Study On Curing Process Monitoring And Signal Processing Of HTPB Liner Based On Ultrasonic Wave Mixing Techniques

The semi curing state of HTPB liner is extremely critical to determine the charging time of solid rocket engine.Therefore,it is very important in theory and practice to study the curing process and determine the semi curing state of HTPB liner.The key problems in the HTPB liner curing process monitoring by ultrasonic noncollinear wave mixing techniques are analyzed and studied in this paper.In order to solve the problem of monitoring and characterization the HTPB liner curing process,ultrasonic wave mixing theory,monitoring of the HTPB liner curing process using wave mixing techniques,ultrasonic detection signal processing and characterization of the HTPB liner curing state are presented in this thesis.Firstly,the theory of nonlinear ultrasonic wave mixing techniques is studied and analyzed,and the mixing phenomenon in LY12 aluminum material is investigated in the simulation and experiment.From the view of nonlinear interaction of elastic waves in an isotropic solid,the mechanism of wave-mixing and the resonant interaction principle of nonlinear resonant scattered waves and are explicated.The change of wave interaction angle?,propagation angle?and amplitude coefficient W with the change of frequency ratio d in LY12 aluminum alloy are analyzed and discussed through simulation experiments.The simulation results show that the mode SV??₁?+SV??₂??L??₁+?₂?and mode SH??₁?+SH??₂??L??₁+?₂?are suitable for designing the noncollinear wave mixing monitoring experiment.The resonant conditions are set according to the conclusion of theoretical research and simulation analysis,and the experimental noncollinear wave mixing for the mode SV??₁?+SV??₂??L??₁+?₂?and SH??₁?+SH??₂??L??₁+?₂?are tested on a40mm thick LY12 aluminum alloy specimen.The test results verify the correctness of theoretical analysis and simulation experimental results.Secondly,a noncollinear wave mixing device was designed to monitor the HTPB liner curing process,and the real-time noncollinear wave mixing monitoring of HTPB liner was carried out by the designed device in laboratory environment.In order to solve the problem of HTPB liner is too thin in practical engineering,which leads to time-domain aliasing of the detection echo in traditional nonlinear ultrasonic testing technology,the aluminum plate-HTPB liner-aluminum plate detection structure is designed.In this structure,the nonlinear resonant volume is divided into three parts with the center HTPB liner.In the lower aluminum layer,the resulting amount of nonlinear wave energy is expected to depend on the HTPB liner properties during the curing process.Because of changes in the wave velocity during the curing,transmission and refraction of the ultrasonic waves vary between the HTPB liner and aluminum interfaces.Then constraint relationship between wedge tilt angle and frequency ratio is deduced based the designed structure when the propagation angle?of the resonant wave is optimal.Based on this,an experimental device is designed to monitor the curing process of HTPB liner by noncollinear wave mixing techniques,and the real-time monitoring of curing process of HTPB liner material is realized.The experimental results show that the designed aluminum plate-HTPB liner-aluminum plate structure,which can effectively avoid the time-domain aliasing of the initial wave signal and the primary echo signal,is sensitive to HTPB liner changes during the curing process,and the result of ultrasonic detection signal parameters are consistent with that of theoretical analysis.Therefore,the presented structure can be used to monitor the curing process of HTPB linerThirdly,aiming at the problem that the target wave mixing signal energy is very small and often submerged by noise,based on sparse decomposition theory and particle swarm optimization algorithm,a parameter estimation method of weak ultrasonic detection signal in strong noise is proposed.In this method,the problem of parameter estimation and noise reduction of ultrasonic detection signal is transformed into the problem of function optimization in parameter space.First,based on the theory of sparse decomposition and the structural characteristics of ultrasonic signal,a super complete dictionary of ultrasonic detection echo is constructed,and then the problem of parameter estimation of ultrasonic detection echo is transformed into the problem of finding the optimal atom in the super complete dictionary.Then,according to the characteristics of particle swarm optimization that can be used to optimize the continuous parameter space,an improved adaptive particle swarm optimization algorithm is used to optimize the objective function in the super complete dictionary.Finally,the optimal atom is determined according to the optimization results of the objective function in the dictionary,then the estimation signal and its parameters are reconstructed by the estimated optimal atom.The processing results of simulated and measured ultrasonic signals show that the proposed method in this paper can effectively extract weak ultrasonic signals in the strong noise,which lays a foundation for the following chapters of signal processing and parameter estimation of wave mixing signals.Finally,in order to solve the problem that the curing state of HTPB liner mainly depends on the experience of engineers,the signal of noncollinear wave mixing monitoring in curing process of HTPB liner is processed,and the characterization and decision the semi curing state of HTPB liner material are realized through three links:signal preprocessing,feature extraction and analysis,and characterization of curing process of HTPB liner material.In the preprocessing process,the signal-to-noise ratio of wave mixing signal is effectively enhanced by using the variational mode decomposition,while the end-point effect and mode aliasing are avoided.By analyzing the characteristics of mixing signal,a nonlinear wave mixing coefficient is proposed and applied to the parametric characterization of HTPB curing state to realize the determination of HTPB semi curing state.