Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Basic Studies of Water on Deck
Basic Studies of Water on Deck
Pages 126-142
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From page 126... ...
In particular, the unsteady interaction between free surface and ship is analyzed by solving the inviscid two-dimensional fully nonlinear problem numerically. Both water on deck resembling dam breaking as well as due to plunging waves are investigated.
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From page 127... ...
Clearly, figure 1.C, three-dimensional effects are relevant, though less than for cases with forward speed. In the latter, the steady wave pattern is characterized by an increase of the water level due to a local disturbance and bow waves generation which by themselves decrease the effective freeboard, non uniformly along the longitudinal ship direction (Turin & Wu 19961.
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From page 128... ...
Along the free surface and the impermeable boundaries, the following kinematic constraint applies 0~ ~ At, VP ~ OFFS U ~QBO (2) where VHQFB is the displacement velocity of the surface, and r' is the unit normal vector, pointing out of the fluid domain.
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From page 129... ...
The collocation points are taken at the edges of each element, resulting in a continuous distribution of the velocity potential along the free surface. The tangential velocity 0,o/~ is simply determined by finite difference operators, while the normal velocity component is obtained from the integral equations.
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From page 130... ...
The following analysis is for the first water on deck occurrence caused by incident waves with wavelength A/L = 0.75 and height H/A = 0.09. Top plot of figure 5 shows the free surface just after the start of the water shipping and during the later evolution, after the impact with the superstructure.
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From page 131... ...
When the number of shipping events increases, the local wave steepness in the bow region decreases and in this case the resulting amount of water wetting the deck reduces, as well as the propagating flow velocity. Effect of main geometric parameters A simplified parametric analysis of the deck wetness can be made taking the amount of shipped water, Q
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From page 132... ...
~ = 0 H// -a 0.032 -a 0.064 ~ 0.095 deck wetness severity changes a lot from case to case, though the nonlinearities associated with the incoming waves are the same. In particular, the worst conditions occur for large wavelength-to-draft ratios, for which a weaker wave reflection is observed, and which are also the more interesting from a practical point of view.
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From page 133... ...
11. For each event, free surface configurations are plotted for the maximum freeboard exceedance (circles)
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From page 134... ...
to/T 10.626 10.783 10.783 10.783 10.783 twod /T 10.795 10.841 10.844 10.795 10.790 10.783 10.777 summary of cases In figure 13, restrained body conditions are considered, and some free surface configurations are presented. The wave, reaching the bow, is steep and unsymmetric but its tendency to break is reduced during the run-up along the bow.
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From page 135... ...
By 'instantaneous freeboard' we consider the mean freeboard plus the change in vertical position due to heave. The upwards motion of the bow causes lower trough ahead of the breaking wave and a bow impact occurs.
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From page 136... ...
The analysis here considered is not complete and therefore no conclusive statement about the occurrence of the plunging wave event can be given. However, in the cases so far studied, the run-up along the bow eventually caused the more common dam breaking type of event.
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From page 137... ...
Right plots of figure 20 present the pressure distributions corresponding to the free surfaces configurations on the left. According to the numerical results (solid lines)
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From page 138... ...
For longer time, the pressure distributions seem to diverge faster than the free surface elevations. As can be expected, in the "exact" computations, the max imum pressure decreases while in the zero gravity case remains constant.
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From page 139... ...
In particular they suggest a hump in the free surface close to the contact point. This is not visible in the dam breaking free surface profiles in Dressier (1954)
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From page 140... ...
The relative amount of shipped water depends nonlinearly on Hi/. - For small A/L, where L is ship length, the bow wave reflection reduces or prevents the shipping of water, even for large wave steepnesses.
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From page 141... ...
"A B-Spline based BEM for unsteady free surface flows".
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From page 142... ...
CC Mel, The Applied Dynamics of Ocem Surface Waves Singapme: World Scientific (1933) , pp 740 DISCUSSION D 1; P Yue Massachusetts institute of Tech olo a, USA For both long md short waves, She mthors find that stronger wave reflection by She ship ceases less shipping of water on deck In general, one would expect that stronger wave reflection leads to larger local wave height which produces more water on deck according to the dambrecking theory Whet c mses f is co flint?
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