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Glass reinforced plastic (GRP) subsea protection covers are often used to protect offshore pipelines, umbilicals and other important subsea structures from dropped objects released from offshore oil and gas and fishing activities. These covers are often subjected to waves. The study of the GRP subsea cover under wave and current is a challenge, and it is the aim of this study to develop and build a numerical model that can be accurately simulated in response to the experimental implementation difficulties. This study performs a series of numerical simulations of the flow of different geometry structures under different flow condition at a series of KC numbers. The thesis is divided into three main procedures. The Chapter 5, 6 and 7 are the essential parts of this thesis and follow a sequence of modeling, revision, and analysis. In the present study, flows around an oscillating GRP subsea cover and oscillatory flows around a stationary subsea cover are investigated using numerical simulations at three different KC numbers of 5, 11 and 20, which are representative for low, medium and large KC number regions. For comparison, the solid structures of subsea cover are also investigated. The simulations of flows around an oscillating subsea cover are used to compare with the experiments done by SINTEF Ocean (formerly MARINTEK) and validate the present numerical model. This study mainly validates that the drag force and lift force acting on the static subsea cover subjected to the oscillatory flow can be used to predict the forces of flow on a moving subsea cover, which provides the foundation for further studies. It is found that the hydrodynamic forces for the two cases (flows around the oscillating cover and oscillatory flows around the stationary cover) are almost the same, which verifies that the experimental tests of subsea covers with forced motions can be used to study hydrodynamic forces on the stationary cover subjected to waves. The horizontal and vertical force coefficients and the surrounding flow fields around the covers are discussed. For further revision to improve lift forces with different geometry subsea covers is conducted. Three geometry categories are Case 1: cover only shell connected with domain respectively, Case 2: cover on the domain bottom and Case 3: subsea covers with baffles of different lengths. These cases discuss various aspects of the forces on the upper surface of the cover, the effect of the plate, and the effect of the water interaction inside the cover, for fully exploring the mechanism of the interaction between water flow and cover. Finally, the final numerical model that is the best match to the experimental data is determined. For this case, DMD post-processing will be performed to capture the dominant modes that determine flow filed and vorticity.

Master's thesis in Offshore technology: Subsea and marine technology For a few last decades, the Arctic region is considered to be very wealthy in terms of oil and gas resources. Initial estimations show that roughly 100 billion tonnes of oil and gas reserves might be accumulated under the surface of the Arctic region (Kontorovich, 2015). Beginning with the general description of the most explored oilfields located in the southeastern part of the Barents Sea (Pechora Sea), the project comprehensively considers conceptual development of the Medynskoe-more oilfield by utilizing the IRGBS “Prirazlomnaya”, in particular: * development of the optimal oil production strategy for the oilfield; * selection of the appropriate offshore structure; * selection and justification of the possible oil transportation solution; * design and construction of the subsea pipeline from the Medynskoe-more oilfield to the IRGBS “Prirazlomnaya”; * analysis of the processing, storing and offloading systems in the IRGBS “Prirazlomnaya”. Special emphasis is done on a detailed elaboration of a subsea pipeline that should be able to withstand harsh environmental conditions in the Arctic region, including ice presence (formation of stamukhas) and shallow waters (substantial hydrodynamic loads from wave and current). Aspects such as pipeline design, on bottom stability and pipeline trenching are reasonably considered. Moreover, risk analysis procedure is provided by applying hazard identification method (HAZID) with the subsequent bow-tie diagrams construction for the most dangerous risks. In order to evaluate the economic feasibility of the proposed project, the cost-effective analysis is fulfilled. Eventually, a conclusion and recommendations for future work are presented based on the technical and economical results.

Master's thesis in Offshore technology: Marine and subsea technology The risk, price inconsistency and environmental impact associated with oil and gas exploration and production have geared a focus on renewable energy. Wind power, the fastest growing source of renewable power generation in Europe, is a major competitor to oil and gas. The strong and stable wind at offshore locations and the increasing demand for energy have surged the application of wind turbines in deep water. Wind turbines are categorized into Horizontal Axis Wind Turbines (HAWTs) and Vertical Axis Wind Turbines (VAWTs) based on their respective orientation of axis of rotation. A floating wind turbine will experience large loads from wind, waves and rotating blades. Research has focused on the design, structural integrity, platform motion and installation of floating horizontal-axis wind turbines (FHAWTs) to better understand the performance of different concepts and to provide the basis for detailed structural design. However, the application of floating vertical axis wind turbines (FVAWTs) in deep offshore has potentials due to its economic advantage in installation and maintenance. Research in the development of FVAWTs is still green. However, a variety of studies applied different simulation tools to investigate the response characteristics of FVAWTs to provide the conceptual design decriptions and detailed evaluation of technical feasibilities of the various concepts. This thesis adopted a 5MW Baseline FVAWT from Wang’s PhD work. The FVAWT is a novel concept combining the 5MW DeepWind rotor and the DeepCwind semi-submersible from the Offshore code comparison collaboration Continuation (OC4) project. The response characteristics of the FVAWT was evaluated using a coupled non-linear aero-hydro-servo-elastic model (the Simo-Riflex-DMS code) which was developed by Wang for modeling FVAWTs. This coupled model incoorporates the models for the turbulent wind field, aerodynamics, hydrodynamics, structural dynamics and controller dynamics, and the simulation is performed in a fully coupled manner in time domain. The FVAWT has been studied in a systematic manner, which includes a comprehensive investigation of the aerodynamics of the wind turbine to analyze the dynamic response of global motion for the floating system; considering normal operating condition to emergency shutdown event; as well as comparing the FVAWT with a FHAWT. However, the fatigue analysis for structural components such as blades, tower and mooring lines have not been performed. For FVAWTs, the continuously varying aerodynamic loads on the rotor lead to considerably higher load level of the fatigue loads and number of load cycles. Therefore, it is significant to evaluate fatigue damage based on the time history of calculated response. The rainflow counting technique is used for short-term fatigue cycle counting. The Mlife tool from NREL is used to calculate the short-term fatigue damage equivalent loads for the FVAWT. Furthermore, this work is extended to model and evaluate the performance of a 5MW Optimised FVAWT in terms of power production, structural dynamic response, global motion and short-term fatigue damage on structural components. The 5MW Optimised FVAWT is a concept combining the optimised 5MW DeepWind rotor from the Technical University of Denmark (DTU) and the DeepCwind semi-submersible from the OC4 project. The two FVAWT concepts were evaluated under the same environmental condition. The response characteristics of both 5 MW FVAWTs were studied under steady wind and turbulent wind conditions based on the statistical analysis and the spectral analysis of their responses to explore the effects of turbulence. The results identified that the effect of turbulence on the both FVAWTs resulted in an increased power generation, higher power variation, higher excitation for low frequency motions, greater fatigue damage but a reduction in the 2P effects. However, the effect of turbulence is negligible on the bending moment at the blade extremes but leads to higher loads on mooring lines and tower base especially at wind speeds above the rated wind speed. Furthermore, the results of the fatigue analysis showed that at wind speeds farther from the rated wind speed (14 m/s), the internal loads could have lower damaging effects than at wind speeds closer to the rated wind speed. Moreover, the dynamic response of the 5 MW Baseline FVAWT is compared with the 5 MW Optimised FVAWT in terms of power production, bending moment of structural components, global motion and short-term fatigue equivalent loads under turbulent wind condition. The results identified the 5 MW Optimised FVAWT to have lower Fore-Aft (FA) but higher lower Side-Side (SS) bending moment of structural components, lower motions amplitude, lower short-term fatigue equivalent loads and reduced 2P effects.