| With the development trend of high pressure,high power and high precision,the problem of noise and vibration in hydraulic systems becomes more and more serious,which needs to be solved urgently.Pressure pulsation is often regarded as the main source of hydraulic noise,and the installation of dampers to suppress pressure pulsation within the research frequency band is one of the main approach for the reduction of hydraulic vibration and noise at present.As a kind of resistance muffler,expansion chamber hydraulic noise suppressors are widely used for their convenient movement and relatively small volume.Based on the continuous performance improvement of hydraulic systems,the research of expansion chamber pressure dampers has entered a new stage.Therefore,this thesis mainly studies the influence of extended inlet and outlet tubes,cross-section shapes of expansion chambers and locations of extended tubes on the attenuation performance,and improves the structure and performance of the existing expansion chamber dampers.Firstly,the one-dimensional(1D)transfer matrix method(TMM)for frequency characteristic analysis of expansion chamber pressure dampers is described in detail.Since simple expansion chambers,type C for short,and extended tube expansion chambers,type K for short,could be divided into several basic acoustic elements,such as constant cross-section pipes,area mutation structures,and side-branched tubes,transfer matrices of these acoustic units could be derived by the linear plane wave theory.Considering that the insertion loss(IL),which is used as the acoustic performance evaluation index,can be direcly affected by the source impedance and load impedance,hydraulic systems included type C or K pressure dampers could be simulated by the electro-hydraulic analogy.That is to say,hydraulic pump sources can be considered as pressure sources or flow sources separately,loads can be seen as matching or blow-down conditions,and the pressure pulsation and mass flow rate are replaced by the voltage and current.Four kinds of IL models are obtained by theoretical analysis,and the most suitable one could be selected by experiments.Secondly,the acoustic finite element method(FEM)is used to calculate and analyze the end correction of the circular pipes of K-type expansion chamber pressure dampers,and the influence of the length diameter ratio,the wall thickness diameter ratio on the end correction is studied.The results show that the end correction theory will fail if the extended length is too short or too long;when the diameter ratio is fixed,the influence of the wall thickness on the end correction could be neglected;when the wall thickness is fixed(except for some individual values),end corrections will increase with the increase of the diameter ratio.Then,the FEM is used to calculate the end correction of the circular pipes of a non coaxial expansion chamber and the transmission loss(TL)theoretical values obtained by the corrected 1D TMM are compared with the results of the FEM.Within the cut-off frequency band of plane waves,the effects of the insertion depth,the eccentricity and the deflection angle of the extended tubes on the TL are stuied.The results show that these structural parameters could affect the attenuation of high-order mode waves at sudden area changes to some extent,which makes the application of the end correction theory to the prediction of TL performance of non coaxial expansion chamber attenuators have some limitations.Thirdly,structural improvements for traditional single-chamber C-type and K-type expansion chamber pulsation attenuators are put forward;a C-type expansion chamber with flexible lining and three kinds of improved expansion chamber pressure dampers with inserted conical and perforated tubes are proposed.For the flexible lined C-type expansion chamber damper,the lumped parameter model is extablished by the electro-hydraulic analogy,and verified by the distributed parameter model.Then,the influence of the system pressure and the internal acoustic structure of the lining material on the TL is studied;the results show that compared with the unlined C-type expansion chamber and the cavity with unvoided polyurethane lining,the chamber with voided lining can broaden the filtering frequency band.For the three kinds of pressure dampers with inserted conical and perforated tubes,the 1D TMM is used to establish the mathematical models and verified by experiments;the effects of the structural parameters such as the slope of the conical tubes,the porosity and the hole diameters on the IL are studied.The results show that the sound absorption potential of conical and perforated tubes used in expansion chamber hydraulic noise suppressors within the whole concerned frequency band.In addition,considering that the installation space of pressure dampers is limited,this paper proposes the application of the standard genetic algorithm(GA)to optimize the structure of two kinds of expansion chamber pressure dampers with conical and perforated tubes.The results show that the GA could be used as a fast and efficient optimization tool to optimize the filtering performance at a given research frequency.A new method,the Green’s function method(GM),which is different from the 1D TMM and the three dimensional(3D)FEM,is used in the research of expansion chamber pressure dampers.The GM is used to model the dampers with rectangular and square sections;the IL results are in good agreement with the experimental data in the whole research frequency band,which proves the feasibility of the GM.Besides,the influence of three kinds of cross-section shapes,rectangle,square and circle,on the filtering characteristics is discussed.It is found that the circular section has the best performance in the range of 2000 Hz,followed by the square section,while the rectangular one is the worst.Fourthly,several types of double-chamber compound expansion chamber hydraulic attenuators,the compound impedance types,the double-chamber resistance types and the two-stage chambers with inserterd conical tubes,are proposed.For the first type,the lining chamber is modeled by the lumped parameter method,while the straight through perforated pipe section is modeled by the 1D TMM.Then,the effects of the system pressure,the internal structures of the lining,the porosity and the hole diameters on the TL are studied and the results show that the effects of the porosity and the hole diameters are minimal.For the second type,the 1D TMM is used for the theoretical modelling and verified by the experiments.The effects of the porosity,the hole diameters and the perforation patterns on the IL are studied.Besides,the GA is used to optimize the filtering performance at 267 Hz.For the last type,the 1D analytical models are established,and the reliability of the models is verified by the experiments.Based on these models,the effects of the slope of the conical tubes,the inserted length of the straight tube,the porosity and the hole diameters in the range of 2000 Hz are discussed.It is found that the microperforated structure which is widely used in the field of gas elimination is not suitable for pressure dampers. |
PDF Full Text Request