20 results on '"Kai Wünnemann"'
Search Results
2. Subsurface deformation of experimental hypervelocity impacts in quartzite and marble targets
- Author
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Kai Wünnemann, Robert Luther, Thomas Kenkmann, R. Winkler, and Michael H. Poelchau
- Subjects
Geophysics ,010504 meteorology & atmospheric sciences ,Space and Planetary Science ,Hypervelocity ,Geotechnical engineering ,Deformation (meteorology) ,010502 geochemistry & geophysics ,01 natural sciences ,Geology ,0105 earth and related environmental sciences - Published
- 2018
3. Reconstruction of the Morasko meteoroid impact-Insight from numerical modeling
- Author
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Natalia Artemieva, Małgorzata Bronikowska, and Kai Wünnemann
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Meteoroid ,Projectile ,Geophysics ,010502 geochemistry & geophysics ,01 natural sciences ,Strewn field ,Astrobiology ,Atmosphere ,Meteorite ,Impact crater ,Space and Planetary Science ,Atmospheric entry ,Asteroid ,0103 physical sciences ,010303 astronomy & astrophysics ,Geology ,0105 earth and related environmental sciences - Abstract
The Morasko strewn field located near Poznan, Poland comprises seven impact craters with diameters ranging from 20 to 90 m, all of which were formed in glacial sediments around 5000 yr ago. Numerous iron meteorites have been recovered in the area and their distribution suggests a projectile with the trajectory from NE to SW. Similar impact events producing crater strewn fields on average happen every 500 yr and pose a serious risk for modern civilization, which is why it is of utmost importance to study terrestrial strewn fields in detail. In this work, we investigate the Morasko meteoroid passage through the atmosphere, the distribution of its fragments on the ground, and the process of forming individual craters by means of numerical modeling. By combining atmospheric entry modeling, Pi-group scaling of transient crater size and hydrocode simulations of impact processes, we constructed a comprehensive model of the Morasko strewn field formation. We determined the preatmospheric parameters of the Morasko meteoroid. The entry mass is between 600 and 1100 tons, the velocity range is between 16 and 18 km s−1, and the trajectory angle is 30–40°. Such entry velocities and trajectory angles do not deviate from typical values for near-Earth asteroids, although the initial mass we determined can be considered as small. Our studies on velocities and masses of crater-forming fragments showed that the biggest Morasko crater was formed by a projectile about 1.5 m in diameter with the impact velocity ~10 km s−1. Environmental consequences of the Morasko impact event are very localized.
- Published
- 2017
4. Snow carrots after the Chelyabinsk event and model implications for highly porous solar system objects
- Author
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Natalia Artemieva, Kai Wünnemann, Marina E. Ivanova, Robert Luther, and Cyril A. Lorenz
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Solar System ,business.product_category ,010504 meteorology & atmospheric sciences ,Meteorology ,Meteoroid ,Geophysics ,010502 geochemistry & geophysics ,Breakup ,Snow ,01 natural sciences ,Meteorite ,Impact crater ,Space and Planetary Science ,Atmospheric entry ,Funnel ,business ,Geology ,0105 earth and related environmental sciences - Abstract
After the catastrophic disruption of the Chelyabinsk meteoroid, small fragments formed funnels in the snow layer covering the ground. We constrain the pre-impact characteristics of the fragments by simulating their atmospheric descent with the atmospheric entry model. Fragments resulting from catastrophic breakup may lose about 90% of their initial mass due to ablation and reach the snow vertically with a free-fall velocity in the range of 30–90 m s−1. The fall time of the fragments is much longer than their cooling time, and, as a consequence, fragments have the same temperature as the lower atmosphere, i.e., of about −20 °C. Then, we use the shock physics code iSALE to model the penetration of fragments into fluffy snow, the formation of a funnel and a zone of denser snow lining its walls. We examine the influence of several material parameters of snow and present our best-fit model by comparing funnel depth and funnel wall characteristics with observations. In addition, we suggest a viscous flow approximation to estimate funnel depth dependence on the meteorite mass. We discuss temperature gradient metamorphism as a possible mechanism which allows to fill the funnels with denser snow and to form the observed “snow carrots.” This natural experiment also helps us to calibrate the iSALE code for simulating impacts into highly porous matter in the solar system including tracks in the aerogel catchers of the Stardust mission and possible impact craters on the 67P/Churyumov-Gerasimenko comet observed recently by the Rosetta mission.
- Published
- 2017
5. Impacts into quartz sand: Crater formation, shock metamorphism, and ejecta distribution in laboratory experiments and numerical models
- Author
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Meng-Hua Zhu, Kai Wünnemann, and Dieter Stöffler
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010504 meteorology & atmospheric sciences ,Metamorphic rock ,Impact gardening ,Mechanics ,01 natural sciences ,Regolith ,Astrobiology ,Shock (mechanics) ,Shock metamorphism ,Geophysics ,Impact crater ,Space and Planetary Science ,0103 physical sciences ,Ejecta ,010303 astronomy & astrophysics ,Quartz ,Geology ,0105 earth and related environmental sciences - Abstract
We investigated the ejection mechanics by a complementary approach of cratering experiments, including the microscopic analysis of material sampled from these experiments, and 2-D numerical modeling of vertical impacts. The study is based on cratering experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color-coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the cratering and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power-law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock-comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a crater accurately if impact parameters such as impact velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of impact gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies.
- Published
- 2016
6. 2018 Barringer Medal for Thomas Kenkmann
- Author
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Michael H. Poelchau and Kai Wünnemann
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Medal ,Geophysics ,Space and Planetary Science ,media_common.quotation_subject ,Art history ,Art ,media_common - Published
- 2018
7. Scaling and reproducibility of craters produced at the Experimental Projectile Impact Chamber (EPIC), Centro de Astrobiología, Spain
- Author
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D. Elbeshausen, I. Melero-Asensio, Gareth S. Collins, Kai Wünnemann, K. R. Housen, and Jens Ormö
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Reproducibility ,Atmospheric pressure ,Projectile ,Mechanics ,Granular material ,law.invention ,Geophysics ,Impact crater ,Space and Planetary Science ,law ,visual_art ,Light-gas gun ,visual_art.visual_art_medium ,Ceramic ,Scaling ,Geology - Abstract
The Experimental Projectile Impact Chamber (EPIC) is a specially designed facility for the study of processes related to wet-target (e.g., “marine”) impacts. It consists of a 7 m wide, funnel-shaped test bed, and a 20.5 mm caliber compressed N2 gas gun. The target can be unconsolidated or liquid. The gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal. To test the functionality and quality of obtained results by EPIC, impacts were performed into dry beach sand targets with two different projectile materials; ceramic Al2O3 (max. velocity 290 m s−1) and Delrin (max. velocity 410 m s−1); 23 shots used a quarter-space setting (19 normal, 4 at 53° from horizontal) and 14 were in a half-space setting (13 normal, 1 at 53°). The experiments were compared with numerical simulations using the iSALE code. Differences were seen between the nondisruptive Al2O3 (ceramic) and the disruptive Delrin (polymer) projectiles in transient crater development. All final crater dimensions, when plotted in scaled form, agree reasonably well with the results of other studies of impacts into granular materials. We also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results, as well as demonstrated that the EPIC quarter-space experiments are a reasonable approximation for half-space experiments. Altogether, the combined evaluation of experiments and numerical simulations support the usefulness of the EPIC in impact cratering studies.
- Published
- 2015
8. Effect of target properties and impact velocity on ejection dynamics and ejecta deposition
- Author
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Meng-Hua Zhu, Kai Wünnemann, Gareth S. Collins, Robert Luther, and Science and Technology Facilities Council (STFC)
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Geochemistry & Geophysics ,010504 meteorology & atmospheric sciences ,SHOCK METAMORPHISM ,01 natural sciences ,Shock metamorphism ,Impact velocity ,0103 physical sciences ,0201 Astronomical and Space Sciences ,Astrophysics::Solar and Stellar Astrophysics ,DISTRIBUTIONS ,0402 Geochemistry ,Ejecta ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,OBLIQUE IMPACTS ,PROJECTILE DENSITY ,Science & Technology ,FLOW-FIELD ,Mechanics ,Flow field ,MODEL ,Geophysics ,0403 Geology ,Space and Planetary Science ,CRATER FORMATION ,Physical Sciences ,SIMULATION ,Astrophysics::Earth and Planetary Astrophysics ,FRAGMENTATION ,Geology ,QUARTZ SAND - Abstract
Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s−1) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s−1. We compare the derived ejecta deposits with observations from natural craters and experiments.
- Published
- 2018
9. Shock-darkening in ordinary chondrites: Determination of the pressure-temperature conditions by shock physics mesoscale modeling
- Author
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Juulia-Gabrielle Moreau, Kai Wünnemann, Tomas Kohout, and Department of Physics
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1171 Geosciences ,Shock wave ,IMPACT MODELS ,Materials science ,IMPACT ,FOS: Physical sciences ,010502 geochemistry & geophysics ,114 Physical sciences ,01 natural sciences ,Physics - Geophysics ,Shock metamorphism ,Chondrite ,0103 physical sciences ,Porosity ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Earth and Planetary Astrophysics (astro-ph.EP) ,Mechanics ,115 Astronomy, Space science ,Troilite ,Geophysics (physics.geo-ph) ,Shock (mechanics) ,CHONDRITES ,Geophysics ,Space and Planetary Science ,Melting point ,SHOCK ,Grain boundary ,Astrophysics - Earth and Planetary Astrophysics - Abstract
We determined the shock-darkening pressure range in ordinary chondrites using the iSALE shock physics code. We simulated planar shock waves on a mesoscale in a sample layer at different nominal pressures. Iron and troilite grains were resolved in a porous olivine matrix in the sample layer. We used equations of state (Tillotson EoS and ANEOS) and basic strength and thermal properties to describe the material phases. We used Lagrangian tracers to record peak shock pressures in each material unit. The post-shock temperatures (and the fractions of tracers experiencing temperatures above the melting point) for each material were estimated after the passage of the shock wave and after reflections of the shock at grain boundaries in the heterogeneous materials. The results showed that shock-darkening, associated with troilite melt and the onset of olivine melt, happened between 40 and 50 GPa - with 52 GPa being the pressure at which all tracers in the troilite material reach the melting point. We demonstrate the difficulties of shock heating in iron and also the importance of porosity. Material impedances, grain shapes and the porosity models available in the iSALE code are discussed. We also discussed possible not-shock-related triggers for iron melt., Comment: 36 page, 20 figures, 11 tables. In press in Meteoritics & Planetary Science
- Published
- 2017
10. 2015 Barringer Medal for Natalia Artemieva
- Author
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Kai Wünnemann
- Subjects
Medal ,Geophysics ,Space and Planetary Science ,media_common.quotation_subject ,Art history ,Art ,media_common - Published
- 2015
11. Ries crater and suevite revisited-Observations and modeling Part I: Observations
- Author
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W. Uwe Reimold, Dieter Stöffler, Iona A. T. Summerson, Natalia Artemieva, Juliane Jacob, Birgit K. Hansen, and Kai Wünnemann
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Shock metamorphism ,Geophysics ,Impact crater ,Space and Planetary Science ,Clastic rock ,Ejecta blanket ,Sedimentary rock ,Context (language use) ,Petrology ,Ejecta ,Geomorphology ,Geology ,Plume - Abstract
We report results of an interdisciplinary project devoted to the 26 km-diameter Ries crater and to the genesis of suevite. Recent laboratory analyses of “crater suevite” occurring within the central crater basin and of “outer suevite” on top of the continuous ejecta blanket, as well as data accumulated during the past 50 years, are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations (Artemieva et al. 2013). The properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting. In a new approach, we reconstruct the minimum/maximum volumes of all allochthonous impact formations (108/116 km3), of suevite (14/22 km3), and the total volume of impact melt (4.9/8.0 km3) produced by the Ries impact event prior to erosion. These volumes are reasonably compatible with corresponding values obtained by numerical modeling. Taking all data on modal composition, texture, chemistry, and shock metamorphism of suevite, and the results of modeling into account, we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement. Numerical modeling indicates that only a very small fraction of suevite can be derived from the “primary ejecta plume,” which is possibly represented by the fine-grained basal layer of outer suevite. The main mass of suevite was deposited from a “secondary plume” induced by an explosive reaction (“fuel-coolant interaction”) of impact melt with water and volatile-rich sedimentary rocks within a clast-laden temporary melt pool. Both melt pool and plume appear to be heterogeneous in space and time. Outer suevite appears to be derived from an early formed, melt-rich and clast-poor plume region rich in strongly shocked components (melt ≫ clasts) and originating from an upper, more marginal zone of the melt pool. Crater suevite is obviously deposited from later formed, clast-rich and melt-poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper, central zone of the melt pool. Genetically, we distinguish between “primary suevite” which includes dike suevite, the lower sublayer of crater suevite, and possibly a basal layer of outer suevite, and “secondary suevite” represented by the massive upper sublayer of crater suevite and the main mass of outer suevite.
- Published
- 2013
12. Propagation of impact-induced shock waves in porous sandstone using mesoscale modeling
- Author
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Nicole Güldemeister, Kai Wünnemann, Stefan Hiermaier, and Nathanaël Durr
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Shock wave ,Materials science ,Compaction ,Mechanics ,Physics::Geophysics ,Shock (mechanics) ,Geophysics ,Impact crater ,Space and Planetary Science ,Geotechnical engineering ,Particle velocity ,Porous medium ,Porosity ,Material properties - Abstract
– Generation and propagation of shock waves by meteorite impact is significantly affected by material properties such as porosity, water content, and strength. The objective of this work was to quantify processes related to the shock-induced compaction of pore space by numerical modeling, and compare the results with data obtained in the framework of the Multidisciplinary Experimental and Modeling Impact Research Network (MEMIN) impact experiments. We use mesoscale models resolving the collapse of individual pores to validate macroscopic (homogenized) approaches describing the bulk behavior of porous and water-saturated materials in large-scale models of crater formation, and to quantify localized shock amplification as a result of pore space crushing. We carried out a suite of numerical models of planar shock wave propagation through a well-defined area (the “sample”) of porous and/or water-saturated material. The porous sample is either represented by a homogeneous unit where porosity is treated as a state variable (macroscale model) and water content by an equation of state for mixed material (ANEOS) or by a defined number of individually resolved pores (mesoscale model). We varied porosity and water content and measured thermodynamic parameters such as shock wave velocity and particle velocity on meso- and macroscales in separate simulations. The mesoscale models provide additional data on the heterogeneous distribution of peak shock pressures as a consequence of the complex superposition of reflecting rarefaction waves and shock waves originating from the crushing of pores. We quantify the bulk effect of porosity, the reduction in shock pressure, in terms of Hugoniot data as a function of porosity, water content, and strength of a quartzite matrix. We find a good agreement between meso-, macroscale models and Hugoniot data from shock experiments. We also propose a combination of a porosity compaction model (e–α model) that was previously only used for porous materials and the ANEOS for water-saturated quartzite (all pore space is filled with water) to describe the behavior of partially water-saturated material during shock compression. Localized amplification of shock pressures results from pore collapse and can reach as much as four times the average shock pressure in the porous sample. This may explain the often observed localized high shock pressure phases next to more or less unshocked grains in impactites and meteorites.
- Published
- 2012
13. Numerical Modelling of Impact Processes
- Author
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Elisabetta Pierazzo, Gareth S. Collins, Kai Wünnemann, and Natalia Artemieva
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Physics ,Classical mechanics - Published
- 2012
14. The Modification Stage of Crater Formation
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Thomas Kenkmann, Gareth S. Collins, and Kai Wünnemann
- Subjects
Impact crater ,Stage (stratigraphy) ,Geology ,Astrobiology - Published
- 2012
15. Shock experiments in range of 10-45 GPa with small multidomain magnetite in porous targets
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Alexander Deutsch, Tomas Kohout, Lauri J. Pesonen, Kai Wünnemann, Erkki Heikinheimo, D. Nowka, and Ulrich Hornemann
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Pellets ,Mineralogy ,equipment and supplies ,010502 geochemistry & geophysics ,01 natural sciences ,Magnetic susceptibility ,Volcanic rock ,chemistry.chemical_compound ,Geophysics ,chemistry ,13. Climate action ,Space and Planetary Science ,Hardening (metallurgy) ,Sedimentary rock ,Porosity ,Softening ,Geology ,0105 earth and related environmental sciences ,Magnetite - Abstract
– Physical properties of multidomain magnetite-bearing porous pellets shocked up to 45 GPa were measured. The results show general magnetic softening as a result of shock. However, a relative magnetic hardening trend and slight magnetic susceptibility decrease is observed with increasing pressure among shocked samples. Initially, the shock also seems to cause a slight decrease in porosity, but at higher shock pressures macroscopic porosity increases progressively in our pellets. The microscopic porosity remains almost unchanged. Since our samples have distinctly higher initial porosity compared with samples used in previous studies, our results may be representative for impacts into highly porous magnetite-bearing sedimentary or volcanic rocks and are relevant to impacts into such target rocks on Earth and Mars.
- Published
- 2012
16. Insights into the morphology of the Serra da Cangalha impact structure from geophysical modeling
- Author
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Eder Cassola Molina, Wolf Uwe Reimold, Kai Wünnemann, M. A. R. Vasconcelos, Elder Yokoyama, and Alvaro Penteado Crósta
- Subjects
Current (stream) ,Gravity (chemistry) ,Geophysics ,Basement (geology) ,Meteorite ,Impact crater ,Space and Planetary Science ,Context (language use) ,Impact structure ,Geology ,Gravity anomaly - Abstract
– Forward modeling is commonly applied to gravity field data of impact structures to determine the main gravity anomaly sources. In this context, we have developed 2.5-D gravity models of the Serra da Cangalha impact structure for the purpose of investigating geological bodies/structures underneath the crater. Interpretation of the models was supported by ground magnetic data acquired along profiles, as well as by high resolution aeromagnetic data. Ground magnetic data reveal the presence of short-wavelength anomalies probably related to shallow magnetic sources that could have been emplaced during the cratering process. Aeromagnetic data show that the basement underneath the crater occurs at an average depth of about 1.9 km, whereas in the region beneath the central uplift it is raised to 0.5–1 km below the current surface. These depths are also supported by 2.5-D gravity models showing a gentle relief for the basement beneath the central uplift area. Geophysical data were used to provide further constraints for numeral modeling of crater formation that provided important information on the structural modification that affected the rocks underneath the crater, as well as on shock-induced modifications of target rocks. The results showed that the morphology is consistent with the current observations of the crater and that Serra da Cangalha was formed by a meteorite of approximately 1.4 km diameter striking at 12 km s−1.
- Published
- 2012
17. Numerical modeling of oblique hypervelocity impacts on strong ductile targets
- Author
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Anton T. Kearsley, Thomas M. Davison, Gareth S. Collins, Kai Wünnemann, and D. Elbeshausen
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business.industry ,media_common.quotation_subject ,Oblique case ,Mechanics ,Asymmetry ,Strength of materials ,Geophysics ,Optics ,Impact crater ,Meteorite ,Space and Planetary Science ,Hypervelocity ,Target strength ,business ,Material properties ,Geology ,media_common - Abstract
– The majority of meteorite impacts occur at oblique incidence angles. However, many of the effects of obliquity on impact crater size and morphology are poorly understood. Laboratory experiments and numerical models have shown that crater size decreases with impact angle, the along-range crater profile becomes asymmetric at low incidence angles, and below a certain threshold angle the crater planform becomes elliptical. Experimental results at approximately constant impact velocity suggest that the elliptical threshold angle depends on target material properties. Herein, we test the hypothesis that the threshold for oblique crater asymmetry depends on target material strength. Three-dimensional numerical modeling offers a unique opportunity to study the individual effects of both impact angle and target strength; however, a systematic study of these two parameters has not previously been performed. In this work, the three-dimensional shock physics code iSALE-3D is validated against laboratory experiments of impacts into a strong, ductile target material. Digital elevation models of craters formed in laboratory experiments were created from stereo pairs of scanning electron microscope images, allowing the size and morphology to be directly compared with the iSALE-3D craters. The simulated craters show excellent agreement with both the crater size and morphology of the laboratory experiments. iSALE-3D is also used to investigate the effect of target strength on oblique incidence impact cratering. We find that the elliptical threshold angle decreases with decreasing target strength, and hence with increasing cratering efficiency. Our simulations of impacts on ductile targets also support the prediction from Chapman and McKinnon (1986) that cratering efficiency depends on only the vertical component of the velocity vector.
- Published
- 2011
18. Impact cratering in sandstone: The MEMIN pilot study on the effect of pore water
- Author
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Michael H. Poelchau, Thomas Kenkmann, Klaus Thoma, Frank Schäfer, Kai Wünnemann, and Alexander Deutsch
- Subjects
Pore water pressure ,Geophysics ,Volume (thermodynamics) ,Meteorite ,Impact crater ,Space and Planetary Science ,Vaporization ,Mineralogy ,SPHERES ,Geotechnical engineering ,Spall ,Porosity ,Geology - Abstract
– Planetary surfaces are subjected to meteorite bombardment and crater formation. Rocks forming these surfaces are often porous and contain fluids. To understand the role of both parameters on impact cratering, we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter-sized steel spheres. We utilized a 40 m two-stage light-gas gun to achieve impact velocities of up to 5.4 km s−1. Cratering efficiency, ejection velocities, and spall volume are enhanced if the pore space of the sandstone is filled with water. In addition, the crater morphologies differ substantially from wet to dry targets, i.e., craters in wet targets are larger, but shallower. We report on the effects of pore water on the excavation flow field and the degree of target damage. We suggest that vaporization of water upon pressure release significantly contributes to the impact process.
- Published
- 2011
19. The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage
- Author
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Michael H. Poelchau, D. Elbeshausen, H. Nunez Del Prado, Natalia Artemieva, Kai Wünnemann, and Thomas Kenkmann
- Subjects
Shock wave ,Terminal velocity ,Meteoroid ,Geophysics ,Breakup ,Meteorite ,Impact crater ,Space and Planetary Science ,Chondrite ,Meteoritos ,Cráter meteorítico ,Estructuras de impacto ,Ejecta ,Geology - Abstract
pp. 985-1000 The recent Carancas meteorite impact event caused a worldwide sensation. An H4–5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye-witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter-sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100–1000 MJ (0.024–0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12–14 kms-1) and shallow entry angles (
- Published
- 2009
20. Characteristics of oceanic impact-induced large water waves-Re-evaluation of the tsunami hazard
- Author
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Kay Hofmann, Robert Weiss, and Kai Wünnemann
- Subjects
Wave propagation ,Breaking wave ,Geophysics ,symbols.namesake ,Waves and shallow water ,Impact crater ,Space and Planetary Science ,Wave shoaling ,Wind wave ,Hypervelocity ,symbols ,Rayleigh wave ,Physics::Atmospheric and Oceanic Physics ,Geology - Abstract
The potential hazard of a meteorite impact in the ocean is controversial with respect to the destructive power of generated large ocean waves (tsunamis). We used numerical modeling of hypervelocity impact to investigate the generation mechanism and the characteristics of the resulting waves up to a distance of 100150 projectile radii. The wave signal is primarily controlled by the ratio between projectile diameter and water depth, and can be roughly classified into deep-water and shallow-water impacts. In the latter, the collapse of the crater rim results in a wave signal similar to solitary waves, which propagate and decay in agreement with shallow-water wave theory. The much more likely scenario for an asteroid impact on Earth is a relatively small body (much smaller than the water depth) striking the deep sea. In this case, the collapse of the transient crater results in a significantly different and much more complex wave signal that is characterized by strong nonlinear behavior. We found that such waves decay much more rapidly than previously assumed and cannot be treated as long waves. For this reason, the shallow-water theory is not applicable for the computation of wave propagation, and more complex models (full solution of the Boussinesq equations) are required.
- Published
- 2007
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