Entry Velocity Research Articles

The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes

AbstractFusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity.

On the Uncertainty of Modeling the Interaction of a Meteoroid with the Atmosphere at Various Entry Velocities

On the Uncertainty of Modeling the Interaction of a Meteoroid with the Atmosphere at Various Entry Velocities

Once in a summer: Fall history of the JaH 073 strewn field, Sultanate of Oman

AbstractModeling of a prehistoric fall can be successful if a strewn field is very well documented and coordinates, masses, and shapes of all individual stones are recorded. In combination with meteoroid mass and wind model constraints, a detailed scenario of the atmospheric passage is obtained for the ~20 × 6 km‐sized JaH 073 L6 strewn field in Oman. The wide mass ranges from 52.2 kg to <1 g together with the large number of ~3500 stones offer the statistical basis to reconstruct the trajectory and the fragmentation sequence. The size of the meteoroid, constrained by noble gas analyses, corresponds to an initial mass of about 12 t at atmospheric entry using an L‐chondrite bulk density of 3400–3500 kg m−3. Assuming typical ablation behavior, these data are compatible with an entry velocity of 20 ± 3 km s−1. The best model fit is achieved for a serial fragmentation scenario starting at an altitude of ~34 km and showing a main fragmentation at 26 km. A resolved event seems to have occurred at 22 km, followed by a more diffuse fragmentation at 19 km. The vertical trajectory angle is calculated at 43 ± 2° and the azimuth at 329 ± 1°. The position of numerous outlying meteorites in the strewn field can only be reproduced by repeated fragmentation with cumulated transverse velocities from explosive events. The wind model adopted from modern data fits surprisingly well and indicates summer monsoon with strong easterly winds during the fall event, consistent with paleoclimatic data.

Data on 824 fireballs observed by the digital cameras of the European Fireball Network in 2017–2018

A catalog of 824 fireballs (bright meteors), observed by a dedicated network of all-sky digital photographic cameras in central Europe in the years 2017–2018 is presented. The status of the European Fireball Network, established in 1963, is described. The cameras collect digital images of meteors brighter than an absolute magnitude of about −2 and radiometric light curves with a high temporal resolution of those brighter than a magnitude ≈−4. All meteoroids larger than 5 g, corresponding to sizes of about 2 cm, are detected regardless of their entry velocity. High-velocity meteoroids are detected down to masses of about 0.1 g. The largest observed meteoroid in the reported period 2017–2018 had a mass of about 100 kg and a size of about 40 cm. The methods of data analysis are explained and all catalog entries are described in detail. The provided data include the fireball date and time, atmospheric trajectory and velocity, the radiant in various coordinate systems, heliocentric orbital elements, maximum brightness, radiated energy, initial and terminal masses, maximum encountered dynamic pressure, physical classification, and possible shower membership. Basic information on the fireball spectrum is available for some bright fireballs (apparent magnitude <−7). A simple statistical evaluation of the whole sample is provided. The scientific analysis is presented in an accompanying paper.

Study on the Calculation Method of Water Inflow Velocity of Loose Rock Landslide

Landslide surges pose a serious threat to the ecological environment and human life safety. Based on rock structure mechanics and water sediment dynamics, considering the additional resistance caused by the interference of loose landslide particles on flow structure, this paper deduces the resistance calculation formula of loose-rock landslide particles when entering water. It modifies the landslide velocity formula (ASCE) recommended by the American Society of Civil Engineers. The acceleration calculation formula and velocity calculation formula of bulk-rock landslides entering water are obtained, and the determination method of the main parameters in the formula is given. Based on the data of the Xintan Landslide into the Yangtze River, the rationality of the calculation results of this formula and the ASCE formula are compared and analyzed. It shows that the ASCE formula calculates the average velocity of landslide movement on land, and there will be a noticeable deviation from the actual situation when it is used to calculate the water entry velocity of a loose-rock landslide. The formula given in this paper is more practical and can be used to calculate the velocity of loose-rock landslides entering water.

Design and optimisation of a passive Atmosphere-Breathing Electric Propulsion (ABEP) intake

In order to extend the orbital lifetime of spacecraft operating in Very-Low Earth Orbit (VLEO), Atmosphere-Breathing Electric Propulsion (ABEP) can be employed for atmospheric drag compensation. The concept is based on the ingestion of rarefied atmospheric particles to be used as propellant for an electric thruster, thereby removing the need for onboard propellant. The present paper aims to design and analyse a passive ABEP intake optimised for the RF Helicon-based Plasma Thruster (IPT), which is selected as the most promising system due to its electrodeless design, as it removes the issue of thruster corrosion, and reduced susceptibility to atmospheric variations. This is achieved by implementing the analytical model, referred to as the Balancing Model (BM), along with its main performance parameters. The Direct Simulation Monte Carlo (DSMC) solver dsmcFoam+ is thus employed to simulate the transmission probability of cylinders and hexagonal prisms with non-zero entrance velocity, yielding a mean percentage error of 2% when compared to independent DSMC results. In addition, a novel DSMC transmittance investigation of square prisms is performed. Various design configurations are optimised for circular and hexagonal intakes based on the functional requirements of the thruster, leading to a maximum collection efficiency of 45% for a cylindrical intake with a hexagonal honeycomb. The optimal intake is hence simulated via DSMC, showing a good accuracy with the BM with or without intermolecular collisions, yielding a percentage error of 0.22% in the former case and 5.53% in the latter one. The variation of incidence flow angle, accommodation coefficient and thruster transmission probability is finally investigated, and the results are validated by the agreement shown with values retrieved from the literature.

Numerical Analysis of Flow-Induced Vibration of Heat Exchanger Tube Bundles Based on Fluid-Structure Coupling Dynamics

According to the needs generated by the industry, there is an urgent need to investigate the flow vibration response law of the elastic tube bundle of heat exchangers subjected to the coupling effect of shell and tube domain at different inlet flow velocities. In this paper, based on the continuity equation, momentum equation, turbulence model, and dynamic grid technology, the vibration response of the elastic tube bundle under the mutual induction of shell and tube fluids is studied by using pressure-velocity solver and two-way fluid-structure coupling (FSC) method. The results show that the monitoring points on the same connection block have the same vibration frequency, while the vibration amplitude is different. Monitoring point A is the most deformed by the impact of fluid in the shell and tube domain. When the inlet velocity( v shell = v tube = 0.15 , 0.4, 0.5 m/s) of shell and tube is low, the amplitude of tube bundle vibration in the Y direction is greater than that in X and Z direction, and the tube bundle produces periodic vibration in the vertical direction. The vibration equilibrium position of the tube bundle along the shell flow direction gradually moves up with the increase of the inlet velocity. The amplitude in the Y -direction of the elastic bundle decreases with the increase of shell-side and tube-side velocity. The relationship between the vibration amplitude in the Y direction and the entrance velocity is a linear function.

Numerical investigation on the water entry of a 2D seaplane section with heel angles

The accurate prediction of impact loads during water entry is the key to structural strength assessment. However, our understanding on the load characteristics mainly relies on the simplified geometrical shapes such as wedges and ship-like sections. This paper studied the water entry of a 2D seaplane section with the bottom cabin, which focuses on the formation of air cavity, the influence of the cabin to the flow and impact pressure. A compressible air-water two-phase model was established and the free surface was modeled by the VOF (Volume Of Fluid) algorithm. Numerical method was validated by the published experimental data and other numerical results showing good agreements. Some hydrodynamic characteristics related to water impact were discussed including the free surface, pressure distribution and pressure time history. The complicated flow (air cavity and jet flow impact) and obvious multiple pressure peaks were observed, which of them are different to the general impact phenomenon of simplified geometrical shapes. The influence of water entry velocity on the impact loads was further discussed, showing the multiple pressure peaks were affected by the impact velocity. Results of the study are expected to improve the understanding of impact mechanism of special sections with obvious air cavity flows.

Design optimization of suction chamber relying on environmental considerations

Various systems and methods have been developed for the gathering of seawater. One of the most common methods is the use of offshore direct seawater intakes, such as suction chamber. Due to the location of these structures, they can influence marine life by suction of fish. In this research, by considering environmental issues and design parameters, the size of an initial case with a certain condition was optimized. By converting the square cross-section into a polygon and changing the dimensions, it was observed that in addition to the decrease of the structure's volume by 50%, the velocity distribution around the structure becomes more uniform and meets the criteria (entrance velocity > 0.15 m/s). This paper also suggests a flat plate at the inlet for the horizontal flow formation. It is capable of helping fish to react better and preventing them from entering the suction chamber. In this case, as the volume of structure decreased by 54%, the entrance velocity did not show any significant change. Furthermore, for reducing the size of the structure, by considering structural issues, this study recommends that the riser part of the model can be changed. Eventually, according to all parameters, a final model for these conditions was presented.

Time-varying dynamic analysis of a plate entering the finite subsonic airflow field

Devices entering rigid wall constrained finite airflow field are commonly seen in engineering practice. The devices gradually move from the infinite airflow field to the finite airflow field, which makes the device and the outside flow field a complicated time-varying fluid–structure interaction system. During the entry process, the stiffness, damping and mass of the devices change constantly over time, which makes the dynamic behaviors of the system show complex time-varying properties. Hence, it is needed to study the stability and vibration characteristics of the devices entering the finite airflow field. In this study, based on the von Karman nonlinear plate theory and the linear potential flow theory, the governing equation of the plate entering the finite airflow field is established by employing the Hamilton’s principle. By using the generalized eigenvalue method to linear system, the variations of the natural frequencies of the plate in the process of entering the finite airflow field are investigated, from which the stability change rules of the system are obtained. The vibration properties of the system are studied by analyzing the displacement time response of the plate in the process of entering the finite flow field. From the results, the different system parameters such as entry position, entry velocity, aspect ratio, external harmonic excitation amplitude and external harmonic excitation frequency have significant impacts on the stability and vibration properties of the plate entering the finite airflow field.

Probing the nature of dissipation in compressible MHD turbulence

Context. An essential facet of turbulence is the space–time intermittency of the cascade of energy that leads to coherent structures of high dissipation. Aims. In this work, we aim to systematically investigate the physical nature of the intense dissipation regions in decaying isothermal magnetohydrodynamical (MHD) turbulence. Methods. We probed the turbulent dissipation with grid-based simulations of compressible isothermal decaying MHD turbulence. We took unprecedented care in resolving and controlling dissipation: we designed methods to locally recover the dissipation due to the numerical scheme. We locally investigated the geometry of the gradients of the fluid state variables. We developed a method to assess the physical nature of the largest gradients in simulations and to estimate their travelling velocity. Finally, we investigated their statistics. Results. We find that intense dissipation regions mainly correspond to sheets; locally, density, velocity, and magnetic fields vary primarily in one direction. We identify these highly dissipative regions as fast and slow shocks or Alfvén discontinuities (Parker sheets or rotational discontinuities). On these structures, we find the main deviation from a 1D planar steady-state is mass loss in the plane of the structure. We investigated the effect of initial conditions, which yield different imprints at an early time on the relative distributions among these four categories. However, these differences fade out after about one turnover time, at which point they become dominated by weakly compressible Alfvén discontinuities. We show that the magnetic Prandtl number has little influence on the statistics of these discontinuities, but it controls the ohmic versus viscous heating rates within them. Finally, we find that the entrance characteristics of the structures (such as entrance velocity and magnetic pressure) are strongly correlated. Conclusions. These new methods allow us to consider developed compressible turbulence as a statistical collection of intense dissipation structures. This can be used to post-process 3D turbulence with detailed 1D models apt for comparison with observations. It could also be useful as a framework to formulate new dynamical properties of turbulence.

Flow-Induced Vibration and Heat Transfer Analysis for a Novel Hollow Heat Exchanger

A novel hollow shell-and-tube heat exchanger with helical elastic coiled tubes was designed to improve the overall heat transfer performance. Different numbers of helical baffles installed on the hollow helical elastic tubes (HHETs) heat exchanger were compared with the HHET heat exchanger without a baffle. The fluid–solid coupling method was provided to study the effects of the entrance velocity and baffle number on the performances of heat transfer and vibration-enhanced heat transfer. Based on the numerical results, the performances of vibration and heat transfer become more obvious by increasing the entrance velocity. Compared with the HHET heat exchanger without a baffle, adding a baffle or baffles on the HHET heat exchanger can remarkably make the fluid flow more consistent. Whereas a higher number of baffles can weaken the vibration and heat transfer performance of the novel heat exchange, the performance evaluation criteria of the HHET heat exchanger with one baffle, two baffles, and four baffles is improved by 2.04, 4.37, and 2.3%, respectively. It indicates that adding a baffle or baffles to the novel heat exchanger can effectively improve the overall thermal and hydraulic characteristics of the novel heat exchanger.

3-Dimensional CFD Simulation and Experimental Analysis on Performance of a New Diffuser and Wind Channel for a Micro Wind Turbine

Producing electricity from waste energies has been introduced as a useful approach in moving towards stability. Therefore, in the current study a new wind channel has been designed and fabricated to convert created airflow resulting from automobiles movement on the highways to electricity. This channel is fabricated to guide airflow from automobiles movement inside the same directed channel and towards a microturbine located at the bottom of the wind channel. To uniform the airflow inside the channel, a new diffuser has been designed and fabricated. The diffuser minimizes airflow turbulence in a part of the channel where microturbine is located. The maximum velocity is obtained in the horizontal distance is 1.9 m, the vertical distance is 0.95 m, and the angle is 45° according to automobiles' movement. This study also studied fluid behavior through the channel using 3-Dimensional CFD simulation technique and the best type of channel and diffuser fabricated based on numerical results. According to the numerical simulation results, the velocity of wind in channel venturi is 3.9 times more than the channel entrance velocity. As a result of numerical analysis and experimental investigation, by using the new diffuser and the new fabricated wind channel, the wind velocity between blades of the microturbine is 4.5 times more than the inlet velocity of the wind channel.

Numerical analysis of cavitation and impact load characteristics of supercavitating vehicle entering water at high speed

In order to obtain the influence of water entry angle and speed on the cavitation and impact load characteristics of supercavitating vehicle, a high-speed water entry numerical model of supercavitating vehicle based on VOF model is established, and the accuracy of the model is verified by relative experiments. Through simulation, the cavitation evolution process, cavitation size, impact load change and surface pressure distribution of supercavitating vehicle entering water at different angles and velocities are obtained and compared. The results show that with the increase of water entry velocity, the depth of cavitation closing position increases, the cavitation size increases, the peak value of axial load increases and the surface pressure of vehicle increases; With the increase of water entry angle, the bubble closing time remains unchanged, the bubble size decreases, the axial load peak increases, and the asymmetry of pressure distribution decreases. The pressure on the upstream surface of the cavitator increases along the radius to the center of the circle, but the asymmetry decreases when it enters the water obliquely.

Kinematic and Temporal Differences Between World-Class Men's and Women's Hurdling Techniques.

This study aimed to compare joint kinematics and center of mass parameters throughout hurdle clearance between world-class men and women sprint hurdlers, who were competing in a World Championships final. This was the first study to present time-series kinematic data around hurdle clearance, and given the technical ability of the athletes analyzed, it can be used as a template when analyzing the technique of other athletes in similar competitions and training. Video data were collected of the 16 finalists at the 2017 IAAF World Championships using four high-speed cameras (150 Hz). Video files were continuously digitized manually from touchdown before hurdle clearance to toe-off after landing around the sixth hurdle for men and the fifth hurdle for women, and sex-based comparisons were made at key discrete time points using independent t-tests, and throughout the entire hurdle phase using statistical parametric mapping. When calculated relative to hurdle height, the women's center of mass height was significantly greater than the men's throughout the full analyzed sequence (p < 0.001). Men also displayed more hip flexion in the lead leg at take-off before hurdle clearance (p = 0.029) as well as a more extended knee joint at intervals during flight and upon landing (p ≤ 0.037). Women completed the hurdle phase in a significantly shorter time than men (~11% difference, p < 0.001). Finally, women seemed to be more efficient by maintaining and even exceeding their entry velocity for the first 40% of the hurdle phase. These results show a lower technical demand for the women to successfully negotiate hurdle clearance, thus providing further evidence to support the argument that the women's hurdle height is too low for their performance capabilities and should be raised in senior competition.

Numerical Study on the Water Entry Impact Forces of an Air-Launched Underwater Glider under Wave Conditions

In this study, the water entry of an air-launched underwater glider under wave conditions is numerically simulated by the computational fluid dynamics method. The numerical model is validated by the comparison of nondimensional water entry impact force with published experimental and numerical results. And the influence of water entry points, water entry angles, and water entry attack angles on impact force is studied, which provides guidance for the design of air-launched underwater gliders. The results show that the water entry point has a great influence on the peak value of vertical impact force. In the present study, the peak value of the maximum vertical impact force at different water entry points is almost twice the minimum peak value with the same water entry velocity. The water entry angle at the same water entry point has great influence on the peak value of horizontal impact force, which is mainly related to the horizontal component of the impact velocity. The greater the horizontal component of impact velocity, the greater the peak value of impact force. In addition, the attack angle hardly affects the water entry impact force of the glider with hemispherical head.

Experimental investigation on the slamming loads of a truncated 3D stern model entering into water

Slamming load during water impact is one of the main concerns for the design of marine structures. However, accurate prediction of impact pressure largely relies on two-dimensional or simplified three-dimensional structures due to the difficulty in modeling complicated fluid forms such as flow separation and air cavity. In order to improve the prediction of slamming loads in complex three-dimensional models, a truncated stern model impacting water was investigated experimentally through a series of free drop tests. The falling kinemics (water entry depth and acceleration) and slamming loads (pressure and vertical force) were measured through arranging the sensors. Details of impact characteristic including falling kinemics and slamming pressure were presented. In order to clarify the 3D effects, the 2D CFD numerical results were compared with experimental results, showing that the numerical results are larger than the experimental ones with an average of 21%. Finally, influence of water entry velocity on the non-dimensional pressure was further discussed to improve the application. Some factors related to impact velocity such as air pocket and jet flow can influence the pressure which should be paid attention.

Corneal foreign bodies.

Ocular trauma accounts for 8% of emergency department visits; of these, 31% involve corneal foreign bodies.[1][1] A focused history includes presenting symptoms, type of foreign body, penetrability, entry velocity, duration since injury, concurrent contact lens usage and ocular history.[1][1]

Three-Dimensional Effects on Slamming Loads on a Free-Falling Bow-Flare Cylinder Into Calm Water

Abstract Three-dimensional effects on slamming load predictions of a ship section are investigated numerically using the unsteady incompressible Reynolds-averaged Navier–Stokes (RANS) equations and volume of fluid (VOF) method, which are implemented in interDyMFoam solver in open-source library OpenFOAM. A convergence and uncertainty study is performed considering different resolutions and constant Courant (CFL) number following updated ITTC guidelines. The numerical solutions are validated through comparisons of slamming loads and motions between the computational fluid dynamics (CFD) simulations and the available experimental values. The slamming force and slamming pressures on a 2D ship section and the 3D model are compared and discussed. Three-dimensional effects on the sectional force and the pressures are quantified both in transverse and longitudinal directions of the body considering various entry velocities. Comparing with 2D simulations, the 3D models provide lower predictions on slamming loads. The results show that the three-dimensional effects on the maximum slamming force coefficient are about 25%, while the effects on pressures differ from locations and entry velocities, ranging from 11% to 29%.

Turbulence Models Studying the Airflow around a Greenhouse Based in a Wind Tunnel and Under Different Conditions

Turbulence phenomena created around a greenhouse due to different wind loads are key factors in its structural design and significantly affect the ventilation rates through its side and roof openings. Using the turbulence models of ANSYS FLUENT software to investigate the airflow around an arched-roof-greenhouse-shaped obstacle placed inside a wind tunnel was the aim of this study. Velocity and pressure areas around the obstacle were examined by selecting three different turbulence models (Standard, RNG and Realizable k–ε models) under three different airflow entry velocities (0.34, 1.00 and 10.00 m s−1) in the wind tunnel. All k–ε models showed that when the air velocity was intensified, the airflow was identified as turbulent. The horizontal velocity profile predicted more accurately the presence of vortices in contrast with the vector sum of the perpendicular velocity components. Vortices were formed upstream, above the roof and downstream of the obstacle, and the applied models showed that when airflow velocity increases, the size of the upstream vortex decreases. Finally, there was a strong indication from the modeling results that the vortex on the roof of the obstacle was an extension of the vortex that was created downstream.