Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Planing Hull Performance Evaluation Using a General Purpose CFD Code
Planing Hull Performance Evaluation Using a General Purpose CFD Code
Pages 640-654
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From page 640... ...
Planing hulls rise and change trim angle in response to the pressure field generated by the flow. In order to solve for these changes in hull position, the simulation method had to ensure that dynamic equilibrium was achieved in terms of lift and trimming moment.
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From page 641... ...
PHYSICAL MODEL TESTS The physical model experiments were performed in the Clearwater Towing Tank at the National Research Council of Canada's Institute for Marine Dynamics and consisted of a series of resistance tests with a planing craft. Tests covered several ballast 2
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From page 642... ...
It includes several turbulence models and supports fully unstructured hybrid adaptive meshes. Though later used to solve for the dynamic equilibrium position of the hull at speed, the code was first tested to see if it could simulate the flow around a planing hull in general.
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From page 643... ...
The requirements for dynamic equilibrium for the planing hull evaluated in step (7) were that the net flow-induced vertical force must equal the weight of the model, and that the net trimming moment (taken about the tow point)
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From page 644... ...
No Figure 5: Flowchart for Equilibrium Program 0-DEGREE OF FREEDOM RESULTS This section presents the results of CFD simulations where the orientation of the hull was set to match those determined from the physical experiments for each speed (shown in Figure 6~. These tests were used to directly compare the experimental and computational results for the planing hull model.
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From page 645... ...
1 1 6.0 7.0 8.0 Several pressure taps were used in the physical experiments to determine hull pressures at speed. Comparing these results to the CFD simulations gave some indication as to where computed pressures were being over-predicted.
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From page 646... ...
However, the simulations significantly over predicted the net pressure force, suggesting that velocities were indeed being under predicted in the aft region. The results from the zero degree of freedom simulations were found to follow the trends expected for a planing hull, although net pressure was over predicted.
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From page 647... ...
The numerical pressure resistance was computed by directly integrating the pressure forces over the hull area. The results for the 1-degree of freedom CFD simulations closely match those from the experimental results, despite the differences in linkage, wetted area and fictional resistance.
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From page 648... ...
The numerical simulation at 3.0 m/s had a water contact area that still satisfied the 'flat plate' model and therefore had a pressure drag matching the theoretical value. In the physical experiments at this speed, the model was slightly lower in the water and the contact area included a region of the hull hat began sloping upward towards the bow.
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From page 649... ...
In general, the computed flow was qualitatively consistent with experimental observations of planing hull flow, but actual values tended to deviate from the physical data. 2-DEGREES OF FREEDOM RESULTS The last set of simulations involved solving for dynamic equilibrium of the steady state motion of a planing hull through calm water.
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From page 650... ...
, provided the wetted lengths supported the flat plate assumption (Figure 19~. The reduction in values, shown in Figure 26, demonstrates the importance of trim angle when predicting planing vessel performance.
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From page 651... ...
Although the VOF free surface capturing method does allow for fluid to be ejected from the near hull above the free surface, it was not necessarily equivalent to the spray produced in the physical experiments. This phenomena may need to be modeled in future simulations.
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From page 652... ...
Ikeda Y., Yokomizo K., Hamasaki J., Umeda N., Katayama T., "Simulation of Running Attitude and Resistance of a High Speed Craft Using a Database of Hydrodynamic Forces Obtained by Fully Captive Model Experiments", FAST '93~ 2n~ International Conference on Fast Sea Transportation 1993. Lewis E.V (ed.)
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From page 653... ...
It was also determined in our study that the CFD simulations were over predicting the net pressure force on the hull, which contradicts the premise that the computed pressures were too low. Another consideration was raised when the computed peak pressure coefficients, though independent of speed, were found to be dependent on trim angle as shown in Figure 24.
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From page 654... ...
Figure 28: Free Surface at Centerline Plane Figure 29: Free Surface Contours ~ . Figure 30: Wave Profiles from Physical Experiments ~ ._ ~~ ~~_ , s HIT ~ — I ..
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