• The Korean Journal of Rheology
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• 제8권2호
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• pp.139-146
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• 1996

2차원 비점성 Euler 방정식의 Stuart 해에 의하여 주어지는 주기적인 유동장, 소위 말하여 Stuart와동장내에 놓여있는 아주 작은 비대칭성 입자의 다양한 부력 변수에 따른 침 강운동을 고찰하엿다. 본 연구에서 사용한 수치방법은 매질의 준전적인 Stokes 방정식과 입 자의 평형방정식을 연계하였다. 다양한 초기 배향각 또는 형상비에 따른 궤적이나 각변화를 예측하기 위하여 힘과 토오크 관계식을 입자의 운동방정식에 적용하였으며 4차 Runge-Kutta 방정식을 이용하여 입자의 운동을 규명하였다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 한국에너지공학회 1994년도 추계학술발표회 초록집
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• pp.84-89
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• 1994

주유동에 수직으로 분사된 제트 화염의 구조는 이해하기 위하여 화염 길이와 온도를 측정하고 reactive mie scattering 방법을 이용하여 단면 가시화를 실시하였다. 주유동 속도와 제트 분사 속도의 증가에 따라 화염 길이도 함께 증가함을 알 수 있고, 단면 가시화 결과 화염 내부에 존재하는 inner vortical structure는 일반적인 동축제트 화염과 같은 대칭 구조를 갖지 앉고 유동 조건에 따라 inner vortical motion 의 생성 위치가 변화함을 알 수 있다 이는 본 유동장의 특성 중의 하나인 bound vortex와 제트와 주유동이 접하는 상류 면에서 발생하는 rolling-up 의 강도에 좌우됨을 알 수 있다.

• Journal of Korean Society of Steel Construction
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• 제17권4호통권77호
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• pp.499-509
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• 2005

The excessive wind-induced motion of tall buildings most frequently result from vortex-shedding-induced across-wind oscillations. This form of excitation is most pronounced for relatively flexible, lightweight, and lightly damped high-rise buildings with constant cross-sections. This paper discusses the aerodynamic means ofmitigating the across-wind vortex shedding induced in such situations. Openings are added in both the drag and lift directions in the buildings to provide pressure equalization. Theytend to reduce the effectiveness of across-wind forces by reducing their magnitudes and disrupting their spatial correlation. The effects of buildings with several geometries of openings on aerodynamic excitations and displacement responses have been studied for high-rise buildings with square cross-sections and an aspect ratio of 8:1 in a wind tunnel. High-frequency force balance testshave been carried out at the Kumoh National University of Technology using rigid models with 24 kinds of opening shapes. The measured model's aerodynamic excitations and displacement were compared withthose of a square cylinder with no openings to estimate the effectiveness of openings for wind-induced oscillations. From these results, theopening shape, size, and location of buildings to reduce wind-induced vortex shedding and responses were pointed out.

• Journal of the Korean Society for Marine Environment & Energy
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• 제6권2호
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• pp.54-62
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• 2003

The free span of a subsea pipeline due to seabed scouring can result in structural failure by severe ocean environmental loads and vortex induced vibrations. This Paper examines the safety of subsea pipelines with free spans under axial compressive load. The variation of allowable lengths of static and dynamic free spans is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. The static and dynamic free span curves are obtained with a function of non-dimensional parameters. A case study is carried out to introduce the application method of the curve. The results of this study can be usefully applied for the design of subsea pipelines with a free span.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제40권12호
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• pp.1017-1024
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• 2012

The aerodynamic design and analysis on advanced propeller with blade sweep was performed for recent turboprop aircraft. HS1 airfoil series are selected as a advanced propeller blade airfoil. Adkins method is used for aerodynamic design and performance analysis with respect to the design point. Adkins method is based on the vortex-blade element theory which design the propeller to satisfy the condition for minimum energy loss. Propeller geometry is generated by varying chord length and pitch angle at design point of target aircraft. Advanced propeller is designed by apply the modified chord length, the tip sweep which is based on the geometry of conventional propeller. The aerodynamic characteristics of the designed Advanced propeller were verified by CFD(Computational Fluid Dynamic) and evaluated to be properly designed.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제30권1A호
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• pp.27-33
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• 2010

This study addresses a methodology to use small wind turbines for dual purposes, improving aerodynamic performance of flexible bridges and wind energy harvesting. A way to proper placement of small wind turbines on flexible bridges were proposed according on the analogy of conventional aerodynamic appendages. From the wind tunnel tests, it was found that the wind turbine attached like fairing was effective to reduce the vortex-induced vibration of bridge and the optimal spanwise interval of the wind turbine was 3-4.5 time of turbine diameter. Moreover the aerodynamic coefficients of the bridge were improved after installation of the wind turbines. Present results showed the general availability of wind turbine for improvement of aerodynamic performance and energy supply of flexible bridges although the capacity of wind power generation was strongly dependent on wind characteristics of the bridge site.

• The Journal of the Acoustical Society of Korea
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• 제39권5호
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• pp.379-389
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• 2020

In this study, the flow and noise performances of high-speed fan motor unit for cordless vacuum cleaner is improved by optimizing the impeller which drives the suction air through flow passage of the cordless vacuum cleaner. Firstly, the unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equations are solved to investigate the flow through the fan motor unit using the computational fluid dynamics techniques. Based on flow field results, the Ffowcs-Williams and Hawkings (FW-H) integral equation is used to predict flow noise radiated from the impeller. Predicted results are compared to the measured ones, which confirms the validity of the numerical method used. It is found that the strong vortex is formed around the mid-chord region of the main blades where the blade curvature change rapidly. Given that vortex acts as a loss for flow and a noise source for noise, impeller blade is redesigned to suppress the identified vortex. The response surface method using two factors is employed to determine the optimum inlet and outlet sweep angles for maximum flow rate and minimum noise. Further analysis of finally selected design confirms the improved flow and noise performance.

• The Journal of the Acoustical Society of Korea
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• 제40권4호
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• pp.261-269
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• 2021

Without any validation of the incompressible assumption, most of previous studies on cavitation flow and its noise have utilized numerical methods based on the incompressible Reynolds Average Navier-Stokes (RANS) equations because of advantage of its efficiency. In this study, to investigate the effects of the flow compressibility on the Tip Vortex Cavitation (TVC) flow and noise, both the incompressible and compressible simulations are performed to simulate the TVC flow, and the Ffowcs Williams and Hawkings (FW-H) integral equation is utilized to predict the TVC noise. The DARPA Suboff submarine body with an underwater propeller of a skew angle of 17 degree is targeted to account for the effects of upstream disturbance. The computation domain is set to be same as the test-section of the large cavitation tunnel in Korea Research Institute of Ships and Ocean Engineering to compare the prediction results with the measured ones. To predict the TVC accurately, the Delayed Detached Eddy Simulation (DDES) technique is used in combination with the adaptive grid techniques. The acoustic spectrum obtained using the compressible flow solver shows closer agreement with the measured one.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.223-227
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• 2009

In the present study, a least square weighted residual method and Taylor-Galerkin method were formulated and tested for the discretization of the two hyperbolic type equations of level set method; advection and reinitialization equations. The two approaches were compared by solving a time reversed vortex flow and three-dimensional broken dam flow by employing a four-step splitting finite element method for the solution of the incompressible Navier-Stokes equations. From the numerical experiments, it was shown that the least square method is more accurate and conservative than Taylor-Galerkin method and both methods are approximately first order accurate when both advection and reinitialization phase are involved in the evolution of free surface.

• Journal of Ocean Engineering and Technology
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• 제4권2호
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• pp.223-223
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• 1990

A circular cylinder is oscillated in th otherwise quiescent viscous fluid. Numerical analysis performed for this problem by using the fourth-order Runge-kutta method for the unsteady Navier-stokes equations. For K(Kelegan-Carpenter''s No.)=5, the flow developed symmetrically, while for K=10, it revealed random patterns. The coefficient of the rms force is overestimated by 20-30% compared with the experimental result.