Higher Terminal Velocity Research Articles

Harpoon technology development for the active removal of space debris

This paper presents the results of preliminary empirical testing and numerical modelling carried out to demonstrate the effectiveness of using a harpoon in an ADR application. Empirical testing involving the impact of blunt and conical shaped steel tips into 3mm Al plate showed that the ballistic limit varies in proportion to the tip circumference, with conical shapes resulting in a higher relative ballistic limit due to the additional energy required for petaling. The creation of secondary debris was also monitored. It was found that blunt shapes created a plug during penetration as a result of shearing around the periphery of the projectile, whilst conical tips resulted in minor spalling and fragmentation. Preliminary oblique impact testing with conical and blunt tips showed that the ballistic limit increases with obliquity at a greater rate for blunt tips than conical ones.Impact testing of 3mm Al plate with conical projectiles at low temperatures showed a more brittle fracture mode when compared with targets impacted at room temperature. As such, the fragmentation and spalling evident in room temperature targets was absent. The energy required to perforate the cooled plates also increased.Impact testing of Al panel obstructed with fixed heat pipes showed that the harpoon could successfully penetrate a target panel with such an obstruction due to shearing of the pipe flange.Testing of two lock on mechanisms showed that both a spring activated and integrated toggle could reliably open upon impact. This testing also used a tensile testing machine to show that both designs could withstand the force expected during deorbiting manoeuvres after impact with Al H/C panels.A parametric simulation comparing the diameter of conical tips with ballistic limits showed a good agreement with the predictions of De Marre’s formula for normal impact. This suggests that the ballistic limit of plates impacted by conical projectiles can be successfully extrapolated with limited experimental data. A SPH solver, which is better suited to modelling impact into brittle materials, was used to model impact into CFRP targets. This showed that the debris formed by conical tips was less coherent and had a higher terminal velocity than that produced by blunt tips. As a result of conducting these simulations, it was shown that numerical modelling can provide an accurate prediction of impact speeds required for a conical projectile to perforate Al plate, excellent prediction of impact failure modes, and good predictions of debris likely to be created during the impact process.Finally, preliminary studies of harpoon impact into low mass targets with up to 3 DOF showed that the harpoon was still able to penetrate such targets under simulated μ-gravity conditions.

Physical Properties and Concentration of Grain Dust Generated from Post-Harvest Processing of Rough Rice

<abstract><title><italic>Abstract.</italic></title> This research focuses on estimation of the particle size, concentration level, and terminal velocity of grain dust produced during post-harvest processing of rough rice in order to provide critical information for efficient dust collector design. Dust concentration levels were relatively low at indoor processing units, with pre-cleaners, brown rice processes, and milled rice processes indicating 1.3 to 7.7 mg m^-3. Outdoor processing units, such as receiving, drying, and storage, indicated higher dust concentration levels (5.1 to 9.1 mg m^-3). A model of the terminal velocity of grain dust was introduced by two linear regression equations: one for particles smaller than 200 μm, and the other for particles between 200 and 2,000 μm. Coefficients of determination were 0.9266 and 0.9770, respectively, indicating the significance of the model. The particles smaller than 200 μm showed relatively lower terminal velocity (0.15 to 0.26 m s^-1), while the larger particles (200 to 2,000 μm) showed relatively higher terminal velocity (0.9 to 2.2 m s^-1).

Effect of CaO Addition on Iron Recovery from Copper Smelting Slags by Solid Carbon

We investigated the effect of flux (lime) addition on the reduction behavior of iron oxide in copper slag by solid carbon at 1773 K (1500 °C). In particular, we quantified the recovery of iron by performing typical kinetic analysis and considering slag foaming, which is strongly affected by the thermophysical properties of slags. The iron oxide in the copper slag was consistently reduced by solid carbon over time. In the kinetic analysis, we determined mass transfer coefficients with and without considering slag foaming using a gas holdup factor. The mass transfer of FeO was not significantly changed by CaO addition when slag foaming was ignored, whereas the mass transfer of FeO when slag foaming was considered was at a minimum in the 20 mass pct CaO system. Iron recovery, defined as the ratio of the amount of iron clearly transferred to the base metal ingot to the initial amount of iron in the slag phase before reduction, was maximal (about 90 pct) in the 20 mass pct CaO system. Various types of solid compounds, including Mg2SiO4 and Ca2SiO4, were precipitated in slags during the FeO reduction process, and these compounds strongly affected the reduction kinetics of FeO as well as iron recovery. Iron recovery was the greatest in the 20 mass pct CaO system because no solid compounds formed in this system, resulting in a highly fluid slag. This fluid slag allowed iron droplets to fall rapidly with high terminal velocity to the bottom of the crucible. A linear relationship between the mass transfer coefficient of FeO considering slag foaming and foam stability was obtained, from which we concluded that the mass transfer of FeO in slag was effectively promoted not only by gas evolution due to reduction reactions but also by foamy slag containing solid compounds. However, the reduced iron droplets were finely dispersed in foamy and viscous slags, making actual iron recovery a challenge.

Mixing and segregation of binary oxygen carrier mixtures in a cold flow model of a chemical looping combustor

In a typical chemical looping combustion process, the oxygen for fuel combustion is supplied by circulating metal based oxygen carriers between two interconnected fluidised bed reactors. The redox characteristics of oxygen carriers and hence the overall performance of the process can be significantly improved by utilising binary mixtures of oxygen carrier particles. The full potential of such multi-species particle systems however can be only realised when particles segregation is minimised. This study is concerned with gaining an understanding of the mixing and segregation behaviour of binary mixtures of oxygen carrier particles with different sizes and densities in a cold flow model representing a 10kWth chemical looping combustor. The hydrodynamics of such systems were investigated and compared with a typical chemical looping combustion process where single species are used. This was followed by investigating the solids mixing and segregation behaviour in terms of segregation intensity and species weight percentage at each reactor as a function of operating parameters. It was shown that increasing the total solid inventory, particle terminal velocity ratio, composition, and air reactor superficial velocity increases the riser pressure, solid circulation rates, and riser solid holdup. Mixing and segregation regimes of the fuel reactor and the component segregation between the two reactors were also mapped. The results showed that, for mixtures of species with low terminal velocity to high terminal velocity ratios of greater than 0.7, a good mixing in the fuel reactor can be achieved by maintaining the superficial gas velocity to the mixture minimum fluidisation velocity ratio above 5. For the tested conditions, the component segregation between the two reactors was avoided by maintaining the ratio of the riser superficial velocity to the terminal velocity of the species with a high terminal velocity between 1.25 and 2.

Can We Distinguish Plant Species that are Rare and Endangered from Other Plants Using Their Biological Traits?

Understanding the factors responsible for species rarity is crucial for effective species conservation. One possible approach to obtaining information about causes of species rarity is to compare rare and common species. We analyzed the biological and ecological traits of critically endangered (CR) plant species of the Czech Republic. We compared the vegetative, generative and ecological traits of CR species with: i) common closely related species (a form of phylogenetic correction), ii) common closely related species sharing the same habitat (i.e., excluding pairs not sharing the same habitat, because many differences in species traits can be caused by adaptation to a specific habitat type) and iii) all plants of the Czech Republic. Information about species traits was mainly obtained from literature and databases. Comparison with common closely related species showed that CR species are smaller, flower for shorter periods, and have higher proportions of self-compatibility and higher terminal velocities. CR species also differ in their mode of dispersion, and their ecology and distribution. Comparison with species from the same habitat gave similar results. Comparison with the whole flora produced slightly different results, with additional differences in pollination mode and seed mass. The results of all three types of comparison suggest that critically endangered species of the Czech Republic are small, competitively inferior species, with some differences in the generative part of their life cycle, and occur mainly in open, unproductive habitats.

Deposition of micrometer particles in pulmonary airways during inhalation and breath holding

We investigated how breath holding increases the deposition of micrometer particles in pulmonary airways, compared with the deposition during inhalation period. A subject-specific airway model with up to thirteenth generation airways was constructed from multi-slice CT images. Airflow and particle transport were simulated by using GPU computing. Results indicate that breath holding effectively increases the deposition of 5μm particles for third to sixth generation (G3–G6) airways. After 10s of breath holding, the particle deposition fraction increased more than 5 times for 5μm particles. Due to a small terminal velocity, 1μm particles only showed a 50% increase in the most efficient case. On the other hand, 10μm particles showed almost complete deposition due to high inertia and high terminal velocity, leading to an increase of 2 times for G3–G6 airways. An effective breath holding time for 5μm particle deposition in G3–G6 airways was estimated to be 4–6s, for which the deposition amount reached 75% of the final deposition amount after 10s of breath holding.

Fractionation of Distillers Dried Grains with Solubles (DDGS) Through a Narrowing of Particle Size Distribution Followed by Aspiration

Distiller's dried grains with solubles (DDGS) may have more value and utility if they can be separated into high protein and high fiber fractions. A variety of such separation processes have been proposed; two of the most promising processes involve three screening and three air classification unit operations. In the present study, an alternative process involving fewer unit operations is demonstrated. DDGS are subjected to a single screening, and the oversize particles are processed in a mill setup so that it narrows the particle size distribution of the oversize fraction. The milled DDGS is then processed in an air classification device known as an aspirator, which separates it into high and low terminal velocity fractions. The combination of the undersize fraction and the low terminal velocity fraction were substantially enriched in protein. The separation achieved by this process compares favorably to other reported processes while being less complex.

MASSIVE MOLECULAR OUTFLOWS AND NEGATIVE FEEDBACK IN ULIRGs OBSERVED BY HERSCHEL -PACS

Mass outflows driven by stars and active galactic nuclei are a key element in many current models of galaxy evolution. They may produce the observed black hole-galaxy mass relation and regulate and quench both star formation in the host galaxy and black hole accretion. However, observational evidence of such feedback processes through outflows of the bulk of the star forming molecular gas is still scarce. Here we report the detection of massive molecular outflows, traced by the hydroxyl molecule (OH), in far-infrared spectra of ULIRGs obtained with Herschel-PACS as part of the SHINING key project. In some of these objects the (terminal) outflow velocities exceed 1000 km/s, and their outflow rates (up to ~1200 M_sol/yr) are several times larger than their star formation rates. We compare the outflow signatures in different types of ULIRGs and in starburst galaxies to address the issue of the energy source (AGN or starburst) of these outflows. We report preliminary evidence that ULIRGs with a higher AGN luminosity (and higher AGN contribution to L_IR) have higher terminal velocities and shorter gas depletion time scales. The outflows in the observed ULIRGs are able to expel the cold gas reservoirs from the centres of these objects within ~1E6-1E8 years.

Modeling of solids segregation in circulating fluidized bed boilers

Segregation always occurs in a circulating fluidized bed (CFB) because of the wide distribution of particle size and density of the bed material. Terminal velocity has a significant influence on solids segregation; thus, it is convenient to describe the segregation tendency using single particle terminal velocity u t. This paper proposes a segregation model in CFB boilers based on the Cell Model. In each cell along the riser, varied-sized particles have different tendencies toward segregation; finer particles are carried out more easily, while coarser ones tend to sink into the cell. It is assumed that the average terminal velocity $$ \overline {u_t } $$ , corresponding to the mean particle size in the cell, has a segregation index of ξ = 1.0 as the reference point. The segregation index of particles with higher terminal velocity is lower than 1.0, while that for finer particles is larger than 1.0. The empirical formulae of segregation parameters, namely ξ0 and k 1, are derived by optimizing experimental data in published literature. The test result of ash size distribution in a 220 t/h CFB boiler validates the reasonableness of the model.

Wolf–Rayet optically thick winds with Alfvén waves

The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.

Entry, descent, and landing scenario for the mars exploration rover mission

In January 2004, the Mars Exploration Rover (MER) mission successfully landed two landers on the surface of Mars. Both landers delivered a rover to the surface using an entry, descent, and landing (EDL) scenario based on Mars Pathfinder heritage. However, the entry conditions and environments were different from that of Mars Pathfinder. Unique challenges were present due to the entry differences of a heavier entry mass, less dense atmosphere, and higher surface landing site altitude. These differences resulted in a higher terminal velocity and less time for performing all the EDL events as compared to Mars Pathfinder. As a result of these differences, modifications were made to the MER EDL systems to safely deliver the rovers to the surface of Mars. An overview of the design modifications made to the MER EDL system compared to MPF is described.

Modeling air-mediated dispersal of spores, pollen and seeds in forested areas

Dispersal of airborne spores, pollen and seeds is important for various ecological and biological processes, and therefore modeling tools are needed in order to predict the dispersal patterns of these particles. In this study, we use a Lagrangian stochastic (LS) modeling approach to describe airborne particles dispersal in the atmospheric boundary layer. The LS dispersal model is extended to include non-Gaussian turbulence in the upper parts of the atmospheric boundary layer, as well as the reduction of the autocorrelation time in trajectories due to the high terminal velocity of particles. The sensitivity of particle dispersal on biological and atmospheric factors is assessed by simulating dispersal patterns under varying environmental conditions. Similarly, the level of needed model complexity for describing the particle dispersal is examined. Our particle dispersal simulations suggest that the level of model complexity and accuracy needed in the description of biological and atmospheric factors depends on the particle size and the distance and time-scale over which the particle dispersal is monitored. More simplification is justified for light particles, whereas heavy particles require more accuracy in modeling. For example, we found out that the local dispersal of light particles is hardly affected by the atmospheric stability whereas it has a strong effect on the dispersal of heavy particles. Based on our simulations, we developed guidelines for modeling airborne particle dispersal. Together with the detailed description of the LS dispersion model and its parameterization throughout the atmospheric boundary layer, these can serve as basis for various particle dispersal studies and help ecologists and biologists not so familiar with meteorological modeling tools to apply the LS model for spore, pollen and seed dispersal.

Flow Simulation in Bubble Columns in Regard to Bubble Coalescence and Break-up Utilizing LES and DEM

Turbulent flow simulations in bubble columns are performed in the Euler–Lagrange approach. In the simulation, a large eddy simulation (LES) model is used as a turbulence model. In addition, bubble contact is considered by using a distinct element model (DEM), and bubble coalescence is taken into consideration as well as bubble break-up by solving a coalescence model based on the contact time and coalescence time. Furthermore, a new bubble-fluid drag model depending on distances among bubbles is introduced in DEM simulations, and it is shown that bubble clusters with high terminal velocities may play an important role for high superficial gas velocities. The present models are next applied to several simulations for bubble columns, and the comparison of the computational results with experimental data shows their effectiveness.

Variable Winds in Early-B Hypergiants

AbstractEarly-B hypergiants belong to the most luminous stars in the Universe. They are characterized by high mass-loss rates (Ṁ ≈ 10−5Mʘyr−1) and low terminal wind velocities (v∞ʘ400 kms−1) implying very dense winds. They represent a short-lived evolutionary phase and are of particular interest for evolutionary theories of massive stars with mass loss. Due to their high luminosity they play a key role in connection with the “wind momentum - luminosity relation”. Among the main interesting characteristics of early-B hypergiants are the various kinds of photometric and spectroscopic variations. In several recent campaigns our group has performed extensive high dispersion spectroscopy of galactic early-B hypergiants with our fiber-fed echelle spectrograph FLASH/HEROS at the ESO-50 cm telescope. The main outcome was that their dense winds behave hydrodynamically differently to the less luminous supergiants of comparable spectral type. Outwardly accelerated propagating discrete absorption components of the P Cyg-type lines are the typical features rather than rotationally modulated line profile variations. These discrete absorptions could be traced in different spectral lines from photospheric velocities up to 75% of the terminal velocity. The stellar absorption lines show a pulsation-like radial velocity variability pattern lasting up to two weeks as the typical time scale. The radius variations connected with this pulsation-like motions are correlated with the emission height of the P Cyg-type profiles.

The impact of cloud particle gravitational settling on soluble trace gas distributions

The effect of gravitational settling of cloud droplets and ice particles on the tropospheric distributions of soluble trace gases is examined, focusing in particular on nitric acid and hydrogen peroxide. For this study, we separate cloud condensate into two classes: large (rain, snow and graupel) and small (cloud water and cloud ice). The first class has typical fall speeds of several m/s and frequently reaches the ground. The redistribution and loss of soluble trace gases due to this type of precipitation is generally already included in global photochemical models (although the manner in which this is done varies widely between models). However, an additional redistribution can result from the gravitational settling of the second class, small cloud droplets or ice particles, whose mean fall speeds can reach 1 m/s. When we include this additional downward flux term in our model simulations, we find a significant impact on the distributions of the soluble trace gases HNO 3 and H 2 O 2 . In the upper troposphere, the settling of ice particles leads to a strong reduction in the mixing ratios of these gases, due to the relatively high terminal velocities of ice crystals (generally > 10 cm/s). The impact of cloud droplet settling in the lower troposphere is also found to be significant in some regions, though it is generally smaller due to the slower settling velocities of liquid droplets; in addition, the settling loss in the lower troposphere is computed to be frequently overwhelmed by the supply of HNO 3 and H 2 O 2 via sublimating hydrometeors settling in from above. Our findings may help explain the overestimate of free tropospheric HNO 3 found in several global photochemical modeling studies. The reductions computed for HNO 3 and H 2 O 2 also have an effect on the distributions of related trace gases, such as NO x and OH. Gravitational settling might also directly affect other soluble trace gases and aerosols. There are substantial uncertainties involved in computing the global impact of gravitational settling, such as the uptake of gases and aerosols onto and into ice particles and the high degree of variability and complexity of clouds. Results of sensitivity studies examining some of these uncertainties are presented. Even employing a low-end settling velocity for ice particles (5 cm/s) and a minimum ice uptake efficiency for HNO 3 based on laboratory data, we still compute a notable impact on the upper tropospheric HNO 3 and H 2 O 2 distributions. DOI: 10.1034/j.1600-0889.1998.t01-2-00005.x

Simultaneous internal/external flow calculation of a solid fuel ramjet projectile: a design analysis

SFRI has been regarded as a prime mode of secondary propulsion which enables the projectile to achieve a higher terminal velocity. Geometry of SFRJ is quite simple due to the lack of turbomachinery that conventional jet engines need. The complete internal/external flow field of an SFRJ-TGTR projectile at a cruising Mach number is calculated by an unstructured triangular compressible RANSE solver. To complete the analysis, single-component fuel combustion is added in the combustor flow calculation. A commercial CFD package is used with structured rectangular meshes for such computation. The results from the two computations are compared with existing computational and experimental data for validation. The design parameters like thrust, total pressure loss, inlet and nozzle efficiencies and drag coefficient are derived from the detailed flowfield data. Different values of cruising Mach number and nozzle throat area have been tried as a preliminary design procedure. Change in the nozzle throat area directly affects the inlet flow, because the internal flow is mostly subsonic and is linked directly to the nozzle flow.

The impact of cloud particle gravitational settling on soluble trace gas distributions

The effect of gravitational settling of cloud droplets and ice particles on the tropospheric distributions of soluble trace gases is examined, focusing in particular on nitric acid and hydrogen peroxide. For this study, we separate cloud condensate into two classes: large (rain, snow and graupel) and small (cloud water and cloud ice). The first class has typical fall speeds of several m/s and frequently reaches the ground. The redistribution and loss of soluble trace gases due to this type of precipitation is generally already included in global photochemical models (although the manner in which this is done varies widely between models). However, an additional redistribution can result from the gravitational settling of the second class, small cloud droplets or ice particles, whose mean fall speeds can reach 1 m/s. When we include this additional downward flux term in our model simulations, we find a significant impact on the distributions of the soluble trace gases HNO3 and H2O2. In the upper troposphere, the settling of ice particles leads to a strong reduction in the mixing ratios of these gases, due to the relatively high terminal velocities of ice crystals (generally > 10 cm/s). The impact of cloud droplet settling in the lower troposphere is also found to be significant in some regions, though it is generally smaller due to the slower settling velocities of liquid droplets; in addition, the settling loss in the lower troposphere is computed to be frequently overwhelmed by the supply of HNO3 and H2O2 via sublimating hydrometeors settling in from above. Our findings may help explain the overestimate of free tropospheric HNO3 found in several global photochemical modeling studies. The reductions computed for HNO3 and H2O2 also have an effect on the distributions of related trace gases, such as NOx and OH. Gravitational settling might also directly affect other soluble trace gases and aerosols. There are substantial uncertainties involved in computing the global impact of gravitational settling, such as the uptake of gases and aerosols onto and into ice particles and the high degree of variability and complexity of clouds. Results of sensitivity studies examining some of these uncertainties are presented. Even employing a low-end settling velocity for ice particles (5 cm/s) and a minimum ice uptake efficiency for HNO3 based on laboratory data, we still compute a notable impact on the upper tropospheric HNO3 and H2O2 distributions.

In-situ measurement of viscosity and density of carbonate melts at high pressure

We present the first measurements of carbonate melt viscosity and density at mantle pressures and temperatures and provide important data for modelling carbonatite behaviour within the mantle. Synchrotron radiation was used to observe falling spheres with high atomic number in situ, allowing precise determination of high terminal velocities over short fall distances. The measured viscosities of 1.5 (5) × 10 −2 to 5 (2.5) × 10 −3 pas are the lowest of any known terrestrial magma types and these measurements extend the region of measurable viscosity at high pressure by at least 2 orders of magnitude. Accurate measurements of K 2Ca(CO 3) 2 melt density were performed at atmospheric pressure: ϱ(g/cm 3) = 2.39(2) − 3.85(15) × 10 −4 T (°C) and are in complete agreement with the predictions of Wolff (1995). The high-pressure density measurements also agree well with molecular dynamics predictions of carbonate melt compressibility.

Airplane Crash Traumatologic Findings in Cases of Extreme Body Disintegration

A one-engined light aircraft struck the ground at high terminal velocity, producing a large impact crater. The captain and the five passengers were killed, their bodies being dismembered into several hundreds of mostly small tissue pieces. Besides identification, the pathologic investigation dealt with the morphologic features of high-speed impact trauma. In detail, the following peculiarities were found: detachment of the skin with typically sharp-edged margins and sometimes striaelike tears due to overstretching, intracutaneous hemorrhages according to the pleats of the clothing, a strikingly good preservation of the long peripheral nerves as a consequence of their especially high resistance to tearing, thin-layer hemorrhages under articular cartilages, separation of the penis in combination with detachment of its skin and hematoma of the glans or of the prepuce, subepicardial and subendocardial hemorrhages, petechiae of the conjunctivae and of the serous membranes (for example, parietal pleura), and petechial hemorrhages in the mucous membranes of larynx and trachea. Because of immediate circulatory arrest, these numerous hemorrhages must be attributed to mere local tissue bruising at the moment of impact.

Nitrogen abundances in carbon-rich stars that are progenitors to planetary nebulae

Published data for carbon stars losing more than 10 to the -6th solar mass/yr in the neighborhood of the sun are examined. The stars with higher terminal velocities have significantly higher fluxes of the J = 1-0 emission line of HCN relative to their infrared continuum emission at 60 microns. It is argued that this result is probably a reflection of a higher nitrogen abundance by perhaps a factor of 10 in these outflows. Such a high nitrogen abundance is consistent with the hypothesis that the high terminal velocity carbon stars have more massive main-sequence progenitors than average; these high terminal velocity carbon stars may, themselves, be the progenitors of type I planetary nebulae which display enhanced nitrogen abundances.