| Structure-borne noise is one of the main components of cab noise.In the industries such as construction machinery,automobiles and high-speed railway,low-frequency structure-borne noise in confined spaces is easy to generate a "roar",which seriously affects comfort.This type of noise control has been a conundrum of acoustics research.Due to the long wavelength of low-frequency structure-borne noise,traditional noise reduction methods don’t reach the ideal effect,such as sound absorption,sound insulation and vibration isolation.This dissertation analyzes the mechanism of low-frequency structure-borne noise generation and transmission based on an in-depth analysis of the current situation of low-frequency structure-borne noise control research,taking a cab as the research object.From the research of the key transmission links of vibration energy,such as low-frequency structure-borne noise source,transmission path and response point of the cab subsystem,it proposes non-ideal composite acoustic black hole bending wave suppression,comprehensive contribution analysis and multi-objective optimization of the transmission path,CEEMD-FELMS online identification of dual-channel noise reduction and other control strategies.Meanwhile,it adopts the control effect of low-frequency structure-borne noise with the application of an integrated control strategy for sound quality evaluation.The thesis provides a set of valuable theoretical methods and technical basis for the improvement of the noise comfort of construction machinery cabs.The main research contents of the thesis are as follows.(1)The identification of low-frequency structure-borne noise of the cab subsystem is studied.Firstly,the generation and the mechanism of transmission of low-frequency Structure-borne noise were analyzed.The structure-borne noise transmission path from the vibration source to the cab was identified by spectrum analysis,and the mechanism of the low-frequency structure-borne noise transmission path of the cab was established.Thus,a theoretical basis for the research of low-frequency structure-borne noise control strategy was provided;Secondly,the analysis process of low-frequency structure-borne noise energy contribution was established,and independent component analysis Fast ICA and WPA analysis were used to identify low-frequency structure-borne noise.The energy ratio of this noise in cab noise was calculated through correlation and energy contribution amount analysis to clarify the importance of the research of low-frequency structure-borne noise control on noise comfort.(2)The design of composite acoustic black holes and low-frequency noise extension control strategy are studied.Focusing on the low-frequency structure-borne noise source of the cab subsystem,a composite acoustic black hole with non-ideal additional damping for wave manipulation is proposed to solve the problems of insufficient acoustic black hole strength and poor low-frequency noise reduction.The low-frequency bending wave trapping performance of the composite acoustic black hole was analyzed with modal strain energy analysis,time-domain energy harmonic response analysis,and acoustic radiation boundary element analysis.It verified the effectiveness of low-frequency structure-borne noise by numerical simulation and experiments.(3)The comprehensive contribution analysis and multi-objective optimization of low-frequency structure-borne noise transmission paths are studied.A multi-objective optimization method based on the comprehensive contribution analysis transmission path is proposed for the subsystem transmission path.The optimization region was quickly determined with the combination of the improved panel contribution method and the modal strain energy contribution method.And an acoustic structure coupling multi-objective optimization platform was built as the application of NLOP optimization algorithm compiled with Python.Therefore,the design of noise paths in multiple regions was optimized,solving the problems of inconsistent contributions of different frequencies to the same response point and low efficiency of structural optimization.At last,the effectiveness of path optimization for low-frequency structure-borne noise was verified by experiments.(4)Multi-channel active control of low-frequency narrow-band noise in local space is studied.A CEEMD-FELMS online identification dual-channel active noise control method is proposed for the low-frequency structure radiation noise next to the driver’s ear,it solves the problems of the bounce of mid-high frequency noise,narrow effective control area and poor dynamic performance.Based on the complementary empirical modal decomposition CEEMD method to determine the main peak value interval,the driver’s binaural low-frequency structure noise is controlled with the variable step FELMS algorithm,the improved Eriksson online identification and the dual-channel ANC control system.The numerical simulation and experiments verified the effectiveness of this method.(5)The comprehensive experiment and sound quality evaluation of low-frequency structure-borne noise control strategy are studied.A multivariate linear regression model for the sound quality of excavators under static conditions and a sound quality model of the BP neural network for dynamic working conditions were established.Based on these sound quality models,the control effect on the combined application of the strategies,including the bending wave suppression for the composite acoustic black hole,multi-objective optimization of the transmission path and CEEMD-FELMS active noise control in the cab of a small excavator were evaluated.As a result,the static sound pressure level was reduced by 2.8 d B,the subjective satisfaction was increased by 10.5%,and the sound quality was improved by one level,while the dynamic sound pressure level was reduced by 2.31 d B,the subjective satisfaction was increased by 8.3%.The low-frequency peak reduction was larger in both static and dynamic conditions.The test result shows the effectiveness of the integrated control strategy of low-frequency structure-borne noise control. |
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