• 한국태양에너지학회 논문집
• /
• 제35권1호
• /
• pp.35-43
• /
• 2015

A numerical simulation on the wake flow of a wind turbine which is a scaled version of a multi-megawatt wind turbine has been performed. Two different inlet conditions of averaged wind speed including one below and one above the rated wind speed were used in the simulation. Steady-state pitch angles of the blade associated with the two averaged wind speeds were imposed for the simulation. The steady state analysis based on the Reynolds averaged Navier-Stokes equations with the method of frame motion were used for the simulation to find the torque of the rotor and the wake field behind the wind turbine. The simulation results were compared with the results obtained from the wind tunnel testing. From comparisons, it was found that the simulation results on the turbine power are pretty close to the experimental values. Also, the wake results were relatively close to the experimental results but there existed some discrepancy in the shape of velocity deficit. The reason for the discrepancy is considered due to the steady state solution with the frame motion method used in the simulation. However, the method is considered useful for solutions with much reduced calculation time and reasonably good accuracy compared to the transient analysis.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2000년도 춘계 학술대회논문집
• /
• pp.178-183
• /
• 2000

An efficient Newton-GMRES algorithm is presented for computing two-dimensional steady compressible viscous flows on unstructured hybrid meshes. The scheme is designed on cell-centered finite volume method which accepts general polygonal meshes. Steady-state solution is obtained with pseudo-transient continuation strategy. The preconditioned, restarted general minimum residual(GMRES) method is employed in matrix-free form to solve the linear system arising at each Newton iteration. The incomplete LU fartorization is employed for the preconditioning of linear system. The Spalart-Allmars one equation turbulence model is fully coupled with the flow equations to simulate turbulence effect. The accuracy, efficiency and robustness of the presently developed method are demonstrated on various test problems including laminar and turbulent flows over flat plate and airfoils.

• 전력전자학회논문지
• /
• 제4권5호
• /
• pp.474-482
• /
• 1999

본 논문에서는 유도전동기의 전 속도 영역에서 출력토오크를 최대화 할 수 있는 새로운 약계자 제어기를 제시하였다. 전압제한과 전류제한을 모두 고려한 약계자 영역에서의 최적해를 구하였다. 제안된 알고리즘은 자속과 속도를 근거로 하여 변동하는 전압 제한 조건을 만족시키는 전류 기준값을 구하게 된다. 따라서 고정자 전압을 최대한 활용하므로 정상상태 뿐만 아니라 전동기의 자속의 크기가 변화하는 과도상태에서도 최대 출력 토오크와 빠른제어 응답성을 얻을 수 있다. 시뮬레이션 및 실험결과를 통해 제안된 약계자 기법의 효용성을 보였다.

• Nuclear Engineering and Technology
• /
• 제55권3호
• /
• pp.861-869
• /
• 2023

This article proposes a novel approach to measure the performance of Safety-Critical Systems (SCS). Such systems contain multiple processing nodes that communicate with each other is modeled by a Petri nets (PN). The paper uses the PN for the performance evaluation of SCS. A set of ordinary differential equations (ODEs) is derived from the Petri net model that represent the state of the system, and the solutions can be used to measure the system's performance. The proposed method can avoid the state space explosion problem and also introduces new metrics of performance, along with their measurement: deadlock, liveness, stability, boundedness, and steady state. The proposed technique is applied to Shutdown System (SDS) of Nuclear Power Plant (NPP). We obtained 99.887% accuracy of performance measurement, which proves the effectiveness of our approach.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1994년도 추계학술대회논문집; 한국종합전시장, 18 Nov. 1994
• /
• pp.35-39
• /
• 1994

One of the important characteristics of the response of nonlinear systems is the existence of subharmonic resonances. When some conditions in parameter space are satisfied. It is possible even in the presence of damping for a periodically excited nonlinear system to possess a response which is the combination of a contribution at the excitation frequency and a component at the system natural frequency. The system natural frequency being a submultiple of the excitation frequency implies that the resulting response is a subharmonic oscillation. In general, there also co-exists, for the system, a response at the excitation frequency, and initial conditions determine which of the steady-state responses is achieved in an experiment or a numerical simulation. In single-degree-of-freedom systems with harmonic excitation, depending on the type of the nonlinearity, e.g., cubic or quadratic the frequency of subharmonic response is respectively, one-third or one-half of that of the excitation frequency. Although subharmonic resonance is one of the principal characteristics of a nonlinear system the subharmonic responses of structures in the presence of internal resonances have been studied very rarely. In this work, we consider subharmonic responses in the two-mode approximation of the plate equations. It is assumed that the two modes are in one-to-one internal resonance. Constant and periodic steady-state solutions of the averaged equations are studied. Finally, the results of direct time integration of the original equations of motion are presented and compared with those obtained from the averaged equations.

• Nuclear Engineering and Technology
• /
• 제48권3호
• /
• pp.650-659
• /
• 2016

As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1) matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1) they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2) they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained.

• Journal of Advanced Marine Engineering and Technology
• /
• 제20권4호
• /
• pp.50-58
• /
• 1996

The torsional vibration of the propulsion shafting system equipped with viscous damper is investigated. The equivalent system is modeled by a two mass softening system with Duffing's oscillator and the vibratory motion is described by non-linear differential equations of second order. The damper casing is fixed at the front-end of crankshaft and the damper's inertia ring floats in viscous silicon fluid inside of the camper casing. The excitation frenquency is proportional to the rotational speed of engine. The steady state response of the equivalent system is analyzed by the computer and for this analyzing, the harmonic balance method is adopted as a non-linear vibration analysis technique. Frequency response curves are obtained for 1st order resonance only. Jump phenomena are explained. The discriminant for the solutions of the steady state response is derived. Both theoretical and measured results of the propulsion shafting system are compared with and evaluated. As a result of comparisions with both data, it was confirmed that Duffing's oscillator can be used in the modeling of the propulsion shafting system attached with viscous damper with non-linear stiffness.

• Journal of Advanced Marine Engineering and Technology
• /
• 제20권4호
• /
• pp.372-372
• /
• 1996

The torsional vibration of the propulsion shafting system equipped with viscous damper is investigated. The equivalent system is modeled by a two mass softening system with Duffing's oscillator and the vibratory motion is described by non-linear differential equations of second order. The damper casing is fixed at the front-end of crankshaft and the damper's inertia ring floats in viscous silicon fluid inside of the camper casing. The excitation frenquency is proportional to the rotational speed of engine. The steady state response of the equivalent system is analyzed by the computer and for this analyzing, the harmonic balance method is adopted as a non-linear vibration analysis technique. Frequency response curves are obtained for 1st order resonance only. Jump phenomena are explained. The discriminant for the solutions of the steady state response is derived. Both theoretical and measured results of the propulsion shafting system are compared with and evaluated. As a result of comparisions with both data, it was confirmed that Duffing's oscillator can be used in the modeling of the propulsion shafting system attached with viscous damper with non-linear stiffness.

• Wind and Structures
• /
• 제15권4호
• /
• pp.313-329
• /
• 2012

There have existed for a number of years good practice guidelines for the use of Computational Fluid Dynamics (CFD) in the field of wind engineering. As part of those guidelines, details are given for the size of flow domain that should be used around a building of height, H. For low-rise buildings, the domain sizes produced by following the guidelines are reasonable and produce results that are largely free from blockage effects. However, when high-rise or tall buildings are considered, the domain size based solely on the building height produces very large domains. A large domain, in most cases, leads to a large cell count, with many of the cells in the grid being used up in regions far from the building/wake region. This paper challenges this domain size guidance by looking at the effects of changing the domain size around a tall building. The RNG ${\kappa}-{\varepsilon}$ turbulence model is used in a series of steady-state solutions where the only parameter varied is the domain size, with the mesh resolution in the building/wake region left unchanged. Comparisons between the velocity fields in the near-field of the building and pressure coefficients on the building are used to inform the assessment. The findings of the work for this case suggest that a domain of approximately 10% the volume of that suggested by the existing guidelines could be used with a loss in accuracy of less than 10%.

• 대한기계학회논문집
• /
• 제13권4호
• /
• pp.583-594
• /
• 1989

본 연구는 기계적 간극의 존재로 양면 접촉에 의한 강성 및 감쇠가 대칭적 으로 두번 생기는 강제 대칭 편적 선형(forced symmetric piecewise-linear vibarti- on)에 대하여 비선형진동의 분수조화 정상해 과정을 설명한 Stoker 가설로부터 분수조화진동을 포함한 복수의 정상해를 구하고 피로, 마멸 연구를 위한 접촉시간 및 접촉력을 계산하였다. 또한 강제 대칭 편적 선형진동자의 운동방정식을 무차원화 하고 각 무차원 시스템 변수에 따른 주파수응답특성을 살펴보았다.