Stability of pipelines under shoaling finite amplitude waves

approved: Redacted for Privacy Robert Turnet Hudspeth The horizontal stability of a bottom-laid pipeline under finite-amplitude surface gravity waves which are shoaling on a mildly sloping beach is considered. Incipient sliding motion conditions are assumed in which the wave-induced hydrodynamic pressure force is statically balanced by the Coulomb bottom frictional force. The Morison equation, which includes both drag and inertia force components, is employed to determine the wave-induced hydrodynamic pressure force exerted on the pipeline. Water particle kinematics computed both analytically from linear wave theory and numerically from the finite-amplitude Dean (1965) stream function wave theory are used to evaluate the wave-induced hydrodynamic pressure force exerted on the pipeline. Both the analytical and experimental methods of determining the drag and inertia force coefficients are reviewed. Experimental values for the Coulomb bottom frictional force coefficients are summarized and values are recommended for design applications on various benthic materials. The static balance between the wave-induced hydrodynamic pressure force and the Coulomb bottom frictional force results in a stability criterion that may be expressed in terms of a dimensionless wave force acting on the pipeline, P;, a dimensionless stability parameter, PL; and a dimensionless force ratio, W', which includes all of the explicit variables in the pipline horizontal stability problem. Both the experimental data from Wright (1976) and Yamamoto, et al. (1973) are analyzed to construct a set of design curves for the dimensionless force ratio, W'. Using water particle kinematics from linear wave theory, the relative magnitude between the inertia and the drag force components is evaluated. Limiting values for this relative ratio are used to delineate three regions of relative importance on a dimensionless relative displacement, H/D, relative water depth, d/Lo, dissection plane which may be used for design. The horizontal stability criterion of a bottom-laid pipeline is further simplified in each of these three regions of relative importance for design. Using water particle kinematics computed numerically from the finite-amplitude Dean (1965) stream function wave theory, a set of dimensionless curves for the dimensionless wave force acting on the pipeline, q, under various design conditions specified by the dimensionless force ratio, W', the depth parameter, d/T 2 , and the wave height parameter, H/T2, is constructed for design application. A design procedure for the application of the dimensionless design curves (W' and Pii) is enumerated for determining the limiting depth for the horizontal stabilization of a bottom-laid pipeline. Stability of Pipelines under Shoaling Finite Amplitude Waves by Min-Chih Huang A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Ocean Engineering June 1981