Studies Of The Dynamical Response Of Two-dimensional Yukawa Systems Using Simulations

Using molecular dynamical(MD)simulations,the dynamical response of two-dimensional(2D)dusty plasmas under various external forces is systematically studied in this thesis.Here,the completed projects include:the viscosity of 2D Yukawa liquids modified by strong perpendicular magnetic fields,the dynamics of compressional shocks in 2D Yukawa systems,the lattice melting and the energy transport of 2D Yukawa systems under external shears.For the first work,MD simulations are performed to study the dynamical behavior of 2D dusty plasma liquids under strong perpendicular magnetic fields.The viscosity,describing the momentum transport,can be obtained by substituting the velocities and positions of the simulated dust particles under magnetic fields into the Green-Kubo relation.The results show that the strong magnetic field would increase the viscosity of the low-temperature 2D Yukawa liquid,however,it would reduce the viscosity of the high-temperature 2D Yukawa liquid.In the intermediate temperature range,the viscosity of 2D Yukawa liquids would first decrease and then increase briefly as the magnetic field increases.Based on the simulation data,the modification of the viscosity due to the applied perpendicular magnetic field is interpreted,providing the guidance for the future research of magnetized dusty plasmas.In the second work,it is found that compressional shocks can be generated when the boundary of the 2D Yukawa systems is compressed with a constant speed.From the simulation data of compressional shocks,the shock Hugoniot curves of 2D Yukawa systems are obtained at first.Then,using the obtained shock Hugoniot curves with the Rankine-Hugoniot jump relations,analytical expressions of pressure and energy after shocks for 2D Yukawa systems are derived,which are functions of the observable quantities,such as the shock front speed D,the mean particle speed v,or the specific volume ?/?0.Thus,as an application of these obtained expressions,the pressure and internal energy,which cannot be measured in experiments,can be obtained from theses observable quantities.Specifically,it is discovered that,for 2D Yukawa systems with different conditions,there is a universal relationship between the drift and the thermal velocities after shocks.As an application of this universal relationship,the temperature after shocks can be derived analytically.In addition,this relationship between the drift and the thermal velocities after shocks is also derived from the existing equation of state of 2D Yukawa liquids,which is consistent with the universal relationship.This result not only verifies the correctness of the discovered universal relationship,but also indicates that the equation of state obtained from the equilibrium simulation within a certain parameter range can still describe the 2D Yukawa systems after shocks.This project makes a meaningful attempt at the physical mechanism of compressional shocks and provides a theoretical support for the subsequent experimental research.The third work is to simulate the shear-induced melting experiment of dust plasmas.The simulation results show that,under a strong shear,the melting front of the 2D Yukawa lattice would propagate at the longitudinal sound speed.When the shear continues to increase further,shocks would be generated in the 2D Yukawa lattice,and the propagation speed of the melting front would be faster than the longitudinal sound speed.In addition,it is also found that,when the simulated 2D Yukawa system reaches the final steady state,the ratio of the kinetic energy due to the motion in the two directions would roughly decrease to a constant value.Based on the discovered universal relationship above,this kinetic energy ratio can be also derived,and the further discussion is carried out.The prediction from the previous shear-induced melting dusty plasma experiment is validated using the current simulation work,under the conditions which are unlikely to be experimentally realized using the laser manipulation technique.The results reported here can provide a guidance for the future experiments with a larger shear using a different technique.