Shaddy Y. Hanna

Influence of Tension, Weight, and Hydrostatic Pressure on Deepwater TLP Tendons

The effect of increasing water depth on the performance of deep water tendons of tension leg platforms (TLP) is examined. Equations to determine limits on water depths for tendon systems based on strength and hydrostatic collapse requirements are presented. Relations between tendon tensions and reactions on a TLP hull are derived. Conditions for which neutrally buoyant tendons can be utilised are presented. For very deep water, the limiting diameter to thickness ration (D/t) is presented for different tendon variables. For a water depth of 5,000ft, the D/t ratio is limited to about fifteen due to hydrostatic collapse constraints. Composite tendons can provide reduced pretension, improved restoring force, and reduced drag forces. Weight and economic benefits of using light weight composite tendons for a TLP are presented as a function of water depth.

PILE DRIVING DYNAMIC LOADS ON OFFSHORE STRUCTURES

Reducing conservatism in jacket designs based solely on environmental loads can make other loading mechanisms which were not of concern in the past a dominant design parameter. One of these mechanisms is associated with the dynamic loads induced during pile driving. Acceleration and strain measurements during installation of two jackets in the North Sea illustrate that both tubular joints and sacrificial anode attachments can be subjected to a high level of fatigue damage during pile driving operations. The measured vibration response during pile driving can be simulated by performing time-domain dynamic analysis of the jackets. A load pulse with a duration of 0.2 sec is applied at the first pile guide inside the jacket leg. The U.K. Department of Energy T curve appears to be more appropriate for use to predict fatigue damage during pile driving than the API X curve.