The Validation and Verification of LES Modeling Using KIVA

In recent years, the use of large-eddy simulation (LES) has grown into new research methods. LES is preferred when compared to Reynold’s Averaged Navier Stokes (RANS), which separates velocity components into steady and fluctuating components. While RANS is relatively easy to implement, it does not fully resolve the range of turbulence eddies and has limitations that make it inaccurate in many practical circumstances. Direct numerical simulation, DNS, fully resolves all turbulent eddies to the smallest grid scale, but requires an extremely fine grid. This makes it computationally impractical to use as the computational power required to solve even the simplest case is severely high. In LES, the large eddies are resolved while the small eddies are modelled. This can be advantageous as we lower the computational resources required for solving the flow while still maintaining accuracy. The use of RANS as well as DNS make them highly difficult in solving issues involving combustion processes. LES models tend to be simpler and require fewer adjustments when applied to a wide range of flows. In addition to turbulence, LES can also handle species transport and chemical reactions typically found in engine configurations, and makes it a very suitable choice. LES has many different approaches, including the popular Smagorinsky model. The main problem with the elementary Smargoinsky approach is that a model parameter, ����, is assumed constant over the entire region, which is generally not true for turbulent flows. Making the model dynamic to localize the parameter, we still have problems of the parameter varying too much (as much as ten times the mean) and the eddy viscosity becoming negative, resulting in instability. The Vreman LES model, as employed in this work, performs as well if not better than the dynamic Smagorinsky model, and does not require ad hoc procedures, including issues involving clipping. In this study, the LES Vreman model with a finite element method with h-adaptation technique is verified and validated using several benchmark cases. The end result being part of an on-going effort to enhance combustion predictability and increase efficiencies within engines

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is operated by the Ohio Aerospace Institute (OAI) and the NASA Lewis Research Center in Cleveland, Ohio. The purpose of ICOMP is to develop techniques to improve problem-solving capabilities in all aspects of computational mechanics related to propulsion. This report describes the accomplishments and activities at ICOMP during 1993

Parallel H-Matrices accelerated isogeometric boundary element method implementation applied to acoustics internal and external problems

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2020.Uma implementação paralela da formulação do método dos elementos de contorno isogeométrico acelerada pelas matrizes hierárquicas é apresentada neste trabalho. A implementação está disponível online em github.com/alvarocafe/BEM\textunderscore base e contém testes baseados em problemas de acústica interna e externa para os quais soluções analíticas estão disponíveis. A formulação descrita nesse trabalho utiliza curvas de Bézier obtidas de NURBS através de um procedimento de extração de Bézier. Arquivos de CAD com especificações abertas como IGES em geral utilizam curvas NURBS que podem ser utilizadas para a extração, mas um editor de NURBS em Julia é apresentado para construir os modelos utilizados nesse trabalho. É possível também obter os pontos de controle, pesos e ordem de curvas específicas NURBS e obter a representação como curvas de Bézier sem prejuizo em precisão ou continuidade. Uma vez que o domínio é representado como um retalho de curvas ou superfícies de Bézier, esse retalho compõe o contorno da representação direta do método dos elementos de contorno. O domínio consiste no volume apontado pelo vetor oposto ao vetor unitário normal no contorno. Cada curva de Bézier pode ser considerada como um elemento de contorno, com o cuidado de não se utilizar os pontos de controle como os pontos de colocação, pois eles podem e muitas vezes não se encontram no contorno, e sim construir pontos posicionados de forma conveniente na curva. Sendo as condições de contorno aplicadas a elementos individuais, o resultado é um sistema linear $N\times N$, sendo $N$ o número de curvas de Bézier que compõe o contorno. A montagem do sistema é realizada através de matrizes hierárquicas por interpolação utilizando polinômios de Lagrange. Isso significa que as as matrizes de influência serão representadas como matrizes de baixo rank, especificamente, como um produto matricial de outras pequenas matrizes, chamadas blocos. Essa representação é conveniente pois a memória necessária para armazenar uma matriz é reduzida, de acordo com o rank dessa matriz. Utilizando esse método, a matriz de influência completa nunca é armazenada, uma vez que o sistema linear é resolvido utilizando o método dos mínimos resíduos generalizados. Esse procedimento permite que problemas maiores sejam resolvidos para uma mesma configuração de hardware. A implementação é utilizada para resolver um problema inverso usando algoritmos genéticos para obter a configuração de um modelo axissimétrico tridimensional a partir da informação do fluxo acústico em pontos discretos. A otimização foi utilizada para inferir a configuração de um trato vocal utilizando apenas 20 pontos de informação do fluxo acústico em uma linha reta entre a glote e a boca. Um levitador acústico não resonante foi implementado experimentalmente e numericamente e a resposta acústica é comparada com imagens obtidas pelo método de Schlirien com boa concordância. O levitador utilizado é baseado no projeto TinyLev, que usa 72 transdutores ultrassônicos ao invés de falantes de Langevin para produzir a levitação. O levitador é modelado utilizando o BEM e uma bancada experimental é apresentada para providenciar imagens de Schlirien da onda acústica estacionária.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).A parallel implementation of the hierarchical matrices accelerated isogeometric boundary element method formulation is presented in this work. The implementation is available online in github.com/alvarocafe/BEM_base and contains tests based on internal and acoustic problems analytical solutions. The formulation described in this work utilises Bézier curves obtained from NURBS through a Bézier extraction procedure. CAD files with open specifications such as IGES uses NURBS curves from which Bézier patches may be extracted, but a NURBS editor in Julia is presented to build the models used in this work. It's possible to obtain control points, weights and curve degrees such that there is no loss in precision or continuity of the curve. Once the domain is represented as a Bézier patch, this patch is used as the boundary of the direct boundary element method. The volume in the direction the unit normal vector to the boundary is the domain of interest. Each Bézier curve may be considered a boundary element, with the care to no use control points as collocation points, as they may reside outside of the domain, but to position the points conveniently on the curve. As the boundary conditions are applied on individual elements results in a $N\times N$ linear system, for $N$ elements. The system is built using hierarchical matrices using interpolation by Lagrange polynomials. This means that the influence matrices are represented as low-rank, specifically as a matrix product of smaller matrices, called blocks. This representation is convenient as the memory necessary to store the matrix is reduced, accordingly to the its rank. Using this procedure, the full influence matrix is never stored, as the linear system is solved using the generalized minimal residual method. Such procedure allows larger problems to be solved for a given hardware configuration. The implementation was used to solve an inverse method optimization using genetic algorithms to obtain the geometric configuration of a three-dimensional axissymetrical model using only acoustic information. The optimization was used to infer the configuration of a vocal tract using only 20 points of acoustic flux information, displayed in a straight line from the glottis to the mouth. A non-resonant acoustic levitator model was also implemented and the resulting acoustic response is compared to Schlirien imaging showing good accordance. The levitator is based on the TinyLev project, which uses 72 ultrassonic transducers opposed to Langevin horns to produce acoustic levitation. The levitator is modeled using the BEM and an experimental bench is presented to provide Schlirien imaging of the standing acoustic wave

Reservoir Computing: computation with dynamical systems

In het onderzoeksgebied Machine Learning worden systemen onderzocht die kunnen leren op basis van voorbeelden. Binnen dit onderzoeksgebied zijn de recurrente neurale netwerken een belangrijke deelgroep. Deze netwerken zijn abstracte modellen van de werking van delen van de hersenen. Zij zijn in staat om zeer complexe temporele problemen op te lossen maar zijn over het algemeen zeer moeilijk om te trainen. Recentelijk zijn een aantal gelijkaardige methodes voorgesteld die dit trainingsprobleem elimineren. Deze methodes worden aangeduid met de naam Reservoir Computing. Reservoir Computing combineert de indrukwekkende rekenkracht van recurrente neurale netwerken met een eenvoudige trainingsmethode. Bovendien blijkt dat deze trainingsmethoden niet beperkt zijn tot neurale netwerken, maar kunnen toegepast worden op generieke dynamische systemen. Waarom deze systemen goed werken en welke eigenschappen bepalend zijn voor de prestatie is evenwel nog niet duidelijk. Voor dit proefschrift is onderzoek gedaan naar de dynamische eigenschappen van generieke Reservoir Computing systemen. Zo is experimenteel aangetoond dat de idee van Reservoir Computing ook toepasbaar is op niet-neurale netwerken van dynamische knopen. Verder is een maat voorgesteld die gebruikt kan worden om het dynamisch regime van een reservoir te meten. Tenslotte is een adaptatieregel geïntroduceerd die voor een breed scala reservoirtypes de dynamica van het reservoir kan afregelen tot het gewenste dynamisch regime. De technieken beschreven in dit proefschrift zijn gedemonstreerd op verschillende academische en ingenieurstoepassingen

Design of a Programmable Active Acoustic Metamaterial

Metamaterials are artificial materials engineered to provide properties which may not be readily available in nature. The development of such class of materials constitutes a new area of research that has grown significantly over the past decade. Acoustic metamaterials, specifically, are even more novel than their electromagnetic counterparts arising only in the latter half of the decade. Acoustic metamaterials provide a new tool in controlling the propagation of pressure waves. However, physical design and frequency tuning, is still a large obstacle when creating a new acoustic metamaterial. This dissertation describes active and programmable design for acoustic metamaterials which allows the same basic physical design principles to be used for a variety of application. With cloaking technology being of a great interest to the US Navy, the proposed design approach would enable the development of a metamaterial with spatially changing effective parameters while retaining a uniform physical design features. The effective parameters would be controlled by tuning smart actuators embedded inside the metamaterial structure. Since this design is based on dynamic effective parameters that can be electrically controlled, material property ranges of several orders of magnitude could potentially be achieved without changing any physical parameters. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible

Robotics 2010

Without a doubt, robotics has made an incredible progress over the last decades. The vision of developing, designing and creating technical systems that help humans to achieve hard and complex tasks, has intelligently led to an incredible variety of solutions. There are barely technical fields that could exhibit more interdisciplinary interconnections like robotics. This fact is generated by highly complex challenges imposed by robotic systems, especially the requirement on intelligent and autonomous operation. This book tries to give an insight into the evolutionary process that takes place in robotics. It provides articles covering a wide range of this exciting area. The progress of technical challenges and concepts may illuminate the relationship between developments that seem to be completely different at first sight. The robotics remains an exciting scientific and engineering field. The community looks optimistically ahead and also looks forward for the future challenges and new development

Proceedings of the NASA Conference on Space Telerobotics, volume 4

Papers presented at the NASA Conference on Space Telerobotics are compiled. The theme of the conference was man-machine collaboration in space. The conference provided a forum for researchers and engineers to exchange ideas on the research and development required for the application of telerobotic technology to the space systems planned for the 1990's and beyond. Volume 4 contains papers related to the following subject areas: manipulator control; telemanipulation; flight experiments (systems and simulators); sensor-based planning; robot kinematics, dynamics, and control; robot task planning and assembly; and research activities at the NASA Langley Research Center

Adaptive mesh simulations of compressible flows using stabilized formulations

This thesis investigates numerical methods that approximate the solution of compressible flow equations. The first part of the thesis is committed to studying the Variational Multi-Scale (VMS) finite element approximation of several compressible flow equations. In particular, the one-dimensional Burgers equation in the Fourier space, and the compressible Navier-Stokes equations written in both conservative and primitive variables are considered. The approximations made for the VMS formulation are extensively researched; the design of the matrix of stabilization parameters, the definition of the space where the subscales live, the inclusion of the temporal derivatives of the subscales, and the non-linear tracking of the subscales are formulated. Also, the addition of local artificial diffusion in the form of shock capturing techniques is included. The accuracy of the formulations is studied for several regimes of the compressible flow, from aeroacoustic flows at low Mach numbers to supersonic shocks. The second part of the thesis is devoted to make the solution of the smallest fluctuating scales of the compressible flow affordable. To this end, a novel algorithm for $h-$refinement of computational physics meshes in a distributed parallel setting, together with the solution of some refinement test cases in supercomputers are presented. The definition of an explicit a-posteriori error estimator that can be used in the adaptive mesh refinement simulations of compressible flows is also developed; the proposed methodology employs the variational subscales as a local error estimate that drives the mesh refinement. The numerical methods proposed in this thesis are capable to describe the high-frequency fluctuations of compressible flows, especially, the ones corresponding to complex aeroacoustic applications. Precisely, the direct simulation of the fricative [s] sound inside a realistic geometry of the human vocal tract is achieved at the end of the thesis.Esta tesis investiga métodos numéricos que aproximan la solución de las ecuaciones de flujo compresible. La primera parte de la tesis está dedicada al estudio de la aproximación numérica del flujo compresible por medio del método multiescala variacional (VMS) en elementos finitos. En particular, se consideran la ecuación de Burgers unidimensional descrita en el espacio de Fourier y las ecuaciones de Navier-Stokes de flujo compresible escritas en variables conservativas y primitivas. Las aproximaciones hechas para plantear la formulación VMS son ampliamente investigadas; el diseño de la matriz de parámetros de estabilización, la definición del espacio donde viven las subescalas, la inclusión de las derivadas temporales de las subescalas y el seguimiento no lineal de las subescalas son particularidades de la formulación que se analizan para cada una de las ecuaciones consideradas. Además, se incluye la adición de difusión artificial local en forma de técnicas de captura de choque. La precisión de las formulaciones se estudia para varios regímenes del flujo compresible, desde flujos aeroacústicos a bajos números de Mach hasta choques supersónicos. La segunda parte de la tesis está dedicada a hacer asequible la solución de las escalas fluctuantes más pequeñas del flujo compresible. Con este fin, se presenta un algoritmo novedoso para el refinamiento $h$ de las mallas de física computacional usadas en computación distribuida en paralelo. Además, se demuestra la solución en superordenadores de algunos casos de prueba del refinamiento de mallas. También se desarrolla la definición de un estimador de error explícito a posteriori que se puede usar en las simulaciones adaptativas de refinamiento de malla de flujos compresibles; la metodología propuesta emplea las subescalas variacionales como una estimación de error local que induce el refinamiento de la malla. Los métodos numéricos propuestos en esta tesis son capaces de describir las fluctuaciones de alta frecuencia de los flujos compresibles, especialmente los correspondientes a aplicaciones aeroacústicas complejas. Precisamente, la simulación directa del sonido consonántico fricativo [s] dentro de una geometría realista del tracto vocal humano se demuestra al final de la tesis