The current world record water depth for a semi-submersible rig using dynamic positioning is 9,472 ft. Semi-submersible rigs are used to drill wells in water depths up to 9,500 ft. Semi-submersible drilling rigs are considered to be the most stable of the deeper water MODUs. The thrusters are the yellow devices under the pontoons in Figure 8.12. In addition, a system of Thrusters (high energy propellers) is used to control the pitch, roll, and yaw of the vessel and to provide Dynamic Positioning to keep the rig at the same surface location during drilling operations. The columns provide additional stability to the vessel during drilling operations due to their small cross-sectional area as little wind, wave, or tidal energies are imparted to the columns and the vessel (this is called Wave Transparency). This is done to create greater stability during drilling operations by adding mass to the vessel and providing it with a deeper draft. Once on location, water is used as ballast to partially flood the pontoons and columns to allow them to sink to a position below the water level. The paper addresses lessons learnt to improve the CFD computations as well as practical aspects and limitations of thrust efficiency modeling, including all interaction effects, using CFD from an engineering perspective.Source: LinkedIn Slideshare - Semi submersibleĭuring transport (either self-propelled or towed), the pontoons allow the vessel to float in the water until it is on location. ![]() These results are compared to full scale observations and, where possible, improvements to the numerical modeling are assessed. In preparation, CFD simulations are performed for different thrust combinations. A first validation study is performed based on data acquired during a transit of SSCV Thialf in Q4 2011. Scaling CFD from model scale to full scale is not trivial it involves a significant change in Reynolds number, a different description of boundary layer and poses challenges to meshing and grid. The comparison between the CFD and model test data shows that CFD is able to predict the relevant force components within a sufficient accuracy for engineering purposes.Īt present not much is known about the extrapolation of model scale DP-thrust efficiency to full scale DP-thrust efficiency, neither for model test results, nor for CFD results. The model test data include the global forces, the forces on each individual pontoon and the forces of each individual thruster, including the nozzle thrust and propeller thrust. Similar as the previous benchmark studies the numerical data are validated with a series of dedicated model tests. The logical next step is to perform a numerical study on a thruster-hull interaction with current. In previous benchmark studies CFD is used to assess the current loads as well as thruster-hull interaction without current on a semi-submersible vessel. An assessment of the thrust efficiency of the DP thrusters of these vessels has been made by comparing CFD computations with dedicated model tests. Heerema Marine Contractors has two DP-semi-submersible crane vessels the Thialf and Balder. This thruster-hull interaction becomes even more important when the vessel is a semi-submersible vessel the thruster wake of the thruster on the upstream pontoon might impinge on the downstream pontoon resulting in high losses in efficiency and reduced DP-capability. The thrust efficiency of the DP-system depends on the efficiency of the individual thrusters, but also on the interaction of the thruster wake and the hull of the vessel. ![]() The ability of a DP-vessel to keep its position depends highly on the performance of the DP system. Journal of Verification, Validation and Uncertainty Quantification.Journal of Thermal Science and Engineering Applications.Journal of Offshore Mechanics and Arctic Engineering.Journal of Nuclear Engineering and Radiation Science.Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems.Journal of Nanotechnology in Engineering and Medicine.Journal of Micro and Nano-Manufacturing.Journal of Manufacturing Science and Engineering.Journal of Engineering Materials and Technology.Journal of Engineering for Sustainable Buildings and Cities.Journal of Engineering for Gas Turbines and Power.Journal of Engineering and Science in Medical Diagnostics and Therapy.Journal of Electrochemical Energy Conversion and Storage.Journal of Dynamic Systems, Measurement, and Control.Journal of Computing and Information Science in Engineering. ![]() Journal of Computational and Nonlinear Dynamics.Journal of Autonomous Vehicles and Systems.ASME Letters in Dynamic Systems and Control. ![]()
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