Research On Modeling And Diagnosis Methods For Mechanical System With Inner Cracks And Working With High-speed Impacts

High-speed impact mechanical systems are very common in mechanical engineering,especially in the field of national defense science and engineering.Because of the high-speed impact in the working process,crack failure of the mechanism components is easy to happen.If these crack faults cannot be found immediately,unstable propagation may occur without warning,and leads to brittle fracture,which will seriously affect the reliability of the system operation,and may cause safety accidents.Therefore,it is of great significance in engineering to diagnose the weak crack faults of such mechanical systems accurately.On the other hand,the crack faults of such mechanical systems often occur in the inner parts of the system or in the parts moving at high speed.It is very difficult to test their dynamic response directly,which increases the difficulty of crack fault diagnosis of such systems.In this paper,aiming at the problem of crack fault diagnosis of mechanical systems working with high-speed impacts,taking the typical representative of such system—XXX antiaircraft machine gun—as the specific research object,the modeling and diagnosis methods of such systems are studied,in which the former serves the latter.The research on modeling methods includes system-level modeling method and component-level modeling method.The research on diagnostic methods mainly focuses on the effective extraction of multifractal features and the effective utilization of the extracted features.The specific research work of this paper is as follows:(1)Based on Modelica language and the theory of differential algebraic equations,the system-level modeling and simulation of XXX antiaircraft machine gun are carried out in MapleSim environment,and the movement law of each component of the XXX antiaircraft machine gun in its shooting direction is obtained.(2)Based on the theory of elastic wave and strong discontinuity disturbance lines in elastodynamics,a one-dimensional dynamic model of coaxial impact of two cracked elastic rod is established,and the corresponding MATLAB simulation program is developed.The influence of crack location,depth and width on the dynamic response of the impacted rod is obtained by simulation.By comparing the simulation results with those of the professional finite element simulation software MSC.Dytran,it shows that the modeling and simulation method has obvious advantages over the finite element model in simulating such problems.(3)Three kinds of weak crack faults were set up on the locking mechanism of the automatic mechanism of the XXX antiaircraft machine gun,and it fired several times with live ammunition under each fault conditions.The vibration response signals of three orthogonal directions of two measuring points,one on the machine gun body and the other on the gun rack,were sampled during the firing process.The method of forming the original data sample by pretreatments of the original sampled signal,such as interception,down-sampling,or low-pass filtering,is given.The measured signal samples are formed for subsequent research on diagnostic methods.(4)The basic theory of multifractal analysis and the method based on wavelet leader or p-leader for multifractal analysis are systematically rearranged.A method for obtaining multifractal features from multifractal spectrum by morphological curve fitting is proposed.A method for extracting time-frequency coherence multifractal features of synchronously sampled vibration signals by constructing time-frequency coherence network is proposed.(5)Via a benchmark test involving 13 dimensionality reduction methods,a general scheme is given,which can be used to select the best feature fusion method and determine the optimal parameters of the feature fusion method and of the intelligent classifier for a given set of original feature samples.In this paper,many typical key problems have been solved in the process of system modeling and simulating of XXX antiaircraft machine gun,which can provide references for the same work of other mechanical systems.The introduction of Modelica modeling language and MapleSim modeling and simulating environment provides a new technical means for the modeling and simulating analysis of large complex mechanical systems.The method of modeling and simulating the coaxial impact of cracked elastic rods proposed in this paper is of absolute advantage compared with the finite element method,not only because of the very low computational complexity,but also because of the theoretical solution it can obtained.It provides a new and effective means for the study of crack information transfer mechanism in the process of components impacting.In the machine gun experiment,setting of the experimental parameters about faults,measuring points,digital sampling and so on,and the signal preprocessing operations such as interception,down sampling and low-pass filtering of the original signal,can provide references for the experimental research of other mechanical systems.The rearrangement of the basic theory of multifractal analysis and the method for multifractal analysis based on wavelet leader or p-leader can facilitate the research of related studies.The introduction of multifractal analysis method based on wavelet leader or p-leader provides an effective technical means for multifractal analysis of original data.The method of extracting multifractal feature from multifractal spectrum and the technology of extracting time-frequency coherence multifractal feature of synchronously sampled vibration signals proposed in this paper provide new means and ideas for effectively utilizing the results of multifractal analysis.The general scheme proposed in this paper for selecting the best feature fusion method and determining the optimal parameters of the method and of the intelligent classifier provides a basic operational flow for effectively utilizing the original feature samples,which is beneficial to improve the prediction accuracy of intelligent diagnostic techniques.