• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1436-1444
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• 2002

A three dimensional numerical model was developed to analyze the mold filling and solidification processes straightforwardly in a casting processes. On the basis of the SIMPLER algorithm, the VOF method and the Equivalent Specific Heat method were adopted to deal with the free surface behavior and the latent heat evolution. The complete model has been validated using exact solutions and experimental results. The importance of three-dimensional effects has been highlighted by comparing the results from the three-dimensional analysis with those given by a two-dimensional analysis.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06c
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• pp.323-327
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• 2010

본 논문은 차분 진화 알고리즘의 최적해 탐색 능력을 향상시키기 위해 병렬 처리기법을 적용한 기법을 제안한다. 이를 위해서 기존의 개체군들을 5개의 그룹으로 나누어서 독립적으로 최적화 과정을 하도록 하여 일정한 확률에 의해서 각 그룹이 다른 그룹의 Best individual들을 변이 과정에서 참조하도록 하였다. 이러한 방식을 통해서 기존 차분 진화 알고리즘이 가지고 있는 지역해 수렴 문제를 해결하는 할 수 있도록 하였다. 실험을 통해서 제안된 차분 진화 알고리즘(P-DE)의 탐색 능력을 비교 및 분석 하였다. 실험 결과 제안된 차분 진화 알고리즘(P-DE)이 지역해 수렴 문제를 충분히 해결함으로써 기존의 알고리즘에 비해서 우수한 성능을 보이는 것을 확인 하였다.

• Korean Journal of Mathematics
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• v.21 no.2
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• pp.125-150
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• 2013

The stabilized Gauge-Uzawa method (SGUM), which is a second order projection type algorithm to solve the time-dependent Navier-Stokes equations, has been newly constructed in 2013 Pyo's paper. The accuracy of SGUM has been proved only for time discrete scheme in the same paper, but it is crucial to study for fully discrete scheme, because the numerical errors depend on discretizations for both space and time, and because discrete spaces between velocity and pressure can not be chosen arbitrary. In this paper, we find out properties of the fully discrete SGUM and estimate its errors and stability to solve the evolution Navier-Stokes equations. The main difficulty in this estimation arises from losing some cancellation laws due to failing divergence free condition of the discrete velocity function. This result will be extended to Boussinesq equations in the continuous research (part II) and is essential in the study of part II.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.11
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• pp.995-1002
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• 2000

In this paper, fuzzy logic controllers(FLC) are designed for control of flight. For tuning FLC, we used adaptive evolutionary algorithms(AEA) which uses a genetic algorithm(GA) and an evolution strategy (ES) in an adaptive manner in order to take merits of two different evolutionary computations. We used AEA to search for optimal settings of the membership functions shape and gains of the inputs and outputs of FLC. Finally, the proposed controller is applied to the high-angle-of-attack flight system for a supermaneuverable version of the f-18 aircraft and compares with other methods.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.5 no.1
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• pp.21-28
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• 2005

This paper proposes a new method for accelerating the search speed of genetic algorithms by taking derivative evaluation and conditional random selection into account in their evolution process. Derivative evaluation makes genetic algorithms focus on the individuals whose fitness is rapidly increased. This accelerates the search speed of genetic algorithms by enhancing exploitation like steepest descent methods but also increases the possibility of a premature convergence that means most individuals after a few generations approach to local optima. On the other hand, derivative evaluation under a premature convergence helps genetic algorithms escape the local optima by enhancing exploration. If GAs fall into a premature convergence, random selection is used in order to help escaping local optimum, but its effects are not large. We experimented our method with one combinatorial problem and five complex function optimization problems. Experimental results showed that our method was superior to the simple genetic algorithm especially when the search space is large.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.177-178
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• 2006

Digital holographic particle tracking velocimetry (HPTV) is developed by single high-speed camera and single continuous laser with long coherent length. This system can directly capture 4000 hologram fringe images for 1 second through a camera computer memory. The 3D particle location is made of the reconstruction by using a computer hologram algorithm. This system can successfully be applied to instantaneous 3D velocity measurement in the water flow inside a micro-tube. The average of 100 instantaneous velocity vectors is obtained by reconstruction and tracking with the time of evolution of recorded fringes images. In the near future, we will apply this technique to measure 3D flow information inside various micro structures.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.33.1-33
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• 2001

We address a novel approach to identify a nonlinear dynamic system for Wiener models, which are composed of a linear dynamic system part followed by a nonlinear static part. The aim of system identification here is to provide the optimal mathematical model of both the linear dynamic and the nonlinear static parts in some appropriate sense. Assuming the nonlinear static part is invertible, we approximate the inverse function by a piecewise linear function. We estimate the piecewise linear inverse function by using the evolutionary computation approach such as genetic algorithm (GA) and evolution strategies (ES), while we estimate the linear dynamic system part by the least squares method. The results of numerical simulation studies indicate the usefulness of proposed approach to the Wiener model identification.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.45.4-45
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• 2002

In EIT, an array of disjoint electrodes is attached on the boundary of the object and a set of small alternating electrical currents is injected into the object through these electrodes, and then the corresponding set of voltages is measured on the same array of the electrodes. The objective in EIT is to estimate the resistivity distribution inside the object based on the set of measured voltages and injected currents. In this paper, we proposed a new dynamic EIT reconstruction scheme based on the interacting multiple model (IMM) algorithm. The main contribution of the proposed scheme is that multiple models are employed for the state evolution to get around the modeling uncertainty. Extensi...

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.56.1-56.1
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• 2017

The distribution of gas on cosmological scales is vital to our understanding of galaxy formation. Using the RAMSES cosmological hydrodynamical simulation code we have explored the evolution of the gas properties in a cosmological volume. We have identified the effect of the maximum simulation force resolution, and the resolution of the initial conditions, on the gas density power spectrum, as well as artefacts due to the RAMSES algorithm. The RAMSES methodology can add spurious power on small scales, particularly in low resolution simulations. This effect can be expected to have a strong impact on the results of RAMSES simulations, because this additional power appears at specific epochs, implying a sudden change to the system.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1124-1129
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• 2003

In mechanical design, design process is mainly composed of design, explanation and evaluation. In this paper, Using Genetic Algorithms (GA), Evolutionary computation is introduced as new design process. This method promote the efficiency and power of design. Due to the known characteristics of the stage, the approach basically involves a synthetic design method with the composition of building blocks representing the elements of mechanical objects. In order for the building blocks to be more suitable for representation and evolution of mechanical structures, Elementary Cell Blocks (ECBs) are introduced as new building blocks. In this paper, we have demonstrated the implementation of the approach with the design of gear systems.