A consortium of oil company research groups, the Michigan Sea Grant Program, and the department have supported research and education in offshore engineering for about 15 years. Areas of research include marine riser mechanics; experimental measurements of hydrodynamic forces on oscillating cylinders; fully nonlinear hydrodynamic computations on floating platforms; pipeline mechanics; structural redesign of offshore platforms; nonlinear dynamics of mooring systems; development of analytical expressions for hydrodynamic forces on cylinders; and postbuckling of risers.
Spread Mooring System Dynamics. On the basis of nonlinear dynamics and bifurcation theory, a design methodology for Spread Mooring Systems (SMS) has been developed. Analytical expressions for the morphogeneses and bifurcation boundaries exhibited by SMS are used to determine regions of qualitatively different dynamics (i.e., stable, unstable, periodic, quasiperiodic, chaotic). This allows the designer to select appropriate values for the mooring parameters. Sensitivity analysis of these expressions reveals the dependence of SMS on mooring line arrangement. This methodology virtually eliminates trial and error, thus reducing the number of nonlinear time simulations in SMS design.
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Design graph of a 4-line tanker SMS in the two-dimensional parametric design space denoting regions of qualitatively different dynamics. The system is stable in regions I. Operation in Regions I, III, and IV is desirable. (ref. Garza-Rios and Bernitsas, J. Ship Res., December 1996). |
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Fully nonlinear, time-domain computations of
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Riser and Pipeline Mechanics. A decade of research has produced sophisticated static/dynamic, nonlinear, three-dimensional codes for analysis of risers. Constraint/contact and substructuring/condensation techniques were used to solve problems on riser bundles and pipelines.
Buckling and Postbuckling of Risers and Columns. The phenomenon of Euler global buckling of tubular columns due to internal pressure while in tension along their entire length has been identified. Internal pressure values used in drilling operations may cause this phenomenon and may make riser postbuckling precipitous. It was further shown that Willers' theory on stability boundaries of columns, holding since 1941, is incorrect.
Hydrodynamic Forces on Risers. Complete expressions were derived for the inertia forces and moments acting on a small submerged body in 6 d.o.f. motion in three-dimensional unsteady flow in an unbounded ideal fluid. The far field approximation of the body motion by a series of multipoles provides formulas attractive for engineering applications. Thus, the need to solve a hydrodynamic problem for the potential is eliminated.
Fully Nonlinear Wave Load Computations. Non-linear effects are important in many offshore problems. Computational techniques are being developed to compute the fully nonlinear wave loads acting on offshore structures. The mixed Euler-Lagrange approach is used to time step the solution with a computationally fast, desingularized technique used to solve the resulting boundary value problem at each time step.
FACULTY: Beck, Bernitsas, Meadows, Perlin, Troesch