• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.270-279
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• 2022

In this study, numerical analysis and experiments were performed to analyze the viscous damping effect according to the shape of the chamber skirt of the breakwater-linked inclined oscillating water column wave energy converter. Experiments were conducted using a two-dimensional mini wave tank and verified by comparing the results of a computational fluid dynamics numerical analysis. Pointed and rounded skirts were modeled to compare the effect of viscous damping when incident waves enter the chamber, and the difference in the displacement of the water surface in the chamber was compared according to the wave period for the two skirt shapes. The wave elevation in the chamber in the rounded-skirt condition was larger than the pointed-skirt condition in all wave periods, which was approximately 47% greater at 0.9 s of the incident wave period. Therefore, extracting the maximum energy through the optimal orifice is possible while minimizing the energy attenuation in the rounded-skirt condition.

• Journal of Korean Port Research
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• v.10 no.1
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• pp.53-61
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• 1996

This paper describes the effect of wave control using submerged flat plate by the numerical calculation and the hydraulic model test. The boundary element method is used to develop a numerical solution for the flow field caused by monochromatic oblique waves incident upon an infinitely long, sumerged flat plate situated in arbitrary water depth. The effect of wave blocking is examined according to the change of length, submerged depth of flat plate and incident angles. Numerical results show that longer length, shallower submergence of flat plate and larger incident angles enhance the effect of wave blocking. To validate numerical analysis method, hydraulic model test was conducted in 2-D wave flume with 60 cm metal sheet. Reflected waves are extracted from water surface elevation in front of the location of a submerged plate by least square method with 3 wave gages. From comparing experimental results with numerical results, efficiency of numerical analysis method by this study could be confirmed well within wide ranges of wave frequencies.

• Ocean Systems Engineering
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• v.13 no.4
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• pp.325-347
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• 2023

The present work investigates the wave generation and propagation in a 2-D wave flume to assess the effect of wave reflection for varying beach slopes by using a numerical tool based on computational fluid dynamics. At first, a numerical wave flume (NWF) is created with different mesh sizes to select the optimum mesh size for time efficient simulation. In addition, different beach slope conditions are introduced such as 1:3, 1:5 and numerical beach at the far end of the NWF to optimize the wave reflection solutions. In addition, several parameters are analysed in order to optimize the solutions. The developed numerical model and its key findings are compared with analytical and experimental surface elevation results and it reveals a good correlation. Finally, the recommended numerical solutions are validated with the experimental findings.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.291-296
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• 2006

The residual stress in shot-peened Al 7075 alloy was evaluated using surface acoustic wave (SAW). Shot peening was conducted to produce a variation in the residual stress with the depth below the surface under a shot velocity of 30 m/s. The SAW velocity was measured from the V(z) curve using a scanning acoustic microscopy (SAM). The Vickers hardness profile from the surface showed a significant work hardening near the surface layer with a thickness of about 0.25 mm. As the residual stress became more compressive, the SAW velocity increased, whereas as the residual stress became more tensile, the SAW velocity decreased. The variation in the SAW velocity through the shot peened surface layer was in good agreement with the distribution of the residual stress measured by X-ray diffraction technique.

• Ocean Systems Engineering
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• v.5 no.4
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• pp.319-329
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• 2015

Submerged breakwaters are used to prevent shore line erosion and sediment transportation. One of their advantages is low visual impact. In this paper, the effects of discontinuous submerged breakwaters over water surface elevation was numerically studied considering the extended Boussinesq equations as governing equations using MIKE21 software. The result of discontinuous breakwater was compared with a beach without breakwater. The results showed that the gap dramatically effects on surface elevation from shore line to offshore. It is also evident from results that with approaching the center of the gap, fluctuation of surface elevation is generated. It is because of passing longshore currents towards offshore through the gap which leads to an increase in sediment transportation rate. Nevertheless, transferring water mass from breakwater gap results in powerful rip currents leading to high changes on longshore wave profile.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.48-51
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• 2004

This paper is to study the response of flat plate slab-column connections consisting of various types of shear reinforcement and steel plate subjected to gravity loadings, mainly punching shear forces using the non-destructive testing, spectral analysis of surface waves and structural experiments. The base specimen failed due to punching shear generated from the gravity. The three other types of slab shear reinforcement and steel plate showed effective in resisting punching shear for these types of connections under gravity loading. This study has focused in evaluating the velocity response of a Surface wave during the early age as the poured concrete specimens have been hardened, the possibility of damage detection in the slab-column connection and the relationship between the punching shear forces and the surface wave velocities under the condition that the punching shear forces had gradually increased until the flat plate slab in slab-column connection had been failed.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1395-1397
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• 1998

In this paper, we studied the liquid crystal(LC) alignment and generation of pretilt angle in nematic (N) LC with oblique p-wave polarized ultraviolet (UV) light irradiation on the two kinds of the polyimide (PI) surface. The monodomain alignment of NLC is obtained with oblique p-wave polarized UV light irradiated on PI surface at 5$\sim$60min. We obtained that the pretilt angles of the NLC is generated about $2.1^{\circ}$ with angle of incidence of $30^{\circ}$ at 20min. Also, the pretilt angle of NLC decreases with increasing the imidization temperature on PI surface.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.303-306
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• 1999

The paper describes a theoretical study on the speed of the torsional elastic waves propagating in a circular cylinder whose outer radius varies periodically as a harmonic function of the axial coordinate. The approximate solution for the phase speed has been obtained using the perturbation technique for sinusoidal modulation of small amplitude. It is shown that the wave speed in the cylinder with a corrugated outer surface is less than that in a smooth cylinder by the square of the amplitude of the surface perturbation. This theoretical prediction agrees reasonably with an experimental observation reported earlier. It is also shown that the wave speed reduction due to the surface corrugation becomes larger for a thinner cylinder and for a bigger density of corrugation.

• 한국해양학회지
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• v.17 no.2
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• pp.69-73
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• 1982

Wind wave generation is generally accompanied by a strong wind drift currint near the surface. The current can not be considered irrotational. The classical eqration gorerning free surface wave is formulated on the basis of irrptationality. To deal with the situation proterly, an equation governing free surface fluctuation of small amplitude is derived when the mean flow can not be assumed irrotational. The equation encompass the [lassical one as a limiting case as expected.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.46-49
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• 2008

NDE(Nondestructive examination) detects a flaw or discontinuity in materials. Flaws detected by the pre-service or in-service examinations shall be sized for the purpose of analysis and repair. A flaw that is initiated from the surface is difficult to determine its depth by NDE. The depth of the surface flaw can be measured using an ultrasonic diffracted wave. To find the optimum standard for ultrasonic parameter(For example, frequency & size of transducer), a mock-up test and simulation were established and studied. This inspection technology may show the depth sizing possibility of the flaw down to nearly two(2) mm.