• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.3
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• pp.253-265
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• 2007

This study applied the previous results of the NAO model, a tidal correction model, to the open boundary condition for the behavior of tidal elevation and tidal currents in the South Sea. This study used the EFDC model considering the wetting and drying problem and using the $\sigma-coordinate$ as a vertical coordinate and generated two mesh cases of the constant grid size of 2.0 km and the variable grid size of $0.5\sim2.0km$. The numerical results for the tides showed that the predicted results were in quite good agreements with the observational data acquired from the tidal stations of the NORI. The predicted tides were observed to propagate from the east area to the west area in the South Sea. The verification results reveal that the numerical results are more correlated with the measured tidal data as the grid size decreases. The grid size of 2 km results in proper simulation of tidal currents in wide waterway and offshore area whereas the numerical results from the grid size of 0.5 km tend to somewhat underestimate the tidal currents affected by narrow waterway and topography in inner-bay.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.4
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• pp.151-164
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• 1998

Changes in tides and tidal currents in Chonsu Bay caused by the construction of Seosan A and B reclamation regions have been investigated using a depth-integrated two-dimensional tidal model. Three water level recorders were deployed for about one month and used for the specification of the open boundary condition. The computed currents were found to be in a good agreement with the measurements at two stations within Chonsu Bay. Comparison of the absolute velocities computed with the conditions before and after the embankment clearly shows that the reduction in tidal current amplitude is evident throughout the bay and the magnitude of the reduction increases to the north. Calculation shows that the embankment has advanced the time of drying at the northern part of the bay by about 51 minutes and has increased the exposure time by about 23 minutes. The high water time has advanced by about 1 hour, lowering the high water level by about 15 cm.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1195-1200
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• 2008

This study have goal with conceptual design for Offshore Structures of high pressure control valve for localization. Ball valve for development accomplished with flow analysis based on provision of ANSI B16.34, ANSI B16.10, ANSI B16.25 In order to localize the Offshore Structures high pressure control valve. Numerical simulation using CFD(Computational Fluid Dynamic) in order to predict a mass flow rate and a flow coefficient form flow dynamic point of view. The working fluid assumed the glycerin($C_3H_8O_3$). The valve inlet and outlet setup a pressure boundary condition. The outlet pressure was fixed by atmospheric pressure and calculated until increasing 1bar to 10bar. CFD analysis used STAR-CCM+ which is commercial code and Governing equations were calculated by moving mesh which is rotated 90 degrees when ball valve operated opening and closing in 1 degree interval. The result shows change of mass flow rate according to opening and closing angle of valve. Flow decrease observed open valve that equal percentage flow paten which is general inclination of ball valve. Relation with flow and flow coefficient can not be proportional according to inlet pressure when compare with mass flow rate. Because flow coefficient have influence in flow and pressure difference. Namely, flow can be change even if it has same Cv value. The structural analysis used ANSYS which is a commercial code. Stress analysis result of internal pressure in valve showed lower than yield strength. This is expect to need more detail design and verification for stem and seat structure.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.357-362
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• 2008

This study have goal with reverse engineering for petrochemistry of high pressure ball valve for localization. Ball valve for development accomplished with flow analysis based on provision of ANSI B16.34, ANSI B16.10, ANSI B16.25 In order to localize the petrochemistry high pressure control valve. Numerical simulation using CFD(Computational Fluid Dynamic) in order to predict a mass flow rate and a flow coefficient form flow dynamic point of view. The working fluid assumed the water($H_2O$). The valve inlet and outlet setup a pressure boundary condition. The outlet pressure was fixed by atmospheric pressure and calculated inlet velocity 5m/s. CFD solver used STAR-CCM+ which is commercial code. The result shows change of mass flow rate according to opening and closing angle of valve. Flow decrease observed open valve that equal percentage flow paten which is general inclination of ball valve. The structural analysis used ANSYS which is a commercial code. Stress analysis result of internal pressure in valve showed lower than yield strength. This is expect to need more detail design and verification for stem and seat structure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.137-145
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• 1996

Effects of nonlinear terms on the generation of M$_2$ tide residual elevation and M$_4$ tide in the Yellow Sea and the East China Sea are investigated using a depth-integrated two-dimensional nonlinear M$_2$tidal model. The model domain (117$^{\circ}$E-130$^{\circ}$E, 24$^{\circ}$N-41$^{\circ}$N) covers the whole region of the Yellow Sea and the East China Sea with grid resolution of 1/6$^{\circ}$ in longitude and 1/8$^{\circ}$in latitude. A radiational boundary condition is used along the open boundaries. Calculations show that advection terms yield negative residual elevation, while shallow-water terms in continuity equation yield positive residual elevation. The contribution of both advection terms and shallow-water terms to tile generation of the M$_4$ constituent is more than 90 percents, but that of quadratic bottom friction terms to the M$_4$ constituent is comparatively small.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.1
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• pp.93-100
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• 2008

A multi-nesting grid storm surge model, Korea Ocean Research and Development Institute-Storm surge model, was calibrated to simulate storm surges. To check the performance of this storm surge model, a series of numerical experiments were explored including tidal calibration, the influence of the open boundary condition, the grid resolutions, and typhoon paths on the surge heights using the typhoon Maemi, which caused a severe coastal disasters in Sep. 2003. In this study the meteorological input data such as atmospheric pressure and wind fields were calculated using CE wind model. Total 11 tidal gauge station records with 1-minute interval data were compared with the model results and the storm surge heights were successfully simulated. The numerical experiments emphasized the importance of meteorological input and fine-mesh grid systems on the precise storm surge prediction. This storm surge model could be used as an operational storm surge prediction system after more intensive verification.

• Steel and Composite Structures
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• v.38 no.3
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• pp.337-353
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• 2021

Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin-Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.236-245
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• 2021

In this study, direct numerical and large eddy simulations of transitional flows around studs were conducted to investigate the effectiveness of turbulence stimulators at very low speeds for the minimum propulsion power condition of four knots. For simplicity, the studs were assumed to be installed on a flat plate, while the wake was observed up to 0.23 m downstream behind the second stud. For applicability to a model ship, we also studied the flow characteristics behind the first and second studs installed on a curved plate, which was designed to describe the geometry of a bulbous bow. A laminar-to-turbulent transition was observed in the wake at Re_D ≥ 921 (U_∞≥0.290 m/s), and the wall shear stress at Re_D = 1162 (U_∞ = 0.366 m/s) in the second wake was similar to that of the fully developed turbulent boundary layer after a laminar-to-turbulent transition in the first wake. At Re_D = 581 (U_∞ = 0.183 m/s), no turbulence was stimulated in the wake behind the first and second studs on the flat plate, while a cluster of vortical structures was observed in the first wake over the curved plate. However, a cluster of vortical structures was revealed to be generated by the reattachment process of the separated shear layer, which was disturbed by the first stud rather than directly initiated by the first stud. It was quite different from a typical process of transition, which was observed at relatively high Re_D that the spanwise scope of the turbulent vortical structures expanded gradually as it went downstream.

• Steel and Composite Structures
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• v.46 no.4
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• pp.471-483
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• 2023

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier's method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.3
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• pp.167-173
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• 2014

In this work, based on the blade element-momentum theory (BEMT), we proposed the geometry of a lab-scale horizontal axis tidal turbine with a diameter of 80cm, which can demonstrate the maximum power coefficient, and investigated the effect of blade pitch angle increase on the power coefficient. For validation of the computed power coefficients by the BEMT, we also computed the power coefficient using the computational fluid dynamics (CFD) for each case. For the CFD, 15 times of the turbine radius was used for the length and diameter of the computational domain, and the open boundary condition was prescribed at the boundary of the computational domain. The maximum power coefficients of the turbine acquired by the BEMT and CFD were about 48%, showing a good agreement. Both of the power coefficients computed by the BEMT and CFD tended to decrease when the blade pitch angle increases. The two power coefficients for a given tip-speed ratio were in good agreement. Through the present study, we have confirmed that we can trust the proposed geometry and the computed power coefficients based on the BEMT.