| With the development of underwater acoustic detection technologies,the ship hull grillage structure low frequency line spectrum vibration and noise control technologies and acoustic stealth level directly affect the combat effectiveness and vitality of ships.Ship grillage structure is a periodic structure which composed of periodically arranged vertical and horizontal stiffeners with the thin plate attached to the stiffeners,and the ship hull structure is a periodic ship spatial grillage structure composed of various deck,transverse bulkhead,board side,double bottom and other ship grillage structures.Periodic structures have band gaps characteristics,which the flexural wave propagation is prohibited in band gaps frequency ranges.Analysing and studying the flexural wave band gaps and vibration attenuation characteristics in periodic structures and then introducing into the structure low frequency line spectrum vibration and noise control,which provides new ideas and engineering references for the ship low noise structure design.The ship spatial grillage structure is a typical artificial periodic structure in space geometry.In this paper,the frequency spectrum characteristics of flexural wave length in ship spatial grillage structure are analyzed by using the wave analysis method.The wave characteristics of ship spatial grillage structure are expounded,and the vibration transmission and attenuation characteristics are essentially the wave propagation characteristics of elastic waves in the ship spatial grillage structure.The dynamic characteristics of various ship grillage structures and ship hull structures are numerically and experimentally studied,and then the wave characteristics and periodic characteristics of the ship grillage structures are verified,which leads the researches on the internal relationships between the flexural wave band gaps characteristics and vibration attenuation characteristics in ship spatial grillage structures.Combined with the periodic characteristics and low frequency flexural vibration dynamic characteristics in ship spatial grillage structures,a periodic elastic bearing beam-oscillators coupling structure is proposed as the computational model for the flexural wave propagation characteristics analysis of ship grillage structures.And the flexural wave band gaps characteristics in the periodic elastic bearing beam-oscillators coupling structure is calculated using the method of reverberation-ray matrix combined with the Bloch theorem.The analysis results of the flexural wave band gaps characteristics and vibration attenuation characteristics in the computational model show that,the flexural wave propagation in band gaps frequency ranges is prohibited and leads to the significant structural flexural vibration attenuation frequency ranges.Furthermore,the effects of structure and material parameters on the flexural wave vibration band gaps characteristics are respectively investigated,and the results show that the flexural wave vibration band gaps can be adjusted and optimized manually by adjusting structural and material parameters.The low frequency flexural vibration characteristics of ship grillage structures are analyzed,the results show the low frequency flexural wave characteristics in the ship grillage structures can be divided into the low frequency beam flexural vibration of longitudinal stiffeners and transverse stiffeners,and then described by the low frequency flexural vibration of homogeneous beam.Thus,the equivalent method of the ship grillage structure equating to the periodic elastic bearing beam-oscillators coupling structure based on the energy equivalence principle is derived based on the Timoshenko beam motion equation.After that,the flexural wave band gaps characteristics of the ship grillage structure are analyzed by using the equivalent computational model.The vibration attenuation characteristics were carried out using the numerical method and verification test,which demonstrated the effectiveness of the equivalent method and the flexural wave band gaps characteristics analysis method of ship grillage structure.The flexural wave propagation of the ship grillage structure is prohibited in the band gaps frequency ranges,which leads to the significant structural flexural vibration attenuation frequency ranges.Based on the ship grillage structure flexural wave band gaps characteristics analysis method,the effects of the ship spatial grillage structure structural forms designs and structural parameters designs on the flexural wave band gaps characteristics are studied,and it can be concluded that the equivalent computational model parametric studies can be used to guide the ship hull grillage structure low frequency line spectrum vibration and noise control and the ship low noise structure design.The results show that the ship grillage structure flexural wave band gaps characteristics can be adjusted and optimized manually by adjusting structural and material parameters,which provides a theoretical basis and engineering reference for introducing the band gaps characteristics into the ship hull grillage structure low frequency line spectrum vibration control and the ship low noise structure design.Combined with the ship grillage structure periodic characteristics and the ship hull structure dynamic input spectrum characteristics,the effects of the ship grillage structure structural forms designs and structural parameters designs on the low frequency line spectrum vibration and noise in specific frequency ranges are carried out,and then the ship grillage structures low frequency line spectrum vibration and noise control method in target frequency ranges is proposed based on the flexural wave band gaps characteristics.Then,under the guidance of the proposed low frequency line spectrum vibration and noise control method,the ship grillage structure optimization design with low frequency line spectrum vibration and noise control in target frequency ranges is carried out,and the effectiveness of the improved design scheme is verified by model test,which verified the effectiveness of the proposed ship hull grillage structure low frequency line spectrum vibration and noise control method based on the flexural wave band gaps characteristics.And then the study of the ship engine room structure low noise structure design is carried out,demonstrate that,the effectiveness of the low noise structure design method based on flexural wave band gaps characteristics is verified by the underwater acoustic radiation numerical results,which provides a theoretical basis and engineering application references for the ship hull grillage structure low frequency line spectrum vibration ansd noise control method and low noise structura design. |
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