The Propagation, Excitation and Coupling of Acoustic Waves in Phonon Band-gap Materials

Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.

Nonlinear Dynamic Analysis of Coupled Gear-Rotor-Bearing System with the Effect of Internal and External Excitations

Extensive studies on nonlinear dynamics of gear systems with internal excitation or external excitation respectively have been carried out. However, the nonlinear characteristics of gear systems under combined internal and external excitations are scarcely investigated. An eight-degree-of-freedom（8-DOF） nonlinear spur gear-rotor-bearing model, which contains backlash, transmission error, eccentricity, gravity and input/output torque, is established, and the coupled lateral-torsional vibration characteristics are studied. Based on the equations of motion, the coupled spur gear-rotor-bearing system（SGRBS） is investigated using the Runge-Kutta numerical method, and the effects of rotational speed, error fluctuation and load fluctuation on the dynamic responses are explored. The results show that a diverse range of nonlinear dynamic characteristics such as periodic motion, quasi-periodic motion, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. Significantly, the changing rotational speed could effectively control the vibration of the system. Vibration level increases with the increasing error fluctuation. Whereas the load fluctuation has an influence on the nonlinear dynamic characteristics and the increasing excitation force amplitude makes the vibration amplitude increase, the chaotic motion may be restricted. The proposed model and numerical results can be used for diagnosis of faults and vibration control of practical SGRBS.

SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results.

ANALYSIS OF COUPLING INFLUENCES OF LABYRINTH SEAL PARAMETERS ON CROSS COUPLED STIFFNESS AND DIRECT DAMPING COEFFICIENT

Labyrinth seal can cause steam-exciting, the structural and operating parameters of labyrinth seal have effect on stability of rotor-system. For investigating the coupling influences of the structure and operating parameters of labyrinth seals on dynamic coefficients, a model of calculating dynamic coefficients of labyrinth seals is presented using a two control volume model. The coupling influences of parameters on cross-coupled stiffness and direct damping of labyrinth seal are discussed. In the conclusion, a reference of preventing steam-exciting vibration and optimum determination of design parameters of labyrinth seals are provided.

Phase diagram and collective modes in Rashba spin–orbit coupled BEC: Effect of in-plane magnetic field

We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave（PW） phase, striped wave（SW） phase, and zero momentum（ZM） phase. It was shown that with a growing in-plane field,both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.

STUDY ON MECHANISM OF ARC-EXCITED ULTRASONIC

A mechanism of excited arc to be an controlled “ultrasonic emission source” is described. An developed electrical source with an certain frequency bandwidth for the purpose of the arc excited is connected with an conventional welding power supply through coupling the cables for the experiment. Some resonant frequency bands for the arc excited ultrasonic are discovered in the welding process, and its frequency, amplitude and phase'shift are recorded. This principle demonstrates that arc can be used not only for a thermal source, but also for an ultrasonic emission source, which may be extent to the industrial application in some new ways, such as for automatic welding process control and quality inspection.

Firing rates of coupled noisy excitable elements

The dynamics of coupled excitable FitzHugh Nagumo systems under external noisy driving is studied. Different from most of previous work focusing on the noise-induced regularity in the framework of coherence resonance, here the average frequency （or firing rate） of coupled excitable elements is of much more concern. We find that （i） their frequencies first increase and then decrease with the increase of the coupling, and there is a clear crossover from a rush increase to a smooth increase with the increase of noise strength, and （ii） for nonidentical cases, all elements transit to an identical frequency simultaneously only after a certain coupling strength is achieved. These first-increase-thendecrease non-monotonic frequency behavior and isochronous frequency synchronization are believed to be two basic behaviors in coupled noisy excitable systems.