Aerospace Engineering Research Works

Permanent URI for this collectionhttp://hdl.handle.net/1903/1655

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Start date: 2000End date: 2009

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Now showing 1 - 10 of 17
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    Workshop on Control of Micro- and Nano-Scale Systems
    (2005-04) Shapiro, Benjamin
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    Arbitrary Steering of Multiple Particles Independently in an Electro-Osmotically Driven Microfluidic System
    (IEEE, 2006-07) Shapiro, Benjamin; Chaudhary, Satej
    We demonstrate how to use feedback control of microflows to steer multiple particles independently in planar microfluidic systems driven by electro-osmotic actuation. This technique enables the handling of biological materials, such as cells, bacteria, DNA, and drug packets, in a hand-held format using simple and easy-to-fabricate actuators. The feedback loop consists of a vision system which identifies the positions of the particles in real-time, a control algorithm that computes the actuator (electrode) inputs based on information received from the vision system, and a set of electrodes (actuators) that create the required flow through electro-osmotic forces to steer all the particles along their desired trajectories and correct for particle position errors and thermal noise. Here, we focus on the development of control algorithms to achieve the steering of particles: vision system implementation, fabrication of devices, and experimental validation is addressed in other publications. In particular, steering of a single (yeast cell) particle has been demonstrated experimentally in our prior research and we have recently demonstrated experimental steering of three particles independently. In this paper, we develop the control algorithms for steering multiple particles independently and we validate our control techniques using simulations with realistic sources of initial position errors and thermal noise. In this study, we assume perfect measurement and actuation.
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    Using Feedback Control of Microflows to Independently Steer Multiple Particles
    (IEEE, 2006-08) Shapiro, Benjamin; Armani, Michael D.; Chaudhary, Satej; Probst, Roland
    In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.)We show proof-of-concept PDMS devices, having four and eightelectrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once.
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    Modeling the Fluid Dynamics of Electrowetting on Dielectric (EWOD)
    (IEEE, 2006-08) Shapiro, Benjamin; Walker, Shawn
    This paper discusses the modeling and simulation of a parallel-plate Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects.We model the fluid dynamics by using Hele–Shaw type equations with a focus on including the relevant boundary phenomena. Specifically, we show that contact angle saturation and hysteresis are needed to predict the correct shape and time scale of droplet motion.We demonstrate this by comparing our simulation to experimental data for a splitting droplet.Without these boundary effects, the simulation shows the droplet splitting into three pieces instead of two and the motion is over 15 times faster than the experiment. We then show how including the saturation characteristics of the device, and a simple model of contact angle hysteresis, allows the simulation to better predict the splitting experiment. The match is not perfect and suffers mainly because contact line pinning is not included. This is followed by a comparison between our simulation, whose parameters are now frozen, and a new experiment involving bulk droplet motion. Our numerical implementation uses the level set method, is fast, and is being used to design algorithms for the precise control of microdroplet motion, mixing, and splitting.
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    Interconnection of Subsystem Reduced-Order Models in the Electro-Thermal Analysis of Large Systems
    (IEEE, 2007-06) Shapiro, Benjamin; Mathai, Pramod
    Heat conduction in an electronic device is commonly modeled as a discretized thermal system (eg, finite element or finite difference models) that typically uses large matrices for solving complex problems. The large size of electronic-system heat transfer models can be reduced using model reduction methods and the resulting reduced-order models can yield accurate results with far less computational costs. Electronic devices are typically composed of components, like chips, printed circuit boards, and heat sinks that are coupled together. There are two ways of creating reduced-order models for devices that have many coupled components. The first way is to create a single reduced-order model of the entire device. The second way is to interconnect reduced-order models of the components that constitute the device. The second choice (which we call the “reduce then interconnect” approach) allows the heat transfer specialist to perform quick simulations of different architectures of the device by using a library of reduced-order models of the different components that make up the device. However, interconnecting reduced-order models in a straightforward manner can result in unstable behavior. The purpose of this paper is two-fold: creating reduced-order models of the components using a Krylov subspace algorithm and interconnecting the reducedorder models in a stable manner using concepts from control theory. In this paper we explain the logic behind the “reduce then interconnect” approach, formulate a control-theoretic method for it, and finally exhibit the whole process numerically, by applying it to an example heat conduction problem.
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    Analyzing Mistuning of Bladed Disks by Symmetry and Reduced-Order Areodynamic Modeling
    (American Institute of Aeronautics and Astronautics, 2003-03) Shapiro, Benjamin; Willcox, Karen
    The mistuned behavior of bladed disks is analyzed and optimized using an unsteady, transonic, computational fluid dynamic model (CFD). This result is enabled by the integration of two frameworks: the first is based on symmetry arguments and an eigenvalue/vector perturbation scheme, while the second is a reduction technique based on the proper orthogonal decomposition (POD). The first framework reduces the complexity of the problem, reveals engineering trade offs and suggests the existence of an intentional robust mistuning which improves both stability and forced response with respect to random variations in blade parameters. The second framework permits the reduction of state-of-the-art computational fluid dynamic codes to reduced-order models, which capture the accuracy of the original simulation but fit within the mistuning analysis framework. Together, these methodologies allow the analysis of a transonic, bladed disk with stiffness mistuning (see Fig. 1).Moreover, because of the low order of the aeroelasticmodel, a robust control¹ uncertainty analysis can be used to prove that the intentional mistuning suggested by the symmetry analysis framework is indeed robust. Hence this paper contains the first rigorous demonstration that intentional mistuning can robustly improve both the stability and forced response for a model that includes sophisticated aerodynamic effects.
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    A New Experimental Approach to Study Helicopter Blade-Vortex Interaction Noise
    (2007-10-01) Koushik, Sudarshan
    A unique and novel experimental approach has been developed to study the aerodynamics and acoustics of the helicopter Blade-Vortex Interaction in a controlled hover environment. This is achieved by having a non-lifting single-bladed rotor with a rigid hub interact with a carefully con- trolled gust disturbance that replicates the essential characteristics of the vortex velocity. This ex- perimental approach termed the Blade-Controlled Disturbance-Interaction or the BCDI, decouples the rotor parameters from the charactersitics of the incident disturbance velocity, thus providing an ideal setup for studying the blade’s aerodynamics and acoustic response in detail. Moreover, the angle of interaction between the disturbance field and the rotor blade can be controlled by orienting the gust, providing the ability to study both parallel and oblique interactions. The noise data was recorded at thirty different microphone locations. A series of experiments at various rotor tip Mach numbers and interaction angles, replicat- ing many of the conditions of helicopter BVI, were performed. The results show that the the directionality of the BVI noise is strongly determined by the interaction angle. A small change in interaction angle results in the radiation of noise over a larger azimuthal area compared to the parallel interaction. Moreover, as the interaction becomes more oblique, the peak noise elevation angle approaches closer to the rotor plane. A linear unsteady lifting-line aerodynamic theory (corrected for chord-wise non-compactness )was used to estimate the blade aerodynamics during the interaction and hence the radiated noise. Although the theory under-predicted the noise levels for most of the cases, and did not replicate exactly the general pulse shape, the general directionality trends were predicted reasonably well. The theory was used to separate the contribution to the acoustics, from different spanwise blade sections, providing significant insights into the phasing mechanism of BVI noise.
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    Comparison of MSIS and Jacchia atmospheric density models for orbit determination and propagation
    (Univelt, Inc., 2003-02) Akins, Keith A.; Healy, Liam M.; Coffey, Shannon L.; Picone, J. Michael
    Two atmospheric density model families that are commonly chosen for orbit determination and propagation, Jacchia and MSIS, are compared for accuracy. The Jacchia 70 model, the MSISE-90 model, and the NRLMSISE-00 model may each be used to determine orbits over fitspans of several days and then to propagate forward. With observations kept over the propagation period, residuals may be computed and the accuracy of each model evaluated. We have performed this analysis for over 4000 cataloged satellites with perigee below 1000km for September-­October 1999, and the 60 HASDM calibration satellites with a large observation set for February 2001. The purpose of this study is to form a picture of the relative merits of the drag models in a comprehensive view, using all satellites in a manner consistent with the operational practice of US space surveillance centers. A further goal is to refine this knowledge to understand the orbital parameter regions where one of the models may be consistently superior.
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    Student Projects for Space Navigation and Guidance
    (Univelt, Inc., 2003-08) Healy, Liam M.
    "Space Navigation and Guidance," taught every fall at the University of Maryland, is required of all space track undergraduate aerospace engineering majors. Every student is required to participate in a group project where real observations are used in the solution of a navigation problem with estimation from observations. In this paper, I discuss two such projects, an observatory project in which the students use a telescope to track a satellite and determine its orbit, and a GPS project in which they analyze GPS receiver data to determine the receiver's position.
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    Speed and Accuracy Tests of the Variable-Step Störmer-Cowell Integrator
    (Univelt, Inc., 2005-02) Berry, Matthew M.; Healy, Liam M.
    The variable-step Stormer-Cowell integrator is a non-summed, double-integration multi-step integrator derived in variable-step form. The method has been implemented with a Shampine-Gordon style error control algorithm that uses an approximation of the local error at each step to choose the step size for the subsequent step. In this paper, the variable-step Stormer-Cowell method is compared to several other multi-step integrators, including the fixed-step Gauss-Jackson method, the Gauss-Jackson method with s-integration, and the variable-step single-integration Shampine- Gordon method, in both orbit propagation and orbit determination. The results show the variable-step Stormer-Cowell method is comparable with Gauss-Jackson using s-integration, except in high drag cases where the variable-step Stormer-Cowell method has an advantage in speed and accuracy.