Investigation And Application Of Energy Finite Element Method

Forecast and control of Structural vibration and noise is an important project for both naval vessels and other kind of ships because it relates to the structural safety , stealth performance and comfort of passenger. Usually vibration and noise of ship structure lies in high frequency range. The main contents of the dissertation is as follows:1) The variety methods related to vibration noise at high frequency from the point view of energy density were reviewed. The advantage and disadvantage of the methods were discussed. The fundamental of statistical energy analysis was also explained.2) For basic ship structures such as rods and beams the energy density control equations at harmonic excitation were deduced by considering energy density as variables. The expressions of energy density and intensity were obtained for rod. The effects of three components of energy density on total energy density were analyzed. Furthermore, the energy density equation and the equation of heat conduction were compared. Some valuable conclusions were obtained.3) According to the small damping assumption the energy density control equation of infinite plate was deduced and the relation of energy and intensity was obtained. Hereby the energy density control equation of finite plate was deduced by considering the reflection of plate edges. The approximation solution of energy was developed. The exact solution of energy density was also obtained via displacement function.4) The energy balance equations for one and two-dimension structures were developed according to the principle of energy. The energy flow coupling relationships are developed for various structural joints. The power transmission and reflection coefficients were deduced for various structural joints.5) The energy density equations of one-dimensional and two-dimensional coupling structures were solved by Galerkin weighted approximation. Considering the uncontinuity of energy density at the joint, two distinctive features of special procedure were placement of multiple nodes at the joint of multiply-coupled structural elements and the insertion of joint elements at the joint to connect the coupled structural elements. The joint element matrix equations were developed for various structural configurations and wave types.6) The EFEM deduced from above was used to predict the energy density distribution for both the frame structure of a light truck and the engine foundation of a frigate ship. The calculation results were compared with the experiment results and they are in reasonably good agreement with the measurements. Therefore, EFEM is an efficient and reliable method for predicting vibration noise. Besides , some measures to decrease vibration and noise were discussed.