• Journal of Ocean Engineering and Technology
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• v.22 no.4
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• pp.27-33
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• 2008

One of the central problems in astudy of the coastal surface wave environment is predicting the transformation of waves as they propagate toward the shore. The transformation is mainly due to the existence of obstacles, such as breakwaters and vertical cylinders. In general, the types of wave transformation can be classified as follows: wave diffraction, reflection, transmission, scattering, radiation, et al. This research dealtwith wave transmission and dissipation problems for two dimensional irregular waves and vertical circular cylinders. Using the unsteady mild slope equation, a numerical model was developed to calculate the reflection and transmission of regular waves from a multiple-row circular breakwater and vertical cylinders. In addition, hydraulic model experiments were conducted with different values for the properties between tire piles and the opening ratio (distances) between the rows of the breakwater. It was found that the transmission coefficients decreased with a decrease in the opening ratio and an increase in the rows of vertical cylinders. A comparison between the results of hydraulic and numerical experiments showed reasonable agreement.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.573-574
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• 2006

This research deals with the wave transmission and dissipation problems for two dimensional regular waves and s vertical circular cylindersr. Using the unsteady mild slope equation, a numerical model has been developed to calculate the reflection and transmission of regular waves from a multiple-row vertical circular cylinders. In addition hydraulic model experiments have been conducted with different values of properties between the cylinders and opening ratio (distances) between the rows of the cylinders. It is found that the transmission coefficients decrease with decreasing the opening ratio and increasing the rows of vertical cylinders. Comparison between hydralic and numerical experiments results shows resonable agreement.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.8-13
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• 2005

In a multiple array of vertical cylinders, flaw patterns are very complex and very interactive between cylinders. The patterns are turbulent and non-linear depending on various factors. The gap and flow incoming velocity of upstream can affect on the downstream cylinder. In this study, the flaw characteristics around two vertical cylinders are investigated numerically and experimentally. As the gap between cylinders is changed at fixed coming velocity, the pressure distributions around cylinders are observed and compared by experimental and numerical approaches. The F.D.M and multi-block method are applied in the study. The pressures at 12 points around the cylinder are measured in the experiment. The results can be applied in the understanding and design of multiple pile array structures.

• Journal of Navigation and Port Research
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• v.32 no.7
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• pp.543-552
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• 2008

The diffraction of waves by three bottom fixed vertical circular cylinders is investigated by using the boundary element method. This method has been successfully applied to the isolated vertical circular cylinder and now is used to study the interaction between waves and multiple vertical cylinders. In this paper, a numerical analysis by the boundary element method is developed by the linear potential theory. The numerical analysis by the boundary element method is based on Green's second theorem and introduced to an integral equation for the fluid velocity potential around the vertical circular cylinders. To verify this method, the results obtained in present study are compared with the results computed by the multiple scattering method. The results of the comparisons show strong agreement. Also in this paper, several numerical examples are given to illustrate the effects of various parameters on the wave exciting force such are the separation distance, the wave number and the incident wave angle. This numerical computation method might be used broadly for the design of various offshore structures to be constructed in the future.

• Journal of Ocean Engineering and Technology
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• v.36 no.2
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• pp.132-142
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• 2022

We investigate the performance of multi-body wave energy converters (WECs). This investigation considers multiple scattering of water waves by the buoys of a WEC under the generalized mode approach. Predominantly, the effect of a WEC's configuration on its energy extraction is studied in this research. First, single-row terminator and single-column attenuator arrays of vertical cylinders have been studied. The performance of these attenuator arrays shows that the wall effect induced by the periodic buoys influences the wave propagation and energy extraction in these WECs. Further studies show that a single-row terminator array of vertical cylinders performs better than the corresponding single-column attenuator array. Subsequently, multi-row terminator arrays of vertical cylinders are investigated by conducting a parametric study. This parametric study shows that the hydrodynamic property of three resonance phenomena makes energy extraction efficiency drop down, and the magnitude of energy extracted oscillates between the resonance points in these WECs. Finally, a 4×8 terminator array of vertical cylinders is studied to determine the effect of various d_x (x-directional distance between adjacent rows) within this WEC on its performance. In particular, this study enforces at least two equal d_x values within the 4×8 terminator array of vertical cylinders. It shows that a small value of this d_x leads to better energy extraction efficiency in some of these various d_x arrays than that of a corresponding regular array with the same d_x.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.213-216
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• 2002

In this paper, flow patterns around two vertical cylinders were investigated numerically and experimentally Flow patterns between cylinders are very complex and interative. Changing gaps between cylinders the flow patterns are measured and numerically studied at a fixed comming velocity. The experiment has beeen conducted in circulating water channel with PIV system and manometer, and numerical analysis has been made by F.D.M. and multi block method. The results can be applied in the understanding and design of multiple pile array structures.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.12-21
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• 2007

As the economy grows and the population increases, we need to develop our coastal area and make use of it for various purposes. Specifically, investigation of the wave interactions on and around the vertical cylinders is very important in the design of the offshore or coastal structures. The nonlinear potential analysis developed so far, although very useful, has been found to be limited in application, as strong nonlinear waves generated by the interference between multilayered cylinders and wave impact forces by breaking waves can hardly be estimated. In this study, using a 3-Dimensional volume tracking method VOF(Volume of Fluid), based on Namer-Stokes equations, was developed to simulate highly nonlinear effects, such as breaking waves at the interface or complicated interference waves among structures. A numerical method for nonlinear interaction wave and vertical cylinders is newly proposed. The wave forces and wave transformations computed by the newly proposed numerical simulation method were compared to the other researcher's experimental results, and the results agree well. Based on the validation of this study, this numerical method is applied to the two vertical cylinders to discuss their nonlinear wave forces and wave transformations, according to the variations of separate distance of vertical cylinders.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.952-969
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• 2019

This study develops new analytical solutions to water wave diffraction by vertical truncated cylinders in the context of linear potential theory. Three typical truncated surface-piercing cylinders, a submerged bottom-standing cylinder and a submerged floating cylinder are examined. The analytical solutions utilize the multi-term Galerkin method, which is able to model the cube-root singularity of fluid velocity near the edges of the truncated cylinders by expanding the fluid velocity into a set of basis function involving the Gegenbauer polynomials. The convergence of the present analytical solution is rapid, and a few truncated numbers in the series of the basis function can yield results of six-figure accuracy for wave forces and moments. The present solutions are in good agreement with those by a higher-order BEM (boundary element method) model. Comparisons between present results and experimental results in literature and results by Froude-Krylov theory are conducted. The variation of wave forces and moments with different parameters are presented. This study not only gives a new analytical approach to wave diffraction by truncated cylinders but also provides a reliable benchmark for numerical investigations of wave diffraction by structures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.63-70
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• 1989

A numerical analysis of the wave characteristics of wave diffraction and the interference effects for a single cylinder and for two cylinders were carried out by the Boundary Element Method using constant elements. The Present investigation was limited to the diffraction of 2-dimensional linear waves by vertical impervious cylinders. Numerical model has been written to calculate the wave diffraction coefficient both on the boundary of the cylinders and at points away from it. The accuracy of the computational scheme was investigated by comparing the analytical results of the other reseraches. Good agreement was observed.

• Journal of Navigation and Port Research
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• v.36 no.7
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• pp.561-569
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• 2012

In this paper, the boundary element method is applied to solve the diffraction of waves by multiple vertical cylinders under the assumption of linear wave theory. A numerical analysis by boundary element method is based on Green's theorem and introduced to an integral equation for the fluid velocity potential around the cylinders. The numerical results obtained in this study are compared with the experimental data and the results of the theory using multiple scattering techniques. The comparisons show strong agreement. This numerical analysis method developed by using boundary element method could be used broadly for the design of various offshore structures to be constructed in coastal zones in the future.