The Research On Zero-order Energy Flow Analysis And Its Application In Structural Acoustic Problems Of Ship Structure

The forecast and control of middle to high frequency vibration and sound radiation are complex problems,especially to the ship structure.Besides the large dimension and the complicated structure,the marine structures also have strong coupling with fluid,all these make it unable to solve by finite element method or analytic method.Although SEA(Statistic Energy Analysis)can solve the high frequency problem of large structure,but it also has defects such as its weak coupling hypothesis and its coarse division.These disadvantages limit its further application in the acoustic design and vibration control of ships.A new method "Zero-Order Energy Finite Element Analysis"(EFEA~0)based on a simple finite volume implementation of the energy flow analysis is investigated in this dissertation.It uses piecewise constant elements and has essentially the same form as an SEA approximation,which make it can avoid the complex handling of coupling point like PFFEM(Power Flow Finite Element Method)and the formula is more simple.Although it looks like SEA formula,it's not a SEA method.It can be used in the strong coupling and non-conservative systems which the SEA can not solve and It can solve the spatial variation of energy.So,EFEA~0 has huge potential in the vibration control and acoustic design of large structure such as ships.As the basis of EFEA~0,the differential energy density equations of different waveform in one dimension and two dimension basic structures are deduced and concluded.The Power Flow transmission characteristics of different coupling structures are described by energy transmission coefficient and reflection coefficient. After that,EFEA~0 equation of one and two dimension structure was constructed and extended to the more complex coupling structures.The results of deduction show that EFEA~0 equations are zero-order linear equations and need no special handling for coupling point.It is simpler and easier to solve than PFFEM.According to characteristics of ship structure,vibration energy transmission relation of a beam-plate coupling model is studied.The energy transmission and reflection coefficients of different kinds of wave form are derived.Because coupling joint adopts 3D elastic beam of any section,and it can connect more than two plates, this model may be used on many kind of coupling structures in ships besides of stiffened plate studied in this dissertation.The application of EFEA~0 on damping structures widely used in vibration and noise control of ships is also studied.Since EFEA~0 use energy as main variable and each element can have different damping characteristic,it is convenient to apply on structure with different local damping.In order to validate EFEA~0,vibration experiment of a simple supported stiffened plate is designed and carried out.Meanwhile,a dense finite element model and a EFEA~0 model of this plate is also built and solved.By the comparison of the results, the EFEA~0 solutions match the experiments and FEM solutions well in a averaged form.At last,the effect of fluid loading is introduced into the EFEA0 formula.On the basis of it,a new method of radiation noise analysis is developed by using the EFEA0 and Boundary element method(BEM)together.