Half-tapering strategy for conditional simulation with large datasets

Gaussian conditional realizations are routinely used for risk assessment and planning in a variety of Earth sciences applications. Conditional realizations can be obtained by first creating unconditional realizations that are then post-conditioned by kriging. Many efficient algorithms are available for the first step, so the bottleneck resides in the second step. Instead of doing the conditional simulations with the desired covariance (F approach) or with a tapered covariance (T approach), we propose to use the taper covariance only in the conditioning step (Half-Taper or HT approach). This enables to speed up the computations and to reduce memory requirements for the conditioning step but also to keep the right short scale variations in the realizations. A criterion based on mean square error of the simulation is derived to help anticipate the similarity of HT to F. Moreover, an index is used to predict the sparsity of the kriging matrix for the conditioning step. Some guides for the choice of the taper function are discussed. The distributions of a series of 1D, 2D and 3D scalar response functions are compared for F, T and HT approaches. The distributions obtained indicate a much better similarity to F with HT than with T.Comment: 39 pages, 2 Tables and 11 Figure

Multiphysics Modelling of Standing Column Well and Implementation of Heat Pumps Off-Loading Sequence

Abstract: A simplified but fully coupled multiphysics model involving heat transfer and groundwater flow within a SCW and its surrounding ground was implemented in COMSOL Multiphysics 4.2a with MATLAB to simulate a 24-hour heating operation. The heat pumps were modeled using interpolation functions thereby allowing the effect of the pumped water temperature on the capacity and coefficient of performance of the heat pumps to be accounted for. In the model presented here, a three level bleed control is applied when the temperature of the pumped water drops to 7, 6 and 5°C. If the pumped water temperature drops below 4°C, an off-loading sequence implemented via a MATLAB function allows the heat pumps to automatically shut down one by one at 10 minute intervals. Results demonstrate that the numerical model developed in this paper can successfully evaluate the EWT over time and that both bleed and off-loading sequence played a key role in maintaining the EWT within the heat pump's operational range

Hydrogeothermal characterization and modelling of a standing column well experimental installation

Standing column wells (SCW) are efficient ground heat exchangers that offer promising potential for integration in dense urban areas. Recent years have witnessed a growing interest in SCWs, resulting in the development of various simulation models incorporating heat transfer, groundwater flow and geochemical reactions within the well and the surrounding ground. However, these models commonly use a configuration that involves pumping at the bottom of the well and reinjection from its top, which can lead to installation and maintenance difficulties in deep wells. Furthermore, very few SCW models have been validated against reliable field data. This paper presents an original finite element model coupling advection-diffusion of heat and groundwater flow within a top pumped SCW and its surrounding ground as well as the experimental setup used for its validation. Within the scope of this study, experimental data obtained after an extensive field characterization campaign and a thermal response test performed with a large-scale geothermal laboratory were used directly as inputs in the numerical model. Experimental validation shows that without any calibration procedure, the model reproduces the experimental inlet and outlet groundwater temperatures with a mean absolute error of 0.14 °C. It is also shown that the placement of the pump at the top of the well offers a more practical design that has minor impact on the thermal performance of the system

Assessment of the gradient of an objective function by analytical derivation for optimization-based design of ground-coupled heat pump systems

Optimization-based design of ground heat exchangers requires derivation of the objective function with respect to the design parameters, which is usually done through finite-differentiation of the cost or utility function. The approach is however prone to approximation errors and can result in convergence issues or long optimization time. By deriving analytically the ground heat exchanger transfer function, it is possible to obtain an exact representation of the objective function gradient and avoid numerical instabilities. To illustrate the advantages of using analytical expressions, a common design task is expressed as an optimization problem. It is shown that by using an analytical derivation of the gradient in conjunction with strong Wolfe conditions during a line search may reduce significantly computation time by comparison to a finite-differentiation of the gradient

Stationary and non-stationary deconvolution to recover long-term transfer functions

To design a ground heat exchanger, simulations are frequently used. One way to perform simulations is to use the well-known g-functions to obtain the ground temperature. These functions are usually obtained by analytical or numerical models, which limits the precision or takes long simulation time. Recent advances show that the short-term g-functions can also be retrieved by a deconvolution algorithm. However, the known deconvolution algorithm is only validated for a set of operating parameters and duration of less than 10 days. A first objective of this article is to demonstrate that longer g-functions can be retrieved with such an algorithm. Then, a second objective is to extend the application of the deconvolution to consider time varying operating parameters throughout a ground heat exchanger's operation. To achieve those objectives, the deconvolution will be first applied to various numerical year-long simulations of a ground source heat pump system with stationary conditions. Then, an extended multi-signal deconvolution will be applied to a non-stationary thermal response test of 30 days. Both tests show adequate temperature reconstruction with RMSE of less than 0.05 °C and 0.2 °C for the first and second scenarios respectively

The formation of orthogonal joint systems and cuboidal blocks: New insights gained from flat-lying limestone beds in the region of Havre-Saint-Pierre (Quebec, Canada)

ABSTRACT: Vertical orthogonal joints are a common feature in shallow crustal rocks. There are several competing theories for their formation despite the ubiquity. We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec, Canada (north shore of Saint-Lawrence River) to test conceptual models of joint formation in a natural setting. In the region, the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately. The joint-spacing-to-bed-thickness ratios (s/t) are much larger in these beds (s/t = 4.3 for systematic joints, and 6.4 for cross-joints) than those in higher strained strata along the south shore of the Saint-Lawrence River (s/t = 1), highlighting the effect of tectonic strain in decreasing fracture spacing and block size. The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached (as hypothesized in previous studies). We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures. The presence of ladder-shaped orthogonal joints suggests a state of effective stress with σ1∗»0 > σ2∗>σ3∗ and where σ2∗-σ3∗ is within the range of fracture strength variability at the time of fracture. This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks

Automatic generation of feasible mining pushbacks for open pit strategic planning

The design of pushbacks in an open pit mine has a significant impact on the mine's profitability. Automatic generation of practical pushbacks is a highly desirable feature, but current automatic solutions fail to sufficiently account for complex geometric requirements of pushbacks, including slopes, phase bench and bottom width, smoothness, and continuity. In this paper, we present a tool to fill this gap. Our proposed algorithm is based on modification of sets of blocks obtained by parametric optimization of the pit using a maximum flow method. A set of geometric operators is developed to modify the sets to present a feasible geometry for mining. The geometric operators are essentially derived from mathematical morphological tools. Case studies show that the proposed method generates practical pushback designs that meet all geometric constraints. The algorithm can be used to create a solution for medium-size pits in minutes. This significantly improves the efficiency of designing pushbacks for open pit mines

Assortative Mating between European Corn Borer Pheromone Races: Beyond Assortative Meeting

BACKGROUND: Sex pheromone communication systems may be a major force driving moth speciation by causing behavioral reproductive isolation via assortative meeting of conspecific individuals. The 'E' and 'Z' pheromone races of the European corn borer (ECB) are a textbook example in this respect. 'Z' females produce and 'Z' males preferentially respond to a 'Z' pheromone blend, while the 'E' race communicates via an 'E' blend. Both races do not freely hybridize in nature and their populations are genetically differentiated. A straightforward explanation would be that their reproductive isolation is a mere consequence of "assortative meeting" resulting from their different pheromones specifically attracting males towards same-race females at long range. However, previous laboratory experiments and those performed here show that even when moths are paired in a small box - i.e., when the meeting between sexual partners is forced - inter-race couples still have a lower mating success than intra-race ones. Hence, either the difference in attractivity of E vs. Z pheromones for males of either race still holds at short distance or the reproductive isolation between E and Z moths may not only be favoured by assortative meeting, but must also result from an additional mechanism ensuring significant assortative mating at close range. Here, we test whether this close-range mechanism is linked to the E/Z female sex pheromone communication system. METHODOLOGY/PRINCIPAL FINDINGS: Using crosses and backcrosses of E and Z strains, we found no difference in mating success between full-sisters emitting different sex pheromones. Conversely, the mating success of females with identical pheromone types but different coefficients of relatedness to the two parental strains was significantly different, and was higher when their genetic background was closer to that of their male partner's pheromone race. CONCLUSIONS/SIGNIFICANCE: We conclude that the close-range mechanism ensuring assortative mating between the E and Z ECB pheromone races is unrelated to the difference in female sex pheromone. Although the nature of this mechanism remains elusive, our results show that it is expressed in females, acts at close range, segregates independently of the autosome carrying Pher and of both sex chromosomes, and is widely distributed since it occurs both in France and in the US