Study On Vibrational Transfer Path Analysis And Structure-Borne Noise Radiation Control In A Vehicle System

Ride comfort, as one of important performances of automotive product, isincreasingly concerned by manufacturers and customers in recent years. Auto-bodystructural vibration and structure-borne noise in the passenger compartment is one of keyfactors to evaluate ride comfort of a vehicle. Due to a thin-walled structure of theauto-body, the auto-body panels are susceptibly excited to vibrate and radiate noise into thecompartment. The auto-body is a powerless passive structure while many power sources onthe vehicle system should occur during the operation process. Vibrational energy thatgenerated by these sources can be transmitted into the auto-body throughmultiple/multi-dimensional coupling transfer paths and induce the structural vibration andnoise in the low frequency range. Therefore, in order to decrease the vibrational and noiseresponse for improving the ride comfort, it is an important solution to control the structuralvibration transmission and sound radiation of panels.The study begins from analysis of the overall transmission process of structuralvibration and structure-borne noise. The overall structural acoustic process can besubdivided into four main stages, including generation, transmission, propagation andradiation. According to the characteristics of the process, multiple/multi-dimensionaltransmission performances of structural vibration and structure-borne noise are researchedon the base of power flow theory, and control methodologies of vibration transmission andsound radiation are explored in this dissertation. The concrete works and results are mainlyas follows:(1) Study on transmission performances and coupling of multiple/multi-dimensionaltransfer paths The multiple/multi-dimensional vibration transmission in the vehicle system isstudied with the mobility method. According to the analysis idea of source-paths-receiverfor a overall vibration system, all the subsystems can be modeled with mobility method,and then integrated into the analytical model for vibration transmission in the overallsystem with mobility synthesis method. The force and velocity expressions of everyconnected point in the overall system can be deduced from force equilibrium and motioncompatibility conditions for connected points. Then, the power flow expression can beobtained according to the original definition of power flow on the base of the force andvelocity expressions. Furthermore, the advantages using the power flow to evaluate themultiple/multi-dimensional vibration transmission are illustrated via an inverted “L”structure case. For the ubiquitous coupling phenomena in the multiple/multi-dimensionalvibration transmission process, a novel concept of using coupling powers to describe thedegree of coupling among the different components of motion is put forward. Then aprinciple for judging the rationality of simplified coupling issues with the coupling powersis extracted initially. Subsequently, an idea of utilizing coupling phenomena according totheir functions on the transmission process is conceived.(2) Study on equivalent analysis and quantification methods for contributions ofmultiple/multi-dimensional transfer paths in a vehicle systemSources are the origin of energy of vibration and structure-borne noise. For a vibrationor noise problem, the influence of sources is significant for the requirements for control.According to the characterization of source ability to impart vibrational energy into thepassive structure, the equivalent power expression of one-dimensional vibrationaltransmission is deduced. To help address the multiple/multi-dimensional transfer paths theeffective point mobility can be introduced. On the base of the effective point mobility, theequivalent power expression of one-dimensional vibrational transmission is extended tosolve power flow calculation of multiple/multi-dimensional vibrational transfer paths. Allkinds of analytical models for multiple/multi-dimensional vibrational transmission aresummarized, and their corresponding power calculation expressions are given. Then, anovel quantification method of structural vibration and structure-borne noise transfer pathsis proposed to identify the dominant transfer paths. Furthermore, according to the powerflow equivalent calculation expressions, the potential factors in the source, path and receiver subsystem, which are able to have effect on vibrational energy transmission, areanalyzed to provide preconditions for vibrational energy transmission control.(3) Study on transfer path analysis method and vibration transmission control basedon mobility power flow methodAccording to the related theories of complex system model and power flow combinedwith the general methods for structural vibration and structure-borne noise control in avehicle system, a transfer path analysis method based on mobility power flow method ispresented systematically and practically. The method is divided into three parts: analysismodel construction, transfer path analysis and structural modification. Its technical processcontains ten steps, which are explained in detail. To illustrate the method, the transfer pathsof structure-borne noise in the passenger compartment generated by a powerplant areanalyzed with the method. All the transfer paths are ranked orders and identified thedominant paths according to the power flow through every path. Main key parameters onthe dominant paths are identified from the mobilities of all the subsystems referred to thepower flow equivalent calculation expressions. Three plans including connected locationmodification, mount alternative and auto-body structural modification are applied toreduce the structure-borne noise and control vibrational energy transmission.(4) Study on control method of vibrational energy propagation in an auto-bodystructure and sound radiation in the passenger compartmentVibrational energy generated by sources can be transmitted into the auto-bodystructure in the end. For studying propagation characteristics of the transmitted vibrationalenergy, the correlation between the structure-borne noise response and the transmittedvibrational energy propagation is investigated through the power flow or energy flowexpressions in a thin-walled structure and structural-acoustic coupled equations. Then, anevaluation method for judging rationality of vibrational energy distribution with thestructure-borne noise response minimization is obtained. Therefore, in order to reduce thestructure-borne noise response, the present panel acoustic contribution analysis method isimproved firstly.“Acoustic contribution sum”,“acoustic contribution ratio” and “totalsound field contribution”, as three novel parameters, are introduced to analyze the interiorsound field characterized with multiple field points and obvious sound pressure peaks, and evaluate integrated acoustic contributions of auto-body panels. Further, a systematicmethodology for automotive interior sound field refinement is also proposed on the base ofthe modified PACA method. An example of a passenger car model has demonstrated theapplication process of the sound-field-refinement methodology, and showed the advantageto treat with damping layers at the optimum locations on the auto-body. The effects ofnoise reduction are verified by simulations and experiments. The application example hasalso proved that the modified PACA method has practical significance on refining interiorsound field and decreasing added mass in accord with auto-body lightweight trend.