### WAVE FORCE ON A VESSEL TIED AT OFFSHORE DOLPHINS

#### Abstract

The solution of wave scattering by a vertical elliptical cylinder is

applied to calculate the wave forces exerted upon it. The wave forces in

the directions of long and short axes of ellipsis are shown in nondimensional

forms as the functions of the angle of wave approach, the diameter-to-wavelength

ratio, and the aspect ratio of ellipsis. The results of wave force computed

are also shown in terms of the virtual mass coefficients associated with the

reference volume of the circular cylinder the diameter of which is approximately

equal to the apparent width of the elliptical cylinder observed from the direction

of wave approach.

Theory is further applied for the wave forces acting upon a vessel moored

tight at offshore dolphins and the forces transmitted to the dolphins through

the vessel. The vessel is approximated with the fixed elliptical cylinder

having the same width-to-length ratio. The computation with directional wave

spectra shows that a tanker of 200,000 D.W.T. may exert the force of about

1,400 tons at the one-third maximum amplitude to each breasting dolphin when

the tanker is exposed to the incident waves of H,/„=1.0m and T» / =10 sec from

the broadside.

applied to calculate the wave forces exerted upon it. The wave forces in

the directions of long and short axes of ellipsis are shown in nondimensional

forms as the functions of the angle of wave approach, the diameter-to-wavelength

ratio, and the aspect ratio of ellipsis. The results of wave force computed

are also shown in terms of the virtual mass coefficients associated with the

reference volume of the circular cylinder the diameter of which is approximately

equal to the apparent width of the elliptical cylinder observed from the direction

of wave approach.

Theory is further applied for the wave forces acting upon a vessel moored

tight at offshore dolphins and the forces transmitted to the dolphins through

the vessel. The vessel is approximated with the fixed elliptical cylinder

having the same width-to-length ratio. The computation with directional wave

spectra shows that a tanker of 200,000 D.W.T. may exert the force of about

1,400 tons at the one-third maximum amplitude to each breasting dolphin when

the tanker is exposed to the incident waves of H,/„=1.0m and T» / =10 sec from

the broadside.

#### Keywords

wave forces; vessel; dolphin; offshore dolphin

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