SIMULATION OF WHISTLE NOISE USING COMPUTATIONAL FLUID DYNAMICS AND ACOUSTIC FINITE ELEMENT SIMULATION

The prediction of sound generated from fluid flow has always been a difficult subject due to the nonlinearities in the governing equations. However, flow noise can now be simulated with the help of modern computation techniques and super computers. The research presented in this thesis uses the computational fluid dynamics (CFD) and the acoustic finite element method (FEM) in order to simulate the whistle noise caused by vortex shedding. The acoustic results were compared to both analytical solutions and experimental results to better understand the effects of turbulence models, fluid compressibility, and wall boundary meshes on the acoustic frequency response. In the case of the whistle, sound power and pressure levels are scaled since 2-D models are used to model 3-D phenomenon. The methodology for scaling the results is detailed

Integrated modeling and analysis methodologies for architecture-level vehicle design.

In order to satisfy customer expectations, a ground vehicle must be designed to meet a broad range of performance requirements. A satisfactory vehicle design process implements a set of requirements reflecting necessary, but perhaps not sufficient conditions for assuring success in a highly competitive market. An optimal architecture-level vehicle design configuration is one of the most important of these requirements. A basic layout that is efficient and flexible permits significant reductions in the time needed to complete the product development cycle, with commensurate reductions in cost. Unfortunately, architecture-level design is the most abstract phase of the design process. The high-level concepts that characterize these designs do not lend themselves to traditional analyses normally used to characterize, assess, and optimize designs later in the development cycle. This research addresses the need for architecture-level design abstractions that can be used to support ground vehicle development. The work begins with a rigorous description of hierarchical function-based abstractions representing not the physical configuration of the elements of a vehicle, but their function within the design space. The hierarchical nature of the abstractions lends itself to object orientation - convenient for software implementation purposes - as well as description of components, assemblies, feature groupings based on non-structural interactions, and eventually, full vehicles. Unlike the traditional early-design abstractions, the completeness of our function-based hierarchical abstractions, including their interactions, allows their use as a starting point for the derivation of analysis models. The scope of the research in this dissertation includes development of meshing algorithms for abstract structural models, a rigid-body analysis engine, and a fatigue analysis module. It is expected that the results obtained in this study will move systematic design and analysis to the earliest phases of the vehicle development process, leading to more highly optimized architectures, and eventually, better ground vehicles. This work shows that architecture level abstractions in many cases are better suited for life cycle support than geometric CAD models. Finally, substituting modeling, simulation, and optimization for intuition and guesswork will do much to mitigate the risk inherent in large projects by minimizing the possibility of incorporating irrevocably compromised architecture elements into a vehicle design that no amount of detail-level reengineering can undo

Fluid Structure Interaction of Involute Fuel Plates in the High Flux Isotope Reactor Using a Fully-coupled Numerical Approach

This dissertation describes a fully-coupled (FC), finite-element (FE) based, algorithm for modeling and simulation of the fluid-structure interaction (FSI) of involuteshaped fuel plates used in research reactors; specifically the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). Following a graded approach to code and model validation, a cylinder in cross-flow benchmark is used to establish flow physics as well as properly coupling the FSI phenomena with increasing complexity. As an interim step toward HFIR LEU fuel plate simulations, three experiments are used for validation. The first, performed by Smissaert, is used to envelope large plate deflections and understand the validity of various fluid boundary conditions for single plate comparisons. Continuing with Smissaert\u27s data, a 5-plate simulation is presented showing the first-ever multi-plate simulation using this FC and FE approach. Second, a vibrating plate, presented by Liu et al., is simulated showing the same technique to encompass self-excited, periodic plate deflections. Lastly, an experiment for the conceptual Advanced Neutron Source Reactor (ANSR) using involute plates is utilized to validate the ability of this FC and FE algorithm to predict the deflections of the involute-shaped plates used in the HFIR. The method shown herein accurately captures the established `S-shaped\u27 deflection of the first mode of the involute plate providing guidance that researchers and designers can utilize in the forthcoming design of the next generation of low-enriched uranium (LEU) fuel plates for the HFIR. A `Lessons Learned\u27 section which describes external routine coupling, geometry and meshing guidance, and solver settings used in the computational platform used to perform these FSI simulations is also provided

Forced response prediction for industrial gas turbine blades

A highly efficient aeromechanical forced response system is developed for predicting resonant forced vibration of turbomachinery blades with the capabilities of fully 3-D non-linear unsteady aerodynamics, 3-D finite element modal analysis and blade root friction modelling. The complete analysis is performed in the frequency domain using the non linear harmonic method, giving reliable predictions in a fast turnaround time. A robust CFD-FE mesh interface has been produced to cope with differences in mesh geometries, and high mode shape gradients. A new energy method is presented, offering an alternative to the modal equation, providing forced response solutions using arbitrary mode shape scales. The system is demonstrated with detailed a study of the NASA Rotor 67 aero engine fan rotor. Validation of the forced response system is carried out by comparing predicted resonant responses with test data for a 3-stage transonic Siemens industrial compressor. Two fully-coupled forced response methods were developed to simultaneously solve the flow and structural equations within the fluid solver. A novel closed-loop resonance tracking scheme was implemented to overcome the resonant frequency shift in the coupled solutions caused by an added mass effect. An investigation into flow-structure coupling effects shows that the decoupled method can accurately predict resonant vibration with a single solution at the blade natural frequency. Blade root-slot friction damping is predicted using a modal frequency-domain approach by applying linearised contact properties to a finite element model, deriving contact Droperties from an advanced semi-analytical microslip model. An assessment of Coulomb and microslip approaches shows that only the microslip model is suitable for predicting root friction damping

Coupling, Conservation, and Performance in Numerical Simulations

This thesis considers three aspects of the numerical simulations, which arecoupling, conservation, and performance. We conduct a project and addressone challenge from each of these aspects.We propose a novel penalty force to enforce contacts with accurate Coulombfriction. The force is compatible with fully-implicit time integration and theuse of optimization-based integration. In addition to processing collisionsbetween deformable objects, the force can be used to couple rigid bodies todeformable objects or the material point method. The force naturally leads tostable stacking without drift over time, even when solvers are not run toconvergence. The force leads to an asymmetrical system, and we provide apractical solution for handling these.Next we present a new technique for transferring momentum and velocity betweenparticles and MAC grids based on the Affine-Particle-In-Cell (APIC) frameworkpreviously developed for co-locatedgrids. We extend the original APIC paper and show thatthe proposed transfers preserve linear and angular momentum and also satisfyall of the original APIC properties.Early indications in the original APIC paper suggested that APIC might besuitable for simulating high Reynolds fluids due to favorable retention ofvortices, but these properties were not studied further. We use twodimensional Fourier analysis to investigate dissipation in the limit \dt=0.We investigate dissipation and vortex retention numerically to quantify theeffectiveness of APIC compared with other transfer algorithms.Finally we present an efficient solver for problems typically seen inmicrofluidic applications.Microfluidic ``lab on a chip'' devices are small devices that operate on smalllength scales on small volumes of fluid. Designs for microfluidic chips aregenerally composed of standardized and often repeated components connected bylong, thin, straight fluid channels. We propose a novel discretizationalgorithm for simulating the Stokes equations on geometry with these features,which produces sparse linear systems with many repeated matrix blocks. Thediscretization is formally third order accurate for velocity and second orderaccurate for pressure in the $L^\infty$ norm. We also propose a novel linearsystem solver based on cyclic reduction, reordered sparse Gaussian elimination,and operation caching that is designed to efficiently solve systems withrepeated matrix blocks

The discontinuous Galerkin finite element method for the solution of fluid-structure interaction problems

Cílem této práce je navrhnout a implementovat metodiku pro řešení úloh interakce tekutiny s tělesem (označované jako FSI) především pro aplikace v oblasti aeroelasticity, např. pro predikci flutteru. Jedním z hlavních požadavků na algoritmus FSI je vysoká úroveň modularity, což znamená, že řešiče pro tekutinu a strukturu by na sobě měly být nezávislé. Navíc předpokládáme, že výpočtové sítě pro oblast tekutiny a struktury na sebe nemusí navazovat. Z tohoto důvodu byl zvolen oddělený přístup řešení s možností volby slabé nebo silné vazby namísto přístupu monolitického. Velká část této práce je věnována modelování proudění stlačitelné tekutiny. Pro řešení Navierových-Stokesových rovnic v ALE formulaci je odvozeno implicitní schéma nespojité Galerkinovy metody. K aproximaci vazkých toků je použita metoda vnitřních penalty. Pro stabilizaci řešení je použita umělá vazkost, jejíž velikost je řízena senzorem rázových vln. Pro úlohy turbulentního proudění je uvažován Spalartův-Allmarasův model turbulence. Implementovaný CFD řešič je validován na několika testovacích úlohách proudění okolo stacionárních leteckých profilů a okolo leteckých profilů s předepsaným pohybem. V těchto úlohách uvažujeme jak proudění nevazké tekutiny, tak laminární i turbulentní proudění vazké tekutiny. Další uvažovanou úlohou je posouzení vzniku torzního flutteru v kaskádě lopatek pomocí energetické metody, která využívá jednosměrnou vazbu. Vyvinutý CFD řešič je validován pomocí experimentálního měření provedeného na Ústavu termomechaniky Akademie věd České republiky. Pro řešení úloh obousměrné vazby jsou uvažovány dva různé modely struktury a to soustava pružně uložených tuhých těles a elastická struktura s velkými deformacemi. Vyvinutý FSI řešič je validován na dvou úlohách interakce s tuhými tělesy, konkrétně na úloze kmitání válce v tekutině vynuceném vírovou stezkou a na úloze predikce flutteru křídla letadla. Výsledky jsou porovnány s numerickými a experimentálními daty jiných autorů. Pro případ tuhého tělesa je navržen nový efektivní algoritmus deformace sítě založený na řešení eliptické rovnice. Výhodou algoritmu je, že eliptická rovnice se řeší pro každé z tuhých těles před zahájením simulace FSI pouze jednou, čímž se ušetří výpočtový čas. Elastická struktura je popsána nelineárními rovnicemi elastodynamiky, které jsou řešeny metodou konečných prvků s implicitní integrací. Protože výpočtové sítě pro oblast tekutiny a struktury na jejich rozhraní nemusí navazovat, tenzor napjatosti je nutné interpolovat. Jak algoritmus deformace sítě, tak interpolace tenzoru napjatosti jsou založeny na radiálních bázových funkcích. Výhodou zmíněného algoritmu je, že zahrnuje i interpolaci výchylek struktury, které tak nemusí být interpolovány zvlášť.ObhájenoThe ultimate goal of this thesis is to design and implement a fluid-structure interaction (FSI) methodology mainly for applications in aeroelasticity, such as flutter prediction. One of the main requirements for the FSI algorithm is a high level of modularity, meaning that the fluid and structure solvers should be independent of each other and the corresponding meshes do not need to align on the fluid-solid interface. For this reason, the partitioned approach was adopted with the option of either weak or strong coupling. A lot of attention is given to the modelling of the fluid flow, as it tends to be the most complicated part of any FSI problem. In this thesis, an implicit discontinuous Galerkin scheme is derived for the solutions of compressible Navier-Stokes equations in the arbitrary Lagrangian-Eulerian formulation. The interior penalty method is used to approximate viscous fluxes. Artificial viscosity is added to regions with a shock according to a fine-tuned shock sensor to stabilise the solution. The one-equation Spalart-Allmaras turbulence model is applied to problems with turbulent flow. To contend the computational requirement for the fluid-flow simulations, a domain decomposition method is employed for distributed computing. The implemented discontinuous Galerkin solver is benchmarked on a few test problems of flow around stationary aerofoils and aerofoils with prescribed motion. Both laminar and turbulent viscous flows and inviscid flows are considered. Furthermore, torsional flutter in a blade cascade is assessed using the energy method, which uses one-way coupling. The discontinuous Galerkin solver is validated on this problem against experimental measurement conducted at the Institute of Thermomechanics of the Czech Academy of Sciences. In order to solve two-way coupling problems, two different structure models are considered, specifically a system of elastically-mounted rigid bodies interconnected with springs and dampers and an elastic structure with large deformations. The FSI solver is validated on two problems of interaction with rigid bodies, namely on vortex-induce vibration of a cylinder and flutter prediction of a swept-back wing modelled as a two-degree-of-freedom aerofoil. A new efficient mesh-deformations algorithm based on solving an elliptic equation is proposed for the case of rigid structure. The advantage of the algorithm is that the elliptic equation is solved only once for each of the rigid bodies before the FSI simulation starts, thereby saving computational time during simulation. The elastic structure is described by nonlinear equations of elastodynamics, which are solved by an implicit finite-element scheme with Newton's iterative procedure. Since the fluid and structure meshes are mutually nonconforming on the fluid-solid interface, the aerodynamic stress is interpolated using radial basis functions. The mesh-deformation algorithm is also based on radial basis functions, the advantage of which is that it takes care of the interpolation of the structure's displacement on the fluid-solid interface

The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery

Despite the resources devoted to computer graphics technology over the last 40 years, there is still a need to increase the realism with which flexible materials are simulated. However, to date reported methods are restricted in their application by their use of two-dimensional structures and implicit integration methods that lend themselves to modelling cloth-like sheets but not stiffer, thicker materials in which bending moments play a significant role. This thesis presents a real-time, computationally efficient environment for simulations of sheet materials. The approach described differs from other techniques principally through its novel use of multilayer sheet structures. In addition to more accurately modelling bending moment effects, it also allows the effects of increased temperature within the environment to be simulated. Limitations of this approach include the increased difficulties of calibrating a realistic and stable simulation compared to implicit based methods. A series of experiments are conducted to establish the effectiveness of the technique, evaluating the suitability of different integration methods, sheet structures, and simulation parameters, before conducting a Human Computer Interaction (HCI) based evaluation to establish the effectiveness with which the technique can produce credible simulations. These results are also compared against a system that utilises an established method for sheet simulation and a hybrid solution that combines the use of 3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach. The results suggest that the use of a three-dimensional structure does provide a level of enhanced realism when simulating stiff laminar materials although the best overall results were achieved through the use of the hybrid model