| abstract |
A RISER, ARRANGED FOR COMMUNICATION BETWEEN A STRUCTURE AT THE OCEAN FLOOR AND EQUIPMENT ON THE SURFACE WHERE THE WATER DEPTH MAY BE, FOR EXAMPLE, MORE THAN 600 FEET, HAS A LOWER PORTION WITH A RIGIDITY OR STIFFNESS SUFFICIENT TO WITHSTAND THE WORST CONDITION BENDING MOMENT APPLIED THERETO. THE STIFFNESS OF THE UPPER PORTION IS DETERMINED BY THE DESIGN REQUIREMENTS FOR EFFICIENT AND ECONOMICAL PIPING AND COMMUNICATION BETWEEN THE OCEAN FLOOR AND THE OCEAN SURFACE. IN ADDITION, THE SECOND MODULUS OF THE LOWER PORTION DECREASES AT STATIONS DISPOSED FURTHER FROM THE OCEAN BOTTOM AND WHERE THE UPPER AND LOWER PORTIONS JOIN THE SECTION MODULUS ARE SUBSTANTIALLY THE SAME. |