Development of a Snowdrift Model with the Lattice Boltzmann Method

This study developed a new snowdrift model to evaluate the snowdrift height around a snow fence, often installed along a road in a snowy and windy environment. The model consisted of the conventional computational fluid dynamics (CFD) solver by the Lattice Boltzmann method (LBM) and a module for snow particles’ motion and accumulation. The calculation domain was a half channel with a flat free-slip boundary on the top and a non-slip boundary on the bottom, imposing an inflow with artificially generated turbulence from one side to the other outlet side. Besides the reference experiment with no fence, the experiment was set up with a two-dimensional and a three-dimensional fences normal to the dominant wind direction in the channel center. The estimated wind flow over the two-dimensional fence was characterized by a swirling eddy in the cross-section, whereas the wind flow in the three-dimensional fence experiment was horizontally diffluent with a dipole vortex pair in the leeward of the fence. As a result, almost all of snowdrift was formed in the windward of the two-dimensional and three-dimensional fences, but it was also formed as the split streak in the leeward of the three-dimensional fence. The result suggested that the fence should be as long as possible to avoid the snowdrift on roads.

Vortices in Rotating and Gravitating Gas Disk and in a Protoplanetary Disk

Nonlinear equations describing dynamics of 2D vortices are very important in the physics of the ocean and the atmosphere and in plasma physics and Astrophysics. Here linear and nonlinear 2D vortex perturbations of gravitating and light gaseous disks are examined in the geostrophic and post-geostrophic approximations. In the frame of geostrophic approximation, it is shown that the vortex with positive velocity circulation is characterized by low pressure with negative excess mass density of substance. Vortex with negative circulation has higher pressure and is a relatively tight formation with the positive excess mass density. In the post-geostrophic approximation, structures of the isolated monopole and dipole vortex (modons) solutions of these equations are studied. Two types of mass distributions in dipole vortices are found. The first type of modon is characterized by an asymmetrically positioned single circular densification and one rarefaction. The second type is characterized by two asymmetrically positioned densifications and two rarefactions, where the second densification-rarefaction pair is crescent shaped. The constant density contours of a dipole vortex in a light gas disk coincide with the streamlines of the vortex; in a self-gravitating disk, the constant density contours in the vortex do not coincide with streamlines. Possible manifestations of monopole and dipole vortices in astrophysical objects are discussed. Vortices play decisive role in the process of planet formation. Gas in a protoplanetary disk practically moves on sub-Keplerian speeds. Rigid particles, under the action of a head wind drags, lose the angular momentum and energy. As a result, the ~10 cm to meter-sized particles drift to the central star for hundreds of years. Long-lived vortical structures in gas disk are a possible way to concentrate the ~10 cm to meter sized particles and to grow up them in planetesimal. Here the effect of anticyclonic Burgers vortex on formation of planetesimals in a protoplanetary dusty disc in local approach is also considered. It is shown that the Burgers vortex with homogeneously rotating kernel and a converging radial stream of substance can effectively accumulate in its nuclear area the meter-sized rigid particles of total mass ∼1028 g for characteristic time ∼106 year.

Vortex statistics of a cylinder wake flow close to the wall based on IB-LBM

In this paper, statistical behaviors of vortex in the wake flow of a circular cylinder placed near a plane wall in the two-dimensional (2D) channel are investigated by Immersed Boundary Lattice Boltzmann Method. Although vortices shed from the cylinder periodically, there are very complicated interactions between vortices and the solid wall. The gap ratios [Formula: see text] are considered in three cases [Formula: see text] to study vortex statistic behaviors when flow is in steady state. It can be seen that a single row of coherent structures in the same sign varies to dipole vortex shedding as [Formula: see text] increases. The results of vortex statistics by the conditional analysis, which are based on a new and accurate vortex identification criteria called Liutex, show the algebraic number density [Formula: see text], where [Formula: see text] is vortex area. The relationship between the vortex circulation [Formula: see text] and vortex area [Formula: see text] is [Formula: see text] and the one between the kinetic energy of vortex [Formula: see text] and [Formula: see text] is [Formula: see text] in the range where [Formula: see text]. Moreover, it has been found that vortices contain about 30% of the total energy of the flow which is almost conserved as Re varies by studying the energy ratio [Formula: see text] of all vortices to the entire flow field. The statistic behaviors of energy spectrums show that the spectrums contain an inertial range in which [Formula: see text] not only in the coherent structure field but also in the background field. More features of the vortex structure in the wake flow have been described by the empirical mode decomposition (EMD). There is a linear relationship between the frequency and the mode of the form [Formula: see text] e[Formula: see text] in the semi-log coordinates. The period of each mode [Formula: see text] e[Formula: see text] in the semi-log coordinates. The time-dependent intrinsic correlation (TDIC) shows that there is a strong negative correlation relationship between the pressure and the flow velocity in the complex attachment vortex.

TENSOR STRESS ASYMMETRY AS A MECHANISM FOR THE FORMATION OF DIPOLE VORTEX INTO THE JET FLOW IN THE COASTAL ZONE

The theoretical conclusions about the effect of asymmetry of the stress tensor on the formation of dipolar vortex structures are built on the basis of laboratory experiments. The results of computer simulation of the mushroom current are provided.

Robustness of nearshore vortices

Coherent vortices with horizontal swirl arise spontaneously in the wave-driven nearshore surf zone. Here, a demonstration is made of the much greater robustness of coherent barotropic dipole vortices on a sloping beach in a 2D shallow-water model compared with fully 3D models either without or with stable density stratification. The explanation is that active vortex tilting and stretching or instability in 3D disrupt an initially barotropic dipole vortex. Without stratification in 3D, the vorticity retains a dipole envelope structure but is internally fragmented. With stratification in 3D, the disrupted vortex reforms as a coherent but weaker surface-intensified baroclinic dipole vortex. An implication is that barotropic or depth-integrated dynamical models of the wave-driven surf zone misrepresent an important aspect of surf-eddy behaviour.

Harvesting uniform and high bright Sm complex via microwave ultrasound method

The uniform ball-like luminescence down-shifting (LDS) Sm ( TTA )3 Phen materials have been synthesized by microwave ultrasonic method. Microwave ultrasonic plays a synergistic effect of microwave with ultrasonic, including thermal effect, dipole vortex and air bombard make the particles aggregation reach to the lowest energy. Through this method, we successfully synthesised 1–4 μm ball-like uniform Sm ( TTA )3 Phen clusters. The Sm ( TTA )3 Phen can transfer violet light to red-orange flourescence with a feature large Stokes shift and completely avoid self-absorption losses.

Self-organization of ULF electromagnetic wave structures in the shear flow driven dissipative ionosphere

This work is devoted to investigation of nonlinear dynamics of planetary electromagnetic (EM) ultra-low-frequency wave (ULFW) structures in the rotating dissipative ionosphere in the presence of inhomogeneous zonal wind (shear flow). Planetary EM ULFW appears as a result of interaction of the ionospheric medium with the spatially inhomogeneous geomagnetic field. The shear flow driven wave perturbations effectively extract energy of the shear flow increasing own amplitude and energy. These perturbations undergo self organization in the form of the nonlinear solitary vortex structures due to nonlinear twisting of the perturbation's front. Depending on the features of the velocity profiles of the shear flows the nonlinear vortex structures can be either monopole vortices, or dipole vortex, or vortex streets and vortex chains. From analytical calculation and plots we note that the formation of stationary nonlinear vortex structure requires some threshold value of translation velocity for both non-dissipation and dissipation complex ionospheric plasma. The space and time attenuation specification of the vortices is studied. The characteristic time of vortex longevity in dissipative ionosphere is estimated. The long-lived vortices transfer the trapped medium particles, energy and heat. Thus they represent structural elements of turbulence in the ionosphere.