Dissertations and Theses  Aerospace Engineering
http://hdl.handle.net/2142/14800

Structure and defects in highperformance aramid fibers
http://hdl.handle.net/2142/46888
Structure and defects in highperformance aramid fibers
Clawson, Jan
High performance aramid fibers, such as Kevlar, AuTx, and Twaron have been designed for ultrahigh specific strength and stiffness. These fibers derive their superior properties from the high degree of molecular orientation that allows for efficient load transfer to the backbone covalent bond axis. While the experimental Young’s modulus of aramid fibers approaches the theoretical limits, the measured mechanical strength is quite lower than the predicted values. The objective of this dissertation research was to obtain an understanding of the subtle differences in the structure of commercial grade aramid fibers with different tensile strength and modulus values. Towards this goal, single fiber tension experiments were conducted with various fiber gauge lengths to evaluate the existence of fiber length size effects and, therefore, a statistical distribution of defects limiting the fiber strength. The test results were supported by several studies of the fiber structure via various modalities of high resolution microscopy.
Uniaxial tension tests were carried out with AuTx and KM2 fibers with gauge lengths between 100 µm and 10 mm. The average strength of KM2 fibers was 4.4 ± 0.4 GPa, with a high value of 5.2 GPa and a low value of 3.5 GPa. The average tensile strength decreased by 20% as the gauge length increased from 100 µm to 10 mm. The tensile modulus of KM2 fibers was calculated to be 85.6 ± 3.7 GPa. Similarly, the average strength of AuTx fibers was 5.5 ± 0.7 GPa, with a high value of 6.8 GPa and a low value of 4.4 GPa. A reduction of approximately 20% in the average tensile strength value was also established when the gauge length increased from 100 µm to 10 mm. The relative insensitivity of the fiber tensile strength to the gauge length suggests that failure in both kinds of aramid fibers could be due to processes or defects at length scales well below the micronscale.
High resolution SEM images were obtained to understand the surface morphology and the internal structure of KM2 and AuTx fibers. A process of crushing and splitting of KM2 fibers revealed the presence of circular microfibril building blocks that were as small as 5 nm in diameter, with lengths exceeding 500 nm. AuTx fibers formed ribbonlike fibrils when deformed, with finer and more ordered microfibrils compared to those found in the fracture sections of KM2 fibers. Furthermore, the fiber failure sections from tensile tests revealed several distinguishing features. Both types of fibers had distinct skin but with different thickness and morphology. Specifically, the skin of KM2 fibers was relatively featureless in comparison to AuTx. The core of both types of aramid fibers was comprised of microfibrils that were qualitatively more ordered and better oriented in AuTx than in KM2 fibers. Webs of individual microfibrils formed in the interior of failed KM2 and AuTx fibers, whose structure provided evidence for stronger cohesive forces present in AuTx compared to KM2 fibers.
AFM imaging was conducted both on the fiber surface and on fiber crosssections obtained by a microtome blade. Ordinary AFM tips (tip radius of ~10 nm) resolved surface microfibrils that were aligned with the axis of KM2 and Twaron fibers, while more complex surface features were evidenced in AuTx fibers. Ultrasharp AFM tips (tip radius of ~2 nm) revealed a crystallitelike structure of the microfibrils on the surface of KM2 fibers. Longitudinal microtome fiber cuts allowed for excellent resolution images, especially with the use of 2nm radius AFM tips. Unfortunately, transverse microtome fiber cuts were subjected to severe knife damage which prevented detailed AFM imaging.
Finally, TEM imaging was carried out on microtome cut fiber sections. The aramid fibers were resistant to all applied staining methods, and, therefore, the additional information from TEM imaging was limited. KM2 fiber sections demonstrated periodic defect banding along the fiber axis, with larger microtome knife damage near the fiber skin. Meanwhile, AuTx fiber cuts demonstrated a mix of low damage areas, and areas covered with ripples. Finally, transverse microtome sections of AuTx showed both extensive tearing and folding, which prohibited their use for high magnification TEM imaging.
kevlar
aramid
highperformance fiber
AuTx
polymer
liquid crystal
Thu, 16 Jan 2014 18:25:20 GMT

Modal interactions and targeted energy transfers in laminar vortexinduced vibrations of a rigid cylinder with strongly nonlinear internal attachments
http://hdl.handle.net/2142/46870
Modal interactions and targeted energy transfers in laminar vortexinduced vibrations of a rigid cylinder with strongly nonlinear internal attachments
Tumkur Revannasiddaiah, Ravi Kumar
We study the effect of coupling an essentially nonlinear element to a sprung rigid circular cylinder undergoing ``vortexinduced vibration'' (VIV) in an incompressible flow. The essentially nonlinear device is termed a ``nonlinear energy sink'' (NES); in this work we use two configurations of NES: translational NES and rotational NES. For the translational NES, consisting of a mass, a linear damper, and an essentially nonlinear spring, the NES mass is constrained to move perpendicular to the mean flow. For the rotational case, the NES mass is constrained to rotate at a fixed radius about the oscillating center of the cylinder. Using a variational multiscale residualbased stabilized finiteelement method, we consider the intermediate Reynolds number (Re) regime 20 ≤ Re≤ 120, with the cylinder motion constrained to be perpendicular to the mean flow. The nonlinear interaction of the NES and flow via the rigid body motion of the cylinder leads to several new response regimes of the coupled system of flowcylinderNES.
The translational NES promotes nearly oneway transfer of energy to itself from the primary structure (the cylinder) and the flow, resulting in reduction of the amplitude of the limitcycle oscillation (LCO) by as much as 75%, depending on the parameters characterizing the NES. Various mechanisms of VIV suppression by the NES are discussed. A reducedorder model (ROM) based on a singledegreeoffreedom (DOF) selfexcited oscillator is developed to approximate the limitcycle oscillation of the cylinder undergoing VIV. This selfexcited oscillator models the interaction of the flow and the cylinder and, in principle, is similar to other phenomenological ROMs considered in the literature. Then, a coupled twoDOF reducedorder model for the system with the internal NES is constructed by coupling the singleDOF NES to the singleDOF selfexcited oscillator. Hence, the infinitedimensional system of flowcylinderNES is reduced to a twoDOF model. We examine carefully the range of system parameters where the coupled ROM is valid. The two targeted energy transfer mechanisms responsible for passive VIV suppression that are observed in the finiteelement computations are fully reproduced using the twoDOF reducedorder model within the range of validity of the ROM. This reduction of the dynamics to a tractable lowdimensional reducedorder model facilitates the approximate analysis of the underlying dynamics and provides the basis for predictive design of the NES for VIV suppression. Two other approaches of model reduction to obtain a more advanced ROM that can be predictive were also considered, the first based on ``proper orthogonal decomposition'' (POD), and the second based on dynamics of the pressure around the cylinder.
We show that, besides passive VIV suppression, the rotational NES can also lead to a flow state that is qualitatively different from the usual K´arm´an vortex street, with the length and width of the attached vortices significantly altered, and the amplitude and frequency of the lift force and cylinder displacement significantly modified. In fact, our finding is that the nonlinear action of the rotational NES can drastically alter the wake structure downstream, which indicates that the internal NES can affect the external flow, even though no direct contact between the NES and the flow exists. We also explore the dependence of the critical $Re$ for the Hopf bifurcation (from steady, symmetric flow past a motionless cylinder to oscillatory, asymmetric flow past a moving cylinder) on the stiffness of the sprung cylinder, and discuss the effect of a rotational NES on the bifurcation diagram. In addition, we demonstrate the existence of multiple longtime solutions of the NavierStokes equation in the presence of a rotational NES. Finally, we discuss an approximate analytical approach to explain some of the numerical findings, which provides good agreement with our computational results.
This work provides a first study of flowstructure interaction of a bluff body possessing a strongly nonlinear internal attachment, and examines the interesting nonlinear dynamic phenomena that exist in such a system. The underlying nonlinear dynamics that govern these phenomena is passive targeted energy transfer from the flow and the bluff body to the NES, which introduces new interesting dynamics with no counterparts in analogous linear settings. As such, this work can be regarded as a contribution in the new field of constructive use of intentional strong nonlinearity in mechanics and design.
vortexinduced vibration (VIV)
nonlinear energy sink
targeted energy transfer
passive VIV suppression
passive wake modification
bifurcations in laminar VIV
subcritical Re VIV
Thu, 16 Jan 2014 18:19:15 GMT

Effect of grain structure and doping on the mechanical properties of polysilicon thin films for MEMS
http://hdl.handle.net/2142/46816
Effect of grain structure and doping on the mechanical properties of polysilicon thin films for MEMS
Yagnamurthy, Naga Sivakumar
Freestanding devices fabricated for Microelectromechanical Systems (MEMS) employ slender polysilicon flexures that are prone to failure due to large operating stresses. Polycrystalline silicon (polysilicon) films with improved mechanical properties to meet demanding applications could be engineered by modification of the material microstructure. Such advances require detailed experimental studies and quantitative understanding of the convoluted effects of the processing methods on the ensuing mechanical properties. This dissertation investigated the role of grain size and doping on the nature and origin of critical flaws that determine the tensile strength and the local resistance to crack initiation in 1μm thick polysilicon films, as quantified by the effective mode I critical stress intensity factor, KIC,eff.
For the purposes of this study microscale polysilicon thin film specimens were fabricated by a custom process at the Sandia National Laboratories. The films were comprised of either columnar grains (grain size 285 nm) or a laminated structure (grain size 125 nm), and were doped with different concentrations of Phosphorus (P). The columnar grain polysilicon typically had 1  2 grains across the film thickness, while the laminated polysilicon contained ten grains across the film thickness, each confined in a 100nm thick layer. The grain structure and doping concentration had no effect on the elastic stiffness of polysilicon: the average Young’s moduli of all polysilicon films were in the narrow range of 153  158 GPa. On the other hand, the tensile strength values of undoped columnar grain and laminated polysilicon differed significantly, averaging 1.31±0.09 GPa and 2.44±0.28 GPa, respectively. Heavy doping further impacted the strength of the former type of polysilicon (0.92±0.10 GPa) due to the formation of large sidewall defects at high concentrations of P which, however, had no effect on the tensile strength of laminated polysilicon.
The nature and type of the critical sidewall defects were independent of the specimen size: on grounds of the cumulative Weibull probability distribution function, the results of the present experiments predicted quite reasonably the tensile strength of polysilicon specimens that were 180 times smaller in size. The strength of polysilicon films scaled with the sidewall surface area (or equivalently the specimen length), which is also the region where the major critical flaws were identified. Notably, in the absence of the initial critical sidewall defects, the average tensile strength of undoped columnar polysilicon increased by 70%, namely from 1.31±0.09 to 2.2±0.11 GPa, thus approaching the strength of laminated polysilicon. The critical defects in columnar polysilicon were located at the specimen free edges which were defined by reactive ion etching (RIE). These defects were initiated at grain boundaries during RIE and were further exacerbated by the reactions taking place during heavy Pdoping in high temperature annealing.
Measurements of KIC,eff were used to evaluate the effect of grain structure and doping on the resistance of the two types of polysilicon to crack initiation. The values of KIC,eff for all the polysilicon films were in the range of 0.8  1.2 MPa√m. Contrary to the trends in tensile strength values, the KIC,eff of columnar polysilicon was higher than that of laminated polysilicon, but the latter demonstrated a much smaller variability in KIC,eff, which was owed to the averaging effect of its laminated structure. The KIC,eff of columnar polysilicon further increased by 10% as a result of heavy Pdoping, which, on the contrary, had no effect on the KIC,eff of laminated polysilicon. Thus, Pdoping only modestly increased the fracture resistance of columnar polysilicon, although its effect on the tensile strength was clearly detrimental.
Finally, using the measured KIC,eff values and the precise defect geometries determined by Atomic Force and Scanning Electron Microscopy, the tensile strength of different polysilicon films was calculated by linear elastic fracture mechanics models for semielliptical surface cracks and quarter elliptical edge cracks. The strength values estimated by a quarter elliptical edge crack analysis agreed fairly well with the values obtained by uniaxial tension experiments, further supporting the electron microscopy observations and the Weibull scaling predictions that the tensile strength of asfabricated columnar grain polysilicon specimens was governed by sidewall defects. On the other hand, the strength values estimated by an elliptical surface crack analysis agreed fairly well with uniaxial tension experiments with columnar grain polysilicon specimens whose sidewall defects were removed via ion beam milling.
Polysilicon
Effect of microstructure
Effect of doping
Tensile strength
Critical stress intensity factor
Size effects
Microstructure
Phosphorus doping
Thu, 16 Jan 2014 18:17:06 GMT

Experimental study of elastoplastic wave propagation in onedimensional and twodimensional disk arrays
http://hdl.handle.net/2142/46770
Experimental study of elastoplastic wave propagation in onedimensional and twodimensional disk arrays
Waymel, Robert
In this work, a dropweight tower setup and a modified split Hopkinson pressure bar (SHPB) are used to dynamically load one (1D) and twodimensional (2D) arrays of disks in contact. The disks are made of aluminum 6061 T6 and are selected because of their rateindependence, thus allowing static contact forcedisplacement laws to be used in the dynamic case. Although differing considerably between each other, the loading magnitudes in the drop tower and SHPB setups, 2 kN to 30 kN respectively, cause the arrays to deform plastically at the contact points between disks where stress concentrations exist. This allows for elastoplastic wave propagation to be studied in ordered 1D and 2D elastoplastic arrays. Additionally, the loading pulse durations from the two experimental setups are sufficiently different that the effect of the loading time can be studied. The drop tower load times are of the order of milliseconds and are much longer than the solitary wave duration, while the SHPB time scales are in the microseconds regime and are comparable to the solitary wave time scales. Imaging techniques are also used to capture the deformation process and post mortem residual strains. The wave speed is seen to be dependent on force and ranges between 1000 and 2000 m/s. It was also found that there was not a monotonic relationship with respect to force in the drop tower setup, but there was decreasing force and yielding along the 1D disk chain in the SPHB. The difference was attributed to the longer time scales involved in the drop tower experiments. This research is the first to investigate the propagation of elastoplastic waves in 1D and 2D arrays of disks and will form the basis of subsequent studies.
granular media
disk
cylinder
plastic
wave propagation
Thu, 16 Jan 2014 18:01:53 GMT

Numerical simulations of experimental results in a power unit to validate the energy output resulting from gas pressurizations on nanoparticles
http://hdl.handle.net/2142/46765
Numerical simulations of experimental results in a power unit to validate the energy output resulting from gas pressurizations on nanoparticles
Osouf, Anais
This thesis aims to interpret the first temperature measurements recorded by the research group in terms of heat release from pressurizations of specific nanoparticles of alloys by Hydrogen. The number of unknowns was an obstacle to achieve trustful handmade calculations and therefore a numerical model was created using the software COMSOL Multiphysics©. From the model, the order of value of the heat release during the pressurizations has been found to be 400 joules. From the data available, a comparison to the potential chemical energy release has been started in order to state if an unconventional source of energy is present. Further experimental suggestions are made to determine some unknowns so that precise calculations of conventional energy release are performed instead of worst cases scenarios.
lowenergy nuclear reactions (LENR)
gas loading
COMSOL Multiphysics
heat transfer
energy output
Thu, 16 Jan 2014 18:01:41 GMT

Inverse optimal control for deterministic continuoustime nonlinear systems
http://hdl.handle.net/2142/46747
Inverse optimal control for deterministic continuoustime nonlinear systems
Johnson, Miles
Inverse optimal control is the problem of computing a cost function with respect to which observed state input trajectories are optimal. We present a new method of inverse optimal control based on minimizing the extent to which observed trajectories violate firstorder necessary conditions for optimality. We consider continuoustime deterministic optimal control systems with a cost function that is a linear combination of known basis functions. We compare our approach with three prior methods of inverse optimal control. We demonstrate the performance of these methods by performing simulation experiments using a collection of nominal system models. We compare the robustness of these methods by analyzing how they perform under perturbations to the system. We consider two scenarios: one in which we exactly know the set of basis functions in the cost function, and another in which the true cost function contains an unknown perturbation. Results from simulation experiments show that our new method is computationally efficient relative to prior methods, performs similarly to prior approaches under large perturbations to the system, and better learns the true cost function under small perturbations. We then apply our method to three problems of interest in robotics. First, we apply inverse optimal control to learn the physical properties of an elastic rod. Second, we apply inverse optimal control to learn models of human walking paths. These models of human locomotion enable automation of mobile robots moving in a shared space with humans, and enable motion prediction of walking humans given partial trajectory observations. Finally, we apply inverse optimal control to develop a new method of learning from demonstration for quadrotor dynamic maneuvering. We compare and contrast our method with an existing stateoftheart solution based on minimumtime optimal control, and show that our method can generalize to novel tasks and reject environmental disturbances.
optimal control
inverse reinforcement learning
inverse optimal control
apprenticeship learning
learning from demonstration
iterative learning control
Thu, 16 Jan 2014 18:01:02 GMT

New numerical methods for openloop and feedback solutions to dynamic optimization problems
http://hdl.handle.net/2142/46737
New numerical methods for openloop and feedback solutions to dynamic optimization problems
Ghosh, Pradipto
The topic of the first part of this research is trajectory optimization of dynamical systems via computational swarm intelligence. Particle swarm optimization is a natureinspired heuristic search method that relies on a group of potential solutions to explore the fitness landscape. Conceptually, each particle in the swarm uses its own memory as well as the knowledge accumulated by the entire swarm to iteratively converge on an optimal or nearoptimal solution. It is relatively straightforward to implement and unlike gradientbased solvers, does not require an initial guess or continuity in the problem definition. Although particle swarm optimization has been successfully employed in solving static optimization problems, its application in dynamic optimization, as posed in optimal control theory, is still relatively new. In the first half of this thesis particle swarm optimization is used to generate nearoptimal solutions to several nontrivial trajectory optimization problems including thrust programming for minimum fuel, multiburn spacecraft orbit transfer, and computing minimumtime resttorest trajectories for a robotic manipulator. A distinct feature of the particle swarm optimization implementation in this work is the runtime selection of the optimal solution structure. Optimal trajectories are generated by solving instances of constrained nonlinear mixedinteger programming problems with the swarming technique. For each solved optimal programming problem, the particle swarm optimization result is compared with a nearly exact solution found via a direct method using nonlinear programming. Numerical experiments indicate that swarm search can locate solutions to very great accuracy.
The second half of this research develops a new extremalfield approach for synthesizing nearly optimal feedback controllers for optimal control and twoplayer pursuitevasion games described by general nonlinear differential equations. A notable revelation from this development is that the resulting control law has an algebraic closedform structure. The proposed method uses an optimal spatial statistical predictor called universal kriging to construct the surrogate model of a feedback controller, which is capable of quickly predicting an optimal control estimate based on current state (and time) information. With universal kriging, an approximation to the optimal feedback map is computed by conceptualizing a set of statecontrol samples from precomputed extremals to be a particular realization of a jointly Gaussian spatial process. Feedback policies are computed for a variety of example dynamic optimization problems in order to evaluate the effectiveness of this methodology. This feedback synthesis approach is found to combine good numerical accuracy with low computational overhead, making it a suitable candidate for realtime applications.
Particle swarm and universal kriging are combined for a capstone example, a near optimal, nearadmissible, fullstate feedback control law is computed and tested for the heatloadlimited atmosphericturn guidance of an aeroassisted transfer vehicle. The performance of this explicit guidance scheme is found to be very promising; initial errors in atmospheric entry due to simulated thruster misfirings are found to be accurately corrected while closely respecting the algebraic stateinequality constraint.
Trajectory Optimization
Optimal Control Theory
Optimal Feedback Control
Feedback Guidance
PursuitEvasion Games
Dynamic Programming
Particle Swarm Optimization
Swarm Intelligence
Thu, 16 Jan 2014 18:00:46 GMT

L1 adaptive outputfeedback control architectures
http://hdl.handle.net/2142/46694
L1 adaptive outputfeedback control architectures
Kharisov, Evgeny
This research focuses on development of L1 adaptive outputfeedback control. The objective is to extend the L1 adaptive control framework to a wider class of systems, as well as obtain architectures that afford more straightforward tuning.
We start by considering an existing L1 adaptive outputfeedback controller for nonstrictly positive real systems based on piecewise constant adaptation law. It is shown that L1 adaptive control architectures achieve decoupling of adaptation from control, which leads to bounded away from zero timedelay and gain margins in the presence of arbitrarily fast adaptation. Computed performance bounds provide quantifiable performance guarantees both for system output and control signal in transient and steady state. A noticeable feature of the L1 adaptive controller is that its output behavior can be made close to the behavior of a linear timeinvariant system. In particular, proper design of the lowpass filter can achieve output response, which almost scales for different step reference commands. This property is relevant to applications with human operator in the loop (for example: control augmentation systems of piloted aircraft), since predictability of the system response is necessary for adequate performance of the operator.
Next we present applications of the L1 adaptive outputfeedback controller in two different fields of engineering: feedback control of human anesthesia, and ascent control of a NASA crew launch vehicle (CLV). The purpose of the feedback controller for anesthesia is to ensure that the patient's level of sedation during surgery follows a prespecified profile. The L1 controller is enabled by anesthesiologist after he/she achieves sufficient patient sedation level by introducing sedatives manually. This problem formulation requires safe switching mechanism, which avoids controller initialization transients. For this purpose, we used an L1 adaptive controller with special output predictor initialization routine, which provides bumpless transient during switches.
For the second application, our objective was to design a single controller without parameter scheduling, which would cover the whole flight envelope of the first stage of the CLV. This approach has the potential of reducing the design costs by reducing the number of necessary wind tunnel tests. One of the main challenges we encountered was variability of the parameters of the CLV. Both aerodynamic and inertia parameters change dramatically during the CLV operation. The fact that CLV inertia significantly reduces with time allows for demanding faster controller response and more agile CLV behavior as time flows. This inspired us to develop an L1 adaptive controller, which would take into account for changes in the desired control specifications without the need for switching the control laws. This is achieved by employing linear time varying (LTV) state predictor, which results in LTV reference system.
Further we present L1 adaptive outputfeedback controller for minimumphase systems with gradient minimization type adaptation laws. This controller uses a special structure for its reference system. The stability conditions are more intuitive and can be systematically verified using classical control methods.
For completeness, we also consider an extension of the L1 adaptive controller to a class of nonlinear outputfeedback systems. We derive a stability proof and also the performance bounds for passive nonlinear systems with implicit output equation.
Adaptive Control
Robust Adaptive Control
L1 Adaptive Control
Fast Adaptation
Aerospace Applications
Nonlinear Control
Thu, 16 Jan 2014 17:59:19 GMT

Scientific principles for the electric oxygeniodine laser
http://hdl.handle.net/2142/46678
Scientific principles for the electric oxygeniodine laser
Benavides, Gabriel
This work describes a systematic investigation to advance the scientific understanding of the electric oxygeniodine laser (EOIL). The research reported on herein was largely conducted between the years of 2006 and 2011. The work comes on the forefront of EOIL development, recently demonstrated in 2005 with positive gain and lasing through a longterm partnership between the University of Illinois and CU Aerospace in Champaign, IL. Though only first demonstrated in 2005, research towards constructing an EOIL has been carried out periodically since the early 1970s. With low yields of the energy reservoir, O2(a), achievable in an electric discharge, EOIL research has for many years taken a lower priority when compared to the research of highyield chemical oxygeniodine lasers (COIL), which reported successes as early as 1978. While both lasers emit on the same I(2P1/2)→I(2P3/2) transition at 1315 nm, offering nearly equal promise of beam quality and performance, an elusive attractiveness remained with EOIL as a result of nearly four decades of unsuccessful attempts. The reduction in toxicity, complexity, and maintenance of an electrically driven device offers numerous operational and logistical advantages over the COIL. The years of failed attempts with EOIL can largely be explained by the lack of a sufficient body of theoretical and experimental research adequately documenting the technology. This research can be generally classified as: (i) high yield dischargedriven singlet oxygen production, and (ii) the added postdischarge complexity of a diverse media of active oxygen species. The research described herein was fundamental in increasing reported gain and laser power of EOIL devices from approximately 0.01 %/cm and 500 Milliwatts in 2006 to 0.3 %/cm and 481 Watts by mid2011. This represents a factor of 30 increase in gain and two orders of magnitude increase in laser power. Such results were only achievable by systematically analyzing each component of EOIL, developing a theoretical understanding of the requirements for each element of the laser, and devising experimental hardware to validate the work. The technologies considered in this work include dischargedriven singlet oxygen generators (DSOG), species and thermal energy regulation (STER) devices, iodine predissociation (IPD) devices, as well as various implementations of highreflectivity resonators. Though now established by our group, a more complete body of research is prerequisite to EOIL achieving its ultimate potential, matching or exceeding the capabilities of similar high energy lasers. This topic is a final chapter in a group of thesis topics conducted by AE and ECE academics that ultimately contributed to the success of electric oxygeniodine laser research conducted at the University of Illinois.
Electric OxygenIodine Laser (EOIL)
Electric Discharge Excited OxygenIodine Laser (DOIL)
oxygen
iodine
singlet delta
singlet oxygen
laser
1315nm transition
discharge
predissociation
predissociator
Thu, 16 Jan 2014 17:58:48 GMT

Validation of 3D ice accretion documentation and replication method including pressuresensitive paint
http://hdl.handle.net/2142/46651
Validation of 3D ice accretion documentation and replication method including pressuresensitive paint
Monastero, Marianne
Accurate representation of ice accretions is important to the study and understanding of aircraft icing. For research and certification purposes, replicas of ice accretions generated from icing wind tunnels are fabricated to perform aerodynamic tests in dryair wind tunnels. The currently employed replication method consists of creating molds from original ice accretions and producing castings from the molds for wind tunnel testing. While this method reproduces the geometric features and aerodynamic effects of the original ice accretions well in the replicated ice shapes, it has several limitations. This method cannot scale the ice shapes to sizes other than the original and does not produce a digital record of the ice shape. Both of these capabilities are desirable in icedaerodynamics research. To address these needs, NASA developed a methodology to obtain a digital record of ice accretions through the implementation of a laser scanner system. The resulting scan can be used in conjunction with rapidprototype methods to generate ice shapes for wind tunnel testing. This work is a validation of the 3D ice accretion measurement methodology where the ice shapes generated by both the currentlyused and newlydeveloped methods from the same initial ice accretion are compared using force balancederived aerodynamic performance, surface and wake pressures, and pressuresensitive paint (PSP) data.
The 3D features of the tested ice shapes necessitated the use of a technique capable of obtaining high resolution data. The PSP technique allowed pressure coefficient data to be obtained over a larger area and at a greater resolution than is possible by only using the surface pressure tap method. The results discussed show the capability of the PSP technique, as implemented in the 3ft by 4ft subsonic wind tunnel at the University of Illinois, to resolve aerodynamic differences between ice shapes made from both the current and newly developed ice accretion replication methods. The same trends were observed in the PSP data as were found in the aerodynamic performance and pressure tap data, and the newly developed 3D ice accretion measurement methodology produced ice shapes which aerodynamically agreed well with ice shapes generated from the mold and casting method.
icing
pressuresensitive paint
aerodynamics
wind tunnel
Thu, 16 Jan 2014 17:57:34 GMT