Large Eddy Simulation Studies of Island Effects in the Caribbean Trade Wind Region

In dieser Dissertation wird das kompressible, nicht-hydrostatische und dreidimensionale Modell All Scale Atmospheric Model (ASAM) für Grobstruktur- bzw. Large-Eddy-Simulationen (LES) angewendet, um lokale Inseleffekte in der karibischen Passatwindzone zu untersuchen. Da das Modell bis dato noch keine Anwendung im Bereich von LES feuchter atmosphärischer Grenzschichten und heterogener Oberflächen fand, wurden einige Bestandteile zum Modellcode hinzugefügt oder überarbeitet. Ein Hauptaugenmerk liegt dabei auf das Einbeziehen orographischer Strukturen mittels angeschnittener Zellen (engl. cut cells). Sowohl die räumliche und zeitliche Diskretisierung der Modellgleichungen als auch die nötigen physikalischen Parameterisierungen werden in einer umfassenden Modellbeschreibung zusammengefasst. Die Robustheit und Stabilität der Modellformulierung wird durch eine Reihe von Simulationen idealisierter Testfälle bestätigt. Large-Eddy-Simulationen werden für das Gebiet der Karibikinsel Barbados zur Untersuchung von Inseleffekten bezüglich Grenzschichtmodifikation, Wolkenbildung und vertikaler Durchmischung von Aerosolen durchgeführt. Durch das Vorhandensein einer topographisch strukturierten Inseloberfläche in der Mitte des Modellgebietes muss das Modellsetup offene seitliche Randbedingungen beinhalten. Damit das einströmende Windfeld konsistent mit der Dynamik einer turbulenten, marinen Grenzschicht ist, wird eine neue Methode implementiert und angewendet, welche auf Störungen des potentiellen Temperaturfeldes mittels finiter Amplituden basiert. Beobachtungen aus der SALTRACE-Messkampagne werden benutzt, um die Modellläufe anzutreiben. Die Ergebnisse einiger Sensitivitätstests zeigen Probleme der Modellierung im Bereich der \"Terra incognita\" auf. Dabei handelt es sich um die Modellierung auf räumlichen Skalen, welche zwischen denen von LES und wolkenauflösenden Modellen liegen. Außerdem werden Auswirkungen von entweder turbulent oder laminar anströmenden Windfeldern auf die Simulationsergebnisse untersucht. Besonders die Wolkeneigenschaften im Lee von Barbados werden in diesen Simulationen merklich beeinflusst. Ergebnisse einer weiteren Simulation mit einer sehr starken Passatinversion bringt deren Einfluss auf die Dicke und Höhe der simulierten Wolkenschichten zum Vorschein. Die Veränderung von Saharastaubschichten, welche Barbados über weiträumigen Transport über den Atlantik erreichen, wird analysiert. Die Auswirkungen beinhalten sowohl eine Ausdünnung und ein Absinken dieser Schichten als auch turbulenter Transport in Richtung Erdoberfläche. Die genaue Position der beeinflussten Schichten und die Stärke des turbulenten Mischens werden hauptsächlich von der atmosphärischen Schichtung, der Inversionsstärke und Windscherung gesteuert. Vergleiche zwischen den LES-Modellergebnissen und Daten aus Doppler-Windlidarmessungen zeigen gute Übereinstimmungen in der Formierung der konvektiven Strukturen tagsüber und des Vertikalwindfeldes.In this thesis, the fully compressible, three-dimensional, nonhydrostatic atmospheric model called All Scale Atmospheric Model (ASAM) is utilized for large eddy simulations (LES) to investigate local island effects at the Caribbean. Since the model has not been applied to LES for moist boundary layers and heterogeneous surfaces so far, several parts are added to the model code or reworked. A special focus lies on the inclusion of orographical structures via the cut cell method. Spatial and temporal discretization as well as necessary physical parameterizations are summarized in a thorough model description. The robustness of the model formulation is confirmed by a set of idealized test case simulations. Large eddy simulations are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, the newly developed cell perturbation method based on finite amplitude perturbations is applied. Observations from the SALTRACE field campaign are used to initialize the model runs. Several numerical sensitivity tests are carried out to demonstrate the problems related to \"gray zone modeling\" beyond LES scales or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties west of Barbados (downwind) are markedly affected in these simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and height. The modification of Saharan dust layers reaching Barbados via long-range transport over the North Atlantic is analyzed. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom become apparent. The position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability, inversion strength and wind shear. Comparisons of LES model output with wind lidar data show similarities in the formation of the daytime convective plume and the vertical wind structure

A PHYSICS-BASED APPROACH TO MODELING WILDLAND FIRE SPREAD THROUGH POROUS FUEL BEDS

Wildfires are becoming increasingly erratic nowadays at least in part because of climate change. CFD (computational fluid dynamics)-based models with the potential of simulating extreme behaviors are gaining increasing attention as a means to predict such behavior in order to aid firefighting efforts. This dissertation describes a wildfire model based on the current understanding of wildfire physics. The model includes physics of turbulence, inhomogeneous porous fuel beds, heat release, ignition, and firebrands. A discrete dynamical system for flow in porous media is derived and incorporated into the subgrid-scale model for synthetic-velocity large-eddy simulation (LES), and a general porosity-permeability model is derived and implemented to investigate transport properties of flow through porous fuel beds. Note that these two developed models can also be applied to other situations for flow through porous media. Simulations of both grassland and forest fire spread are performed via an implicit LES code parallelized with OpenMP; the parallel performance of the algorithms are presented and discussed. The current model and numerical scheme produce reasonably correct wildfire results compared with previous wildfire experiments and simulations, but using coarser grids, and presenting complicated subgrid-scale behaviors. It is concluded that this physics-based wildfire model can be a good learning tool to examine some of the more complex wildfire behaviors, and may be predictive in the near future

The LHCb RICH PMTs Readout Electronics and the Monitoring of the HPDs Quantum Efficiency

LHCb is one of the four main experiments under construction on the Large Hadron Collider at CERN. Its purpose is to study CP violation in B mesons and to look for new physics effects in rare decays of b-hadrons. Particle identification will be essential to enhance the signal/background ratio in the selection of physics channels. For this reason, the Ring Imaging Cherenkov technique has been implemented: two RICH detectors (RICH1 and RICH2) have been designed to cover the wide momentum range 1-150 GeV/c. The produced Cherenkov photons will be focused on two planes of Hybrid PhotoDetectors (HPDs), which are sensitive to external magnetic fields and then need to be shielded. Despite the shielding, however, there will be some fringe field inside the HPDs volume and so it is necessary to experimentally check what is the behaviour of each photodetector when the LHCb dipole magnet is on and the HPDs are illuminated by test patterns. In RICH2, two LED projectors based on the Digital Light Processing technology are exploited to generate the test patterns, which have to be precisely aligned on the two HPD planes. The matching procedure is carried out using six PMTs permanently placed inside the HPD matrices. The work described in this thesis concerns the design, realization and test of the PMTs readout system, both on the HW and SW level. In the last chapter, I will also try to evaluate the possibility to periodically monitor the HPDs Q.E. using the same beamer selected for the magnetic distortion tests. Chapter 1 is an introduction to CERN and the LHCb experiment. Paragraph 1.2 focuses on the two RICH sub-systems, while in 1.3 the HPD working principle is described. In paragraph 2.1 I describe the PMTs installed in the RICH2, while the rest of the chapter is dedicated to the DLP projectors to be used during the magnetic distortion tests. In particular, 2.2 illustrates the DLP technology, while 2.4 and 2.5 are about the beamers tests. Chapter 3 is dedicated to the PMTs readout electronics design, realization and test. After a theoretical study carried out in paragraph 3.1, in 3.2 I describe the realized shaper amplifier prototype. In 3.3 the choice of the digitiser to be installed in cascade to the shaper is discussed and the DAQ software program is described, while 3.4 summarizes the results obtained testing the prototype with the real signals. In 3.5 the final six-channel shaper amplifier + ADC is presented and tested, while 3.6 describes the installation of this module in the pit environment. Finally, in chapter 4 I estimate the sensitivity of the HPD Q.E. monitoring based on the magnetic distortion test apparatus

Biomechanical study of rigid ankle-foot orthoses in the treatment of stroke patients

Error on title page, date of award is 2021.Rigid Ankle-Foot Orthoses (AFOs) are commonly prescribed for stroke patients who exhibit equinovarus deformity as an orthotic intervention. The main purpose of prescribing a rigid AFO is to provide appropriate control of unwanted ankle and foot motions in any plane. To achieve the optimal effects of the AFO, appropriate stiffness and alignment optimisation (tuning) should be considered. The AFO provides moments (referred to as the orthotic moments) to control ankle motion. Orthotic moments are different from the moments generated by ground reaction forces, the later are known as total ankle moments. Reviewing the literature showed limited research in this area. The aims of this study are to investigate the biomechanical effects of using rigid AFO (before and after tuning) and to investigate the orthotic moment during walking in stroke patients. Gait data were collected from six stroke participants (2 females, 4 males) and six healthy participants (3 females, 3 males) using a Motekforce Link dual belt instrumented treadmill and a Vicon 3-dimensional motion analysis system. Each participant was fitted with a custom made rigid AFO instrumented using four strain gauges. Walking at a self-selected speed was investigated while wearing: (1) Standard shoes only (2) Rigid AFO with standard shoes (3) Rigid Tuned-AFO with standard shoes. Lower limb temporal-spatial, kinetic and kinematic parameters, and electromyographic activity (Delsys TrignoTM) of the knee muscles were compared among the test conditions. The orthotic moments were also quantified using the strain gauges data combined with gait analysis. Repeated measures ANOVA and Friedman’s ANOVA were used for statistical analysis. The rigid AFO showed immediate improvement in the temporal-spatial parameters and the kinematics and the kinetics of post stroke gait. Greater improvement in knee kinematics and kinetics was achieved when tuning the rigid AFO. The rigid AFO (before and after tuning) increased quadriceps muscle activity and reduced hamstring muscle activity compared to walking with standard shoes only. Tuning a rigid AFO further increased quadriceps muscle activity and reduced hamstring muscle activity compared to AFO before tuning. Strain gauges data combined with gait analysis can be used in evaluating the orthotic moment around the ankle in sagittal and frontal planes. Tuning a rigid AFO had no clear changes in the orthotic moment, and it did not alter the anatomical moments at the ankle joint in sagittal and at the subtalar joint in frontal plane.Rigid Ankle-Foot Orthoses (AFOs) are commonly prescribed for stroke patients who exhibit equinovarus deformity as an orthotic intervention. The main purpose of prescribing a rigid AFO is to provide appropriate control of unwanted ankle and foot motions in any plane. To achieve the optimal effects of the AFO, appropriate stiffness and alignment optimisation (tuning) should be considered. The AFO provides moments (referred to as the orthotic moments) to control ankle motion. Orthotic moments are different from the moments generated by ground reaction forces, the later are known as total ankle moments. Reviewing the literature showed limited research in this area. The aims of this study are to investigate the biomechanical effects of using rigid AFO (before and after tuning) and to investigate the orthotic moment during walking in stroke patients. Gait data were collected from six stroke participants (2 females, 4 males) and six healthy participants (3 females, 3 males) using a Motekforce Link dual belt instrumented treadmill and a Vicon 3-dimensional motion analysis system. Each participant was fitted with a custom made rigid AFO instrumented using four strain gauges. Walking at a self-selected speed was investigated while wearing: (1) Standard shoes only (2) Rigid AFO with standard shoes (3) Rigid Tuned-AFO with standard shoes. Lower limb temporal-spatial, kinetic and kinematic parameters, and electromyographic activity (Delsys TrignoTM) of the knee muscles were compared among the test conditions. The orthotic moments were also quantified using the strain gauges data combined with gait analysis. Repeated measures ANOVA and Friedman’s ANOVA were used for statistical analysis. The rigid AFO showed immediate improvement in the temporal-spatial parameters and the kinematics and the kinetics of post stroke gait. Greater improvement in knee kinematics and kinetics was achieved when tuning the rigid AFO. The rigid AFO (before and after tuning) increased quadriceps muscle activity and reduced hamstring muscle activity compared to walking with standard shoes only. Tuning a rigid AFO further increased quadriceps muscle activity and reduced hamstring muscle activity compared to AFO before tuning. Strain gauges data combined with gait analysis can be used in evaluating the orthotic moment around the ankle in sagittal and frontal planes. Tuning a rigid AFO had no clear changes in the orthotic moment, and it did not alter the anatomical moments at the ankle joint in sagittal and at the subtalar joint in frontal plane

AERODYNAMICS AND AEROACOUSTICS OPTIMIZATION OF VEHICLE’S SIDE MIRROR BASE AND EXHAUST PIPE

This thesis is concerned with studying two different vehicle parts in terms of aerodynamics and aeroacoustics. Two main factors determine the efficiency and luxury of the vehicle, the low aerodynamic forces and low noise emission. The aerodynamic drag coefficient is concerned with how easy a vehicle can travel through the air; the lower the value, the less fuel is needed to move the vehicle forward and less air resistance the vehicle faces. The aerodynamic lift coefficient is related to vehicle ground stability, and the more negative the value is, the higher the vehicle\u27s stability. Moreover, the aeroacoustics is concerned with noise generated from air interacting with a body, and the lower the noise emitted, the higher the ride comfort of the passengers.The main objective of this thesis is to optimize the parts\u27 performance in terms of aerodynamics and aeroacoustics. The effect of changing the mirror base orientation on aerodynamics and aeroacoustics is desired. The optimum angle position for the mirror arm that results in the least aerodynamic forces and acoustics is desired. Furthermore, the exhaust pipe generates noise that affects the nearby pedestrians and influences aerodynamic forces. Therefore, the aim is to test nine different height levels for the exhaust pipe on the rear of the vehicle and record the drag and lift coefficient effect on the entire vehicle. The desired optimization is to lower the drag and lift force values and the generated acoustics from the part. The software ANSYS fluent is used for simulating each case.The results show that by changing the mirror\u27s base while keeping the projected area constant, there is no noticeable effect on the aerodynamic forces but has a significant effect on acoustics. Furthermore, the optimum angle orientation for the base is ~85±3.75 degrees, as this position results in the least acoustics generated. The mirror\u27s base orientation has a significant difference of up to 32 decibels in sound pressure level when comparing them side mirror base at 85 degrees to 45 degrees. The exhaust pipe is added at different heights, and resulting aerodynamic forces are compared with the original model without an exhaust outlet. When the exhaust pipe is placed 100 mm (position 5) above the bottom rear, it results in the lowest drag coefficient value (0.9% difference) compared to the original DrivAer model without an exhaust system. Furthermore, the position for the highest negative lift coefficient is located 125 mm (position 6) above the bottom rear, with a difference of ~7.7%.The mirror base has been completely ignored and overlooked in the literature. However, this thesis contributed significantly to the base mirror by determining a standard position that results in the lowest acoustics generation. The exhaust system\u27s effect on aerodynamic forces is lacking in studies compared to other vehicle parts. This thesis contributed to the aerodynamic optimization of a vehicle by studying the effect of the exhaust system and determining a design standard position that results in the lowest aerodynamic forces

Machine Learning and Its Application to Reacting Flows

This open access book introduces and explains machine learning (ML) algorithms and techniques developed for statistical inferences on a complex process or system and their applications to simulations of chemically reacting turbulent flows. These two fields, ML and turbulent combustion, have large body of work and knowledge on their own, and this book brings them together and explain the complexities and challenges involved in applying ML techniques to simulate and study reacting flows. This is important as to the world’s total primary energy supply (TPES), since more than 90% of this supply is through combustion technologies and the non-negligible effects of combustion on environment. Although alternative technologies based on renewable energies are coming up, their shares for the TPES is are less than 5% currently and one needs a complete paradigm shift to replace combustion sources. Whether this is practical or not is entirely a different question, and an answer to this question depends on the respondent. However, a pragmatic analysis suggests that the combustion share to TPES is likely to be more than 70% even by 2070. Hence, it will be prudent to take advantage of ML techniques to improve combustion sciences and technologies so that efficient and “greener” combustion systems that are friendlier to the environment can be designed. The book covers the current state of the art in these two topics and outlines the challenges involved, merits and drawbacks of using ML for turbulent combustion simulations including avenues which can be explored to overcome the challenges. The required mathematical equations and backgrounds are discussed with ample references for readers to find further detail if they wish. This book is unique since there is not any book with similar coverage of topics, ranging from big data analysis and machine learning algorithm to their applications for combustion science and system design for energy generation