Research On The Vibration Transmission Characteristics And Attenuation Measures Of Typical Hull Structures

With the improvement of tonnage and automation level,the scale and power of equipment on board is bigger and bigger,thus causing a series of problems about vibration and noise,such as reducing acoustical stealth?habitability and so on.At present,the study on air borne sound is comparatively mature,but the transmission characteristics of structural borne sound are relatively complicated.Hull is a big irregular complicated structure which consists of plates and beams.Simplified theoretical models are abstracted from practical ship structure,Wave approach is used to analyze the vibration transmission characteristics and attenuation measures of typical hull structures.Based on the thought of “simple to complex and infinite to finite structure”,first of all,this paper investigates the vibration transmission characteristics of semi-finite hull structures with single joint or multiple joints.The result shows that not only reflectance and transmission occurs,but also probable conversion of wave types appears in the joints.The allocation and conversion of vibration energy are decided by structural form and wave impedance.The corners of hull structure with multiple joints can be seen as independent vibration sources,the vibration waves emitted by which superpose and create standing waves in finite structure.In the flexural or longitudinal resonance frequency,the vibration energy concentrates in certain parts of structures.Afterwards,the vibration attenuation characteristics of blocking mass and damping are studied.The blocking mass can create high transmission loss in high frequency,which acts like a low-pass filter.The characteristic frequencies are decided by the characteristic impedance of blocking mass and plate.Inheriting the character of single blocking mass,multiple blocking masses can also blocking the transmission of flexural wave energy in high frequency,but the transmission loss is much lower in some penetration frequencies.Damping can not only attenuate vibration energy,but also weaken the peak value.At last,the paper analyzes the vibration attenuation measures of simplified cabin structures.Using the blocking character of blocking mass and the damping character of damping layer,their independent vibration attenuation measures are compared.According to their advantages,the composite attenuation measure of combing blocking mass and damping layer is presented.The composite attenuation measure can not only offset the disadvantage of penetration frequency and widen the blocking frequency band of blocking mass,but also enhance the vibration damping effect of damping layer.It is instructive to acoustic design of hull structures.In addition to theoretical derivation and numerical analysis,the paper also uses wave impedance to simulate the non-reflection boundary of infinite structures,then simplified models are calculated by FEM.The results coincide reasonably well with those of analytical prediction,which validated the equations from theoretical analysis.The study provides a theoretical analysis and numerical experiment basis for the vibration attenuation of hull structures.