A fast GPU Monte Carlo Radiative Heat Transfer Implementation for Coupling with Direct Numerical Simulation

We implemented a fast Reciprocal Monte Carlo algorithm, to accurately solve radiative heat transfer in turbulent flows of non-grey participating media that can be coupled to fully resolved turbulent flows, namely to Direct Numerical Simulation (DNS). The spectrally varying absorption coefficient is treated in a narrow-band fashion with a correlated-k distribution. The implementation is verified with analytical solutions and validated with results from literature and line-by-line Monte Carlo computations. The method is implemented on GPU with a thorough attention to memory transfer and computational efficiency. The bottlenecks that dominate the computational expenses are addressed and several techniques are proposed to optimize the GPU execution. By implementing the proposed algorithmic accelerations, a speed-up of up to 3 orders of magnitude can be achieved, while maintaining the same accuracy

hp-FEM for Two-component Flows with Applications in Optofluidics

This thesis is concerned with the application of hp-adaptive finite element methods to a mathematical model of immiscible two-component flows. With the aim of simulating the flow processes in microfluidic optical devices based on liquid-liquid interfaces, we couple the time-dependent incompressible Navier-Stokes equations with a level set method to describe the flow of the fluids and the evolution of the interface between them

Proceedings, MSVSCC 2014

Proceedings of the 8th Annual Modeling, Simulation & Visualization Student Capstone Conference held on April 17, 2014 at VMASC in Suffolk, Virginia

Deep Model for Improved Operator Function State Assessment

A deep learning framework is presented for engagement assessment using EEG signals. Deep learning is a recently developed machine learning technique and has been applied to many applications. In this paper, we proposed a deep learning strategy for operator function state (OFS) assessment. Fifteen pilots participated in a flight simulation from Seattle to Chicago. During the four-hour simulation, EEG signals were recorded for each pilot. We labeled 20- minute data as engaged and disengaged to fine-tune the deep network and utilized the remaining vast amount of unlabeled data to initialize the network. The trained deep network was then used to assess if a pilot was engaged during the four-hour simulation

Balanced-force two-phase flow modelling on unstructured and adaptive meshes

Two-phase flows occur regularly in nature and industrial processes and their understanding is of significant interest in engineering research and development. Various numerical methods to predict two-phase phase flows have been developed as a result of extensive research efforts in past decades, however, most methods are limited to Cartesian meshes. A fully-coupled implicit numerical framework for two-phase flows on unstructured meshes is presented, solving the momentum equations and a specifically constructed continuity constraint in a single equation system. The continuity constraint, derived using a momentum interpolation method, satisfies continuity, provides a strong pressure-velocity coupling and ensures a discrete balance between pressure gradient and body forces. The numerical framework is not limited to specific density ratios or a particular interface topology and includes several novelties. A further step towards a more accurate prediction of two-phase flows on unstructured meshes is taken by proposing a new method to evaluate the interface curvature. The curvature estimates obtained with this new method are shown to be as good as or better than methods reported in literature, which are mostly limited to Cartesian meshes, and the accuracy on structured and unstructured meshes is shown to be comparable. Furthermore, lasting contributions are made towards the understanding of convolution methods for two-phase flow modelling and the underlying mechanisms of parasitic currents are studied in detailed. The mesh resolution is of particular importance for two-phase flows due to the inherent first-order accuracy of the interface position using interface capturing methods. A mesh adaption algorithm for tetrahedral meshes with application to two-phase flows and its implementation are presented. The algorithm is applied to study mesh resolution requirements at interfaces and force-balancing for surface-tension-dominated two-phase flows on adaptive meshes.Open Acces

Numerical Simulation of Droplets with Dynamic Contact Angles

The numerical simulation of droplet impact is of interest for a vast variety of industrialprocesses, where practical experiments are costly and time-consuming. In these simulations, the dynamic contact angle is a key parameter, but the modeling of its behavior is poorly understood so far. One of the few models, which considers the overall physical context of the involved 'moving contact line problem' is Shikhmurzaev’s interface formation model. In addition to keeping the problem well-posed, all surface and bulk parameters, such as the contact angle, are determined as part of the solution rather than being prescribed functions of contact line speed. In this thesis, we couple an asymptotic version of the interface formation model with our three-dimensional incompressible two-phase Navier-Stokes solver NaSt3DGPF developed at the Institute for Numerical Simulation, Bonn University. With this sophisticated model, the droplet shapes, heights and diameters compare very well with those from a range of practical experiments

Investigation of propeller stall flutter

Propeller flutter can manifest in a variety of ways. This includes classical bending-torsion flutter, stall flutter and whirl flutter. Classical bending-torsion flutter for propeller blades is driven by the coupling, and excitement, of selected modes of motion. Such flutter problems are often a result of structural coupling and in the linear aerodynamic regime. As a result, low-fidelity, fast calculations can be used to determine boundaries and mitigate the effects via changes in the structural design. Whirl flutter is the most complex and involves the coupling of the aircraft wing modes of motion to the gyroscopic and aerodynamic effects of the propeller. This phenomenon can be highly non-linear due to both the structure and flow-field, and any mitigation involves sophisticated modelling efforts with respect to the airframe. Propeller stall flutter is less complex in terms of the structure, however, involves the highly non-linear aerodynamics associated with detached flow. This phenomena, like classical flutter, is driven by the propeller design and conditions, but due to its nature, the stall flutter boundary significantly reduces the overall flutter boundary of a propeller. Hence, the understanding of this limitation must be known to ensure safe operation. The development of modern propeller blades utilising high sweep/taper with thin aerofoil sections can result in a change in the flutter boundary. In addition to this, propellers are coming back into focus due to the development of electrically driven Vertical Take-off/Landing (eVTOL) vehicles and, due to the nature of such a vehicle design, the propellers are being pushed into significantly different operating conditions. This motivation, coupled with the increased computational power available in the modern era, requires the need to reassess what is required to understand the stall flutter boundary associated with a modern, in-service, propeller blade. To this end, a numerical investigation using Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) was conducted on the Commander propeller blade of Dowty Propellers. This blade was selected from the list of experimentally investigated blades due to the availability of geometry, structural data and applicability in real life applications. A validation procedure was conducted to assess the effects of the computational setup. This included the effects of turbulence, structural modelling and implementation, with a validated process found whilst using Scale-Adaptive-Simulation (SAS) with interpolated structural modes. An attempt was made to extract aerodynamic damping data of the stall flutter phenomenon via the development of a method from the aeroelastic simulations. Such values give an indication of the stability, with links made to typical two-dimensional modelling. The thesis ends on the parametric study of the validated Commander simulation. This was conducted in order to gain greater detail on the effects of key structural and aerodynamic parameters on the blade stall flutter response. The key outcome from this investigation is the need for scale-resolving methods in propeller stall flutter investigations. This study utilises a hybrid RANS/LES model to capture the key detached flow content. This detached flow content results in significant pressure fluctuations, not observed in traditional statistical models, which drive the aeroelastic deformations. In addition, the requirement for a well validated structural model is highlighted including the setup of the structural solver for which an interpolated modal response method is used. It is also found from this investigation that there is a need for a modern experimental test case focusing on propeller stall flutter. The last comprehensive study was conducted in the 1980’s and, with improvements in experimental techniques, greater understanding and data can now be extracted. This new data can be used to validate modern CFD efforts. The novelty of this work lies within the derivation of a method for the extraction of the aerodynamic damping data from three-dimensional simulations. This had previously not be done before and the extracted results correlated with equivalent two-dimensional aerodynamic damping data. Additionally, the development and application of three-dimensional Navier-Stokes based CFD, with a coupled structural model, had not been conducted on propeller stall flutter

Optimization-based finite element methods for evolving interfaces

This thesis is concerned with the development of new approaches to redistancing and conservation of mass in finite element methods for the level set transport equation. The first proposed method is a PDE- and optimization-based redistancing scheme. In contrast to many other PDE-based redistancing techniques, the variational formulation derived from the minimization problem is elliptic and can be solved efficiently using a simple fixed-point iteration method. Artificial displacements are effectively prevented by introducing a penalty term. The objective functional can easily be extended so as to satisfy further geometric properties. The second redistancing method is based on an optimal control problem. The objective functional is defined in terms of a suitable potential function and aims at minimizing the residual of the Eikonal equation under the constraint of an augmented level set equation. As an inherent property of this approach, the interface cannot be displaced on a continuous level and numerical instabilities are prevented. The third numerical method under investigation is an optimal control approach designed to enforce conservation of mass. A numerical solution to the level set equation is corrected so as to satisfy a conservation law for the corresponding Heaviside function. Two different control approaches are investigated. The potential of the proposed methods is illustrated by a wide range of numerical examples and by numerical studies for the well-known rising bubble benchmark

Toward a translingual composition: ancient rhetorics and language difference

The purpose of this dissertation is to outline a pedagogy that promotes language difference in college composition classrooms. Scholarship on language difference has strived for decades to transform teaching practices in mainstream, developmental, and second-language writing instruction. Despite compelling arguments in support of linguistic diversity, a majority of secondary and postsecondary writing teachers in the U.S. still privilege Standard English. However, non-native speakers of English now outnumber native speakers worldwide, a fact which promises to redefine what "standard" means from a translingual perspective. It is becoming clearer that multilingual writers, versed in flexible hermeneutic strategies and able to draw on a variety of Englishes and languages to make meaning, have significant advantages over monolingual students. My dissertation anticipates the pedagogical and programmatic changes necessitated by this global language shift. To this end, I join a number of scholars in arguing for a revival of classical style and the progymnasmata, albeit with the unique agenda of strengthening pedagogies of language difference. Although adapting classical rhetorics to promote translingual practices such as code-meshing at first seems to contradict the spirit of language difference given the dominant perception of Greco-Roman culture as imperialistic and intolerant of diversity, I reread neglected rhetoricians such as Quintilian in order to recover their latent multilingual potential