Numerical computations of hydrodynamic forces and motions of TLP using 3D source distribution technique

Abstract

Due to urbanization, the production and consumption of oil and other petroleum products have been increasing rapidly over the years which led to the scarcity of easily retrieved oil. As a result, oil producers are motivated to go to deeper ocean to extract oil and other resources. Offshore platforms in deep water like TLPs are used for exploration of oil and gas from under Seabed and processing. But it is challenging to design precisely such type of giant structure in deep sea as it experiences huge forces, motion and other environmental loads which are non-linear in nature and difficult for evaluation. However there are sophisticated techniques for determination of these forces and motions both theoretically and experimentally. Theoretical techniques are complicated and tedious while experimental methods are expensive to apply. In the present study wave exciting forces and motions of free floating TLP are carried out in frequency domain analysis using three dimensional source distribution techniques within the scope of linear wave theory.

A developed mathematical program has been modified based on linear wave theory and 3D source distribution technique to compute the forces and motions where six degrees of freedom is considered. The same geometrical data are used as an input to HydroStar which is based on linear wave theory. Results obtained from both the programs are compared which shows a good agreement and also validated with the published results.

The mathematical model has been modified incorporating tendon as the TLP is connected to the sea bed and tether to diminish the heave motion which strongly affect the loading and unloading system. Comparison of heave motion with and without tether are illustrated where it can be easily understood the effect of tendon. Results are satisfactory which inspires to design the tendon system and future research.

Forces and motions predictions of TLP are emphasized which has been done precisely in the present research work and in future it will help us to design the TLPs as well as the tendon system in deep sea. Finally, a number of recommendations have been made for further research based on the present study.