Grain crushing in geoscience materials-Key issues on crushing response,measurement and modeling:Review and preface     

Yang Xiao  Chandrakant SDesai  Ali Daouadji  Armin WStuedlein  Hanlong Liu  Hossam Abuel-Naga 《地学前缘(英文版)》2020,(2):363-374

Grain crushing is commonly encountered in deep foundation engineering,high rockfill dam engineering,railway engineering,mining engineering,coastal engineering,petroleum engineering,and other geoscience application.Grain crushing is affected by fundamental soil characteristics,such as their mineral strength,grain size and distribution,grain shape,density and specimen size,and also by external factors including stress magnitude and path,loading rate and duration,degree of saturation,temperature and geochemical environment.Crushable material becomes a series of different materials with the change in its grading during grain crushing,resulting in a decrease in strength and dilatancy and an increase in compressibility.Effects of grain crushing on strength,dilatancy,deformation and failure mechanisms have been extensively investigated through laboratory testing,discrete element method(DEM)modelling,Weibull statistics,and constitutive modelling within the framework of the extended crushing-dependent critical state theory or the energy-based theory.Eleven papers summarized in this review article for this special issue addressed the above issues in grain crushing through the advanced testing and modelling.  相似文献   

On the Non-monotonic Variation of the Entrainment Buoyancy Flux with Wind Shear     

Fodor  Katherine  Mellado  Juan Pedro  Haghshenas  Armin 《Boundary-Layer Meteorology》2022,184(3):463-477

Boundary-Layer Meteorology - The magnitude of the entrainment buoyancy flux, and hence the growth rate of the convective boundary layer, does not increase monotonically with wind shear....  相似文献   

Serviceability limit state design for uplift of helical anchors in clay     

Armin W. Stuedlein  Marco Uzielli 《Geomechanics and Geoengineering》2014,9(3):173-186

Presently, no displacement-based design methodology exists for helical anchors subjected to tensile or uplift loading. This study investigates the statistical and probabilistic aspects of the load-displacement uncertainty associated with a database of thirty-seven uplift loading tests of helical anchors founded within cohesive soils. Initially, an ultimate resistance model is identified, and the semi-empirical uplift breakout factor statistically characterized. A relationship between ultimate resistance and slope tangent capacity is established, and used to form the basis for normalizing the load-displacement response. Hyperbolic and power law models are statistically evaluated for use in serving as a reference load-displacement model; the hyperbolic curve was selected based on goodness-of-fit statistics. Monte Carlo reliability simulations are used to establish an equivalent-deterministic load factor that associates the selected load factor with a probability of exceeding a pre-determined allowable uplift displacement, given uncertainty in the undrained shear strength, ultimate resistance model, transformation uncertainty, uncertainty in the allowable displacement, and variability in uplift loading. A practical example is provided to show the intended use of this probabilistic helical anchor displacement model.  相似文献   

The FORS Deep Field: the photometric catalog     

Jochen Heidt  Immo Appenzeller  Armin Gabasch  Klaus Jäger  Stella Seitz  The FDF-Team 《Astrophysics and Space Science》2003,284(2):385-388

The FORS Deep Field project is a multi-colour, multi-object spectroscopical investigation of a ∼ 7′ × ′' region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and evolution of galaxies in the young Universe. In this contribution, the photometric observations are presented. In particular, a combined B and I selected UBgRIJKs photometric catalog of 8753 objects in the FDF is presented and its content is briefly described. The formal 50% completeness limits for point sources, derived from the coadded images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57in U, B, g, R, I, J and Ks, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Hydroelastic impact of a wedge-shaped body     

Kevin J. Maki  Donghee Lee  Armin W. Troesch  Nickolas Vlahopoulos 《Ocean Engineering》2011,38(4):621-629

In this paper a hydroelastic method for the design of marine structures is used to study the impact of a wedge-shaped body onto a calm free-surface. The method combines computational fluid dynamics and dynamic finite-element techniques to predict the hydroelastic response of a structure in the time domain. The basic idea of the method is to predict the stress field on the fluid-structure interface due to rigid-body impact, and then to transfer the information to a wet modal model. The one-way transfer of information from the fluid simulation to the structure has two important advantages with respect to a fully coupled simulation: a single rigid-body motion computation can be reused for subsequent analyses after the structure has been redesigned, and cost of the fluid dynamic simulation is not increased due to iteration which is required in coupled simulations. The maximum displacement of an elastic wedge during the impact and penetration stages are compared with published results from a fully coupled theoretical model and a fully coupled numerical solver. The present method requires approximation of the flexural added mass, and the comparison with other results shows that the approximation is satisfactory for predicting maximum displacement.  相似文献   

Estimation of extreme slamming pressures using the non-uniform Fourier phase distributions of a design loads generator     

Laura K. Alford  Dae-Hyun Kim  Armin W. Troesch 《Ocean Engineering》2011,38(5-6):748-762

Slamming pressures are predicted using a nonlinear ship motion program whose input is an ensemble of short wave trains tailored to produce a large, linear pitch response. These short wave trains are calculated via a design methodology that first creates short time series containing a specified, large ship response and then back-calculates the incident wave trains using linear systems theory. The background simulations and theory used to create these short time series are presented here. Monte Carlo simulation of moderately rare events of a random process indicate the random Fourier component phase PDFs are non-uniform, non-identically distributed, and dependent on the rarity of the target event. These PDFs are modeled using a single parameter, Modified Gaussian distribution and used to generate design time series with a given expected value at a specific time. To predict rare events without resorting to Monte Carlo simulation, the parameters of the Modified Gaussian distributions are calculated via characteristic function comparison. The characteristic functions compare a target PDF calculated from extreme value theory to a PDF based on a discrete Fourier representation of the stochastic process with non-uniform component phases. The comparison to extreme value theory helps to quantify the risk associated with rare events.  相似文献   

Eruptive history and magmatic evolution of the 1.9 kyr Plinian dacitic Chiltepe Tephra from Apoyeque volcano in west-central Nicaragua   总被引：1，自引：1，他引：0  

Steffen Kutterolf  Armin Freundt  Cosima Burkert 《Bulletin of Volcanology》2011,73(7):811-831

The youngest dacitic Plinian eruption in west-central Nicaragua, forming the 18 km³ Chiltepe Tephra (CT), occurred about nineteen hundred years ago at Apoyeque stratovolcano, which dominates the Chiltepe volcanic complex 15 km north of the capital Managua, where the CT is 2 m thick. We have traced the CT from its proximal facies at the crater rim, through the medial facies in the lowlands around Apoyeque, and to the distal facies up to 550 km offshore in the Pacific. While medial and distal facies consist of widespread Plinian fall deposits, the proximal facies reveals the complexity of this eruption, which we divide into four phases (I–IV). Interaction of rising magma with a pre-existing crater lake generated the phreatomagmatic opening phase I of the eruption, which produced ash fall with accretionary lapilli. Phase II marked a rapid change to persistent magmatic activity that yielded several large Plinian eruptions, declining through a period of unstable eruption conditions, followed by a short hiatus. Phase III began with unstable conditions, probably as a result of eastward migration and widening of the vent, leading to a second period of Plinian eruptions with three major events reaching magma discharge rates five times larger than those of phase II. Phase III again declined through unstable eruption conditions before magmatic activity terminated. Numerous explosions in the shallow hydrothermal system during the final phase IV resulted in the formation of a phreatic tuff ring on the rim of Apoyeque crater. The white, highly-vesicular, dacitic CT pumice contains plagioclase (An_45–68), orthopyroxene, clinopyroxene, and minor hornblende, apatite and titanomagnetite phenocrysts. A very subordinate fraction of gray pumice has the highest crystal content, the least evolved bulk-rock, but the most evolved matrix-glass composition. The CT dacite has two unusual compositional features: (1) all white dacite has the same melt (matrix-glass) composition such that variations in bulk-rock compositions (64–68 wt% SiO₂) simply reflect different phenocryst contents of 10–35%, interpreted as the result of gradual phenocryst settling in the magma chamber. (2) Abundant olivine crystals with a bimodal distribution in Mg# (modes at Mg# = 0.75 and Mg# = 0.8) are dispersed throughout the erupted dacite. These are clearly out of equilibrium with the dacitic melt and are interpreted as xenocrysts derived from the basaltic Nejapa-Miraflores volcanic lineament that intersects the Chiltepe volcanic complex and was contemporaneously active. Thermobarometric estimates place the dacitic CT magma reservoir in the upper crust (<250 MPa), with a temperature of about 890°C and about 5 wt% water dissolved in the melt. Comparing water and chlorine contents with respective solubility models suggests that volatile degassing began in the magma reservoir and triggered the CT eruption. From the vertical compositional variation pattern of the CT we deduce that the conduit tapped the magma chamber not at the top but from the side, at some deeper level, and that subsequent magma withdrawal was governed by both variations in discharge rate and possible upward migration and/or widening of the conduit entrance.  相似文献   

Discussion of the Paper: A State-of-the-Art Review of Stone/Sand-Column Reinforced Clay Systems by Shadi S. Najjar     

Armin W. Stuedlein  Robert D. Holtz 《Geotechnical and Geological Engineering》2013,31(5):1617-1619

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Nature of magmatism and sedimentation at a Columbia active margin: Insights from combined U–Pb and Lu–Hf isotope data of detrital zircons from NW India     

Parampreet Kaur  Armin Zeh  Naveen Chaudhri  Axel Gerdes  Martin Okrusch 《Gondwana Research》2013,23(3):1040-1052

Detrital zircons from a Palaeoproterozoic quartzite, deposited between 1.85 and 1.82 Ga in the northern Aravalli orogen of NW India, show a distinctive age peak of ca. 1.85 Ga and variable, but largely subchondritic εHf_{1.85 Ga} between ? 1.3 and ? 21.0 corresponding to hafnium model ages of 2.5 to 3.6 Ga. These data indicate an important period of reworking of ancient (Eo- to Neoarchaean), strongly heterogeneous continental crust at this time. Prevalence of ca. 1.85 Ga subduction-related granitoids, almost identical U–Pb age spectra and εHf_t of detrital zircons in ca. 1.85 Ga metasedimentary rocks in the Aravalli orogen and the inner Lesser Himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late Palaeoproterozoic. All together, the data constrain a rapid succession of sedimentation, metamorphism and subduction-related magmatic activity and support the interpretation of an active geodynamic realm along the entire north Indian margin at ca. 1.85 Ga. Comparison of detrital zircon data in conjunction with published paleomagnetic data from north India and other crustal blocks of the Columbia supercontinent, additionally, suggest a close affinity of north India with Madagascar, the Cathaysia block of South China and South Korea during Columbia times.  相似文献   

Capability of ETM+ in estimates standing stock in beech stands of mountain forest     

Seyed Armin Hashemi  Mir Mozaffar Fallahchai  Farahzad Jahan Bakhsh 《Arabian Journal of Geosciences》2013,6(9):3371-3376

Stand volume is an important criterion in forest sciences for monitoring status and function of forests, estimation of productivity, prediction and modeling of forest disturbance, economic and environmental issues, and forest planning. The aim of this research is to evaluate the ETM+ sensor of Landsat 7 satellite data ability for forest timber volume estimation. For this purpose, 40 selective sample plots with 60?×?60 m dimension were selected, and in each sample plot, standing volume was calculated. Correspondent digital data to plots were extracted from spectral and considered as independent variables. Original stand volume data, square root, and logarithm of them were considered as dependent potential for stand volume estimation. Variables using stepwise regression, the best model with coefficient of determination, and adjusted coefficient of determination with regard to determining the appropriate model were modified Log?V=?07.546?+?0.85Greenness???10.564NDWI???28 0.063Band1. In this model, the coefficient of determination and adjusted coefficient of determination were obtained 0.778 and 0.770, respectively. Result showed that spectral data of the mentioned sensor have a moderate.  相似文献