Advanced Design Concepts and Efficient Finite Element Modeling for Dielectric Elastomer Devices

Dielectric elastomers (DEs) offer their use in numerous applications, due to their advantages compared to conventional actuators and sensors. They excel in properties such as lightweight, energy efficiency, low-noise and inherent compliance, just to name a few. In particular, actuator and sensor systems based on membrane DEs show their potential in many fields, from the automotive industry to consumer electronics. Defined procedures which permit an efficient design process are required in order to allow the development of novel DE devices. Additionally, numerical methods for the optimization of such processes are of interest. The first part of this dissertation provides advanced design methods for actuator and sensor applications. For DE actuators, systems biased with permanent magnets are investigated and design rules are derived in order to maximize the stroke for a given load case. For DE sensors, the field of high pressure measurements is developed, introducing concepts for intrusive and nonintrusive sensor systems. In the second part of this dissertation, numerical methods for membrane DE actuators based on the Finite Element method are derived. The main focus is fast computation time and numerical efficiency. Two approaches are presented, one based on a two-dimensional continuum formulation and one based on a three-dimensional membrane formulation. The resulting models allow the investigation of local field distributions, such as stresses, thickness and electric field.Dielektrische Elastomere (DE) bieten sich durch ihre Vorteile gegenüber herkömmlichen Aktoren und Sensoren für viele Anwendungen an. Sie zeichnen sich aus durch geringes Gewicht, hohe Energieeffizienz, geräuschlosen Betrieb und inhärente Dehnbarkeit. Um die Entwicklung neuer DE Anwendungen voranzutreiben, werden effiziente Auslegungsprozesse benötigt. Zusätzlich sind numerische Methoden zur Optimierung solcher Prozesse von Interesse. Der erste Teil dieser Dissertation entwickelt fortgeschrittene Entwicklungsmethoden für Aktorund Sensorsysteme. Für DE Aktoren werden Systeme mit Permanentmagneten als Vorspannmechanismus untersucht und eine Prozedur zur Maximierung des Aktorhubs für eine vorgegebene Last hergeleitet. Für DE Sensoren wird das Feld der Hochdruckmessung erschlossen, indem Konzepte für intrusive und nicht-intrusive Druckmessungen entwickelt werden. Der zweite Teil dieser Dissertation leitet numerische Modelle für die Simulation von DE Aktoren basierend auf der Finite Elemente Methode her. Der Hauptfokus liegt hierbei auf schnellen Rechenzeiten und numerischer Effizienz. Der erste diskutierte Ansatz basiert auf einer zweidimensionalen Kontinuumsformulierung, während der zweite Ansatz auf einer dreidimensionalen Membranformulierung basiert. Die resultierenden Modelle erlauben die Untersuchung lokaler Feldverteilungen, beispielsweise der mechanischen Spannung, der Dickenänderung und dem elektrischen Feld

Turbomachinery

The discipline research in turbomachinery, which is directed toward building the tools needed to understand such a complex flow phenomenon, is based on the fact that flow in turbomachinery is fundamentally unsteady or time dependent. Success in building a reliable inventory of analytic and experimental tools will depend on how the time and time-averages are treated, as well as on who the space and space-averages are treated. The raw tools at disposal (both experimentally and computational) are truly powerful and their numbers are growing at a staggering pace. As a result of this power, a case can be made that a situation exists where information is outstripping understanding. The challenge is to develop a set of computational and experimental tools which genuinely increase understanding of the fluid flow and heat transfer in a turbomachine. Viewgraphs outline a philosophy based on working on a stairstep hierarchy of mathematical and experimental complexity to build a system of tools, which enable one to aggressively design the turbomachinery of the next century. Examples of the types of computational and experimental tools under current development at Lewis, with progress to date, are examined. The examples include work in both the time-resolved and time-averaged domains. Finally, an attempt is made to identify the proper place for Lewis in this continuum of research

Numerical assessments of a nonintrusive surrogate model based on recurrent neural networks and proper orthogonal decomposition: Rayleigh Benard convection

Recent developments in diagnostic and computing technologies offer to leverage numerous forms of nonintrusive modeling approaches from data where machine learning can be used to build computationally cheap and accurate surrogate models. To this end, we present a nonlinear proper orthogonal decomposition (POD) framework, denoted as NLPOD, to forge a nonintrusive reduced-order model for the Boussinesq equations. In our NLPOD approach, we first employ the POD procedure to obtain a set of global modes to build a linear-fit latent space and utilize an autoencoder network to compress the projection of this latent space through a nonlinear unsupervised mapping of POD coefficients. Then, long short-term memory (LSTM) neural network architecture is utilized to discover temporal patterns in this low-rank manifold. While performing a detailed sensitivity analysis for hyperparameters of the LSTM model, the trade-off between accuracy and efficiency is systematically analyzed for solving a canonical Rayleigh-Benard convection system

Optical diagnostics of gas-dynamic flows using advanced laser measurement techniques

Using laser-induced fluorescence to probe nitrogen flows seeded with small amounts of nitric oxide, simultaneous measurements of all three thermodynamic scalar quantities temperature, density, and pressure, were demonstrated in a supersonic turbulent boundary layer. Instrumental uncertainty is 1% for temperature and 2% for density and pressure, making the techniques suitable for measurements of turbulent fluctuations. This technology is currently being transferred to an experimental program designed to use these optical techniques in conjunction with traditional methods to make measurements in turbulent flowfields that were not possible before. A detailed descritpion of the research progress and pertinent results are presented

Identifying Stagnation Zones and Reverse Flow Caused by River-Aquifer Interaction: An Approach Based on Polynomial Chaos Expansions

Fluctuating stream stages and peak-flow events can significantly influence the interactions between streams and aquifers and modify the hydraulic gradient, the flux exchange and the subsurface flow paths. As a result, stagnation zones and reverse flow may appear in different parts of an aquifer and at different times. These features of the flow field play a relevant role in the transport, transformation, and residence time of solutes, pollutants, and nutrients in the subsurface. However, their identification using numerical models is complex not only because of highly nonlinear dynamics, but also due to significant uncertainties in the model input data which propagate into the quantities of interest. In this work, we use an approach based on polynomial chaos expansions to map the probability of occurrence of stagnation zones and reverse flow during a flood event. We quantify the propagation of uncertainty into the groundwater flow field due to the applied river boundary conditions. Then, we evaluate the responses of the posterior probabilities in an element-wise fashion using a set of flow classification criteria and kernel density estimations. The proposed methodology is flexible because it employs a nonintrusive pseudo-spectral technique and, consequently, it can be applied straightforwardly in preexisting models. The regions near the confluence of two streams in the studied area are prone to present transient stagnation and reverse flow.publishedVersio

NASA Tech Briefs, April 2011

Topics covered include: Amperometric Solid Electrolyte Oxygen Microsensors with Easy Batch Fabrication; Two-Axis Direct Fluid Shear Stress Sensor for Aerodynamic Applications; Target Assembly to Check Boresight Alignment of Active Sensors; Virtual Sensor Test Instrumentation; Evaluation of the Reflection Coefficient of Microstrip Elements for Reflectarray Antennas; Miniaturized Ka-Band Dual-Channel Radar; Continuous-Integration Laser Energy Lidar Monitor; Miniaturized Airborne Imaging Central Server System; Radiation-Tolerant, SpaceWire-Compatible Switching Fabric; Small Microprocessor for ASIC or FPGA Implementation; Source-Coupled, N-Channel, JFET-Based Digital Logic Gate Structure Using Resistive Level Shifters; High-Voltage-Input Level Translator Using Standard CMOS; Monitoring Digital Closed-Loop Feedback Systems; MASCOT - MATLAB Stability and Control Toolbox; MIRO Continuum Calibration for Asteroid Mode; GOATS Image Projection Component; Coded Modulation in C and MATLAB; Low-Dead-Volume Inlet for Vacuum Chamber; Thermal Control Method for High-Current Wire Bundles by Injecting a Thermally Conductive Filler; Method for Selective Cleaning of Mold Release from Composite Honeycomb Surfaces; Infrared-Bolometer Arrays with Reflective Backshorts; Commercialization of LARC (trade mark) -SI Polyimide Technology; Novel Low-Density Ablators Containing Hyperbranched Poly(azomethine)s; Carbon Nanotubes on Titanium Substrates for Stray Light Suppression; Monolithic, High-Speed Fiber-Optic Switching Array for Lidar; Grid-Tied Photovoltaic Power System; Spectroelectrochemical Instrument Measures TOC; A Miniaturized Video System for Monitoring Drosophila Behavior; Hydrofocusing Bioreactor Produces Anti-Cancer Alkaloids; Creep Measurement Video Extensometer; Radius of Curvature Measurement of Large Optics Using Interferometry and Laser Tracker n-B-pi-p Superlattice Infrared Detector; Safe Onboard Guidance and Control Under Probabilistic Uncertainty; General Tool for Evaluating High-Contrast Coronagraphic Telescope Performance Error Budgets; Hidden Statistics of Schroedinger Equation; Optimal Padding for the Two-Dimensional Fast Fourier Transform; Spatial Query for Planetary Data; Higher Order Mode Coupling in Feed Waveguide of a Planar Slot Array Antenna; Evolutionary Computational Methods for Identifying Emergent Behavior in Autonomous Systems; Sampling Theorem in Terms of the Bandwidth and Sampling Interval; Meteoroid/Orbital Debris Shield Engineering Development Practice and Procedure; Self-Balancing, Optical-Center-Pivot, Fast-Steering Mirror; Wireless Orbiter Hang-Angle Inclinometer System; and Internal Electrostatic Discharge Monitor - IESDM

Three-dimensional computed tomography from interferometric measurements within a narrow cone of views

A theory to determine the properties of a fluid from measurements of its projections was developed and tested. Viewing cones as small as 10 degrees were evaluated, with the only assumption being that the property was space limited. The results of applying the theory to numerical and actual interferograms of a spherical discontinuity of refractive index are presented. The theory was developed to test the practicality and limits of using three-dimensional computer tomography in internal fluid dynamics

A characterization of laminar and turbulent boundary layers for use in an investigation of boundary layer state effects on turbine blade film colling schemes

The boundary layer region of a flow is a primary area of interest when analyzing the effects of various flow phenomena, heat transfer, and skin friction near an immersed object\u27s surface. Characterizing this region yields a proper understanding of mass, momentum, and energy transfer to or from the region near the immersed body surface. Such characterization includes the boundary layer height, displacement, and momentum boundary layer thicknesses among many attributes. These factors offer a description of the flow for a laminar state, but also must include length scales, turbulence intensities, and distribution of turbulent kinetic energy to fully describe a boundary layer in the turbulent regime. This investigation will experimentally find these boundary layer characterization parameters for four scenarios. Two independent flow variations will be introduced and their effects upon the boundary layer examined and compared to previous and theoretical data. The first two scenarios examine the effects of wall suction on and off and the resulting effect on a non-tripped laminar boundary layer. The last two scenarios maintain the cases of suction on and off but introduce a turbulence generator within the boundary layer in order to trip the boundary layer to a turbulent state. Confirmation of turbulence and to what degree the flow is turbulent is found through calculating the turbulence intensity and length scale. This investigation is experimentally conducted in the West Virginia University Turbine Aerodynamic and Advanced Cooling (TAAC) Wind Tunnel facility, which has been recently recommissioned by the author. Pitot-static and hotwire anemometry were used to record data. Freestream turbulence was controlled by a passive turbulence generator and held constant for each scenario. It was found that a non-tripped flow with no suction yielded a boundary layer height of 1.045 inches taken 9.625 inches downstream of the turbulence grid location. Once suction is introduced, this height reduces to 0.795 inches. Similarly, suction decreased the boundary layer height for the tripped boundary flow from 2.25 inches to 1.17 inches. Due to the way the investigation originally defined the boundary layer height at 99% freestream conditions, conclusions yield that resolutely maintaining this definition slightly deviates this investigation\u27s results from prior benchmarked data prior to facility recommissioning. However, general trends in boundary layer parameters are consistent, and turbulence intensities along with turbulent length scales from the tripped flow scenario validate a turbulent boundary layer. Turbulence intensities and other boundary layer characteristics detail for the non-tripped flow scenarios, which assume a laminar boundary layer, more closely align instead with a transitional flow regime as opposed to a completely laminar one as assumed. Understanding the influence of suction and turbulence within the boundary layer aids this facility\u27s goal of matching flow parameters nondimensionally as experienced on actual turbine blades in the hot section of gas turbine engines. Serving as a new benchmark for this lab, future turbine blade cooling schemes can be tested in nondimensionally matched conditions. While these future experiments will employ advanced nonintrusive measurement techniques, the author utilizes this precursor investigation for conceptual understanding of flow field conditions and the influence of parameters such as suction and turbulence on the boundary layer

Nonlinear model order reduction for problems with microstructure using mesh informed neural networks

Many applications in computational physics involve approximating problems with microstructure, characterized by multiple spatial scales in their data. However, these numerical solutions are often computationally expensive due to the need to capture fine details at small scales. As a result, simulating such phenomena becomes unaffordable for many-query applications, such as parametrized systems with multiple scale-dependent features. Traditional projection-based reduced order models (ROMs) fail to resolve these issues, even for second-order elliptic PDEs commonly found in engineering applications. To address this, we propose an alternative nonintrusive strategy to build a ROM, that combines classical proper orthogonal decomposition (POD) with a suitable neural network (NN) model to account for the small scales. Specifically, we employ sparse mesh-informed neural networks (MINNs), which handle both spatial dependencies in the solutions and model parameters simultaneously. We evaluate the performance of this strategy on benchmark problems and then apply it to approximate a real-life problem involving the impact of microcirculation in transport phenomena through the tissue microenvironment

Aircraft engine hot section technology: An overview of the HOST Project

NASA sponsored the Turbine Engine Hot Section (HOST) project to address the need for improved durability in advanced aircraft engine combustors and turbines. Analytical and experimental activities aimed at more accurate prediction of the aerothermal environment, the thermomechanical loads, the material behavior and structural responses to loads, and life predictions for cyclic high temperature operation were conducted from 1980 to 1987. The project involved representatives from six engineering disciplines who are spread across three work disciplines - industry, academia, and NASA. The HOST project not only initiated and sponsored 70 major activities, but also was the keystone in joining the multiple disciplines and work sectors to focus on critical research needs. A broad overview of the project is given along with initial indications of the project's impact