Mooring system using cables and buckled riser pipe

Abstract

Abstract THIS INVENTION RELATES TO A MOORING SYSTEM FOR A FLOATING STRUCTURE. SPECIAL BOUYANCY CHAMBERS SUPPORT THE STRUCTURE, INCLUDING A WORK DECK, ABOVE A BODY OF WATER. THE STRUCTURE IS CONNECTED TO ANCHORS AT THE FLOOR OF THE BODY OF WATER BY ELONGATED MEMBERS SUCH AS CABLES AND PIPES HAVING DIFFERENT ELONGATIONS PER UNIT OF STRESS. THE MAIN ANCHORING LOAD IS CARRIED BY THE CABLES AND THE PIPES ARE USED PRIMARILY IN DRILLING OPERATIONS OR FOR TRANSPORTING PETROLEUM FROM AN UNDERWATER WELL. BECAUSE OF WAVE ACTION, THE FLOATING PLATFORM IS SUBJECT TO VERTICAL HEAVE FORCES. THE MAXIMUM VERTICAL STRESS APPLIED TO THE CABLES CAUSES THEM TO ELONGATE A LENGTH $L. THE RISER PIPE IS INSTALLED UNDER SUFFICIENT COMPRESSION SO THAT IT IS IN A BUCKLED CONFIGURATION WHEN THE FLOATING STRUCTURE IS IN A NEUTRAL POSITION. THE LENGTH OF THE BUCKLED RISER PIPE EXCEEDS THE VERTICAL DISTANCE FROM THE BOUYANCY MEANS TO THE WELL HEAD BY AN AMOUNT EQUAL TO THE MAXIMUM $ OF THE CABLE. AS THE VERTICAL DISTANCE INCREASES BY $L. THE BUCKLED RISER WILL STRAIGHTEN, RATHER THAN ELONGATE, WITHOUT A CHANGE IN AXIAL FORCE. THUS THE BASIC LOAD-CARRYING MEMBER REMAINS THE CABLE. IN A PREFERRED EMBODIMENT THE CABLE IS SLIDEABLY CONNECTED TO THE POINTS ALONG THE BUCKLED RISER PIPE CORRESPONDING TO THE NODES OF THE BUCKLED CONFIGURATION.

Inventors

• 👤 David A Dixon
• 👤 Kenneth A Blenkarn

Bibliographic Details