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Hydrodynamic, suspension and bed-form measurements were made 2 km off the Dutch coast near Noordwijk aan Zee in ∼14 m water depth for a period of 32 days in 2003. Tidal currents were just able to suspend sand at the bed at peak spring tide but most suspension and transport occurred as a result of the combination of waves and currents. Burst-average (17 min) sand concentration profiles (C¯-profiles) from an acoustic backscatter instrument were used to define the (varying) location of the sea-bed, following the method used by Green et al. [Green, M.O., Dolphin, T.J., Swales, A., Vincent, C.E., 1999. Transport of mixed-size sediments in a tidal channel. Coastal Sediments ‘99, edited by N.C. Kraus, and W.G. McDougal, ASCE, Long Island, New York, pp. 644–658]. Reference concentrations at the sea-bed (C0) and at 1 cm (C1) were examined in relation to both the hydrodynamic conditions and the type of bed forms present. The C0 predictive equations of Green and Black [Green, M.O., Black, K.P., Suspended sediment reference concentration under waves: field measurements and critical analysis of two predictive models, Coastal Engineering, 38, 115–141, 1999](short-wave ripples) and Nielsen [Nielsen, P., Suspended sediment concentrations under waves, Coastal Engineering, 10, 23–31, 1986](all bed forms; includes ripple steepness), both of which require knowledge of the bed-form type, were not as successful in explaining the variance in our C0 data as a regression of C0 against the skin-friction Shields parameter θ′cw that ignored bed-form type (73% of variance explained). The values of the reference concentration C1 were compared with the Lee et al. [Lee, G.-H., Dade, W.B., Friedrichs, C.T., Vincent, C.E., Examination of Reference Concentration Under Waves and Currents on the Inner Shelf., Journal of Geophysical Research, 109, 1–10, 2004] equation which predicts C1 from the product of the Shields parameter and the inverse Rouse parameter; 51% of the variance in C1 was explained. 相似文献
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Richard J. Bathurst Tony M. Allen Yoshihisa Miyata Sina Javankhoshdel Nezam Bozorgzadeh 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):214-225
ABSTRACTMechanically stabilized earth (MSE) walls must be designed with adequate margins of safety against internal stability failure described by tensile strength and pullout limit states. Probabilities of failure (or reliability index) will vary strongly with the accuracy of the underlying models that appear in limit state performance functions. In this paper, prior work by the authors and co-workers on this topic is reviewed. Relative performance is explored in the context of the reliability (or probability of failure) of steel and polymeric reinforcing elements in MSE walls using limit state performance functions with load and resistance models having different accuracy. 相似文献
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Omar A. Alharbi Michael R. Phillips Allan T. Williams Tony Thomas Mohammed Hakami Jehad Kerbe Abdoul Jelil Niang ElSayed Hermas Khalid Al-Ghamdi 《Arabian Journal of Geosciences》2017,10(16):360
Jizan is one of the Saudi Arabian coastal cities endowed with diverse natural settings, which includes Ash Shuqayq in the north, Turfah in the centre and Jizan in the South. This work analysed specific environmental characteristics, such as spits, sabkhas and wadis. Assessments used Landsat imagery to examine coastal change between 1973 and 2011. The cumulative temporal change identified regression trends given by coefficients of determination that explained a significant percentage of data variation for Jizan (R 2 = 69%) and Turfah (R 2 = 72%), while Ash Shuqayq was insignificant (R 2 = 14%). Inter-survey results predicted future change, although trends were not significant, i.e. Jizan (R 2 = 22%), Turfah (R 2 = 14%) and Ash Shuqayq (R 2 = 3 and 61% with outlying value removed). Aerial photos showed regional coastal changes, which included a maximum accretion of 36.4 m and maximum erosion of 12.9 m. These are scientifically effective techniques to monitor regional coastal change, i.e. erosion and accretion and identified rates of 0.59, 1.80 and 3.53 myr?1 for Ash Shuqayq, Turfah and Jizan. Changes were linked to infrastructure developments, e.g. tourism, port development and natural causes, e.g. spit formations and wadi outfalls. 相似文献
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Earthquake response of a multiblock nuclear reactor graphite core: Experimental model vs simulations 下载免费PDF全文
Elia Voyagaki Panos Kloukinas Matt Dietz Luiza Dihoru Tony Horseman Olafur Oddbjornsson Adam J. Crewe Colin A. Taylor Alan Steer 《地震工程与结构动力学》2018,47(13):2601-2626
The complex dynamics of a quarter‐scale model of a graphite nuclear reactor core, representative of the second generation of British advanced gas‐cooled nuclear reactors, is investigated numerically and experimentally. Advanced gas‐cooled nuclear reactor cores are polygonal, multilayer, arrays of graphite bricks, with each brick allowed to rock by design relative to each other in accordance with the boundary conditions. A 35 000 DOF, nonlinear finite element model of the core created by Atkins Nuclear, was analysed on a high performance computing facility at the University of Bristol, and a corresponding 8 t physical model, equipped with 3200 data acquisition channels, was built and tested on the University of Bristol 6‐DOF shaking table. In this paper, the two models are subjected to a series of (1) synthetic earthquake and (2) idealised harmonic input motions. The experimental data are used to compare and verify the two models and explore the dynamics of the core. A kinematic model of the response is also developed based solely on geometric constraints. The results are presented in the form of response maps and graphs. Important conclusions are drawn as to the dynamics and earthquake response of such systems, which inform numerical model validation. It is found that contrary to the case of a small number of rocking blocks that exhibit highly complex response patterns, the behaviour of the model at hand is both smooth and repeatable. An analogy between the response of the core and that of dense granular matter exhibiting particle interlocking and dilatancy is highlighted. 相似文献
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Julien Charreau Pierre-Henri Blard Jéna Zumaque Léo C.P. Martin Tony Delobel Lucas Szafran 《地球表面变化过程与地形》2019,44(12):2349-2365
The calculation of denudation rates from the measured cosmogenic nuclide concentrations in river sediments requires assumptions and approximations. Several different approaches and numerical tools are available in the literature. A widely used analytical approach represents the muogenic production with one or two exponentials, assumes the attenuation length of muons to be constant and also neglects temporal variations in the Earth's magnetic field. The denudation rates are then calculated directly and analytically from the measured concentrations. A second numerical and iterative approach was more recently proposed and considers a more rigorous muogenic production law based on pre-calculated variable attenuation length of muons and accounts for temporal changes of the magnetic field. It also assumes a specific distribution of denudation rates throughout the basin and uses an iterative approach to calculate the basin average denudation rates. We tested the two approaches across several natural basins and found that both approaches provide similar denudation results. Hence, assuming exponential muogenic production and constant attenuation length of muons in the rock has little impact on the derived denudation rates. Therefore, unless a priori known distributions of denudation rates are to be tested, there does not appear to be any particular gain from using the second iterative method which is computationally less effective. Based on these findings, we developed and describe here Basinga , a new ArcGIS® and QGIS toolbox which computes the basin average scaling factors, cosmogenic production rates and denudation rates for several tens of drainage basins together. Basinga follows either the Lal/Stone or the Lifton/Sato/Dunai scaling schemes and includes several optional tools for correcting for topographic shielding, ice cover and lithology. We have also developed an original method for correcting the cosmogenic production rates for past variations in the Earth's magnetic field. © 2019 John Wiley & Sons, Ltd. 相似文献
108.
Andrea Román-Sánchez Tony Reimann Jakob Wallinga Tom Vanwalleghem 《地球表面变化过程与地形》2019,44(10):2051-2065
The interplay of bioturbation, soil production and long-term erosion–deposition in soil and landscape co-evolution is poorly understood. Single-grain post-infrared infrared stimulated luminescence (post-IR IRSL) measurements on sand-sized grains of feldspar from the soil matrix can provide direct information on all three processes. To explore the potential of this novel method, we propose a conceptual model of how post-IR IRSL-derived burial age and fraction of surface-visiting grains change with soil depth and along a hillslope catena. We then tested this conceptual model by comparison with post-IR IRSL results for 15 samples taken at different depths within four soil profiles along a hillslope catena in the Santa Clotilde Critical Zone Observatory (southern Spain). In our work, we observed clear differences in apparent post-IR IRSL burial age distributions with depth along the catena, with younger ages and more linear age–depth structure for the hill-base profile, indicating the influence of lateral deposition processes. We noted shallower soils and truncated burial age–depth functions for the two erosional mid-slope profiles, and an exponential decline of burial age with depth for the hill-top profile. We suggest that the downslope increase in the fraction of surface-visiting grains at intermediate depths (20 cm) indicates creep to be the dominant erosion process. Our study demonstrates that single-grain feldspar luminescence signature-depth profiles provide a new way of tracing vertical and lateral soil mixing and transport processes. In addition, we propose a new objective luminescence-based criterion for mapping the soil-bedrock boundary, thus producing soil depths in better agreement with geomorphological process considerations. Our work highlights the possibilities of feldspar single grain techniques to provide quantitative insights into soil production, bioturbation and erosion–deposition. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
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