| The construction machinery industry is one of the fastest-growing industries in China since the reform and opening-up,and it has the greatest impact on the country's infrastructure construction.The products have become one of the main products of export earning,and China has become a veritable construction machinery manufacturing country.However,the overall level of China's construction machinery products still lags that of the developed countries,especially in the level of engineering machinery safety protection,noise emission,and there is still a big gap between the world's engineering machinery manufacturing powers,and the products are quite difficult to enter the markets in developed regions.With the development of modernization,the construction machinery is becoming more and more complex,and the vibration and noise problems are now more prominent.Therefore,the control of NVH performance of construction machinery has become one of the important ways to improve the competitiveness of products in the international market.The noise level of construction machinery cabin is one of the most important indicators to evaluate the NVH performance of construction machinery.It is the key and difficult point of NVH performance control of construction machinery vehicles.As we all know,the construction machinery cab usually contains many thin-plate structures,and structural-acoustic coupling problems caused by the vibration of the thin plates have been the research hotspots in the past decades.In recent years,in the process of vehicle lightweight development,the humming noise in low frequency generated by the vibroacoustic coupling of the cab has become one of the main noise sources of vehicle interior noise,which seriously affects the ride comfort of passengers.Therefore,the study of the coupling mechanism and characteristics has important application value for improving the acoustic design of the vehicle cab and reducing the vibroacoustic coupling noise.Besides,with the development of technology,although most products have no substantial changes in function,there is a significant increasing demand for the sound quality of vehicle cab noise.Therefore,it is necessary to study the vibroacoustic coupling characteristics of classical panel-enclosure systems,and explore the sound quality characteristics and sound quality evaluation methods of construction machinery cabins.This research was funded by the Jiangsu Province Industry-University-Research Joint Research Project(BY2014127-01)and the Jiangsu Science and Technology Support Program(BE2014133).The coupling models of classical panel-enclosure systems are modelled based on the modal analysis method.The influence of structural parameter variations on the global coupling characteristics between multi-order panel modes and multi-order acoustic enclosure modes is investigated.The finite element method(FEM)and experimental method are used to study the influence of multiple influencing factors on the acoustic response of the panel enclosure system under excitation,and the sound quality test and evaluation method of the internal noise of the construction machinery cab is studied as well.The main research contents and innovations of this paper are as follows:(1)Based on the modal analysis method,the vibroacoustic coupling model of the rectangular panel-enclosure system was established.Global coupling level was first proposed to describing the degree of coupling between multi-order panel modes and acoustical cavity modes.The influence of enclosure depth,panel thickness,panel aspect ratio,panel boundary condition,panel area and the panel material on the global coupling characteristics of the coupled systems was analyzed by using the control variable method.The influence of the comprehensive variation of structural parameters on the global coupling characteristics of the rectangular panel-enclosure coupled system was obtained.Results show that:compared with the simply supported boundary conditions,the influence of the structural parameters on the transfer factor between the clamped panel mode and the acoustic mode of the coupled system is more sensitive and significant.Besides,under the same panel boundary conditions,the values of the structural parameters of the coupled system with different panel materials are the same when the maximum global coupling level occurs.Moreover,the area where the strong vibroacoustic coupling occurs of the coupled system gradually increases as the panel area increases,indicating that the density of the strong couplings of the system become greater.Therefore,it can be concluded that reducing the panel area can effectively reduce the probability of occurrence of the vibroacoustic coupling noise in coupled system,which could provide theoretical guidance for the low vibroacoustic coupling design of the rectangular construction machinery cabins.(2)Based on the modal analysis method,the vibroacoustic coupling model of the trapezoidal panel-enclosure system was established.Firstly,the effect of the variation of the inclination angle on the modal frequencies of the trapezoidal cavity was analyzed.And the influence of the number of boundary acoustic cavity modes on the calculation accuracy of the trapezoidal cavity mode frequencies was discussed.Then,the control variable method was employed to analyze the influence of the structural parameters on the global vibroacoustic coupling characteristics of the coupled system.Finally,the differences of structural parameters on the global coupling characteristics between trapezoidal panel-enclosure system and the rectangular panel-enclosure system was analyzed.Results demonstrate that:in the case that the calculation errors of the modal frequencies of the front N orders of trapezoidal enclosure modes is guaranteed to be smaller than 1%,the number of the rectangular boundary cavity modes involved in calculation needs to be more than 2N.The errors between the modal cavity resonance frequency calculated by this conclusion and the result calculated by the finite element method don't exceed 0.4%,which verifies the accuracy of the conclusion.Besides,the condition of coupling between trapezoidal cavity mode(l,m,n)and panel mode(u,v)occurs only when m+n is nonzero and l+u is odd,or m+n is zero and l+u&m+v are odd.Hence,compared with the rectangular coupled system,the coupling phenomenon is more likely to occur between the panel mode and acoustical cavity mode of the trapezoidal coupled system.Furthermore,when the panel aspect ratio?(?=L_x/L_y)ranges from 1 to 2,the global coupling levels of the trapezoidal enclosure system is lower than 60dB,which is beneficial to the acoustical design of the trapezoidal construction machinery cabins with low coupling noise in low frequency range.(3)Referred to the vibroacoustic coupling model of trapezoidal panel-enclosure system,the theoretical model of the vibroacoustic coupling of the complex panel-enclosure system with two inclined walls was established based on the modal analysis method.Firstly,the influence of the number of rectangular boundary cavity modes on the accuracy of complex cavity modes was studied.And the effect of angels of the inclined walls on the acoustical modal frequencies of complex cavity was then discussed.Afterwards,the influence of structural parameters on the global vibroacoustic coupling characteristics of the complex panel-enclosure system was obtained.Results indicate that:when the structural ratio?(?=W_y/L_y)is smaller than 5/8,in the case that the calculation error of modal frequencies of the front N orders of complex cavity modes is guaranteed to be 1%,the number of the boundary-rectangular cavity modes involved in the numerical calculation needs to be at least 2N;otherwise,the number of the rectangular boundary cavity modes should be more than 3N.In addition,the condition of coupling between the panel mode(u,v)and the complex cavity(with multiple inclined surfaces,and each inclined surface is parallel to a certain coordinate axis)mode(l,m,n)is consistent with the coupling condition of the trapezoidal panel-enclosure system.Moreover,when the structural parameter W_y is constant,the global coupling characteristics of the complex acoustic cavity system is weakly affected by the angles of the inclination walls,and the global coupling degree of the system is the lowest when the inclination angle?equals to?,which is good for the acoustical design of the complex construction machinery cabins with low coupling noise in low frequency range.(4)Taking the complex panel cavity system with two inclined surfaces as the object,the finite element analysis method was used to explore the acoustic response of the coupled system under different excitation conditions.Experiments were carried out to investigate the feasibility of different measures for reducing the low frequency noise in the coupled system.The effectiveness of different schemes on controlling the low-frequency noise in the panel-enclosure system were verified by experiments.Results demonstrate that:the acoustic response of the complex panel-enclosure system calculated by the finite element method verifies that the conditions of the vibroacoustic coupling of the coupled system with inclined wall(s).Besides,under the same conditions,the cabin seat with the cloth surface has better sound absorption performance when compared with leather surface seat.And the experimental results show that the insertion loss of the cloth seat the leather surface seat are 6.56dB and 1.89dB,respectively.Moreover,the through-holes on the rigid walls weakly affects the peak frequencies and amplitudes of the acoustic response of the coupled system.Furthermore,the modal frequencies of the coupled system gradually increase with the increase of interior diameter of through-holes,while the amplitudes corresponding to the peak frequencies gradually decreases.These conclusions have significant guidance for the acoustical design of construction machinery cabs with low frequency noise.(5)Taking the interior cabin noise and the offboard noise of wheel loaders as samples,the sound quality characteristics along with the subjective and objective evaluation methods were studied based on the psychoacoustic theory.The subjective evaluation tests of the sound quality were carried out,and the correlation between the subjective evaluation results and the objective parameters of sound quality was then analyzed.Based on BP neural network method,the subjective evaluation models of sound quality of wheel loader under four working conditions were established,and the subjective evaluation results of some vehicle noise were predicted and analyzed.Results show that:under idle condition,there is a high correlation between the four parameters of A-weighted sound pressure level(SPL),speech intelligibility,speech intelligibility index and loudness and the subjective evaluation results of sound quality,while under the maximum speed condition,the four parameters are A-weighted SPL,speech intelligibility index,sharpness and loudness.Besides,the errors between the subjective evaluation results and the results predicted by the subjective evaluation models do not exceed 5%,indicating that the models have high prediction accuracy and reliability.These conclusions have important guidance and application value for the establishment and improvement of sound quality evaluation methods and the sound quality evaluation criteria of construction vehicles.In conclusion,this work focuses on the modelling,analysis and understanding the global vibroacoustic coupling characteristics of the panel-enclosure systems,which are simplified by the corresponding classical cabins of construction machinery.Various measures are discussed on the noise control in low frequency range for the panel-enclosure system,and the sound quality evaluation and the sound quality subjective model are also investigated.The research results are of great significance for reducing the low frequency noise in the cab of construction machinery both in the process of acoustical design,and it provides a novel method for the evaluation of the noise in the construction machinery cabins as well. |
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