Opus An Offshore Platform Upending Simulation System
Authors: Metcalf Michael F. 
Published: October 2008

This paper presents a radically different approach to investigating the upending of an offshore platform structure from a horizontal floating position to a vertical position. Upending motion is caused by selectively ballasting the structure, by hoisting with a barge crane, or by altering any other controllable physical parameter that can affect structure position. A man-computer system is described in which an engineer engages in a graphical dialogue with an interactive computer to perform an heuristic investigation of structure upending motion. Through an experimental process relying more on discovery than proof, the engineer formulates and tests hypotheses about structure responses to physical parameter alterations that are not amenable to rigorous analysis. The system in this way represents an extension of the analytical abilities of an experienced and intuitively motivated engineer, providing the engineer a means for attaining insight into the upending phenomenon through free interaction with the computing system. Used frequently during the overall platform design process, the system can be an invaluable tool for developing upending procedures as part of overall design.

A Newtonian analysis of upending motion is discussed, and an analytical model based on hydrostatics is proposed as an alternative approach for simulating structure response as a slow-motion phenomenon. The system structure and command language are described. Guidelines are offered on how the hydrostatic model is used to predict total upending motion by a process of synthesizing the engineer's understanding of incremental structure motions.

The man-computer system has been implemented with a simple graphics configuration providing limited graphics capability. A brief example session demonstrates that an heuristic approach to studying upending motion with a hydrostatic modeling technique can be supported. Experiments with a sophisticated interactive graphics system, however, suggest that a far more powerful man computer system can be developed. The expanded range of graphics capability indicate enhanced interactive potential between the engineer and the computer, and represent a desirable and reasonable extension to the system implemented. 1.

AN INTRODUCTION

1.1 Nature of the Problem

The offshore industry has long been familiar with stationary (or fixed) offshore platforms that are supported by the sea floor with their decks above the sea level. Fixed platforms have served the petroleum industry for more than thirty years as facilities for drilling rigs, production facilities, well protectors and housing for on-site personnel. Non-petroleum applications of offshore platforms range from oceanographic research and weather gathering stations, ship loading facilities for mining operations and offshore terminals, dolphins for berthing complexes in harbors and deep water terminals, and even as stations for harvesting fish.

Offshore platform designs vary considerably according to specific environmental conditions and service requirements, and as new requirements arise in unfamiliar environments, designs and construction methods will necessarily change. The platforms of interest in this study, however, consist of a deck structure supported by a tower. The tower is a rigid space frame of long slender tubular shapes, whose legs (column members) are fixed to the sea floor by piles.