Dynamic Stiffness Method For Beam-Stiffened Plate Assemblies With Fluid-loading

Vibration characteristics is one of the major concerns in ship structure design since excessive vibrations can inevitably challenge the comport of passengers and crews,equipment durability,structure integrity,and even acoustic ship stealth.In this thesis,initiated by the fundamental issue of ship structural vibrations,a dynamic stiffness formula is developed for the vibrations of beam-stiffened plate assemblies under fluid-loadings.Firstly,a dynamic stiffness method for the vibrations of beam-stiffened plate assemblies is proposed.Based on Kirchhoff plate theory,the dynamic stiffness matrix of rectangular plate structure is derived,accounting for both in-plane and out-of-plane vibrations.Based on Euler beam theory,the dynamic stiffness matrix of a beam is derived with consideration of bending,torsional,and longitudinal vibrations.The global dynamic stiffness matrix of the beam-stiffened plate structures is obtained through coordinate transformation and matrix assembly procedure,like the way in conventional finite element technique.A finite element model is designed and utilized to validate the present dynamic stiffness model for beam-stiffened plates.Secondly,a dynamic stiffness method for the vibrations of fluid-loaded plate assemblies is proposed.The fluid loading induced by the vibrations of the plates is expressed in terms of wave radiation impedance.As a result,the dynamic stiffness matrix for the fluid-loaded plate structures is derived,which provides a new method for structural fluid coupling vibration analysis.A structure-fluid coupling finite element model is employed to validate the present method.Thirdly,the vibration transmission characteristics of a periodic stiffened plate structure are analyzed based on the present dynamic stiffness method.A normalized transmission factor is adopted to evaluate vibration transmission,and the influence of different structural parameters is investigated.Finally,a dynamic stiffness model for the vibrations of a representative ship hull is designed,which is verified by finite element method.The influences of structure parameters are investigated based on the present dynamic stiffness method,which provides theoretical guidance for engineering applications.In comparison with conventional finite element method,the present dynamic stiffness method exhibits remarkable advantages such as higher computation efficiency,less frequency dependence,and minimum discretization requirements.Compared to classical analytical methods,since matrix assembling procedure like that in finite element method,it has practical capability in modeling the dynamics of complex ship structures.Hence,it is highly anticipated that it would play a peculiar role in modeling vibrational characteristics of complex ship structures,including frequency spectrum,vibration transmission,wave conversion,and etc.