Mars Tension Leg Platform - Use of Scale Model Testing in the Global Design
Authors: Mercier R.S. , Schott W.E. , Howell C.T. , Denison E.B. , Gopalkrishnan R. , Ekvall A.G.C. 
Published: October 2008

In the global design, sizing and analysis process for the Mars Tension Leg Platform, scale model testing methods were used extensively. Aerodynamic and hydrodynamic scale model test programs for the preliminary configuration of the Mars TLP were carried out. In each case a numerical model of the physical model was used to relate the measured responses to numerically computed responses. The wind tunnel and towing tests served as calibration points for a comprehensive wind, wave and current model test program of a dynamic scale model of the Mars TLP. The results of the model tests were used to calibrate and supplement the numerical modeling procedures and global design recipes. These procedures werein turn applied in the final sizing and detailed global analysis of the as-built configuration of the Mars TLP.

Introduction

The global design of a TLP relies on an precise assessment of the wind, wave, and current loads and the induced platform motions and tether loads. Due to theoretical and computational limitations, it is not possible to numerically simulate all the relevant loads and load effects with the requisite level of accuracy, The TLP designer must eitherresort to model tests to provide the needed information or incorporate conservative design allowances in the global design of the platform. The former is the preferred approach since it leads to a more reliable and optimized design.

The global design of the Mars TLP relied on scale model tests for critical information on the high frequency resonant tension responses, platform offset, and wave elevations beneath the deck. In addition, the model tests provided datafor validating the numerical model used to analyze low and wave frequency motion and tendon tension responses. The tests were integral to the design process and the results wereused in the final sizing of the platform and tendons.

This paper presents an overview of the entire test program. The primary design issues and information needs addressed by the model test program are discussed. The test objectives and requirements are presented, as well as the plans, procedures, and results from the various phases of testing. Finally, the assimilation of the test results in the global design of the Mars TLP is summarized.

Design Issues

TLP Sizing. The primary factor affecting TLP sizing that is a consequence of environmental loading is tendon tension, in particular as it determines the level of pretension to be provided by the hull. The pretension level must be sufficientto maintain bottom tension and small enough to limit the maximum stress in the tendon in response to design events.

The larger the pretension, the larger the hull, and the greater the dynamic tension. This results in greater tendon and foundation loads. Lower pretension results in greater offset and setdown, hence the requirement for greater column height to achieve a given underdeck clearance. Greater deckheight results in a higher center of gravity and greater inertia loads to be reacted by the tendons.