| With the depletion of oil and gas resources on land and the increasing demand of oil and gas,the exploitation of offshore oil and gas continues develop to deep water and ultra-deep water.Semisubmersible platform with less investment,more deck space and variable deck load(VDL),greater range of water depth,easier modification,drilling,and production,will be a better choice for meeting the deep-sea operation.Motion response of semi-submersible platform is the design basis,which is the precondition for the analysis of the structural strength.Because of the complex structure and working environment,the motion response of semi-submersible platform is affected by many parameters.Working water depth,loading condition,environment condition and the positioning methods have certain influence on the platform motion response.It is found that the effects of these parameters for the platform motion response are obvious throughout the process of basic design for some semi-submersible platform.The sensitivity researches of the platform motion response with respect to a number of important parameters have been performed;these provide a useful reference for grasping the motion response laws and guiding the scientific design.The weight control and variable deck load of semi-submersible have become more and more important accompanied by the development of offshore engineering to deep water and ultra-deep water.Meanwhile,the more stringent requirements of the working environment are required.Therefore,the vibration and noise on the platform is also not negligible.Because of the advantages such as lower density,higher strength and corrosion resistance,the composite materials have been applied to the offshore structure.The application of the composite materials can reduce the structure weight and vibration as meeting the requirements of structural strength.Meanwhile,the variable deck load can be improved.The power equipment foundation with metal-composite material not only can reduce the structure weight,but also can solve the vibration and noise problem.In this paper,the design method of reducing weight and vibration for semi-submersible platform has been studied.The results provide a reference for the technology application in the future.Relying on the project of HYSY982 basic design and project of national natural science foundation “Optimization design theory and test study on the reduction of vibration and noise for metal-composite material hybrid structure of naval vessel”.The following researches have been carried out in this paper:1.Taking a typical semi-submersible drilling platform as an example,the mainly applied analysis method of motion response of semi-submersible in engineering field has been introduced.2.Because of the change of ballast water and variable deck load(VDL)position and the number,the radius of gyration will be modified.Meanwhile,the range of the semi-submersible platform working depth is relatively large(100m~3000m).Taking above platform as an example,the sensitivity analysis of the motion response,air gap,wave load and design wave with respect to the radius of gyration and water depth are carried out with the methods ahead.3.The wind,wave and current loads are difficult to be realized simultaneously in the model test due to the limitation of the test condition.Moreover,due to the increase of water depth,the mooring system is also very difficult to simulate in full size.The one method is proposed through the tuned numerical simulation model method and wind tunnel test.This method can accurately consider the effect of wind,wave,current and full-size mooring system on the hydrodynamic performance,simultaneously.According to the Class rules,there is no clear description whether to consider current and wind effects on semi-submersible platform air gap analysis.Therefore,the sensitivity analysis of air gap and wave slamming load of deckbox with respect to the wind,current and mooring system by the Double Damping Tuned Method in time domain is conducted.4.In this paper,based on DNV rules,the positioning capability analysis method of mooring positioning system,DP system and ATA system are introduced in the present engineering field taking the platform as an example.The step by step to increase couple method is proposed for the capability analysis of DP system.This method can better consider the effective thruster force for the current,shell of ship and adjacent thruster in different directions.The method is achieved by the Matlab for the positioning capability analysis of DP system.Furthermore,the anchoring method optimization of a semi-submersible platform is proposed by fuzzy control method.It reveals the different positioning methods for the sensitivity of the platform motion in the same draft.5.The brace structure of semi-submersible platform will be subjected to wave slamming in survival conditions and towing condition.Furthermore,the slamming force effect for structure strength analysis is required by Class rules.In this paper,an evaluation method is proposes for the brace structure.This method can consider the global load effect and wave slamming load on brace structure for buckling and yielding analysis.Using the platform as an example,the brace strength analysis has been carried out by this method.The analysis results and the method are approved by the CCS and DNV class.The brace structure strength is sensitive to wave slamming load.6.According to the requirement of weight control and VDL of deep semi-submersible platform and the characteristics of the composite material,the optimization study of vibration and weight reduction for the metal-composite material hybrid structure has been carried out.An optimization method is proposed combining the LCM and SIMP method.This method can concurrently carry out the size optimization,material selection and topology optimization.The feasibility and superiority of this method are proved by a three bar truss,a ten bar truss structure and the floating raft metal-composite material hybrid structure.7.The dynamic characteristics studies in different orthogonal joints(T,L and Pi type)are performed by an example of vibration reduction of floating raft through the MATLAB and ANSYS software.The static,modal and harmonic response of the different type joints in floating raft have been analyzed and studied.The sensitivity analysis of the radius and thickness of the joint plate with respect to the modal and harmony response have been performed.These studies provide some valuable references for the design of semi-submersible platform and the vibration and noise reduction of naval vessel and offshore platforms. |
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