Research On Distributed Load Identification Method Of Plate Frame Structure

Propeller excitation is one of the main excitation sources of ship vibration.It can be divided into two categories,the first is the bearing force caused by the non-uniformity of wake flow;The second type is the pulsating pressure caused by the water pressure on the hull surface below the waterplane near the propeller when the propeller is running.Propeller pulsating pressure can arouse stern vibration,superstructure vibration and local vibration,which is the main source of stern vibration.Therefore,it is of great significance to reduce the vibration and noise of the ship tail if a simple and non-damaging method is developed to identify the pulsating pressure of the frame structure above the propeller(distributed load of the frame structure).The main work contents and research results are as follows:In this paper,the load identification method is studied firstly and the distributed load identification method in frequency domain is determined.Then,two-dimensional and threedimensional Chebyshev polynomials are derived from one-dimensional Chebyshev polynomials,and two-dimensional orthogonal polynomials are used to fit distributed loads.Secondly,this paper studies the relationship between pulsating pressure and hull vibration,propeller pulsating pressure test,prediction and estimation according to reference specifications.The corresponding estimation method,two simulation forms of propeller pressure and pulsation pressure and four working conditions(125r/min,136r/min,146r/min and 155r/min)were determined by the existing data.Modeling and simulation were carried out in ANSYS APDL and Fluent,and the single propeller-hull pressure simulation coupling model and double propeller-hull pressure simulation coupling model were established respectively according to the actual situation.By comparing with the results obtained from the estimation method proposed in the Ship Vibration Control Guide,the validity of the estimation method on the simulation results of single propeller pressure and the inapplicability of the estimation method on the simulation results of double propeller pressure are proved,and the correctness of parameter setting is also proved.Then,the pulsating pressure simulation data and real ship test data are used to provide data support for identifying distributed load(pulsating pressure).Firstly,the coupling model of twin propeller-hull simulation was established,and the relevant data of pulsating pressure simulation were extracted to complete the relevant verification work.Then a real ship test is carried out to filter and intercept the strain data to get the real signal.Finally,this paper uses two-dimensional orthogonal polynomial to fit the two-dimensional function and carries out error analysis,proving the feasibility of two-dimensional orthogonal polynomial fitting pulsating pressure.According to the characteristics of pulsating pressure generated by propeller,a distributed load(pulsating pressure)identification model is established,and the distributed load(pulsating pressure)identification of frame structure is completed by bringing in test and pulsating pressure simulation data.And the relative deviation analysis.