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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
371

A Hearing-Based, Frequency Domain Sound Quality Model for Combined Aerodynamic and Power Transmission Response With Application To Rotorcraft Interior Noise

SONDKAR, PRAVIN BANDU 22 April 2008 (has links)
No description available.
372

Aircraft Thermal Management Using Loop Heat Pipes

Fleming, Andrew J. 13 May 2009 (has links)
No description available.
373

Aerodynamic Modeling of an Unmanned Aerial Vehicle Using a Computational Fluid Dynamics Prediction Code

Rose, Isaac D. 27 April 2009 (has links)
No description available.
374

Human and Animal Exposure to Airborne Methicillin-resistant Staphylococcus aureus (MRSA): Laboratory Evaluations and Veterinary Hospital Pilot Study

Lutz, Eric Anthony 09 September 2010 (has links)
No description available.
375

Aerodynamic Control of Slender Bodies from Low to High Angles of Attack through Flow Manipulation

Lopera, Javier 02 July 2007 (has links)
No description available.
376

Lifting body design and CFD analysis of a novellong range pentacopter, the TILT LR drone / Design och CFD analys av lyftgenererande ytor för "the TILTLR drone",en ny drönare med fem propellrar för lång räckvidd

Catagay, Daniel, Yuan, Haoqian January 2016 (has links)
In the thesis, a lifting body has been designed aiming to generate lift force for the pentacopter,called TILT LR (Long Range), at higher velocities during flights to improve the aerodynamicperformances. The configuration, which is used as the skeleton of the long range drone for upto 75 kilometers flights, is based upon a tilting system allowing the rotors to rotate around theirown axis in both pitch and roll angles. This offers the possibility to the TILT LR flying withoutany vertical excess thrust at a proper angle of attack and velocity. This new drone can be directlyapplied to missions require long flight time or cover long distance, such as Search & Rescue(SAR), power lines and off-shore structures inspection, fire monitoring or surveillance.Several main CAD models have been created during the process of design and presented in thereport together with the final design. For each model in the process, CFD simulations have beenapplied to observe the behaviors of the flows around the surfaces of the body during steadyflights, followed by a brief analysis for further modification. A series of simulations withvarying velocities and angle of attack have been performed for the final design, analyzing itsperformances under different air conditions. Flight envelope of the design has been presentedalso, together with some ideas of possible further studies on the pentacopter.
377

Aerodynamic Modeling in Nonlinear Regions, including Stall Spins, for Fixed-Wing Unmanned Aircraft from Experimental Flight Data

Gresham, James Louis 28 June 2022 (has links)
With the proliferation of unmanned aircraft designed for national security and commercial purposes, opportunities exist to create high-fidelity aerodynamic models with flight test techniques developed specifically for remotely piloted aircraft. Then, highly maneuverable unmanned aircraft can be employed to their greatest potential in a safe manner using advanced control laws. In this dissertation, novel techniques are used to identify nonlinear, coupled, aerodynamic models for fixed-wing, unmanned aircraft from flight test data alone. Included are quasi-steady and unsteady nominal flight models, aero-propulsive models, and spinning flight models. A novel flight test technique for unmanned aircraft, excitation with remote uncorrelated pilot inputs, is developed for use in nominal and nonlinear flight regimes. Orthogonal phase-optimized multisine excitation signals are also used as inputs while collecting gliding, aero-propulsive, and spinning flight data. A novel vector decomposition of explanatory variables leads to an elegant model structure for stall spin flight data analysis and spin aerodynamic modeling. Results for each model developed show good agreement between model predictions and validation flight data. Two novel applications of aerodynamic modeling are discussed including energy-based nonlinear directional control and a spin flight path control law for use as a flight termination system. Experimental and simulation results from these applications demonstrate the utility of high-fidelity models developed from flight data. / Doctor of Philosophy / This dissertation presents flight test experiments conducted using a small remotely controlled airplane to determine mathematical equations and parameter values, called models, to describe the airplane's motion. Then, the models are applied to control the path of the airplane. The process to develop the models and predict an airplane's motion using flight data is described. New techniques are presented for data collection and analysis for unusual flight conditions, including a spinning descent. Results show the techniques can predict the airplane's motion very well. Two experiments are presented demonstrating new applications and the usefulness of the mathematical models.
378

Dynamic flow quality measurements in a transonic cryogenic wind tunnel

Rosson, Joel Christopher January 1985 (has links)
Two instruments mounted in a piggyback arrangement were developed for time-resolved measurements of dynamic flow quality in a transonic cryogenic wind tunnel. The first one is a dual hot-wire aspirating probe for measurement of stagnation pressure and temperature. The second is a miniature high-frequency response angle probe consisting of surface mounted pressure sensors. The aspirating probe was tested in the 0.3-m Transonic Cryogenic Tunnel (TCT) at NASA-Langley Research Center. Stagnation pressure and temperature measurements were taken in the free-stream of the settling chamber and test section. Data were also obtained in the unsteady wake shed from an airfoil oscillating at 5 Hz. The investigation revealed the presence of large stagnation pressure and temperature fluctuations in the settling chamber occurring at the blade passing frequency of the tunnel driving fan. The fluctuations in the test section are of a much more random nature and have amplitudes much lower than those in the test section. The overall results are consistent with previous tunnel disturbance measurements in the 0.3-m TCT. In the unsteady wake shed from the oscillating airfoil, stagnation temperature fluctuations as high as 42 K rms were observed. The high-frequency angle probe is a four sensor, pyramid type probe capable of simultaneously measuring time resolved stagnation and static pressures and two orthogonal flow angles. Using measurements from both probes, all flow parameters of interest can be deduced. Aerodynamic behavior of a full size model of the probe was established in an open air jet of known conditions. / M.S.
379

Mars Precision Entry Vehicle Guidance Using Internal Moving Mass Actuators

Atkins, Brad Matthew 30 October 2014 (has links)
Many landing sites of scientific interest on Mars including most of the Southern Hemisphere at elevations above 2km Mars Orbiter Laser Altimeter reference are inaccessible due to current limitations in precision entry guidance and payload deceleration. Precision guidance and large payload deceleration is challenging due to the thin Martian atmosphere, large changes in free stream conditions during entry, and aerothermal and aerodynamic instability concerns associated with control systems with direct external flow field interaction. Such risks have descoped past Mars missions to unguided entry with the exception of Mars Science Laboratory's (MSL) bank angle guidance. Consequently, prior to MSL landing ellipses were on the order of 100's of km. MSL has approached the upper limit of payload deceleration capability for rigid, blunt body sphere cone aeroshells used on all successful Mars entry missions. Hypersonic Inflatable Aerodynamic Decelerators (HIADS) are in development for larger payload deceleration capability through inflated aeroshell diameters greater than rigid aeroshells constrained by the launch rocket diameter, but to date there has been limited dynamics, control, and guidance development for their use on future missions. This dissertation develops internal moving mass actuator (IMMA) control systems for improving Mars precision entry guidance of rigid capsules and demonstrating precision guidance capability for HIADs. IMMAs provide vehicle control moments without direct interaction with the external flow field and can increase payload mass delivered through reducing propellant mass for control and using portions of the payload for the IMMAs. Dynamics models for entry vehicles with rotation and translation IMMAs are developed. IMMA control systems using the models are developed for two NASA vehicle types: a 2.65 m, 602 kg Mars Phoenix-sized entry capsule and an 8.3 m, 5.9 metric ton HIAD approaching payload requirements for robotic precursor missions for future human missions. Linear Quadratic controllers with integral action for guidance command tracking are developed for translation and rotation IMMA configurations. Angle of attack and sideslip guidance laws are developed as an alternative to bank angle guidance for decoupling range and cross-range control for improved precision entry guidance. A new variant of the Apollo Earth return terminal guidance algorithm is implemented to provide the closed-loop angle of attack range control commands. Nonlinear simulations of the entire 8 degree of freedom closed-loop systems demonstrate precision guidance to nominal trajectories and final targets for off-nominal initial entry conditions for flight path angle, range, cross-range, speed and attitude. Mechanical power studies for IMMA motion show rotation IMMA require less total mechanical power than translation actuators, but both systems have low nominal mechanical power requirements (below 100 Watts). Precision guidance for both systems to terminal targets greater than 38 km down-range from an open-loop ballistic entry is shown for low mechanical power, low CM displacement, (< 4.5 in) and at low internal velocities (< 2 in/s) over significant dynamic pressure changes. The collective precision guidance results and low mechanical power requirements show IMMA based entry guidance control systems constitute a promising alternative to thruster based control systems for future Mars landers. / Ph. D.
380

Design and Optimisation of a Virtual Prototype of a Ground Transportation System at Very High-Speeds in Conditions Close to Vacuum

Lluesma Rodríguez, Federico 20 January 2023 (has links)
[ES] Hyperloop es considerado el quinto medio de transporte, después del coche, barco, tren y avión. Consiste en una capsula de levitación magnética que viaja dentro de un tubo en el que la presión de aire ha sido reducida. Entonces, la fricción con el suelo y resistencia aerodinámica son minimizadas, alcanzando ultra altas velocidades a nivel de tierra. Actualmente hay en desarrollo varios trenes maglev y conceptos hyperloop. La mayoría proponen levitar usando Suspensión Electromagnética (EMS). Zeleros, la compañía donde esta Tesis ha sido realizada, tiene una propuesta similar. Zeleros usa un EMS Híbrido (HEMS), combinando imanes y electroimanes para reducir los requerimientos de energía. Respecto a la propulsión, la propuesta es única ya que hace uso de un compresor de la industria aeroespacial. Simulaciones CFD prueban que usar un compresor reduce considerablemente la resistencia aerodinámica en el ambiente cerrado, ya que el efecto pistón es mitigado. Para el mismo tamaño de tubo y presión, un hyperloop con compresor requiere hasta 70 % menos potencia. En otros términos, si la misma potencia es instalada en el vehículo, el diámetro de la infraestructura puede ser 2.8 veces más pequeño. Esta Tesis desarrolla un simulador 0D para evaluar el rendimiento de la solución hyperloop propuesta. Resolver su aerodinámica requiere solucionar un fujo interno y externo de Fanno. El último combina efectos de Couette y Poisuille en un dominio anular. Así, se desarrolla un modelo simplificado para flujos de Fanno, acelerando así el modelado básico. Esta aproximación matemática incluye información de la velocidad de la pared y de la forma del dominio, evitando integrar un sistema de EDOs. La solución tiene una desviación en la ratio de presiones de 5 % respecto a CFD, y del 10 % en la longitud crítica. El simulador modela toda la termodinámica del vehículo, incluyendo el compresor, conductos, turbina, tobera y flujo externo. Este modelado es similar al del ciclo de Bryton, sin cámara de combustión. Además, se incluye un modelo para predecir la masa y longitud de la cápsula y sus componentes. Así, las pérdidas de fricción y requerimientos de potencia y energía son obtenidos. Estos resultados presentan una desviación máxima del 20 % respecto a CFD. Además, un proceso de optimización para encontrar la solución más eficiente se ha desarrollado con el código, para vehículos de 50 y 150 pasajeros. Se ha encontrado que es más beneficioso absorber menos gasto másico con el compresor, ya que la energía requerida para comprimir el flujo interno es más alta que las pérdidas en el canal externo. Comparando el consumo de energía específico de esta solución con otros medios de transporte, el hyperloop se encuentra cercano al rendimiento de los maglev. Éste es, también, entre tres y cinco veces más eficiente que los aviones. Además, es más competitivo que el avión en términos de velocidad media en una ruta hasta los 800 km. Por último, se desarrolla un modelo similar para un sistema de escala media. Este prototipo, cuya velocidad objetivo es de 500 km/h, es diseñado por Zeleros previo al sistema de escala real. Su simulador incluye además los efectos transitorios y la termodinámica del tubo, asumiendo una velocidad del sonido infinita. Gracias a este código, se puede obtener el rendimiento en una misión. Inicialmente, el prototipo incrementa la presión del tubo aguas arriba, y la reduce aguas abajo debido al efecto pistón, generando una velocidad inducida. Al final de la misión, el flujo puede ser transferido otra vez, y las presiones se equilibran otra vez. Este modelo también predice el par y potencia del motor eléctrico, además de los parámetros de la batería (voltaje, corriente y profundidad de descarga). / [CA] Hyperloop és considerat el cinquè mitjà de transport, després del cotxe, vaixell, tren i avió. Consisteix en una càpsula de levitació magnètica que viatja dins d'un tub on la pressió d'aire es reduïda. Aleshores, la fricció amb el sòl i resistència aerodinàmica són minimitzades, aconseguint ultra altes velocitats a nivell de terra. Actualment hi ha en desenvolupament diversos trens maglev i conceptes hyperloop. La majoria proposen levitar usant Suspensió Electromagnètica (EMS). Zeleros, la companyia on aquesta Tesi ha sigut realitzada, té una proposta similar. En particular, el concepte de Zeleros utilitza un EMS Híbrid (HEMS), combinant imants i electroimants per reduir els requeriments d'energia. Pel que fa a la propulsió, la proposta és única, ja que fa ús d'un compressor de la indústria aeroespacial. Simulacions CFD proven que utilitzar un compressor redueix considerablement la resistència aerodinàmica en un ambient tancat, ja que l'efecte pistó és mitigat. Per a la mateixa grandària de tub i pressió, un hyperloop amb compressor requereix fins a 70 % menys potència. En altres termes, si la mateixa potència és instal·lada al vehicle, el diàmetre de la infraestructura pot ser 2.8 vegades més menut. Aquesta Tesi desenvolupa un simulador 0D per avaluar el rendiment de la solució hyperloop proposada. Resoldre l'aerodinàmica del hyperloop requereix solucionar un flux intern i extern de Fanno. L'últim combina efectes de Couette i Poiseuille en un domini anular. Així, es desenvolupa un model simplificat per a fluxos de Fanno, accelerant així el modelatge bàsic. Aquesta aproximació matemàtica inclou informació de la velocitat de la paret i de la forma del domini, evitant integrar un sistema de EDOs. La solució té una desviació a la ràtio de pressions de 5 % respecte a CFD, i del 10 % a la longitud crítica. El simulador modela tota la termodinàmica del vehicle, incloent-hi el compressor, conductes, turbina, tovera i flux extern. Aquest modelat es similar al del cicle de Bryton, sense càmera de combustió. A més, s'inclou un model per predir la massa i la longitud de la càpsula i els seus components. Així, les pèrdues de fricció i requeriments de potència i energia són obtinguts. Aquests resultats presenten una desviació màxima del 20 % comparat amb CFD. A més, un procés d'optimització per trobar la solució més eficient ha estat desenvolupat amb el codi, per a vehicles de 50 i 150 passatgers. S'ha trobat que és més beneficiós absorbir menys massa amb el compressor, ja que l'energia requerida per comprimir el flux intern és més alta que les pèrdues al canal extern. Comparant el consum d'energia específic d'aquesta solució amb altres mitjans de transport, el hyperloop és proper al rendiment dels maglev. Aquest també és entre tres i cinc vegades més eficient que els avions. A més, és més competitiu en termes de velocitat mitjana en una ruta fins a 800 km. Finalment, es desenvolupa un model semblant per a un sistema d'escala mitjana. Aquest prototip, la velocitat objectiu del qual és de 500 km/h, és dissenyat per Zeleros previ al sistema d'escala real. El seu simulador inclou a més els efectes transitoris i la termodinàmica del tub, assumint una velocitat del so infinita. Gràcies a aquest codi, es pot obtenir el rendiment en una missió. Inicialment, el prototip incrementa la pressió del tub aigües amunt, i la redueix aigües avall degut a l'efecte pistó, generant una velocitat induïda. Al final de la missió, el flux pot ser transferit una altra vegada, i les pressions s'equilibren una altra vegada. Aquest model també prediu el parell i potència del motor elèctric, a més dels paràmetres de la bateria (voltatge, corrent i profunditat de descàrrega). / [EN] Hyperloop is considered the fifth means of transportation, after the car, boat, train and plane. It consists of a magnetically levitating capsule that travels within a tube in which the air pressure has been reduced. Thus, the ground friction and aerodynamic drag are minimised, reaching ultra high-speeds at ground level. Several maglev trains and hyperloop concepts being developed currently. Most of them propose levitating using Electromagnetic Suspension (EMS). Zeleros, the company where this Thesis was done, has a similar approach. It employs a Hybrid EMS (HEMS)In particular, the Zeleros approach employs a Hybrid EMS (HEMS), combining permanent and electromagnets to reduce energy requirements. As for the propulsion, the approach is unique as it uses a compressor from the aeronautical industry. CFD simulations prove that using a compressor considerably reduces the aerodynamic drag in the closed environment, as the piston effect gets mitigated. For the same tube size and pressure, a hyperloop with compressor requires up to 70 % less power. In other terms, if the same power is installed on the vehicle, the infrastructure diameter can be 2.8 times smaller. This Thesis develops a 0D simulator to evaluate the performance of the proposed hyperloop solution. Solving the aerodynamics of the hyperloop requires solving internal and external Fanno flows. For the latter, the flow combines Couette and Poiseuille effects in an annular domain. Thus, a simplified model for Fanno flows is developed to accelerate the basic modelling. This mathematical approach includes the information of the wall speed and the shape of the domain, avoiding integrating an ODE system. The solution has a deviation in the pressure ratio of 5 % and 10 % in the critical length regarding CFD. The simulator models all the vehicle thermodynamics, including the compressor, duct, turbine, nozzle, and external flow. This modelling is similar to a Bryton cycle, without a combustion chamber. Also, a model to predict the mass and length of the capsule and its components is included. Thus, the friction losses and the energy and power requirements can be extracted. These outputs are compared with CFD results, with a maximum deviation of 20 %. Moreover, an optimisation process is conducted with the code to find the most efficient solution for 50- and 150-passenger vehicles. It is found that shallowing less mass flow with the compressor is better, as the energy required to compress the internal flow is higher than the losses on the external channel. Comparing the specific energy consumption of this solution with other means of transportation, the hyperloop is close to the maglev performance. It is also between three and five times more efficient than aeroplanes. Furthermore, the hyperloop is more competitive than the plane in terms of average speed on a route, up to 800 km. The last part of this work develops a similar model for a middle-scale system. This prototype, which aims to reach 500 km/h, is being designed by Zeleros before the real-scale one. Its simulator also includes the transient effects and the tube thermodynamics, assuming an infinite sound speed. Thanks to this code, the performance in a mission is obtained. The prototype initially increases the upstream tube pressure and reduces the downstream one due to the piston effect, generating an induced speed. At the end of the mission, the flow can be transferred again, and the pressures equilibrate again. This model also predicts the electric motor torque and power and the battery parameters (voltage, current, and deep of discharge). / Este trabajo ha recibido una subvención parcial del Ministerio de Ciencia, Innovación y Universidades bajo la ayuda “Doctorandos Industriales” número DI-17-09616. / Lluesma Rodríguez, F. (2022). Design and Optimisation of a Virtual Prototype of a Ground Transportation System at Very High-Speeds in Conditions Close to Vacuum [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/191409

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