Transverse Motion Research Articles

Galloping Stability and Aerodynamic Characteristic of Iced Transmission Line Based on 3-DOF

A new calculation method of critical wind speed based on three degrees of freedom (3-DOF) is proposed for galloping problem of iced transmission line. Based on the quasistatic theory, the aerodynamic load of iced transmission line is obtained, which considers the influence of transverse and torsional motion on the relative wind angle of attack. Finally, the equivalent galloping model of 3-DOF iced transmission line is established. At the initial angle of attack, the aerodynamic load is expanded by Taylor, and the unsymmetrical linear aerodynamic coefficient matrix is obtained. The Routh–Hurwitz criterion is used to judge the stability of iced transmission line system, and then the critical wind speed is calculated. The in-plane and out-plane frequencies corresponding to the first-order mode of the transmission line are solved by the analytical method and numerical simulation method. The results obtained by the two methods are compared and verified. The influence of dimensionless transmission line parameterλon the in-plane and out-of-plane frequencies is discussed. The aerodynamic coefficients of the iced transmission line are measured by wind tunnel test and the aerodynamic characteristics are analyzed. According to the theoretical formula, the critical wind speed is calculated by MATLAB. The critical wind speed determined in this paper is compared with the critical wind speed determined by Den Hartog and Nigol theory. The influences of torsional vibration frequency, ice thickness, and ice shape on critical wind speed are analyzed. The research results of this paper have important theoretical significance for the stability judgment of iced transmission lines.

Vibration characteristics of multiple functionally graded nonuniform beams

Based on the Euler–Bernoulli beam theory, the natural vibration behavior of functionally graded nonuniform multiple beams has been investigated. It is assumed that the beams are joined by elastic translational springs, and the properties of the beams vary along the axial direction. The Chebyshev spectral collocation method has been used to convert the governing differential equations of transverse motion into a system of algebraic equations that are put in the matrix–vector form. Then, the dimensionless transverse frequencies are obtained by solving the eigenvalue problem. The influence of several factors, such as the stiffness parameters of the coupling translational springs, the properties of the cross section of the beams, and the boundary conditions on the frequencies, has been carried out. The results generated from the Chebyshev spectral collocation method have been verified by comparing them with those reported in other studies and references from the literature. Several numerical examples have been presented and discussed to analyze the system under consideration. The authors hope that the findings of the current study are helpful in designing and characterizing multiple nonuniform thin engineering structures.

Applicability analysis of high-speed railway system under the action of near-fault ground motion

Studying the applicability of existing bridge and track systems of high-speed railway in near-fault areas is crucial and urgent, because the current seismic design methods seldom consider the characteristics of the near-fault ground motion. By comprehensively considering the uncertainties in ground motion and structural parameters, a large-sample analysis method for near-faults area was proposed. In addition, an integrated finite element model for beam bridge-track system of high-speed railway was used to calculate the seismic response of the structure under the action of near-fault ground motion. The over-limit state and applicability of seismic response of key components and systems were predicted and evaluated. The analysis results indicate that the statistical characteristics of structural seismic response and over-limit state tend to be stable with increasing number of samples. Under the near-fault ground motion: (i) the piers of high-speed railway are hard to yield (ii) bearings are damaged severely, and (iii) the piers have insufficient shear capacity and the characteristics of structural seismic damage are not in accordance with the concept of ductility design. The sliding layer of the track structure is severely damaged by the transverse and longitudinal ground motions, while the CA mortar layer and fastener are mainly damaged by the transverse ground motion. The applicability of bearings, the anti-shearing behavior of piers, and the inter-layer structure of tracks make it difficult to achieve the goal of the near-fault fortification against ground motion.

Friction-Drag Reduction by Transverse Wall Motion – A Review

ABSTRACTThe quest for drag reduction is driven by environmental concerns, in general, and the need to reduce fuel consumption in transport applications, in particular. Turbulent friction is especially important in civil aviation, accounting for over 50% of the total drag in cruise. In this context, spatially and/or temporally varying in-plane wall motion, while undoubtedly difficult to implement in practice, has attracted major interest, because of the large drag-reduction margins it yields. It is also a forcing method that is of fundamental interest, as it provokes intriguing interactions between the spanwise Stokes layer induced by the wall motion and the near-wall turbulence-regeneration mechanisms. This article provides a relatively brief, ‘entry-level’, review of research in this area, principally over the past two decades. While far from being exhaustive, the review conveys a reasonably detailed picture of some major physical issues as well as of the outcome of the most important computational and experimental studies. Particular emphasis is placed on the question of how results obtained in idealised laboratory conditions and by simulation at relatively low Reynolds-number values pertain to high values typical of high-speed transport.

Experimental study on near-bed flow turbulence of sinuous channel with downward seepage

The presence of a small seepage velocity in streams and rivers induces transfer of mass and momentum near the sediment boundary, causing bank failure and instability of hydraulic structures. This experimental study is intended to report near-bed hydrodynamics and morphological characteristics under the impact of downward seepage. A laboratory investigation was conducted in a sinuous rectangular alluvial channel with rigid sides and movable uniform sand bed. From the distribution of Reynolds shear stress (RSS), the transverse or radial motion of the sediment across the bend was identified. High values of RSS in the outer region relate to higher momentum flux, eroding the outer bend. The contribution probability of ejection and sweep events are highest in the bend region. For seepage, the contribution probability of the events has increased. Moreover, the altered flow with seepage affected the transport of sediment and caused noticeable modifications along the channel bed. With seepage, the erosion rate has been enhanced along the outer bend of the channel.

Aerodynamic analysis of a supersonic expander

In this paper, a numerical investigation was conducted into the impact of the tip clearance height and the relative motion between the casing and the strake wall tip on the tip clearance leakage flow of a supersonic expander. Besides, an analysis was carried out to characterize the flow under varying operating conditions. Numerical results show that the remarkable characteristics of motion within the tip gap region are the leakage fluid around the trailing edge passing through the tip gap and then returning to the pressure side. As the tip clearance height increases, the intensity and scale of the tip leakage vortex show an upward trend. Also, the mix with the surrounding airflow contributes to a significant increase in the leakage losses and a reduction of the losses in the rampart and the mainstream region. It can be found that an excellent aerodynamic performance will be achieved when the tip clearance height ranges between 0.9% h0 and 1.5% h0. The relative motion of the casing not only reduces the transverse motion of the leakage vortex but also increases the tip leakage mass flow and the intensity of the tip leakage vortex, thus causing a significant rise in the flow losses. A lower [Formula: see text] will result in a severe deterioration in the performance of the supersonic expander. Furthermore, when the [Formula: see text] reaches a certain threshold (or above 12 times the atmospheric pressure to be precise), the main performance parameters of the supersonic expander will show no change with the increase of [Formula: see text]. Nevertheless, the continued improvement of [Formula: see text] means that the requirement becomes more demanding on engine performance.

Application of systematic scanning and variance analysis method to evaluation of pores arrangement in sintered steel

The porosity characteristics of sintered specimens, made of the Distaloy AB powder, subjected to various deformation modes have been examined within the work. The sintering technological parameters were adjusted to obtain 15% volume fraction of pores. The sintered specimens were plastically deformed by conventional uniaxial compression, compression with the cyclic torsion (3°, 0.5 Hz and 6°, 1 Hz), compression with the cyclic transverse motion of the punch and finally compression with the cyclic torsion and superimposed cyclic transverse motion of the punch. The systematic scanning and two-way ANOVA analysis were carried out to describe the spatial arrangement of the porosity in the microstructure before and after deformation. The mean values of pores area fractions were also analysed. Based on the investigation, it was identified that all specimens after plastic deformation are characterized by significantly smaller porosity fraction in comparison with the initial state (as-sintered). The lowest mean area fraction of the pores equal to 4.18% was obtained in the specimen after compression with the cyclic torsion (3°, 0.5 Hz) and with the cyclic transverse motion of the punch. However, in this case, the arrangement of pores in the sample was inhomogeneous. On the contrary, the compression with only cyclic torsion led to the homogenous arrangement of pores. A similar situation was in the case study of compression with only cyclic transverse motion of the punch. However, it was pointed out that the most advantageous, from porosity level reduction and arrangement homogeneity point of view, is the plastic deformation by compression with the cyclic transverse motion of the punch, and without cyclic torsion.

Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project

Abstract We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]–[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1″ yr−1; our fastest-moving discovery is WISEA J155349.96+693355.2 (μ ≈ 2.″15 yr−1), a possible T-type subdwarf. We also report a newly discovered wide-separation (∼400 au) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5.′5 projected separation (∼8700 au if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf.

A Catalog of 531 White Dwarf Candidates in the Local Galactic Halo from Gaia Data Release 2

Abstract We present a catalog of 531 white dwarf candidates that have large apparent transverse motions relative to the Sun ( km s−1), thus making them likely members of the local Galactic halo population. The candidates were selected from the Gaia Data Release 2 and are located in a great circle with 20° width running across both Galactic poles and the Galactic center and anticenter, a zone that spans 17.3% of the sky. The selection used a combination of kinematic and photometric properties, derived primarily from Gaia proper motions, G magnitudes, and color, and including parallax whenever available. Additional validation of the white dwarf candidates is made using PanSTARRS photometric (gri) data. Our final catalog includes not only stars having full kinematic and luminosity estimates from reliable Gaia parallax, but also stars with presently unreliable or no available Gaia parallax measurements. We argue that our method of selecting local halo objects with and without reliable parallax data leads us to round up all possible halo white dwarfs in the Gaia catalog (in that particular section of the sky) with recorded proper motions mas yr−1 and that pass our km s−1 threshold requirement. We expect this catalog will be useful for the study of the white dwarf population of the local Galactic halo.

Enhanced smoothing by spectral dispersion via insertion of complex coaxial vortex plate

An enhanced smoothing by spectral dispersion (SSD) scheme via the insertion of a complex coaxial vortex plate in the beamline is proposed. The complex coaxial vortex plate is comprised of an inner vortex plate that induces an azimuthal charge on the beam, and a surrounding vortex plate that induces an opposite charge on the beam. The surrounding vortex plate is supported by a base of same material that generates a time delay between the inner and the outer sub-beams. The time delay then brings about the frequency shift of the sub-beams with frequency modulation and spectral dispersion. As a result of the coherent superposition of the sub-beams, the focal spot exhibits a dominant envelope with transverse motion, and the inside speckles rotate rapidly in the picosecond regime. The simulation shows that the irradiation uniformity is slightly improved via the insertion of the complex coaxial vortex plate. More importantly, the laser-plasma interaction length is significantly shortened and then the reflectivity of stimulated Brillouin scattering is reduced by the use of the enhanced SSD scheme.

Temperature analysis in flighted rotary drums and the influence of operating parameters

Flights in rotary drums are used to improve the mixing and the heat transfer. They lift particles out of the solid bed to shower them as curtains through the gas phase of the drum. The number of particles and their distribution are influenced by several operational parameters. An indirectly heated flighted rotary drum was designed and constructed to conduct experiments relating transverse particle motion to heat transfer. Batch experiments divided into heating and cooling periods were performed with glass beads as reference material. The axial, circumferential and radial temperature distributions were measured. It was found that increasing the rotational speed as well as the volumetric airflow rate leads to quick temperature changes, while an increase in the filling degree results in a gradual decrease of the temperature drop during cooling.

Direct laser acceleration of electrons assisted by strong laser-driven azimuthal plasma magnetic fields.

A high-intensity laser beam propagating through a dense plasma drives a strong current that robustly sustains a strong quasistatic azimuthal magnetic field. The laser field efficiently accelerates electrons in such a field that confines the transverse motion and deflects the electrons in the forward direction. Its advantage is a threshold rather than resonant behavior, accelerating electrons to high energies for sufficiently strong laser-driven currents. We study the electron dynamics via a test-electron model, specifically deriving the corresponding critical current density. We confirm the model's predictions by numerical simulations, indicating energy gains two orders of magnitude higher than achievable without the magnetic field.

Three-dimensional thoracic and pelvic kinematics and arm swing maximum velocity in older adults using inertial sensor system.

Understanding characteristics of torso motion and arm swing of older adults is important. A comprehensive database of three-dimensional thoracic and pelvic kinematics and arm swing maximum velocity of older adults during overground walking is still lacking. Moreover, the relationships between these variables are not fully understood. Therefore, we investigated age and gender effects of three-dimensional thoracic and pelvic ranges of motion and arm swing maximum velocity in 113 healthy old adults (aged 60–89 years) in a 2-min walk test using APDM Movement Monitoring inertial sensor system by two-way ANOVA, and post hoc Bonferroni correction was applied for multiple comparisons between age groups. A paired t-test was used to study the side preference of arm swing maximum velocity. The relationships between variables were investigated via multiple linear regression models. In general, thoracic and pelvic motions showed reduced amplitude with aging. Gait speed, pelvis coronal plane motion and arm swing maximum velocity significantly declined with age. Only the pelvic sagittal plane motion showed a gender main effect. Coronal plane motions of the thorax and pelvis were closely associated, as were sagittal plane motions. Thoracic coronal plane motion was the significant variable influencing pelvic transverse plane motion and vice versa. Gait speed, pelvic coronal and transverse plane motions and thorax sagittal plane motion were significant independent variables that influenced dominant arm maximum velocity. A larger maximum velocity was seen in the left arm. This investigation is valuable for better understanding of gait phenomena and will contribute to identification of gait dysfunction and development of rehabilitation measures.

The influence of kinematics of blades on the flow structure in deep dynamic stall

This study considers the effect of kinematics on the aerodynamic loads and flow structure around moving blades of micro air vehicles (MAVs) in deep dynamic stall. The transversal (pure heaving) and rotational (pure pitching) motions are considered distinctly to investigate the dynamic stall. An equivalent effective angle of the attack profile is given to both motions. This method helps to figure out the influence of kinematics on flow structures when all boundary conditions and effective angles of attack profiles are the same. An experiment is conducted in fully turbulent flow at Re = 1.5×104 to avoid any transition regime in the boundary layer, and make the results relatively independent of the flow characteristics. A NACA 0012 airfoil is chosen at high reduced frequencies (k = 0.25 and 0.375) and high angles of attack to reach deep dynamic stall conditions. Additionally, time-resolved particle image velocimetry (PIV) and post-processing are used to compute the aerodynamic loads using a control-volume approach. The flow field is also reconstructed using proper orthogonal decomposition (POD) to separate the flow structures in different modes. It is shown that the kinematics can significantly influence the flow structure and aerodynamic loads. In the pre-stall region, the pure pitching motion usually produces higher lift force, while the pure heaving motion has a higher lift peak. However, in the post-stall region, the pure heaving motion usually has higher lift than the pure pitching motion. The pure heaving motion produced lower drag force than the pure pitching motion. For pure heaving motion, the POD analysis reveals there is a high-energy mode in the flow structure that helps to make the vortices more stable compared to pure pitching motion. Furthermore, the pure heaving motion adds extra kinetic energy to the boundary layer, which decelerates the reversal flow and the transfer of the separation point on suction side of the airfoil.

Analytic responses of slender beams supported by rotationally restrained hinges during support motions

This paper presents an analytic solution procedure of the rotationally restrained hinged-hinged beam subjected to transverse motions at supports based on EBT (Euler-Bernoulli beam theory). The EBT solutions are compared with the solutions based on TBT (Timoshenko beam theory) for a wide range of the rotational restraint parameter (kL/EI) of slender beams whose slenderness ratio is greater than 100. The comparison shows the followings. The internal loads such as bending moment and shearing force of an extremely thin beam obtained by EBT show a good agreement with those obtained by TBT. But the discrepancy between two solutions of internal loads tends to increase as the slenderness ratio decreases. A careful examination shows that the discrepancy of the internal loads originates from their dynamic components whereas their static components show a little difference between EBT and TBT. This result suggests that TBT should be employed even for slender beams to consider the rotational effect and the shear deformation effect on dynamic components of the internal loads. The influence of the parameter on boundary conditions is examined by manipulating the spring stiffness from zero to a sufficiently large value.

Transverse drag of slow light in moving atomic vapor.

The Fresnel-Fizeau effect of transverse drag, in which the trajectory of a light beam changes due to the transverse motion of the optical medium, is usually extremely small and hard to detect. We observe transverse drag in a moving hot-vapor cell, utilizing slow light due to electromagnetically induced transparency (EIT). The drag effect is enhanced by a factor 3.6×105, corresponding to the ratio between the light speed in vacuum and the group velocity under EIT conditions. We study the contribution of the thermal atomic motion, which is much faster than the mean medium velocity, and identify the regime where its effect on the transverse drag is negligible.

Inferring Plasma Flows at Granular and Supergranular Scales With a New Architecture for the DeepVel Neural Network

The wealth of observational data available has been instrumental in investigating physical features relevant to solar granulation, supergranulation and Active Regions. Meanwhile, numerical models have attempted to bridge the gap between the physics of the solar interior and such observations. However, there are relevant physical quantities that can be modelled but that cannot be directly measured and must be inferred. For example, direct measurements of plasma motions at the photosphere are limited to the line-of-sight component. Methods have consequently been developed to infer the transverse plasma motions from continuum images in the case of the Quiet Sun and magnetograms in the case of Active Regions. Correlation-based tracking methods calculate the optical flows by correlating series of images locally while other methods like “Coherent Structure Tracking” or "Balltracking” exploit the coherency of photospheric granules to track them and use the group motions of the granules as a proxy of the average plasma flows advecting them. Recently, neural network computing has been used in conjunction with numerical models of the Sun to be able to recover the full velocity vector in photospheric plasma from continuum images. We experiment with a new architecture for the DeepVel neural network which takes inspiration from the U-Net architecture. Simulation data of the Quiet Sun and Active Regions are then used to evaluate the response at granular and supergranular scales of the aforementioned method.

ESTIMATION OF BBU THRESHOLD CURRENT IN AN INHOMOGENEOUS ACCELERATING SECTION

In this work we describe the procedure of estimation of regenerative beam blowup threshold current in an inhomogeneous accelerating section. The self-consistent problem of transverse motion of particles in the field of dipole mode excited by the beam is solved. The distribution of dipole field near the structure axis and the energy variation of beam particles were calculated before simulating the transverse dynamics. The threshold current for S-band industrial linac designed for radiation sterilization of medical products is estimated.

Long-time dynamics of a nonlinear Timoshenko beam with discrete delay term and nonlinear damping

The purpose of this manuscript is to establish well posedness as well as the existence of global and exponential attractor for a nonlinear Timoshenko system subject to control terms in the two equations of the system. Since the control terms act on both equations, we will not use the nonphysical relationship known as equal speeds of propagation of waves. A combination involving friction-delay and friction controls will act on the angle of rotation equation, while a nonlinear friction control will act on the transverse motion equation. The result will be established by showing that the system is quasi-stable and by using a relationship involving the size of the friction type controls inserted in the rotation angle equation.

Continuous Gesture Recognition Based on Time Sequence Fusion Using MIMO Radar Sensor and Deep Learning

Gesture recognition that is based on high-resolution radar has progressively developed in human-computer interaction field. In a radar recognition-based system, it is challenging to recognize various gesture types because of the lacking of gesture transversal feature. In this paper, we propose an integrated gesture recognition system that is based on frequency modulated continuous wave MIMO radar combined with deep learning network for gesture recognition. First, a pre-processing algorithm, which consists of the windowed fast Fourier transform and the intermediate-frequency signal band-pass-filter (IF-BPF), is applied to obtain improved Range Doppler Map. A range FFT based MUSIC (RFBM) two-dimensional (2D) joint super-resolution estimation algorithm is proposed to obtain a Range Azimuth Map to obtain gesture transversal feature. Range Doppler Map and Range Azimuth Map then respectively form a Range Doppler Map Time Sequence (RDMTS) and a Range Azimuth Map Time Sequence (RAMTS) in gesture recording duration. Finally, a Dual stream three-dimensional (3D) Convolution Neural Network combined with Long Short Term Memory (DS-3DCNN-LSTM) network is designed to extract and fuse features from both RDMTS and RAMTS, and then classify gestures with radial and transversal change. The experimental results show that the proposed system could distinguish 10 types of gestures containing transversal and radial motions with an average accuracy of 97.66%.