Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
Currently Skimming:
A Hybrid Approach to Capture Free-Surface and Viscous Effects for a Ship in a Channel
A Hybrid Approach to Capture Free-Surface and Viscous Effects for a Ship in a Channel
Pages 743-755
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From page 743... ...
An integrated propeller model interacts automatically with the R ANSE computations. Results for flow details agree well with experiments for deep water and reproduce qualitatively all influences of the shallow water.
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From page 744... ...
The nonlinear free surface bound a~y condition is met in an iterative scheme that fin earizes differences from arbitrary approximations of the potential and the wave elevation, Fig.1, [12~. The radiation and open-boundary conditions are enforced by shifting sources versus collocation points on the free surface.
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From page 745... ...
The distribution obtained by this method depends on the propeller inflow and has to determined by art iterative procedure: 1) Solve the RANSE for the ship without pros pelter Calculate the wake distribution at the propeller plane Define the required propeller thrust es ship ret sistance minus corrective towing force Calculate the propeller force distribution using a propeller program with inflow alla required thrust (as computed above)
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From page 747... ...
i. ~ t~ ~ ~ ~ ~ ~ ~ ~ ~ — - = ~ — ~ ~ — ~ ~ ~ : ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ -- ~ Fig.4b: Detail of RANSE grid at aftbody I_==== ~-t ~ I I I ~ ~ l l -- -- - 1 -- J - l- ~ ~ , ~ ~ ~ ~ ~ ~ I .
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From page 748... ...
for Series 60 at F" = 0.15 experunent RSM h/T ~T/L ~ ~ ~T/L ~ ~ 3.2 0.00118 0.00050 ~ 0.00120 0.00040 1.5 0.00285 0.00083 0.00269 0.00087 AN = 0.16 experiment h/T aT/L 3;2 0.00139 0.00058 1.S 0.00348 0.00116 RSM ~T/L 0.00135 0.00051 _ 0.00326 0.001Q7 The pressure at the channel bottom is dominated by free surface effects, namely the primary slave system with its long wave trough along the ship lengths. Towards the ends, the pressure at the channel bottom shows local maxima.
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From page 749... ...
The strong wave trough for shallow water such a slender hull, it 'should not have such a large gives an additional blockage effect over the central impact on the contour lines. Cura uses a different part of the ship that leads to higher velocities and turbulence model and his results are quite similar to lower pressures.
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From page 750... ...
Fig.8. Contour lines of the axial velocity Duo at 5%L before AP, If" = 0.18, fin = 8~4 104 h/T—3.2 (left)
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From page 751... ...
AP AP .~ ~a,, 0.1 · -— _. Fig.11: Pressure distribution for propulsion test, Fn = 0.16, .
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From page 752... ...
disagreement bee tentisl flow code may be already sufficient for cases tween computed alla measured contour lines is sim- where only the pressure on the channel bottom is of liar to the resistance test. Fig.ll shows the cam- interest.
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From page 753... ...
(1993) , "A numerj.cal calculation of free surface potential flow field and of ship wave resistance in shallow water by fully nonlinear wave theory," Ad Japan Korea Workshop, Osaka, pp.
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From page 754... ...
In advanced RANSE procedures, the trim and sinkage at the latest iteration are included in the next calculation. Even though He authors' RANSE free surface grid does not seem to follow or express the local depression of mean free surface around the midship region.
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From page 755... ...
As the problem of insufficient resistance prediction is shared by many other colleagues, it appears that we will need considerable more shared research worldwide before we see consistently accurate resistance predictions for real ship geometries, especially for the more complicated shallow-water hydrodynamics. The propulsion test simulations predicted trim and sinkage using the RSM without propeller action, i.e., the same trim and sinkage as for the resistance test.
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