• Korean Journal of Hydrosciences
• /
• v.3
• /
• pp.61-79
• /
• 1992

In oder to predict the dispersion of a thermal discharge with strong turbulent and buoyant effects, the development of a numerical model using turbulence model and its application are significantly increased. In this study, a three-dimensional steady-state model for the surface discharge heated water into quiescent water body is developed. For the model closure of turbulent terms the four-equation turbulence model is used. For economic mumerical simulation, the elliptic governing equations are transformed to the partially parabolic equations. In general, the simulated results by the present model agree well with the experimental results by Pande and Rajratnam (1977). The model characteristics are presented in comparison with the predicted results from the two-eqauation turbulence model by McGuirk and Rodi (1979).

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1997.10a
• /
• pp.171-178
• /
• 1997

This paper describes the application of discretized continuum-type optimality criteria (DCOC) for the multispan partially prestressed concrete beams. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non-prestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. Two numerical examples of multispan PPC beams with rectangular cross-section are solved to show the applicability and efficiency fo the DCOC-based technique.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.3
• /
• pp.954-962
• /
• 1991

본 연구에서는 횡 방향으로 속도구배를 타내는 a=.part.W/.part.z에 대한 방정식을 3차원 운동량 방정식으로 부터 유도한 준 3차원 수학적 모델을 성정하여 해석하였다. 또한 수치 해석을 위하여 Chen에 의하여 고안된 유한 해석법과 2-방정식 저 레이놀즈 K-.epsilon. 난류모델, 그리고 Maeng에 의해 제시된 경계 공정 좌표계를 사용하였다. 그리 고 프로그램의 검증을 위하여 G.Ber geles가 수행한 실험치와 비교하여 그 타당성을 입증하였다.

• Journal of Ocean Engineering and Technology
• /
• v.35 no.1
• /
• pp.82-90
• /
• 2021

Owing to the advantages of assuring the best views and seawater exchange, submerged breakwaters have been widely installed along the eastern coast of Korea in recent years. It significantly contributes to promoting the advancement of shorelines by partially inhibiting incident wave energy. Observations were carried out by a pressure-type wave gauge in the Bongpo Beach to evaluate the coefficients of wave transmission via a submerged breakwater, and the results obtained were compared with those of existing conventional equations on the transmission coefficient derived from hydraulic experiments. After reviewing the existing equations, we proposed a transmission coefficient equation in terms of an error function. Although it exhibited robust relationships with the crest height and breaking coefficient, deviations from the observed data were evident and considered to be triggered by the difference in the incident wave climate. Therefore, in this study, we conducted a numerical experiment to verify the influence of wave period on the coefficients of wave transmission, in which we adopted a parabolic-type mild-slope equation model. Consequently, the deviation from calculated results appears to practically cover all deviation range in the observed data. The wave period and direction of the incident wave increased, the transmission coefficient decreased, and the wave direction was determined to demonstrate a relatively significant influence on the transmission coefficient. It was inferred that this numerical study is expected to be used practically in evaluating the design achievement of the submerged breakwater, which is adopted as a countermeasure to coastal beach erosion.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.5
• /
• pp.755-761
• /
• 1987

Two-Dimensional incompressible laminar boundary layer with the reversed flow region is computed using the parially parabolized Navier-Stokes equations in primitive variables. The velocities and the pressure are explicity coupled in the difference equation and the resulting penta-diagonal matrix equations are solved by a streamwise marching technique. The test calculations for the trailing edge region of a finite flat plate and Howarth's linearly retarding flows demonstrate that the method is accurate, efficient and capable of predicting the reversed flow region.

• Water for future
• /
• v.23 no.4
• /
• pp.445-457
• /
• 1990

In order to predict the dispersion of a thermal discharge with strong turbulent and buoyant effects, the development of a numerical model using turbulence model and its application are significantly increased. In this study, a 3-dimensional steady-state model for the surface discharge of heated water into quiescent water body is developed. For the model closure of turbulent terms the 4-equation turbulence model is used. For economic numerical simulation, the elliptic governing equations are transformed to the partially parabolic equations. In general, the simulated results by the present model agree well to the experimental results by Pande and Rajaratnam. The model characteristics are presented in comparison with the predicted results of the 2-equation turbulence model by McGuirk and Rodi. Applying the 4-equation turbulence model to the Korea nuclear unit 1 at Kori site, feasibility and efficiency of the present model are validated.

• Korean Journal of Optics and Photonics
• /
• v.16 no.1
• /
• pp.50-55
• /
• 2005

A method for measuring the wavefront error and the modulation transfer function(MTF) of large aperture optics using an unequal path interferometer is presented. A bidirectional shearing interferometer is used for collimation testing of the measurement system. A large aperture Fizeau interferometer with long optical path difference measures the wavefront error of the optics under test by using a $\Phi$ 400 mm off-axis parabolic mirror. The MTF is also measured at the wavelength of the interferometer by changing the laser light into partially incoherent light. Test results of a $\Phi$ 300 mm Cassegrain type satellite telescope made in Korea are presented.