| dc.description.abstract | This thesis encompasses on drilling riser technology, modeled and simulated the drilling riser with more emphasize on heave compensation system. More particularly the heave compensation properties and its effect to the riser response. The models have been modeled in some scenarios with various water depth,various environmental conditions, and varying heave compensation properties. Since the analysis for deep water drilling riser is quite complex, it is required to address operational limitation, tension requirements, manage deflection angle on flexible joint and material capacities. The model was carried out usingRIFLEX in static linear, static nonlinear and dynamic linear analysis. And some post processing program was used such as Matrix Plot and MATLAB.
The initial condition of the riser can be determined by simulated the model in the quasi-static analysis.The initial configuration that required small deflection angle at the bottom of the riser can be set up by adjusting some parameters such as vessel offset, top tension of the riser and buoyancy configuration. Oneof the methods to model the buoyancy here is by applying small density material at the buoyancyelement. Higher top tensions will require increased wall thickness and vessel capability. The effective tension of the riser shall remain in tension condition in order to protect the well head. Sufficient buoyancy element and top tension are required to establish tension condition along the riser, hence the collapse due to buckling also can be avoided.
Structural nonlinearities response is determined by dynamic time domain analysis. Heave compensation system properties here is represented by damping c and spring k coefficient and its modeled followingThe Kevin-Voigt Model by putting spring and dashpot in set in parallel. Spring and damping effect give compensation to heave relative motion between the vessel and riser. By increasing the spring and damping effect, the tension variation is increased as well. The stroke of the riser is influenced by some factors such as, heave compensation properties, water depth, environmental load, riser system, type of vessel and mooring method.
By assuming the heave compensation properties we studied the sensitivity of dynamic tension variation with varying heave compensation system properties under several environment conditions. During severe environment condition, the total stress will be very high. Design limitation for material strength is shall be following NORSOK-N001. In case for drilling riser during severe environment condition the operation will be stopped, and riser will be hang off. By riser response from constant tension and varying tension analyses such the effective tension from constant tension is expected value effective tension from varying tension analyses. Hence, the needed of heave system properties is identified for each environmental condition and riser system and defined the design limitation. | nb_NO |
