| Faults of hydraulic system in large agricultural machinery equipment have become a key factor affecting the reliability of agricultural machinery equipment.Developing an efficient and accurate non-interventional pressure detection method can effectively avoid hydraulic system faults caused by hydraulic pipeline overload.Due to its unique advantages,ultrasonic guided wave technology has been widely used in non-destructive detection of rod,tube and plate structures in the fields of aviation,mechanical equipment,facility agriculture and other fields,and has achieved good application results.Ultrasound guided wave acoustic elastic effect has potential advantages in stress detection and can be used to evaluate the absolute stress level of structures.Especially for large-scale agricultural machinery equipment hydraulic pipeline pressure can achieve non-interventional detection,and enriching and exploring non-interventional pressure measurement methods and improving the reliability of agricultural machinery equipment,will have important practical significance and widely application prospects.However,when considering the influence of pressure in pipeline,the effect of strain energy should be considered.The theoretical model needs to use the third-order elastic constants to establish the hyperelasticity model,so the fluctuation characteristics are more complex,which makes the theoretical analysis of the acoustoelasticity characteristics combined action of multi-modes and dispersion characteristics of ultrasonic guided waves under pressure are more difficult.It seriously restricts the application of ultrasonic guided wave technology in pipeline pressure detection.In order to figure out the propagation characteristics of ultrasonic guided waves in pipe structures under internal pressure,considering the stress analysis of pipeline under internal pressure,a non-linear wave equation with initial stress conditions is established based on Murnaghan hyperelastic model.The dispersion characteristics of cylindrical guided waves under two initial stresses are numerically solved.Then the dispersion curve of acoustoelasticity is established to analyze the pressure sensitivity of each mode excitation frequency.By means of analysis the theoretical of cylindrical guided wave acoustoelasticity,a suitable excitation modes and frequencies for engineering detection are selected,and the internal pressure detection model of pipeline is numerically simulated to further optimize the optimal excitation modes and frequencies.A magnetostrictive sensor and a controllable hydraulic pipeline pressure testing system are developed.The longitudinal L(0,2)and torsional T(0,1)modes are used to detect the internal pressure of pipelines.The feasibility of non-interventional pipeline pressure testing method based on ultrasonic guided wave acoustoelastic effect is demonstrated.The main research work is as follows:(1)Based on Murnaghan hyperelastic model,a nonlinear wave equation with initial stress conditions is established.The dispersion eigenvalues of four kinds of cylindrical guided waves L(0,m),F(1,m),F(2,m)and T(0,m)under two initial stress conditions are solved numerical.Acoustoelastic dispersion curves characterizing acoustoelastic sensitivity modes and excitation frequencies are obtained.It is found that the acoustoelastic effect of cylindrical guided waves is greatly influenced by the excitation frequency.The acoustoelastic constants at different excitation frequencies have obvious differences,and the dispersion of the acoustoelastic constants is large.The excitability,dispersion and sensitivity of the modes and excitation frequencies suitable for pressure measurement should be considered comprehensively.(2)Based on the Multi-physical field coupling software COMSOL,the propagation characteristics of longitudinal and torsional modes under initial pressure and temperature fields are simulated.Based on the cross-correlation function method,the delay values of guided wave propagation under two pressure conditions and two initial temperatures are calculated.The acoustoelastic constants and temperature effects of the numerical simulation are calculated based on the time-delay values.The results show that the numerical simulation results are in good agreement with the theoretical calculation,and the suitable modes and excitation frequencies for testing are obtained.The influence of temperature on pressure testing should be taken into account in testing.(3)In order to realize single mode excitation and avoid the influence of other factors such as coupling agent on acoustoelasticity test,magnetostrictive sensors with longitudinal mode and torsional mode are developed respectively.Based on C OMSOL solid mechanics module and AC/DC module,multi-field coupling simulation of guided wave propagation characteristics in pipeline excited by magnetostrictive sensor is carried out.Verified the performance of the sensor and analyze the layout distance suitable for pressure sensor.Confirm that the performance of the sensor can meet the needs of acoustic-elastic pressure detection.(4)A hydraulic pipeline pressure testing system based on acoustoelastic characteristics of ultrasonic guided waves was built.The environmental temperature effects of longitudinal and torsional modes and acoustoelastic characteristics were studied experimentally.The results show that the ambient temperature has a great influence on the acoustoelastic pressure measurement,and the temperature needs to be calibrated in the actual measurement;The trend of acoustoelastic constants is in good agreement with the theoretical results,but there is a large deviation in the numerical values.The measurement accuracy of 106 kHz L(0,2)longitudinal mode pressure is low,and the torsional mode 32 kHz T(0,1)under pressure frequency will dispersion.The acoustoelastic effect of 64 kHz T(0,1)mode is strong,but the error is large.When temperature is considered in 128kHz T(0,1)mode,non-interventional pressure detection of pipeline can be realized. |
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