Features of Currents on the Black Sea Northwestern Shelf Based on the Numerical Simulation Results

Purpose. The work is aimed at studying the features of currents on the Black Sea northwestern shelf based of the reanalysis results, and at analyzing the reasons of these features. Methods and Results. To analyze the currents on the northwestern shelf, applied were the results of physical reanalysis of the Black Sea fields performed by the authors earlier, namely, the arrays of hydrodynamic fields on a regular grid with the 21-year duration (1992–2012). Surface currents on the northwestern shelf of the Black Sea are directed mainly to the southwest. Throughout the whole year (except for the summer months when the wind effect weakens), an intensive compensatory current directed to the south is formed along the western coast. The waters near the western coast are highly horizontally stratified that is caused by fresh water inflowing with the river runoffs. In winter seasons, the stratification is most pronounced, whereas in summer, the horizontal density gradient decreases. The horizontal density stratification leads to the following: starting from the depth ~ 20 m, the pressure gradient changes its sign and the along-coastal jet countercurrent directed to the north, occurs. Conclusions. The performed studies have shown that the water circulation on the Black Sea northwestern shelf is determined mainly by the following factors: the wind-induced water flows across the shelf boundary and strong horizontal water stratification near the western coast resulted from the river runoffs. As the currents on the sea surface are directed mainly to the southwest, the compensatory current directed to the south is formed near the western coast. Due to the strong horizontal stratification resulted from the river runoffs, a countercurrent directed to the north is formed in the subsurface layer near the western coast. In case the seawater flows to the shelf are extremely high, the countercurrent may be absent.

Features of Currents on the Black Sea Northwestern Shelf Based on the Numerical Simulation Results

Purpose. The work is aimed at studying the features of currents on the Black Sea northwestern shelf based of the reanalysis results, and at analyzing the reasons of these features. Methods and Results. To analyze the currents on the northwestern shelf, applied were the results of physical reanalysis of the Black Sea fields performed by the authors earlier, namely, the arrays of hydrodynamic fields on a regular grid with the 21-year duration (1992–2012). Surface currents on the northwestern shelf of the Black Sea are directed mainly to the southwest. Throughout the whole year (except for the summer months when the wind effect weakens), an intensive compensatory current directed to the south is formed along the western coast. The waters near the western coast are highly horizontally stratified that is caused by fresh water inflowing with the river runoffs. In winter seasons, the stratification is most pronounced, whereas in summer, the horizontal density gradient decreases. The horizontal density stratification leads to the following: starting from the depth ~ 20 m, the pressure gradient changes its sign and the along-coastal jet countercurrent directed to the north, occurs. Conclusions. The performed studies have shown that the water circulation on the Black Sea northwestern shelf is determined mainly by the following factors: the wind-induced water flows across the shelf boundary and strong horizontal water stratification near the western coast resulted from the river runoffs. As the currents on the sea surface are directed mainly to the southwest, the compensatory current directed to the south is formed near the western coast. Due to the strong horizontal stratification resulted from the river runoffs, a countercurrent directed to the north is formed in the subsurface layer near the western coast. In case the seawater flows to the shelf are extremely high, the countercurrent may be absent.

Study of Interconnected Physical Processes in the Magnetic Fluid Sealer

The purpose of this work is creation of an interconnected numerical model of the magnetic and hydrodynamic fields of the ferrofluid sealer to analyze the effect of centrifugal forces during shaft rotation on the retained pressure drop. The set goal was achieved by selection of the necessary equations, boundary conditions, assumptions and properties concerning the ferrofluids when building a numerical model of the sealer gap in the Comsol Multiphysics simulation environment. The important results of the work were the obtained and analyzed distributions of the magnetic field and pressure field in the ferrofluid, the evaluation results of the of the effect of centrifugal forces arising during the shaft rotation, on the pressure drop held by the sealer. It was shown that with a shaft radius of up to 50 mm and speed up to 3000 rpm, the change in the retained pressure drop was insignificant, and it was up to 2 % of the values with a stationary shaft. Significant manifestation of centrifugal force for the investigated shaft radii began at 6000 rpm. It was shown that the decrease in the retained pressure drop with an increase in the working gap was associated with the decrease in the magnetic field gradient. The significance of the results consisted in the possibility of using the developed model for the study of the ferrofluid sealer gap processes. Comparison with the data obtained using the analytical formulas showed that the latter overestimated the retained pressure drop

Spin polarization induced by the hydrodynamic gradients

We systematically analyze the effects of the derivatives of the hydrodynamic fields on axial Wigner function that describes the spin polarization vector in phase space. We have included all possible first-order derivative contributions that are allowed by symmetry and compute the associated transport functions at one-loop using the linear response theory. In addition to reproducing known effects due to the temperature gradient and vorticity, we have identified a number of potentially significant contributions that are overlooked previously. In particular, we find that the shear strength, the symmetric and traceless part of the flow gradient, will induce a quadrupole for spin polarization in the phase space. Our results, together with hydrodynamic gradients obtained from hydrodynamic simulations, can be employed as a basis for the interpretation of the Λ (anti-Λ) spin polarization measurement in heavy-ion collisions.

Self-organized biotectonics of termite nests

The termite nest is one of the architectural wonders of the living world, built by the collective action of workers in a colony. Each nest has several characteristic structural motifs that allow for efficient ventilation, cooling, and traversal. We use tomography to quantify the nest architecture of the African termite Apicotermes lamani, consisting of regularly spaced floors connected by scattered linear and helicoidal ramps. To understand how these elaborate structures are built and arranged, we formulate a minimal model for the spatiotemporal evolution of three hydrodynamic fields—mud, termites, and pheromones—linking environmental physics to collective building behavior using simple local rules based on experimental observations. We find that floors and ramps emerge as solutions of the governing equations, with statistics consistent with observations of A. lamani nests. Our study demonstrates how a local self-reinforcing biotectonic scheme is capable of generating an architecture that is simultaneously adaptable and functional, and likely to be relevant for a range of other animal-built structures.

Directing the far-from-equilibrium assembly of nanoparticles in confined liquid crystals by hydrodynamic fields

The assembly of nematic colloids relies on long-range elastic interactions that can be manipulated through external stimuli.

Correction for non-stationary of hydrodynamic fields in the rheological relationship of liquid

Эксплуатация различного рода технических устройств, в которых реализуются течения жидкости в каналах и трубах, всегда сопровождается нестационарными гидродинамическими процессами. Однако решение задач нестационарных течений жидкостей и газов зачастую приводит к существенных погрешностям, что дает основание исследователям основание сомневаться в справедливости реологических соотношений, учитывающих только неоднородность гидродинамических полей, но не учитывающих их нестационарность. Для устранения этих погрешностей при решении нестационарных задач течения жидкости в каналах и трубах в работах под руководством профессора С.К.Матвеева в выражение для касательного напряжения введена поправка, содержащая производную по времени скорости жидкости. Однако обобщение этой поправки на общий случай течения в тензорном виде оказывается невозможным. Поэтому в данной работе предлагается запись выражения для всего тензора напряжений в жидкости с поправкой на нестационарность, содержащей производную скорости, которая пригодна для описания пространственных течений жидкости. Рассмотрен частный случай нестационарного течения жидкости в плоском канале в одномерной постановке при использовании этой поправки. Показано, что такая модификация реологического соотношения приводит к решениям, согласующимися с решениями С.К.Матвеева. Также эта модификация может привести к уточнениям результатов решения для некоторых задач нестационарных течений. The operation of various technical devices in which fluid flows in channels and pipes are realized is always accompanied by non-stationary hydrodynamic processes. However, the solution of problems of unsteady flows of liquids and gases often leads to significant errors, which gives reason to researchers to doubt the validity of rheological relations, taking into account only the heterogeneity of the hydrodynamic fields, but not taking into account their unsteadiness. To eliminate these errors in solving unsteady problems of fluid flow in channels and pipes, in the work under the guidance of Professor S.K. Matveev, a correction containing the time derivative of the fluid velocity is introduced into the expression for shear stress. However, this correction is generalized to the general case of flow in tensor form turns out to be impossible. Therefore, in this paper, we propose writing an expression for the entire stress tensor in a fluid, adjusted for non-stationarity, containing the derivative of velocity, which is suitable for describing spatial fluid flows. A special case of unsteady fluid flow in a flat channel in a one-dimensional formulation using this correction is considered. It is shown that such a modification of the rheological relation leads to solutions matching the decisions of S.K. Matveev. Also, this modification can lead to more precise results of the solution for some problems of unsteady flows.