Research On Elastic Wave Propagation Characteristics Of Typical Grillage Structures In Ship Hull

Hull structure is an important pathway of converting vibration of mechanical equipment into underwater radiation noise.Dynamic behaviors of the hull structure are key factors affecting its underwater acoustic radiation characteristics.Excitations from mechanical equipment always transmit through the base to the hull grillage structure and cause its vibration response,which propagates in the hull grillage structures along the longitudinal,transverse and vertical directions of the ship.Such a conversion is essentially a mechanical wave motion phenomenon.Propagation and attenuation characteristics of the dynamic responses caused by mechanical equipment in the hull structure have always been a hot topic in the field of vibration and noise reduction.Research on this topic plays a significant role in dynamic performance evaluation and optimization of ship structures.The main hull structure is a complex three-dimensional beam-plate coupling construction assembled by spatial plate structures composed of decks,bulkheads,side shells and double bottoms,by transverse frame structures consisting of bottom ribs,side ribs and deck beams and by longitudinal frame structures constituted by stringers attached on decks,bulkheads,side shells and bottom plates.Beam and plate are basic components of the hull structure.With respect to these basic components,use the numerical analysis method to study their wave propagation and attenuation characteristics.Firstly,in this paper,the theories of Euler-Bernoulli beam and classical plate theory and Mindlin plate are respectively introduced.And the Fourier transform and other related theories are studied.These theories are the basis for studying the wave motion characteristics of plate structure.Secondly,the Artificial Boundary Condition(ABC)of plate structure is studied,and the reasonable ABC in numerical analysis of plate structure is given.In the ABC,the accuracy and validity of the numerical analysis method are verified.Aiming at the characteristics of longitudinal wave and flexural wave in plate structure,the corresponding analysis method of wave characteristics is proposed.Thirdly,the longitudinal wave in typical plate structures of ships are studied.The longitudinal wave characteristics in a single stiffened plate are studied first,including wave velocity,waveform conversion phenomenon and attenuation rate of wave amplitude.Then the longitudinal wave characteristics of unidirectional multi-stiffened plates and cross-stiffened plates are studied with the spacing of bars as a variable.Fourthly,the characteristics of flexural waves in periodic plate frame structures are studied.In the single stiffened plate,the influence of the stiffened strength on the wave characteristics of flexural wave is discussed,including the wave propagation speed and the attenuation rate of flexural wave.In the unidirectional multi-stiffened plate,the influence of the change of the strength of the stiffened plate and the change of the laying distance of the stiffened plate on the wave characteristics of the flexural wave in the unidirectional multi-stiffened plate is discussed respectively,including the propagation speed of the flexural wave and the attenuation rate of the transmission of the flexural wave.In the cross-stiffened plate,the influence of the change of the strength of the stiffened plate and the change of the laying distance of the stiffened plate on the wave characteristics of the flexural wave in the cross-stiffened plate is discussed respectively,including the propagation speed of the flexural wave and the attenuation rate of the transmission of the flexural wave.Based on the research results of bending wave propagation speed of plate structures,the formulas for calculating flexural wave propagation speed of various types of plate structures are derived.Finally,the characteristics of flexural waves in typical plate structures of ships are studied.In this paper,the bending wave propagation velocity and the attenuation of bending wave propagation of some typical plate and frame structures are analyzed...