Debris Velocity Research Articles

A Two Micron All‐Sky Survey View of the Sagittarius Dwarf Galaxy. IV. Modeling the Sagittarius Tidal Tails

M giants recovered from the Two Micron All-Sky Survey have recently been used to map the position and velocity distributions of tidal debris from the Sagittarius (Sgr) dwarf spheroidal galaxy around the entire Galaxy. We compare this data set to both test-particle orbits and N-body simulations of satellite destruction run within a variety of rigid Milky Way potentials, and we find that the mass of the Milky Way within 50 kpc of its center should be × 1011 M☉ in order for any Sgr orbit to simultaneously fit the velocity gradient in the Sgr trailing debris and the apocenter of the Sgr leading debris. Orbital pole precession of young debris and leading debris velocities in regions corresponding to older debris provide contradictory evidence in favor of oblate/prolate Galactic halo potentials, respectively, leading us to conclude that the orbit of Sgr has evolved over the past few gigayears. In light of this discrepancy, we consider constraints from only the younger portions of the debris within three models of the flattening of the Galactic potential [q = 0.90 (O), 1.0 (S), and 1.25 (P), i.e., oblate, spherical, and prolate] in our further N-body simulations. On the basis of the velocity dispersion and width along the trailing tidal stream, we estimate the current bound mass of Sgr to be MSgr = × 108 M☉ independent of the form of the Galactic potential; this corresponds to a range of mass-to-light ratios (M/L)Sgr = 14-36(M/L)☉ for the Sgr core. Models with masses in this range best fit the apocenter of leading Sgr tidal debris when they orbit with a radial period of roughly 0.85 Gyr and have perigalactica and apogalactica of about 15 and 60 kpc, respectively. These distances scale with the assumed distance to the Sgr dwarf and the assumed depth of the Galactic potential. The density distribution of debris along the orbit in these models is consistent with the M giant observations, and debris at all orbital phases in which M giants are obviously present is younger (i.e., was lost more recently from the satellite) than the typical age of a Sgr M giant star.

The effect of simulated hypervelocity space debris on polymers

Space debris population in low Earth orbit has been increasing constantly with the increase in spacecraft missions. Hypervelocity space debris impacts limit the functionality of polymeric outer surfaces and, in extreme cases, might cause a total loss of a spacecraft. In this work, the fracture of Kapton films by ultrahigh velocity impacts was studied. A laser-driven flyer ground simulation system was used to accelerate aluminum flyers to impact velocities as high as 2.9 km/s against polymer films with different thicknesses. Scanning electron microscopy was used to characterize the fracture morphology. Impact effects on the internal structure of the polymer were studied by means of X-ray microtomography. It was found that with an increase in debris velocity, a ductile-to-brittle transition occurred. However, fractures created by impacts at velocities above 1.7 km/s showed central impacts regions, which experienced the highest strain rate and were of ductile-type fracture, while the outer regions, which experienced a lower strain rate, failed through brittle cracking. A model explaining this phenomenon, based on the temperature gradient developed within the impacted region during collision, is presented.

Modeling Concrete Masonry Walls Subjected to Explosive Loads

Concrete masonry unit walls subjected to blast pressure were analyzed with the finite element method, with the goal of developing a computationally efficient and accurate model. Wall behavior can be grouped into three modes of failure, which correspond to three ranges of blast pressures. Computational results were compared to high-speed video images and debris velocities obtained from experimental data. A parametric analysis was conducted to determine the sensitivity of computed results to critical modeling values. It was found that the model has the ability to replicate experimental results with good agreement. However, it was also found that, without knowledge of actual material properties of the specific wall to be modeled, computational results are not reliable predictors of wall behavior.

Reach‐scale channel geometry of a mountain river

AbstractMountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall. Nonetheless, adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers. Mountain rivers can differ in that imposed reach‐scale gradient is an especially important control on reach‐scale channel characteristics, as indicated by examination of North St Vrain Creek in Colorado.North St Vrain Creek drains 250 km2 of the Rocky Mountains. We used 25 study reaches within the basin to examine controls on reach‐scale channel geometry. Variables measured included channel geometry, large woody debris, grain size, and mean velocity. Drainage area at the study reaches ranged from 2·2 to 245 km2, and gradient from 0·013 to 0·147 m m−1.We examined correlations among (1) potential reach‐scale response variables describing channel bankfull dimension and shape, hydraulics, bedform wavelength and amplitude, grain size, flow resistance, standard deviation of hydraulic radius, and volume of large woody debris, and (2) potential control variables that change progressively downstream (drainage area, discharge) or that are likely to reflect a reach‐specific control (bed gradient). We tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels.Results from simple linear regression analyses indicate that most response variables correlate best with gradient, although channel width and width/depth ratio correlate best with discharge. Multiple regression analyses using Mallow's Cp selection criterion and log‐transformation of all variables produced similar results in that most response variables correlate strongly with gradient. These results suggest that the hypothesis is partially supported: channel bed gradient is likely to be a good predictor for many reach‐scale response variables along mountain rivers, but discharge is also an important predictor for some response variables. Copyright © 2004 John Wiley & Sons, Ltd.

An analytical solution for unconfined, unsteady, inviscid jets; with applications to penetration problem debris cloud formation

Here we derive a closed form analytical solution for an unsteady inviscid jet using linearized, acceleration potential theory and classical analytical methods. Use is made of both the Laplace transformation and reduction to a self-similar form to solve the associated governing equations. The convolution theorem provides a closed form mapping from the transformed plane to the real plane. The streamwise diffusion term, e.g., χχ is shown to be second order and is neglected. This analytical model is used to estimate the debris cloud geometry and velocity field as a function of location and time. Though formal solutions of the potential equation yield good results for debris cloud expansion near the initial impact point, χ ≪ 1, the debris cloud expansion front behavior is not recovered. The steady state eigenfunction expansion solution is used to extend the unsteady solution in an approximate manner. The extended solution retains physically correct expansion behavior for χ ≪ 1 but also provides a reasonable model near the debris cloud expansion front. Since debris cloud dynamics and witness plate impact are readily obtained from experimental observations, this model provides a simple, but useful supplement to conventional hydrocode simulation of impact and penetration phenomenon.

Maximum Impact Force of Woody Debris on Floodplain Structures

We collided woody debris (i.e., logs) with structures using flume and test basin laboratory facilities to investigate the maximum impact force that floodplain structures are exposed to from floating woody debris. The tests also investigated the influence of collision geometry, determined by the debris orientation on impact, on the maximum impact forces. We reviewed the three approaches that represent the existing guidance for estimating maximum impact forces. Each approach estimates the maximum impact force based on the debris velocity and mass. We show that all the existing approaches can be derived from a single-degree-of-freedom model of the collision and can be considered to be equivalent. The laboratory data show that the maximum impact force was associated with a log striking a rigid structure with its end. Oblique and eccentric collisions reduced the maximum impact load in a predictable and consistent manner. The approach we refer to as contact stiffness, a linear, one-degree-of-freedom model with no damping, was able to reproduce the laboratory results over the entire range of data, with an effective contact stiffness of 2.4 MN/m.

Gas Transport and Density Control in the HYLIFE Heavy-Ion Beam Lines

The effective propagation and focusing of heavy-ion beams in the final-focus magnet region of inertial fusion target chambers require controlling the background gas density and pressure in the beam tubes. Liquid vortexes will coat the inside of the tubes next to the beam ports and will help eliminate the need for mechanical shutters to mitigate the venting of target chamber background gas into the final-focus magnet region. Before the neutralizing region, the beam space charge is high, and ablation and target debris deposition in the final-focus magnet region may cause voltage breakdown. Previous studies focused on evaluating the amount of target chamber debris reaching the entrance of the beam ports. The TSUNAMI code has now been used to assess the density, temperature, and velocity of the vortex debris transported ~3 m up the beam tubes and reaching the final-focus magnet region, assuming that the liquid vortexes are perfectly absorbing surfaces. To further mitigate debris deposition in the final-focus magnet region, and prevent voltage breakdown, a “magnetic shutter” has been envisaged to divert the debris out of the final-focus region. This shutter will prevent the hot ablation debris from reaching the magnet region and, coupled to some ionizing scheme, will conveniently suppress early ingression of debris into the final-focus magnet region.

HABITAT ASSOCIATIONS WITH UPLAND STREAM FISH ASSEMBLAGES IN BANKHEAD NATIONAL FOREST, ALABAMA

Fishes and habitat were sampled at nine sites in the Sipsey Fork River drainage in Bankhead National Forest, Alabama. Stream width, depth, current velocity, substrate type, bank height and amount of large woody debris (LWD) were measured at each site to test for association of these habitat variables with upland stream fish assemblages. Regression of habitat variables onto species richness indicated that only bank height was significantly associated with species richness in our study area. The lack of habitat associations with species richness seemingly contradicts findings by several previous investigators working in lowland streams. The availability of large substrate and both deep and shallow habitats at all sites may have reduced the observed association of these variables and LWD with stream fish assemblages. Stream width and current velocity, though not significant, did show strong positive correlations with species richness. The significant association between high banks and species richness may reflect a more intact riparian zone due to inaccessibility of streams in gorges.

Radiation-driven shock and debris propagation down a partitioned pipe

Two experiments have been performed to measure the effects of pulsed radiation loads on the front of small tubular structures, using as an energy source the X-ray fluence produced by a Z-pinch at the Sandia National Laboratories Z Facility. The project had two major goals: to establish the feasibility of using the Z machine to study the phenomenology associated with debris generation and propagation down tubular structures with partitions; and to use the resultant experimental data to validate numerical hydrocodes (shock physics codes) so that we have confidence in their use in analyzing these types of situations. Two tubular aluminum structures (5 and 10 cm long and 1 cm inside diameter) were prepared, with aluminum partitions located at the front, halfway down the pipe, and at the rear. Interferometry (VISARs) provided multiple velocity histories for all of the partitions. In both experiments, the first barrier, which was exposed directly to the x-ray fluence, was launched into the pipe at a velocity of ∼2 km/s, accelerating to give a mean velocity of ∼2.6 km/s. Loss of plate integrity is inferred from the dispersed launch of the second partition at ∼1 km/s. Wall shocks propagating at 4.5 km/s were inferred. Post-test metallography showed evidence of melting and partial vaporization of the plates, and turbulent mixing with material from the walls. Calculations qualitatively agree with the observed results, but slightly overpredict debris velocity, possibly due to overestimates of total energy fluence. An application for this work is the study of techniques for line-of-sight shock and debris mitigation on high-power pulsed power facilities such as Z and its follow-on machines.

Debris Effects on EHL Contact

A model was developed to study the effects of a rigid debris on elastohydrodynamic lubrication of rolling/sliding contacts. In order to achieve the objectives the time dependent Reynolds equation was modified to include the effects of an ellipsoidal shaped debris. The modified time dependent Reynolds and elasticity equations were simultaneously solved to determine the pressure and film thickness in EHL contacts. The debris force balance equation was solved to determine the debris velocity. The model was then used to obtain results for a variety of loads, speeds, and debris sizes. The results indicate that the debris has a significant effect on the pressure distribution and causes a dent on the rolling/sliding bounding surfaces. Depending on the size and location of the debris the pressure generated within the contact can be high enough to plastically deform the bounding surfaces. Debris smaller than the minimum film thickness do not enter the contact and only large and more spherical debris move toward the contact. [S0742-4787(11)00501-7]

A DISCUSSION ON MECHANISM OF VISCOUS DEBRIS FLOW VIA SURFACE VELOCITY ANALYSIS

The viscous debris flow occurs frequently in the southwest of China. This natural event inflict damage on people or property. For the purpose of mitigation planning, it need to elucidate the mechanism of viscous debris flow. And then, it is necessary to analyze the motion of it.On July 24th, 1997, a viscous debris flow was recorded with a digital video camera in JiangJia Gully, Dongchuan City, Yunnan Province, China. These images were saved as files formatted as BMP by computer interface board. Since the absolute coordinates of targets which were near the channel were surveyed by an infrared-light distance meter, the distance of a pixel of images about motion of debris flow is estimated in x and y direction, respectively. A new image analysis method, the auto-correlation method, is used to analyze the surface velocity of debris flow.In this paper, the two results of image analysis are shown: one is the mean surface velocity change of central of several surges, another is the change of surface velocity vector in a fixed cross section. According to these results and the field experiment, it could be concluded that viscous debris flow is a kind of complex flow. It is a turbulence in the front of a surge; in the middle of a surge, it could be considered as a kind of cohesive flow; and due to the cohesion or yield strength, the flow almost stops in the end of a surge.

Model for ballistic fragmentation and behind-armor debris

The fracture of the target and projectile during normal penetration is described using a model of chaotic disintegration modifying the theory of chaotic disintegration of liquids. The radius of the locally smallest fragment is calculated equating its kinetic energy of deformation with its surface energy of fracture. The probability of lacunae opening in the target and projectile materials increases near the target/projectile interface. The percolation threshold for this probability determines the boundary of the fractured zone. When this fractured zone reaches the rear surface of the target the fragments can leave it. Mass distribution of the fragments was calculated with the help of percolation theory. Then, the shape of the debris cloud and the direction, velocity and range of its propagation are calculated to estimate vulnerability behind the perforated target. The calculations were compared with results of normal impact experiments performed with tungsten sinter alloy rods ( D=20 mm, L/ D=6) against 40 and 70 mm rolled homogeneous armor (RHA) at an impact velocity of 1700 m/s [1,2]. For observation of the bulging, breakup and fragmentation of the bulge as well as debris cloud formation and expansion, flash X-ray and laser stroboscope techniques have been applied. From the X-ray photographs and soft recovery tests the shape of the debris cloud and velocity field of the fragments as well as the fragment number and mass distributions have been determined, respectively. The calculations predict well the experimental data.

Temperature, Size, and Energy of the Shoemaker–Levy 9 G-Impact Fireball

The fortunate position of the Galileo spacecraft provided us with a unique opportunity to directly observe the Shoemaker–Levy 9 impacts as they occurred on the far side of Jupiter, and we present observations of the G fireball obtained by the Near Infrared Mapping Spectrometer (NIMS). These measurements were performed using 10 spectral bands, 4 representing continua and spanning the wavelength range 1.84 to 4.38 μ. Fireball signals were evident for up to 80 sec, with the time of intensity maxima and duration being greater for longer wavelengths. Color temperatures and effective emitting areas were estimated by fitting blackbody functions at the four continuum wavelengths. Good blackbody fits were found, and their intensities at shorter wavelengths show excellent agreement with the Galileo Photopolarimeter/Radiometer measurements. Temperatures near the beginning are above 3000 K, decreasing to ∼1000 K after 1 min. The corresponding areas range from 400 to 20,000 km2. The effective diameter of the luminous fireball shows approximately linear time variation, at least for the first 45 sec. From the temperature–effective diameter relation we find an adiabatic coefficient of γ = 1.2 ± 0.1, much as expected from theoretical considerations. The luminosity, when integrated over the period of observations and assuming a Stephan—Boltzmann radiator, gives an above-cloud radiative energy loss of 0.48 ± 0.13 × 1025erg.As a conceptual aid, we developed a simple, heuristic theory of the fireball phenomenon, considering the penetrating fragment's wake (termed debris channel) to consist of high-temperature jovian and cometary material, which undergoes radial expansion and acceleration back along the wake axis. The outer layer of the material in this debris channel is presumed optically thick, radiating as a blackbody to produce the observed emissions (we speculate that the opacity is produced by condensed refractories such as MgO and SiO2, probably containing impurities). One-dimensional, variable-area axial flow of a radiating, compressible, inviscid gas is concurrently solved with the radial shock motion occurring in the non-axisymmetric atmosphere. We calculate debris surface radii and velocities using Sedov's theory for line explosions. The assumed initial debris surface temperature is consistent with entry shock heating. Our simple model shows good agreement with the observations, for both the temperature and luminous area, and suggests that the diameter of the G fragment (assumed spherical and of unit density) was 300 ± 100 m, with a nominal energy of 2.5 × 1026erg. The measured luminous energy is within a factor of 2 of that predicted for the nominal impactor size, whereas the amount of water in the splashback, as measured by G. L. Bjorakeret al. (1996,Icarus121,411–421) and Th. Encrenazet al., (1997,Planet. Space Sci.) agrees to a factor of 3 with the model results; however, the large CO abundance obtained by E. Lellouchet al. (1995,Nature373,592–595) is inconsistent with the suggested size. This diameter estimate must be considered provisional and probably a lower limit; precise estimates require comparison of the measurements with comprehensive numerical simulations, which we encourage.

The Munich Dust Counter on board the MUSES-A mission: Calibration of impacts inside and in front of the detector

The Munich Dust Counter (MDC) is a scientific space experiment that flew aboard the Japanese satellite HITEN (MUSES-A) for 3 years in the vicinity of the Earth and the Moon and also aboard the university satellite BREMSAT for more than one year in LEO. The plasma that is generated by dust particles impacting on a gold target, is measured to determine the mass, velocity, and crude flight direction of cosmic dust particles and space debris. After a short introduction describing the experiment setup the new aspects concerning the calibration of the experiments will be presented. There is special emphasis on impacts in front of the MDC onto an aluminum-frame. It will be shown that impacts outside an ionization detector can produce enough charge to be measured by the experiment. After a short discussion about detection possibility of charged particles, the implications of the achieved results during three years of operation of the MDC on board the HITEN spacecraft will be discussed.

Conceptual design for an orbiting debris detection radar

There exists a large amount of man-made debris in low Earth orbit. The quantity of this debris is growing every year as a result of on-going activities in space. Much of the debris consists of particles which are too small to be tracked from the ground, but nevertheless pose a threat to spacecraft. This paper examines the possibility of an orbiting radar which, over a period of time, could measure debris positions and velocities and thereby build up a database of debris orbits. Spacecraft could use this database for advance warning of impending collisions and maneuver themselves out of the collision path, thereby mitigating the long-term risk of collision damage.

Comparisons of cadmium and aluminum debris clouds

Results of a study comparing the debris clouds produced by hypervelocity impacts of cadmium spheres on cadmium bumper-sheets and aluminum spheres on aluminum bumper-sheets are presented. The shape, fragment size and distribution, and phase state of the cadmium and aluminum debris clouds were qualitatively compared and matched. The front, rear, and radial velocities of particles in the cadmium debris clouds were determined from radiographs and normalized by dividing by the impact velocity. These data were compared with similar aluminum debris velocity data to determine whether the debris velocities could be scaled by a constant value. Comparisons were made at the same bumper-thickness-to-projectile-diameter ratios ( t D ). The normalized debris velocities scaled reasonably well. The impact velocities for the aluminum tests were about two times greater than those of the cadmium tests to achieve the same normalized debris velocities. A velocity scaling technique is proposed in which the cadmium impact velocities are scaled using this factor and momentum is converted. Use of this scaling technique allows aluminum projectile impacts on aluminum bumper shields to be simulated to about 14 km/s using cadmium projectiles and cadmium bumper shields at velocities attainable with current launcher technology. A brief description is included on the phase transition from solid to liquid and liquid to vapor.

The validation of hydrocodes for orbital debris impact simulation

Orbital debris pose a danger for spacecraft in orbit. Protection against this threat is obtained by shielding. One or more shields placed at some distance from the structure to be protected can minimize the damage inflicted by projectiles at high velocity. The range of velocity between 0 and 8 km/s is well covered by tests. Unfortunately, the average velocity of debris in low earth orbit is above 10 km/s with a maximum velocity around 15 km/s. The methodology presented in this paper aims to validate the numerical approach. It will predict and extrapolate the behavior of multishock shields in the velocity range between 8 and 15km/s. The formation and propagation of the debris cloud, after perforation of the shields and the generation of damage in the backwall, are key factors. These phenomena are examined, discussed and illustrated with correlation between numerical simulation with EFHYD TM analytical formulae and test results.

On Protection of Freedom’s Solar Dynamic Radiator From the Orbital Debris Environment: Part I—Preliminary Analysis and Testing

A great deal of experimentation and analysis has been performed to quantify penetration thresholds of components which will experience orbital debris impacts. Penetration has been found to depend upon mission-specific parameters such as orbital altitude, inclination, and orientation of the component; and upon component specific parameters such as material, density, and the geometry particular to its shielding. Experimental results are highly dependent upon shield configuration and cannot be extrapolated with confidence to alternate shield configurations. Also, current experimental capabilities are limited to velocities which only approach the lower limit of predicted orbital debris velocities. Therefore, prediction of the penetrating particle size for a particular component having a complex geometry remains highly uncertain. This paper describes the approach developed to assess on-orbit survivability of the solar dynamic radiator due to micrometeroid and space debris impacts. Preliminary analyses are presented to quantify the solar dynamic radiator survivability, and include the type of particle and particle population expected to defeat the radiator bumpering (i.e., penetrate a fluid flow tube). Results of preliminary hypervelocity impact testing performed on radiator panel samples (in the 6 to 7 km/sec velocity range) are also presented. Plans for further analyses and testing are discussed. These efforts are expected to lead to a radiator design which will perform to Space Station Freedom requirements over the expected lifetime.

BUMPER DEBRIS CLOUD STRUCTURE ESTIMATED BY SHOCK CALCULATIONS

BUMPER DEBRIS CLOUD STRUCTURE ESTIMATED BY SHOCK CALCULATIONS

Successes and Failures with Oil Spills in the Southeastern Inland Waters

ABSTRACT This paper presents a brief review of several spill cases that have occurred in the Southeast in the recent past. Each case describes a unique situation — either in terms of containment, retention or removal methodology. At Athens, Georgia, a pipeline break caused the closure of the Athens Water Supply System for twenty-four (24) hours. Poor initial retention allowed taste, odors, and some light sheens to pass through the filters at the water plant into the home, causing some sixty-four (64) complaints within a matter of hours. Several inexpensive changes in retention procedures and water treatment techniques returned the situation to normal in a matter of hours. A pipeline break near Shepherdsville, Kentucky, forced some 16,000 gallons of crude oil into a subsurface layer of gravel. Storage of the oil in this fashion constituted a leaching source for the nearby water course that could have persisted for a year or more. Interception trenches were used to tap the gravel layers and water was forced into the layer up the gradient in order to “flush” the system. Ninety percent recovery was achieved at moderate expense. A vandalized storage tank adjacent to the Congaree River was emptied of 10,000 gallons of Bunker “C” near Columbia, South Carolina. Elaborate containment and recovery procedures were employed downstream. The oil, however, disappeared — save for minor vegetation stain. Not even a sheen reached the recovery site. River velocity, wind speed, temperature of the water and turbidity are discussed as contributors to this phenomena. At Jackson, Mississippi, a broken sludge pond dyke at a drilling operation dumped 40,000 gallons of “oil slops” and brine into the Big Black River. Retention on the surface was impossible because of the eight to ten knot river velocity. Light disposable sorbing booms were used to recover an estimated eighty percent of the oil. At Memphis, Tennessee, a piston film “Herder” was used to aid in recovering a portion of a 100,000 gallon spill. Because of surface debris, wind and river velocity, the Herder forced the oil into difficult tree and brush infested areas. The oil literally “ringed” every obstacle floating – or fixed — in the area. Cleanup costs soared. Pictures and sketches will be utilized to emphasize technical aspects of each situation.