API REPORT 80-31 Hydrodynamic Coefficients for Cylinders with Pronounced Marine Growths

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API REPORT 80-31 Document Information:

Title
Hydrodynamic Coefficients for Cylinders with Pronounced Marine Growths

American Petroleum Institute

Publication Date:
Oct 1, 1981

Scope:

Scope of the Work and Test Program

A smooth cylinder was tested in order to show how well the equipment and analyses reproduce the results of other investigators. A sand covered cylinder with k/D = 0.02 was also tested in order to compare with the most rough condition tested in the laboratory by past investigators. (The symbol k is the equivalent sand diameter and D is the cylinder diameter--see Fig. 16 of Appendix G for a photo of this uniform sand roughened condition.) A cylinder with artificially constructed marine growths was also tested with the thought that the coefficients obtained therefrom would be at least a first approximation of some of the conditions that actually exist at sea. This test condition is referred to as the marine roughened cylinder. (See Fig. 17 of Appendix G.)

Data were recorded in digital form, filtered, and processed by computer. Computer programs and other data processing were lengthy, time consuming to develop, and expensive. Fortunately, the companion projects were able to help absorb the added cost.

The original test schedule specified the following:

Steady Towing--Tow each of three cylinders with from very slow speed to the maximum possible speed with the equipment, measuring horizontal and vertical forces on the two-feet long center test sections. A minimum of 20 runs were planned.

Periodic Waves--Test each of the cylinders in the following waves.

A total of 15 runs, plus a few for replications, were planned.

Waves plus towing--The previous tests for periodic waves only and maximum tow speeds were to be superimposed, plus a towing at 5, 10 or 20% of the maximum orbital velocities, for a total of about 20 runs.

Random waves--About two wave spectra with moderate to high significant wave heights (ranging from 2.5 ft. to 3.3 ft.) for each of the three cylinders for six-runs.

In total, from 61 to 70 runs were planned. However, about 252 runs were actually selected for processing for this report.

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