Publications
420 results found
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation, EAGE annual conference and exhibition
Salinas P, Pain C, Osman H, et al., 2018, Vanishing artificial capillary pressure as a mechanism to accelerate convergence, Interpore
Hu R, Fang F, Salinas P, et al., 2018, Unstructured mesh adaptivity for urban flooding modelling, Journal of Hydrology
Salinas P, Lei Q, Jacquemyn C, et al., 2018, DYNAMIC UNSTRUCTURED MESH ADAPTIVITY FOR IMPROVEDSIMULATION OF GEOTHERMAL WATER EXTRACTION INRESERVOIR-SCALE MODELS, 3rd Thermal and Fluids Engineering Conference
Salinas-Cortes P, Pain CC, Osman H, et al., 2018, Vanishing artificial capillary pressure for improved real-size reservoir simulations
© 2018 European Association of Geoscientists and Engineers EAGE. All rights reserved. A common approach to stabilise the system arising from the discretisation of the advection equation is to introduce artificial diffusion. However, introducing artificial diffusion affects the result, therefore a balance has to be found so that the introduced artificial diffusion does not affects the final result. Recently, a vanishing artificial diffusion was presented. In that method, the diffusion was controlled by the convergence of the non-linear solver by multiplying the artificial diffusion term by the difference between the most recent saturation estimation and the one obtained in the previous non-linear iteration. This approach showed that it is capable to help to reduce the computational effort required by the non-linear solver, as classical artificial diffusions do. However, this approach could lead to an introduction of an artificial source/sink in the system, therefore not conserving mass. A conservative vanishing artificial diffusion is presented here. It improves the convergence and convergence rate of the non-linear solver by reducing the non-linearity of the equations. Moreover, it is tailored to specially help to deal with the capillary pressure. The vanishing artificial diffusion is introduced using the same model employed to introduce the capillary pressure, obtaining a vanishing artificial capillary pressure diffusion term. By solving this term implicitly in the saturation equation, a very efficient method to model multiphase porous media flow with physical capillary pressure is obtained. This is tested in real-size reservoir simulations with realistically high capillary numbers to prove its efficiency. The presented method provides accurate results and significantly reduces the effort required by the non-linear solver to achieve convergence. It enables to carry out very demanding numerical simulations, e.g. when the physical capillary pressure effects are
Heaney CE, Pain CC, Buchan AG, et al., 2018, Reactor simulators and reduced order modeling, Nuclear Future, Vol: 14, Pages: 49-54, ISSN: 1745-2058
The high quality real-time solutions offered by Reduced Order Modelling (ROM) could greatly improve the resolution of the solution available in training simulators and would add significantly to a student's understanding. ROM will be a key component of the modelling of reactor simulators, the operational modelling of reactors and accident analysis. The computational speed of this unique framework will enable real-time interactive use, uncertainty analysis, rapid data assimilation and better-informed reactor management. The goal of a real-time response has been realised in the reduced-order model of a fuel assembly presented here.
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation
© 2018 Society of Petroleum Engineers. All rights reserved. Recently, a novel method for heat extraction from geothermal reservoirs has been proposed, it is named radiator enhance geothermal system (RAD-EGS). In this method, the heat is extracted by placing two horizontal wells separated vertically, and injecting the cold water in the deepest one. Modelling a geothermal reservoir with wells can be very challenging as the scales to be considered can span several orders of magnitude. Around the wells (metres scale) it is well known that there is a high-pressure drawdown, while the dimensions of the reservoir are typically of many kilometres. Modelling across these scales using a fixed mesh can be computationally very expensive. Here, an unstructured dynamic mesh optimisation method is used to dynamically optimise the mesh to the fields of interest such as temperature and/or pressure to ensure that a certain precision across the domain is obtained. This methodology places the resolution where and when necessary, reducing the number of elements to ensure a certain accuracy when compared to an equivalent fixed mesh. Wells are represented using a 1D line which is represented by a line vector, whose position is not modified when adapting the mesh.
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation
Recently, a novel method for heat extraction from geothermal reservoirs has been proposed, it is named radiator enhance geothermal system (RAD-EGS). In this method, the heat is extracted by placing two horizontal wells separated vertically, and injecting the cold water in the deepest one. Modelling a geothermal reservoir with wells can be very challenging as the scales to be considered can span several orders of magnitude. Around the wells (metres scale) it is well known that there is a high-pressure drawdown, while the dimensions of the reservoir are typically of many kilometres. Modelling across these scales using a fixed mesh can be computationally very expensive. Here, an unstructured dynamic mesh optimisation method is used to dynamically optimise the mesh to the fields of interest such as temperature and/or pressure to ensure that a certain precision across the domain is obtained. This methodology places the resolution where and when necessary, reducing the number of elements to ensure a certain accuracy when compared to an equivalent fixed mesh. Wells are represented using a 1D line which is represented by a line vector, whose position is not modified when adapting the mesh.
Heaney CE, Salinas P, Pain CC, et al., 2018, Well optimisation with goal-based sensitivity maps using time windows and ensemble perturbations
Knowledge of the sensitivity of a solution to small changes in the model parameters is exploited in many areas in computational physics and used to perform mesh adaptivity, or to correct errors based on discretisation and sub-grid-scale modelling errors, to perform the assimilation of data based on adjusting the most sensitive parameters to the model-observation misfit, and similarly to form optimised sub-grid-scale models. We present a goal-based approach for forming sensitivity (or importance) maps using ensembles. These maps are defined as regions in space and time of high relevance for a given goal, for example, the solution at an observation point within the domain. The presented approach relies solely on ensembles obtained from the forward model and thus can be used with complex models for which calculating an adjoint is not a practical option. This provides a simple approach for optimisation of sensor placement, goal based mesh adaptivity, assessment of goals and data assimilation. We investigate methods which reduce the number of ensembles used to construct the maps yet which retain reasonable fidelity of the maps. The fidelity comes from an integrated method including a goal-based approach, in which the most up-to-date importance maps are fed back into the perturbations to focus the algorithm on the key variables and domain areas. Also within the method smoothing is applied to the perturbations to obtain a multi-scale, global picture of the sensitivities; the perturbations are orthogonalised in order to generate a well-posed system which can be inverted; and time windows are applied (for time dependent problems) where we work backwards in time to obtain greater accuracy of the sensitivity maps. The approach is demonstrated on a multi-phase flow problem.
Salinas-Cortes P, Pain CC, Osman H, et al., 2018, Vanishing artificial capillary pressure for improved real-size reservoir simulations
A common approach to stabilise the system arising from the discretisation of the advection equation is to introduce artificial diffusion. However, introducing artificial diffusion affects the result, therefore a balance has to be found so that the introduced artificial diffusion does not affects the final result. Recently, a vanishing artificial diffusion was presented. In that method, the diffusion was controlled by the convergence of the non-linear solver by multiplying the artificial diffusion term by the difference between the most recent saturation estimation and the one obtained in the previous non-linear iteration. This approach showed that it is capable to help to reduce the computational effort required by the non-linear solver, as classical artificial diffusions do. However, this approach could lead to an introduction of an artificial source/sink in the system, therefore not conserving mass. A conservative vanishing artificial diffusion is presented here. It improves the convergence and convergence rate of the non-linear solver by reducing the non-linearity of the equations. Moreover, it is tailored to specially help to deal with the capillary pressure. The vanishing artificial diffusion is introduced using the same model employed to introduce the capillary pressure, obtaining a vanishing artificial capillary pressure diffusion term. By solving this term implicitly in the saturation equation, a very efficient method to model multiphase porous media flow with physical capillary pressure is obtained. This is tested in real-size reservoir simulations with realistically high capillary numbers to prove its efficiency. The presented method provides accurate results and significantly reduces the effort required by the non-linear solver to achieve convergence. It enables to carry out very demanding numerical simulations, e.g. when the physical capillary pressure effects are dominant, with Courant numbers that are at least two orders of magnitude bigger than withou
Salinas P, Lei Q, Jacquemyn C, et al., 2018, Dynamic unstructured mesh adaptivity for improved simulation of geothermal water extraction in reservoir-scale models, Pages: 1245-1248
A novel method to simulate near-wellbore flow in geothermal reservoirs by using dynamic unstructured mesh optimisation and the Double Control Volume Finite Element method (DCVFEM) is presented. The mesh resolution is dynamically adapted to a field of interest, allowing to focus the mesh resolution only when and where it is required. Geology is represented by bounded surfaces whose petrophysical properties are constant within each of this surfaces. We demonstrate that the method has wide application in reservoir-scale models of geothermal fields, and regional models of groundwater resources.
Salinas P, Pavlidis D, Jacquemyn C, et al., 2017, Simulation of geothermal water extraction in heterogeneous reservoirs using dynamic unstructured mesh optimisation, AGU FALL
Salinas P, Pavlidis D, Xie Z, et al., 2017, A robust control volume finite element method for high aspect ratio domains with dynamic mesh optimisation, American Physical Society Division of Fluid Dynamics meeting
Aristodemou E, Boganegra LM, Mottet L, et al., 2017, How tall buildings affect turbulent air flows and dispersion of pollution within a neighbourhood, Environmental Pollution, Vol: 233, Pages: 782-796, ISSN: 0269-7491
The city of London, UK, has seen in recent years an increase in the number of high-rise/multi-storey buildings (“skyscrapers”) with roof heights reaching 150 m and more, with the Shard being a prime example with a height of ∼310 m. This changing cityscape together with recent plans of local authorities of introducing Combined Heat and Power Plant (CHP) led to a detailed study in which CFD and wind tunnel studies were carried out to assess the effect of such high-rise buildings on the dispersion of air pollution in their vicinity. A new, open-source simulator, FLUIDITY, which incorporates the Large Eddy Simulation (LES) method, was implemented; the simulated results were subsequently validated against experimental measurements from the EnFlo wind tunnel. The novelty of the LES methodology within FLUIDITY is based on the combination of an adaptive, unstructured, mesh with an eddy-viscosity tensor (for the sub-grid scales) that is anisotropic. The simulated normalised mean concentrations results were compared to the corresponding wind tunnel measurements, showing for most detector locations good correlations, with differences ranging from 3% to 37%. The validation procedure was followed by the simulation of two further hypothetical scenarios, in which the heights of buildings surrounding the source building were increased. The results showed clearly how the high-rise buildings affected the surrounding air flows and dispersion patterns, with the generation of “dead-zones” and high-concentration “hotspots” in areas where these did not previously exist. The work clearly showed that complex CFD modelling can provide useful information to urban planners when changes to cityscapes are considered, so that design options can be tested against environmental quality criteria.
Salinas P, Pavlidis D, Xie Z, et al., 2017, A Discontinuous Control Volume Finite Element Method for Multi-Phase Flow in Heterogeneous Porous Media, Journal of Computational Physics, Vol: 352, Pages: 602-614, ISSN: 0021-9991
We present a new, high-order, control-volume-finite-element (CVFE) method for multiphase porous media flow with discontinuous 1st-order representation for pressure and discontinuous 2nd-order representation for velocity. The method has been implemented using unstructured tetrahedral meshes to discretize space. The method locally and globally conserves mass. However, unlike conventional CVFE formulations, the method presented here does not require the use of control volumes (CVs) that span the boundaries between domains with differing material properties. We demonstrate that the approach accurately preserves discontinuous saturation changes caused by permeability variations across such boundaries, allowing efficient simulation of flow in highly heterogeneous models. Moreover, accurate solutions are obtained at significantly lower computational cost than using conventional CVFE methods. We resolve a long-standing problem associated with the use of classical CVFE methods to model flow in highly heterogeneous porous media.
Soucasse L, Dargaville S, Buchan AG, et al., 2017, A goal-based angular adaptivity method for thermal radiation modelling in non grey media, JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, Vol: 200, Pages: 215-224, ISSN: 0022-4073
Dargaville S, Buchan A, Smedley-Stevenson R, et al., 2017, Adaptive angle and parallel multigrid for deterministic shielding problems, 13th International Conference on Radiation Shielding (ICRS) / 19th Topical Meeting of the Radiation-Protection-and-Shielding-Division-of-the-American-Nuclear-Society (RPSD), Publisher: E D P SCIENCES, ISSN: 2100-014X
Xie Z, Lu L, Stoesser T, et al., 2017, Numerical simulation of three-dimensional breaking waves and its interaction with a vertical circular cylinder, JOURNAL OF HYDRODYNAMICS, Vol: 29, Pages: 800-804, ISSN: 1001-6058
Wave breaking plays an important role in wave-structure interaction. A novel control volume finite element method with adaptive unstructured meshes is employed here to study 3-D breaking waves. The numerical framework consists of a “volume of fluid” type method for the interface capturing and adaptive unstructured meshes to improve computational efficiency. The numerical model is validated against experimental measurements of breaking wave over a sloping beach and is then used to study the breaking wave impact on a vertical circular cylinder on a slope. Detailed complex interfacial structures during wave impact, such as plunging jet formation and splash-up are captured in the simulation, demonstrating the capability of the present method.
Salinas P, Pavlidis D, Jacquemyn C, et al., 2017, A Robust Control Volume Finite Element Method for Highly Distorted meshes, SIAM Conference on Mathematical and Computational Issues in the Geosciences
Wang Z, Xiao D, Fang F, et al., 2017, Model identification of reduced order fluid dynamics systems using deep learning, International Journal for Numerical Methods in Fluids, Vol: 86, Pages: 255-268, ISSN: 0271-2091
This paper presents a novel model reduction method: deep learning reduced order model, which is based on proper orthogonal decomposition and deep learning methods. The deep learning approach is a recent technological advancement in the field of artificial neural networks. It has the advantage of learning the nonlinear system with multiple levels of representation and predicting data. In this work, the training data are obtained from high fidelity model solutions at selected time levels. The long short-term memory network is used to construct a set of hypersurfaces representing the reduced fluid dynamic system. The model reduction method developed here is independent of the source code of the full physical system.The reduced order model based on deep learning has been implemented within an unstructured mesh finite element fluid model. The performance of the new reduced order model is evaluated using 2 numerical examples: an ocean gyre and flow past a cylinder. These results illustrate that the CPU cost is reduced by several orders of magnitude whilst providing reasonable accuracy in predictive numerical modelling.
Xie Z, Hewitt G, Pavlidis D, et al., 2017, Numerical study of three-dimensional droplet impact on a flowing liquid film in annular two-phase flow, Chemical Engineering Science, Vol: 166, Pages: 303-312, ISSN: 0009-2509
Annular flow with liquid entrainment occurs in a wide variety of two-phase flow system. A novel control volume finite element method with adaptive unstructured meshes is employed here to study three-dimensional droplet deposition process in annular two-phase flow. The numerical framework consists of a ‘volume of fluid’ type method for the interface capturing and a force-balanced continuum surface force model for the surface tension on adaptive unstructured meshes. The numerical framework is validated against experimental measurements of a droplet impact problem and is then used to study the droplet deposition onto a flowing liquid film at atmospheric and high pressure conditions. Detailed complex interfacial structures during droplet impact are captured during the simulation, which agree with the experimental observations, demonstrating the capability of the present method. It is found that the effect of the ambient pressure on the fluid properties and interfacial tension plays an important role in the droplet deposition process and the associated interfacial phenomena.
Xiao D, Fang F, Pain C, et al., 2017, Towards non-intrusive reduced order 3D free surface flow modelling, Ocean Engineering, Vol: 140, Pages: 155-168, ISSN: 1873-5258
In this article, we describe a novel non-intrusive reduction model for three-dimensional (3D) free surface flows. However, in this work we limit the vertical resolution to be a single element. So, although it does resolve some non-hydrostatic effects, it does not examine the application of reduced modelling to full 3D free surface flows, but it is an important step towards 3D modelling. A newly developed non-intrusive reduced order model (NIROM) (Xiao et al., 2015a) has been used in this work. Rather than taking the standard POD approach using the Galerkin projection, a Smolyak sparse grid interpolation method is employed to generate the NIROM. A set of interpolation functions is constructed to calculate the POD coefficients, where the POD coefficients at previous time steps are the inputs of the interpolation function. Therefore, this model is non-intrusive and does not require modifications to the code of the full system and is easy to implement.By using this new NIROM, we have developed a robust and efficient reduced order model for free surface flows within a 3D unstructured mesh finite element ocean model. What distinguishes the reduced order model developed here from other existing reduced order ocean models is (1) the inclusion of 3D dynamics with a free surface (the 3D computational domain and meshes are changed with the movement of the free surface); (2) the incorporation of wetting-drying; and (3) the first implementation of non-intrusive reduced order method in ocean modelling. Most importantly, the change of the computational domain with the free surface movement is taken into account in reduced order modelling. The accuracy and predictive capability of the new non-intrusive free surface flow ROM have been evaluated in Balzano and Okushiri tsunami test cases. This is the first step towards 3D reduced order modelling in realistic ocean cases. Results obtained show that the accuracy of free surface problems relative to the high fidelity model is maintained
Salinas P, Pavlidis D, Xie Z, et al., 2017, Improving the robustness of the control volume finite element method with application to multiphase porous media flow, International Journal for Numerical Methods in Fluids, Vol: 85, Pages: 235-246, ISSN: 1097-0363
Control volume finite element methods (CVFEMs) have been proposed to simulate flow in heterogeneous porous media because they are better able to capture complex geometries using unstructured meshes. However, producing good quality meshes in such models is nontrivial and may sometimes be impossible, especially when all or parts of the domains have very large aspect ratio. A novel CVFEM is proposed here that uses a control volume representation for pressure and yields significant improvements in the quality of the pressure matrix. The method is initially evaluated and then applied to a series of test cases using unstructured (triangular/tetrahedral) meshes, and numerical results are in good agreement with semianalytically obtained solutions. The convergence of the pressure matrix is then studied using complex, heterogeneous example problems. The results demonstrate that the new formulation yields a pressure matrix than can be solved efficiently even on highly distorted, tetrahedral meshes in models of heterogeneous porous media with large permeability contrasts. The new approach allows effective application of CVFEM in such models.
Obeysekara, Lei Q, Salinas P, et al., 2017, Modelling the evolution of a fracture network under excavation-induced unloading and seepage effects based on a fully coupled fluid-solid simulation, 51st US Rock Mechanics/Geomechanics Symposium
Latham J-P, Yang P, Lei Q, et al., 2017, Blast fragmentation in rock with discontinuities using an equation of state gas model coupled to a transient dynamics fracturing and fragmenting FEMDEM code, 51st US Rock Mechanics/Geomechanics Symposium
Candy AS, Pain CC, 2017, An implicit wetting and drying approach for non-hydrostatic flows in high aspect ratio domains, Advances in Water Resources, ISSN: 0309-1708
A wetting and drying approach for free surface flows governed by thethree-dimensional, non-hydrostatic Navier-Stokes equations in high aspect ratiodomains is developed. This has application in the modelling of inundationprocesses in geophysical domains, where dynamics takes place over a largehorizontal extent relative to vertical resolution, such as in the evolution ofa tsunami, or flooding scenario. The approach is novel in that it solves forthree dimensional dynamics in these very high aspect ratio domains, to includenon-hydrostatic effects and accurately model dispersive processes. These becomeimportant in shallow regions with steep gradients, a particularly acute problemwhere man-made structures exist such as buildings or flood defences in an urbanenvironment. It is implicit in time to allow efficient time integration over arange of mesh element sizes. Specific regularisation methods are introduced toimprove conditioning of the full three-dimensional pressure Poisson problem inthese high aspect ratio domains and it is demonstrated in standard wetting anddrying benchmarks that these are critical for the success of this model.
Salinas P, Pavlidis D, Xie Z, et al., 2017, A Double Control Volume Finite Element Method with Dynamic Unstructured Mesh Optimization, SPE Reservoir Simulation Conference 2017
Salinas P, Pavlidis D, Xie Z, et al., 2017, A Double Control Volume Finite Element Method with Dynamic Unstructured Mesh Optimization, Reservoir SImulation Conference
Xiao D, Fang F, Pain C, et al., 2017, A parameterized non-intrusive reduced order model anderror analysis for general time-dependent nonlinear partialdifferential equations and its applications, Computer Methods in Applied Mechanics and Engineering, Vol: 317, Pages: 868-889, ISSN: 0045-7825
A novel parameterized non-intrusive reduced order model (P-NIROM) based onproper orthogonal decomposition (POD) has been developed.This P-NIROM is ageneric and efficient approach for model reduction of parameterized partial differen-tial equations (P-PDEs). Over existing parameterized reduced order models (P-ROM)(most of them are based on the reduced basis method), it is non-intrusive and inde-pendent on partial differential equations and computational codes. During the trainingprocess, the Smolyak sparse grid method is used to select a set of parameters over aspecific parameterized space (Ωp∈ RP). For each selected parameter, the reduced ba-sis functions are generated from the snapshots derived froma run of the high fidelitymodel. More generally, the snapshots and basis function sets for any parameters overΩpcan be obtained using an interpolation method. The P-NIROM can then be con-structed by using our recently developed technique [50,53] where either the Smolyakor radial basis function (RBF) methods are used to generate aset of hyper-surfacesrepresenting the underlying dynamical system over the reduced space.The new P-NIROM technique has been applied to parameterizedNavier-Stokesequations and implemented with an unstructured mesh finite element model. The ca-pability of this P-NIROM has been illustrated numerically by two test cases: flow pasta cylinder and lock exchange case. The prediction capabilities of the P-NIROM havebeen evaluated by varying the viscosity, initial and boundary conditions. The resultsshow that this P-NIROM has captured the quasi-totality of the details of the flow withCPU speedup of three orders of magnitude. An error analysis for the P-NIROM hasbeen carried out.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.