Numerical evaluation of aerodynamic roughness of the built environment and complex terrain

Aerodynamic drag in the atmospheric boundary layer (ABL) is affected by the structure and density of obstacles (surface roughness) and nature of the terrain (topography). In building codes and standards, average roughness is usually determined somewhat subjectively by examination of aerial photographs. For detailed wind mapping, boundary layer wind tunnel (BLWT) testing is usually recommended. This may not be cost effective for many projects, in which case numerical studies become good alternatives. This thesis examines Computational Fluid Dynamics (CFD) for evaluation of aerodynamic roughness of the built environment and complex terrain. The present study started from development of an in-house CFD software tailored for ABL simulations. A three-dimensional finite-volume code was developed using flexible polyhedral elements as building blocks. The program is parallelized using MPI to run on clusters of processors so that micro-scale simulations can be conducted quickly. The program can also utilize the power of latest technology in high performance computing, namely GPUs. Various turbulence models including mixing-length, RANS, and LES models are implemented, and their suitability for ABL simulations assessed. Then the effect of surface roughness alone on wind profiles is assessed using CFD. Cases with various levels of complexity are considered including simplified models with roughness blocks of different arrangement, multiple roughness patches, semi-idealized urban model, and real built environment. Comparison with BLWT data for the first three cases showed good agreement thereby justifying explicit three-dimensional numerical approach. Due to lack of validation data, the real built environment case served only to demonstrate use of CFD for such purposes. Finally, the effect of topographic features on wind profiles was investigated using CFD. This work extends prior work done by the research team on multiple idealized two-dimensional topographic features to more elaborate three-dimensional simulations. It is found that two-dimensional simulations overestimate speed up over crests of hills and also show larger recirculation zones. The current study also emphasized turbulence characterization behind hills. Finally a real complex terrain case of the well-known Askervein hill was simulated and the results validated against published field observations. In general the results obtained from the current simulations compared well with those reported in literature

Turbulent boundary layer: comparison between a flat plate and a rotating disk with and without periodic roughness

In order to understand and predict the behavior of a flow around an object it is necessary to study the phenomenon present on the close-to-the-wall region of the flow, where the viscous forces cannot be neglected nor the variations of the properties of the flow. This region is called the boundary layer. In many situations, the contribution of the viscous friction in the boundary layer into the total drag can be substantial, and understanding of the effect of the roughness on the boundary layer is of importance. This project is focused on the study of the boundary layer created near two different objects: a flat plate and a rotating disk. The flat plate is widely used in fundamental studies and in the engineering industry as an approximation of more complex models, for instance the ship hull in the naval engineering. The influence of the roughness on the friction drag can be obtained from testing of different plate models in a towing tank. Although this approximation usually offers a good agreement, experimental data and measurements are expensive to obtain. In order to reduce the cost of the experiments, a rotating disk is used an approximation of a flat plate since the installation and design of the experiment is not only cheaper but also simpler. The validation of this approximation is the main objective of this project and it is carried out by a study which is focused on finding similarities between both boundary layer properties with the aid of Computational Fluid Dynamics (CFD). Also, experimental measurements are compared with CFD result with the aim of a validation of the CFD results.Outgoin

Adaptive spectral elements for diffuse interface multi-fluid flow

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SEEK: A FORTRAN optimization program using a feasible directions gradient search

This report describes the use of computer program 'SEEK' which works in conjunction with two user-written subroutines and an input data file to perform an optimization procedure on a user's problem. The optimization method uses a modified feasible directions gradient technique. SEEK is written in ANSI standard Fortran 77, has an object size of about 46K bytes, and can be used on a personal computer running DOS. This report describes the use of the program and discusses the optimizing method. The program use is illustrated with four example problems: a bushing design, a helical coil spring design, a gear mesh design, and a two-parameter Weibull life-reliability curve fit

Modelling of friction and convective coefficients in a dry transformer

This thesis stands for a 2D axisymmetric study of convection heat transfer, within cooler ducts of dry type transformers, by means of CFD simulations (ANSYS Fluent). The purpose was the definition of descriptive functions for the mean heat transfer and friction coefficients, regarding free and forced convection, within a vertical cylindrical annular duct, under isoflux conditions (uniform wall heat flux). Dry-transformer type uses air as cooling system by natural convection and an AC system is assumed at the base of the transformer for forced convection. All system conditions and fluid properties were constructed and defined at Fluent program. Several pre-tests were performed, mainly in order to properly select the studied mesh and fluid-dynamic model. The parametric study was assembled accounting for 45 geometry’s designs, 8 values for wall heat flux, 4 velocities for forced convection simulations, while for natural convection a linear correlation heat flux-velocity was assumed. This corresponds to 1800 simulations. After data analysis and treatment, a non-linear regression was performed in MATLAB, aiming for the descriptive functions of convection heat transfer and friction coefficients, obtained thru CFD. A successful fitting was obtained through artificial neural networks (ANN), providing predictions for convective coefficient of relative errors inferior to 12% for approximately 80% of cases and inferior to 15% for approximately 70% of cases for friction coefficient. It was concluded an overcome accuracy of the ANN’s predictions shown, compared to the most fitted literature’s model considered, for convective heat transfer coefficient.Esta dissertação baseia-se no estudo, axi-simétrico 2D, de transferência de calor por convecção, em condutas de refrigeração de transformadores secos, por meio de simulações de CFD (ANSYS Fluent). O objetivo foi a definição de um modelo matemático descritivo dos coeficientes médios de transferência de calor por convecção e de fricção, em relação à convecção natural e forçada, num canal cilíndrico vertical anular, sob condições de fluxo de calor uniforme nas paredes. O fluido de refrigeração neste tipo de transformador é o ar, por convecção natural e um sistema AC é assumido na base do transformador para convecção forçada. Todas as condições do sistema e propriedades do fluido foram construídas e definidas no programa Fluent. Foram realizados vários testes prévios, principalmente para selecionar adequadamente a malha de estudo e o modelo fluido-dinâmico. O estudo paramétrico foi construído tendo em conta 45 geometrias, 8 fluxos de calor na parede, 4 velocidades para simulações de convecção forçada, enquanto para convecção natural foi criada e assumida uma correlação linear de velocidade de fluxo de calor. Isto corresponde a 1800 simulações. Após análise e tratamento dos dados, foi realizada uma regressão não linear no MATLAB, visando as funções descritivas dos coeficientes referidos. Obteve-se um ajuste adequado através de redes neurais artificiais (RNA), fornecendo previsões do coeficiente de convecção de erros relativos inferiores a 12% para aproximadamente 80% dos casos e inferior a 15% para aproximadamente 70% dos casos de coeficiente de atrito, relativamente aos resultados obtidos das simulações. Concluiu-se uma precisão superada das previsões de RNA, comparada com o modelo mais adequado de literatura considerado, para o coeficiente de transferência de calor por convecção.Mestrado em Engenharia Químic

Particle simulation of a Langmuir probe in quiescent and flowing plasmas

A three dimensional electrostatic Particle-In-Cell (PIC) code has been developed to simulate a Langmuir probe in both quiescent and flowing plasmas. The code was \\\u27ritten to model the use of the Langmuir probe in plasma regimes for which no closedform analytical solutions exist; this is the case for a probe in an ion beam, such as the plume of an ion thruster. Langmuir probes a.re used to determine local plasma properties, such as electron tPmperature, by careful dissection of the probe\u27s Voltage-Current (V-I) characteristic. To interpret experimental data from a Langmuir probe, one must separate ion from P]Pctron current. This process is well documented for quiescent plasmas; however, uo systematic techniques a.re available for interpreting data obtained using an electric probe in an ion beam. Ad hoc estimates of probe ion current in beam plasmas may lead to order of magnitude errors in the calculation of electron temperature. The PIC code described in this thesis was written to elucidate the beam-probe interaction and provide systematic techniques for legitimately interpreting experimental data

Characterization and numerical simulation of the microstructural and micromechanical viscoelastic behavior of oil sands using the discrete element method

Oil sands are naturally geologic formations of predominantly quartz sand grains whose void spaces are filled with bitumen, water, and dissolved gases. The electric rope shovel is the primary equipment used for excavating the Athabasca oil sand formations. The equipment\u27s static and dynamic loads are transferred to the formation during excavation and propel. These loads cause ground instability leading to sinkage or rutting, crawler wear, and fracture failures. These problems result in unplanned downtimes, production losses, and high maintenance costs. In order to address these problems, there is a need to develop valid models that capture the behavior and performance of oil sands under these loads. Particle-based physics methods, such as the discrete element method (DEM) can provide useful insight into the micromechanical and microstructural behavior of oil sands. This research is a pioneering effort towards contributing to the existing body of knowledge in oil sands formation characterization and numerical simulation using the DEM. These areas include oil sands as a four-phase material, shovel-formation interactions, and coupled deformation-stress under dynamic loading. A 2-D DEM model of the oil sands is built and simulated in PFC2D. The simulation results show that the generalized Burgers model with five Kelvin-Voigt elements fully characterized the microscopic viscoelastic response of the material. The micromechanical and microstructural viscoelastic model developed in this study can predict the dynamic modulus and phase angle of the material with a maximum error of 13.6%. This research initiative is a pioneering effort toward understanding shovel-oil sands formation interactions using a micromechanical and microstructural particle-based mechanics approach --Abstract, page iii

Models for Flow Rate Simulation in Gear Pumps: A Review

Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated by gerotor, external gear and crescent pumps. As far as the lumped parameter models are concerned, different ways of selecting the control volumes into which the pump is split are analyzed and the main governing equations are presented. The principles and the applications of distributed models from 1D to 3D are reported. A specific section is dedicated to the methods for the evaluation of the necessary geometric quantities: analytic, numerical and Computer-Aided Design (CAD)-based. The more recent studies taking into account the influence on leakages of the interactions between the fluid and the mechanical parts are explained. Finally the models for the simulation of the fluid aeration are described. The review brings to evidence the increasing effort for improving the simulation models used for the design and the optimization of the gear machines

Dimension reduction of image and audio space

The reduction of data necessary for storage or transmission is a desirable goal in the digital video and audio domain. Compression schemes strive to reduce the amount of storage space or bandwidth necessary to keep or move the data. Data reduction can be accomplished so that visually or audibly unnecessary data is removed or recoded thus aiding the compression phase of the data processing. The characterization and identification of data that can be successfully removed or reduced is the purpose of this work. New philosophy, theory and methods for data processing are presented towards the goal of data reduction. The philosophy and theory developed in this work establish a foundation for high speed data reduction suitable for multi-media applications. The developed methods encompass motion detection and edge detection as features of the systems. The philosophy of energy flow analysis in video processing enables the consideration of noise in digital video data. Research into noise versus motion leads to an efficient and successful method of identifying motion in a sequence. The research of the underlying statistical properties of vector quantization provides an insight into the performance characteristics of vector quantization and leads to successful improvements in application. The underlying statistical properties of the vector quantization process are analyzed and three theorems are developed and proved. The theorems establish the statistical distributions and probability densities of various metrics of the vector quantization process. From these properties, an intelligent and efficient algorithm design is developed and tested. The performance improvements in both time and quality are established through algorithm analysis and empirical testing. The empirical results are presented