<p> Astronaut hand fatigue during Extravehicular Activity (EVA) and EVA training is a critical risk in human space exploration. Improved glove designs over the past forty years have reduced hand fatigue, but limitations of the technology prevent major improvements to reduce hand fatigue. Therefore, a mechanism to assist astronauts by reducing hand fatigue was explored. Many organizations have already developed exoskeletons to assist astronauts, but all mechanisms developed required electrically powered actuators and control systems to enhance grip strength. However, astronauts already possess the strength required to actuate the glove; what is needed is a method to reduce fatigue without introducing electromechanical complexity. A passive mechanical system was developed as a proof-of-concept to test the feasibility of an unpowered exoskeleton to maintain static grip around an object. The semi- rigid nature of an inflated pressure glove provided an ideal substrate to mount a mechanism and associated components to allow an astronaut to release his/her grip inside the glove while maintaining attitude, as the mechanism will keep the glove closed around an object.</p><p> Three prototypes were fabricated and tested to evaluate the architecture. The final two prototypes were tested on a real pressure suit glove at Final Frontier Design (FFD), and the third mechanism demonstrated attachment and basic operating principles. At University of California (UC) Davis, pressure glove analogs were fabricated from a baseball batting glove and polystyrene to simulate a real pressure glove without the risk of testing in a reduced pressure environment (i.e. a glove box). Testing of the third prototype showed a reduction in fatigue as measured by Maximum Voluntary Contraction (MVC) grip force over a 30 second period when the mechanism assisted gripping an object.</p>

Thesis (Ph.D.)--Syracuse University, 2008. / "Publication number: AAT 3333572."

<p> It is estimated that the rotor hub of a helicopter is responsible for up to 30% of the parasite drag of a helicopter. This is because the hub is a group of rotating bluff-body shapes exposed to high-velocity flow, which may produce hub revolution-dependent flow structures in the hub wake. These structures also interact with a helicopter&rsquo;s empennage and tail rotor, negatively impacting stability and performance. While some specific helicopter hubs have been studied, no study of a generalized hub shape has taken place. Because the hubs that have been studies are very geometrically complex, computational prediction of hub flow physics is not yet mature enough to be of use to industry. The objective of this study is to characterize the long-age wake of a geometrically simple configuration of canonical bluff bodies to model a helicopter hub. Three scale models were examined, each with four larger arms to represent rotor blade shanks and two smaller arms to represent scissor links. The models were identical in dimension, but one had a smoother arm profile and another had a variation in phase angle between the two sets of arms. The models were mounted in the Experimental Flow Physics Laboratory Large Water Tunnel, and tested at a hub diameter-based Reynolds number of 7.6 &times; 10⁵. Time-resolved velocity measurements were taken 14 hub radii downstream of one model, while phase-averaged velocity measurements were taken 7 hub radii downstream of the other two. Similar trends to previous works were observed, including two-per-hub revolution, four-per-hub revolution, and 6-per-hub revolution frequency content in the velocity spectra. This study therefore aids in the uncovering of fundamental flow physics of rotor hubs, creating a baseline case to which further parametric variations may be compared.</p><p>

<p> Applications of sealant and adhesive technologies in aerospace industries require appropriate and reliable sealing materials and tools to provide suitable sealing. Due to a growing use of integral fuel tanks, which utilize the aircraft structure for fuel containment, this study focuses on nozzle geometry optimization of aircraft fuel tank sealant in order to develop and facilitate sealant approval process and to ensure the implementation of suitable fuel tank sealing. </p><p> Computational Fluid Dynamics (CFD) analyses were performed to study the sealant flow characterization and behavior using Star-CCM+ software. An empirical model was developed by the aid of Design of Experiments (DOE) techniques in order to develop a reliable mathematical model based on the collected data from numerical results. Scanning Electron Microscopy (SEM) was utilized to investigate the fracture/deformation of hollow glass microballoons and entrapped air bubbles within the cured sealant. </p><p> The results of this research concluded that the bent in nozzle geometry increases the sealant pressure drop throughout the nozzle. There is an optimized value for travel distance and cross sectional dimension and geometrical shape within the nozzle geometry that minimizes overall dynamic viscosity of the sealant.</p><p>

<p> The flight conditions of a hypersonic vehicle on an ascent trajectory are computed and Reynolds-averaged Navier-Stokes (RANS) simulations of the turbulent boundary layers are performed across a Mach number range of 0.3 up to 16 using the computational fluid dynamics (CFD) software, VULCAN. The boundary conditions and leading edge geometry are varied from the simple case of adiabatic and sharp to cooled and blunted to reveal the physics of how these effects impact the results of flat plate boundary layer methods as applied to practical aerospace systems. The law of the wall, the Van Driest transformation, and a shear stress preserving transformation's ability to collapse boundary layer velocity profiles under the conditions of variable wall boundary condition and leading edge geometry is explored. </p><p> Boundary layer related quantities examined include the boundary layer thickness, local skin friction coefficient, displacement thickness, momentum thickness, heat flux, and integrated loads. It is found that cooling the surface serves to increase the density of the boundary layer, making it thinner. This thinning of the boundary layer thickness increases the velocity gradients, thus increasing the shear stresses and the local skin friction coefficient. The effects on turbulent boundary layers of blunting the leading edge are explained by the difference in properties, particularly viscosity, caused by a detached bow shock instead of a Mach wave that comes off of a sharp nose plate. Heat flux into a vehicle is found to be insignificant at low speeds, but increases drastically as the Mach number rises into the supersonic and hypersonic regimes. It is observed that the integrated skin friction coefficient decreases as Mach number increases and the leading edge becomes blunted, however, it increases as more cooling is applied at the boundary. The integrated heat flux computed from a sharp leading edge geometry is greater compared to a blunted leading edge due to greater temperature gradients in the sharp nose case relative to the blunt nose case. </p><p> The shear stress preserving transformation, derived with the inclusion of a stress balance condition, is found to produce a better collapse of the velocity profile data than the Van Driest transformation and the incompressible law of the wall regardless of Mach number, boundary condition or leading edge geometry. The normalized untransformed velocity gradients are compared to the velocity gradients resulting from the Van Driest and shear stress preserving tranformation. It is shown that the velocity gradients from the shear stress preserving match the normalized untransformed velocity gradients more closely than the Van Driest velocity gradients do. The advantages, disadvantages, and limitations of each transformation are discussed.</p><p>

<p> Composite sandwich plates are widely used in aerospace, automobile and shipbuilding industries. Composite sandwich plates have many different types of failure modes. A comparative study of composite sandwich plates with different finite element modeling approaches for predicting buckling and wrinkling failure response is described in this thesis. The research considers composite sandwich plates with isotropic and anisotropic face-sheets with a thick core. Finite element solutions are obtained using Abaqus/CAE 2016 software by conventional shell element models and conventional shell/solid element models. This study investigates results obtained using finite element methods and compares them to experimental and analytical solutions for overall buckling and face-sheet wrinkling. Results of the study indicate that finite element methods provide an accurate and effective modeling approach for predicting both overall buckling and wrinkling response. </p><p> Furthermore, the study also explored buckling response of composite sandwich panels with different core thickness and face-sheet fiber angle orientation. The study found that the shell/solid element model provides an appropriate and effective modeling method to predict both overall buckling and local wrinkling behavior in composite sandwich plates.</p><p>

<p> In recent decades, heterogeneous materials are extensively used in various industries such as aerospace, defense, automotive and others due to their desirable specific properties and excellent capability of accumulating damage. Despite their wide use, there are numerous challenges associated with the application of these materials. One of the main challenges is lack of accurate tools to predict the initiation, progression and final failure of these materials under various thermomechanical loading conditions. Although failure is usually treated at the macro and meso-scale level, the initiation and growth of failure is a complex phenomena across multiple scales. </p><p> The objective of this work is to enable the mechanics of structure genome (MSG) and its companion code SwiftComp to analyze the initial failure (also called static failure), progressive failure, and fatigue failure of heterogeneous materials using micromechanics approach. The initial failure is evaluated at each numerical integration point using pointwise and nonlocal approach for each constituent of the heterogeneous materials. The effects of imperfect interfaces among constituents of heterogeneous materials are also investigated using a linear traction-displacement model. Moreover, the progressive and fatigue damage analyses are conducted using continuum damage mechanics (CDM) approach. The various failure criteria are also applied at a material point to analyze progressive damage in each constituent. The constitutive equation of a damaged material is formulated based on a consistent irreversible thermodynamics approach. The overall tangent modulus of uncoupled elastoplastic damage for negligible back stress effect is derived. The initiation of plasticity and damage in each constituent is evaluated at each numerical integration point using a nonlocal approach. The accumulated plastic strain and anisotropic damage evolution variables are iteratively solved using an incremental algorithm. The damage analyses are performed for both brittle failure/high cycle fatigue (HCF) for negligible plastic strain and ductile failure/low cycle fatigue (LCF) for large plastic strain. </p><p> The proposed approach is incorporated in SwiftComp and used to predict the initial failure envelope, stress-strain curve for various loading conditions, and fatigue life of heterogeneous materials. The combined effects of strain hardening and progressive fatigue damage on the effective properties of heterogeneous materials are also studied. The capability of the current approach is validated using several representative examples of heterogeneous materials including binary composites, continuous fiber-reinforced composites, particle-reinforced composites, discontinuous fiber-reinforced composites, and woven composites. The predictions of MSG are also compared with the predictions obtained using various micromechanics approaches such as Generalized Methods of Cells (GMC), Mori-Tanaka (MT), and Double Inclusions (DI) and Representative Volume Element (RVE) Analysis (called as 3-dimensional finite element analysis (3D FEA) in this document). </p><p> This study demonstrates that a micromechanics based failure analysis has a great potential to rigorously and more accurately analyze initiation and progression of damage in heterogeneous materials. However, this approach requires material properties specific to damage analysis, which are needed to be independently calibrated for each constituent.</p><p>

<p> Two electrospray sources were developed to operate on an ionic liquid ferrofluid; one source was a pressure?fed capillary electrospray source and the other was a novel electrospray source which used a magnetically?induced instability to produce a peak from which an electric field could extract electrospray. Multiple characteristics of electrospray operation were examined for both sources using faraday plates/cups, a quartz crystal microbalance, a retarding potential analyzer, and a time-of-flight mass spectrometer. The ILFF electrosprays for a capillary source were shown to operate in a mixed ion/droplet regime. The mass flow of the electrospray beam was primarily transported by larger particles (potential droplets) within it. The magnetic nanoparticles increased the required flowrate and extraction potential of the source, as well as the emission current at a given flowrate. The nanoparticles also influenced the beam divergence and energy of an electrospray, increasing and decreasing each respectively with higher concentrations of NPs. The magnetic field had significant influence on the required flowrate of the electrospray, as it reduced the minimum stable flowrate by upwards of 16 percent. It also was shown to decreased the emission current of ILFF electrosprays for a given flowrate, while concurrently increasing the beam energy of particles in the electrospray. Other effects of magnetic field on electrospray characteristics were either inconclusive or insignificant.</p><p>

<p> An in-process, in-situ cure monitoring technique utilizing a guided wave-based concept for carbon fiber reinforced polymer (CFRP) composites was investigated. Two automated cure monitoring systems using guided-wave ultrasonics were developed for characterizing the state of the cure. In the first system, surface mounted high-temperature piezoelectric transducer arrays were employed for actuation and sensing. The second system motivated by the success of the first system includes a single piezoelectric disc, bonded onto the surface of the composite for excitation; fiber Bragg gratings (FBGs) and/or phase-shifted fiber Bragg gratings (PSFBGs) were embedded in the composite for distributed cure sensing. </p><p> Composite material properties (viscosity and degree of cure) evolved during cure of the panels fabricated from Hexcel^&reg; IM7/8552 prepreg correlated well to the amplitude, time of arrival, and group velocity of the guided wave-based measurements during the cure cycle. In addition, key phase transitions (gelation and vitrification) were clearly identified from the experimental data during the same cure cycle. The material properties and phase transitions were validated using cure process modeling software (e.g., RAVEN^&reg;).</p><p> The high-temperature piezoelectric transducer array system demonstrated the feasibility of a guided wave-based, in-process, cure monitoring and provided the framework for defect detection during cure. Ultimately, this system could provide a traceable data stream for non-compliance investigations during serial production and perform closed-loop process control to maximize composite panel quality and consistency. In addition, this system could be deployed as a &ldquo;smart&rdquo; caul/tool plate to existing production lines without changing the design of the aircraft/structure.</p><p> With the second system, strain in low frequency (quasi-static) and the guided wavebased signals in several hundred kilohertz range were measured almost simultaneously using the same FBG or PS-FBG throughout the cure cycle. Also, the residual strain can be readily determined at the end of the cure. This system demonstrated a real-time, in-situ, cure monitoring system using embedded multiplexed FBG/PS-FBG sensors to record both guided wave-based signals and strain. The distinct advantages of a fiber optic-based system include multiplexing, small size, embedding, utilization in harsh environments, electrically passive operation, and electromagnetic interference (EMI) immunity. The embedded multiplexed FBG/PS-FBG fiber optic sensor can monitor the entire life-cycle of the composite structure from curing, post-cure/assembly, and in-service for creating &ldquo;smart structures&rdquo;.</p><p>

<p> A heliogyro solar sail concept, dubbed `HELIOS', is proposed as an alternative to deep space missions without the need for on-board propellant. Although this type of solar sail has existed in concept for several decades, and some previous studies have investigated certain aspects of its operation, a significant amount of research is still needed to analyze the dynamic and control characteristics of the structure under the projected range of orbital conditions. This work presents an improvement upon the existing discrete-mass models of the heliogyro blade, and the extension of its application from a single membrane blade to a fully-coupled approximation of the dynamics of the HELIOS system with multiple spinning membrane blades around a central hub. The incorporation of structural stiffness and external forcing effects into the model is demonstrated to add a further degree of fidelity in simulating the stability properties of the system. Additionally, the approximated dynamics of multiple-blade heliogyro structures are examined under the effect of solar radiation pressure. Lastly, this study evaluates a control algorithm at each blade root to impose structural integrity and attitude control by coordinating well-known helicopter blade pitching profiles.</p><p>