Research On The Properties Of The Flexural Vibrational Band Gap In The Periodic Pipe Conveying Fluid

The pipe systems conveying fluid are applied broadly in the military and industry. The vibro-acoustic energy that caused by the fluid and structure vibrations of pipe systems will paralyze the pipe system and machines. Flexural vibration is the main propagation mode in the pipe system. It is useful to control the propagation of flexural vibration through the pipe.Phononic Crystals (PCs) are periodic composite materials or structures, which can forbid the transmission of sound and vibration within special frequencies. The existence of flexural vibration gaps in periodic pipe gives anew idea in vibration control of pipe.This dissertation makes research into the control of the propagation of vibration throughout the pipe conveying fluid. The idea of the PCs theory is introduced into the design of the pipe conveying fluid. We will prove theoretically and experimentally that the band gaps in periodic can be used to control the propagation of flexural vibration effectively. The main work and achievements are given as follows:1. Basing on the PC theory, we calculate the band structures with the Bragg scattering mechanism and locally resonant mechanism. And the influence factors of the material and geometrical parameters on band gaps are analyzed.2. Different boundary conditions will affect the band gaps properties of the periodic pipes. We calculate the flexural vibration band structures and the frequency response functions (FRF) of the finite straight periodic pipe system with different boundary conditions, such as elastic foundations, elastic supports, axial force, the velocities and pressures of the fluid, etc.3. The periodic pipe experiment system is designed and constructed to test the propagation of flexural vibration through straight periodic pipe. And the effects of different boundary conditions on band gaps are also tested.To sum up, the thesis has studied the band structure and the FRF of the periodic pipe conveying fluid theoretically and experimentally. The effect of various parameters and boundary conditions on the band gap are discussed. Meanwhile, the experiment system is designed to validate the theoretical results. This research work will provide some support for the design of vibration and noise reduction of pipe system conveying fluid.