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In this paper, a decoupled characteristic Galerkin finite element procedure is provided for simulating growth-mediated autochemotactic pattern formation in self-propelling bacteria. In this procedure, a modified characteristic Galerkin method is established to solve the bacterial density equation, while the classical finite element procedure is considered for the self-secreted chemical density and polarization dynamics equations system. The convergence of this proposed method is considered under some regularity assumptions and the corresponding error estimate is derived. Numerical experiments are carried out to support the theoretical analysis. Furthermore, several new wave type pattern formations are found.

We present a highly efficient lattice Boltzmann (LB) kinetic model for thermal liquid-vapor system. Three key components are as beow: (i) a discrete velocity model by Kataoka \emph{et al.} [Phys. Rev. E \textbf{69}, 035701(R)(2004)]; (ii) a forcing term $I_{i}$ aiming to describe the interfacial stress and recover the van der Waals equation of state by Gonnella \emph{et al.} [Phys. Rev. E \textbf{76}, 036703 (2007)]; and (iii) a Windowed Fast Fourier Transform (WFFT) scheme and its inverse by our group [Phys. Rev. E \textbf{84}, 046715 (2011)] for solving the spatial derivatives, together with a second-order Runge-Kutta (RK) finite difference scheme for solving the temporal derivative in the LB equation. The model is verified and validated by well-known benchmark tests. The results recovered from the present model are well consistent with previous ones[Phys. Rev. E \textbf{84}, 046715 (2011)] or theoretical analysis. The usage of less discrete velocities, high-order RK algorithm and WFFT scheme with 16th-order in precision makes the model more efficient by about $10$ times and more accurate than the original one., Comment: Accepted for publication in Int. J. Mod. Phys. C

Cavity growth in ductile metal materials under dynamic loading is investigated via the material point method. Two typical cavity effects in the region subjected to rarefaction wave are identified: (i) part of material particles flow away from the cavity in comparison to the initial loading velocity, (ii) local regions show weaker negative or even positive pressures. Neighboring cavities interact via coalescence of isobaric contours. The growth of cavity under tension shows staged behaviors. After the initial slow stage, the volume and the dimensions in both the tensile and transverse directions show linear growth rate with time until the global tensile wave arrives at the upper free surface. It is interesting that the growth rate in the transverse direction is faster than that in the tensile direction. The volume growth rate linearly increases with the initial tensile velocity. After the global tensile wave passed the cavity, both the maximum particle velocity in the tensile direction and the maximum particle velocity in the opposite direction increase logarithmically with the initial tensile speed. The shock wave reflected back from the cavity and compression wave from the free surface induce the initial behavior of interfacial instabilities such as the Richtmyer-Meshkov instability, which is mainly responsible for the irregularity in the morphology of deformed cavity. The local temperatures and distribution of hot spots are determined by the plastic work. Compared with the dynamical process, the heat conduction is much slower.

In this mini-review we summarize the progress of Lattice Boltzmann(LB) modeling and simulating compressible flows in our group in recent years. Main contents include (i) Single-Relaxation-Time(SRT) LB model supplemented by additional viscosity, (ii) Multiple-Relaxation-Time(MRT) LB model, and (iii) LB study on hydrodynamic instabilities. The former two belong to improvements of physical modeling and the third belongs to simulation or application. The SRT-LB model supplemented by additional viscosity keeps the original framework of Lattice Bhatnagar-Gross-Krook (LBGK). So, it is easier and more convenient for previous SRT-LB users. The MRT-LB is a completely new framework for physical modeling. It significantly extends the range of LB applications. The cost is longer computational time. The developed SRT-LB and MRT-LB are complementary from the sides of convenience and applicability., Comment: to be published in Frontiers of Physics, 37 pages, 16 figures

In this paper we present an improved lattice Boltzmann model for compressible Navier-Stokes system with high Mach number. The model is composed of three components: (i) the discrete-velocity-model by Watari and Tsutahara [Phys Rev E \textbf{67},036306(2003)], (ii) a modified Lax-Wendroff finite difference scheme where reasonable dissipation and dispersion are naturally included, (iii) artificial viscosity. The improved model is convenient to compromise the high accuracy and stability. The included dispersion term can effectively reduce the numerical oscillation at discontinuity. The added artificial viscosity helps the scheme to satisfy the von Neumann stability condition. Shock tubes and shock reflections are used to validate the new scheme. In our numerical tests the Mach numbers are successfully increased up to 20 or higher. The flexibility of the new model makes it suitable for tracking shock waves with high accuracy and for investigating nonlinear nonequilibrium complex systems.