Measuring Ocean Surface Current in the Kuroshio Region Using Gaofen-3 SAR Data

The Kuroshio is the strongest warm current in the western North Pacific, which plays a crucial role in climate and human activities. In terms of this, the accurate acquisition of ocean surface current velocity and direction in the Kuroshio region is of great research value. Gaofen-3 synthetic aperture radar (SAR) provides data support for the study of ocean surface current measurements in the Kuroshio region, but no relevant experimental result has been published yet. In this paper, four available stripmap mode SARs’ data acquired by Gaofen-3 in the Kuroshio region are used for measuring the ocean surface current field. In general, the Doppler centroid anomaly (DCA) estimation is a common method to infer ocean surface currents from single-antenna stripmap data, but only the radial velocity component can be retrieved. In order to measure current vectors, a novel method combining the sub-aperture processing and the least squares (LS) technology is suggested and demonstrated by applying to the Gaofen-3 SAR data processing. The experiment’s results agree well with model-derived ocean current data, indicating that the Gaofen-3 SAR has the capability to accurately retrieve the ocean surface current field in the Kuroshio region and motivate further research by providing more data.

Impact of driving forces on molten pool in gas metal arc welding

A numerical scrutiny was performed to analyze the effect of driving forces on molten pool in gas metal arc welding. In addition to the basic governing equations required for a general heat and mass transfer analysis by computational fluid dynamics, a volume-of-fluid equation for free surface tracking and additional conservation equations for calculating the distribution of alloy elements were used. Driving forces—buoyancy, drag force, arc pressure, electromagnetic force, Marangoni pressure, and droplet impingement—and the arc heat source were mathematically modeled and applied to the simulation. In order to examine the effect of driving forces, a two-dimensional axisymmetric simulation was performed, and the effect of each driving force was analyzed using the velocity components. In the radial velocity component, the effect of droplet impingement and the Marangoni force was large, and in the vertical velocity component, the droplet impingement effect was dominant. A three-dimensional simulation was also performed considering all the driving forces together, and the result was verified by comparison with experimental results. Relatively high alloying element contents were found at the bottom of the fusion zone, which was due to the droplet impingement generating a high vertical velocity.

Peculiarities of marine eddy manifestation in the structure of surfactant slick band

<p>Slick structures on the sea surface can mark processes occurring in upper ocean and atmosphere. Spiral shape of slicks observed in optical and radar images of water surface is traditionally interpreted through the manifestation of marine eddy which length scale is supposed to be equal to the scale of spiral. This assumption implies that wind has no effect on the kinematics of forming slick band, which, according to our estimation, is incorrect even at moderate wind velocities. This approach can cause misinterpretation of remote sensing data when estimating the characteristics of observed marine eddies. This study is devoted to the investigation of conditions necessary for the formation of slick spiral and to some peculiarities of its shape and scale.</p><p>The system of equations for the description of kinematics of Lagrangian particle (element of water surface covered with surface active substance) in the fields of axisymmetric eddy with non-zero radial velocity component and homogeneous wind was obtained. It is demonstrated that the spiral center is not collocated with the center of the eddy; the distance between them can achieve the eddy length scale. It is shown that the displacement of the spiral center and the direction of the main axis is quasi perpendicular to the wind direction when radial component of the eddy is small compared to the tangential component. The presence of the threshold wind velocity corresponding to the breakdown of the spiral structure is demonstrated analytically. The possibilities of correct retrieval of length scales and character velocities of observed sub mesoscale marine eddies are discussed.</p><p>The research was funded by the Russian Science Foundation (Project RSF 18-77-10066).</p>

Dynamics and Stability Analysis of Rotating Cylindrical Shells in Annular Fluid Medium

Stability and dynamics of rotating coaxial cylindrical shells conveying incompressible and inviscid fluid are investigated. The interior shell is assumed to be flexible while the exterior cylinder is rigid. Using Sander’s–Koiter theory assumptions and following Hamilton’s principle, governing equations of motion are determined in their integral form. Employing the extended Galerkin method of solution, the integral equations of motion are projected to their equivalent system of algebraic equations. Fluid equations are fundamentally based on the linearized inviscid Navier–Stokes equations. Impermeability condition on the fluid and structure interface as well as the zero radial velocity component on the exterior shell give the coupled equations of motion governing the dynamics of fluid-loaded coaxial cylindrical shells. Using the coupled fluid–structural model, stability boundaries are determined for the rotating interior shell. Various parameter studies are conducted and effects of mass ratio, gap distance between the interior and exterior shells, boundary conditions of the interior shell, length to radius ratio on the stability margins are thoroughly investigated and reported.

The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators

ABSTRACT Stellar activity is the major roadblock on the path to finding true Earth-analogue planets with the Doppler technique. Thus, identifying new indicators that better trace magnetic activity (i.e. faculae and spots) is crucial to aid in disentangling these signals from that of a planet’s Doppler wobble. In this work, we investigate activity related features as seen in disc-integrated spectra from the HARPS-N solar telescope. We divide high-activity spectral echelle orders by low-activity master templates (as defined using both $\log {R^{\prime }_{HK}}$ and images from the Solar Dynamics Observatory, SDO), creating ‘relative spectra’. With resolved images of the surface of the Sun (via SDO), the faculae and spot filling factors can be calculated, giving a measure of activity independent of, and in addition to, $\log {R^{\prime }_{HK}}$. We find pseudo-emission (and pseudo-absorption) features in the relative spectra that are similar to those reported in our previous work on α Cen B. In α Cen B, the features are shown to correlate better to changes in faculae filling factor than spot filling factor. In this work, we more confidently identify changes in faculae coverage of the visible hemisphere of the Sun as the source of features produced in the relative spectra. Finally, we produce trailed spectra to observe the radial velocity component of the features, which show that the features move in a redward direction as one would expect when tracking active regions rotating on the surface of a star.

New Approach to Modeling and Simulation of Chemical and Mass Transfer Processes in Column Apparatuses

Objective: The classical mass transfer theory is not applicable for modeling the mass transfer of chemical, absorption, adsorption and catalytic processes in column apparatuses, where the velocity distributions and interphase boundaries are unknown. The modeling of these processes is related with the creation of new type of convection-diffusion models (for qualitative analysis) and average-concentration models (for quantitative analysis), where the surface reactions are replaced by equivalent volume reaction, while the velocity and concentration distributions are replaced by average velocity and concentrations. The effect of the radial non-uniformity of the velocity in the average-concentration models is introduced by model parameters, which must be obtained experimentally. Methods: The new convection-diffusion and average-concentration models are obtained in the cases of different processes in column apparatuses: simple and complicated chemical reactions, physical and chemical absorption, physical and chemical adsorption, heterogeneous catalytic processes (physical and chemical adsorption mechanism). These models are presented in the monograph Chr. Boyadjiev, M. Doichinova, B. Boyadjiev, P. Popova-Krumova, “Modeling of Column Apparatus Processes” (Second edition), Springer- Verlag, Berlin Heidelberg, 2018. Results: Two hydrodynamic situations are considered, when the radial velocity component is equal to zero, in the cases of an axial modification of the radial non-uniformity of the axial velocity component and when the radial velocity component is not equal to zero. Conclusion: The use of experimental data, for the average concentrations at the column end, for a concrete process and column, permits to obtain the model parameters, related with the radial non-uniformity of the velocity. These parameter values permit to use the averageconcentration models for modeling of different processes.

MHD slip flow of chemically reacting UCM fluid through a dilating channel with heat source/sink

The present article explores the effects of uniform heat source and first order destructive chemical reaction on an upper convected Maxwell fluid through an expanding or contracting channel with the porous slip condition at the upper plate. It is assumed that the fluid is sucked or injected through the upper plate. The temperature and concentration at the plates is maintained constant. Using suitable similarity transformations, nonlinear coupled ODEs are developed from the governing PDEs. The subsequent ODEs are converted into a first order system and integrated via shooting method. The effect of various prominent parameters on heat, flow and mass transfer characteristics are studied in detail through graphs and tables. The present results suggest that the presence of chemical reaction and heat source yields in the reduction of concentration and of the enhancement of temperature the fluid. It is also observed that the wall expansion shows an increasing effect on the radial velocity component, but the slip parameter exhibits an opposing effect. The viscous case has been studied as a special case where the present results are found to be close to the earlier ones. The flow of such nonlinear viscoelastic fluids has important applications in separation processes like petroleum and medical industries.

Modelling transport and deposition of non-spherical micro- and nano-particles in composites manufacturing

In liquid moulding processes, a fabric is impregnated with a fluid that may contain particles aimed at giving the final product additional and possible smart properties. It is therefore interesting to be able to reveal how the distribution and orientation of such particles are affected by the processing condition. During the manufacturing of the fabric, relatively large channels are formed between bundles of fibres where the impregnating fluid may flow. There are also micro-channels within the bundle that are impregnated by the fluid in the larger channels mainly by capillary action. With focus on fibre bundles along the main flow direction, three main stages of the flow are the flow is leading within the bundles, the flow is moving at equal rate within the bundles and between them and the flow is leading in the channels between the bundles. The latter one of these is in focus in this study, and the capillary action from the larger channels to the micro-channels is modelled as a constant radial velocity. Brownian, gravitational and hydrodynamic forces acting on the particles are studied. The introduction of a radial velocity component drastically increases the deposition rate, and it is clear that while particle shape has a great influence on deposition rates in a flow moving strictly in the direction of the channel, when a radial flow component is introduced the differences seem to disappear.

Using Simulations and Computational Analyses to Study a Frequency-Modulated Continuous-Wave Radar

This paper describes a method for simulating Frequency-Modulated Continuous-Wave (FMCW) radar. The developments presented target classroom lectures and can form the basis of student projects. Computational analysis and simulation are critical elements of science and engineering education in which students need to acquire these competencies. FMCW radar system simulations are an example of a real-world application, invested in rich mathematical/physical content that exercise these competencies. Unlike conventional radars that operate in the time domain, FMCW radars operate in the frequency domain. Spectral and phase analyses are required to infer range and the range resolved velocity of meteorological targets such as rain or drizzle. Hence to proceed with simulations, students are first introduced to signals processing topics such as discretization and sampling of signals, Fourier Transforms, Z-transforms, and filters. Computations and the display of results are subsequently performed using Elanix System Vue and Matlab software. To aid the interpretation of the results, a brief description of FMCW physical principles of operation is provided. The computational technique is general and efficient, allowing the range-resolved radial velocity component of precipitation to be computed in real-time. Simulations of range are in excellent agreement with field test measurements of experimental, operational X-band radar currently being evaluated at NASA Goddard Spaceflight Center while computations of the range-resolved velocity component of precipitation agree with the setup conditions of the simulations.

Mixed Convection Heat Transfer in an Annulus With Rotating Inner Cylinder

Natural as well as mixed convection heat transfer are studied in an annulus formed by concentric cylinders where the outer cylinder is the enclosure and the inner cylinder is either stationary or rotating about its axis at various angular speeds. The parameters involved in this study are Rayleigh number (Ra), Richardson number (Ri), Rotational Reynolds number (Re) and Nusselt Number (Nu). The present study uses a two Dimensional steady state Finite Volume method with a coupled scheme approach of pressure-velocity coupling. Three cases of Ra with a temperature difference of 5K, 50K and 90K are investigated. For each case, natural convection and mixed convection heat transfer is studied by varying Ri. For mixed convection study, the range of values used for Ri are 10−3–103 in multiples of 10 and hence the rotational speed of inner cylinder is varied suitably. For each case of Ra, for each Ri, local Nu variation on the rotating cylinder as well as the enclosure are presented. Surface averaged values of Nu are plotted against Ri for different values of Ra. Further, radial velocity component variation is also examined along a particular region in the domain.