• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.682-688
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• 1994

LSM(Least-Squares Method) has inherent limitation that precise system identification over wide frequency band is difficult especially at low frequency hand. In this paper we propose to use decimation, a spectrum analysis method widely used in signal processing. The merits of decimation are the flexibility of selection of the frequency hand concerned and the function of LPF(Low Pass Filter). In this paper, frequency-domain is divided into separate frequency bands which will be combined into full frequency-domain by using MDM(Multiple Decimation Method). In this way, free selection of sampling frequency for each hand is possible and the low frequency oscillation modes of LSM are avoided.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.43-48
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• 1998

The development of unsteady three-dimensional incompressible viscous solver based on unsteady physical curvilinear coordinate system is presented. A 12-point finite analytic scheme based on local uniform grid spacing is extended for nonuniform grid spacing. The formulation of a condition is suggested to avoid the oscillation of the series summations produced by the application of the method of separation of variables. SIMPLER and pressure Poisson equation techniques are used for solving a velocity-pressure coupled problem. The matrix is solved using the Generalized Minimal RESidual (GMRES) method to enhance the convergence rate of unsteady flow solver and the Kinematic boundary condition of a free surface flow. It is demonstrated that the numerical solutions of these equations are less mesh sensitive.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.28-38
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• 2001

A numerical method for the assessment and correction of tunnel wall interference effects on forced-oscillation testing is presented. The method is based on the wall pressure signature method using computed wall pressure distributions. The wall pressure field is computed using unsteady three-dimensional full Navier-Stokes solver for a 70-degree pitching delta wing in a wind tunnel. Approximately-factorized alternate direction implicit (AF-ADI) scheme is advanced in time by solving block tri-diagonal matrices. The algebraic Baldwin-Lomax turbulence, model is included to simulate the turbulent flow effect. Also, dual time sub-iteration with, local, time stepping is implemented to improve the convergence. The computed wall pressure field is then imposed as boundary conditions for Euler re-simulation to obtain the interference flow field. The static computation shows good agreement with experiments. The dynamic computation demonstrates reasonable physical phenomena with a good convergence history. The effects of the tunnel wall in upwash and blockage are analyzed using the computed interference flow field for several reduced frequencies and amplitudes. The corrected results by pressure signature method agree well with the results of free air conditions.

• 대한조선학회지
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• 제18권4호
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• pp.13-20
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• 1981

The hydrodynamic added mass of two dimensional cylinders oscillating vertically at high frequencies in the free surface is of interest to ship vibration problems. Conformal transformation is one of the methods commonly in use for computing the inertia coefficient. Especially, Schwarz-Christoffel transformation has been employed to evaluate the inertia coefficient for the cylinders of straight frames and chines. In this paper, the inertia coefficient for the cylinders with round corners in vertical oscillation at high frequencies are evaluated by employing the Schwarz-Christoffel transformation for the concave corner. The results of calculation by employing the Schwarz-Christoffel transformation are found to be well within the expected range of values compared to Lewis form and the results obtained by source distribution method.

• Nuclear Engineering and Technology
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• 제25권3호
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• pp.371-380
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• 1993

운전원의 언어적인 제어 논리를 이용한 모델과 무관한 제어기가 증기 발생기의 수위 제어를 위해 개발되었다. 오직 9개의 룰을 수위 오차와, 응축 수위 변화를 표현하는 유량 오차로부터 얻어졌다. 벨형의 소속함수는 민감도 분석을 통하여 조절되었고, 결과 과도 상태와 정상상태 공히 양호한 제어성능을 보였다. 저출력에서 전 출력까지의 다단계 출력 증가에 대하여, 전 운전 영역에서 좋은 제어를 보였다.

• Applied Science and Convergence Technology
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• 제23권3호
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• pp.128-133
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• 2014

We study the ballistic spin transport properties in a two-dimensional electron gas system in the presence of magnetic barriers using a transfer matrix method. We concentrate on the size-effect of the magnetic barriers parallel to a two-dimensional electron gas plane. We calculate the transmission probability of the ballistic spin transport in the magnetic barrier structure while varying the width of the magnetic barriers. It is shown that resonant tunneling oscillation is affected by the width and height of the magnetic barriers sensitively as well as by the inter-spacing of the barriers. We also consider the effect of additional electrostatic modulation on the top of the magnetic barriers, which could enhance the current spin polarization. Because all-semiconductor-based devices are free from the resistance mismatch problem, a resonant tunneling structure using the two-dimensional electron gas system with electric-magnetic modulation would play an important role in future spintronics applications. From the results here, we provide information on the physical parameters of a device to produce well-defined spin-polarized current.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.233-236
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• 2008

To analyze the saline intrusion in the place, such as an estuary, the three-dimensional numerical model is developed. In this study, the advection terms of the governing equations are discretized by upwind scheme. By using an explicit scheme for the longitudinal direction and an implicit scheme for the vertical direction, the numerical model is free from the restriction of temporal step size caused by a relatively small grid ratio. The equation of state is used to consider the density, and the scalar transport equation for salinity is employed the third order TVD to scheme to prevent unphysical oscillation near discontinuity. In order to verify saline intrusion, the numerical model is conducted to compare the previous model in the lock exchange. The present model generally show a good agreement with the previous one.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 하계학술발표회
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• pp.48-49
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• 2003

원자가 전자기파와 상호작용할 때 원자 전이의 결맞음 여기 (coherent excitation of atomic transitions)는 일반적인 현상이다. 이 상호작용은 라비 진동 (Rabi oscillation), 자유 유도 감쇠 (free induction decay), 단열 밀도 이송 (adiabatic population transfer), 결맞음 과도 (coherent transients； CT) 등 다양한 결과를 가져온다. 특히, 전자기파의 주파수가 원자의 공진주파수를 중심으로 스윕될 때 결맞음 과도 현상 (coherent transient phenomenon)은 밀도 반전 (population reversal)을 유도하기도 한다. (중략)

• Advances in concrete construction
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• 제15권4호
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• pp.269-286
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• 2023

In the present study, we aim to utilize the numerical solution frequency results of functionally graded beam under thermal and dynamic loadings to train and test an artificial neural network. In this regard, shear deformable functionally-graded beam structure is considered for obtaining the natural frequency in different conditions of boundary and material grading indices. In this regard, both analytical and numerical solutions based on Navier's approach and differential quadrature method are presented to obtain effects of different parameters on the natural frequency of the structure. Further, the numerical results are utilized to train an artificial neural network (ANN) using AdaGrad optimization algorithm. Finally, the results of the ANN and other solution procedure are presented and comprehensive parametric study is presented to observe effects of geometrical, material and boundary conditions of the free oscillation frequency of the functionally graded beam structure.

• 전기전자학회논문지
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• 제15권1호
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• pp.49-56
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• 2011

본 논문에서는 고주파 발진회로의 공진기를 패치 안테나로 사용하는 능동발진 안테나를 2.4GHz 대역에서 제안하여 소형 무선도플러 센서로서 이동체의 거리나 속도 등을 측정할 수 있게 하였다. 이동체의 움직임은 고주파 발진 주파수의 천이를 발생시키며 이를 검출하는 회로를 통해 제안된 구조의 동작을 확인하였다. 설계 제작된 무선 도플러 센서는 직경이 30mm, 높이 4.2mm 정도로 매우 작은 원형디스크 형태를 갖으며, 안테나는 2.373GHz에서 약 130도의 빔폭과 전방향 방사특성을 나타내었다. 센서의 감도 측정결과, 1m 떨어져 움직이고 있는 도체판에 대해 최소 190mV의 도플러 신호 전압을 얻었고, 센서의 자유낙하 실험으로부터 지표상의 4.5m 지점에서 부터 지표면까지 전압크기가 선형적으로 증가하였다.