Hydrodynamic Forces From Wave and Current Loads on Marine Pipelines

Abstract

The weight coating requirements for assuring the on-bottom stability of several pipelines in the Arabian Gulf have been determined through an integrated design procedure including mathematical modelling for determining extreme wave conditions, field measurements of currents and physical model testing to establish the magnitude of the hydrodynamic forces.

New model to determine forces at on-bottom slender pipelines

“…13) proves to be less variable because the changes in the flow field for each half period break the natural growth of the vortices around the pipeline (Longoria et al, 1991;Sumer and Kozakiewicz, 1995). The reduction of the values of the hydrodynamic coefficients is in agreement with the results from the experiments for bottom-mounted pipelines carried out by Bryndum et al (1983Bryndum et al ( , 1992 addressed to calibrate the Morison coefficients. Although the incident wave is random, the values of the hydrodynamic coefficients denote a quite regular distribution of the peaks.…”

“…In the adopted experimental range of KC, the inertia coefficient shows a general reduction and a certain stabilization when the external surface of the pipeline is rougher (PR). This feature was observed during the experiments to determine the Morison force coefficients for rough slender horizontal cylinders (Bryndum et al, 1983(Bryndum et al, , 1992Longoria et al, 1991). The effect of random motion on the smooth cylinder gives a slight reduction on the values of C M associated with the great influence of the quick changes in the vortex-flow regime (Longoria et al, 1991;Sumer and Kozakiewicz, 1995).…”

“…Tables 3 and 4 show the values of H s , T p , u m0 , Re and KC for random waves using, respectively, the smooth cylinder (RS) and the rough cylinder (RR). Moreover, Tables 5 and 6 report the values of H s , T p , Q (water discharge), u cL , u m0 , α, Re and KC respectively for combined periodic waves and currents (PC), and for combined random waves and currents (RC) using a smooth cylinder, where α = u cL /u m0 is the current ratio (Bryndum et al, 1983(Bryndum et al, , 1992. All experiments were carried out in the vortex shedding regime (KCN 4).…”

“…Since the experiments refer to non-sinusoidal waves, the flow field at the pipeline has been characterized by KC = u m0 T p /D, where u m0 is the significant bottom velocity at the transversal axis of the cylinder (Bryndum et al, 1983(Bryndum et al, , 1992 and represents the horizontal velocity amplitude for a non-sinusoidal wave motion. Specifically, u m0 = 2σ u , where σ u is the measured root-mean square of the total free stream horizontal velocity, u, at the cylinder axis.…”

“…For bottom-mounted submarine pipelines, values of Morison hydrodynamic coefficients have been evaluated for different wave and current conditions based on field investigations (Grace and Zee, 1981;Lambrakos et al, 1987) and small and large scale laboratory experiments (Sarpkaya and Rajabi, 1980;Norwegian Hydrodynamic Laboratories, 1985;Cheong et al, 1987;Veritas Offshore Technology, 1988;Bryndum et al, 1983Bryndum et al, , 1992Benassai, 1993;Neill and Hinwood, 1998;Chevalier et al, 2000;Tomasicchio et al, 2007). Some authors (Sarpkaya, 1981;Bearman et al, 1984;Sarpkaya and Wilson, 1984;Chaplin and Subbiah, 1997;Sarpkaya, 2001) proposed, for limited KC and Re ranges, additional terms in the basic Morison equations in order to minimize the differences between the experimental and the simulated forces.…”