Impulse and energy in deepsea riser collisions owing to wake interference

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Impulse and energy in deepsea riser collisions owing to wake interference

Huse, E. / Kleiven, G.

The paper describes model testing of top tensioned, deep sea riser arrays, conducted by MARINTEK for the Norwegian Deepwater Programme. The original purpose of the tests was to determine criteria for on-set of clashing or collisions between individual risers in current. Furthermore, force and acceleration measurements made possible the determination of the impulse and energy involved in the collisions. The results show that the previously published theory based on turbulent wakes and momentum balance, predicts on-set of collisions to an accuracy which is in most cases within 10 to 15 percent, referring to velocity. For risers without strakes collision energies up to 65 kJ, prototype, were measured. With strakes fitted to the risers the maximum measured collision energy was one order of magnitude lower. An approximate empirical formula for the collision energy of bare risers is suggested. The paper also discusses possible practical solutions to the problem of current induced riser clashing.