Study On Vibro-acoustic Energy Flow Of Ship Structure By Vibration Intensity Visualization Technique

Reduction of vibration and noise of marine structures has been an important issue to designers. In these fields the accurate investigation of vibration energy transmission and distribution is of particular importance for structural noise and vibration control. This dissertation addresses a study on numerical analysis of vibration and radiation intensity. The major contents of the dissertation are as follows.The various methods related to vibration and noise radiated problems are introduced. The advantages and disadvantages of the approaches are discussed. The basic principle and development status of structural vibration intensity measurement and calculation technology are explained. The research prospects of angular spectrum approach and Visualization of Scientific Computing (ViSC) are also discussed.Three typical stiffened plate models under harmonic point force exciting are calculated to predict the vibration intensity's components by finite element approach. Then, the intensity vector map visualization is used to indicate the location of vibration source and the sinking position where the energy is dissipated. The effects of stiffeners on the changes of energy transmission path through plate are also discussed. Moreover the input energy at the exciting point and dissipated energy at the damper are investigated. Also, an application of structural vibration intensity technique towards the design for platform of ship is explored.Based on the Matlab software, the Vibration Energy Flow Graphical User Interface(VEF-GUI) is designed by combing the dynamic analysis and mathematical processing capabilities. Furthermore, the Interactive Visual Interface containing numerical simulation and engineering test module is developed, which can save a lot of work and costs in research and practical engineering applications. The transmission and distribution of vibration energy flow in coupled plates are studied by VEF-GUI. The intensity vector, streamline map and energy distribution of coupled plates subject to a point force excitation are calculated and visualized to predict vibration energy transmission. The vibrational energy flows are very complex and dependent on the excitation frequencies, junction forms and boundaries. The vibration intensity method together with visualization techniques provides a powerful tool for vibration control.The energy flow visualization and control in vibrating stiffened plates with a cutout are studied using finite element method. The vibration intensity streamline, vibration energy and strain energy distribution of stiffened plates with cutout at different excitation frequencies are calculated respectively and visualized for the various cases. The cases of different size and boundaries conditions of cutouts are also investigated. It is found that the cutout or opening completely changes the paths and distributions of the energy flow in stiffened plate. The magnitude of energy flow is significantly larger at the edges near the cutout boundary. The position of maximum strain energy distribution is not corresponding to the position of maximum vibrational energy. Furthermore, the energy-based control using constrained damping layer (CDL) for vibration suppression is also analyzed. According to the energy distribution maps, the CDL patches are applied to the locations that have higher energy distribution at the targeted mode of vibration. The present energy visualization technique and energy-based CDL treatments can be extended to the vibration control of vehicles structures.The vibration energy flow in a fluid-loaded stiffened plate and the structural-acoustic coupling from the energy flow point of view are investigated using intensity vector technique in this paper. The spatial distribution of the vibration and acoustic energy flow is visualized to show the position of energy source, the direction of flowing energy and the amount of radiation sound energy with visualization technique. The numerical results show that the fluid loading changes the vibrational and sound energy flows. The structural-acoustic energy flow under air loading condition is generally at a smaller rate than that of under water loading condition from the spectrum plot. From GUI plots the sound energy flow clearly shows the structural near field behavior where the intensity vectors bend back to the panel surface. Furthermore, significant discrepancy between the sound energy distribution near the surface of the plate and the vibration energy in the stiffened plate is observed. The external damper significantly influences the vibrational and sound energy flows and the damping control strategies are investigated. The visualizations of the energy clearly show that the damper should be placed close to the energy input source and more damping involved more energy dissipated.An efficient Fourier transform technique to address the vibration structural and sound characteristics of a fluid-loaded plate excited by a mechanical force is presented. The process is based on the formulation in the wave number domain of the transversal response of the plate and of the acoustic response in the fluid domain. Analytical expressions in wave number space is obtained for these fields in the case of an infinite plate with point force and unform line force and a simply supported plate with point force. The cases using the two-dimensional Fourier transform to deduce the wave number fields of simply supported plate are discussed concerning structural intensity results on the plate.The angular spectrum function of various limited radiation source is developed and visualized to model the propagation of a wave field. This technique provides an efficient tool to analyse the vibro-acoustic behaviour of the structure.The characteristic of structural and sound energy transmission and distribution is invested in detail. The application of the vibration intensity methods together with Graphical User Interface visualization technique has improved the quality of structure-borne noise diagnostics and has made it possible to visualize energy wave phenomena in a vibrating structure.