Image transforms for determining fit-for-purpose complexity of geostatistical models in flow modeling

Increased diversity of water or energy resources has led to an increased complexity in models aimed at representing accurately dynamic behavior and geological variability in such systems. In terms of variability of properties at least, simple layered models have mostly been replaced with more complex geostatistical models. The newest trend is to replace covariance-based models with geologically more realistic models such as Boolean, multiple-point, surface-, or process-based models. In this paper, we address the following question: given some design purpose or a set of flow-based decision variables, does adding more complexity increase predictability and ultimately improve decisions based on such models? In this paper, we do not attempt to make any generalizing statements or answer this question with yes/no, but provide some initial ideas on practical workflows to discover the needed complexity. We do treat complexity only in the context of decision making under uncertainty. Two workflows are proposed: complexifying versus simplifying. In these workflows, we attempt to extract, using image transforms, relevant features of the variability between geostatistical realizations that are related to uncertainty in flow dynamics. A simple distance-based calibration between the static variability and dynamic variability provides a means to decide on what the relevant complexity of geostatistical models should be for the given purpose.     

A finite volume / discontinuous Galerkin method for the advective Cahn–Hilliard equation with degenerate mobility on porous domains stemming from micro-CT imaging

A numerical method is formulated for the solution of the advective Cahn–Hilliard (CH) equation with constant and degenerate mobility in three-dimensional porous media with non-vanishing velocity on the exterior boundary. The CH equation describes phase separation of an immiscible binary mixture at constant temperature in the presence of a conservation constraint and dissipation of free energy. Porous media / pore-scale problems specifically entail images of rocks in which the solid matrix and pore spaces are fully resolved. The interior penalty discontinuous Galerkin method is used for the spatial discretization of the CH equation in mixed form, while a semi-implicit convex–concave splitting is utilized for temporal discretization. The spatial approximation order is arbitrary, while it reduces to a finite volume scheme for the choice of element-wise constants. The resulting nonlinear systems of equations are reduced using the Schur complement and solved via inexact Newton’s method. The numerical scheme is first validated using numerical convergence tests and then applied to a number of fundamental problems for validation and numerical experimentation purposes including the case of degenerate mobility. First-order physical applicability and robustness of the numerical method are shown in a breakthrough scenario on a voxel set obtained from a micro-CT scan of a real sandstone rock sample.     

Spatial Statistical Properties of Pressure Solution Seams in Clastic Rocks in Southwest Ireland

Length, height, thickness and spacing measurements of pressure solution seams at outcrop, hand sample and thin section scale were taken from clastic rocks located in the southwest of Ireland. The lengths and spacings of pressure solution seams have similarly shaped (approximately log-hyperbolic) distributions at the observed scales suggesting that length and spacing distributions are scale-independent over the scales studied with a fractal dimension in the range of 1.4 to 1.6. Pressure solution seam lengths and thicknesses are related by a power-law and their spacings have a linear relationship to bed thickness. Although pressure solution seams are often considered as anticracks (forming under the same remote stresses as joints, but with opposite sign) we describe how the mechanism of pressure solution differs substantially from that of jointing. We use an existing mechanical model to show that stresses around pressure solution seam tips are much lower than those for joints under equal but opposite loading conditions. Pressure solution seams also have a decreasing tendency to lengthen as they grow, which is reflected in their length distributions. We propose that pressure solution seams, unlike joints, do not reach fracture saturation spacing because of transverse coalescence.     

Reservoir operation using system dynamics under climate change impacts: a case study of Yamchi reservoir,Iran

This paper proposes a decision support system for Yamchi reservoir operation in semi-arid region of Iran. The paper consists of the following steps: Firstly, the potential impacts of climate change on the streamflow are predicted. The study then presents the projections of future changes in temperature and precipitation under A2 scenario using the LARS-WG downscaling model and under RCP2.6, RCP4.5, and RCP8.5 using the statistical downscaling model (SDSM) in the northwestern of Iran. To do so, a general circulation model of HadCM3 is downscaled by using the LARS-WG model. As a result, the average temperature, for the horizon 2030 (2011–2030), will increase by 0.77 °C and precipitation will decrease by 11 mm. Secondly, the downscaled variables are used as input to the artificial neural network to investigate the possible impact of climate change on the runoffs. Thirdly, the system dynamics model is employed to model different scenarios for reservoir operation using the Vensim software. System dynamics is an effective approach for understanding the behavior of complex systems. Simulation results demonstrate that the water shortage in different sectors (including agriculture, domestic, industry, and environmental users) will be enormously increased in the case of business-as-usual strategy. In this research, by providing innovative management strategies, including deficit irrigation, the vulnerability of reservoir operation is reduced. The methodology is evaluated by using different modeling tests which then motivates using the methodology for other arid/semi-arid regions.     

Increasing numerical efficiency of iterative solution for total least-squares in datum transformations

Cartesian coordinate transformation between two erroneous coordinate systems is considered within the Errors-In-Variables (EIV) model. The adjustment of this model is usually called the total Least-Squares (LS). There are many iterative algorithms given in geodetic literature for this adjustment. They give equivalent results for the same example and for the same user-defined convergence error tolerance. However, their convergence speed and stability are affected adversely if the coefficient matrix of the normal equations in the iterative solution is ill-conditioned. The well-known numerical techniques, such as regularization, shifting-scaling of the variables in the model, etc., for fixing this problem are not applied easily to the complicated equations of these algorithms. The EIV model for coordinate transformations can be considered as the nonlinear Gauss-Helmert (GH) model. The (weighted) standard LS adjustment of the iteratively linearized GH model yields the (weighted) total LS solution. It is uncomplicated to use the above-mentioned numerical techniques in this LS adjustment procedure. In this contribution, it is shown how properly diminished coordinate systems can be used in the iterative solution of this adjustment. Although its equations are mainly studied herein for 3D similarity transformation with differential rotations, they can be derived for other kinds of coordinate transformations as shown in the study. The convergence properties of the algorithms established based on the LS adjustment of the GH model are studied considering numerical examples. These examples show that using the diminished coordinates for both systems increases the numerical efficiency of the iterative solution for total LS in geodetic datum transformation: the corresponding algorithm working with the diminished coordinates converges much faster with an error of at least 10^-5 times smaller than the one working with the original coordinates.     

Evaluation of diaphragm conditions in AAC floor structures with RC beams

Diaphragm action in floor structures is an important aspect that affects both local behaviors of individual members and consequently, the global response of a structure. The diaphragm action of a built structure, therefore needs to be compatible with the assumed diaphragm condition in the design phase to prevent unpredicted overloading of load bearing members in a seismic action. Autoclaved aerated concrete (AAC) is a cost-effective, lightweight and energy efficient material, and its usage as a construction material has rapidly increased in recent decades. However, there is a limited experience regarding the in-plane behavior of the floor structures made of AAC panels in terms of diaphragm action. In this paper, the in-plane response of AAC floors is experimentally investigated and the floor performance of a typical building is analytically investigated according to ASCE 7-16 (ASCE/SEI in Minimum design loads for buildings and other structures, The American Society of Civil Engineers, Reston, 2016). Full-scale experiments carried out through loading AAC floors in lateral directions to the panels, either parallel or perpendicular, provided important information about the damage progress and overall performance of such floors. A number of finite element modeling techniques that are generally used for modeling of AAC floors were examined and then validated through comparisons with test results. Finally, the diaphragm condition of a three-story building made of AAC walls and floor panels was assessed. The results indicated that the AAC floors in the examined building can be idealized as rigid diaphragms according to ASCE 7-16.     

Spatio-Temporal Prediction of Ionospheric Total Electron Content Using an Adaptive Data Fusion Technique

Geomagnetism and Aeronomy - The ionosphere, a part of upper atmosphere, plays an important role on the propagation of radio waves. Hence, understanding, remote sensing and monitoring of the...