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TECHNICAL PAPERS

Boundary-Element Methods In Offshore Structure Analysis

[+] Author and Article Information
J. N. Newman

MIT, Cambridge, MA 02139e-mail: jnn@mit.edu

C.-H. Lee

WAMIT Inc., Chestnut Hill, MA 02467e-mail: chlee@wamit.com

J. Offshore Mech. Arct. Eng 124(2), 81-89 (Apr 11, 2002) (9 pages) doi:10.1115/1.1464561 History: Received July 01, 2001; Revised November 01, 2001; Online April 11, 2002
Copyright © 2002 by ASME
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References

Hess,  J. L., and Smith,  A. M. O., 1964, “Calculation of nonlifting potential flow about arbitrary three-dimensional bodies,” J. Ship Res., 8, pp. 22–44.
Korsmeyer, F. T., Lee, C.-H., Newman, J. N., and Sclavounos, P. D., 1988, “The analysis of wave interactions with Tension-Leg Platforms,” Proc. OMAE Conf., Houston.
Molin, B., and Chen, X. B., 1990, Vertical resonant motions of tension leg platforms, unpublished report, Institut Français du Pétrole, Paris.
Herfjord, K., and Nielsen, F. G., 1992 “A comparative study on computed motion response for floating production platforms: Discussion of practical procedures,” Proc. 6th Intl. Conf. on Behaviour of Offshore Structures (BOSS’92), 1 , London, pp. 19–37.
Eatock,  T. R., and Chau,  F. P., 1992, “Wave diffraction theory-some developments in linear and nonlinear theory,” J. Offshore Mech. Arct. Eng., 114, pp. 185–194.
Lee, C.-H., and Newman, J. N., 1994 “Second-Order wave effects on offshore structures,” Proc. of 7th, Intl. Conf. on Behaviour of Offshore Structures (BOSS ’94), 2 , Pergamon, pp. 133–145.
Maniar, H., 1995, “A three dimensional higher order panel method based on B-splines,” Ph.D. thesis, MIT, Cambridge, MA.
Lee, C.-H., Maniar, H. D., Newman, J. N., and Zhu, X., 1996, “Computations of wave loads using a B-spline panel method,” Proc. of 21st Symposium on Naval Hydrodynamics, Trondheim, Norway, pp. 75–92.
Lee, C.-H., 1997, “Wave interaction with huge floating structure,” Proc. of 8th. Intl. Conf. on Behavior of Offshore Structures (BOSS ’97), Delft, The Netherlands, pp. 253–265.
Phillips,  J. R., and White,  J. K., 1997, “A precorrected-FFT method for electrostatic analysis of complicated 3-D structures,” IEEE Trans. Comput.-Aided Des., 16(10), pp. 1059–1072.
Korsmeyer, F. T., Klemas, T. J., White, J. K., and Phillips, J. R., 1999, “Fast hydrodynamic analysis of large offshore structures,” Proc. of Int. Symp. on Offshore and Polar Engineering, ISOPE ’99, Brest, France.
Wehausen, J. V., and Laitone, E. V., 1960, “Surface waves,” Encyclopedia of Physics, Springer, 9 , pp. 446–778.
Anon., 2000, “WAMIT User Manual,” WAMIT, Inc. (available from the website www.wamit.com).
McIver,  P., and McIver,  M., 1997, “Trapped modes in an axisymmetric water-wave problem,” Q. J. Mech. Appl. Math., 50, pp. 165–178.
Newman,  J. N., 1999, “Radiation and diffraction analysis of the McIver toroid,” J. Eng. Math., 35, pp. 135–147.
Lee, C.-H., and Newman, J. N., 2001, “Solution of radiation problems with exact geometry,” Proc. of 16th Int. Workshop on Water Waves and Floating Bodies, Hiroshima, Japan, pp. 93–96.
Molin, B., 2000, “On the sloshing modes in moonpools, or the dispersion equation for progressive waves in a channel through the ice sheet,” Proc. of 15th Int. Workshop on Water Waves and Floating Bodies, Caesaria, Israel, pp. 122–125.
Maniar,  H. D., and Newman,  J. N., 1997, “Wave diffraction by a long array of cylinders,” J. Fluid Mech., 339, pp. 309–330.
Newman, J. N., 2001, “Wave effects on multiple bodies,” Conf. on Hydrodynamics in Ship and Ocean Engineering, Kyushu Univ., Japan, pp. 3–26.
Newman, J. N., and Lee, C.-H., 1992, “Sensitivity of wave loads to the discretization of bodies,” Proc. of 6th Int. Conf. on Behavior of Offshore Structures (BOSS ’92), 1 , London, 1992, pp. 50–64.
Hsin, C.-Y., Kerwin, J. E., and Newman, J. N., 1993, A two dimensional higher-order panel method based on B-splines, theory and program documentation, Report 93-3, Dept of Ocean Engineering, MIT, Cambridge MA.
Lee,  C.-H., and Newman,  J. N., 2000, “An assessment of hydroelasticity for very large hinged vessels,” J. Fluids Struct., 14, pp. 957–970.
Lee,  C.-H., and Newman,  J. N., 1991, “First- and second- order wave effects on a submerged spheroid,” J. Ship Res., 35, pp. 183–190.
Ferreira, M. D., and Lee, C.-H., 1994, “Computation of second-order mean wave forces and moments in multibody interaction,” Proc. of 7th. Intl. Conf. on Behaviour of Offshore Structures (BOSS ’94), 2 , Pergamon, pp. 303–313.

Figures

Grahic Jump Location
Schematic description of the evaluation of the influence from the source or normal dipole distribution on the panel ‘S’ to the panel ‘N’ in the near field and to the panel ‘F’ in the far field. The large gray area is the near field where the influence of ‘S’ on ‘N’ is evaluated directly by (9) and (10). The indirect evaluation between ‘S’ and ‘F’ using FFT is denoted by a dotted line. The projection of ‘S’ to the nearby grid nodes is denoted by the white outward arrows. The interpolation of the potential on ‘F’ from the potentials at the nearby grid nodes is denoted by white inward arrows.
Grahic Jump Location
Perspective view of the MOB, made up of five semi-subs (lower figure) and the array of truncated cylinders corresponding to the columns of the semi-subs without the pontoons (upper figure).
Grahic Jump Location
Modulus of the free-surface elevation along the centerline of the MOB configuration shown in the lower part of Fig. 8. Results are shown for five different wave periods (T). Note that different vertical scales are used for each wave period. The incident wave is traveling toward the negative x-axis. The elevation is normalized by the incident-wave amplitude.
Grahic Jump Location
Modulus of the free-surface elevation along the centerline of the array of cylinders shown in the upper part of Fig. 8. Note that different vertical scales are used for each wave period. Other definitions are the same as in Fig. 9.
Grahic Jump Location
Perspective view of the McIver toroid generated by a ring source of unit radius, with the inner waterline at r=0.2 and the outer waterline at r=2.4687. The view is from above the free surface, and the two waterlines are circular. The geometry is defined by one patch, in the first quadrant (x>0,y>0).
Grahic Jump Location
Perspective view of the array of nine cylinders with spherical buoyancy caps. Only the submerged portions are shown. The top edge of each cylinder is in the plane of the free surface.
Grahic Jump Location
Perspective view of the FPSO. The bow is a semi-elliptical cylinder. The stern is prismatic with a vertical transom. All transverse sections are rectangular. The upper figure shows the geometry for the higher-order method, including the patches (six on each side, bounded by dark lines) and panels (light lines, with the obscured panels hidden from view). The panels in the bow have smooth continuous curvature, although this is not clear from the plot. The lower figure shows a typical low-order panel arrangement (with obscured panels hidden from view).
Grahic Jump Location
Results for the McIver toroid. The left figure shows the heave added-mass coefficient, including results from the low-order analysis with N=128, 512, 2048 panels on one quadrant of the body surface, and higher-order results with explicit geometry definition (N=100 unknowns). The latter results are converged within graphical accuracy. The right figure shows the convergence of the low- and higher-order results to the singular wavenumber J0(k)=0.IRR=1 denotes that the irregular-frequencY effects are removed.
Grahic Jump Location
Exciting force (solid line), and the force on the middle element (long dashed line), for the array shown in Fig. 2. The force on a single isolated body is represented by the short dashed line, for comparison. The maximum value of the exciting force is at K=0.932, with the peak value equal to 111. All forces are in the direction parallel to the array axis, and the incident wave propagates in the same direction.
Grahic Jump Location
Mean yaw moment about the mid-section of the FPSO, as a function of the period, T. the solid line is evaluated from the higher-order method using momentum analysis. the corresponding results from the low-order momentum analysis are shown by solid square symbols. The open squares (low-order) and circles (higher-order) represent the corresponding results using the pressure analysis. The moment is normalized by the product of water density, gravity, wave amplitude squared and the square of unit length.

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