• Journal of Ocean Engineering and Technology
• /
• v.24 no.1
• /
• pp.39-46
• /
• 2010

The calmness inside a harbor plays an important role in the appropriate disposition of harbor structures. However, it is not easy to acquire accurate computational results because these are affected by many factors concerned with wave transformation. Recently, numerical model tests, which are quicker and more economical than hydraulic model experiments, were carried out for the purpose of analyzing wave height distributions in harbors. This paper presents a numerical model that is able to calculate wave heights inside a harbor. It is based on a time-dependent mild slope involving wave refraction, diffraction, shoaling effect, and reflection. In particular, arbitrary reflectivity is used at the boundary in order to simulate the real harbor reflection condition. The proposed numerical model is applied to Samcheon new-harbor in order to investigate harbor calmness.

• Journal of Ocean Engineering and Technology
• /
• v.6 no.2
• /
• pp.94-102
• /
• 1992

This paper presents the method of numerical analysis concerned with the hydropdynamic forces and moments of the floating bodies exerted by waves. The analytic methods of hydrodynamic wave forces and moments for large volume structures are generally classified into four categories ; the strip method, the boundary element method, the finite element method, and the potential matching method. In the case of the comparatively large structures, diffraction theory can be applied. However, there are no application limits of diffraction theory which have been known concerning with the analytic method of the rectangular structures. In this paper, the two-dimensional B.E.M. is treated for a moored small rectangular structure in order to evaluate applicability of diffraction theory. Numerical calculation is carried out for the structure. The results are compared with some other ones for verification. The result shows that diffraction theory is applicable to structures smaller than 0.15 in the ratio of the representative structure length d to wave length L for rectangular ones.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.9
• /
• pp.757-763
• /
• 2013

This study discusses the multiple knife-edge diffraction loss with the receiver and jammer located in the Seoul metropolitan northwestern region. The considered positioning and jamming signals are the GPS L1 C/A signal and several jamming signals such as the wideband Gaussian noise, matched spectrum, and continuous wave signals. To calculate the accurate diffraction effects, the 3-dimensional topography data at the Seoul metropolitan northwestern region was used.

• Journal of the Society of Naval Architects of Korea
• /
• v.47 no.3
• /
• pp.369-376
• /
• 2010

In this study, a radiation and a diffraction problems of a floating body in two-layer fluids were solved by the Numerical Wave Tank(NWT) technique in the frequency domain. In two-layer fluids, two different wave modes exist and the hydrodynamic coefficients can be obtained separately for each mode. The two-domain Boundary Element Method(BEM) in the potential fluid using the whole-domain matrix scheme was used to investigate the characteristics of wave forces, added mass and damping coefficients. The effects of the ratio of density and water depth in the lower domain were also evaluated and compared with given references.

• Journal of the Korea Safety Management & Science
• /
• v.11 no.4
• /
• pp.139-145
• /
• 2009

The present study is to investigate the effect of wave-structure interaction such as wave oscillation. The theoretical method is based upon the linear diffraction theory obtained by the boundary element method. The water depth and incident wave period in fluid region are assumed to be constant. To investigate the wave interaction due to offshore structures, the numerical program has been developed and the simulation has been carried out by varying the conditions of distance and width of offshore structures. This study can effectively be utilized for safety assessment to various breakwater systems and layout of offshore breakwater in the ocean and coastal field. It can give information for the safety to construct offshore structure and revetment in coastal region.

• Journal of Korean Ophthalmic Optics Society
• /
• v.4 no.1
• /
• pp.37-43
• /
• 1999

Ocular lens failure can be verified by measuring the elastic wave velocity diffraction patterns of monochromatic wave applied with elastic wave were detected using optical heterodyne method. The elastic wave velocity was measured by analysing the diffraction patterns. According to measured results of the longitudinal elastic wave velocity of the middle index-refraction and high index-refraction lens are 6588.5575 m/s and 3973.53 m/s, respectively.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.2 no.3
• /
• pp.146-154
• /
• 2010

In the present study, the wave excitation forces acting on an array of porous circular cylinders are examined based on diffraction problems. To calculate the wave forces, the fluid domain is divided into three regions i.e. a single exterior region, N interior regions and N beneath regions, and the diffraction in each fluid region is expressed by an eigenfunction expansion method with using 3-dimension liner potential theory (Williams and Li, 2000). Especially, the present method is extended to the case of an array of truncated porous circular cylinders to calculate the heave forces as well as surge and sway forces. To verify this method, the numerical results obtained by eigenfunction are compared with these results obtained by higher order boundary element method (Choi et al., 2000). The numerical results obtained by this study are in good agreement with those results. By changing the numbers of porous circular cylinders, the angle of incident wave and the porosity rate of circular cylinders, the wave excitation forces such as surge, sway and heave on an array of truncated porous circular cylinders are investigated.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.18 no.1
• /
• pp.19-27
• /
• 1981

The surge motion of a freely-floating sphere in a regular wave is studied within the framework of a linear potential theory. The fluid is assumed to be perfect and only the steady-state harmonic motion in a water of infinite depth is considered. A velocity potential describing the fluid motion is decomposed into three parts; the incident wave potential, the diffraction potential and the radiation potential. In this paper the diffraction potential and the radiation potential are analysed by using multipole expansion method. Upon calculating pressures over the immersed surface of the sphere, the hydrodynamic forces are evaluated in terms of Froude-Krylov, diffraction, added mass and damping forces as functions of the frequency of the incident wave. Finally the frequency dependence of two pertinent parameters, the amplitude ratio and the phase lag between the motion of the sphere and that of the incident wave is derived from the equation of motion. As for numerical results the general tendency of the present calculation shows good agreement with Kim's work who also treated this problem utilizing the Green's function method.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.6
• /
• pp.397-407
• /
• 2016

The traveling waves of the left and right of the detached breakwater are bent behind the detached breakwater by diffraction, causing phase interference, superimposed and propagated. If the direction of the waves becomes same and they head to the entrance of a port due to the geographical conditions, superimposed wave energy could influence inside of a port. In this study, we investigated the influence of the phase difference of the left and right diffraction waves generated according to the length of the detached breakwater on the wave heights in a port through numerical experiments when the detached breakwater at a port entrance is installed. From this result, it was confirmed that the wave heights in a port is increased or decreased by the influence of superimposed caused by the phase difference of the left and right diffraction waves due to the length of the detached breakwater.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.6
• /
• pp.349-356
• /
• 2013

The purpose of this study is to review and overcome the limits of the existing design wave model applied to such waters as those located inside bays or near islands where the impact of wind influenced waves are more dominant, due to the nature of topographic isolation, than the influence of direct waves coming from the open sea. Although the existing model for an inside bay design wave is excellent for considering wind factors and very adaptable to topographically complicated areas compared to other models, it is difficult to show the wave diffractions and reflections caused by large scale structures or topographic features in the region. The study examined the various methods capable of taking into account wave diffraction, the angle of wave reflection, and changes in water depth. As a result of applying the modified design wave model to the target situation (inside bay or near island areas), it was found that the reliability of the design wave height around marine structures was improved, compared to the existing models. Therefore, it is fair to predict that the new model could provide more accurate design waves in the design of marine structures.