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Simultaneous Wave And Current Forces On A Cylinder Near The Bottom Boundary
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1981
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Description:The interaction of waves and currents and their relationship to the forces on submerged pipelines was investigated at Texas A&M University. A model pipeline in a wave-current test facility is used to obtain experimental force values which are compared to values predicted by various theoretical methods of representing wave propagation in a current. The Morison equation is employed to evaluate the forces on the horizontal cylinder. The major input parameters required by this equation are the water particle kinematics of velocity and acceleration and the coefficients of drag and inertia. Each of these parameters is investigated individually in order to ensure that compensating errors in the force calculations are eliminated. The coefficient of drag is determined from the simultaneous measurements of the horizontal water particle kinematics and the fluid force on the cylinder. Several wave theories for waves propagating in still water are modified to include currents by various combinations of their respective horizontal velocity fields. These water particle kinematics are compared directly to experimentally determined values. The measured forces are compared to the forces obtained by the Morison equation with the coefficients determined in this study and the kinematics predicted by the modified wave theories. The data are also compared to previous results for the individual cases of waves or currents. These comparisons demonstrate the changes of the coefficients of drag for the combined wave and current conditions. The primary purpose of this paper is not to provide explicit prototype design criteria, but to provide the design engineer with an insight into the fluid force parameters of interacting waves and currents. The results are presented in a manner that demonstrates the apparent acceptability of superimposing the velocity fields of the wave and current to predict the total velocity field for the determination of the fluid force by the Morison equation.
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Rights Information:Public Domain
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