The Mooring Dynamics Experiment - A Major Study Of The Dynamics Of Buoys In The Deep Ocean
Authors: Walden Robert G. , DeBok Donald H. , Gregory John B. , Meggitt Dallas G. , Vachon William A. 
Published: October 2008

Measurements of acceleration, pressure, temperature, tension and orientation were taken of five different deep-sea mooring configurations. Separate measurements of wind, current and waves were made to specify the environmental forcing functions. The experimentally derived data provides a base for use in validation of dynamic analytical models of deep-sea moorings. The experiment was conducted at an acoustic tracking range in the Pacific Ocean.

INTRODUCTION

The verification of the equations and the subsequent numerical solution of the non-steady state boundary value problem that describes a buoy moored in deep water has long been hampered by the lack of experimental data. Unlike many problems encountered by the ocean engineer or naval architect, deep moored buoy systems are not suitable for modeling in the test tank. Typically, scale model testing is used in cases of surface phenomena where Froude scaling predominates or of submerged applications where Reynolds scaling can be applied. The moored buoy includes both surface and submerged responses in addition to the interaction between them. The resultant is a system that requires experimental data at the full scale level.

For more than a decade scientists have been able to install deep-ocean moored instrumented cable systems capable of recording oceanographic data. These moorings were first designed by "handbook engineering" followed by the application of tabular data which resulted from parametric analyses of current flow on the systems. Finally, these tables were supplanted by so-called "static" or "quasi-static" computerized analyses of moorings. Such analyses assumed two dimensional ocean current profiles which were tapered from top to bottom or stepped in some manner to represent what was thought to be a typical forcing function of the ocean upon the mooring.

These computerized solutions were not sufficient to represent anything but a given set of conditions which could satisfy a design for mooring survival but did not allow the scientist an understanding of the effects of the mooring motions upon instruments from it. If the scientist were to obtain data of sufficient accuracy to meet his ever increasing scientific needs he would have to know how the dynamics of the mooring biased his instruments.

By the early Seventies, many static and a few dynamic computerized programs were introduced. In fact, it appeared that static and dynamic analyses were proliferating throughout the ocean engineering community, presenting obvious questions as to their application and worth. Other questions arose concerning their engineering coefficients and assumptions, and indeed, the most obvious comment of all was: "Are there any good engineering data to evaluate these models?"

In 1972, the Ocean Technology Program of the Office of Naval Research tasked the Hydrospace Research Group of EG&G to determine the applications and merits for whatever static and dynamics models could be found. The published results showed a definite need for in situ measurements to evaluate models.