Improving the quality of finite volume meshes through genetic optimisation

Author's accepted version. The final publication is available at Springer via http://dx.doi.org/10.1007/s00366-015-0423-0Mesh quality issues can have a substantial impact on the solution process in Computational Fluid Dynamics (CFD), leading to poor quality solutions, hindering convergence and in some cases, causing the solution to diverge. In many areas of application, there is an interest in automated generation of finite volume meshes, where a meshing algorithm controlled by pre- specified parameters is applied to a pre-existing CAD geometry. In such cases the user is typically confronted with a large number of controllable parameters, and ad- justing these takes time and perserverence. The process can however be regarded as a multi-input and possi- bly multi-objective optimisation process which can be optimised by application of Genetic Algorithm tech- niques. We have developed a GA optimisation code in the language Python, including an implementation of the NGSA-II multi-objective optimisation algorithm, and applied to control the mesh generation process us- ing the snappyHexMesh automated mesher in Open- FOAM. We demonstrate the results on three selected cases, demonstrating significant improvement in mesh quality in all cases

A comparison of interpolation techniques for non-conformal high-order discontinuous Galerkin methods

The capability to incorporate moving geometric features within models for complex simulations is a common requirement in many fields. Fluid mechanics within aeronautical applications, for example, routinely feature rotating (e.g. turbines, wheels and fan blades) or sliding components (e.g. in compressor or turbine cascade simulations). With an increasing trend towards the high-fidelity modelling of these cases, in particular combined with the use of high-order discontinuous Galerkin methods, there is therefore a requirement to understand how different numerical treatments of the interfaces between the static mesh and the sliding/rotating part impact on overall solution quality. In this article, we compare two different approaches to handle this non-conformal interface. The first is the so-called mortar approach, where flux integrals along edges are split according to the positioning of the non-conformal grid. The second is a less-documented point-to-point interpolation method, where the interior and exterior quantities for flux evaluations are interpolated from elements lying on the opposing side of the interface. Although the mortar approach has significant advantages in terms of its numerical properties, in that it preserves the local conservation properties of DG methods, in the context of complex 3D meshes it poses notable implementation difficulties which the point-to-point method handles more readily. In this paper we examine the numerical properties of each method, focusing not only on observing convergence orders for smooth solutions, but also how each method performs in under-resolved simulations of linear and nonlinear hyperbolic problems, to inform the use of these methods in implicit large-eddy simulations.Comment: 37 pages, 15 figures, 5 tables, submitted to Computer Methods in Applied Mechanics and Engineering, revision

Analyzing And Addressing Pollution In Northwestern Indiana

Northwestern Indiana is an area recognized for its prosperous industry, but it is also known for the numerous pollution emissions that coincide with manufacturing. In order to qualify and quantify the presence of hazardous industrial byproducts in the local ecosystems, samples from the environment need to be examined periodically. Two types of samples were collected for this project. Road dust sediment (RDS), an accumulation of particulate matter on the street surface, can indicate what pollutants are present in an area due to the settling of atmospheric and anthropogenic particles on the surface of roads. The RDS samples used in this experiment were collected from areas near pollution sources. Water and sediment samples were collected from Lake George, a local body of water situated next to a portable toilet manufacturing company, to quantify the microplastic pollutants. A number of methods were used to process and analyze the samples, such as infrared spectroscopy, X-ray fluorescence and microscopy. The results conveyed an excessive amount of microplastics in the Lake George water and sediment samples as well as unnatural contaminants in our RDS. In comparison to previous years, results showed a drastic escalation of microplastic at all points of testing. Concerning RDS, contaminants that may be of concern, such as lead and arsenic, were found within our samples. We plan to continue our research of RDS in order to provide reliable, public air quality information through a comparison between RDS and air quality monitors

CFD Simulations for Sensitivity Analysis of Different Parameters to the Wake Characteristics of Tidal Turbine

articleThis paper investigates the sensitivity of width proximity and mesh grid size to the wake characteristics of Momentum Reversal Lift (MRL) turbine using a new computational fluid dynamics (CFD) based Immersed Body Force (IBF) model. This model has been added as a source term into the large eddy simulation (LES), which is developed for solving two phase fluids. The open source CFD code OpenFOAM was used for the simulations. The simulation results showed that the grid size and width proximity have had massive impact on the flow characteristics and the computational cost of the tidal turbine. A fine grid size and large width inflicted longer computational time. In contrast, a coarse grid size and small width reduced the computational time but showed poor description of the flow features. In addition, a close proximity of the domain’s wall boundary to the turbine affected the free surface, the air body, and the flow characteristics at the interface between the two phases. These results showed that careful investigation of a suitable grid size and spacing between the wall boundary and the turbine is important to minimise the effect of these parameters on the simulation results.University of Exete

Investigation of flow through a computationally generated packed column using CFD and additive layer manufacturing

Preprint submitted to Computers and Chemical Engineering 18 March 2014. © The AuthorsThe version of record is available from the publisher via doi:10.1016/j.compchemeng.2014.04.005.When analysing packed beds using CFD approaches, producing an accurate geometry is often challenging. Often a computational model is produced from non-invasive imaging of the packed bed using 3d MRI or μ-CT. This work pioneers the exact reverse of this, by creating a physical bed from the computational model using Additive Layer Manufacturing (ALM). The paper focuses on both experimental analysis and computational analysis of packed columns of spheres. A STL file is generated of a packed column formed using a Monte-Carlo packing algorithm, and this is meshed and analysed using Computational Fluid Dynamics. In addition to this, a physical model is created using ALM on a 3d printer. This allows us to analyse the identical bed geometry both computationally and experimentally and compare the two. Pressure drop and flow patterns are analysed within the bed in detail. © 2014 Elsevier Ltd

Computational fluid dynamics as a tool for urban drainage system analysis: a review of applications and best practice

Computational Fluid Dynamics (CFD) can be applied to gain insights into most fluid processes and associated phenomena and so presents potential to add value in the analysis of urban drainage systems. This paper presents a review of CFD studies carried out in this field, with the objective of developing an appreciation of how and where it can be applied. Existing work has tended to focus around the analysis of four types of urban drainage structure, including Combined Sewer Overflows (CSOs), storage and attenuation systems, stormwater sediment interceptors and sewerage conveyance structures. Within the respective studies, the prediction of flowfields, particulate behaviour, water surface profiles and Residence Time Distributions (RTDs) are found to form the main focus, and as such, these are considered in most detail in the paper. It is concluded that CFD presents a number of opportunities in urban drainage system analysis, and that the scope of this opportunity will further develop as both computational hardware and software resources become more advanced

Experimental Investigation of Scour and Pressures on a Single Span Arch Bridge Under Inundation

This paper presents two experiments, carried out in a 605mm-wide flume, to investigate scour and hydrodynamic pressure on a scaled model of a single span arch bridge. The geometry of the bridge model is scaled down according to a prototype bridge, with hydraulic conditions of the experiments representing a small river. Measured scour depths showed that flow vertical contraction by the arch bridge is higher than that of flat-deck bridges. Effect of a single cylindrical debris on scour was also evaluated and found to be negligible at the considered flow depth. Temporal variation of hydrodynamic pressure with scour evolution was also measured. It was found that temporal evolution of scour can reduce hydrodynamic pressure significantly at the initial base of the abutment at downstream face of the bridge, which can erode mortar from the masonry composition of an arch bridge

Magnetically Responsive Materials based on Polymeric Ionic Liquids and Graphene Oxide for Water Clean-up

Hypothesis Owing to attractive interactions between negatively charged graphene oxide (GO) and a paramagnetic cationic polyelectrolyte (polyallydimethylammonium chloride with a FeCl4− counterion (Fe-polyDADMAC) it should be possible to generate magnetic materials. The benefit of using charge-based adsorption is that the need to form covalently linked magnetic materials is offset, which is expected to significantly reduce the time, energy and cost to make such responsive materials. These systems could have a wide use and application in water treatment. Experiments Non-covalent magnetic materials were formed through the mixing of Fe-pDADMAC and GO. A systematic study was conducted by varying polymer concentration at a fixed GO concentration. UV–Vis was used to confirm and quantify polymer adsorption onto GO sheets. The potential uses of the systems for water purification were demonstrated. Findings Fe-polyDADMAC adsorbs to the surface of GO and induces flocculation. Low concentrations of the polymer (20 mmol/L) induce restabilization. Difficult-to-recover gold nanoparticles can be separated from suspensions as well as the pollutant antibiotic tetracycline. Both harmful materials can be magnetically recovered from the dispersions. This system therefore has economical and practical applications in decontamination and water treatment

Comparison of multiple surrogates for 3D CFD model in tidal farm optimisation

Marine currents have been identified as a considerable renewable energy source. Therefore, in recent years, research on optimising tidal stream farm layouts in order to maximise power output has emerged. Traditionally, computational fluid dynamics (CFD) models are used to model power output, but their computational cost is prohibitive within an optimisation algorithm. This paper uses surrogate models in place of CFD simulations to optimise the layout of tidal stream farm layouts. Surrogates are functions which are designed to emulate the behaviour of other models with radically reduced computational expense. Two surrogate models are applied and compared: artificial neural network (ANN) and k-nearest neighbours regression (k-NN). We measure their suitability by four criteria: accuracy, efficiency, robustness and performance within an optimisation algorithm. The results reveal that the ANN surrogate is superior in every criteria to the k-NN surrogate. However, the k-NN surrogate is also able to perform adequate optimisation. Finally, we demonstrate that optimisation relying solely on surrogate models is a viable approach, with dramatically reduced computational expense of optimisation. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.Procedia Engineerin

Numerical simulation of a new type of cross flow tidal turbine using OpenFOAM - Part II: Investigation of turbine-to-turbine interaction

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Renewable Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Renewable Energy, Volume 50 (2013), DOI: 10.1016/j.renene.2012.08.064Prediction of turbine-to-turbine interaction represents a significant challenge in determining the optimized power output from a tidal stream farm, and this is an active research area. This paper presents a detailed work which examines the influence of surrounding turbines on the performance of a base case (isolated turbine). The study was conducted using a new CFD based, Immersed Body Force (IBF) model, which was validated in the first paper, and an open source CFD software package OpenFOAM was used for the simulations. The influence of the surrounding turbines was investigated using randomly chosen initial lateral and longitudinal spacing among the turbines. The initial spacing was then varied to obtain four configurations to examine the relative effect that positioning can have on the performance of the base turbine