Measurement And Simulation Of Nonlinear Motion Response Of The Large Scale Ship Model

With improvement of the ship experimental technology,it becomes a trend that the ship model experiment should be more aligned with the practice when simulating the navigation state of ship and can provide more practical test data.Under the circumstance of ocean,the motion of ship model would be closer to the practice when suffering from the three-dimensional wave rather than that generated in experimental tank.Therefore,the large-scale model test can reflect the characteristics of real ship movement in three-dimensional non-linear wave.Meanwhile,how to use the ship model test data to extrapolate and predict the actual movement of the ship is of great significance to the safety of the ship and the improvement of operational efficiency.Therefore,this paper uses the system identification method combined with the experimental data to solve the ship motion frequency response function,and then lays a foundation for the ship motion extrapolation forecast.This article is mainly focused on the following contents:Firstly,the identification model of ship motion response is established by AR model combined with the least squares method,Kalman filter method and high order cumulative method,at the same time the RAO of ship motion is solved by the ship model test motion data.The non-linear model NARMAX is used to identify the ship motion response based on the experimental data and wave data of ship model test,and then the frequency function of ship motion response is solved by harmonic detection method,which provides a basis for the subsequent extrapolation prediction of real ship motion movement.Secondly,the second-order Volterra series model under the least square method is combined with the motion data of ship model test to predict the short-term motion response of ship model.Through this method,a short-term prediction method of ship model nonlinear motion response is determined.Thirdly,the design of the test system,the design and processing of the model,the design of the test implementation process,the debugging of the relevant test equipment,the collection of test data,and the processing of the test data are completed.Then the AR model and NARMAX model are used to solve the frequency response function of ship motion based on the test data of large-scale model test.The Volterra series model is used to predict short-term motion response.Fourthly,VegePrime visual simulation software is used to build the three-dimensional simulation model,set up the marine environment,define and establish the program files,design the data connection,and establish the simulation system.Through the relevant programming,carry out the visual simulation of the motion attitude of the large-scale ship model test.Through this research it is found that:Firstly,the main frequency band and peak value of AR model determined by least squares method,Kalman filter method and higher order cumulative method correspond well with cross-spectrum method,so the least squares method is more advantageous than the three other methods.Secondly,the error of NARMAX model in motion prediction is small,and the frequency response function obtained by NARMAX model is similar to that by cross-spectrum method,and the analytical expression can be obtained.Thirdly,by using the Volterra series model for short-term motion response prediction,the prediction results have smaller errors in overall trend and amplitude compared with the actual motion.