Study On The Key Vibro-acoustic Prediction Technologies Of Composite Ship Cabins

Composite materials are widely used in the manufacture of lightweight ships due to the outstanding material properties,such as forming a seamless hull easily and other remarkable features.It has even gradually shown the trend of replacing traditional shipbuilding materials.As a typical composite ship,the yacht is a kind of water entertainment top grade consumer goods with navigation,relaxation and other functions,and its related industries are all long-chain industries with knowledge-intensive,technology-intensive,labor-intensive,and capital-intensive characteristics.As a result,yacht industry has a powerful ability to stimulate economy which has become an important growth point in marine economy.However,China is only a major yacht manufacturing country currently which is relatively backward in the key technologies of original designs in comparison with the European and American countries.In particular,the design level of vibration and noise comfort,which determines the quality of yachts,needs to be improved urgently.The waste of manpower and resources could be effectively avoided after reconstruction if the requirements of comfort are considered in the early stage of yacht design,particularly when the vibration and noise reduction technology is penetrated into each stage of yacht design and construction.Therefore,the research on the vibro-acousitc prediction method of yacht cabins,not only helps identify the reasons of vibration and noise pollution early but also provides a simulation platform which could be used to evaluate the comfort improvement measures.As a result,it will help improve the quality of yachts and increase its added value and competitiveness which is of great significance to the development and manufacturing level of yacht industry in China.The hull manufacturing materials of composite and traditional steel ships are obviously different.And the complex vibro-acousitc characteristics of the composite materials restrict the application of the existing method for yachts.In order to solve the key technical problems encountered in the vibro-acousitc prediction process of yacht cabins,the main research contents and conclusions are formed as follows:In order to study the influence on the uncertainty of Statistical energy analysis(SEA)parameters estimation to the vibro-acousitc response,a three-subsystems SEA model with the objective function of noise reduction was established based on the global sensitivity analysis.The analysis results show that the coupling loss factor under resonance transmission is the most important influence parameter to the vibro-acousitc response in wide band.The coupling loss factor under non-resonant transmission could be ignored in the optimization design of vibration and noise reduction.The coincidence effect could change the sensitivity index ranking of parameters at the critical frequency.At critical frequency,the influence of the plate damping loss factor attains a minimum while the impact of acoustic cavity loss factor is relatively high.The governing differential equation of the analytic model for the yacht composite laminated panel was established firstly and modal density estimation model for anisotropic thin panel and isotropic core was proposed with the wave number space integration method.The transverse shear stiffness factor was included to improve the accuracy of modal density in the whole frequency band.Three-channels driving point mobility method was performed to verify the mathematical model.The discussion of effects for different panel design parameters indicates that the transverse shear stiffness affects the modal density in high frequency band,and the modal density decreases with its increase;the vibration characteristic in low frequency band is controlled by bending stiffness,and changing the fiber angle of skin panel exerts influence only in this band.The trend of modal density curve could not be adjusted by the panel area,but the curve would move upward with the increase of the area.For sandwich panel with soft core,the increase of elastic modulus of core will reduce the modal density.The damping loss factor of the typical structure for yacht was experimentally studied with Power Input Method(PIM)and Impulse Response Decay Method(IRDM).The validity of the two methods was verified on the single degree of freedom model analytically.The scope of application and errors of the two methods were also analyzed.On this basis,a hybrid identification method of damping loss factor was proposed:Divide the whole broadband into low-medium and high frequency bands using modal density;impulse response decay method could be used in low-medium frequency band,while power input method in high frequency band.The identification result of the damping loss factor in wide frequency band could be obtained by the proposed hybrid method.The structural intensity simulation platform of composite laminated panel was developed by Python and Matlab using the finite element method.The validity was verified by the natural frequencies,mode shapes and structural intensity vector field distribution.And the transmission of energy flow which gives information on the position of source and dominated transmission paths after the power injected into the panel were displayed by the program.According to the study of influence for different structural intensity components,it is shown that the shear component is close to the total intensity in terms of maximum and average amplitude.And the shear component is also close to the structural intensity vector in energy flow path.While the bending component and torsion component hardly influence the direction and amplitude of energy.In practical vibration and noise reduction applications,the vibration energy transmission of composite structures under force could be efficiently reduced by suppressing the shear component.The prediction result of yacht cabins in wide frequency band under the harbor condition was obtained with the SEA parameters calculation results and test data of vibration and acoustic radiation sources.The noise test results onboard was consistent with the trend of simulation,and the maximum errors was less than 5 dB(A)which satisfied the accuracy requirements.And the causes of errors were explained from two aspects of model building technology and accuracy of input parameters.The research results of this thesis could be summarized into the following innovations:(1)A statistical energy analysis model was solved based on the global sensitivity analysis method,the influence of different SEA parameters on the noise reduction was quantitatively analyzed,and the key parameters which affect the vibro-acousitc response of different frequency bands were obtained.(2)Considering the shear deformation factor,the modal density estimation model of sandwich structure with anisotropic thin panel and isotropic core was proposed,and this model could improve the modal density identification accuracy of the composite laminated panels at high frequency.(3)A simulation platform of the vibration energy transmission for composite laminated structure was developed with structural intensity method.The structural intensity field of streamline and cloud chart was used to clearly demonstrate the energy attenuation and transmission process of vibration.