Debris Velocity Research Articles

Study on plasma characteristics from hypervelocity impacts by small space debris

Dense plasma cloud can be produced by small debris impact on spacecraft surface, with the diffusion of plasma which can induce the electrostatic discharge (ESD) and electromagnetic interference (EMI). By this way, spacecraft will experience electrical anomalies. In this paper, a plasma drag particle accelerator is used to study the characteristics of impact-generated plasma due to crash of small debris with mass 10-5 g. The relation between plasma charge and debris velocity is acquired by analyzing experimental data. In addition, the diffusion velocity of the impact-generated plasma is observed by two retarding potential analyzers. By theoretical analysis, the change law of the electron density with time and dimension is calculated. Experiment results will be helpful to reveal the physical mechanism of spacecraft anomalies by small debris impacts.

Nonlinear dynamics analysis of multi-cutting wire electrode in WEDM-HS subjected to working fluid considering the effect of debris

A reasonable dielectric fluid velocity and better exclusion of debris are very important to obtain a stable machining performance in multi-cutting of WEDM-HS. We investigated the dynamic characteristics of multi-cutting wire electrode in WEDM-HS subjected to working fluid considering the effect of debris. First, a fluid-solid coupling nonlinear vibration model is derived by analyzing the forces acting on the multi-cutting wire which locate in the dielectric fluid. The additional axial force arising from the transverse vibration of the multi-cutting wire is considered as a nonlinear term in the model. Considering that the debris accumulation in discharge gap severely influences the stability of multi-cutting wire electrode, the relationship between the debris volume concentration and debris-working fluid two-phase flow drag coefficient is obtained using the Einstein two-phase flow viscosity theory. Finally, the influences of several parameters on the multi-cutting wire displacement are discussed in detail.

Dynamic cratering of graphite: Experimental results and simulations

The cratering process in brittle materials under hypervelocity impact (HVI) is of major relevance for debris shielding in spacecraft or high-power laser applications. Amongst other materials, carbon is of particular interest since it is widely used as elementary component in composite materials. In this paper we study a porous polycrystalline graphite under HVI and laser impact, both leading to strong debris ejection and cratering. First, we report new experimental data for normal impacts at 4100 and 4200 m s−1 of a 500-μm-diameter steel sphere on a thick sample of graphite. In a second step, dynamic loadings have been performed with a high-power nanosecond laser facility. High-resolution X-ray tomographies and observations with a scanning electron microscope have been performed in order to visualize the crater shape and the subsurface cracks. These two post-mortem diagnostics also provide evidence that, in the case of HVI tests, the fragmented steel sphere was buried into the graphite target below the crater surface. The current study aims to propose an interpretation of the results, including projectile trapping. In spite of their efficiency to capture overall trends in crater size and shape, semi-empirical scaling laws do not usually predict these phenomena. Hence, to offer better insight into the processes leading to this observation, the need for a computational damage model is argued. After discussing energy partitioning in order to identify the dominant physical mechanisms occurring in our experiments, we propose a simple damage model for porous and brittle materials. Compaction and fracture phenomena are included in the model. A failure criterion relying on Weibull theory is used to relate material tensile strength to deformation rate and damage. These constitutive relations have been implemented in an Eulerian hydrocode in order to compute numerical simulations and confront them with experiments. In this paper, we propose a simple fitting procedure of the unknown Weibull parameters based on HVI results. Good agreement is found with experimental observations of crater shapes and dimensions, as well as debris velocity. The projectile inclusion below the crater is also reproduced by the model and a mechanism is proposed for the trapping process. At least two sets of Weibull parameters can be used to match the results. Finally, we show that laser experiment simulations may discriminate in favor of one set of parameters.

Numerical evaluation of tsunami debris impact loading on wooden structural walls

Water-based disasters such as tsunami, hurricane, and flood can cause significant structural damage to coastal areas and ultimately result in human and socioeconomic losses. Recent studies have highlighted the difficulties associated with estimating tsunami impact loads on residential structures with greater challenges pertaining to estimating the debris impact loads. The main challenges are associated with large variations in debris mass, shape, velocity, and impact angle. According to FEMA P-646 [1], although impact of floating debris is required to be considered by the codes, the added mass of water behind the debris and/or the potential for damming when debris is blocked by structural elements are ignored. Additionally, there is a lack of 3D numerical models that can accurately predict debris impact loads. Due to the three-dimensional dynamic nature of the problem, coupled with highly variable factors affecting debris loads, a 3D finite element (FE) analysis is necessary to determine the debris impact on structures as accurately as possible. To date, one of the major obstacles in modeling tsunami impact on structures is the intense computational demand linked with such models. This paper presents the formulation of an efficient 3D FE model with computational fluid dynamic (CFD) capabilities to study debris impact on interior and exterior wood structural panels. Several important parameters such as initial water volume, water velocity, debris shape, and debris density are varied throughout the analysis in order to determine the individual effect of each parameter as well as the overall effect on wood structural walls. The results for an interior wall panels showed that contribution from water height and velocity is more significant the debris mass in the impact force as water height and velocity increase. Additionally, as the water height increases, the impact force due to debris decreases for an interior panel when debris mass is constant. An exterior panel is significantly closer to a rigid structure, therefore, an increase in impact force due to debris is observed with the increase in water height and debris mass. The results can be used by engineers to estimate debris impact load on wood panels with similar dimension and material properties.

Impacts of nitrogen limitation on the sinking rate of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae)

Pantorno A., Holland D.P., Stojkovic S. and Beardall B. 2013. Impacts of nitrogen limitation on the sinking rate of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae). Phycologia 52: 288–294. DOI: 10.2216/12–064.1The biological carbon pump in the ocean plays an important role in controlling atmospheric CO2 levels. Approximately 1% of the yearly 50–60 Pg C of marine primary production settles in the deep ocean, where it is effectively sequestered for centuries to millennia. Central to the strength of the pump is the sinking velocity of phytoplankton cells and other organic debris. Stokes' Law indicates that the sinking velocity of a spherical cell will depend on its size and density, where larger, heavier cells will sink at a faster rate. Given that growth conditions can result in changes in cell size and macromolecular composition of phytoplankton, it might be expected that such changes could cause alterations in sinking velocity and carbon drawdown via the biological carbon pump. In the future, phytoplankton cells in the open ocean are predicted to be more subject to nutrient limitation. In this study we examined the effects of nitrogen limitation on the sinking velocity of Emiliania huxleyi, a coccolithophore responsible for significant phytoplankton blooms and biological drawdown of carbon. Nitrogen limitation caused changes in macromolecular composition, especially lipid content and coccosphere thickness. However, the overall density of the cells remained similar, and, as a consequence, cell size was the major determinant of sinking rate with N-limited cells in exponential phase sinking more slowly than N-replete cells. Cells in stationary phase showed the reverse trend with N-limited cells sinking faster, although not as fast as N-replete cells in exponential phase. N-limited cells produced more transparent exopolymers, suggesting an increased capacity for marine snow formation. These observations have implications for the efficiency of the biological carbon pump in areas that have increased nutrient stress caused by global climate change.

대형 사력댐에서의 전단파속도 평가를 위한 단측선 빔형성기법

대형 사력댐의 내진성능 평가에서 필히 요구되는 입력상수는 사력재료, 코아매질의 전단파 속도이다. 이를 표면파 시험으로 평가하기 위해서는 사력골재의 불연속, 매질의 비균질, 사면 경계면 등 표면파 시험결과의 신뢰도를 떨어뜨리는 조건을 극복해야 한다. 본 연구에서는 이러한 표면파시험의 한계를 극복하기 위하여 기존 빔형성기법의 원리를 응용한 SBF (Short-Array Beamforming) 기법을 제안하였다. SBF 기법은 3~9 m의 짧은 측선과 원거리 발진원을 이용함으로써, 빔형성기법 고유의 장점인 측정자료의 자동화분석뿐만 아니라 근접장 문제의 해결, 국부적 이상대의 발견 등의 기능을 가지도록 개발되었다. 본 연구에서는 이러한 SBF 기법과 IRF(Impulse-Response Filtration) 기법을 활용하여 대형 사력댐의 전단파속도를 신뢰성 있게 평가하는 방법을 정립하였다. 정립된 기법은 사력댐의 사력재료와 유사한 암버럭으로 매립 성토된 철도 노반에서 다운홀 시험, CapSASW (Common-Array-Profiling SASW) 시험과의 비교를 통하여 그 신뢰성과 실용성을 검증하였다. One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

Laboratory test and numerical simulation of laminated glass window vulnerability to debris impact

This paper presents results of laboratory tests and numerical simulations on the vulnerability of laminated glass windows subjected to windborne wooden block impact. Wooden debris weighing 2 kg, 4 kg and 8 kg with a velocity of 9 m/s to 35 m/s impacting on the glass windows is considered in this study. Performances of typical windows of sizes 2000 mm × 1100 mm and 1200 mm × 600 mm with 3 mm thick float glass plies laminated by 1.52 mm, 1.88 mm, 2.28 mm and 2.66 mm PVB interlayer are evaluated. It has been found that interlayer thickness plays a dominating role in the penetration resistance capacity of the laminated glass windows subjected to windborne debris impact. The vulnerability curves of laminated glass windows with various thicknesses and dimensions are generated. A predictive method based on laboratory observation is also developed to estimate glass fragments induced by debris impact. The fragment mass and launching speed are estimated with respect to the impact debris mass and velocity.

Dynamic Behavior of a Porous Brittle Material: Experiments and Modeling

The purpose of our research is to study porous polycrystalline graphite under various loading conditions. New experimental data are provided. Some of them concern impacts of a 500μm diameter steel sphere at velocities above 4000 m/s on thick carbon targets, leading to strong debris ejection and cratering. A high speed frame camera showed the debris velocity distribution to lie in the 10-200 m/s range. Post-mortem tomographies have also been performed. They reveal some subsurface cracks, but also provide some evidence that the fragmented sphere lies below the target surface. Dynamic loadings involving similar energy densities (above 2000J/cm2) can also be reached through the interaction of a nanosecond intense laser focalized on a carbon target. An experimental result obtained on a laser facility is presented. Numerical simulations have been performed in order to explain the observed results. An Eulerian hydrocode has been chosen because of the large deformation occurring under considered experiments. We have used a classical model to describe the porous behavior, including equation of state, elasticity, shear strength and densification. In this paper, we focus on the effect of the addition to this porous model of a failure criterion relying on the Weibull theory. The selection of the parameters is based on one set of data and the fit is demonstrated against another test. The overall agreement with the experimental data is good.

Debris flood risk assessment for Mosquito Creek, British Columbia, Canada

Mosquito Creek drains a 15.5 km2 watershed on the North Shore Mountains north of Vancouver, British Columbia, Canada, and flows through the densely urbanized District and then City of North Vancouver. Previous studies determined that the creek is subject to debris floods (hyperconcentrated flows). The National Research Council of Canada is applying multi-hazard risk assessment procedures for various regions in B.C. and chose Mosquito Creek as one of its target areas. As part of its natural hazard management plan, the District of North Vancouver (DNV) requested an assessment of debris flood hazards and associated risk to life. Using a combination of empirical methods, dendrochronology and some judgment, BGC Engineering Inc. assessed debris flood hazard extent, velocity and depth for estimated 100-, 200-, 500- and 2,500-year debris flow return periods. Based on the results from the hazard assessment, risk for individuals and groups living within the hazard area, including residential homes and a fire hall, was estimated. Compared to risk tolerance criteria accepted on an interim basis by the DNV, we estimate that societal risk exceeds tolerable standards and that individual risk exceeds tolerable standards for 10 homes. The results from the risk to loss of life study have prompted DNV to implement a series of risk reduction measures including installation of a debris containment net and watershed restoration measures.

Radiometric considerations for the detection of space debris with an optical sensor in LEO as a secondary goal of the AsteroidFinder mission

The German Aerospace Center (DLR) is pursuing a national space program based on a Standard Satellite Bus (SSB) belonging to the compact class. After a review process, AsteroidFinder was selected to be the first mission featuring a DLR SSB. The mission is presently in its Phase-B development stage, with a launch planned for 2013. In addition to its primary goal of discovering Inner Earth Objects (IEOs), a secondary goal of the AsteroidFinder mission is to demonstrate the feasibility of the detection and statistical classification of cm-sized space debris with a satellite-based optical instrument. The increasing risk for astronauts and spacecraft caused by the growing number of space debris requires a deeper involvement in space debris investigations. Ground-based measurements of the particle population supported by either radar or optical instruments have become worldwide a standard method of research. However, the space-based detection is still in its infancy. As the debris' signal is not disturbed by the atmosphere in space, this method shall help to observe particularly small particles. In this paper the mission and payload will be introduced and the first simulations on the optical detectability of small objects will be discussed. The results of the radiometric considerations, which include the interaction of the debris size, the debris velocity and the particle's distance to the camera, indicate that it is well possible to detect cm-sized objects with AsteroidFinder. Thus, information on statistics of the orbital debris population can be obtained.

Windborne debris and damage risk models: a review

This review paper discusses research from the last few years relating to windborne debris risk models and the essential elements of engineering damage prediction models. Generic types of windborne debris are discussed. The results of studies of debris trajectories that are relevant to damage models are described - in particular the horizontal component of debris velocity as a function of distance travelled. The merits of impact momentum versus impact kinetic energy as a relevant parameter for predicting damage are considered, and how published data from generic cannon Impact tests can be used in risk models. The quantitative variation of debris impact damage with wind speed is also discussed. Finally the main elements of previously-proposed debris damage models are described.

Effects of Finescale Debris on Near-Surface Tornado Dynamics

Debris clouds provide an important visual signature of tornadoes and can potentially significantly affect the wind structure, damage potential, and Doppler radar measurements of tornado wind speeds. To study such issues, the dynamics of finescale debris have been added to an existing high-resolution large-eddy simulation model of tornado dynamics. A so-called “two-fluid” or “Eulerian–Eulerian” approach is employed, together with a surface layer model for lofting and depositing debris. In this paper the debris implementation is described, three critical dimensionless parameters governing tornado debris effects are identified, and sample results from a large set of simulations of tornadoes with idealized debris are presented. The results demonstrate that the accumulation of small-scale debris within the surface layer and corner flow can significantly alter the wind speeds and flow structure of the tornado vortex within a few hundred meters of the surface. They suggest that the total mass of the debris cloud can reach tens of thousands of tons. Near the surface, the debris mass loading can be well above 1, the peak mean velocities can be reduced by as much as half, and the total momentum (air plus debris) can either significantly increase or decrease. Local air and debris velocities can differ significantly and in a nontrivial fashion, thereby complicating the interpretation of Doppler radar measurements of tornado structure. Debris fluctuations, centrifuging, negative buoyancy, and angular momentum transport are all significant mechanisms for the debris effects. A negative physical feedback reduces the sensitivity of the results to changes in the parameterization of the surface debris fluxes. The realistic simulation of tornado debris clouds and surface damage tracks should prove useful in identifying the dynamics governing their observed counterparts.

A comparison of NASA, DoD, and hydrocode ballistic limit predictions for spherical and non-spherical shapes versus dual- and single-wall targets, and their effects on orbital debris penetration risk

Abstract All earth-orbiting spacecraft are susceptible to impacts by these particles, which can occur at extremely high speeds and can damage flight- and mission-critical systems. The traditional damage mitigating shield design for this threat consists of a “bumper” that is placed several cm away from the main “inner wall” of the spacecraft. Typical orbital debris risk analyses that include ballistic limit equations (BLEs) and curves (BLCs) assume that orbital debris particles are spherical in shape. However, spheres are not a common shape for orbital debris; rather, debris fragments might be better represented by other regular or irregular solids. This paper presents the results of a study comparing BLCs developed by NASA and the DoD for velocities up to 4 km/s considering spheres, cubes, and a “flake” shape that was proposed within NASA's Standard Breakup Model to represent orbital debris. It also compares performance of these shapes using hydrocodes at higher velocities (7–12 km/s), and generates a combined BLC for these shapes for the entire orbital debris velocity regime. In addition to shape, a multi-view method is used to examine the effects of a variety of cube and flake impact orientations on BLC, as well as a “characteristic length” parameter developed by NASA to compare the particle shapes on the basis of their radar cross section. The developed non-spherical BLCs are then evaluated for overall penetration risk considering the orbital debris environment. Their predictions of risk are compared to that predicted using sphere-based BLCs. This methodology is then extended to a single-wall shield design for velocities up to 15 km/sec, and the results of DoD predictions for a sphere and cube are compared with NASA predictions for a sphere having the same characteristic length. The results indicate that we may be over-predicting orbital debris risk for dual-wall shields by a factor of two—and for single walls by a factor of four—by limiting our analyses to spheres instead of using more representative debris shapes, such as cubes and flakes, and its characteristic length as the primary particle parameter.

Laser copper plasma X-ray source debris characterization

Laser copper plasma sources are a compact, economical means of producing high intensity X-rays at the correct wavelengths for X-ray lithography. Copper debris in the form of vapor, ions, dust, and high speed particles is an unwanted byproduct of the laser copper plasma technique. Improved methods for debris mitigation are essential for production X-ray lithography using laser copper plasma sources.The main objective of this project is to characterize the debris, particularly the size, amount, and velocity spectrum of high speed particles. The measurements used a source-laser-pulse-synchronized high speed spinning disc. An optical scanning boom microscope analyzed debris collected on a target. Kinematic triangulation using the location of the debris indicates the velocity of debris particles.Velocities of copper debris particles were found to be in the hundreds of meters per second, roughly one order of magnitude slower than previously believed. The precision of results was limited by a mismatched sampling rate for particle collection. This discovery opens up the possibility of a host of mechanical debris blocking countermeasures previously thought to be too slow to effectively stop high speed debris particles. This study also suggests that X-rays emitted at high laser pulse rates could be blocked by debris generated during the previous laser pulse. An area requiring further refinement and study is in the mechanics of plasma generation. The target location and laser spot size and focal point are critical factors in the process and have a low tolerance for variation.

A universal throw model and its applications

A deterministic model has been developed that describes the throw of debris or fragments from a source with an arbitrary geometry and for arbitrary initial conditions. The initial conditions are defined by the distributions of mass, launch velocity and launch direction. The item density in an exposed area, i.e. the number of impacting debris or fragments per unit of area, has been expressed analytically in terms of these initial conditions. While existing models make use of the Monte Carlo technique, the present model uses the source function theorem, an underlying mathematical relation between the debris density and the initial distributions. This gives fundamental insight in the phenomenon of throw, and dramatically reduces the required number of trajectory calculations. The model has been formulated for four basic source geometries: a point source, a vertical cylinder, a horizontal cylinder, and a vertical plane. In combination with trajectory calculations the item density can be quantified. As an illustration of the model, analytical results are presented and compared for the vertical plane and the vertical cylinder geometry under simplified assumptions. If uncertainties exist in the initial conditions, the model can be used to investigate these initial conditions based on experimental data. This has been illustrated on the basis of a trial with 5 ton of ammunition stacked in an ISO container. In this case the model has been successfully applied to determine the debris launch angle and velocity distribution, by means of backward calculations. If, on the other hand, sufficient information on the initial conditions is available, the model can be used as an effect model in risk assessment methods, or for the requirements on protective measures. The model can be used to predict safety distances based on any desired criterion.

Molecular Dynamics Study of Impact Angle Dependence of Structure of Debris Cloud under Hyper Velocity Impact

A molecular dynamics simulation is carried out to study the fractureunder hyper-velocity impact conditions when a space debris attack to aman-made satellite. In this paper, oblique-impact simulations areperformed since most orbital debris impacts are oblique in the realcondition. Aluminum projectile impacts aluminum target at 0−, 30−, and 45−degrees obliquity. Impact velocity is 8km/s, and target thickness-projectile diameter ratio t/D is 0.684. As the angle of obliquity isincreasing, the velocity of debris after impact is decreasing, whilethe deviation of the line of flight is increasing. These resultsqualitatively agrees well with experimental results.

Prediction of debris launch velocity of vented concrete structures under internal blast

The debris hazard resulting from an internal explosion is a major concern in the design of explosives storage magazines and protective structures. This paper presents a simple predictive method for the debris launch velocity from a concrete storage magazine subjected to internal blast load, with particular focus on the effect of initial vent openings. The method is developed using a combined theoretical–empirical approach, in which the debris launch velocity is formulated based on energy considerations, whereas the reduction coefficient of pressure caused by the flow of explosive gas from the vent openings is established from experimental data. The analytical model is verified against available experimental data and other numerical predictions. Example cases are given to demonstrate the application of the general formulation to particular structures and illustrate the effect of venting and its location on the debris velocity for structures of different sizes.

A rational method for estimating maximum discharge of a landslide-induced debris flow: A case study from southwestern China

This paper presents a rational method for estimating the maximum discharge of a landslide-induced debris flow. The method has five basic principles or steps: (a) to identify and measure representative bends and straight zones along a channel through which a debris flow went down; (b) to evaluate peak debris flow velocity in the bends; (c) to assess peak debris flow velocity in the straight channel zones; (d) to use the peak velocities to estimate the distribution of peak discharge along the entire channel; and (e) to find the maximum velocity and discharge of the debris flow. The method is illustrated with a case study of a landslide-induced debris flow at a mountainous region near Chengdu, southwestern China. The results show that the peak debris velocity was between 2.4 and 4.7 m s − 1 and the peak debris discharge was between 6.7 and 35.7 m 3 s − 1 . The peak discharge initially increased at the upper portion of the channel, then decreased at the lower portion, indicating that the upper channel experienced erosion but the lower channel experienced deposition. The location with the maximum debris flow discharge corresponds to the point where the volume of the debris flow started to decrease. The method presented in this paper can help to prevent or mitigate debris flow hazards.

Debris velocity of concrete structures subjected to explosive loading

When designing above-ground ammunition storage facilities, one has to take into account the debris hazard resulting from accidental explosions. The purpose of this paper is to develop a predictive method for debris dispersion around an ammunition storage site in case of an accidental detonation in a reinforced concrete storage structure. The concrete slabs/walls break up into debris when it is overloaded by the internal blast. The debris velocity is one of the important parameters to describe the debris dispersion. The parameters that affect the debris velocity are complex. This study adopts the energy approach to simplify the formulation. The failure process in a relatively thin concrete slab/wall is treated using the concept of expansion. Based on energy conservation, a general formula is derived for the debris launch velocity in a cubicle structure subjected to internal blast loading. The dynamic strength of concrete and reinforcement are considered in the fracture process. The analytical results are found to be consistent with the relevant experimental results. Copyright © 2006 John Wiley & Sons, Ltd.

Toward Nonintrusive Flood Discharge Measurement

The current discharge measurement methods in rivers are known to be accurate for low and mean discharges, but large debris and high velocities prevent the use of these conventional methods during flood season. Therefore, a nonintrusive method to measure discharge during floods has been developed. The method elaborated in a laboratory channel proceeds in two steps. In a first step the water surface was recorded with three calibrated charge coupled device (CCD) cameras using identical frequency. To determine the geometry and the velocity field of the free surface, floating tracer particles were added to the flow. In a second step a finite element program was employed to compute the discharge based on recorded surface information. An iterative procedure using the commercial finite element program CFX allows one to determine discharge. This approach considers river portions with a locally strong variable bed geometry such as drop structures whose bed profile is measured conventionally prior to or after the flood event. Laboratory experimentation demonstrated an average error in discharge measurement of 2–3%.