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김태우(T.W. Kim) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.3
The purpose of the paper is to compare the differences in computational fluid dynamics analysis results with or without viscous heating effect in internal and external flows. To this end, the energy equation applied to the pressure-based compressible flow solver was modified to take into account the viscous heating effect. In addition, a method using the dimensionless parameters was proposed in order to understand the overall trend of the flow that should consider viscous heating. Through the 2D external flow analysis, it was confirmed that the change in pressure due to the viscous heating effect was hardly observed, but the change in temperature and density was cleary at the body surface. In addition, it was also confirmed that the effect of viscous heating, which is a surface effect, did not show a large change in the entire analysis domain in the external flow. Through the 2D internal flow analysis, it was confirmed that the viscous heating effect, which is a surface effect, causes a large change in the overall internal flow.
동축 로터 해석을 위한 Actuator Model을 포함한 압력 기반의 압축성 유동 해석자 개발
김태우(T.W. Kim) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.4
The purpose of present study is to develop a pressure based compressible flow solver with actuator models to estimate the performance of coaxial rotor. In order to aim this purpose, actuator models which used developed for the single rotor performance was modified to analyze the coaxial rotor performance by isolating and correcting the effect of each rotor blade. In addition, the suggested Actuator models were combined with a pressure based compressible solver which was developed previous research. The hovering rotor analysis results calculated by the developed solver were compared with Full-CFD results with a body fitted mesh. The proposed actuator methods can predict the thrust and power of a coaxial rotor as accurately as a full-CFD method. Moreover, the suggested actuator surface model well predicts the interaction effects between near blades than previous manner.
다양한 마하수 영역의 유동 해석을 위한 Coupled 방식의 개선된 속도-압력-엔탈피 연계 알고리즘
김태우(T.W. Kim),신재렬(J.R. Shin) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.4
In this paper, a pressure-based coupled computational fluid dynamics algorithm for numerical analysis of all mach number region flow is developed. For this purpose, an enhanced pressure based coupled algorithm was developed through the pressure-velocity coupled algorithm and the pressure-enthalpy coupled algorithm were combined. In additional, the Kurganov-Tadmor flux splitting scheme, which is mainly used in density-based solvers, was applied to a developed pressure-based coupled solver. To confirm the analytical ability of developed solver, the variety of mach number flow problems were performed using the developed solver. It was confirmed that the developed solver had the similar analytical ability with that of the other numerical codes through the analysis of the shock tube problems. In order to verify the analytical ability for the variety mach number flow region of the developed solver, 2D bump and nozzle problems and 3D missile problem were analyzed and compared with results of experiments and other numerical analysis codes. It is confirmed that the analytical ability of developed solver in the all speed flow region is somewhat improved than the commercial analysis package and is similar to the density based in-house CFD code.
유연촉각 센서의 열 경화 조건을 고려한 레이저 소착에 의한 노이즈 저감
김태우(T. Kim),이인환(I. H. Lee),최재원(J. W. Choi),김호찬(H. C. Kim) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
최근 산업에 로봇의 사용이 증가하면서 그 용도가 점차로 다양해지고 있다. 이러한 로봇의 응용 분야 중에서 사람의 오감 중 하나인 촉각에 대한 연구가 활발히 이루어지고 있다. 이러한 연구들은 사람이 많이 필요한 단순 반복 작업부터 아주 정밀한 작업까지 매우 다양한 분야에서 사람의 작업을 대체하거나 도울 예정이다. 이들 연구 중에서 유연 촉각 센서는 로봇이 좀 더 사람과 같은 유연한 작업을 할 필요가 있는 분야에 활용되기 위하여 연구되고 있다. 이들 중 폴리머를 기본으로 하여 압력에 따라 저항 또는 정전용량 등이 변화되는 물질을 이용한 센서도 다양하게 연구되고 있으며, 본 연구는 PDMS 와 CNT 를 기반으로 하는 유연 촉각 센서를 다루고 있으며, 특히 유연한 센서를 사용할 때 발생하는 주요한 문제점인 연결 단자와의 접촉 저항에 의한 노이즈를 저감할 수 있는 방안을 모색하고자 한다. PDMS 의 열 경화 온도와 경화 시간에 따른 압력에 의한 저항 변화의 효과를 실험적으로 측정하고 이를 일반적인 배선과 연결할 때에 레이저 소착을 활용하여 그 접촉 노이즈를 저감할 수 있는지 실험을 통하여 확인하고자 한다. 실험에 사용된 센서의 제조 방법과 실험의 내용 및 그 결과치를 소개하고 결과적으로 센서의 안정도가 향상되는지의 여부를 소개하고자 한다.
김태우(T.W.Kim),진기호(K.H.Chin),강안종(A.J.Kang),김학성(H.S.Kim) 전력전자학회 2003 전력전자학술대회 논문집 Vol.2003 No.7(1)
This paper proposes a novel ZVZCS-PWM Boost Converter, It enables the main switch to be turned on and off with both zero voltage and zero current and the auxiliary switch to be turned on and off with ZCS, the rectify diode to be turned on and off with ZVS Moreover, This converter is suitable for not only minority carrier device but also majority carrier device, The auxiliary resonant circuit of the proposed boost converter is placed out the main power path, therefore, there are no voltage/current stresses on the main switch and diode, The operation of the proposed boost converter is explained and analyzed theoretical and experimentally, from a prototype operating at 100kHz, with an input voltage rated at 50V
OpenFOAM 해석자 알고리즘 확장을 통한 Actuator Disk 기반의 로터 성능 해석자 개발
김태우(T. Kim),오세종(S. Oh),강희정(H. J. Kang),이관중(K. Yee) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
The purpose of this study is to develop and verify the newly developed solver for analyzing rotor flow field using the open-source CFD code. For helicopter fuselage aerodynamic evaluations an actuator disc model is sufficient unless a transient solution is sought that requires the modeling of the passage of the blades and associated tip vortices. In the present study, a rotor analysis solver has the formal algorithm of SIMPLE in simpleFoam, and the individual procedure for considering rotor influence. The flow chart of rotor analysis solver algorithm. The flow field around complex rotor-fuselage configurations can be modeled as a simple single block grid with unstructured meshes. For the calculation of the rotor thrust, the virtual blade method based on the blade element theory is employed. The inflow velocities on the rotor disk used to specify the effective angles of attack, have been included in the solver. The time-averaged mean flow of the unsteady rotor in forward flight is calculated by modeling the rotor as an actuator disk in which source term is added in the momentum equation. The ROBIN configuration is designed for the experimental study of rotor-fuselage interactional aerodynamics and inflow analysis. The time-averaged inflow velocity is normalized by the rotor tip rotational speed and compared with the experimental data at four azimuthal positions for the rotor-fuselage configuration with or without the fuselage at the test conditions. For hovering validation, caradonnas and ballard’s experiments were employed. The validation cases in forward and hovering flight were computed and good agreement with the experiment is obtained. It is demonstrated that the present method for estimation of rotor influence and OpenFOAM for numerical fluid analysis could a useful tool to predict the complicated rotor-fuselage interactional aerodynamic phenomena and to estimate inflow on rotor disk in an efficient time-averaged manner.
동유체력 계산을 이용한 수중운동체의 횡동요 계수 변화 예측
김태우(T. W. Kim),강태진(T. J. Kang),박원규(W. G. Park),정철민(C. M. Jung) 한국전산유체공학회 2015 한국전산유체공학회지 Vol.20 No.2
For Underwater vehicles, Unwanted roll excursions are inevitable as they are caused by induced propeller torque, disturbances, and banking motion during turns. To estimate the manoeuvring performance of underwater vehicle, it is necessary to obtain the roll coefficient of body. This paper was covered estimation of roll coefficient of underwater vehicle using STAR-CCM+, commercial CFD(Computational Fluid Dynamics) code. The RANS equations for incompressible fluid flows was solved numerically by using a finite volume method. An MRF(Moving Reference Frame) Method was Also adopted for rotations of body. For the validation, the flow around a DARPA SUBOFF bare hull model was simulated and good agreement with experiments was obtained. And Pure roll coefficients were calculated and campared with the experimental data which were presented by Seoul National University. Finally, an underwater vehicle model with propeller was simulated and analyzed for estimation of roll coefficient variation caused by induced propeller torque.