Research Of Low And Medium Frequency Shock Response Spectrum Correction Method

Underwater non-contact explosive experiment is the most direct and effective way to test the shock resistance of ships and shipboard equipment.The shock response spectrum calculated using accelerometers to measure the acceleration response of the equipment base during the test is an important basis for the design calibration of the equipment's shock resistance.Directly obtained acceleration data usually contain trend term errors,resulting in drifting of the lowfrequency spectral lines in the calculated shock response spectrum,with calculated spectral values 1-2 orders of magnitude greater than the true spectral values,which can lead to overshoot problems for devices in this frequency interval.In this paper,two low and medium frequency shock response spectrum correction methods are proposed to address the problem of low and medium frequency spectrum line drift in the shock response spectrum due to trend term error,and shock validation tests are conducted to test the correction ability of the correction methods.The shock environment in shipboard equipment shock experiment is typically characterized by the shock response spectrum calculated from the acceleration signal.Firstly,the current state of development of shock environment measurement technology is investigated.Accelerometers,as a traditional vibration signal measurement means,usually contain a trend term error component in the measurement data in the shock environment,resulting in drift of the low frequency spectrum in the shock response spectrum,which cannot accurately describe the low and medium frequency shock environment during the test.To address these issues,researchers have developed low and medium frequency shock ambient measurement devices such as reed instruments,shock pendulums and spring oscillators as complementary measurements to the acceleration sensors.By applying Fourier transform analysis and numerical integration method to the signals,it is found that the signals containing trending acceleration often contain highenergy low-frequency components,and the velocity and displacement curves obtained by integration have serious zero drift problem.The length of the signal affects the drift of the lowfrequency spectral lines in the shock response spectrum,where the drift of the low-frequency spectral lines is improved by shorter shock signals containing fewer trend term components.Then,two methods for correction of low and medium frequency shock response spectrum,Fourier transform-spring oscillators correction method and wavelet transform-spring oscillators correction method,are proposed,and the theoretical feasibility and completeness of the two methods are deduced.The test data analysis showed that the test acceleration data contained a trend term error component,the spring oscillators was stable during the shock test,and the test data were true and reliable.Last but not least,the above two correction methods were applied to the experimental data,and the results showed that the two correction methods proposed in this paper can effectively correct the drift of the low-frequency spectral line in the shock response spectrum caused by the trend term errors,and the corrected shock response spectrum regresses on the isotropic characteristics of the low-frequency spectral line,while the high-frequency spectral line is almost unaffected.Compared with the Fourier transform-spring oscillator correction method,the wavelet transform-spring oscillator correction method has better robustness and stronger correction ability,the maximum percentage difference between the slope of the spectral line and the standard 6dB/oct slope of the corrected wavelet method is only 3.84%,and the correlation coefficient between the corrected spectral line and the spring oscillator isotropic line is above 0.9984,with strong correlation.The modified low-frequency spectral line regression isotropy in the shock response spectrum more accurately reflects the low-frequency shock environment in the shock test,and provides an accurate basis for the evaluation and calibration of the equipment,which has important research significance and considerable application value.