A Study Of Band Gap And Vibration Reduction Performances Of The Periodic Rib-skin Structure

Periodic rib-skin structure connected by a series of identical elements, which are composed by ribs and skins, along one direction is designed to achieve excellent vibration band gaps in it. Corresponding wave cannot propagate freely in the frequency ranges of the band gaps, thus vibration transmitted through the periodic rib-skin structure can be substantially attenuated. A simple band gap and band pass characteristic can be observed when only a single wave propagates in the structure. Excellent longitudinal and flexural vibration band gap exist in the periodic rib-skin structure, thus studying on the band gap characteristics of the periodic structure can demonstrate vibration attenuation mechanism of the structure. Furthermore, studying on vibration reduction performance of the rib-skin structure can provide references of applying periodic structure in engineering vibration control.Structural vibration and noise control is always one of the hottest subjects and is urgent to be solved both in theoretical and practical engineering. Periodic structure, as a kind of Phononic crystal, becomes a hotspot topic in condensed matter physics recently. Phononic crystals exhibit rich new physics and promising potential applications, which have attracted much attention from various disciplines. The main aim of this dissertation is to improve dynamic behavior of one dimensional periodic structure in both low and high frequency ranges and to utilize the periodic structure to reduce the vibration transmission in engineering. Thus, periodic mass-spring structures carrying multiple types of oscillators are established to reveal the Bragg and Locally Resonant(LR) band gap characteristics of periodic structure. Then, asymmetric periodic structure is designed to demonstrate the coupling between multiple types of waves propagating in the structure. Finally, periodic rib-skin structure are designed to achieve excellent vibration reduction performance both in low and high frequency ranges, and the periodic structure is further used to control vibration transmitting in the marine vibration isolation system. The detailed research and main conclusions in this dissertation are summarized as follows:(1) A detailed literature reviews on longitudinal and flexural vibration band gaps in periodic structures, wave coupling effects and application of periodic structures in vibration control engineering are summarized, and the advantages and disadvantages of applying periodic structure in designing base structure are pointed out in this dissertation.(2) Coupling vibration mobility matrices of Euler beams, vibration absorber and rigid body are given out. Mobility matrices of the periodic elements in periodic structures are derived by using of transfer matrix method, and are further used for calculating the propagation constants of the waves and for deriving dynamic responses of semi-infinite and finite structure. Periodic mass-spring structure is established to demonstrate the Bragg band gap characteristics of the structure, and then, evenly spaced oscillators are attached to the periodic structure to achieve one or multiple LR band gaps in the periodic structure. Effects of structural parameters on the bounding frequencies of the Bragg and LR band gaps are discussed in detail.(3) Symmetric and asymmetric periodic structures are designed to investigate coupling effects of longitudinal and flexural waves propagating in the structures. The multiple types of waves are divided into two categories to avoid ill-conditioning matrices in numerical calculation. The propagation constants of the longitudinal and flexural waves are calculated, harmonic response of semi-infinite periodic structure in symmetric and asymmetric arrangements are obtained. Relationships between the propagation constants and the dynamic responses are revealed by numerical simulations.(4) Periodic rib-skin structure is designed to achieve excellent longitudinal and flexural vibration band gaps in it. Wave propagating method is used for studying band gaps and vibration reduction performances of the periodic structure. Furthermore, vibration attenuation characteristics of the rib-skin structure below 3000 Hz are especially optimized. Finally, test model of the periodic rib-skin structure is established to measure the acceleration frequency responses and to validate the correctness of the numerical results.(5) Evenly spaced vibration absorbers are attached to the periodic rib-skin structure to improve the vibration reduction performance of the structure in low frequency range. The flexural LR and Bragg band gaps and vibration reduction performance both in low and high frequency range of the LR periodic structure are discussed in detailed. Test model of the periodic rib-skin structure carrying LR oscillators is established to measure the acceleration frequency responses.(6) Combined rib-skin base is designed by using the idea of LR band gap and Bragg scattering mechanisms to reduce vibration transmission in marine vibration isolation system. Dynamic response on the pressure hull of the marine is substantially attenuated in the band gaps, and substantial vibration attenuations are achieved both in LR and Bragg band gaps. The dynamic characteristics of the combined base structure are validated by experimental work.