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Dynamic analysis of multiple-body floating platforms coupled with mooring lines and risersKim, Young-Bok 30 September 2004 (has links)
A computer program, WINPOST-MULT, is developed for the dynamic analysis of a multiple-body floating system coupled with mooring lines and risers in the presence of waves, winds and currents. The coupled dynamics program for a single platform is extended for analyzing multiple-body systems by including all the platforms, mooring lines and risers in a combined matrix equation in the time domain. Compared to the iteration method between multiple bodies, the combined matrix method can include the full hydrodynamic interactions among bodies. The floating platform is modeled as a rigid body with six degrees of freedom. The first- and second-order wave forces, added mass coefficients, and radiation damping coefficients are calculated from the hydrodynamics program WAMIT for multiple bodies. Then, the time series of wave forces are generated in the time domain based on the two-term Volterra model. The wind forces are separately generated from the input wind spectrum and wind force formula. The current is included in Morison's drag force formula. In case of FPSO, the wind and current forces are generated using the respective coefficients given in the OCIMF data sheet. A finite element method is derived for the long elastic element of an arbitrary shape and material. This newly developed computer program is first applied to the system of a turret-moored FPSO and a shuttle tanker in tandem mooring. The dynamics of the turret-moored FPSO in waves, winds and currents are verified against independent computation and OTRC experiment. Then, the simulations for the FPSO-shuttle system with a hawser connection are carried out and the results are compared with the simplified methods without considering or partially including hydrodynamic interactions.
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Loads on Tie-Down Systems for Floating Drilling Rigs during Hurricane ConditionsBae, Yoon Hyeok 16 January 2010 (has links)
Tie-down systems are used to fasten drilling rigs to the deck of offshore
structures during harsh environmental conditions such as hurricanes. During Hurricane
Ivan (2004) and Katrina (2005), a number of offshore structures were moved and several
tie-down systems were damaged. In the present study, the reaction force and connection
capacity of tie-down systems for a TLP and SPAR are investigated. The environmental
conditions are taken from the API Bulletin 2INT-MET which has been updated after
several major storms during 2004-2005. The hydrodynamic coefficients of the TLP and
SPAR are obtained using a 3D diffraction/radiation panel method. The motions of the
TLP and SPAR are then simulated in the time domain by using the hull-mooring-riser
coupled dynamic analysis tool CHARM3D. Based on the simulated motion and
acceleration time series, the inertial and gravity loads on derrick and skid base footing
are calculated. In addition to the inertial-gravity loads, wind forces exerted on the derrick
are also calculated. All the external forces and resultant hull motions are simulated for
100-year, 200-year and 1000-year storms to observe the derrick structural integrity with
increasing environmental intensity. Various environmental headings are also considered to find the maximum reaction forces. In the present method, the phase differences
between gravity-inertia forces and wind forces are taken into consideration to obtain
more realistic loads on derrick and skid base footings. This research shows that the
maximum and minimum load values are appreciably higher for the SPAR. In addition,
the direction of external forces is also important to determine maximum reaction forces
on footings. The capacities of the clamps in slip, bolt tension, and bolt shear can be also
analyzed using the resultant data to provide guidance on appropriate design values.
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Dynamic analysis of multiple-body floating platforms coupled with mooring lines and risersKim, Young-Bok 30 September 2004 (has links)
A computer program, WINPOST-MULT, is developed for the dynamic analysis of a multiple-body floating system coupled with mooring lines and risers in the presence of waves, winds and currents. The coupled dynamics program for a single platform is extended for analyzing multiple-body systems by including all the platforms, mooring lines and risers in a combined matrix equation in the time domain. Compared to the iteration method between multiple bodies, the combined matrix method can include the full hydrodynamic interactions among bodies. The floating platform is modeled as a rigid body with six degrees of freedom. The first- and second-order wave forces, added mass coefficients, and radiation damping coefficients are calculated from the hydrodynamics program WAMIT for multiple bodies. Then, the time series of wave forces are generated in the time domain based on the two-term Volterra model. The wind forces are separately generated from the input wind spectrum and wind force formula. The current is included in Morison's drag force formula. In case of FPSO, the wind and current forces are generated using the respective coefficients given in the OCIMF data sheet. A finite element method is derived for the long elastic element of an arbitrary shape and material. This newly developed computer program is first applied to the system of a turret-moored FPSO and a shuttle tanker in tandem mooring. The dynamics of the turret-moored FPSO in waves, winds and currents are verified against independent computation and OTRC experiment. Then, the simulations for the FPSO-shuttle system with a hawser connection are carried out and the results are compared with the simplified methods without considering or partially including hydrodynamic interactions.
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