Vibration And Sound Coupling Behavior And Control Method Of Double-layer Cylindrical Shells

Sound and vibration problem of the medial space of double shells is focused in thisdissertation, and the research on the sound and vibration transfer mechanism of medial space ofdouble shells together with its control methods are carried out. Modal expansion method isadopted to establish the math-physical model for the sound and vibration problem ofdouble-layer ribbed cylinder of finite length. Based on the power transmission characteranalysis of medial water layer and connecting structure, sound and vibration insulationstructure of air pipe layer and annular connected plates is presented. The noise reduction effectof sound insulation layer and vibration isolation annular connected plates is verified by modeltest, which provides theoretical foundation and practical solution for sound and vibrationcontrol problem of medial space of double shells. The work has specific engineeringapplication background and is practically useful. The main research content and innovation areas follows:Aimed at the complex coupling system consist of double layered shells, bulkhead plates，ring rib，annular connected plates，circular discrete connected plates，keel，acoustic coatingbetween medial space of double shells, medial water layer and outside acoustic medium，theconcept of state vector and impedance matrix expression is adopted to establish the vibrationmatrix equation of coupling system with modal displacement vector of vibrating shell asvariable. The modification of control function is achieved by increasing or decreasing theimpedance matrix of sub-structure and acoustic media which facilities the analysis of the effectof different sub-structure on the sound and vibration coupling character of medial space ofdouble shells. Every step of sub-structure modeling method is checked out by FEM software.The sound power transmission model of medial water layer and annular connected platesis established, the transmitting characteristics of sound power of medial water layer and annularconnected plates is analyzed with the model, which shows that the medial water layerdominates the sound power transmitting between double shells below the half ring frequency,10dB of the sound power over the annular connected plates by, while above the half ring frequency, the annular connected plates take the predominance of sound radiation power. As aresult, to reduce the sound radiation in low frequency, the sound power transmitted by medialwater layer should be taken into account superiorly; as for the sound control in mid-highfrequency, the vibration and sound transmission of annular connected plates should beconcerned.To investigate coupling of acoustical coating and cylindrical shell, the axial wave numberexpansion correction method is proposed, then the multiple layers equivalent impedance modelof acoustical coating by measurement of acoustical impedance is raised from the correctionmethod. The characteristics parameters of multiple layers acoustical coating are interpolated,then the vibration and sound radiation of cylindrical shell with acoustical coating is simulated,as well as the noise reduction in medial space of double shells. The analyze results show thatthe noise reduction induced by the acoustical coating works above300Hz, and the noisereduction is about2-3dB around300Hz, while more than7dB above700Hz. However, thenoise reduction of acoustical coating is ineffective below300Hz.According to the acoustic power transmission character of medial water layer and annularconnected plates, complex sound and vibration isolation methods for medial space of doubleshells are introduced: air pipe as isolator to reduce sound transmission, arc-section sandwichconnected plates to reduce vibration transmission. The noise reduction effect of complex soundand vibration isolation methods are calculated and analyzed. A large scale double-layer circularshells model is adopted in the experiment to verify the calculation results. Experiment resultsshow that, complex sound and vibration isolation methods bring good noise reduction effects inthe frequency span more than100Hz, the radiation power of double-layer circular shell modelreduced2-10dB. All the results show that complex sound and vibration isolation methods arenew technology to control the sound and vibration transmission of medial space of doubleshells.Sound and vibration coupling model of medial space of double shells is extended tomulti-shell model, the oscillation coupling character and radiation sound field distribution ofmulti-shell model are calculated, the calculation results show that, oscillation couplingphenomenon of multi-shell exists under50Hz, the sound masking effect of three-shell exists at abeam direction, and become larger when the frequency rise. According to the sound fieldcoupling character of three-shell, pipe-array sound isolation model are designed based onimpedance mismatching, which bring good sound isolation effects in low-frequency,5dB at200Hz,15dB at2kHz.