Average Vertical Velocity Research Articles

Biofouling changes the settling dynamics of macroplastic plates

Plastic pollution transported in rivers remains poorly understood due to the diversity of shapes, sizes, and densities of plastics, as well as their complex interactions with biofilms. While previous studies have explored the settling velocities of plastics and their interactions with biofilms, they often overlook how biofouling alters plastic dynamics and settling behaviour. To address this, over 800 settling experiments were conducted to demonstrate that the dynamics and falling velocities of isotropic (spheres) and anisotropic (square and rectangle plates) macroplastics of different densities (1050 to 2200 kg/m3) are significantly impacted by biofouling. Three-dimensional tracking of plastic trajectories revealed that biofilm colonisation on the surface of anisotropic plastic plates triggered them to exhibit more chaotic trajectories, larger horizontal dispersion and higher oscillatory frequencies. These dynamics reduced the average vertical settling velocity of anisotropic biofouled plates by up to 12%—despite greater plastic densities and considering the multimodal distribution of a plate’s fall velocity—compared to their pristine counterparts. Results highlight the necessity of accounting for the intricate multimodal settling dynamics of plastics, including their interactions with biofilms, to provide more reliable predictions of plastic transport and fate in aquatic environments.

Numerical simulation and experimental study of microplastic transport under open channel shear flow: Roles of particle physical properties and flow velocities

Microplastic (MP) transport patterns under open channel shear flow remain unclear. This study investigates the transport laws of MPs at various flow velocities, MP densities, sizes and concentrations in the U-shaped experimental flume and the numerical flume based on Lattice Boltzmann Method (LBM). The results indicate that the average horizontal particle velocity and the transport distances of Polyvinyl chloride (PVC) and Polystyrene (PS) particles increase with the average cross-sectional flow velocity, while the average vertical particle velocity decreases with it. The total average particle velocity closely matches the average vertical particle velocity, regardless of the variation in MP size, density and concentration. Formula-based analysis reveals that the acceleration of spherical MP transport mainly depends on the particle size and its consequent relative drag force term (RDFT) under the conditions with a single type of MP particles, but on the particle density and its consequent RDFT and relative gravity term (RGT) in the case concerning different types of MP particles with identical particle sizes. The average horizontal particle velocity maximum of PVC and PS are both strongly correlated with the average flow velocity maximum in the cross-section. This correlation lowers with the MP particle size and concentration, and is independent of MP density. Our findings can provide reference for the prevention and control of MP pollution in rivers.

The tangled warp of the Milky Way

Aims.We aim to determine the influence of the Milky Way’s warp on the kinematics of stars across the disc, and therefore measure its precession rate and line of nodes under different assumptions.Methods.We applied Jeans’ first equation to a model of a rigidly precessing warp. The predictions of these models were fitted to the average vertical velocities of stars with measured line-of-sight velocities inGaiaDR3 data. We tested models in which the warp’s line of nodes and precession speed are fixed, and models in which they are allowed to vary linearly with radius. We also tested models in which the velocity of stars radially in the disc is included in Jeans’ equation.Results.The kinematic data are best fit by models with a line of nodes that is 40° offset from the Sun’s Galactic azimuth, significantly leading the line of nodes found from the positions of stars. These models have a warp precession speed of around 13 km s−1kpc−1in the direction of Galactic rotation, close to other recent estimates. We find that including the velocity of stars radially in the disc in our kinematic model leads to a significantly worse fit to the data, and implausible warp parameters.Conclusions.The Milky Way’s warp appears to be rapidly precessing, but the structure and kinematics of the warped disc are not consistent within the approximation of a fixed, precessing, warp shape. This implies that the Milky Way’s warp is dynamically evolving, which is a challenge to models of the warp’s creation, and must be considered in the context of other known disturbances of the disc.

Step type is associated with loading and ankle motion in tap dance.

Tap dance generates forces and joint motions that can lead to injury; however, little is known about the magnitude of load across different tap steps. The purpose of this study was to calculate peak vertical forces, average vertical foot velocities, and maximum/minimum ankle angles produced by tap dancers with different levels of experience performing the toe cannon, heel cannon, flap, and cramp roll. This prospective cross-sectional study included 14 female tap dancers aged ≥18 years with varying tap experience. Participants were recorded by three cameras while performing a choreographed tap combination containing four steps of interest on a force platform. Adjusting for experience and dancer-level clustering, we identified the steps-cramp roll and toe cannon-that had the highest peak vertical ground reaction force, angles, and velocities compared to flap and heel cannon. There was no effect of experience. The results supported our hypothesis and provide new insights into step production. Over time, the larger forces associated with these steps could pose an increased risk of injury to bones and joints when compared to smaller forces, which may suggest the importance of adjusting routines to reduce or avoid injury.

Quantification of surface layer turbulence using sensible heat values from energy balance versus aerodynamic methods

Surface layer optical turbulence values in the form of the refractive index structure function C n 2 are often calculated from surface layer temperature, moisture, and wind characteristics and compared to measurements from sonic anemometers, differential temperature sensors, and imaging systems. A key derived component needed in the surface layer turbulence calculations is the sensible heat value. Typically, the sensible heat is calculated using the bulk aerodynamic method that assumes a certain surface roughness and a friction velocity that approximates the turbulence drag on temperature and moisture mixing from the change in the average surface layer vertical wind velocity. These assumptions/approximations generally only apply in free convection conditions. To obtain the sensible heat, a more robust method, which applies when free convection conditions are not occurring, is via an energy balance method such as the Bowen ratio method. The use of the Bowen ratio––the ratio of sensible heat flux to latent heat flux––allows a more direct assessment of the optical turbulence-driving surface layer sensible heat flux than do more traditional assessments of surface layer sensible heat flux. This study compares surface layer C n 2 values using sensible heat values from the bulk aerodynamic and energy balance methods to quantifications from sonic anemometers posted at different heights on a sensor tower. The research shows that the sensible heat obtained via the Bowen ratio method provides a simpler, more reliable, and more accurate way to calculate surface layer C n 2 values than what is required to make such calculations from bulk aerodynamic method-obtained sensible heat.

Experiments investigation on atomization characteristics of a liquid jet in a supersonic combustor

The atomization characteristics of a liquid jet in a supersonic combustor were studied experimentally for the first time. A phase doppler anemometry (PDA) system was utilized for the measurement of droplets properties along the cross-sectional area of spray plumes inside the cavity. The results were obtained under the inflow conditions of Ma = 2.0 supersonic crossflow with a stagnation pressure of 0.55 MPa and a stagnation temperature of 300 K. The size and velocity distribution of droplet inside the cavity are obtained based on the PDA measurements. It was found that the Sauter Mean Diameter (SMD) distribution of droplets inside the cavity ranged from 30 to 55 μm. The average streamwise velocity ranged from −20 to 150 m/s and the average vertical velocity ranged from −20 to 30 m/s. Large droplets distribute in the central area of the cavity. Small droplets spread around the central area of the bottom and sidewall areas of the cavity. The area near the sidewall may be an ideal ignition location due to the lower SMD and velocity of droplets. The time-averaged motion trend of droplets in the cavity is proposed experimentally based on the streamwise and spanwise velocity distribution profiles of droplets. The presence of a recirculation zone within the cavity is confirmed. The recirculation area inside the cavity is mainly distributed in the front half of the cavity. The droplets in the cavity show a good tracking performance. With the effect of the airflow, the droplets in the top area of the cavity move toward the bottom and rear wall of the cavity. In addition, the droplets in the middle and bottom area of the cavity move toward the front wall of the cavity especially for droplets near the sidewall. These universal curves can potentially be used for the modeling of a liquid jet in a supersonic combustor.

Deep propagation of wind-generated near-inertial waves in the Northern South China Sea

Using a subsurface mooring deployed at a depth of ∼2290 m in the northern South China Sea, the characteristics of deep-propagating near-inertial waves (NIWs) (>1500 m) generated by a combination of a winter storm and a typhoon were examined. The NIWs had a large vertical wavelength and showed a high coherence in near-full water depth. Correspondingly, the strong vertical shear and energy of the NIWs were concentrated at vertical scales larger than ∼500 m. The average vertical group velocity was ∼160 m/day. The horizontal wavelength decreased from ∼600 km in the upper layer to a few tens of kilometers below a depth of 1500 m. Interestingly, the near-inertial energy did not decrease obviously at depths of 100–1500 m, where the average downward near-inertial energy flux (Fz) was (2.3 ± 0.9) × 10−3 W/m2 and nearly equaled that at 100 m depth. Combined with the slab model, the mean Fz at a depth of 100–1500 m can reach 19%–43% of that in the mixed layer. During the deep propagation of NIWs, the near-inertial shear was not strong in the upper layer. However, in the deep layer, the total shear was dominated by deep-propagating NIWs and was significantly enhanced. Correspondingly, the estimated diapycnal diffusivity increased, reaching a maximum value of ∼270% of the averaged value. This study contributes to our understanding of the deep propagation of wind-generated NIWs in the open ocean.

Dependency of vertical velocity variance on meteorological conditions in the convective boundary layer

Abstract. Measurements of vertical velocity from vertically pointing Doppler lidars are used to derive the profiles of normalized vertical velocity variance. Observations were taken during the FESSTVaL (Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg) campaign during the warm seasons of 2020 and 2021. Normalized by the square of the convective velocity scale, the average vertical velocity variance profile follows the universal profile of Lenschow et al. (1980). However, daily profiles still show a high day-to-day variability. We found that moisture transport and the content of moisture in the boundary layer could explain the remaining variability of the normalized vertical velocity variance. The magnitude of the normalized vertical velocity variance is highest on clear-sky days and decreases as the absolute humidity increases and surface latent heat flux decreases on cloud-topped days. This suggests that moisture content and moisture transport are limiting factors for the intensity of turbulence in the convective boundary layer. We also found that the intensity of turbulence decreases with an increase in the boundary layer cloud fraction during FESSTVaL, while the latent heating in the cloud layer was not a relevant source of turbulence in this case. We conclude that a new vertical velocity scale has to be defined that would take into account the moist processes in the convective boundary layer.

Enhancement of thrust force of an atmospheric pressure positive corona discharge by DC superimposed AC high voltage

The ability of corona discharge as an electrohydrodynamic propulsion system has been considered by many physicists and aerospace researchers. The results show that the most important factor in increasing the thrust force and thrust effectiveness is increasing the momentum transmission frequency in other words reduction of ion mobility that leads to a reduction of the average velocity. By configuring the wire-cylinder in atmospheric conditions, in an experimental study, using a new strategy in generating corona discharge, and without changing the system configuration, the thrust force is increased by increased of exciting species and reducing the ion mobility. DC superimposed AC (AC-DC) voltage source was utilized to achieve higher thrust force efficiency. Results show that the thrust force generated by the AC-DC source is increased by 4–2 times, with the applied voltage range of 10–20 kV compared to the DC source, respectively; while the thrust effectiveness has also been increased. A theory is introduced to calculate the thrust force due to ionic wind generation in the corona discharge regime. Accordingly, a relation is obtained for calculating thrust force and ion mobility using the average vertical ionic wind velocity on the side of the grounded electrode to support experimental results.

Assessment of the steady glide phase in ski jumping

The purpose of this investigation was to compare how key variables of the steady glide phase relate to performance in the two hill sizes used in World Cup and Olympic competitions, i.e, normal and large hills. In this study, 38 and 33 jumps of elite ski jumpers were measured with a differential global navigation satellite system (dGNSS) on a normal (HS106) and large hill (HS140), respectively. For the steady glide phase, the average aerodynamic forces, lift-to-drag-ratio (LD-ratio), vertical and horizontal acceleration and velocity were measured and related to the jump distance as a performance outcome. The aerial time difference between the two hill sizes was 1.1s, explained by the time spent in the steady glide phase. The results for HS106 were in line with the assumptions in recent literature, which propose that the performance is largely determined by the take-off and glide preparation. Hence for normal hills, skiers should aim to reduce vertical acceleration through high aerodynamic forces during the glide phase. Also, no correlation was observed between the LD-ratio and jump length. The data from the large hill indicate that the performance during the steady glide is very important for performance; hence clear differences were found compared to the normal hill. On a large hill, the aim should be to minimize the horizontal deceleration by reducing the aerodynamic drag. A high LD-ratio was correlated to jump length for HS140 and seen to be one of the most important performance factors.

Energetics and Mechanics of Steep Treadmill Versus Overground Pole Walking: A Pilot Study.

To compare energetics and spatiotemporal parameters of steep uphill pole walking on a treadmill and overground. First, the authors evaluated 6 male trail runners during an incremental graded test on a treadmill. Then, they performed a maximal overground test with poles and an overground test at 80% (OG80) of vertical velocity of maximal overground test with poles on an uphill mountain path (length = 1.3km, elevation gain = 433m). Finally, they covered the same elevation gain using poles on a customized treadmill at the average vertical velocity of the OG80. During all the tests, the authors measured oxygen uptake, carbon dioxide production, heart rate, blood lactate concentration, and rate of perceived exertion. Treadmills required lower metabolic power (15.3 [1.9] vs 16.6 [2.0]W/kg, P = .002) and vertical cost of transport (49.6 [2.7] vs 53.7 [2.1]J/kg·m, P < .001) compared with OG80. Also, oxygen uptake was lower on a treadmill (41.7 [5.0] vs 46.2 [5.0]mL/kg·min, P = .001). Conversely, respiratory quotient was higher on TR80 compared with OG80 (0.98 [0.02] vs 0.89 [0.04], P = .032). In addition, rate of perceived exertion was higher on a treadmill and increased with elevation (P < .001). The authors did not detect any differences in other physiological measurements or in spatiotemporal parameters. Researchers, coaches, and athletes should be aware that steep treadmill pole walking requires lower energy consumption but same heart rate and rate of perceived exertion than overground pole walking at the same average intensity.

The Regional Hadley Cells Response to the Sea Surface Temperature Distribution Across the Indo-Pacific Ocean

Hadley Cells are thermally driven cell in the tropics. On its occurrence, these cells are strongly influenced by the sea surface temperature (SST) distribution across the tropical ocean or the Pacific Ocean as the investigated location in this study. The SST shifting in the Pacific Ocean is mainly due to the ENSO. An opposite SST polarity between the western and eastern Pacific Ocean are captured during ENSO events. This means that ENSO could trigger an anomalous regional Hadley Cells that behave oppositely between Indonesia or the western Pacific and the eastern Pacific. This study examines the strength of the regional Hadley Cells related to the ENSO event across the Indonesian region and the Pacific Ocean. A significant correlation between the Hadley Cells and ENSO as the tropical climate variability in the Pacific Oceans are found. The strength of the Hadley Cells associated with ENSO event is examined by using the zonally average vertical velocity across the Pacific Ocean. During La Nina, the regional Hadley Cells over Indonesia or the western Pacific strengthened, whereas the regional cells over the eastern Pacific weakened. In contrast, during El Nino where the warm pool shifted to the eastern Pacific, the regional cell in the eastern Pacific strengthened, while the cell over the western Pacific weakened. These anomalous conditions clearly show that the meridional temperature gradient is strongly affecting the regional Hadley Cells strength. The stronger the meridional temperature gradient, the stronger the regional Hadley Cells.

Research on average vertical velocity of rubber particles in vertical screw conveyor based on bp neural network

Research on average vertical velocity of rubber particles in vertical screw conveyor based on bp neural network

Influence of Cross-Wind on CO2 Arc Welding of Carbon Steel

The purpose of this study is to develop a novel welding torch with high wind resistance, which can be used for welding outside a building under strong cross-wind. In this paper, a parametric study was carried out using different torch nozzle designs and shield gas flow rates for their optimization. The gas flow around the torch nozzle exit was visualized through the shadowgraph method to evaluate the interaction between the shielding gas flow and the cross-wind. Nitrogen fraction in a weld bead was measured for confirming the shielding effect. Furthermore, CFD simulation was also carried out for obtaining shielding gas flow velocity at the torch nozzle exit. From the result of the above experiments and simulation, effective parameters for improving the shielding effect against the cross-wind were comprehensively discussed. As a result, the nitrogen fraction was found to be decreased by increasing the averaged vertical gas velocity at the torch nozzle exit. For achieving this, it is especially effective to decrease the nozzle diameter or increase the gas flow rate.

Use of multifrequency (C‐band and L‐band) SAR data to monitor peat subsidence based on time‐series SBAS InSAR technique

AbstractPeatlands in tropical regions like Indonesia are undergoing irreversible subsidence due to changes in land use (e.g., deforestation) and land management practices (e.g., drainage alteration), resulting in massive amounts of soil carbon loss. Several satellite‐borne synthetic aperture radar (SAR) sensors are operating concurrently at different frequencies, providing potentially useful data for monitoring surface motion over tropical peatlands. This study focused on the capability of C‐band (SENTINEL‐1) and L‐band (PALSAR‐2) SAR data to monitor the surface changes in the tropical peatlands area of Bengkalis Island, Indonesia, by applying time‐series interferometric SAR (InSAR) with the small baseline subset (SBAS) technique. The average vertical velocity measured by SENTINEL‐1 and PALSAR‐2 for the period of 2018–2019 was −1.41 and −2.65 cm yr−1, respectively. We also explored the potential of groundwater level (GWL) data converted to vertical displacement for validating SBAS InSAR. PALSAR‐2 performed the best, exhibiting lower RMSE values for each land use compared to SENTINEL‐1, with an overall RMSE of 1.383 and 1.988 cm yr−1, respectively. Also, the subsidence rates of SENTINEL‐1 were underestimated, showing a significantly lower mean subsidence difference (0.96 cm yr−1) than the reference. Our GWL‐based subsidence data offered an alternative validation method for InSAR‐based subsidence estimation. Therefore, the integration of time‐series InSAR and GWL data can provide crucial information for monitoring the degradation of tropical peatlands.

Mechanisms governing the settling velocities and spatial distributions of inertial particles in wall-bounded turbulence

We use theory and Direct Numerical Simulations (DNS) to explore the average vertical velocities and spatial distributions of inertial particles settling in a wall-bounded turbulent flow. The theory is based on the exact phase-space equation for the Probability Density Function describing particle positions and velocities. This allowed us to identify the distinct physical mechanisms governing the particle transport. We then examined the asymptotic behavior of the particle motion near the wall, revealing the fundamental differences to the near wall behavior that is produced when incorporating gravitational settling. When the average vertical particle mass flux is zero, the averaged vertical particle velocity is zero away from the wall due to the particles preferentially sampling regions where the fluid velocity is positive, which balances with the downward Stokes settling velocity. When the average mass flux is negative, the combined effects of turbulence and particle inertia lead to average vertical particle velocities that can significantly exceed the Stokes settling velocity, by as much as ten times. Sufficiently far from the wall, the enhanced vertical velocities are due to the preferential sweeping mechanism. However, as the particles approach the wall, the contribution from the preferential sweeping mechanism becomes small, and a downward contribution from the turbophoretic velocity dominates the behavior. Close to the wall, the particle concentration grows as a power-law, but the nature of this power law depends on the particle Stokes number. Finally, our results highlight how the Rouse model of particle concentration is to be modified for particles with finite inertia.

Settling of inertial nonspherical particles in wavy flow

Motivated by the problem of microplastics in the ocean, we experimentally investigate settling of plastic rods, disks, and spheres in wavy flows. We find that particle average vertical velocity can both increase and decrease in waves, relative to particle settling velocity in quiescent flow. This variation is a function of flow inertia at the particle length scale, characterized by particle Reynolds number Re${}_{p}$, and also of particle shape. We find that even though the relative vertical velocities between particles and flow remain constant with Re${}_{p}$, the particles nonuniformly sample the flow as a function of particle shape and Re${}_{p}$.

Characterizing tilt effects on wind plants

Tilting the nacelle of a wind turbine modifies entrainment into the wind plant and impacts total efficiency. Wakes are deflected vertically by tilt and in the case of large angles can disrupt entertainment from the undisturbed flow or dissipate on the ground. The effect of nacelle tilt on wake behavior is investigated in a series of wind tunnel experiments for the first time. Scale model turbines with a hub height and a diameter of 12 cm are arranged in a Cartesian array composed of four rows of three turbines each. The tilt angle was varied in the third turbine row from −15° to 15° in chosen 5° increments. Stereo particle image velocimetry measurements of the instantaneous velocity field were recorded at four locations for each angle. Tilted wakes are described in terms of the average streamwise velocity, vertical velocity, and Reynolds stresses. Mean kinetic energy quantities are presented, and conditional sampling is employed to quantify the importance of sweep to ejection events in vertical momentum transfer. Additionally, the effect of nacelle tilt on net power production is presented and compared to existing models. Numerical simulations accurately predict losses in net efficiency for positive angles but diverge for negative tilt angles. The results demonstrate that the tilt angle influences wake magnitude, displacement, and recovery. Positive angles deflect wakes above the wind plant, while negative angles encourage entrainment into the wind plant and exhibit rapid recovery.

DEM study on the effects of pellet characteristics on particle flow in rectangular hopper

In this work, a non-cohesive and multi-element particle model of discrete element method (DEM) was constructed, which was used in combination with experiments to investigate the particle flow characteristics in retangular hopper equipped with the screw discharging machine. On this basis, different diameter pellets (dp = 20 mm, 25.02 mm) with various sphericities (φ = 0.868, 0.985, 1) and particle size distribution (a = 0:1, 0.1:0.9, 0.15:0.85, 0.2:0.8) were selected to examine the effects of sphericity and particle size distribution on the distribution of particle average velocity, motion distance and voidage. Our results showed that as the a increased, the particle average vertical velocity was first decreased and then increased. The motion distance of particles at 1/2 bed height was relatively stable. Furthermore, the average voidage of cylindrical particles was the largest and that of ellipsoidal particles was the smallest. Finally, the specific position of the lag of particle motion is revealed.

The Effects of Multiple Sets of Squats and Jump Squats on Mechanical Variables.

Rossetti, ML, Munford, SN, Snyder, BW, Davis, SE, and Moir, GL. The effects of multiple sets of squats and jump squats on mechanical variables. J Strength Cond Res 34(4): 1017-1023, 2020-The mechanical responses to 2 nonballistic squat and 2 ballistic jump squat protocols performed over multiple sets were investigated. One protocol from each of the 2 nonballistic and ballistic conditions incorporated a pause between the eccentric and concentric phases of the movements in order to determine the influence of the coupling time on the mechanical variables and postactivation potentiation (PAP). Eleven men (age: 21.9 ± 1.8 years; height: 1.79 ± 0.05 m; mass: 87.0 ± 7.4 kg) attended 4 sessions where they performed multiple sets of squats and jump squats with a load equivalent to 30% 1-repetition maximum under one of the following conditions: (a) 3 × 4 repetitions of nonballistic squats (30N-B); (b) 3 × 4 repetitions of nonballistic squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PN-B); (c) 3 × 4 repetitions of ballistic jump squats (30B); (d) 3 × 4 repetitions of ballistic jump squats with a 3-second pause between the eccentric and concentric phases of each repetition (30PB). Force plates were used to calculate variables including average vertical velocity, average vertical force (GRF), and average power output (PO). Vertical velocities during the ballistic conditions were significantly greater than those attained during the nonballistic conditions (mean differences: 0.21-0.25 m·s, p < 0.001, effect sizes [ES]: 1.70-1.89) as were GRFs (mean differences: 478-526 N, p < 0.001, ES: 1.61-1.63), and PO (mean differences: 711-869 W, p < 0.001, ES: 1.66-1.73). Moreover, the increase in PO across the 3 sets in 30B was significantly greater than the changes observed during 30N-B, 30PN-B, and 30PB (p ≤ 0.015). The pause reduced the mechanical variables during both the nonballistic and ballistic conditions, although the differences were not statistically significant (p > 0.05). Ballistic jump squats may be an effective exercise for developing PO given the high velocities and forces generated in these exercises. Furthermore, the completion of multiple sets of jump squats may induce PAP to enhance PO. The coupling times between the eccentric and concentric phases of the jump squats should be short in order to maximize the GRF and PO across the sets.