. We demonstrate the convergence of this method. Efficiency and restoration capability of the proposed method were tested and illustrated through numerical experiments.

• Journal of applied mathematics & informatics
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• 제6권1호
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• pp.175-184
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• 1999

Along with the computation and analysis for nonlinear system being more and more involved in the fields such as automation control electronic technique and electrical power system the nonlin-ear theory has become quite a attractive field for academic research. In this paper we derives the solutions for state equation of nonlinear system by using the inverse operator expression of the so-lutions is obtained. An actual computation example is given giving a comparison between IOM and Runge-kutta method. It has been proved by our investigation that IOM has some distinct advantages over usual approximation methods in that it is computationally con-venient rapidly convergent provides accurate solutions not requiring perturbation linearization or the massive computation inherent in discrietization methods such as finite differences. So the IOM pro-vides an effective method for the solution of nonlinear system is of potential application valuable in nonlinear computation.

• 한국전자파학회논문지
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• 제12권7호
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• pp.1139-1146
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• 2001

일차원 매질에 대한 역산란법을 이용하여 테이퍼형 임피던스 정합선로를 설계한다. 역산란법으로 유전율 분포를 추정하는 과정에서 오타를 줄이기 위하여 위상 보정인자(PCF: Phase Compensation Factor)를 도입한다. 설계하고자 하는 정합선로와 동일한 반사특성을 갖는 가상(virtual) 일차원 유전체의 유전율 분포를 추정하여 정합선로를 합성한다. 이 설계법은 등가회로에 대한 회로망 이론을 적용하지 않고 임의의 대역 특성을 갖는 정합선로를 설계할 수 있다. 주파수 영역의 반사계수를 사용함으로써 시간 영역의 반사계수를 사용하는 설계법에서 필연적으로 나타나는 오차를 피할 수 있다.

• 한국지반공학회논문집
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• 제15권4호
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• pp.153-166
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• 1999

일반적으로 도심지에서 이루어지는 굴착은 안정성의 중요도에 비하여 해석의 정확도가 떨어지기 때문에 시공 중 현장계측관리가 필수적으로 수반된다. 그러나 계측은 이미 진행된 공정의 거동을 나타내는 것이고, 실제로 시공관리에 도움이 되는 향후 예정된 공정에 대한 예측에는 한계가 있다. 본 연구에서는 계측결과를 해석에 반영하여 예측 결과의 신뢰성을 제고하는 역해석기법을 이용하여 굴착 시공 중 차후 공정의 거동예측을 정확하게 예측할 수 있는 굴착 관리 정보화 시스템을 개발하였다. 개발시스템은 탄소성 지반스프링 모델을 이용한 탄소성 기법을 토대로 측정변위와 모델에 의하여 계산된 변위간의 최소자승 오차를 최소화하는 역해석 기법을 사용하였으며, 정해석, 계측관리, 역해석을 시스템 내에서 일관되게 수행할 수 있고, 실시간 적용과 사용자의 편의를 감안하였다. 개발된 시스템을 두 가지 사례에 적용한 결과 굴착 지반의 거동을 정확하게 예측할 수 있음을 확인하였다.

• 한국정보통신학회논문지
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• 제18권4호
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• pp.920-926
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• 2014

본 연구에서는 지하굴착공사에서 굴착단계별 변위형상도를 미리 예측하는 기법에 관하여 역해석 알고리즘을 이용하여 현장시공사례에 적용하고 그 타당성을 검증하고자 한다. 이를 위해 IT 분야의 정보 처리 지식이 필요하고 전공융합의 필요성이 대두되어 건설 분야에 알고리즘의 적용을 시도하고자 한다. 본 연구의 기법에서 예측변위형상도는 굴착시공 시 연속벽체에 작용하는 토압과 연관이 있으며 이는 앵커 제거 후 시공하는 연속벽체의 안정성에 영향을 미치기 때문에 굴착단계별 변위형상도를 미리 예측하는 것은 아주 중요한 문제이다. 본 연구에서는 이를 위해 3곳의 지하연속벽을 사용한 현장에 반복적 역해석 알고리즘 기법을 세 단계로 적용하여 최종굴착 시 계측변위와 비교하였다. 그 결과 계측치와의 변위형상도가 잘 일치하고 있어 본 연구의 해석기법에 대한 타당성이 있음을 알 수 있었다.

• 대한기계학회논문집B
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• 제33권1호
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• pp.17-27
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• 2009

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number.

• 전기학회논문지
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• 제68권2호
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• pp.262-268
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• 2019

Previous dynamic models of hysteresis motor use an extended induction machine equivalent circuit or somewhat different equivalent circuit with conventional one, which makes unsatisfiable results. In this paper, the hysteresis dynamic characteristics of the motor rotor are analyzed using the inverse Preisach model and the hysteresis motor equivalent circuit considering eddy current effect. The hysteresis loop for the rotor ring is analyzed under full-load voltage source static state. The calculated hysteresis loop is then approximated to an ellipse for simplicity of dynamic computation. The permeability and delay angle of the elliptic loop apply to the dynamic analysis model. As a result, it is possible to dynamically analyze the hysteresis motor according to the applied voltage and the rotor material. With this method, the motor speed, generated torque, load angle, rotor current as well as synchronous entry time, hunting effect can be calculated.