Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Towards the Simulation of Seakeeping and Manoeuvering Based on the Computation of the Free Surface Viscous Ship Flow
Towards the Simulation of Seakeeping and Manoeuvering Based on the Computation of the Free Surface Viscous Ship Flow
Pages 268-281
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From page 268... ...
Vogt (Hamburg Ship Model Basin, Germany) ABSTRACT The simulation of ship motions due to rudder manoeuvres and/or to incoming waves based on free surface viscous flow computations will be one of the most fascinating challenges in ship hydrodynamics for the coming years.
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From page 269... ...
The elements of the rows of T are the components of the earth fixed unit vectors expressed in the ship fixed system. Motion equations of the ship The motion of the assumed rigid ship is described by the momentum and the moment of momentum equations.
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From page 270... ...
+ Np The directional cosine of the gravity force, in the ship fixed coordinate system, costar, i = 1, 2, 3 coincide with the components of the earth fixed basis vector K and as such, with the elements of the third row of the transformation matrix T By integrating the pressure and shear stresses on the hull we get the hydrodynamic forces Fish, Fyh' Fzh and moments Kh, Mh, Nh in Eqn.
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From page 271... ...
t114. Among the first ship hydrodynamics related applications of the Level Set method was reported in t133.
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From page 272... ...
Because of the very intensive computational time, fine grid computations have been restricted to the model fixed condition till now. NUMERICAL METHOD The mathematical model described in the previous section was implemented by the authors in the RANSE code Neptun in the course of several research projects.
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From page 273... ...
and the undisturbed velocity field (red) in the water plane of a twin rudder RoRo ship in steady turning The computed vector field at the waterplane of the twin rudder FSG RoRo ship in steady turn ing (black)
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From page 274... ...
of the computation Fig.6 shows the result of the reinitialization at a cross section of the KRISO container ship mentioned before, moving straight ahead in calm water. On the left hand side of the figure, the initial o distribution is shown.
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From page 275... ...
Uw, Vw and Ww are the earth fixed velocity components in the generated incoming waves. The values at the inlet boundary consist of two parts, the contribution from the rigid motion of the ship fixed coordinate system and the absolut values in the far field.
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From page 276... ...
Non-dimensional time steps of the order 0.001 and 3 to 5 SIMPLE iterations were sufficient for achieving the very satisfactory results obtained. APPLICATIONS The method described in the previous sections has first been used to calculate the flow around ship models moving steadily straight ahead against incoming waves.
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From page 277... ...
.~ ... 5 ~ 5 ~ ~-3——__= ~ + ~,;~ ~-.3-~ A= -= ~ I =, —;, ..~ ~ I.= ~ ~~ :::— .—:::,—~ .—: _ ~=.~ :-~ >3 += — zest (~ ~~:-~,-:~ .~P~:~ Figure 13: Wall shear stress field at the hull of the C-Box container ship in head waves computed on the coarse and on the fine grid container ship has got a relatively large block coeflicient CB = 0.74 and was not provided with a bulbous bow.
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From page 278... ...
The predictions of forces and moments on the hull of this twin screw, twin rudder ship model are compared with experimental data obtained with the Computarized Planar Motion Carriage (CPMC) in the towing tank of the Hamburg Ship Model Basin.
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From page 279... ...
Comparison of a snapshot of the simulation on the fine grid with a photo of the model test The flow features at the fore body of the RoRo ship turning with constant yaw rate r'=0.4 and drift angle p=10°, which represents a realistic situation, look very similar to those of a ship in straight motion. Because the bow shows towards the center of the circle, the local drift angle at the bow is practically zero.
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From page 280... ...
1 -. ~ : ~ - 1 3 1.5 1 5 o -A t Figure 21: Comparison of measured and computed non-dimensional yaw moment on the FSG RoRo ship for different yaw/drift combinations Figure 20: Comparison of measured and computed non-dimensional side force on the FSG RoRo ship for different yaw/drift combinations Figure 22: Stern of the model of the FSG RoRo ship with rudders and propellers, shafts and Vbrackets
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From page 281... ...
(1998) , "A Numerical Investigation of the Level Set Method for Computing Free Surface Waves", Licensiate Thesis at Chalmers University of Technology, Gothenburg, Sweden [14]
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