• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.191-200
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• 1994

사각형 유체저장탱크의 바닥에 놓여져 있는 사각형 블럭의 크기 및 위치가 자유수면의 유동진동수와 모드형상에 미치는 영향에 대하여 선형파이론을 적용하여 검토하였다. 유체의 영역을 3부분으로 나누고 각 영역에서의 속도포텐셜을 입사파와 블럭으로 인해 발생되는 반사파 및 전달파의 항으로써 표현하였다. 그리고 블럭에 의한 파의 반사율과 전달율은 유체영역의 경계에서 속도포텐셜과 유체입자의 속도가 연속인 조건을 사용하여 구하였다. 연구결과 블럭의 높이와 폭은 자유수면의 고유진동수에 크게 영향을 미치며 높이와 위치는 모드형상에 주로 영향을 준다. 블럭이 높고 폭이 넓을수록 고유 진동수는 감소하며 블럭이 높고 탱크의 벽면으로 이동할수록 모드형상은 크게 변한다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.615-622
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• 2000

Numerical simulation is performed with Denton's code to get pressure loss coefficients in wide range of reverse flow incidence(from -90 degree to +85 degree) for an axial compressor cascade. As a results, it is found that the pressure loss coefficient is increased with incidence and there exist critical incidence which corresponds to the maximum pressure loss coefficient. Pressure loss coefficient with bigger incidence than its critical value is decreased. The effect of increasing incidence in a cascade extremely reduce the mass flow rate by the large flow separation region. Consequently this effect reduce the portion of dynamic pressure in the total pressure loss and beyond the critical incidence the pressure loss coefficient decrease.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.273-279
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• 2011

Turbulent flow analysis around a wind turbine blade was performed to evaluate the power performance of offshore wind turbine. Fluent package was utilized to solve the Reynolds-averaged Navier-Stokes equations in non-inertial rotating coordinates. The realizable k-$\varepsilon$ model was used for turbulence closure and the grid system combining structured and unstructured grids was generated. In the first, lift and drag forces of 2-D foil section were calculated and compared with existing experimental data for the validation. Then torque and thrust of the wind turbine blade having NACA 4-series sections were calculated with fixed pitch angle and rpm. Tip speed ratio was varied by changing wind speed. In the next, three kinds of end plate were attached at the tip of blade in order to increase the power of the wind turbine. Among them the end plate attached at the suction side of the blade was found to be most effective. Furthermore, performance analysis with tilt angle and rake was also performed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.35-40
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convertive terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. In this paper k-$\varepsilon$ turbulence model with wall function is used to increase efficiency of computation times.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.3
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• pp.29-36
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Wavier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convective terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. Considering computation times, $\kappa$-$\varepsilon$ turbulence model with wall function is used.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.146-158
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• 1991

The flow around a two-dimensional foil section Is measured by a LDV(Laser Doppler Velocimetry) system which is capable of measuring the datailed flow field without interfering the original flow field. A 2-color 3-beam LDV system, which is capable of mea,;tiring 2 velocity components simultaneously and uses 2W Ar-Ion laser source, is used to measure the flow field around an NACA0012 foil section. The measured flow velocities are analysed iii order to study the boundary layer characteristics, flow separation and the detail structure of the flow near the trailing edge of the foil. The boundary layer characteristics are compared with the results by the head's momentum integral method. For the case of small angle of attack at relatively higher Reynolds number, both results show good agreements. The measured data of the velocity field around an NACA0012 foil section would be valuable data to validate the CFD(Computational Fluid Dynamic) calculation results. The developed experimental technique to evaluate the characteristics of two-dimensional foil sections is essential tool to develope new blade sections which have good lift characteristics and better cavitation performances.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.2
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• pp.67-73
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• 2005

The characteristics of the floating breakwater is briefly reviewed and their performance is numerically investigated. The numerical scheme is a boundary integral method for inviscid potential flows, and various two-dimensional floating breakwater modules are studied focusing on the transmission coefficient. The general characteristics of pontoons is studied as function of mooring line stiffness, mass moment inertia and draft. Trapezoidal-, hat- and table-shape cross-sections are also studied with varying shape-parameters. The efficiency varies with changes in each shape-parameter and for some cases satisfying tranquility can be expected with even longer waves.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.53-59
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• 1991

By employing multiple-scale expansion techniques, the diffraction of sinusoidally-modulated nonlinear Stokes waves by a stationary thin wedge has been studied within the framework of potential theory. It is found that the evolution of diffracted waves can be described by the Zakharov equation to the leading order and it can be replaced by the cubic $Schr\ddot{o}dinger$ equation with an additional linear term for stable modulations. Computations are made for the cubic $Schr\ddot{o}dinger$ equation with different values of nonlinear and dispersion parameters. Numerical results well reflect the experimental findings in the amplitude and width of generated stem waves. It is numerically confirmed that the nonlinearity dominates the wave field, while the dispersion hardly affects the wave evolution, and stem waves are likely to be formed for steep incident waves in the case of stable sinusoidal modulations.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.25-32
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• 2003

In the present paper, a computational study on the hydrodynamic behavior of the inducer are presented including the effect of the mass flow rate. The adopted inducer showed very low head rise with high volume flow rates, which may be caused by the small passage area near the trailing edge. The static pressure distributions at the shroud surface are compared with experimental results showing very good agreements. The overall performance of the inducer such as, efficiency, head rise is also compared with experiments. The computational results are generally in good agreements with experimental ones near the design point, but at the high flow rate, the two results shows discrepancy.

• Journal of Power System Engineering
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• v.4 no.4
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• pp.32-40
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• 2000

A study on the fluid flow with ultrasonic forcing was carried out to get the enhancement of turbulence by laying emphasis on the ultrasonic incidence angles and reflectors. A large water tank was made of the transparent acrylic plates and city water of $25^{\circ}C$ was used as working fluid. 7 angles ($30^{\circ},\;45^{\circ},\;60^{\circ},\;90^{\circ},\;120^{\circ},\;135^{\circ},\;150^{\circ}$) as the ultrasonic incidence angle and 4 materials (wood, acryl, glass, iron) as the reflector were selected arid experiments for the above were made. The velocity vector distribution, kinetic energy and turbulence intensity of the turbulence flow fields enhanced by ultrasonic forcing were measured, compared and discussed by using the PIV measurement which was possible to measure the velocities of simultaneous multipoints. In results, it was cleared that the incidence angle of ultrasonic and material of reflector influenced the enhancement of turbulence.