Research On Digital Twin Model Of Crankshaft Health Prediction For Marine Medium-speed Diesel Engine

In recent years,the intelligent ship has been paid more and more attention in the world.As the main power source of the ship,the steady and reliable operation of the diesel engine is the basis and premise of realizing the ship’s intelligent navigation.Therefore,it is very important to improve the reliability and intelligence level of marine diesel engine health management.But the marine diesel engine is a complex power machinery which involves many fields.In order to realize the condition monitoring of marine diesel engine,a lot of sensors and data are needed.The digital twinning technology creates the simulation model of the physical entity digitally.The model accepts the real-time/quasi-real-time data or historical data measured by the sensor to simulate and compute the working state of the physical entity,so as to understand and grasp the physical entity’s behavior in various environments in virtual space.With the development of communication technology,the virtual mapping of the running state of marine diesel engine in digital space and the realization of long-distance intelligent operation and maintenance of marine diesel engine will be the development trend of intelligent engine room in the future.Based on the idea of digital twin,this paper presents a digital twinning framework for marine diesel engine health management.Since marine diesel engine is a very complicated system,it is a very complicated work to model the whole diesel engine in the early stage of digital twinning research.Crankshaft is one of the key components that affect the service life of marine diesel engine,and it is one of the important contents of health state evaluation of marine diesel engine.Taking the crankshaft of a medium speed marine diesel engine as the research object,the digital twinning method is used to study the health prediction of the crankshaft,and the effectiveness of the digital twinning integral frame of marine diesel engine is verified.The main work of this paper includes:(1)Through summing up the application of digital twinning theory,aiming at the problem of health management and maintenance in the whole life cycle of marine diesel engine under the development background of intelligent autonomous ship,this paper puts forward the framework of marine diesel engine health management based on digital twins,introduces the composition and key technologies of the framework,and takes crankshaft as an example,puts forward a model for the application of digital twinning technology in the field of marine diesel engine.(2)The mechanical load of diesel engine mainly comes from the cylinder pressure,but the cylinder pressure sensor used for long-term monitoring is in bad working conditions and has limited service life.Based on BP neural network and RBF neural network,a neural network model for predicting the cylinder pressure signal is established,and the "virtual measurement" of the cylinder pressure can be used to preliminarily judge the combustion state in the cylinder and calculate the crankshaft load,providing a feasible solution for the calculation of the crankshaft load of diesel engine.(3)Analysis of the finite element calculation results It is known that the rounded corner of the transition between the crank and the journal is the key part of determining the service life of the crankshaft,and is the key point of the crankshaft stress monitoring and health evaluation,In order to meet the requirements of digital twinning for the realtime performance of the model,the data fitting method based on BP neural network is adopted to reduce the model order of the stress analysis model,and a stress real-time monitoring module is constructed.(4)Based on the idea of digital twinning,a digital twinning application software for crankshaft health assessment is developed,which integrates the real-time monitoring module,cylinder pressure prediction module and stress monitoring module to realize the visual display of crankshaft stress,stress peak value monitoring,fatigue life assessment,abnormal alarm and other functions.Digital twinning technology fully considers the coupling relationship between each subsystem of diesel engine,and makes real-time/quasi-real-time mapping of diesel engine state in digital space by using various sensor data.With the increasing demand of intelligent and autonomous ships for power systems,the application potential of digital twinning technology in the field of marine diesel engines will be released gradually.Based on the idea of digital twins,this paper constructs a health management framework for marine diesel engine,and takes crankshaft as the research object to realize a component level health prediction digital twins.