Theory-guided machine learning to predict density evolution of sand dynamically compacted under Ko condition

Acta Geotechnica - This paper introduces a theory-guided machine learning (TGML) framework, which combines a theoretical model (TM) and a machine learning (ML) algorithm to predict compaction...     

Compounding effects of human activities and climatic changes on surface water availability in Iran

Climatic Change - By combining long-term ground-based data on water withdrawal with climate model projections, this study quantifies the compounding effects of human activities and climate change...     

A laboratory investigation of bed-load transport of gravel sediments under dam break flow

Dam break flows and resulting river bed erosion can have disastrous impacts on human safety,infrastructure,and environmental quality.However,there is a lack of research on the mobility of non-uniform sediment mixtures resulting from dam break flows and how these differ from uniform sized sediment.In this paper,laboratory flume experiments revealed that coarse and fine fractions in non-uniform sediment had a higher and a lower bed-load parameter,respectively,than uniform sediments of the same size.Thus,the finer fractions were more stable and the coarser fractions were more erodible in a nonuniform bed compared to a uniform-grained bed.These differences can be explained by the hiding and protrusion of these fractions,respectively.By investigating changes in mobility of the mixed-size fractions with reservoir water levels,the results revealed that at low water levels,when the coarser fractions were only just mobile,the bed-load parameter of the finer fractions was higher than the coarser fractions.The opposite was observed at a higher water level,when a significant proportion of the coarsest fractions was mobilized.The higher protrusion of these grains had an important effect on their mobility relative to the finer grains.The transported sediment on these mixed-sized beds was coarser than the initial bed sediment,and became coarser with an increase in reservoir water level.     

A global method for coupling transport with chemistry in heterogeneous porous media

Modeling reactive transport in porous media, using a local chemical equilibrium assumption, leads to a system of advection–diffusion PDEs coupled with algebraic equations. When solving this coupled system, the algebraic equations have to be solved at each grid point for each chemical species and at each time step. This leads to a coupled non-linear system. In this paper, a global solution approach that enables to keep the software codes for transport and chemistry distinct is proposed. The method applies the Newton–Krylov framework to the formulation for reactive transport used in operator splitting. The method is formulated in terms of total mobile and total fixed concentrations and uses the chemical solver as a black box, as it only requires that one be able to solve chemical equilibrium problems (and compute derivatives) without having to know the solution method. An additional advantage of the Newton–Krylov method is that the Jacobian is only needed as an operator in a Jacobian matrix times vector product. The proposed method is tested on the MoMaS reactive transport benchmark.     

Elasticity of a beryllium silicate (phenacite: Be2SiO4)

The adiabatic single-crystal elastic moduli of a beryllium silicate (phenacite: Be₂SiO₄, trigonal, have been determined at atmospheric pressure and 22° C by Brillouin spectroscopy. The elastic stiffness moduli in gigapascals are: C ₁₁=341.9 C ₃₃=391.0 C ₄₄=91.4 C ₆₆= 96.9 C ₁₂=148.0 C ₁₃=136.0 C ₁₄= 0.1 C ₁₅= 3.5Overall, the elastic stiffness moduli for phenacite parallel and perpendicular to the c axis are comparable (i.e., it is almost cubic in its elastic signature). The elastic moduli can be rationalized in terms of division of the structure into two types of coordination polyhedra (1Si+2Be) with slightly different stiffnesses, which are linked to form a three dimensional framework. Values of the isothermal bulk modulus and the linear compressibilities, as determined from hydrostatic compression experiments of Hazen and Au (1986), are in good agreement with those obtained here. Combining the two studies indicates a low pressure derivative of the bulk modulus for phenacite.     

An Assessment of Changes in Winter Cold and Warm Spells over Canada

The recent Third Assessment Report (TAR) of the Intergovernmental Panel onClimate Change (IPCC) indicated that observed 20th century changes in severalclimatic extremes are qualitatively consistent with those expected due to increasedgreenhouse gases. However, a lack of adequate data and analyses make conclusiveevidence of changing extremes somewhat difficult, particularly, in a global sense.In Canada, extreme temperature events, especially those during winter, can havemany adverse environmental and economic impacts. In light of the aforementionedIPCC report, the main focus of this analysis is to examine observed trends andvariability in the frequency, duration, and intensity of winter (Jan–Feb–Mar) cold and warm spells over Canada during the second half of the 20th century.Cold spell trends display substantial spatial variability across the country. From1950–1998, western Canada has experienced decreases in the frequency, duration, and intensity of cold spells, while in the east, distinct increases in the frequency and duration have occurred. These increases are likely associated with morefrequent occurrences of the positive phase of the North Atlantic Oscillation (NAO)during the last several decades. With regard to winter warm spells, significantincreases in both the frequency and duration of these episodes were observedacross most of Canada. One exception was found in the extreme northeasternregions, where warm spells are becoming shorter and less frequent. The resultsof this study are discussed within the context of climate warming expectations.     

The role of visual saliency in the automation of seismic interpretation

In this paper, we propose a workflow based on SalSi for the detection and delineation of geological structures such as salt domes. SalSi is a seismic attribute designed based on the modelling of human visual system that detects the salient features and captures the spatial correlation within seismic volumes for delineating seismic structures. Using this attribute we cannot only highlight the neighbouring regions of salt domes to assist a seismic interpreter but also delineate such structures using a region growing method and post‐processing. The proposed delineation workflow detects the salt‐dome boundary with very good precision and accuracy. Experimental results show the effectiveness of the proposed workflow on a real seismic dataset acquired from the North Sea, F3 block. For the subjective evaluation of the results of different salt‐dome delineation algorithms, we have used a reference salt‐dome boundary interpreted by a geophysicist. For the objective evaluation of results, we have used five different metrics based on pixels, shape, and curvedness to establish the effectiveness of the proposed workflow. The proposed workflow is not only fast but also yields better results as compared with other salt‐dome delineation algorithms and shows a promising potential in seismic interpretation.     

Application of artificial neural networks in optimal tuning of tuned mass dampers implemented in high-rise buildings subjected to wind load

High-rise buildings are usually considered as flexible structures with low inherent damping. Therefore, these kinds of buildings are susceptible to wind-induced vibration. Tuned Mass Damper (TMD) can be used as an effective device to mitigate excessive vibrations. In this study, Artificial Neural Networks is used to find optimal mechanical properties of TMD for high-rise buildings subjected to wind load. The patterns obtained from structural analysis of different multi degree of freedom (MDF) systems are used for training neural networks. In order to obtain these patterns, structural models of some systems with 10 to 80 degrees-of-freedoms are built in MATLAB/SIMULINK program. Finally, the optimal properties of TMD are determined based on the objective of maximum displacement response reduction. The Auto-Regressive model is used to simulate the wind load. In this way, the uncertainties related to wind loading can be taken into account in neural network’s outputs. After training the neural network, it becomes possible to set the frequency and TMD mass ratio as inputs and get the optimal TMD frequency and damping ratio as outputs. As a case study, a benchmark 76-story office building is considered and the presented procedure is used to obtain optimal characteristics of the TMD for the building.     

Mapping dune dynamics by InSAR coherence

It is generally held that subtle changes in sandy environments are very difficult to detect in imagery. Nonetheless, this study demonstrates how synthetic aperture radar (SAR) interferometric decorrelation can be used to identify changes in individual sand dunes. The use of coherence maps over time facilitates the analysis of dune dynamics, both temporally and spatially. The Ashdod‐Nizzanim coastal dunes, along the southern coastal plain of Israel, were chosen as an illustrative example of the analysis of dune dynamics. High‐resolution TerraSAR‐X (TSX) radar images covering the entire research area were acquired for the period February to July 2012, together with meteorology data (wind and rain) for the area. The coherence results enabled the stability of individual dunes to be described as a function of time. It was found that the dune crests were more stable than the windward slopes and that the degree of stability was dependent on the distance of the dune from the sea. The results of this study show the potential of using interferometric synthetic aperture radar (InSAR) decorrelation for aeolian studies, even in areas characterized by low coherence. Copyright © 2017 John Wiley & Sons, Ltd.