Research On The Sound Performance Of Marine Single Stiffened Thin Plate

In order to investigate the vibro-acoustic performance of thin stiffened plates which arecommonly used in marine structures, by using Space-harmonic expansion method and Fouriertransform method, the sound radiation and sound transmission characteristics of an infinitesubmerged single stiffened plate when the fluid medium is at rest, the sound transmissioncharacteristics of an infinite submerged orthogonally stiffened plate both in stationary andconvected fluids, are theoretically analyzed. The influences of mean flow, sound incidenceangle, driving force, stiffeners and other structural parameters are discussed detailed,respectively.First, an accurate theoretical model is established to study the sound transmissioncharacteristics of an infinite single stiffened plate when subjected to a plane harmonic wave instationary fluids. In this theoretical model, the vibration equation of the coupledvibro-acoustic system is derived by accounting for the forced bending and torsional motion ofthe stiffeners adequately and by using an equivalent approach in which the influences of thestiffeners on the plate will be replaced by the equivalent exerting forces and moments. Thenthe wave equation and the boundary conditions at the interface are also considered. Byapplying the Space-harmonic expansion method or Fourier transform method for thetheoretical model yields an infinite set of simultaneous algebraic coupled equations about thestructural responses, which will be numerically solved by truncating them in a finite rangeinsofar as the solution converges. Based on this, the Transmission Loss (TL) formulation ofthe structures is obtained. In the numerical calculation, the validity of the present theoreticalmodel is qualified by comparing model predictions with existing results. Specifically, theinfluences of incident angle, material properties of the stiffened panel, and structuralparameters on the sound insulation performance of the single stiffened plate are quantifiedand conclusions of significant practical implications are drawn.Then, the single stiffened plate in the stationary field is still taken as an object for the study.An efficient technique to analyze the vibration and sound radiation from the stiffenedfluid-loaded plate excited by a mechanical point force is present. In this approach, thevibration governing equation of the vibro-acoustic coupled system, the bending and torsional motion equation of the stiffeners, acoustic wave equation and the fluid-structure coupledcondition in physical space are firstly transformed to the wavenumber domain by using theFourier Transform method. By solving these equations together, an infinite set of algebraiccoupled equations about the transversal displacement of the plate in wavenumber domain willbe obtained. Then the variable replace technique will be used to calculate the paneldisplacement. At last, by applying the stationary phase method, the formulation of the far fieldradiated sound pressure can be found. With the application of the same numerical method, theuncoupled infinite algebraic equations can be solved by truncating them in a finite range. Onthe basis of this, the influences of the excitation location, thickness of the plate, and thespacing, width and height of the stiffeners on the sound radiation characteristic of thestiffened panel are analyzed detailed.After that, the theoretical model of the single stiffened plate will be further developed.Through a detailed theoretical analysis, a theoretically analytic model is established toinvestigate sound transmission characteristics of an infinite thin plate reinforced by two setsof orthogonal stiffeners when subjected to plane wave in air. By applying the truncatednumerical method, the influences of the reinforcement form of the stiffeners, incident angle,thickness, and the periodicity spacing and moment of inertia on the sound insulationperformance of the orthogonally stiffened plate are studied, respectively.Finally, because all marine structures are actually in moving state, the convected waveequation and the displacement continuity condition at the fluid-structure interface in movingstate should be taking into account sufficiently to ensure the exact handling of the complexaeroelastic coupling between panel vibration and fluid disturbances, when calculating thesound pressure in the moving fluid. Based on these, a theoretically analytic model isdeveloped to analyze the sound transmission characteristics of an infinite orthogonallystiffened plate excited by a plane sound wave in convected fluids. Through the truncatednumerical method, the mean flow effects on refraction angel and the sound insulationperformance of infinite panel, single stiffened plate and orthogonally stiffened plate,meanwhile, the influences of different system parameters on sound insulation performance ofthe orthogonally stiffened plate are discussed.