Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Water Shipping on a Vessel in Head Waves
Water Shipping on a Vessel in Head Waves
Pages 393-412
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From page 393... ...
Near the fore portion of the deck, the local ship geometry affects shape and complexity of the cavity evolution, always characterized by free-surface breaking and dispersion of bubbles in the main water field. To deal with this flow conditions, we present a Domain Decomposition (DD)
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From page 394... ...
During the tests, a restrained nearly rectangular ship model was exposed to head-sea waves generated by a flap wavemaker in a small wave flume. We discovered that water on deck starts in the form of a very localized plunging wave that breaks onto the deck, close to the bow.
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From page 395... ...
The flow evolution was monitored through a black/white video camera with a frame rate of 30 Hz. The video camera was placed inside the ship model and directed towards a mirror parallel to the ship deck and located onto the internal bottom of the model, as shown in the bottom sketch of figure 2.
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From page 396... ...
Right: example of time history of the wave elevation at the location along the tank where the focusing phenomenon occurs, without the ship model present. are two-dimensional but the wave field in the vicinity of the ship will be three-dimensional due to the scattering of the incident waves.
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From page 397... ...
There, the plunging waves from the two sides of the bow interact with each other and with the flow entering the deck along the ship centerline. The water fronts coming from the two ship edges interact along the ship center plane, and are reflected outwards leaving laterally the deck.
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From page 398... ...
, bottom view. Enlarged view of the flow region near the ship centerline at the time instant show n in third plot of figure 8.
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From page 399... ...
shipping, the second water on deck could be strongly affected by the modifications in the wave field around the ship bow due to the water-off-deck phenomenon associated with the previous event. Steepness influence on the water shipping Figure 13 shows snapshots of the water along the deck after the collapse of the cavities associated with wateron-deck events due to wave packets with ~ = 4.33 m and ha = 0.125, 0.15, 0.175, 0.2 and 0.225, respectively (cases a-e)
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From page 400... ...
In the plots, the water enters the deck from the bottom and the fore portion of the ship deck is represented by the straight lines forming an angle of about hundred degrees. The time interval between two water-front configurations is equal to the frame rate of the video camera (1/30 s)
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From page 401... ...
In this way, the advantages of the BEM method can be combined with the capabilities of a field method. In particular, the latter will be used to describe the flow evolution in proximity of the ship bow and on the ship deck.
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From page 402... ...
, while the BEM solution gives the velocity distribution required by the field method along the VOF boundary. In the numerical implementation, the time step is governed by the stability constraints of the field method, more stringent than those requested by the free-surface evolution in the BEM domain, where a standard fourthorder Runge-Kutta method is adopted.
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From page 403... ...
, a Lagrangian meshless field method, Tulin and Landrini (2000) , as the comparison for the two latest time instants confirms (ci figure 19, ct Colicchio et al.
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From page 404... ...
Soon after, the water fronts move inwards, and meet each other along the ship centerplane, giving rise to a vertical splash up, eventually reversing outwards. In the meanwhile, the cavities are stretched and finally broken into bubbles of variable size.
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From page 405... ...
"Unsteady Free Surface Waves by Domain Decomposition Approach".
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From page 406... ...
2. Quarteroni, A., and Valli, A., Domain Decomposition Methods for Partial Differential Equations Oxford Science Publications 1999.
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From page 407... ...
O,04 0,03 0,02 0,01 0,00 -0,01 -0,02 -0,03 -0,04 0,10 0,08 0,06 E 0~04 0,02 0,00 -0,02 -0,0d 0,12 0,10 0,08 _ O,06 E 0,04 O,02 O,OO -O,02 -O,04 O,10 O,08 O,06 O,04 0,02 0,00 -0,02 -0,04 0,08 0,06 0,04 E 0,02 0,00 -0,02 -0,04 -0,06 0,08 0,06 0,04 0,02 E 0,OO -0,02 -0,04 -O,06 -O,08 _ o _ 1N (i =' 0 5 10 15 20 25 30 35 40 ,^ x=24.04m o 1C 1 1 '` .? ` ~ 5 10 -~ ~E t 25 30 35 40 0 5 10 15 20 25 30 30 44 m _ 10 15 x = 37.04m ~'~ ~ f`\/ -qll ~ V~ 1 1 1 ~ 1 1 l l 5 10 15 20 25 40 20 25 30 35 40 Figure 11: Records of wave elevation at 6 different wave-probe locations for an initially harmonic wave of period 2.525 s and amplitude 0.029 m propagating over an uneven bottom (see Figure 12)
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From page 408... ...
and Garner, J.: "Seabed modifications to prevent wake wash from fast ferries," Proceedings of the RINA International Conference on Coastal Ships and Inland Waterways, London, 1999. Henn, R., Sharma, S
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From page 409... ...
and Grollius, W.: "Fast vessels on inland waterways," Proceedings of the RINA International Conference on Coastal Ships and Inland Waterways, London, 1999.
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From page 410... ...
However, we would emphasize again our statement that due to the nonlinear and unsteady nature of ship waves in shallow water the linear theory remains to be a restricted approximation. Furthermore, it should be clarified that the vertical distribution of the transversal velocity components is explicitly described as an analytical function of the averaged horizontal velocity in the Boussinesq's shallow-water theory.
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From page 411... ...
In the present work, a 'slender-body' type condition is used: the passage of the ship imposes a lateral velocity distribution, which is averaged over the entire water depth. This is consistent with Boussinesq theory; but intuitively one would expect that this is less accurate for higher water depth / draught ratio's.
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From page 412... ...
In the present work, a 'slender-body' type condition is used: the passage of the ship imposes a lateral velocity distribution, which is averaged over the entire water depth. This is consistent with Boussinesq theory; but intuitively one would expect that this is less accurate for higher water depth / draught ratio's.
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