• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.439-445
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• 2017

Plunging breaker slamming pressures on vertical or sloping sea dikes are one of the most severe and dangerous loads that sea dike structures can suffer. Many studies have investigated the impact forces caused by breaking waves for maritime structures including sea dikes and most predictions of the breaker forces are based on empirical or semi-empirical formulae calibrated from laboratory experiments. However, the wave breaking mechanism is complex and more research efforts are still needed to improve the accuracy in predicting breaker forces. This study proposes a semi-empirical formula, which is based on impulse-momentum relation, to calculate the slamming pressure due to plunging wave breaking on a sloping sea dike. Compared with some measured slamming pressure data in two literature, the calculation results by the new formula show reasonable agreements. Also, by analysing probability distribution function of wave heights, the proposed formula can be converted into a probabilistic expression form for convenience only.

• Journal of Ocean Engineering and Technology
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• v.30 no.3
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• pp.151-160
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• 2016

The diffraction and radiation of linear waves by an array of truncated floating multiple buoys are solved using the interaction theory based on a matched eigenfunction expansion method (MEEM). The interaction processes between multiple buoys are very complex and numerous, because the scattered and radiated waves from each buoy affect the others in the array. Our primary aim is therefore to construct the rigorous wave exciting forces and hydrodynamic forces to deal with the problem of multiple interactions. This present method is applied to a square array of four buoys with two incidence angles, and the results are given for the wave excitation forces on each buoy, heave RAO for each buoy heaving independently, and wave elevations around the buoys and wave run-up. The analytical solutions are in good agreement with the numerical solutions obtained from commercial code (WAMIT).

• Water for future
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• v.27 no.4
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• pp.155-160
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• 1994

External foces acting on a pipe bend change when a transient pressure wave propagates through the bend. Analytical expressions are derived to compute the changes of these forces when the instantaneous pressure wave passes through the bends. This analysis reveals that these forces depend mainly on static pressure rather than fluid momentum. The analysis also reveals that the change of the vertical component of the force acting on a pipe bend with an angle larger than 90$^{\circ}$ may reverse in direction during the passage of a pressure wave through the bend.

• Journal of Ocean Engineering and Technology
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• v.14 no.4
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• pp.1-8
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• 2000

The time simulation of motion responses of dolphin-moored BMP in waves is presented. The equation of motion based on Cummin's theory of impulse responses are employed, and solved in time domain by using the Newmark $\beta$ method. The hydrodynamic coefficient and first order wave exciting forces involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The second order wave drift forces and mooring for dolphin system are taken into account. As for numerical example, time domain analysis are carried out for a BMP in irregular wave condition.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.3
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• pp.1-9
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• 1986

Herein the dynamic response of an axisymmetric buoy to regular wave is studied within linear potential theory. The buoy has a particular geometry so that it should experience minimum wave-exiting force on the vertical direction at a precribed wave number in water of finite depth. Invoking the Green's theorem a velocity potential is generated by distributing pulsating sources and doublets on the immersed surface of the buoy at its mean position. Hydrodynamic forces and moments are obtained approximately by summation of the products of linear pressure and directional mesh area over the immersed surface. Model tests are carried out to measure the wave-exciting forces, hydrodynamic forces and motion responses. The experimental results in general agree fairly well with the numerical ones. From the analytical and experimental works it is found that the pitching motion and its coupling effect affect significantly the motion characteristics of the freely-floating axisymmetric buoy in regular waves.

• Proceedings of KOSOMES biannual meeting
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• 2003.11a
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• pp.149-153
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• 2003

The hydrodynamic forces acting on the submerged plate are composed of diffraction and radiation forces. Thus we have carried out the extensive experiments and numerical simulations to make clear the characteristics of the diffraction and radiation forces on the submerged plate. These experimental results are compared with the numerical ones, and we discuss the effect of nonlinear on the hydrodynamic forces acting on the submerged plate. As a result, we get the conclusion that the submerged plate is useful for reducing the wave exciting forces on the structure behind the submerged plate.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.3
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• pp.141-148
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• 1999

The magnitude of breaking wave forces given by plunging breakers incident on a pile structure is much greater than the forces calculated by Morison's formula, but those forces may act on pile for very short duration in the range of a few multiples of 0.01 second. Hence, a dynamic analysis for the impact forces of breaking waves may be necessary for the accurate determination of pile displacements in the first stage of design. The time series of the impact force along the pile length is thus required, which may be estimated from the pressure distribution. In the present study, breaking wave pressures are measured for a vertical pile at real field which is easily subjected to plunging breakers in stormy weather conditions. The measured data are analyzed and compared with other results to quantify the characteristics of breaking wave pressures in real fields.

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.9-15
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• 2013

This paper calculates the mating dynamic forces of a semi-submersible offshore structure's topside module, where a hull moored in the sea is combined with a topside module carried by a heavy lift vessel, as a mating installation method. The environmental conditions include various wave directions and wave heights, with constant wind and current speeds. Appropriate ballast and de-ballast plans for the heavy lift vessel and hull of the semi-rig should be performed in order to safely obtain these forces, whereas a fixed platform or the GBS (Gravity based structure) type of offshore structure only needs a ballast plan for the heavy lift vessel. From this paper, the allowable wave height or wave direction for the mating procedure can be investigated based on the standard DAF (Dynamic amplitude factor) of the rules and regulations.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.33-42
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• 1998

In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.2
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• pp.150-158
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• 2011

Present study aims to investigate the influence of relative breakwater width W/L (W=width of breakwater, L=wavelength), wave steepness $H_i/gT^2$ (Hi=incident wave height, T=wave period) and relative wave height d/W (d=water depth) on forces in the moorings of horizontal interlaced multi-layered moored floating pipe breakwater (HIMMFPB) model. Studies were conducted on scaled down physical models having three layers of Poly Vinyl Chloride (PVC) pipes, wave steepness $H_i/gT^2$ varying from 0.063 to 0.849, relative width W/L varying from 0.4 to 2.65 and relative spacing S/D=2 (S=horizontal centre-to-centre spacing of pipes, D=diameter of pipes). Peak mooring forces were also measured and data collected is analyzed by plotting non-dimensional graphs depicting variation of $f_s/{\gamma}W^2$ ($f_s$=Sea side Mooring force, ${\gamma}$=specific weight of water) & $f_l/{\gamma}W^2$ ($f_l$=Lee side Mooring force) with $H_i/gT^2$ for d/W varying from 0.082 to 0.276 and also variation of $f_s/{\gamma}W^2$ and $f_l/{\gamma}W^2$ with W/L for $H_i$/d varying from 0.06 to 0.400.