The Propagation Characteristics Of Elastic Wave In Periodic Grid Structures And Grid Sandwich Structures

As the most promising new generation of advanced, lightweight, super-tough multifunctional structures, periodic grid structures and grid sandwich structures have extensive and important application prospects in the field of vehicles, aerospace engineering, shipbuilding, weapon equipment and so on. It is important for periodic grid structures and grid sandwich structures to reduce vibration and noise that the propagation of elastic wave is effectively suppressed. The regulation of elastic wave propagation characteristics provides a new way for vibration and noise control of periodic grid structures and grid sandwich structures.The work of this thesis is from some projects funded under national natural science foundation of china, and the purpose is to investigate some crucial theoretical and technical problems systematically to promote the applications of periodic grid structures and grid sandwich structures in the field of vibration and noise control. The following three aspects have been considered:(1) the methods for calculating propagation characteristics of elastic wave;(2) the elastic wave propagation mechanism and its influencing factors of periodic grid structures and grid sandwich structures;(3) the elastic wave propagation mechanism and its influencing factors of beams and lattice structures with periodically attached piezoelectric patches connected with shunting circuits.The main findings of this thesis are listed as follows:1. The bandgap characteristics and directional propagation characteristics of periodic lattice structures with the negative Poisson’s ratio are studied. The regulation rule of bandgap characteristic of the two typical structures by changing parameters and geometric parameters is analyzed in a systematic manner, and the bandgap formation mechanism is revealed. It is confirmed that there are lower-frequency and wider-width bandgaps in periodic lattice structures with the negative Poisson’s ratio than in traditional periodic lattice structures. Topology optimization of unit cells can help to improve the the performance of elastic wave attenuation in the structures.2. The bandgap characteristics of periodic grid-stiffened plates and periodic grid sandwich plates are studied are studied. It is proved that the forming and the width of band gaps are effected by the coupling of the elastic wave propagation between the skin and the stiffeneds in the periodic lattice stiffened plate structures. The same applies for the case of the periodic lattice sandwich plate structures. Specific as: 1) when the thickness ratio between the skin and the stiffeners is relatively small, the coupling is weak, and the stiffeners play a major role in the elastic wave propagation;With the increasing of the thickness ratio between the skin and the stiffeners,some band gaps appear and the width of band gaps are gradually increasing up to a maximum value, and then decrease;When the thickness of the skin is considerable to that of the stiffeners, bandgap properties determined primarily by uniform plate. 2) Because of the existence of the two skins in the grid sandwich plate structures, the coupling between the cores and two skins becomes stronger than that in the grid siffened plate structures, and the regulation of elastic wave propagation is weaker.3. The exploration research is also carried out for vibration reduction of periodic grid structure with periodically attached piezoelectric patches connected with shunting circuits. The tuning mechanism and its influencing factors of three type piezoelectric shunting circuits, i.e., resonant shunting circuits, enhanced resonant shunting circuits and feedback shunting circuits, are systematically analyzed and studied. To be specific, 1) The same low-frequency bandpap of the structures can be achieved wiht resonant shunting circuits as traditional locally resonant bandgap, but the bandgap can be tuned. Without introducing mechanical oscillator, the additional mass is small. With enhanced resonant shunting circuits, the width of the bandgaps of the structures can be further widened and the the vibration attenuation near the band gaps can be also increased. 2) Using feedback shunting circuit, the attenuation of elastic wave propagation within the bandgaps and outside the band gaps are significantly enhanced. These studies provide technical support for the active control of low-frequency vibration of periodic grid structures and grid sandwich structures.In summary, this thesis is concerned with some crucial theoretical and technical problems involved in the investigations and applications of periodic grid structures and grid sandwich structures for the purpose of reducing structural vibration and noise. The results of this thesis further deepen and expand elastic wave propagation theory in periodic structures and present significant theoretical foundations and technical guidelines to facilitate the application of periodic grid structures and grid sandwich structures with active and tunable bandgaps in reducing structural vibration and noise.