Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Calculations of Pressure Fluctuations on the Ship Hull Induced by Intermittently Cavitating Propellers
Calculations of Pressure Fluctuations on the Ship Hull Induced by Intermittently Cavitating Propellers
Pages 882-897
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From page 882... ...
MIT-PUF-3A is then used to analyze the unsteady flow around propellers in the effective wake, and to compute the propeller induced potentials on the hull surface. Finally, a potential based higher order panel method is used to calculate the flow around 882
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From page 883... ...
In this panel method, a quadratic dipole distribution is distributed over each panel on the body surface, and an internal Dirichlet boundary condition is imposed at the control point of each panel. The pressure fluctuations on the hull surface can then be calculated from solutions of the dipole strength by applying Bernoulli's equation.
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From page 884... ...
are used for this fitting process by the least squares method. By introducing this quadratic dipole strength into the governing equation, and calculating the induced potentials, a linear system is finally obtained for the solutions of the dipole strength at the control point of each panel.
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From page 885... ...
We have discussed how ship hulls are modeled by a higher order panel method in the last section, and we will briefly introduce how PUF-3A simulates propeller erects. 3.1 Calculation of the Effective Wake When we calculate the flow field around propellers, a ship model wake measured in the towing tank is usually used to be the inflow.
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From page 886... ...
Therefore, the Fourier coefficients of the velocities can be obtained. Figure 7 and Figure ~ show the nominal wake measured in the towing tank and the effective wake calculated by PUF-3A of an 1100 TEU container ship built by CSBC (China Ship Building Corporation)
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From page 887... ...
4 Propeller Generated Pressure Fluctuations The calculations of the propeller generated pressure fluctuations include the considerations of the ship hull, propellers and the water surface (free surface.~. As described in the last two sections, the solutions of the ship hull problems can be obtained by a panel method.
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From page 888... ...
On the other words, for each panel on the hull surface, the total induced potentials include these from the hull, from the image hull, from the propeller, and from the image propeller. Therefore, if we define the propeller induced potentials as jpr, then the solutions of the dipole strength on the hull surface panels can be obtained by solving the following equation: 41r J/ '\~6)
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From page 889... ...
Computational Results In this section, we will show computational results from the present method. 5.l Pressure Fluctuations on a Flat Plate Generated by Propellers The calculations of propellers generated pressure fluctuations on a flat plate are similar to those of propellers generated pressure fluctuations on ship hulls.
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From page 890... ...
Figure 16 shows the nominal wake, and Figure 17 shows the calculated effective wake, and the model mean elective wake coefficient we calculate is 0.35. It is larger than the full-scale mean effective wake coefficient, 0.29 t2]
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From page 891... ...
Figure 20 shows the contour plot of up at the blade frequency for zero-frequency free surface (rigid surface) , and Figure 21 shows the contour plot of Kp at the blade frequency for highfrequency free surface.
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From page 892... ...
The differences between the rigid surface results and the high-frequency free surface results are larger than those of Gage 3, and it is because that the free surface effect is strong at these two points. The computational results of twice blade 892 Q12 311 Q10 QO9 QO9 Q07 Q06 QOS Q04 ~3 Q03 Q02 QO1 0.00
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From page 893... ...
Amplitudes Meas'd/Calc'd Free Free I Rigid Free I Rigid Rigid Blade Frequency 0.165 0.254 0.282 0.650 0.585 0.901 0.105 0.082 0.117 1.280 0.897 0.701 0.069 0.054 0.090 1.278 0.767 0.600 Twice Blade Frequency 0.065 0.128 0.146 0.508 0.445 0.877 0.024 0.040 0.054 0.600 0.445 0.741 0.016 0.020 0.038 0.800 0.421 0.526 ~ "G" is the gage numbers frequency Up are all larger than the measured values, and this is because the calculated cavitation extensions are larger than those of model tests. 6 Conclusions In this paper, the flow field around a ship hull and its propeller is solved by coupling a higher order potential based panel method and a lifting surface vortex lattice method.
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From page 894... ...
A higher order panel method for general analysis and design applications in subsonic flow. In Proceedings of fifth International Conference on Numerical Methods in Fluid Dynamics, Springer Verlag, 1976.
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From page 895... ...
The I and H integrals are defined in Johnson t7~. The internal Dirichlet boundary condition specifies the total internal potential to be zero, and (foo~i = VOO Ri (31)
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From page 896... ...
Therefore, the dipole strength coefficients can be obtained from equation (29) , and the dipole strength distribution at each panel can be calculated by equation (23~.
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From page 897... ...
This is apparently because the ship hull is modeled differently by two methods. Anyhow, we have to point out that the computations of the effective wake distributions in the present paper are rough due to the simplicity of the model.
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