The TLP 2-DOF as an alternative model for extreme wave application

Tension Leg Platform (TLP) is an offshore platform structure used for deep-sea oil and gas exploration. The main structure of the TLP consists of a deck, pontoon, mooring system, and foundation. TLP operates in a balance of buoyancy, structural weight, and mooring tension. The problem is the construction of TLP in the deep sea, where sometimes extreme waves appear could damage the TLP structure. This paper proposes a new model of TLP that is more stable to extreme waves. The method is to separate the mass of the deck and the mass of the pontoon into two flexible parts, which are connected by a cantilever spring system. Thus the TLP motion becomes two degrees of freedom (TLP 2-DOF). Using the dynamic vibration absorber (DVA) method, the ratio of the deck mass, pontoon mass, and spring stiffness are adjusted so that the primary mass movement is minimal. Furthermore, the ratio of the amplitude of the deck movement as the primary mass to the wave amplitude is analyzed, which is known as the operator response amplitude (RAO). The results showed that the TLP 2-DOF model was more stable. As an illustration, at resonance conditions, this model can reduce RAO to about 67%.

Vibration Control of Offshore Platform Structure with Friction Dampers

The performance of friction dampers to mitigate waves and earthquakes in tower-type offshore platform is investigated in this paper. Taking the offshore platform of TOWER-1 as an example, the equation of motion of offshore platform structure under earthquake and wave loads was established. The response reductions of offshore platform structure by different peak earthquakes were analyzed. The results show that the responses of the tower-type offshore platform structure under wave and earthquake could be effectively reduced by friction damper, and the energy dissipation ability of the friction damper differs in the different floors. The friction dampers give good response reductions in different peak earthquakes, and the response reductions of displacement are better than those of acceleration.

Research on the Effect of Seasonal Environmental Loads on Bohai Bay Offshore Platform

In recent decades jacket platforms are widely used for facilitating the offshore oil industries in order to reach their demands of producing oils. In this regard given analyses shows the influence of seasonally based environmental loads acting on the offshore platform structure situated at Bohai Bay northeast of China. This paper studies and summarizes the structure reliability theory with jacket platform as the research object; it is the first time to aim and finds the most dangerous season effecting Bohai Bay offshore platforms by considering seasonal environmental loads. Finite element analysis ANSYS software is used for model analyses and optimisation of the structure spatial correlation seasonal loads. Environmental design data is extracted according to its geographical conditions in the form of wave, wind and current forces. Since most of the control management nodes work below the surface of the water so the distribution of stress and fatigue life of the pipe node under multi-axial loading is in different forms. The analysis mainly focuses on the stress and fatigue life appropriate characteristics to the actual situation of multi-axial loading case of the K-joint welding location and mainly environmental effect on the platform.

The Research Development of the Mechanism of Fatigue Crack Initiation Based on Microstructure for Offshore Platform

In the capricious marine environment, the offshore platform structure is exposed to the multiaxial fatigue loading in which damage would be formed in different directions and planes. Evolution of the structural damage physical mechanism caused by marine environment load is more complicated. Based on the analysis of a large number of literatures, this paper reviews the research status of the fatigue crack mechanism in China and abroad, and predicts the development direction in the future.

An Innovative Study on the Fluid-Sloshing Wave-Energy Conversion System (FSWECS)

In this study, a new type of energy converting system is developed and installed in an offshore platform structure to take the advantage of strong motion of the platform subjected to waves. It is a device that by utilizing the sloshing power of the fluid stored in a U-shape tube, the turbine of the electric power generator is driven and electricity can be generated. By following previous experimental studies in basic vibration behavior for the FSWECS device that under various periods and amplitudes of the stroke in the experimental tests, can effectively convert vibration motion into electricity power, a further test for the effectiveness of energy converted from the FSWECS device was performed in a water-tank. Parameters identified in previous studies including the natural periods of the FSWECS device, the strokes of the vibration and the relationship between the amount of the liquid filled in the tube and the dynamic character of the device are further studied when subjected to a simulated wave.

Fatigue Damage Mechanism Experiments of the K-Joint of Offshore Platform Model

Ocean environment loads such as wave, current and wind load shows random distribution. The coupling of different kinds of load can easily lead to the fatigue damage of offshore platform structure. The damage presented the multiaxial characteristics would be formed in different directions and planes. K-joint is the key but weak part of the platform structure. This paper associated macro ocean environment factors with material interior micro structure change to reveal the microscopic mechanism of fatigue damage evolution and fatigue damage evolution regularity. By building finite element model of the offshore platform K-joint and physical model, an experiment is done under the function of wave and current load and makes a good result. In this way, the relationship between them and fatigue life was established, and the result agreed with the theoretical predictions.