Fan Wei-Li

Controlling the transition between Turing and antispiral patterns by using time-delayed-feedback

The controllable transition between the Turing and antispiral patterns is studied by using time-delayed-feedback strategy in a FitzHugh-Nagumo model. We treat the time delay as perturbation and analyze the effect of the time delay on the Turing and Hopf instabilities near the Turing-Hopf codimension-two phase space. Numerical simulations show the transition between the Turing patterns (hexagon, stripe, and honeycomb), the dual-mode antispiral, and the antispiral by applying appropriate feedback parameters. The dual-mode antispiral pattern originates from the competition between the Turing and Hopf instabilities. Our results have shown the flexibility of the time delay on controlling the pattern formations near the Turing-Hopf codimension-two phase space.

Spatio-Temporal Distribution of Individual Filaments in a Square Superlattice Pattern in Atmospheric Dielectric Barrier Discharge

Spatio-temporal distribution of individual filament in a square superlattice pattern, which consists of large and small spots (filaments), is studied in atmospheric dielectric barrier discharges. The spatial distributions of the two discharges for individual large filament along the direction perpendicular to the electrode are estimated by the distributions of light signals along the electrode. It is found that the discharge at the rising edge of the applied voltage is with a wider column, weaker current, and longer current pulse duration in comparison with that at the falling edge.

Spontaneous transition of one-dimensional plasma photonic crystal's orientation in a dielectric barrier discharge

A novel one-dimensional plasma photonic crystal whose crystal orientation can change spontaneously is demonstrated using a dielectric barrier discharge with two liquid electrodes. The orientation of the plasma photonic crystal will vary from transverse to longitudinal or vary from longitudinal to transverse and then revert to longitudinal by self-adjustment, while the experimental conditions are kept fixed. The dispersion relation of these plasma photonic crystals are calculated, and the changes of the photonic band diagrams during the orientation transition are studied.

Study on the dark-ring white-eye square super-lattice pattern in dielectric barrier discharge

The dark-ring white-eye square super-lattice pattern was studied in dielectric barrier discharge system for the first time. Each unit cell of the pattern consisted of a central bright spot surrounded by a dark ring. The structure of dark ring around the center bright spot was similar to the white-eye, which was called the dark-ring white-eyes. The spatial-temporal dynamics of the dark-ring white-eye square super-lattice pattern was investigated by high speed frame camera (HSFC). The results showed that the dark-ring white-eye square super-lattice pattern was an interleaving of four different sub-structures. The discharge sequence was center bright dot-bright dot halo-vertex square-vertex connection in each half voltage cycle. The formation mechanism of dark-ring white-eye square super-lattice pattern and dark ring was explained by surface charges theory.

Dynamic Energy Absorption of Circular Honeycomb Under In-plane Impact Loading

To effectively control the dynamic energy absorption, a density graded circular honeycomb model is proposed, based on the concept of functionally graded materials. The influences of density gradient and impact velocity on the dynamic energy absorption ability of circular honeycomb are investigated by adopting explicit dynamic finite element method. Numerical results show that the density gradient affects greatly in the energy absorption. These findings will provide valuable suggestions in the dynamic energy absorption design of cellular materials.

Effects of Defects on the In-plane Dynamic Energy Absorption of Metal Honeycombs

The in-plane dynamic energy absorption of metal honeycombs with defects consisting of missing cells are analyzed using explicit dynamic finite element method. Two types of structural defects (a single defect located in the center of the model and a double defect) are firstly introduced. Then the influence of the defects and the impact velocities on the energy absorption abilities of metal honeycombs is investigated. Researches show that single and isolated defects reduce the absorbed energy of cellular materials. The separation distance between two defects has little effect on the dynamic energy absorption, while the size of the single defect has great influence on it. These results will provide some useful guides for the safety evaluation and the dynamic energy absorption design of metal honeycombs.

Nonlinear Interaction and Coherent Structure in Tokamak Plasma Turbulence

The nonlinear interaction in the coherent structure in the CT-6B tokamak plasma turbulence is studied by using the wavelet bicoherence technique. The results show that the coherent structure mainly results from the nonlinear interaction between waves.