Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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A Panel-Free Method for Time-Domain Analysis
A Panel-Free Method for Time-Domain Analysis
Pages 963-976
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From page 963... ...
It allows evaluation of preliminary designs or ship performance at a relatively low cost compared with experimental tests. Strip theory was applied as the first analytical ship motion theory for computations and has been used as a practical prediction method, but it gives unsatisfactory predictions at low frequencies and at high forward speeds, and it is not applicable to ships of low length-beam ratios due to its 1 slender body assumptions.
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From page 964... ...
They applied the panel-free method to the radiation and the diffraction problems of a hemisphere. Computed response functions, added mass and damping coefficients showed excellent agreement with published results by the analytical solution and the panel method.
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is the source distribution on Sb which makes the body surface an equipotential surface of potential on and satisfies the homogeneous integral equation )
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n j=1 r=1 s=1 Np Nj Mj rs rs F(P, Qj; t)
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Figure 2 shows the computed heave and pitch response functions at a time step dt = 0.25s using 6x21 and 6x25 Gaussian points on the hull represented by NURBS surfaces. In order to investigate the convergence of the computation, lOx30 Gaussian points were also applied on the analytically represented surface.
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The computed radiation and diffraction response functions, hydrodynamic coefficients and wave exciting forces for the Wigley hull agree well with published results. The oscillatory error of the memory function at large time tends to be reduced by PFM in comparison with the panel method.
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(1985~. Seakeeping Computations Using Time Domain Analysis.
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\ I PFM (analy.,lOx30) 1 \ ~ ==~ -2 0 1 2 3 4 5 6 Nondimensional time Figure 2: Heave and pitch radiation force response functions for a Wigley hull 8
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~ | ~ \ 1 , 0 2 4 6 8 10 12 14 16 Nondimensional frequency Figure 3: Heave and pitch added mass for a Wigley hull 9
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. O :z 4 ~ A r TO 12 Nondimensional frequency Figure 4: Heave and pitch damping coefficients for a Wigley hull 10 14 16
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n j=1 r=1 s=1 Np Nj Mj rs rs F(P, Qj; t)
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King (1987) Strip theory i''/ ,, -200 ~ ~ ~ ~ _ 0 2 4 6 kL 10 14 10 12 14 Figure 6: Heave wave exciting forces and phases for a Wigley hull 12
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. 2 4 6 8 kL 10 12 14 Figure 7: Pitch wave exciting forces and phases for a Wigley hull 13
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AUTHORS' REPLY The irregular frequencies shown in the computed obtained by Fourier transform of the response function computed in the time domain. They were due to the oscillation of the response added mass and damping coefficients in the frequency domain were function in the time domain, particularly at large time.
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