Horizontal Speed Research Articles

Bouncing along a horizontal surface

If a billiard ball bounces along a smooth horizontal surface, the bounce height decreases after every bounce. One might expect that the horizontal speed will also decrease after every bounce. In fact it remains constant. By comparison, the horizontal speed of a superball sometimes increases and sometimes decreases after each bounce.

Optimal-time quadcopter descent trajectories avoiding the vortex ring and autorotation states

It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade’s lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for quadcopters, which is not necessarily the case for helicopters. A model is proposed for the velocity constraints that the quadcopter must meet in order to avoid these regions. Then, the problem of designing optimal time descent trajectories that avoid the VRS and WBS regions is tackled. Finally, the optimal trajectories are implemented on a quadcopter. The flight tests show that by following the designed trajectories, the quadcopter can descend considerably faster than purely vertical trajectories that also avoid the VRS and WBS.

ВАРИАНТЫ ПЛОСКОПАРАЛЛЕЛЬНОГО ДВИЖЕНИЯ ЗЕРНОВКИ В СКРЕБКОВОМ ТРАНСПОРТЕРЕ

The kinematics of plane-parallel motion of a wheat or rye grain when moving in an inclined position in a scraper conveyor is considered. A kinematic diagram of the plane-parallel motion of the grain in the scraper conveyor was compiled, the position of the instantaneous center of the flat figure was determined, and options for the movement of grain in an inclined position at various possible positions of instantaneous center were considered. The profile of the grains is outlined by an elliptical curve. The point of contact of the elliptical profile of the caryopsis with the scraper makes a complex motion, while the horizontal speed of the scraper is portable for it, the sliding speed on the surface of the scraper is relative. The speed of the touch point of the grain with the pan is horizontal. For six possible positions of the instantaneous center, the directions of the velocities of the points of contact of the grains and the friction forces acting in them are determined. Grains of wheat or rye, moved in a scraper conveyor, in some cases can make plane-parallel movement. The point of contact of the elliptical profile of the caryopsis with the scraper makes a complex motion, while the horizontal speed of the scraper is portable for it, the sliding speed on the surface of the scraper is relative. The speed of the touch point 2 of the grain with the pan is horizontal.

Research on spiral angle optimization for longitudinal road header's cutting head

The cutting head is the key component of a road header in tunnel excavation, where the concept of the spiral angle design directly affects the comprehensive performance, which includes cutting resistance, fluctuation coefficient, specific energy consumption, cutting head stress distribution, and so on. Based on the theory of rock-breaking by pick, the mechanical model of pick was established, and the three-dimensional force vector in the WORKBENCH coordinate system was determined. The 3D model of the proposed cutting head was designed using PRO/E and the static simulation was carried out using WORKBENCH, while the stress information of key parts was obtained. Furthermore, a four-dimensional fitting method was used to investigate the influence of the horizontal swing speed, rotational speed, and spiral angle of the cutting head, on the stress of the cutting head assembly. By setting the horizontal swing speed, rotational speed and the spiral angle as design variables and the specific energy consumption, total cutting resistance, fluctuation coefficient, power consumption, and stress on cutting head assembly as the objective function; the multiobjective optimization function of the cutting head was established. By using genetic algorithm, the complex problem has been solved. The solution of this optimization function provides the horizontal swing speed, rotational speed, and spiral angle values, where the optimal performance is achieved, in the aspect of energy consumption, cutting resistance, fluctuation coefficient, cutting power, and cutting motor power. This method provides solid guidance and is a great reference in spiral angle design and optimization.

Interface Kinematics of Laser Impact Welding of Ni and SS304 Based on Jet Indentation Mechanism

With the application of high-velocity impact welding (HVIW) technology, the research on the mechanism of the formation and evolution of interface waveforms has become an important research direction in HVIW. Understanding the mechanism of interface motion can help control and improve HVIW. Laser impact welding (LIW), a branch of HVIW, lacks research on the formation and evolution of interface waveforms. Therefore, LIW experiments of Ni and SS304 are carried out. The jet indentation mechanism and the smoothed particle hydrodynamics method are used to simulate and analyze the formation and evolution of the LIW interface waveform. Results show that the interface materials exhibit fluid behavior during LIW. The jet indentation mechanism can explain the formation and evolution of waveforms in LIW. Jet velocity, normal stress, and flyer horizontal welding speed are the main factors affecting the variation of the interface waveform size in LIW. At the collision point, the smaller the horizontal welding speed of the flyer, the larger the wavelength; the smaller the jet velocity, the smaller the amplitude. In addition, the propagation of the normal stress deviating from each other at the welding interface along the welding direction is the fundamental cause of springback and cracking.

A Novel Model-Based Framework for Power Consumption Prognosis in Multirotors Applied to the Battery End of Discharge Prognostics

Abstract Accurately estimating the time of battery end of discharge (EOD) in electric unmanned aerial vehicles (UAVs) provides assurance that a given mission can be completed before the energy stored in the battery runs out and aids decision-making processes such as mission replanning to mitigate shortcomings associated with the available energy. The accuracy of the predicted battery EOD time is strongly correlated to the accuracy of the expected power consumption during the mission. This paper reports on a novel model-based framework for power consumption prognosis in multirotors which includes an improved power consumption model that characterizes the power required by a multirotor in axial and nonaxial translation and incorporates the wind effects on the required power. A particle filter is used in conjunction with the concept of artificial evolution to estimate and monitor wind speed, wind direction, and thrust based on measurements of power. Monte Carlo sampling-based predictor is used to predict the trajectories of power used in battery EOD prognostic. The framework is applied to battery EOD prognostic of a quadcopter that performs a delivery mission with low horizontal speed (where rotor tilt is not a significant factor). Results show that predicted trajectories of power accurately represent the uncertainty of future power consumption. Even when certain information (such as aircraft weight) is not available at every time-step, the framework allows tracking the actual EOD time because of its capability to monitor thrust. These results demonstrate the effectiveness of the proposed framework.

Propeller Selection by Means of Pareto-Optimal Sets Applied to Flight Performance

Selection process of the propeller for short take-off and landing (STOL) category aircraft is described. The aim is to achieve the highest possible performance with fixed propeller, i.e., high maximal horizontal and cruise speed, short take-off and high rate of climb. These requirements are contradictory and so Pareto sets were used in order to find the optimal propeller. The method is applied to a family of geometrically similar propellers that are suitable for 73.5 kW (100 hp) piston engine designed for ultralight category aircraft with maximal take-off weight of 472.5 kg. The propellers have from two to eight blades, blade angle settings from 15° to 40° and diameter from 1.1 m to 2.65 m. Pareto frontier is designed for each pair of flight conditions, and the optimal propeller is selected according to these results. For comparison, the optimal propeller selection from the propeller family by means of a standard single-optimal process based on the speed power coefficient cs is also used. Use of Pareto sets leads to considerable performance increase for the set of contradictory requirements. Therefore, high performance for a low price for the given aircraft can be achieved. The described method can be used for propeller optimization in similar cases.

Flame propagation in gasoline vapor–air mixtures with concentration gradient in a closed duct

Once gasoline leaks in confined spaces, vapor–air mixtures with concentration gradients will form above the liquid surface owing to evaporation, and explosion may occur if ignition occurs at a suitable location. This study aims to measure the concentration gradient of gasoline vapor–air mixtures and to investigate the effect of the ignition delay (tig) on the flame behavior and overpressure in a closed duct. The results reveal that the flammable layer of the gasoline vapor–air mixtures exist only at a certain time period. After ignition of the stratified vapor–air mixtures, a blue olive-shaped premixed flame bubble is formed, followed by a bright diffusion flame at its bottom, and subsequently, two symmetrical eddies form. The horizontal speed of the premixed flame tip first increases to approximately 3.5–4.3 m/s and then decreases to 1.5–2.0 m/s. The maximum overpressure of the current stratified gasoline–air mixture initially increases from approximately 320 to 450 kPa as tig increases from 6 to 10 min, and then remains nearly unchanged with further increase in tig. A maximum value of 450 kPa is obtained, which is lower than the results of homogeneous gasoline–air mixtures in previous research.

Characterization of longshore currents in southern East China Sea during summer and autumn

Current characteristics and vertical variations during summer and autumn in the southern East China Sea were investigated by measuring current profile, tide, wind, and wave data for 90 d from July 28 to October 25, 2015. Our results are: (1) The current was mainly a (clockwise) rotating flow, displaying reciprocating flow characteristics, and vertically the current directions were the same throughout the vertical profile. (2) The horizontal current speed was strongest during August (summer) with an average speed of 51.8 cm/s. The average current speeds during spring tides were highest in August and weakest in September, with speeds of 59.9 and 42.8 cm/s, respectively. (3) Considerable differences exist in average current speeds in different layers and seasons. The highest average current speeds were found in the middle–upper layers in August and in the middle–lower layers in September and October. (4) The residual current speed was highest in August, when the speed was 12.5–47.1 cm/s, whereas the vertical average current speed was 34.3 cm/s. The depth-averaged residual current speeds in September and October were only 50% of that in August, and the residual current direction gradually rotated in a counter-clockwise direction from the lower to surface layers. (5) Typhoon waves had a significant influence on the currents, and even affected the middle and lower water layers at depths of >70.0 m. Our results showed that the currents are controlled by the dynamic interplay of the Taiwan Warm Current, incursion of the Kuroshio Current onto the continental shelf, and monsoonal changes.

INS/CNS Integrated Calibration based on Speed Reference Information

CNS needs INS to provide horizon attitude information as the horizon reference. The non-damping INS on critical conditions is easy to cause error fluctuation and divergence when the accelerometer zero is changed, directly affecting horizon reference information precision of assistant CNS. Therefore, under on-board use conditions, the INS short-term high-precision characteristics are used in CNS/INS/LOG integrated system to design Kalman filter with horizontal speed damping and compensate dynamic error of INS. The calibration and readjustment technology of on-board CNS/INS integrated system is based on horizontal speed damping. The accurate reference information of CNS is used to finish correction of position error, misalignment angle and main gyro drift error. In this way, the readjustment period will be extended to realize long-time and high-precision navigation of the integrated system.

Neap-spring variability of tidal dynamics in the Northern Arabian Gulf

Small-scale (periods < 24 h and horizontal length < 10 km) hydrodynamics are significantly influenced by tides in the Northern Arabian Gulf (NAG). Here we characterize, for the first time, the neap-spring variability of tidal currents and mixing in the NAG from field observations. During the experiment between 14–28 July 2017, measurements in the near bottom layer (~1.5–6.5 m above bottom) show: (1) semi-diurnal horizontal velocities induced by tides, with a maximum horizontal speed of ~0.5 m/s; (2) quarter-diurnal cycles in turbulent kinetic energy (TKE) dissipation rates, with inequalities between the daily two floods and two ebbs; (3) well-correlated relations between turbulent diffusivity and gradient Richardson number. Both current velocities and mixing intensity near the bottom increased from neap to spring tides: the mean horizontal speeds increased from 0.18 to 0.26 m/s; the mean TKE dissipation rates increased from 2.2 × 10-7 to 5.5 × 10-7 W/kg and the mean stratification decreased from 2.1 × 10-5 to 5.5 × 10-6 s-2. Thus, the enhanced near bottom turbulent mixing is likely to contribute more significantly to the vertical transports of nutrients and sediments during spring tides in this region. The mean tidal power input (2.6 × 10-2 W/m2), was found to be one order of magnitude larger than the mean wind power input (1.1 × 10-3 W/m2) with ~39% of the tidal energy being dissipated locally by turbulent mixing near the bottom.

Wildfire Fighting by Unmanned Aerial System Exploiting Its Time-Varying Mass

This letter presents an approach for accurately dropping a relatively large amount of fire retardant, water or some other extinguishing agent onto a wildfire from an autonomous unmanned aerial vehicle (UAV), in close proximity to the epicenter of the fire. The proposed approach involves a risky maneuver outside of the safe flight envelope of the UAV. This maneuver exploits the expected weight reduction resulting from the release of the payload, enabling the UAV to recover without impacting the terrain. The UAV is tilted to high pitch angles, at which the thrust may be pointed almost horizontally. The vehicle can therefore achieve higher horizontal speeds than would be allowed by conventional motion planners. This high speed allows the UAV to significantly reduce the time spent close to the fire. As a result, the overall high heat exposure is reduced, and the payload can be dropped closer to the target, minimizing its dispersion. A constrained optimal control problem (OCP) is solved taking into account environmental parameters such as wind and terrain gradients, as well as various payload releasing mechanisms. The proposed approach was verified in simulations and in real experiments. Emphasis was put on the real time recalculation of the solution, which will enable future adaptation into a model predictive controller (MPC) scheme.

Effect of Mass-Center Position of Spinal Segment on Dynamic Performances of Quadruped Bounding with a Flexible-Articulated Spine

Driven by the layout design of devices arranged on the spine of quadruped robot which has a symmetry spine with a flexible joint, we explore the effect of mass-center position of spinal segment (MCPSS) on dynamic performances of quadruped bounding. A simplified model is introduced with MCPSS set as an independent parameter. Periodically quadruped bounding motions are generated to calculate different dynamic performances related to different MCPSS at the low, medium, and high horizontal speeds, respectively. The results indicate MCPSS corresponding to the optimal or suboptimal dynamic performances mainly gather at two positions: the hip joint and the geometric center of spinal segment. MCPSS near the hip joint leads to the largest stride period, stride length, and spinal oscillation-margin at all speeds. The smallest duty factor can also be obtained at the medium and high speeds. These improved inherent characteristics offer advantages in leg-orientation control and fast movement effectively. MCPSS near the geometric center of spinal segment brings the best self-stability, the smallest mass-center vertical fluctuation, and the smallest maximum foot-end force at all speeds, which should greatly enhance resistances to vertical jitters and reduce torque-demands of joint-drivers. This study should give useful suggestions to robot designs in reality.

Average Radial Structures of Gas Convection in the Solar Granulation

Abstract Gas convection is observed in the solar photosphere as granulation, i.e., having highly time-dependent cellular patterns, consisting of numerous bright cells called granules and dark surrounding channels called intergranular lanes. Many efforts have been made to characterize the granulation, which may be used as an energy source for various types of dynamical phenomena. Although the horizontal gas flow dynamics in intergranular lanes may play a vital role, they are poorly understood. This is because the Doppler signals can be obtained only at the solar limb, where the signals are severely degraded by a foreshortening effect. To reduce such a degradation, we use Hinode's spectroscopic data, which are free from a seeing-induced image degradation, and improve the image quality by correcting for stray light in the instruments. The data set continuously covers from the solar disk to the limb, providing a multidirectional line-of-sight (LOS) diagnosis against the granulation. The obtained LOS flow-field variation across the disk indicates a horizontal flow speed of 1.8–2.4 km s−1. We also derive the spatial distribution of the horizontal flow speed, which is 1.6 km s−1 in granules and 1.8 km s−1 in intergranular lanes, and where the maximum speed is inside intergranular lanes. This result newly suggests the following sequence of horizontal flow: a hot rising gas parcel is strongly accelerated from the granular center, even beyond the transition from the granules to the intergranular lanes, resulting in the fastest speed inside the intergranular lanes, and the gas may also experience decelerations in the intergranular lane.

On the spreading of non-canonical thermals from direct numerical simulations

We present results from direct numerical simulations on laminar and turbulent non-canonical thermals with an initial rectangular density distribution at a Reynolds number of Re = 500 and Re = 5000, respectively. We find the non-canonical shape to induce strong azimuthal variations in the thermal for both the laminar and turbulent cases. These include noticeable differences in downward and horizontal propagation speeds as well as differences in the strength of the vortex tube. These differences persist over a significant period of time and help generate a cross-flow component that is otherwise not present in canonical cases. The cross-flow component is in the opposite direction to that observed in gravity currents with the same initial density distribution. This is counterintuitive seeing that both flows are solely driven by buoyancy. By extracting the three-dimensional streamlines, we find the descending vortex tube to force the dense fluid to follow a helical path.

Measuring Low-Altitude Winds with a Hot-Air Balloon and Their Validation with Cabauw Tower Observations

AbstractA field experiment with a hot-air balloon was conducted in the vicinity of the meteorological observatory of Cabauw in The Netherlands. Recreational hot-air balloon flights contain useful wind information in the atmospheric boundary layer (ABL). On a yearly basis between 8000 and 9000 flights are taking place in The Netherlands, mainly during the morning and evening transition. An application (app) for smartphones has been developed to collect location data. We report about a feasibility study of a hot-air balloon experiment where we investigated the accuracy of the smartphone’s Global Navigation Satellite System (GNSS) receiver using an accurate geodetic GNSS receiver as a reference. Further, we study the dynamic response of the hot-air balloon on variations in the wind by measuring the relative wind with a sonic anemometer, which is mounted below the gondola. The GNSS comparison reveals that smartphones equipped with a GNSS chip have in the horizontal plane an absolute position error standard deviation of 5 m, but their relative position error standard deviation is smaller. Therefore, the horizontal speeds, which are based on relative positions and a time step of 1 s, have standard deviations of σu = 0.8 m s−1 and συ = 0.6 m s−1. The standard deviation in altitude is 12 m. We have validated the hot-air balloon derived wind data with observations from the Cabauw tower and the results are encouraging. We have studied the dynamics of a hot-air balloon. An empirical value of the response length has been found which accounts for the balloon’s inertia after a changing wind, and which compared favorable with the theoretical derived value. We have found a small but systematic movement of the hot-air balloon relative to the surrounding air. The model for the balloon dynamics has been refined to account for this so-called inertial drift.

Comparison of optimal actuation patterns for flagellar magnetic micro-swimmers

In this article, we present a simplified model of a flagellar magnetic micro-swimmer based on shape discretization and the simplification of the hydrodynamical interactions. We numerically solve the optimal control problem of finding the actuating magnetic fields that maximizes its horizontal propulsion speed over a fixed time. Depending on the chosen constraints on the control, the optimal trajectories of the swimmer can be planar or three-dimensional. Simulations show the periodicity of the optimal magnetic fields and the shape of the swimmer under optimal actuation. All the simulated magnetic fields out-perform the standard sinusoidal actuation method that is prevalent in the litterature and in experiments. Moreover, the non-planar actuation patterns leads to novel trajectories for flagellar low-Reynolds swimmers and perform significantly better than planar actuation.

Impact and Adhesion of Surfactant-Amended Water Droplets on Leaf Surfaces Related to Roughness

Highlights The relationship between impacting droplet deposition and leaf surface roughness was examined. Complete deposition occurred on smooth leaves with roughness heights shorter than 1.5 micrometers. Droplet deposition on rough leaves was best achieved at low initial travel speeds and high surfactant concentrations. This research provides understanding of increasing droplet adhesion on plants for pesticide spray applications. Abstract. Understanding the effects of the microscopic-scale surface roughness of targeted leaves on spray droplet retention and spread can help develop optimal strategies to improve pesticide application efficiency. Improved spray deposition would minimize the amounts of chemicals to be applied and reduce off-target losses and production costs while protecting the environment. A 3D optical surface profiler was used to measure the arithmetic mean roughness height (Sa), providing a reliable metric for microscopic-scale leaf surface roughness. The relationship between leaf surface roughness and droplet deposition was examined by correlating droplet adhesion with the Sa of six leaf types for spray solutions at five surfactant concentrations (0.0% to 0.75%) and eight initial droplet horizontal travel speeds (0.5 to 4.5 m s-1). Leaf roughness and wettability, in terms of Sa and contact angle (θc), ranged from smooth and easy-to-wet to rough and difficult-to-wet (37° 1.6 μm), deposition decreased with increasing Sa and initial droplet horizontal flight velocity, while it increased as surfactant concentration increased. Thus, spray deposition on rough leaf surfaces could be greatly improved with slow initial droplet flight speeds and high surfactant concentrations. In contrast, greater deposition on smoother leaf surfaces could be achieved at any initial droplet flight velocity and with low concentrations of non-ionic surfactant, or possibly none.

Movement patterns of whale sharks in Cenderawasih Bay, Indonesia, revealed through long-term satellite tagging

Whale sharks, Rhincodon typus, are found circumglobally in tropical and warm temperate seas, exhibiting a range of residency and movement patterns. To determine spatio-temporal habitat use by juvenile male whale sharks in Cenderawasih Bay, Indonesia, we collected data from June 2015 to November 2016 using 16 fin-mounted satellite tags that provided exceptionally long track durations. Fifteen tags transmitted for 48–534 days (mean=321±33, s.e.), with 13 tags transmitting for ≥220 days. Four sharks remained within the bay for the duration of the study, while of the 11 sharks that travelled outside the bay, eight left between March and May 2016. They ranged throughout coastal and offshore waters, travelling up to 5144km away from Cenderawasih Bay, with a mean horizontal speed of only 3.3km day−1±0.70, s.e. A switching state space model was fitted to satellite fix data to identify behavioural states. It revealed that sharks spent an average of 81% of their time in foraging-related behaviours, mostly in shallow waters (median depth=35m), with travelling observed mainly over deeper waters (median depth=1284m). The movement patterns reveal variable periods of residency, with individual patterns of horizontal movement most likely in response to different abiotic and biotic factors, including food availability, which may trigger seasonal dispersal.

Comparative Analysis of Starting Technique in Competitive Swimming and Finswimming

The study purpose was to determine time characteristics of the start phases: “jump” and “flight” performed by highly-skilled swimmers in competitive swimming and finswimming during the start from the starting block.&#x0D; Materials and methods. The participants of the pedagogical study were 8 competitive swimming female athletes, 7 – bifin swimming athletes, 4 – monofin swimmers. The swimmers were highly-skilled: among them were three international masters of sport, thirteen masters of sport of Ukraine, and three candidate masters of sport. The study recorded the following indicators: motor reaction time, horizontal flight speed (in different sections); flight acceleration (in different sections).&#x0D; Results. The difference in horizontal speed in the first section is not statistically significant (p &gt; 0.05). The bifin swimming athletes show higher speed in sections 2 and 4; in section 3, higher speed is shown by the monofin swimmers (p &lt; 0.001). The bifin swimmers show higher results in flight acceleration in sections 1, 2 and 4; in section 3, higher acceleration is shown by the monofin swimmers (p &lt; 0.001).&#x0D; Conclusions. For comparative analysis of the starting technique, it is advisable to use such indicators as motor reaction time, horizontal flight speed, flight acceleration, and flight trajectory indicators as the main criteria.&#x0D; The study found that the time of motor reaction in competitive swimming is the shortest and it is the longest in monofin swimming. The athletes show the highest horizontal flight speed in section 3, the highest acceleration in section 2. The monofin swimming athletes show the highest acceleration in section 3. The second discriminant function with the emphasis on the most informative variables can be used to select the most rational starting technique in finswimming.