• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.3-12
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• 2001

In physical modeling of plucked string instruments, the vibration of a string is typically simulated by the linear system. Currently the Digital Waveguides of J.O.Smith[1] are widely used to get a high quality sound of the plucked string instrument. He used the wave equation to derive the Digital Waveguides and emphasized the time variable. In this thesis, new model of plucked string is proposed to improve the sound quality emphasizing the spatial variable of the wave equation. In our model, we used the fixed sampling interval which is not dependent on the speed of the wave. So we could get more detailed description of wave movement by the time variable. As a result, the new model could produce a higher quality sound of plucked string instrument.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.1
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• pp.65-71
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• 2006

In this paper, a novel motor control method is proposed to improve the performance of sensorless drive of BLDC motors. In the terminal voltage sensing method, which is a great portion of sensorless control, a precise rotor position cannot be obtained when excessive input is applied to the drive during synchronous operation mode. Especially in the transient state, the response characteristic decreases. To cope with this problem, the unknown input (back-EMF) is modelled as the additional state of system in this paper. Taking into account the disturbance adopted by the back-EMF, the observer can be obtained by the augmented system equation. An algorithm to detect the back-EMF of the BLDC motor using the state observer is constructed. As a result, the novel sensorless drive of BLDC motors that can strictly estimate rotor position and speed is proposed.

• Journal of computational fluids engineering
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• v.8 no.4
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• pp.16-25
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• 2003

The design method for transonic turbine blades has been developed based on Wavier-Stokes equations. The present computing process is done on the four separate steps, i.e., determination of the blade profile, generation of the computational grids, cascade flow simulation and analysis of the computed results in the sense of the aerodynamic performance. The blade shapes are designed using the cubic polynomials under the control of the design parameters. Numerical methods for the flow equations are based on Van-Leer's FVS with an upwind TVD scheme on the finite volume. In the present study, numerical simulation has been done to investigate the effects of the design parameters on the aerodynamic peformance of the axial-flow turbine blades. Applications are made to the VKI transonic rotor blades. Computed results are analyzed with respect to four parameters and compared with the experimental data.

• Journal of Engineering Education Research
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• v.8 no.3
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• pp.69-76
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• 2005

The crisis of science-engineering field is a significant problem which hinders the improvement of national competitiveness. In this study, we use a structural equation model to propose two kinds of satisfaction indices of engineering education: m index for major and p index for personality. They are used to improve the current situation of engineering education in Korea. Based on the resulting feedback information, we suggest several strategic plans for science-engineering field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.52-59
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• 2006

To construct its complex permittivity from the reflection coefficient of a thin film such as PCB substrate measured by open-ended coaxial probe, an integral equation is formulated using modal analysis and equivalent source. The accuracy of the conversion model based on the integral equation is confirmed in both cases of converted complex permittivities calculated from numerically computed and actually measured reflection coefficients. And the maximum valid frequency of open-ended coaxial probe is limited by the size of its flange.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.21-27
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• 2015

An improved method based on direct extraction and simultaneous optimization is developed to determine model parameters of symmetric inductors fabricated by the high resistivity(HR) silicon-on-insulator(SOI) RF CMOS process. In order to improve modeling accuracy, several model parameters are directly extracted by Y and Z-parameter equations derived from two equivalent circuits of symmetric inductor and grounded center-tap one, and the number of unknown parameters is reduced using parallel resistance and total inductance equations. In order to improve optimization accuracy, two sets of measured S-parameters are simultaneously optimized while same model parameters in two equivalent circuits are set to common variables.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1265-1272
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• 2011

We performed numerical simulations of the recirculation flow of an electrolyte fluid in a circular container driven by an AC electromagnetic force for solving continuity and momentum equations. We also conducted an experiment to obtain flow data, which were in good agreement with the numerical simulation results. Furthermore, we performed a parametric study on both numerical and experimental aspects and found that the fluid velocity increases with an increase in the electrolyte concentration and magnetic intensity and with a decrease in the fluid depth and AC frequency.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.2
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• pp.107-120
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• 1993

This paper presents a new modal solution of linear three-dimensional hydrodynamic equations using similarity transform technique. The governing equations are first separated into external and internal mode equations. The solution of the internal mode equation then proceeds as in previous modal models using the Galerkin method but with expansion of arbitrary basis functions. Application of similarity transform to resulting full matrix equations gives rise to a set of uncoupled partial differential equations of which the unknowns are coefficients of mode vector. Using the transform technique a computationally efficient time integration is possible. In present from the model use Chebyshev polynomials for Galerkin solution of internal mode equations. To examine model performance the model is applied to a homogeneous, rectangular basin of constant depth under steady, uniform wind field.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.163.1-163.1
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• 2013

플라즈마 시뮬레이션을 수행하기 전에 현 컴퓨터의 계산 능력범위 내에서 물리적으로 타당하게 설명할 수 있는 수치 해석 방법을 먼저 정한다. 예를 들면, 가스 반응이 많고 각 가스 반응 중에 중요가스 반응을 빠르고 선택적으로 선별하고자 할 때, 혹은 외부 입력 변화에 따른 플라즈마 종의 온도 또는 밀도를 대략적으로 파악하고자 할 때는 공간적인 분포를 고려하지 않는 0차원 global 모델링을 이용한다. 압력이 높고 충돌이 빈번한 경우에는 플라즈마를 유체적인 관점에서 기술이 가능하므로, 볼츠만 방정식에서 속도에 관한 0차, 1차, 2차 모멘텀을 이용하여 유도된 유체 방정식을 이용한다. 반대로 압력이 낮고 충돌이 거의 없는 경우에는 플라즈마 입자를 개별적으로 추적하는 입자 전산 모사 방법을 이용한다. 지금까지는 앞에서 언급한 예와 같이, 개별 플라즈마 상태에 맞는 시뮬레이션 코드를 각각 만들어야 했고, 각 코드를 개별적으로 유지 보수해야 했다. 하지만, 개별적으로 코드를 유지 보수를 해야 할 경우에는, 동일한 기능을 하는 함수를 반복적으로 각 코드에 입력해야 하는 불편함이 따르고, 각 수치해석 방법의 장점을 모은 하이브리드 방법과 같은 전사모사를 개발할 때 각 기능을 통합해야 하는 어려움이 따른다. 또한 지금까지 개발된 대부분의 플라즈마 코드는 외부 입력에 대해 유연하지 못한 대처로 새로운 가스 반응을 추가하거나 새로운 수치해석 방법을 추가할 경우에는 코드를 전체적으로 수정해야 하는 어려움이 있었다. 따라서 코드를 통합적으로 관리할 수 있고, 외부 입력에 대해 유연하게 대처할 수 있는 시뮬레이터가 필요했다. 여기에서는 객체 지향 언어인 C++ 언어를 이용하여, 사용자 입력에 대해 유연하게 대처할 수 있고, 복잡한 화학 반응을 특정 수치 해석 방법에 상관없이 통합적으로 관리할 수 있는 코드를 개발하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.1-6
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• 2010

In this paper, RF Capacitance-Voltage(C-V) curve of short-channel MOSFET has been extracted from the room temperature to $225^{\circ}C$ using a RF method based on measured S-parameter data, and its high-temperature dependent characteristics are empirically modeled. It is observed that the voltage shift according to the variation of temperature in the weak inversion region of RF C-V curves is lower than the threshold voltage shift, but it is confirmed that this phenomenon is unexplainable with a long-channel theoretical C-V equation. The new empirical equation is developed for high-temperature dependent modeling of short-channel MOSFET C-V curves. The accuracy of this equation is demonstrated by observing good agreements between the modeled and measured C-V data in the wide range of temperature. It is also confirmed that the channel capacitance decreases with increasing temperature at high gate voltage.