Research On Fault Diagnosis Method For Hinge Joints Of Soft Yoke Arm

FPSO(Floating Production Storage and Off-loading)has become the mainstream equipment for offshore oil development in Bohai Sea area in China due to its superior reliability,strong adaptability and good economy.Single point mooring with flexible rigid arm is one of the most commonly used mooring forms at present.The reliability of flexible rigid arm mooring system directly determines whether FPSO can produce normally and the safety of upper personnel and facilities.However,the harsh marine environment and the complex structure of the soft rigid arm often cause various faults in the soft rigid arm mooring system,which will affect the normal production and life of FPSO.Therefore,monitoring and fault diagnosis of FPSO soft rigid arm mooring system is of great significance.The flexible rigid arm mooring system is composed of many hinge points,which can release the rotational freedom of FPSO hull,minimize the cooperative force of FPSO,avoid structural damage and ensure that the ship system is moored in a fixed range.Therefore,these articulated joints are the guarantee of the mooring function of the flexible rigid arm.Once a failure occurs at one of the articulated joints,it will directly affect the mooring performance of the flexible rigid arm,and even cause structural damage or damage of the flexible rigid arm.Among them,the thrust roller bearing at the upper hinge of the mooring leg is located in the interior of the mooring leg,where the bearing is liable to damage because of its complex force,and where the bearing fault signal interferes a lot,it is not easy to carry out fault diagnosis and analysis.Thrust roller bearing of mooring leg is an important part of the structure of FPSO soft rigid arm mooring system.Serious bearing failure will cause FPSO to stop production,overhaul and even cause major safety accidents.Because the mechanical structure of mooring system is complex,it is impossible to carry out on-site disassembly and inspection.Therefore,it is necessary to introduce a new theory or method,such as vibration signal,to diagnose and analyze the fault of FPSO soft rigid arm mooring system by indirect method,so as to provide reference for the daily maintenance,maintenance and replacement of the soft rigid arm system.In this paper,the thrust roller bearing in FPSO soft rigid arm mooring system is taken as the research object.According to the characteristics of long transmission path and large attenuation of vibration signal of thrust roller bearing,the theory of Minimum Entropy Deconvolution(MED)is introduced.The fault diagnosis and analysis of the research object arecarried out by combining time domain index analysis and envelope spectrum analysis.The main research contents are as follows.As follows:Firstly,the characteristics of amplitude spectrum entropy are introduced from the angle of entropy,and the application of amplitude spectrum entropy in the field of information processing is explained.Based on this theory,FIR filter is designed.Secondly,the filtering and noise reduction ability of minimum entropy deconvolution is tested by using bearing fault simulation signal,and the applicability and effectiveness of time domain index analysis and envelope spectrum analysis are verified.The effectiveness of the proposed method is demonstrated by the fault design experiment of the upper hinge bearing.The conclusion shows that the minimum entropy deconvolution theory combined with time domain index and envelope spectrum analysis method has certain effect on fault diagnosis of thrust roller bearings in FPSO soft rigid arm mooring system.The minimum entropy deconvolution can highlight impulse impulse components of vibration signals very well.The time domain index and envelope spectrum analysis can also accurately judge the working state of bearings,which has good engineering application value.