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We study pinning and unpinning of superfluid vortices in the inner crust of a neutron star using three-dimensional dynamical simulations. Strong pinning occurs for certain lattice orientations of an idealized, body-centered-cubic lattice and occurs generally in an amorphous or impure nuclear lattice. The pinning force per unit length is ∼1016 dyn cm−1 for a vortex–nucleus interaction that is repulsive and ∼1017 dyn cm−1 for an attractive interaction. The pinning force is strong enough to account for observed spin jumps (glitches). Vortices forced through the lattice move with a slipstick character; for a range of superfluid velocities, the vortex can be in either a cold, pinned state or a hot, unpinned state, with strong excitation of Kelvin waves on the vortex. This two-state nature of vortex motion sets the stage for large-scale vortex movement that creates an observable spin glitch. We argue that the vortex array is likely to become tangled as a result of repeated unpinnings and repinnings. We conjecture that during a glitch, the Kelvin-wave excitation spreads rapidly along the direction of the mean superfluid vorticity and slower in the direction perpendicular to it, akin to an anisotropic deflagration.

A novel octocopter with an overlapping rotor arrangement is proposed in this paper to increase the payload with a limited size. The aerodynamic performance was obtained by both experiments and numerical simulations with the rotor spacing ranging from 1.2 D to 2.0 D (L= 1.2 D, 1.4 D, 1.6 D, 1.8 D, 2.0 D). Also, the aerodynamic parameter was evaluated by the thrust, power consumption, thrust coefficient, power coefficient, and figure of merit (FM) in hover. Compared with a traditional co-axial octocopter, the results indicated that the overlapping octocopter at L= 1.8 D presented an increasing thrust up to 15.98%, and the FM increment was up to 6%. Additionally, the streamline distribution showed that the symmetry of the vortex movement in the downwash flow for the overlapping rotors will offset the rotor interference with an increase in thrust. Meanwhile, the vortex deformation resulting from the induced velocity from the upper rotor also led to an increase in power consumption. Finally, the optimal aerodynamic performance of the overlapping octocopter was obtained with a rotor spacing of L= 1.8 D at 1800 RPM.

Microbubbles have been widely used in power, chemical, mining and petroleum applications to improve energy efficiency. The venture-type bubble generator can improve reaction efficiency in chemical engineering as an efficient bubble generation method. Studying the flow field and bubble bursting mechanism can enhance the bubble generation performance. The volume of fluid (VOF) multiphase flow model was used in the Open Field Operation and Manipulation (OpenFOAM) framework to study the deformation and fragmentation behaviour of a single bubble in a Quasi three-dimensional. The relationship between the mechanism of bubble breakup and the flow field in the diverging section of a Venturi-type bubble generator was revealed. The reasons for the uneven distribution of bubble size were analyzed and discussed. The numerical simulation result shows that the fragmentation of a single bubble injected by the converging section is more substantial than that injected by the throat in the axial direction. Bubble fragmentation occurs mainly in the diverging section. The bubble's trajectory is highly similar to the vortex trajectory of the diverging section. The size of sub-bubbles generated by single bubble fragmentation decreases with the diverging angle and liquid flow rate increase. The differential distribution of turbulent kinetic energy in the radial position directly leads to the uneven distribution of the bubble size of the broken bubbles. As the liquid Reynolds number increases, static and dynamic erosion breakup are more prominent. The size of the sub-bubbles is much smaller.

One possible mechanism for the effect of gravity-field inhomogeneities (GFIs) on the atmosphere dynamics has been investigated theoretically. It is shown that the vertical heat exchange in an air layer in an inhomogeneous gravity field can disrupt the state of hydrostatic equilibrium and lead to the generation of vortex flows. Estimates of the amplitude of velocity perturbations are made on the basis of a linear stationary hydrodynamic model that takes planetary rotation into account. The magnitude of the vortex component of the velocity can reach values on the order of the product of the buoyancy frequency and amplitude of the geoid deviations. The amplitude of the emerging vertical motions, in addition to the parameters mentioned, also depends on the intensity of the turbulent exchange and horizontal scales of the inhomogeneities.

It is suggested that the downward helicity flux (through the upper boundary of the viscous turbulent boundary layer) be treated as a measure of the intensity of atmospheric vortices, including tropical cyclones, tornadoes, and dust devils. As follows immediately from the general helicity balance equation known in the literature, this flux is determined by the product of the cubed maximum wind speed and the width of the strip swept by the maximum wind during vortex movement. For intense vortices in their steady-state, mature stage, this helicity flux can also serve as a measure of the rate of helicity destruction by the forces of viscous turbulent friction. Examples of applying the introduced notion to the diagnostics of tornadoes and their classification according to a destructive force are given. A comparative analysis (according to helicity flux values) of dust devils on the Earth and Mars, on the one hand, and tornadoes, on the other, is presented.

This article studies the response of the distribution pattern and the physiological characteristics of the ecosystem to the spontaneous precipitation and the interaction between vegetation and the atmosphere on multiple scales in arid and semi-arid zones, based on measured data of the ecological physiological parameters in the Ordas Plateau of northern China. The results show that the vegetation biomass and the energy use efficiency of photosynthesis are especially sensitive to the annual precipitation; strong and complex interactions exist between the vegetation and the atmosphere on multiple scales leading to supernormal thermal heterogeneity of the underlying surface, the strong vortex movement and turbulence. This study can facilitate understanding of the land surface processes and the influences of global climate change as well as human activities on the human environment in the arid and semi-arid zones. It also aids in improving the parameterization schemes of turbulent fluxes of a heterogeneous underlying surface for land surface processes in climate models.

A series of thermodynamic property of the atmospheric system can be deducted, in accordance with re-striction of the general thermodynamics theory or other nature principle to saddle on the phenomenological relation. The relationship between the turbulence transport coefficients of K turbulence close theory and the phenomenological coefficients are deduced using the linear thermodynamics of nonequilibrium state. A cross coupling between the heat transportation and the vapor transportation in the atmospheric system is proved. Even a turbulence intensity theorem is demonstrated. The distributional heterogeneity of velocity and potential temperature is the turbulence fountainhead and the turbulence intensity is proportional to the scalar product of velocity and potential temperature gradient in the non-compressed and isotropy turbu-lence atmosphere. More about an atmospheric vortex theorem is demonstrated. The shear of potential tem-perature leads to a vortex movement or sundry circumfluence movement and the velocity vorticity equals to the vector product of velocity and potential temperature gradient. An application foreground of the linear thermodynamics is exhibited to the atmosphere system.

Vortex-induced vibrations of bluff bodies occur when the vortex shedding frequency is close to the natural frequency of the structure. Of interest is the prediction of the lift and drag forces on the structure given some limited and scattered information on the velocity field. This is an inverse problem that is not straightforward to solve using standard computational fluid dynamics methods, especially since no information is provided for the pressure. An even greater challenge is to infer the lift and drag forces given some dye or smoke visualizations of the flow field. Here we employ deep neural networks that are extended to encode the incompressible Navier–Stokes equations coupled with the structure’s dynamic motion equation. In the first case, given scattered data in space–time on the velocity field and the structure’s motion, we use four coupled deep neural networks to infer very accurately the structural parameters, the entire time-dependent pressure field (with no prior training data), and reconstruct the velocity vector field and the structure’s dynamic motion. In the second case, given scattered data in space–time on a concentration field only, we use five coupled deep neural networks to infer very accurately the vector velocity field and all other quantities of interest as before. This new paradigm of inference in fluid mechanics for coupled multi-physics problems enables velocity and pressure quantification from flow snapshots in small subdomains and can be exploited for flow control applications and also for system identification.

The stratospheric polar vortices play a significant role in stratospheric ozone distribution, air mass movement and temperature changes in the polar and subpolar stratosphere. To characterize the main parameters of the stratospheric polar vortices, in particular, vortex area, wind speed along the vortex edge, average temperature and ozone mass mixing ratio inside the vortex, vortex delineation is necessary. In this work, we use a new method of vortex delineation based on geopotential values determined from the maximum temperature gradient and maximum wind speed, thus, characterizing the polar vortex edges. Using the vortex delineation method based on the ERA5 reanalysis data for 1979–2020, we show a comparative characteristic of the Arctic and Antarctic polar vortices in the lower and middle stratosphere. The average polar vortex area in winter from 1979 to 2020 at the 50 and 10 hPa pressure levels equals 28.6 and 35.3·10 6 km 2 in the Arctic, and 41.6 and 54.8·10 6 km 2 in the Antarctic. The average wind speed along the vortex edge in winter at the 50 and 10 hPa pressure levels equals 35.5 and 55.5 m/s in the Arctic, and 52.7 and 79.2 m/s in the Antarctic. The average temperature inside the polar vortex in winter at the 50 and 10 hPa pressure levels equals respectively –69.0 and –61.7°C in the Arctic, and –81.9 and –74.2°C in the Antarctic. Research highlights Mean values of the area of the Arctic and Antarctic polar vortices are estimated. Mean wind speed along the edges of the Arctic and Antarctic vortices are estimated. Mean temperatures inside the Arctic and Antarctic polar vortices are estimated.

The motion of several plates in an inviscid and incompressible fluid is studied numerically using a vortex sheet model. Two to four plates are initially placed in line, separated by a specified distance, and actuated in the vertical direction with a prescribed oscillatory heaving motion. The vertical motion induces the plates’ horizontal acceleration due to their self-induced thrust and fluid drag forces. In certain parameter regimes, the plates adopt equilibrium ‘schooling modes’, wherein they translate at a steady horizontal velocity while maintaining a constant separation distance between them. The separation distances are found to be quantised on the flapping wavelength. As either the number of plates increases or the flapping amplitude decreases, the schooling modes destabilise via oscillations that propagate downstream from the leader and cause collisions between the plates, an instability that is similar to that observed in recent experiments on flapping wings in a water tank (Newbolt et al., 2024, Nat. Commun., vol. 15, 3462). A simple control mechanism is implemented, wherein each plate accelerates or decelerates according to its velocity relative to the plate directly ahead by modulating its own flapping amplitude. This mechanism is shown to successfully stabilise the schooling modes, with remarkable impact on the regularity of the vortex pattern in the wake. Several phenomena observed in the simulations are obtained by a reduced model based on linear thin-aerofoil theory.