Abstract: For deep-water oil and gas exploration, spar platform is considered to be the most economic and suitable floating offshore structure. Analysis of spar platform is complex due to various nonlinearities such as geometric, variable submergence, varying pretention, etc. The Finite Element Method (FEM) is an important technique to deal with this type of analysis. However, FEM is computationally very expensive and highly time-consuming process. Artificial Neural Network (ANNs) can provide meaningful solutions and can process information in extremely rapid mode ensuring high accuracy of prediction. This paper presents dynamic response prediction of spar mooring line using ANN. FEM-based time domain response of spar platform such as surge, heave and pitch is trained by ANN. Mooring line top tension is predicted after 7200 sec (2 hours) of wave loading. The response obtained using ANN is validated by conventional FEM analysis. Results show that ANN approach is found to be very efficient and it significantly reduces the time for predicting long response time histories. Thus ANN approach is recommended for efficient designing of floating structures.
Abstract: It is a common practice to model multi-storey tall buildings as frame structures where the loads for structural design are supported by beams and columns. Intrinsically, the structural strength provided by the walls and slabs are neglected. As the building height increases, the effect of lateral loads on multi-storey structures increases considerably. The consideration of walls and slabs in addition to the frame structure modelling shall theoretically lead to improved lateral stiffness. Thus, a more economic structural design of multi-storey buildings can be achieved. In this research, modelling and structural analysis of a 61-storey building have been performed to investigate the effect of considering the walls, slabs and wall openings in addition to frame structure modelling. Sophisticated finite element approach has been adopted to configure the models, and various analyses have been performed. Parameters, such as maximum roof displacement and natural frequencies, are chosen to evaluate the structural performance. It has been observed that the consideration of slabs alone with the frame modelling may have negligible improvement on structural performance. However, when the slabs are combined with walls in addition to frame modelling, significant improvement in structural performance can be achieved.
Abstract: Offshore oil and gas industry is blooming up towards the deep-water region of ocean deposit. Far off the
continental shelf, the traditional jacket type fixed platform and bottom supported compliant platform are not
suited to be economic offshore structure in deep water oil and gas exploration. Floating Spar platform is
essentially most economic and efficient in these sea states. In the present study coupled analysis of integrated
Spar platform has been carried over. A fully coupled integrated model is developed which includes the
contribution of mooring lines and risers with Spar hull in a consistent manner. This model is capable in
matching the forces and displacements at fairlead position along with all structural and environmental
nonlinearities. Nonlinear dynamic responses have been evaluated for long span of wave hitting under
unidirectional regular wave of varying heights. An automatic Newmark-β time integration technique has been
adopted to conduct the analysis in time domain. Wave kinematics follows Airy’s wave theory and the Morison’s
equation is utilized to cope with the forces. The damping effect of mooring lines in coupled model is significant
and increases with the depth of sea bed. Displacement, rotation, velocities at surge, heave and pitch direction
along with mooring line tension has been evaluated for 6 m and 7 m wave height in 1018 m water depth. The
responses indicating spar movements follow similar pattern. But the greater peak values occur earlier for larger
wave height case. Mooring line tensions are showing sensitive result showing significant value for higher wave
period. Sudden increase of mooring tension indicates the possibility of instability and failure of the sparmooring
system. Hence, associated with the coupling effect the response behaviours alter at wave of larger
height with respective probabilities of occurrences. The design consideration should include the optimum and
worse conditions to avoid severity.
