Similitude Of Structure-borne Sound For Typical Ship Structure Based On Wave Approach

It’s generally acknowledged that structural vibration has significant effects to the on-board habitability,operation of equipment or even structural damage,thus the control of vibration becomes an import issue.Although numerical approaches are widely adopted by the industry in acoustic prediction,the accuracy of numerical approach is not satisfied due to ideal assumptions during calculation.The cost of model experiment is also unaffordable.In this case,using similarity experiment is an ideal but practical way to predict structural vibration.In the past,similitude analysis was carried out by either Dimensionbased Analysis or Equation-based Analysis.As Dimension-based approach estimates the similitude relations in a rough way,while Equation-based method has trouble in handling complicated structures,Wave Approach would be used in our similitude investigation.First,the propagation of waves under three different conditions are deduced: transmission/reflection efficiencies at discontinuous corners,phase change in continuous structure and reflection efficiencies at impedance boundaries.Wave equations are non-dimensionalized and several non-dimensional efficiencies effecting wave propagation are concluded.Similitude relations are carried out based on those non-dimensional efficiencies,including the influence of boundary impedance.After that numerical calculation is conducted,which verifies the similitude principles.The results shows that for scaled structures,the similarity of frequency is related with scaled ratio,density ratio and modules ratio,while boundary impedance ratio is only related with scaled ratio and modules ratio.The conclusions drawn by theoretical analysis and numerical calculation are extended to industrial practices.The similitude principles are applied to the investigation of abnormal vibration of certain ship’s aft-part,which was caused by propellers.With experiments on scaled model,the vibration properties of propellers are predicted,which verifies the fact that the abnormal vibration is caused by the resonance of propellers’ lower order modals,proving possibility of applying similitude principles into complicated 3-Dimension structures.In general,our research not only verifies the similitude principles among scaled built-up structures,but also provide reference for further similarity experiment.