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Chapter 9 Applications of Hybrid Wave Models to Irregular Waves

9.1 Computation of Wave Kinematics. Problems of computing wave kinematics using Linear wave theory Revisit of HW 3Modifications to LWT (widely used by the offshore industry)(see Zhang et al. 1991, OTC 6522) Wheeler Stretching Linear Extrapolation Vertical Extrapolation

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Chapter 9 Applications of Hybrid Wave Models to Irregular Waves

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    1. Chapter 9 Applications of Hybrid Wave Models to Irregular Waves 9.1 Computation of Wave Kinematics 9.2 Prediction of Wave Elevation 9.3 Prediction of Wave Elevation Based on Wave Pressures 9.4 Prediction of Wave Properties of Short-crested Waves. 9.5 Accurate determine Wave Energy Loss Due to Wave Breaking. 9.6 Wave Forces on Slender Bodies

    2. 9.1 Computation of Wave Kinematics

    5. Heuristic Interpretations for the horizontal velocity under the crest -Steep wave crests are caused by many waves of different frequencies. -Waves of high frequencies are on the top of waves of low frequencies. Hybrid Wave Model (HWM) considers these factors -The still water level to a SW is the LW’s surface - Considering Waves of high frequencies are on the top of waves of low frequencies

    8. Wave Kinematics Prediction

    27. Plan View of Sensor Layout

    28.

    29. Fig. 4 Power spectrum density according to pressure head time series

    30. Fig. 5 Initial phases of each component of pressure and velocity

    32. Fig. 7 Comparison of free-wave directions based on DHWM and Waverider (9803011020)

    33. Comparison between prediction & measurement of Marex before & after the orientation of S4 was corrected

    34. Comparison between prediction & measurement of SAAB before and after the orientation of S4 was corrected

    35. Comparison of free-wave directions based on DHWM and Waverider (9803051040)

    36. Comparison between prediction & measurement of SAAB before & after the orientation of S4 was corrected

    37. Comparison of free-wave directions based on DHWM and Waverider (9804131100)

    38. Comparison between prediction & measurement of Marex before & after the orientation of S4 was corrected

    39. Comparison between prediction & measurement of SAAB before & after the orientation of S4 was corrected

    52. Spar Platform

    55. Quasi-static Analysis mooring/tendon/risers modeled as nonlinear springs. mooring line damping estimated or neglected Coupled Dynamic Analysis structure motion equations and mooring/tendon /riser dynamic equations solved simultaneously. mooring line damping included. Empirical formulation for VIV.

    56. Numerical Code: COUPLE

    57. Methodology of Coupled Dynamic Analysis hinged boundary condition Motion equations of a structure

    58. Two Choices of Computation Methods Morison equation (Slender Body Structure) Wave Kinematics using Hybrid Wave Model (HWM). Inertia, drag and lifting (VIV) forces. Ship Type Structures, (2nd order Wave Diffraction numerical codes, i.e.WAMIT) Drag and lifting force based on Morison Equation

    59. Use of the Hybrid Wave Models

    61. Comparison with Measurements

    62. Main Characteristics of JIP Spar (1:55)

    66. Environment Conditions Wave 100-year West Africa storm (JONSWAP Spectrum, H1/3=4m & TP =16 s). (Wind & Current). 0 and 45 degree wave heading. Set-up (1:40) Fixed model tests (no risers and tendons) Compliant model tests (4 tendons & 4 (12) risers). Measurements Motions of Hull (TLP) in 6 degrees of freedom. Tensions at the bottom of each riser and tendon.

    71. Numerical Code: COUPLE

    74. Approach A: Morsion equation+HWM, quasi-static Approach B: WAMIT+viscous, quasi-static Approach C: Morison equation+HWM, coupled dynamic Approach D: WAMIT+viscous, coupled dynamic

    75. Morison Element Model Four Column diameter: 8.64m, length: 43.5m Cm=1.0 (Guichard,2001) Cd=0.7 ( 0 degree heading) (Teign & Niedzwechi,1998) Cd=1.0 (45 degrees heading) Four Pontoons diameter: 7.02m, length: 19.935m Cm=1.5 Cd=1.2 ( 0 degree heading) Cd=1.4 (45 degrees heading)

    83. Accurate Boundary Conditions for Numerical Simulation T. Liu & Prof. Chen

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