Rotational Velocity Component Research Articles

Rotational and translational motions in a homogeneously cooling granular gas

A granular gas composed of monodisperse spherical particles was studied in microgravity experiments in a drop tower. Translations and rotations of the particles were extracted from optical video data. Equipartition is violated, the rotational degrees of freedom were excited only to roughly 2/3 of the translational ones. After stopping the mechanical excitation, we observed granular cooling of the ensemble for a period of three times the Haff time, where the kinetic energy dropped to about 5% of its initial value. The cooling rates of all observable degrees of freedom were comparable, and the ratio of rotational and translational kinetic energies fluctuated around a constant value. The distributions of translational and rotational velocity components showed slight but systematic deviations from Gaussians at the start of cooling.

Platonic solids bouncing on a vibrating plate.

The energy transfer between bouncing particles and rigid boundaries during impacts is crucially influenced not only by restitution coefficients of the material but also by particle shapes. This is particularly important when such particles are mechanically agitated with vibrating plates. Inertial measurement units are able to measure all acceleration and rotational velocity components of an object and store these data for subsequent analysis. We employ them to measure the dynamics of cubes and icosahedra on vibrating plates to study the efficiency of energy transfer into the individual degrees of freedom (DOFs) of the excited object. The rotational DOFs turn out to be much less excited than the vertical translational motion. Most remarkably, there is only little difference between the two Platonic solids in both the absolute energies and the energy partition ratios.

Development of a scattering model for diatomic gas–solid surface interactions by an unsupervised machine learning approach

This work proposes a new stochastic gas–solid scattering model for diatomic gas molecules constructed based on the collisional data obtained from molecular dynamics (MD) simulations. The Gaussian mixture (GM) approach, which is an unsupervised machine learning approach, is applied to H2 and N2 gases interacting with Ni surfaces in a two-parallel wall system under rarefied conditions. The main advantage of this approach is that the entire translational and rotational velocity components of the gas molecules before and after colliding with the surface can be utilized for training the GM model. This creates the possibility to study also highly nonequilibrium systems and accurately capture the energy exchange between the different molecular modes that cannot be captured by the classical scattering kernels. Considering the MD results as the reference solutions, the performance of the GM-driven scattering model is assessed in comparison with the Cercignani–Lampis–Lord (CLL) scattering model in different benchmarking systems: the Fourier thermal problem, the Couette flow problem, and a combined Fourier–Couette flow problem. This assessment is performed in terms of the distribution of the velocity components and energy modes, as well as accommodation coefficients. It is shown that the predicted results by the GM model are in better agreement with the original MD data. Especially, for H2 gas the GM model outperforms the CLL model. The results for N2 molecules are relatively less affected by changing the thermal and flow properties of the system, which is caused by the presence of a stronger adsorption layer.

Analytical modelling of flame transfer functions for technically premixed flames

The linear response to harmonic acoustic excitation of the total heat release rate in technically premixed flames (Flame Transfer Function, FTF) is studied in case of an ideal swirl burner. The analysis is based on the linearization of the production rate for the mean reaction progress variable modelled with a turbulent flame speed closure. Three main components of the FTF are identified which are generated by: I) direct fluctuations in the fuel mixture fraction (formation enthalpy contribution), II) direct fluctuations in the turbulent flame speed and III) flame surface area fluctuations driven by velocity and turbulent flame speed fluctuations. The velocity fluctuation is separated into an irrotational acoustic displacement and a rotational convective component. The effect of the rotational velocity component on the FTF is modelled here in a semi-empirical way, related to swirl number fluctuations at the flame base due to the phase shift between convected tangential velocity fluctuations and acoustically propagating axial velocity fluctuations. It is finally shown that fuel mixture fraction fluctuations can be generated not only by air mass flow rate fluctuations but also by fuel flow rate fluctuations which depend upon the air side impedance at the fuel injection location. It is shown that this impedance changes with the geometry of the plenum placed upstream the burner affecting in this way also the FTF.

INFLUENCE OF THE MEASURING TOOLS ON THE FLOW CHARACTERISTICS IN VORTEX CHAMBER PUMP

Problem. Perturbation of the flow by measuring instruments forces researchers to choose optical research methods. But these methods significantly increase the cost of experimental research, due to the high cost of optical-type measuring equipment. On the other hand, using contact methods for measuring the flow velocity, such as Pitot tubes, hot-wire anemometers, the researcher must be sure that the measurement results can really be compared with the calculations results and the equipment influence on the flow parameters is minimal. The aim of this work is to study the measuring tool influence on the flow characteristics in the swirl chamber pump, as well as to compare the results obtained due to the measurements with the parameters of the undisturbed flow. The research methodology consisted of two stages: 1) modeling the flow in the model pump; 2) comparison of flow characteristics, as well as the values of velocity and pressure at the points of installation of the measuring tool. Results. Although the total velocity at the measuring point is practically independent of the measuring tool, the tangential component of the velocity is significantly reduced. It indicates that there is a significant error in velocity measuring. For a more accurate rotational velocity component measurement, it is necessary to orient the instrument perpendicular to the measured component. Scientific novelty. Installing the measuring tool in the end cover of the swirl chamber reduces the flow rate sucked by the pump through the lower axial channel. The size of the tool has practically no effect on the energy characteristics of the swirl chamber pump. Practical value. To ensure measurement accuracy, the ratio of the swirl chamber dimensions and the tool should be ensured in the way that the relative diameter of the tool does not exceed 0.25 of the swirl chamber neck diameter.

Vorticity, Kinetic Energy, and Suppressed Gravitational-Wave Production in Strong First-Order Phase Transitions.

We have performed the first three-dimensional simulations of strong first-order thermal phase transitions in the early universe. For deflagrations, we find that the rotational component of the fluid velocity increases as the transition strength is increased. For detonations, however, the rotational velocity component remains constant and small. We also find that the efficiency with which kinetic energy is transferred to the fluid falls below theoretical expectations as we increase the transition strength. The probable origin of the kinetic energy deficit is the formation of reheated droplets of the metastable phase during the collision, slowing the bubble walls. The rate of increase in the gravitational wave energy density for deflagrations in strong transitions is suppressed compared to that predicted in earlier work. This is largely accounted for by the reduction in kinetic energy. Current modeling therefore substantially overestimates the gravitational wave signal for strong transitions with deflagrations, in the most extreme case by a factor of 10^{3}. Detonations are less affected.

Clustering of Floating Tracer Due to Mesoscale Vortex and Submesoscale Fields

AbstractFloating tracer clustering is studied in oceanic flows that combine both a field of coherent mesoscale vortices, as simulated by a regional, comprehensive, eddy‐resolving general circulation model, and kinematic random submesoscale velocity fields. Both fields have rotational and divergent velocity components, and depending on their relative contributions, as well as on the local characteristics of the mesoscale vortices, we identified different clustering scenarios. We found that the mesoscale vortices do not prevent clustering but significantly modify its rate and spatial pattern. We also demonstrated that even weak surface‐velocity divergence has to be taken into account to avoid significant errors in model predictions of the floating tracer patterns. Our approach combining dynamically constrained and random velocity fields, and the applied diagnostic methods, are proposed as standard tools for analyses and predictions of floating tracer distributions, in both observational data and general circulation models.

Gap flow with circumferential velocity in annular skirt of vortex gripper

The vortex gripper is a noncontact gripper that uses vortex flow that enables it to grip objects without coming into physical contact with them, thus avoiding such damage to the workpiece as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study involves theoretically and experimentally investigating the flow characteristics of the gap flow with a rotational velocity component between the workpiece and the annular skirt of the vortex gripper. Based on this, we discuss the effect of an important structural parameter of the gripper, i.e., the width of the annular skirt, on its performance. We first propose a theoretical model of the pressure gradient of the gap flow in the radial direction, where the pressure gradient is determined by the viscous term dominated by radial velocity, and the inertial terms are dominated by the radial and circumferential velocities. According to this theoretical model, we then analyze the distributions of radial velocity and circumferential velocity in the radial direction when the gap between the workpiece and the gripper varies, and the influence of the viscous term and the inertial terms on the pressure gradient. Further, we clarify the significance of the inertial term dominated by circumferential velocity on the pressure distribution. The validity of the theoretical model was verified by comparing its output with the results of experiments. Finally, by analyzing the force characteristic curves and pressure distributions of the grippers with annular skirts of four widths, we concluded that an increase in the width of the annular skirt can increase the influence of the inertial term dominated by circumferential velocity, and can thus change the region of stable suspension of the gripper and increase its suction capacity.

Quantum State and Doppler-Resolved Scattering of Thermal/Hyperthermal DCl at the Gas–Liquid Interface: Support for a Simple “Lever Arm” Model of the Energy-Transfer Dynamics

Supersonically cooled deuterium chloride (10 K, DCl(J ≈ 0, 1)) has been scattered from the gas–liquid interface under thermal (Einc = 1.5(1) kcal/mol) and hyperthermal (Einc = 11.5(5) kcal/mol) conditions for a series of prototypical liquids (perfluoropolyether (PFPE), squalane, and glycerol), with the final DCl quantum states detected with narrow-band IR laser absorption methods to achieve rotational (J) and transverse Doppler (vy) resolutions. First of all, we see direct evidence for both trapping desorption (TD) and impulsive scattering (IS) components in the DCl distributions, with both TD rotational and transverse velocity components fully equilibrated with the liquid (TS ≈ Trot ≈ TDopp). Second, high-resolution laser dopplermetry on the IS component reveals quite efficient transfer from Einc into out-of-plane scattering of the DCl, in contrast with the notably inefficient channeling of the collision energy into end-over-end rotation. Third, though the rotational excitation efficiency is low, the imp...

Fire whirls behind an L-shaped wall in a crossflow

This paper studies fire whirls formed behind an L-shaped wall in a crossflow. Wind-tunnel experiments at various crossflow velocities were conducted, and it was found that there was a narrow range of crossflow velocity that led to the formation of an intense and stable fire whirl, i.e., the existence of a critical wind velocity. Scaling analysis and computational fluid dynamics (CFD) calculations of different scales suggested that the Froude number is the governing parameter of the phenomenon; the critical wind velocity is therefore roughly proportional to the square root of the fire size. Particle image velocimetry (PIV) measurements showed that the rotational velocity component was reduced near the bottom floor, which then induced a fast radial inflow toward the axis in the vicinity of the floor. This radial inflow pushes the flame toward the fuel surface, enhancing heat transfer between flame and fuel and thereby leading to the formation of an intense fire whirl. The inflow velocity was much slower when the crossflow velocity was outside the critical range. Finally, it was demonstrated that the formation of an intense fire whirl could be prevented by blocking the near-floor flow using an obstacle.

Fuzzy-Based Hybrid Control Algorithm for the Stabilization of a Tri-Rotor UAV.

In this paper, a new and novel mathematical fuzzy hybrid scheme is proposed for the stabilization of a tri-rotor unmanned aerial vehicle (UAV). The fuzzy hybrid scheme consists of a fuzzy logic controller, regulation pole-placement tracking (RST) controller with model reference adaptive control (MRAC), in which adaptive gains of the RST controller are being fine-tuned by a fuzzy logic controller. Brushless direct current (BLDC) motors are installed in the triangular frame of the tri-rotor UAV, which helps maintain control on its motion and different altitude and attitude changes, similar to rotorcrafts. MRAC-based MIT rule is proposed for system stability. Moreover, the proposed hybrid controller with nonlinear flight dynamics is shown in the presence of translational and rotational velocity components. The performance of the proposed algorithm is demonstrated via MATLAB simulations, in which the proposed fuzzy hybrid controller is compared with the existing adaptive RST controller. It shows that our proposed algorithm has better transient performance with zero steady-state error, and fast convergence towards stability.

The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

The intermediate Helium subdwarf B star LS IV$-$14$^\circ$116 is a unique object showing extremely peculiar atmospheric abundances as well as long-period pulsations that cannot be explained in terms of the usual opacity mechanism. One hypothesis invoked was that a strong magnetic field may be responsible. We discredit this possibility on the basis of FORS2 spectro-polarimetry, which allows us to rule out a mean longitudinal magnetic field down to 300 G. Using the same data, we derive the atmospheric parameters for LS IV$-$14$^\circ$116 to be $T_{\rm eff}$ = 35,150$\pm$111 K, $\log{g}$ = 5.88$\pm$0.02 and $\log{N(\rm He)/N(\rm H)}$ = $-$0.62$\pm$0.01. The high surface gravity in particular is at odds with the theory that LS IV$-$14$^\circ$116 has not yet settled onto the Helium Main Sequence, and that the pulsations are excited by an $\epsilon$ mechanism acting on the Helium-burning shells present after the main Helium flash. Archival UVES spectroscopy reveals LS IV$-$14$^\circ$116 to have a radial velocity of 149.1$\pm$2.1 km/s. Running a full kinematic analysis, we find that it is on a retrograde orbit around the Galactic centre, with a Galactic radial velocity component $U$=13.23$\pm$8.28 km/s and a Galactic rotational velocity component $V$=$-$55.56$\pm$22.13 km/s. This implies that LS IV$-$14$^\circ$116 belongs to the halo population, an intriguing discovery.

Modeling Maxwell’s Demon

The interesting article “Engineering Maxwell’s demon” by Zhiyue Lu, Dibyendu Mandal, and Christopher Jarzynski in the August 2014 issue (page 60) includes a link to a video, created using the three-dimensional animation software Blender, of the device. I’ve used GlowScript to make an interactive version at http://www.glowscript.org/#/user/Bruce_Sherwood/folder/Pub/program/MaxwellDemon.The program lets the user zoom and rotate to inspect the device, and it plots the demon’s rotational velocity component as a function of time. The plot demonstrates the counterclockwise bias over long times that the authors describe. A user can observe the increased informational entropy in the paddle positions. A modern browser that supports the 3D graphics library WebGL and a graphics card with graphics processing units are required; click “Help” in the upper right corner for details on system requirements. Click “Edit this program” to see the code, which is short for a program of this complexity. I thank the article’s authors for helpful advice.© 2015 American Institute of Physics.

Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel

Friction-stir spot welding (FSSW) has been shown to be capable of joining advanced high-strength steel, with its flexibility in controlling the heat of welding and the resulting microstructure of the joint. This makes FSSW a potential alternative to resistance spot welding if tool life is sufficiently high, and if machine spindle loads are sufficiently low that the process can be implemented on an industrial robot. Robots for spot welding can typically sustain vertical loads of about 8 kN, but FSSW at tool speeds of less than 3000 rpm cause loads that are too high, in the range of 11–14 kN. Therefore, in the current work, tool speeds of 5000 rpm were employed to generate heat more quickly and to reduce welding loads to acceptable levels. Si3N4 tools were used for the welding experiments on 1.2-mm DP 980 steel. The FSSW process was modeled with a finite element approach using the Forge® software. An updated Lagrangian scheme with explicit time integration was employed to predict the flow of the sheet material, subjected to boundary conditions of a rotating tool and a fixed backing plate. Material flow was calculated from a velocity field that is two-dimensional, but heat generated by friction was computed by a novel approach, where the rotational velocity component imparted to the sheet by the tool surface was included in the thermal boundary conditions. An isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of strain, strain rate, and temperature. The model predicted welding temperatures to within 4%, and the position of the joint interface to within 10%, of the experimental results.

Measuring the translational and rotational velocities of particles in helical motion using structured light.

We measure the rotational and translational velocity components of particles moving in helical motion under a Laguerre-Gaussian mode illumination. The moving particle reflects light that acquires an additional frequency shift proportional to the velocity of rotation in the transverse plane, on top of the usual frequency shift due to the longitudinal motion. We determined both the translational and rotational velocities of the particles by switching between two modes: by illuminating with a Gaussian beam, we can isolate the longitudinal frequency shift; and by using a Laguerre-Gaussian mode, the frequency shift due to the rotation can be determined. Our technique can be used to characterize the motility of microorganisms with a full three-dimensional movement.

Bow Wave Effect in Aerial Refueling: Computational Analysis and Modeling

Mechanisms contributing to the “bow wave” effect of a receiver on a tanker are investigated, and a modeling method for dynamic simulation is developed. Vortex lattice and Cart3D codes are used to calculate the aerodynamic forces and moments for a C-141B behind a KC-135. The vortex lattice code significantly underpredicts the bow wave effect, whereas the Cart3D code shows good agreement with available flight data. The modeling method uses stream functions for inviscid flow around solid bodies. The flowfield induced by the presence of aircraft bodies is superimposed on the flowfield generated by horseshoe vortices. The resultant flowfield is approximated by the effective uniform translational and rotational velocity components, which are used in the buildup equations for the aerodynamic force and moment coefficients of both tanker and receiver aircraft. This method applied to a flying wing behind a KC135 shows good agreement with Cart3D results. It is concluded that the major contribution to the “bow wave” effect is the effect of the displacement of air due to the volume of the receiver and not upwash from the bound vortex due to the lift of the receiver. This disagrees with earlier studies that did not have the benefit of flight data to use as a benchmark.

Note: Rotaphone, a new self-calibrated six-degree-of-freedom seismic sensor

We have developed and tested (calibration, linearity, and cross-axis errors) a new six-degree-of-freedom mechanical seismic sensor for collocated measurements of three translational and three rotational ground motion velocity components. The device consists of standard geophones arranged in parallel pairs to detect spatial gradients. The instrument operates in a high-frequency range (above the natural frequency of the geophones, 4.5 Hz). Its theoretical sensitivity limit in this range is 10(-9) m/s in ground velocity and 10(-9) rad/s in rotation rate. Small size and weight, and easy installation and maintenance make the instrument useful for local-earthquake recording and seismic prospecting.

Numerical simulations of incompressible aerodynamic flows using viscous/inviscid interaction procedures

Steady two-dimensional laminar incompressible flows over airfoils are simulated using a Helmholtz velocity decomposition where the velocity vector is split into a gradient of a potential and a correction representing the rotational components. For most aerodynamic flows, the rotational components of the velocity vanish outside the boundary layer and the wake region. Therefore, the near and far velocity fields can be represented by a potential function and the pressure can be obtained there from Bernoulli’s law. In the viscous flow region, the momentum equations are integrated to calculate the rotational velocity components. Conservation of mass leads to a Poisson’s equation for the potential function, where the right hand side, the forcing function, is given in terms of the divergence of the rotational velocity component. The latter represents a distribution of sources in the viscous layer and results in a displacement effect on the outside potential field. In this formulation, the pressure in the momentum equations does not play an essential role since the conservation of mass is imposed through the augmented potential equation. After the velocity field is obtained, the correct pressure distribution in the viscous flow region is calculated by integrating the normal momentum equation. Numerical results are presented to confirm the validity and the merits of the present formulation. Solving a Poisson’s equation for the potential function, rather than the pressure as in standard methods for solving Navier–Stokes equations, is the main advantage since the calculations of the rotational velocity components are restricted to the viscous flow region only. Standard numerical methods are applicable to the present formulation including multigrid acceleration techniques for the augmented potential equation.

Unsteady MHD rotating flow over a rotating sphere near the equator

The unsteady rotating flow of a laminar incompressible viscous electrically conducting fluid over a rotating sphere in the vicinity of the equator has been studied. The fluid and the body rotate either in the same direction or in opposite directions. The effects of surface suction and magnetic field have been included in the analysis. There is an initial steady state that is perturbed by a sudden change in the rotational velocity of the sphere, and this causes unsteadiness in the flow field. The nonlinear coupled parabolic partial differential equations governing the boundary-layer flow have been solved numerically by using an implicit finite-difference scheme. For large suction or magnetic field, analytical solutions have also been obtained. The magnitude of the radial, meridional and rotational velocity components is found to be higher when the fluid and the body rotate in opposite directions than when they rotate in the same direction. The surface shear stresses in the meridional and rotational directions change sign when the ratio of the angular velocities of the sphere and the fluid λ≥λ0. The final (new) steady state is reached rather quickly which implies that the spin-up time is small. The magnetic field and surface suction reduce the meridional shear stress, but increase the surface shear stress in the rotational direction.

Kinetic Sunyaev‐Zeldovich Effect from Halo Rotation

We discuss the kinetic Sunyaev-Zeldovich (SZ) contribution to cosmic microwave background (CMB) temperature fluctuations due to the coherent rotational velocity component of electrons within halos. This effect produces a distinct dipole-like temperature distribution across the cluster and provides a promising way to measure the angular momentum distribution of gas inside clusters. Information obtained from such a measurement may provide new insights to the origin and evolution of angular momentum in hierarchical structure formation theory. For typical well-relaxed clusters of mass a few times 1014 M☉, the peak fluctuation is of the order of a few μK, depending on the rotational velocity and the inclination angle of the rotational axis. For clusters that had undergone a recent merger, the contribution to temperature fluctuations could be even larger. This dipole signature is similar to the one produced by lensed CMB toward galaxy clusters, although the lensing contribution spans a larger angular extent than the one due to rotational scattering, since the former depends on the gradient of the cluster potential. Since the lensing contributions toward clusters are aligned with the large-scale CMB gradient, when higher resolution observations toward clusters are combined with a wide-field CMB map, these two effects can be separated. An additional, but less important, source of confusion is the dipolar pattern produced by the moving-lens effect involving, again, the gradient of the cluster potential and the transverse velocity. The angular power spectrum of temperature anisotropies produced by the halo rotation is expected to be smaller than those due to the thermal SZ and peculiar-velocity kinetic SZ effects.