Dissertations / Theses on the topic 'Aircraft wake'
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1
Stephan, Anton. "Wake vortices of landing aircraft." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-167566.
2
Bertényi, Tamás. "Merger of aircraft wake vortices." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620288.
3
Rodenhiser, Rebecca J. "An Ultrasonic Method for Aircraft Wake Vortex Detection." Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-theses/1004.
Abstract:
"This thesis documents the experimental proof of concept study for an ultrasonic method of wake vortex detection. A new acoustic technique is utilized to measure the circulation produced in the wake of lift-generating aircraft. Ultrasonic signals are transmitted in a path around the wake vortex, and are used to determine the average in-line velocity component along the acoustic path. It is shown herein that this velocity component is directly proportional to the net circulation value within the acoustic path. This is the first study to take this methodology and implement it in a realistic airport setting. This project included constructing a prototype and conducting field tests to prove the validity of this technology in a realistic environment setting. During field tests an acoustic path enclosed the vorticity shed behind one wing of a Piper PA-28 aircraft. Fourteen initial test flights were conducted in calm atmospheric conditions, and results show circulation values measured are comparable in magnitude and direction to expected circulations generated by the Piper PA-28 aircraft. Additional testing in various atmospheric conditions revealed the scope of practice for such a measurement technology. This study demonstrates the validity of the acoustic method in detecting aircraft wake vortices. Future investigations and applications utilizing this technique are discussed within."
4
Rodenhiser, Rebecca J. "An ultrasonic method for aircraft wake vortex detection." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-083105-160931/.
5
Marles, David. "Effect of an axial jet aircraft wake vortices." Thesis, University of Bath, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488899.
Abstract:
An experimental study has been performed to evaluate the effect of a cold axial jet on a variety of typical aircraft wake vortex systems in the near-field. This research attempted to alleviate the vortex hazard imposed on trailing aircraft, which is especially important in the crowded skies around airfields.
6
Andronache, Constantin. "A study of aerosol interactions in aircraft wake and background atmosphere." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/26008.
7
Stephan, Anton [Verfasser], and George C. [Akademischer Betreuer] Craig. "Wake vortices of landing aircraft / Anton Stephan. Betreuer: George C. Craig." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1049393155/34.
8
Roa, Perez Julio Alberto. "Development of Aircraft Wake Vortex Dynamic Separations Using Computer Simulation and Modeling." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/96199.
Abstract:
This dissertation presents a research effort to evaluate wake vortex mitigation procedures and technologies in order to decrease aircraft separations, which could result in a runway capacity increase. Aircraft separation is a major obstacle to increasing the operational efficiency of the final approach segment and the runway.
An aircraft in motion creates an invisible movement of air called wake turbulence, which has been shown to be dangerous to aircraft that encounter it. To avoid this danger, aircraft separations were developed in the 1970s, that allows time for wake to be dissipated and displaced from an aircraft's path. Though wake vortex separations have been revised, they remain overly conservative.
This research identified 16 concepts and 3 sub-concepts for wake mitigation from the literature. The dissertation describes each concept along with its associated benefits and drawbacks. All concepts are grouped, based on common dependencies required for implementation, into four categories: airport fleet dependent, parallel runway dependent, single runway dependent, and aircraft or environmental condition dependent.
Dynamic wake vortex mitigation was the concept chosen for further development because of its potential to provide capacity benefit in the near term and because it is initiated by air traffic control, not the pilot. Dynamic wake vortex mitigation discretizes current wake vortex aircraft groups by analyzing characteristics for each individual pair of leader and follower aircraft as well as the environment where the aircraft travel. This results in reduced aircraft separations from current static separation standards.
Monte Carlo simulations that calculate the dynamic wake vortex separation required for a follower aircraft were performed by using the National Aeronautics and Space Administration (NASA) Aircraft Vortex Spacing System (AVOSS) Prediction Algorithm (APA) model, a semi-empirical wake vortex behavior model that predicts wake vortex decay as a function of atmospheric turbulence and stratification. Maximum circulation capacities were calculated based on the Federal Aviation Administration's (FAA) proposed wake recategorization phase II (RECAT II) 123 x 123 matrix of wake vortex separations.
This research identified environmental turbulence and aircraft weight as the parameters with the greatest influence on wake vortex circulation strength. Wind has the greatest influence on wake vortex lateral behavior, and aircraft mass, environmental turbulence, and wind have the greatest influence on wake vortex vertical position.
The research simulated RECAT II and RECAT III dynamic wake separations for Chicago O'Hare International (ORD), Denver International Airport (DEN) and LaGuardia Airport (LGA). The simulation accounted for real-world conditions of aircraft operations during arrival and departure: static and dynamic wake vortex separations, aircraft fleet mix, runway occupancy times, aircraft approach speeds, aircraft wake vortex circulation capacity, environmental conditions, and operational error buffers. Airport data considered for this analysis were based on Airport Surface Detection Equipment Model X (ASDE-X) data records at ORD during a 10-month period in the year 2016, a 3-month period at DEN, and a 4-month period at LGA.
Results indicate that further reducing wake vortex separation distances from the FAA's proposed RECAT II static matrix, of 2 nm and less, shifts the operational bottleneck from the final approach segment to the runway. Consequently, given current values of aircraft runway occupancy time under some conditions, the airport runway becomes the limiting factor for inter-arrival separations.
One of the major constraints of dynamic wake vortex separation at airports is its dependence on real-time or near-real-time data collection and broadcasting technologies. These technologies would need to measure and report temperature, environmental turbulence, wind speed, air humidity, air density, and aircraft weight, altitude, and speed.PHD
9
Craig, Margaret Elizabeth. "Trailing-Edge Blowing of Model Fan Blades for Wake Management." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/30886.
Abstract:
Model fan blades designed to implement the wake management technique of trailing-edge blowing were tested in a linear cascade configuration. Measurements were made on two sets of blowing blades installed in the Virginia Tech low-speed linear cascade wind tunnel. The simple blowing blades were identical to the baseline GE Rotor B blades, aside from a slight difference in trailing-edge thickness, a set of internal flow passages, and a blowing slot just upstream of the trailing-edge on the suction side of the blade. The Kuethe vane blades were also slightly thicker at the trailing-edge, and had a set of nine evenly spaced vortex generators upstream of the blowing slot on the suction side. The cascade tunnel accommodates eight blades with adjustable tip-gap heights, although only the center four blades were replaced by blowing blades in this study. The tunnel has an inlet angle of 65.1â a, a stagger angle of 56.9â a and a flow turning angle of 11.8â a. The tip-gap was set to 0.004125c and the freestream velocity of 24.7m/s led to a Reynolds number based on the chord of 385,000.
Blowing slot uniformity measurements made with a single hot-wire immediately behind the trailing-edge revealed that the blowing becomes more spanwise uniform as blowing rate is increased. The same occurs with the Kuethe vane blades, despite a spanwise serrated pattern that appears as a result of the upstream vortex generators.
Cross-sections made perpendicular to the blade span gave preliminary evidence that the simple blowing wake deficit increases from the passive suction case at a blowing rate of 1.4% and becomes overblown by 2.6%. The Kuethe vane wake deficit does not increase at low blowing rates. Both sets of blowing blades indicated a slight angling of the wake towards the pressure side with blowing.
Pitot-static full cross-sections of the simple blowing blades at x/ca = 0.839 and 1.877 verified the increase in wake depth and width at 1.4% as compared to the passive suction and non-blowing baseline cases, and the wake overblowing that occurs as blowing rate is increased to approximately 2.6%. The Kuethe vane blades only achieve partial wake cancellation at the maximum tested rate of 2.6% for these measurements.
The results of the baseline study of Geiger (2005) are used for comparison with the mid-span velocity profiles made at four downstream locations. The velocity profiles clearly confirm the results of the normal-to-span and full cross-sections, while also revealing a decrease from the baseline of at least 25% in most of the maximum Reynolds normal stresses and turbulent kinetic energies at all rates between 1.4% and 2.7% for both sets of blowing blades. Spectral measurements of the simple blowing blades show clear reductions of the energy in the wake for all blowing rates over the majority of the range of normalized frequencies, while the Kuethe vane blades show reductions at all rates and all frequencies.
By performing Fourier decompositions, the tone noise benefits over the non-blowing baseline blades are directly comparable in decibels. The optimum blowing rate for the simple blowing blades is clearly 2.5%, since this rate shows the most potential tone noise reduction. The Kuethe vane blades suggest decreases in tone noise over all of the tested blowing rates.Master of Science
10
Schroeder, Nataliya. "Analysis of Potential Wake Turbulence Encounters in Current and NextGen Flight Operations." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/40924.
Abstract:
Wake vortices pose a threat to a following aircraft, because they can induce a roll and compromise the safety of everyone on board. Caused by a difference in pressure between the upper and the lower part of the wings, these invisible flows of air are a major hazard and have to be avoided by separating the aircraft at considerable distances. One of the known constraints in airport capacity for both departure and arrival operations is the large headway resulting from the wake spacing separation criteria. Reducing wake vortex separations to a safe level between successive aircraft can increase capacity in the National Airspace System (NAS) with corresponding savings in delay times.
One of the main goals of the Wake Encounter Model (WEM) described in this thesis is to assess the outcome from future reduced separation criteria in the NAS. The model has been used to test probable encounters in todayâ s operations, and can also be used to test NextGen scenarios, such as Close Parallel Approaches and reduced in-trail separation flights.
This thesis presents model enhancements to account for aircraft turning maneuvers, giving the wake a more realistic shape. Three major airspaces, New York, Southern California and Atlanta, were analyzed using the original and the enhanced WEM to determine if the enhanced model better represents the conditions in todayâ s operations. Additionally, some analysis on the wake lateral travel for closely spaced runways is presented in this thesis. Finally, some extension tools for post -analysis, such as animation tool and various graphs depicting the interactions between wake pairs were developed.Master of Science
11
Hall, Jacob Thomas. "Modeling and analysis of a maneuvering aircraft and cable towed body with wake effects." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59671.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 105-107).
This thesis report covers the analysis and modeling of a cable towed endbody that incorporates an aircraft, wake effects, a towline, and a tow body. The aircraft is modeled as a generic tactical aircraft which is able to conduct maneuvers. The towline is treated as an elastic cable that connects the aircraft and endbody while also being affected by the aircraft wake. The endbody is treated as a simple drag sphere with allocation to continue to various shapes and sizes. A parametric study is conducted which highlights the effect of changing the parameters of towline material, length, and load factor. Three maneuvers are conducted including a turn and acceleration. The results show that longer cable lengths, those of 500 m or greater, exhibit little response to the addition of a trailing wake. However, shorter cables are affected, especially during the turn and climb maneuvers. A 50 m cable experiences an extra 8m deflection when compared to a wake-less example. During the climb maneuver, it is shown that an endbody may pass ahead of the towing aircraft, as well as above it. The effect of changing cable material is shown to be minimal, with small differences expected due to the difference in cable mass.
by Jacob Thomas Hall.
S.M.
12
Myers, Theodore J. "Determination of Bragg Scatter in an Aircraft Generated Wake Vortex System for Radar Detection." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30719.
Abstract:
Remote detection and tracking of wingtip generated wake vortices is important for hazard avoidance especially near airports. Aircraft that fly through these hazardous vortices experience sudden induced roll. Experiments have demonstrated that there is sufficient radar cross section for remote detection at frequencies ranging from VHF to C band (100 MHz to 5 GHz).
The mechanism that yields this radar cross section is Bragg scattering from the index of refraction variations due to the atmospheric water vapor and potential temperature fields being mixed by the wake vortex system.
Refractive index variations of the size that correspond to half the operating radar wavelength produce the observed radar return. Previous analysis has postulated turbulence within the wake vortex to be the generator of the index of refraction variations.
In this work, a new mechanism is identified that does not assume turbulence within the wake vortex system. This "laminar flow mechanism" causes refractive index structuring that stretches into successively smaller spirals over time as the wake vortex system swirls and descends through the stratified atmosphere.
The results are quantitatively consistent with experimental data. Results indicate that this new mechanism has a sharply peaked doppler spectrum which is encouraging for coherent detection by doppler radar.Ph. D.
13
Fonti, Elio. "Measurements of aircraft wake vortices in ground proximity within an atmospheric boundary layer wind tunnel." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/5635.
Abstract:
The vortex wake characteristics of aircraft during landing and take-off are of interest in connection with both the safety of following aircraft penetrating the vortex and the dispersion of engine exhaust plumes. A series of measurements were carried out in an Atmospheric Boundary Layer Wind Tunnel (ABLWT) to identify and characterise both the mean and turbulent flow field of a pair of wake vortices in ground proximity. Cont/d.
14
Trupka, Andrew Tristan. "Tracer gas mapping of beverage cart wake in a twin aisle aircraft cabin simulation chamber." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/8853.
Abstract:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Mohammad H. Hosni
Byron W. Jones
In 2010, over 786 million passengers flew on commercial flights in the United States according to the Bureau of Transportation Statistics (2011). With the average flight length over 1300 miles for domestic flights, this amounts to billions of hours spent aboard airliners by passengers each year. During these flights, diseases and other harmful contaminates, some malicious, can spread throughout aircraft cabins, harming passengers. Aircraft ventilation systems are designed to remove these harmful contaminates as quickly as possible to minimize spread in cabin air. Disruptions to the design airflow pattern can hinder the effectiveness of contamination removal efforts. A common form of this airflow disruption is longitudinal air movement through cabin aisles. To examine the effect of contaminate transport down aircraft aisles by a moving body, a motorized beverage cart is past by a contamination source as it traverses the length of the cabin aisle. An experimental study is performed in a mockup Boeing 767 cabin section consisting of eleven rows with seven seats per row. Carbon Dioxide (CO2) tracer gas is injected at a constant flow rate at a location of interest until concentrations in the cabin reach steady state. Ventilation equipment and flow rates representative of an actual aircraft are used for all experiments. Seats in the mockup are occupied by thermal manikins to simulate passenger heat load. A motorized beverage cart traverses the length of the cabin aisle passing by the injection location. The concentrations of tracer gas displaced by the cart are measured at locations throughout the cabin. Comparing these measurements to baseline readings taken with no cart movement, a map of the degree to which contaminant transport is affected by the beverage cart is calculated. The cabin mockup is supplied by 100% outdoor air through actual Boeing supply ductwork and linear diffusers along the cabin length above the aisles. The CO2 level is measured in the inlet air, measurement locations in the cabin, and exhaust air using nondispersive infrared (NDIR) sensors. Measured results are reported for all (54) seat locations downstream of the cart traverse/injection location for an injection location near the rear of the cabin. Analogous measurements are also conducted examining the effect of variations in cart speed and modified injection location. It was found the beverage cart movement had an effect of up to a 35% increase in tracer gas concentration relative to the local steady state concentration for several seat locations adjacent to the aisle. This increased concentration continued for only a few minutes in all cases, but was generally less than the steady state exposure one row closer to the injection location. Moving in the lateral direction away from the aisle, the variance in tracer gas concentration due to the cart movement diminished quickly. The significance of increased concentration for such short periods of time in comparison to the length of actual commercial flights may require further biological analysis. The data showed general tracer gas concentration increases due to cart movement in a small section of the cabin mockup which could warrant further analysis, but increases were generally insignificant when considering entire flight contamination exposure levels.
15
Mauermann, Tobias [Verfasser], and L. [Akademischer Betreuer] Tichy. "Flexible Aircraft Modelling for Flight Loads Analysis of Wake Vortex Encounters / Tobias Mauermann ; Betreuer: L. Tichy." Braunschweig : Technische Universität Braunschweig, 2010. http://d-nb.info/1175825352/34.
16
Frink, William D. Jr. "Hot-wire surveys in the vortex wake downstream of a three-percent fighter aircraft model at high angles of attack." Thesis, Monterey, California: Naval Postgraduate School, 1990. http://hdl.handle.net/10945/27586.
Abstract:
Approved for public release; distribution is unlimited.A low-speed wind tunnel investigation was conducted to examine the vortex wake downstream of a three-percent scale model of the YF-17 lightweight fighter prototype at high angles of attack. The study was in support of NASA ames Research Center's wind tunnel investigation of a full scale FA-18 as part of NASA's High Alpha Technology Program. Smoke flow visualization was used to locate the downstream vortex wake. Hot-wire surveys were taken through the vortex at two stations; one directly aft of the model and the other at a station three model lengths downstream of the model. The effect of adding a fence to the leading edge extension (LEX) was studied. Power spectra from the hot-wire were recorded for the survey station directly aft of the model. Results show that: peak turbulent fluctuation at this station occurred at 25 deg angle of attack; lateral turbulent fluctuation greatly diminished at the far downstream station; and the addition of the LEX fence shifted energy content of turbulence toward higher frequencies.
17
Frink, William D. "Hot-wire surveys in the vortex wake downstream of a three-percent fighter aircraft model at high angles of attack." Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241869.
Abstract:
Thesis (M.S. in Engineering Science)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Hebbar, Sheshagiri K. ; Platzer, Max F. "December 1990." Description based on title screen as viewed on March 31, 2010. DTIC Identifier(s): Trailling Vortices, Wake, Trubulent Flow, Jet Fighters, High Alpha (High Angle of Attack), Vortex Wake, Angle of Attack, Extendable Structures, Leading Edges, Fences, Lex Fences, Wind Tunnel Models, F-17 Aircraft, F/A-18 Aircraft, Wind Tunnel Tests, Hot Wire Anemometers, Theses. Author(s) subject terms: High Angle-of-Attack Aerodynamics, Hot-Wire Measurements, Wind Tunnel Studies. Includes bibliographical references (p. 24-25). Also available in print.
18
Geiger, Derek Henry. "Comparative Analysis of Serrated Trailing Edge Designs on Idealized Aircraft Engine Fan Blades for Noise Reduction." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/40542.
Abstract:
The effects of serrated trailing edge designs, designed for noise reduction, on the flow-field downstream of an idealized aircraft engine fan blade row were investigated in detail. The measurements were performed in the Virginia Tech low speed linear cascade tunnel on one set of baseline GE-Rotor-B blades and four sets of GE-Rotor-B blades with serrated trailing edges. The four serrated blade sets consisted of two different serration sizes (1.27 cm and 2.54 cm) and for each different serration size a second set of blades with added trailing edge camber. The cascade row consisted of 8 GE-Rotor-B blades and 7-passages with adjustable tip gap settings. It had an inlet angle of 65.1º, stagger angle of 56.9º and a turning angle of 11.8º. The tunnel was operated with a tip gap setting of 1.65% chord, with a Reynolds number based on the chord of 390,000.
Blade loading measurements performed on each set of blades showed that it was slightly dependent on the serration shape. As the serration size was increased the blade loading decreased, but adding droop increased the blade loading.
The Pitot-static cross-sections showed that flow-fields near the upper and lower endwalls cascade tunnel were similar with the baseline or the serrated blade downstream of the blade row. In the wake region, the individual trailing edge serrations tips and valleys could be seen. As the wake convected downstream, the individual tips and valleys became less visible and the wake was more uniform in profile. The tip leakage vortex was only minimally affected by the trailing edge serrations. This conclusion was further reinforced by the three-component hot-wire cross-sectional measurements that were performed from the lower endwall to the mid-span of the blade. These showed that the mean streamwise velocity, turbulence kinetic energy and turbulence kinetic energy production in the tip leakage region were nearly the same for all four serrated blades as well as the baseline. The vorticity in this region was a more dependent on the serration shape and as a result increased with serration size compared to the baseline.
Mid-span measurements performed with the three-component hot-wire showed the spreading rate of the wake and the decay rate of the wake centerline velocity deficit increased with serration size compared to the baseline case. Drooping of the trailing edge only minimally improved the spreading and decay rates. This improvement in these rates was predicted to reduce the tonal noise at the leading edge of the downstream stator vane because the periodic fluctuation associated with the sweeping of the rotor blade wakes across it, was due to the pitchwise variation in the mean streamwise velocity. The wakes were further compared to the mean velocity and turbulence profiles of plane wakes, which the baseline and the smallest serration size agreed the best. As the serration size was increased and drooping was added, the wakes became less like plane wakes. Spectral plots at the wake centerline in all three velocity directions showed some evidence of coherent motion in the wake as a result of vortex shedding.Master of Science
19
Mirmohammadsadeghi, Navid. "Improvements to Airport Systems Capacity and Efficiency Using Computer Models and Tools." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/84301.
Abstract:
This thesis presents two aspects of air transportation systems, capacity and efficiency. The first study improved a runway capacity simulation model for estimating the capacity of airports under various conditions. The main contribution of this study was to develop a simulation model which is able to analyze different airports with individual aircraft types. Many air traffic regulations were added to the simulation model to give more realistic results to the potential users of the model. Analysis of different separation systems between aircraft pairs show that the capacity of airports can improve by using more efficient separation systems specially under tough weather conditions. One of the outputs of the study, is an upgraded user interface which can be used by airport authorities for estimating their facilities' available capacity under different scenarios.
The second study represents a new method for estimating unimpeded taxi times for taxing airplanes at airports. This study focused specifically on 6 large airports in the United States and the real ground radar data for all of the movements at those facilities. By tracking the real trajectories of every operation, the taxing behavior of each flight was analyzed. A standalone application was designed to summarize the flights information at each airport and represent the taxing behavior. The results show that using the ground radar data at airports can represent the taxing behavior in the highest fidelity.Master of Science
20
Saulgeot, Pierre. "Contributions à la compréhension de la formation et de l'atténuation possible des traînées de condensation de l'aviation." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAX143.
Abstract:
Les traînées de condensation sont des nuages de glace qui se forment dans le sillage des avions. Leur étude, y compris leur impact météorologique, est rendue difficile par la nécessité de comprendre de nombreuses échelles spatiales et temporelles, depuis la sortie du moteur jusqu'aux cirrus induits dont l'extension peut atteindre plusieurs centaines de kilomètres carrés. Cette thèse s'intéresse à l'influence des tourbillons de sillage, aussi appelés tourbillons marginaux, sur la distribution du panache moteur et la condensation de la vapeur d'eau en glace, de leur enroulement à leur déstabilisation, en passant par une phase bidimensionnelle où la dynamique de ces tourbillons longitudinaux est dominante. La stratification thermique de l'atmosphère joue un rôle majeur dans leur évolution. En particulier, le mouvement naturel des tourbillons est descendant, mais un sillage secondaire peut se former à leur proximité et remonter ensuite jusqu'à l'altitude de vol. Le sillage dynamique est alors séparé en deux composantes distinctes. Les panaches des moteurs peuvent se trouver pris dans l'une ou l'autre, en fonction de leur position initiale. Dans les zones sursaturées, cela a une forte influence sur la condensation à l'intérieur du panache, compte tenu des variations de température avec l'altitude, et donc sur son impact optiqueContrails are ice clouds that form in the wake of aircraft. Their study, including their meteorological impact, is made difficult by the need to understand numerous spatial and temporal scales, from engine output to induced cirrus clouds whose extension can reach several hundred square kilometers. This thesis focuses on the influence of wake vortices, also known as tip vortices, on the distribution of the engine plume and the condensation of water vapour into ice, from their rolling up to their destabilization, passing through a two-dimensional phase where the dynamics of these longitudinal vortices are dominant. The thermal stratification of the atmosphere plays a major role in their evolution. In particular, the natural movement of vortices is downwards, but a secondary wake can form in their vicinity and then rise back up to flight altitude. The dynamic wake is then separated into two distinct components. Engine plumes can find themselves caught in one or the other, depending on their initial position. In supersaturated zones, this has a strong influence on condensation within the plume, given temperature variations with altitude, and therefore on its optical impact
21
Brundin, Desirée. "An Experimental Study of the High-Lift System and Wing-Body Junction Wake Flow Interference of the NASA Common Research Model." Thesis, KTH, Optimeringslära och systemteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209242.
Abstract:
This thesis investigates the turbulent flow in the wake of the wing-body junction of the NASA Common Research Model to further reveal its complex vortical structure and to contribute to the reference database used for Computational Fluid Dynamics validation activities. Compressible flows near two wall-boundary layers occurs not only at the wing-body junction but at every control surface of an airplane, therefore increased knowledge about this complex flow structure could potentially improve the estimates of drag performance and control surface efficiency, primarily for minimizing the environmental impact of commercial flight. The airplane model is modified by adding an inboard flap to investigate the influence from the deflection on the vorticity and velocity field. Future flap designs and settings are discussed from a performance improvement point of view, with the investigated flow influence in mind. The experimental measurements for this thesis were collected using a Cobra Probe, a dynamic multi-hole pressure probe, for Reynolds numbers close to one million based on the wing root chord. A pre-programmed three-dimensional grid was used to cover the most interesting parts of the junction flow. The facility used for the tests is a 120 cm by 80 cm indraft, subsonic wind tunnel at NASA Ames Research Center’s Fluid Mechanics Lab, which provides an on-set flow speed of around Mach 0.15, corresponding to approximately 48 m/s.Den här avhandlingen undersöker det turbulenta flödet runt övergången mellan flygplanskropp och vinge på en NASA Common Research Model för att vidare utforska den komplexa, tredimensionella strukturen av flödet och bidra till NASA’s officiella databas för jämförelser med simulerade flöden. Kompressibla flöden nära tvåväggsgränsskikt uppkommer inte bara vid övergången mellan flygplanskropp och vinge utan även vid varje kontrollyta på ett flygplan. Ökad kunskap om flödets beteende vid sådana områden kan därför bidra till en bättre uppskattning av prestanda och effektivitet av kontrollytorna och flygplanet i sin helhet, vilket kan bidra till minskad miljöpåverkan från kommersiell flygtrafik. Flygplansmodellen är modifierad genom montering av en vingklaff på den inre delen av vingen, detta för att undersöka hur olika vinklar på klaffarnas nedböjning påverkar flödets struktur och hastighetsfält. Framtida klaffdesigner och inställningar för ökad prestanda diskuteras även utifrån denna påverkan. Mätningarna i vindtunneln gjordes med en Cobra Probe, ett dynamisk tryckmätningsinstrument, speciellt designad för turbulenta och instabila flöden. Reynoldsnumren som generades av den subsoniska, indrags-vindtunneln var ungefär en miljon baserad på vingrotens längd, vilket motsvarar knappt en tiondel av normala flygförhållanden för samma flygplansmodell.
22
Jugier, Rémi. "Stabilité bidimensionnelle de modèles de sillage d’aéronefs." Thesis, Toulouse, ISAE, 2016. http://www.theses.fr/2016ESAE0021/document.
Abstract:
Le contrôle des tourbillons de sillages d'aéronefs permet de réduire leur dangerosité et d'augmenter par conséquent le débit de décollages et d'atterrissages dans les aéroports. Ce contrôle permettrait également d'agir sur la formation des rainées de condensation et des cirrus artificiels en haute atmosphère dans le but de réduire le forçage radiatif terrestre causé par l'aviation. Brion (2014) ont montré par analyse de stabilité modale que le dipôle de Lamb-Chaplygin, souvent utilisé comme un modèle représentatif des tourbillons de sillage en champ lointain, est bidimensionnellement instable à des nombres de Reynolds faibles. Nous étendons premièrement cette analyse de stabilité modale bidimensionnelle à des modèles de dipôles plus réalistes, pour une large gamme de rapport d'aspect, et obtenons, à faibles nombre de Reynolds, des instabilités de même nature (modes de déplacement) que pour le dipôle de Lamb-Chaplygin. Nous montrons cependant que la croissance des instabilités observées dépend fortement du rapport d'aspect du dipôle, et que cette croissance est fortement diminuée lorsque la diffusion du dipôle est prise en compte. Nous étudions ensuite la stabilité bidimensionnelle transitoire en champ lointain (dipôles) et en champ proche (nappes de vorticité), en atmosphères homogène et stratifiée. Dans tous les cas, les perturbations optimales sont des spirales de vorticité orientées à contre-cisaillement et situées en périphérie des tourbillons, qui conduisent in fine aux instabilités écrites par l'analyse modale grâce à un mécanisme de contamination du cœur des tourbillons, initialement identifié par Antkowiak & Brancher 2004 sur un tourbillon isoléAircraft wake vortex control allows for reducing of their dangerousness and consequently improve airport take-off / landing requencies. Contrails and artificial cirrus clouds formation could also be influenced through this control of wake vortices and allow for reducing of terrestrial radiative forcing generated by aviation. Brion (2014) have shown by a modal stability analysis that the Lamb-Chaplygin dipole, often used as a far-field model for aircraft wake vortices, is unstable to two-dimensional perturbations at Iow Reynolds numbers. We first extend this twodimensional modal stability analysis to more realistic dipole models, for a Wide range of aspect ratios, and obtain, for Iow Reynolds numbers, instabilities of the same nature (displacement modes) as for the Lamb-Chaplygin dipole. However, we show that the growth of those modes depends greatly on the dipole aspect ratio, and that this growth is greatly diminished hen the dipole diffusion is taken into account. We then study two-dimensional transient growth for far-field models (dipoles) and near-field models (vorticity sheets), in homogeneous and stratified atmospheres. ln all cases, optimal perturbations are vorticity spirals oriented against shear and located at the periphery of the vortices, which eventually lead to development of the instabilities described in the modal analysis through a contamination mechanism of the vortex cores, initially identified by Antkowiak & Brancher (2004) for an isolated vortex
23
Bardell, N. S. "Wave propagation in periodically stiffened plates and shells." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256281.
24
Shen, G.-C. "The interaction between a plane shock wave and a cylindrical afterbody." Thesis, University of Hertfordshire, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.483961.
25
Yeung, Chong Pui. "A study of three-dimensional interaction of wakes and boundary-layers." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319566.
26
Materano, Blanco Gilberto Ignacio. "Numerical modelling of pressure rise combustion for reducing emissions of future civil aircraft." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9259.
Abstract:
This work assesses the feasibility of designing and implementing the wave rotor
(WR), the pulse detonation engine (PDE) and the internal combustion wave
rotor (ICWR) as part of novel Brayton cycles able to reduce emissions of future
aircraft. The design and evaluation processes are performed using the
simplified analytical solution of the devices as well as 1D-CFD models. A code
based on the finite volume method is built to predict the position and
dimensions of the slots for the WR and ICWR. The mass and momentum
equations are coupled through a modified SIMPLE algorithm to model
compressible flow. The code includes a novel tracking technique to ensure the
global mass balance. A code based on the method of characteristics is built to
predict the profiles of temperature, pressure and velocity at the discharge of the
PDE and the effect of the PDEs array when it operates as combustion chamber
of gas turbines. The detonation is modelled by using the NASA-CEA code as a
subroutine whilst the method of characteristics incorporates a model to capture
the throttling and non-throttling conditions obtained at the PDE's open end
during the transient process. A medium-sized engine for business jets is
selected to perform the evaluation that includes parameters such as specific
thrust, specific fuel consumption and efficiency of energy conversion. The ICWR
offers the best performance followed by the PDE; both options operate with a
low specific fuel consumption and higher specific thrust. The detonation in an
ICWR does not require an external source of energy, but the PDE array
designed is simple. The WR produced an increase in the turbine performance,
but not as high as the other two devices. These results enable the statement
that a pressure rise combustion process behaves better than pressure
exchangers for this size of gas turbine. Further attention must be given to the
NOx emission, since the detonation process is able to cause temperatures
above 2000 K while dilution air could be an important source of oxygen.
27
Menday, Roger. "The forced vibration of a partially delaminated beam." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/27082.
Abstract:
The forced vibration of a partially delaminated structure such as an aircraft wing can result in catastrophic crack growth. In order to look at the underlying mechanism of the dynamics and failure of the material, a simplified model of a cantilever beam with a single delamination at its free end is considered. We investigate a number of aspects of this system, using mathematical models to gain insight into its behaviour.
28
Kural, Aleksander. "Ultrasonic lamb wave energy transmission system for aircraft structural health monitoring applications." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/58395/.
Abstract:
In this project an investigation of a wireless power transmission method utilising ultrasonic Lamb waves travelling along plates was performed. To the author’s knowledge, this is the first time such a system was investigated. The primary application for this method is the supply of power to wireless structural health monitoring (SHM) sensor nodes located in remote areas of the aircraft structure. A vibration generator is placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device travel through the aircraft structure to a receiver in a remote wireless sensor node. The receiver converts the mechanical vibration of the ultrasonic waves back to electricity, which is used to power the sensor node. An experimental setup comprising a 1000 × 821 × 1.5 mm aluminium plate was designed to model an aircraft skin panel. Pairs of piezoelectric transducers were positioned along the longer edges of the plate. The electric impedance characteristics of three transducer types were measured. A circuit simulation MATLAB code was written. An input and output power measurement system was developed. The MFC M8528-P1 transducer type was identified as providing the best performance. The use of inductors to compensate for the capacitive characteristics of transducers was shown to provide up to 170-fold power throughput increase. The propagation of Lamb waves in the experimental plate was mapped using a scanning laser vibrometer and simulated using LISA finite difference method software. An optimised laboratory system transmitted 17 mW of power across a distance of 54 cm while being driven by a 20 V, 224 kHz signal. This figure can be easily increased by using a higher drive voltage. This shows that the system is capable of supplying sufficient power to wireless SHM sensor nodes, which currently have a maximum power requirement of approximately 200 mW.
29
Lambert, Luke. "Efficient probabilistic structural response prediction for aircraft turbulence and offshore wave loading." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2010819/.
Abstract:
This thesis takes an interdisciplinary approach to the problem of the aleatory uncertainty manifest in the design of engineering structures that are subject to random loading, with specific application to continuous gust loading on aircraft and wave loading on offshore structures. The main focus is on aircraft gust loading because this is the area in which more significant progress is made. A review of the literature on gust loading is carried out to evaluate the sufficiency of existing methods and the possibility of a unified certification model is discussed. In order to obtain reliable probabilistic design loads using conventional stochastic simulation techniques, a large number of simulations are required to derive probability distributions that have adequately low sampling variability in the area of interest. A novel method, called the Efficient Threshold Upcrossing method, is developed that reduces the required number of simulations by at least 2 orders of magnitude. The method is initially developed for the efficient derivation of short-term offshore structural response statistics and is subsequently applied to the modelling of aircraft response to continuous turbulence. The ETU method was successfully extended to take into account long-term statistics of nonlinear aircraft response and it was shown that reliable design exceedance curves can be obtained by as little as 4\% of the computational cost of the conventional method. The current methods for the computation of design loads for nonlinear aircraft are limited to discrete, `1~-~cosine' gust encounters as the continuous turbulence models are only applicable to linear aircraft response. However, the most significant outcome of this thesis is that this is no longer the case, because the ETU method provides a way to calculate nonlinear response statistics in the time domain at a significantly lower computational cost. Mathematical models of a simple offshore structure, and both linear and nonlinear aircraft, are developed and a more robust technique is introduced for simulating patches of continuous turbulence. These models, which have the ability to generate random inputs, are used to derive response probability distributions for each of the test structures. The results obtained by applying the new approaches to these data sets show that they offer a marked improvement in performance.
30
Huang, Haidong. "Optimal design of a flying-wing aircraft inner wing structure configuration." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7439.
Abstract:
Flying-wing aircraft are considered to have great advantages and potentials in
aerodynamic performance and weight saving. However, they also have many
challenges in design. One of the biggest challenges is the structural design of
the inner wing (fuselage). Unlike the conventional fuselage of a tube
configuration, the flying-wing aircraft inner wing cross section is limited to a
noncircular shape, which is not structurally efficient to resist the internal
pressure load. In order to solve this problem, a number of configurations have
been proposed by other designers such as Multi Bubble Fuselage (MBF),
Vaulted Ribbed Shell (VLRS), Flat Ribbed Shell (FRS), Vaulted Shell
Honeycomb Core (VLHC), Flat Sandwich Shell Honeycomb Core (FLHC), Y
Braced Box Fuselage and the modified fuselage designed with Y brace
replaced by vaulted shell configurations. However all these configurations still
inevitably have structural weight penalty compared with optimal tube fuselage
layout. This current study intends to focus on finding an optimal configuration
with minimum structural weight penalty for a flying-wing concept in a preliminary
design stage.
A new possible inner wing configuration, in terms of aerodynamic shape and
structural layout, was proposed by the author, and it might be referred as
‘Wave-Section Configuration’. The methodologies of how to obtain a structurally
efficient curvature of the shape, as well as how to conduct the initial sizing were
incorporated.
A theoretical analysis of load transmission indicated that the Wave-Section
Configuration is feasible, and this was further proved as being practical by FE
analysis. Moreover, initial FE analysis and comparison of the Wave-Section
Configuration with two other typical configurations, Multi Bubble Fuselage and
Conventional Wing, suggested that the Wave-Section Configuration is an
optimal design in terms of weight saving. However, due to limitations of the
author’s research area, influences on aerodynamic performances have not yet
been taken into account.
31
DeLaurentis, Daniel A. "A probabilistic approach to aircraft design emphasizing stability and control uncertainties." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12948.
32
Ramasamy, Thaiyal Naayagi. "Bidirectional DC-DC converter for aircraft electric energy storage systems." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/bidirectional-dcdc-converter-for-aircraft-electric-energy-storage-systems(34423ae1-ebfb-48bd-a66d-fd03b45615e7).html.
Abstract:
Future aircraft are likely to employ electrically powered actuators for adjusting flight control surfaces, and other high power transient loads. To meet the peak power demands of aircraft electric loads and to absorb regenerated power, an ultracapacitor-based energy storage system is examined in which a bidirectional dual active bridge DC-DC converter is used. This Thesis deals with the analysis, design, development and performance evaluation of the dual active bridge (DAB) converter, which can act as an interface between the ultracapacitor energy storage bank and the aircraft electrical power network. A steady-state analysis is performed for the DAB converter producing equations for the device RMS and average currents and the peak and RMS currents in the coupling inductor. This analysis focuses on understanding converter current shapes and identifying the zero-voltage switching (ZVS) boundary condition. A converter prototype was designed and built and its operation verified through SABER simulations confirming the accuracy of the analysis. Experimental results are included to support the analysis for 7kW, 20 kHz operating conditions giving a measured efficiency of 90%. To enhance the performance of the converter under light-loads, a quasi-square-wave mode of operation is proposed in which a dead-time is introduced either on the transformer primary voltage, or on the transformer secondary voltage, or simultaneously on both transformer primary and secondary. A similar detailed analysis as that for square-wave operation has been undertaken for all three cases and the converter performance was analysed focusing on ZVS operating range, impact of the RMS/peak inductor currents and converter efficiency. The theoretical work was validated through SABER simulations and proof of concept experimental measurements at 1kW, 20 kHz, which resulted in converter efficiency well above 91%. A 9%-17% improvement in efficiency and a 12%-17% improvement in ZVS operating range over square-wave operation are observed for similar operating conditions. Furthermore, a novel bidirectional current control technique for the DAB converter is presented. A SABER simulation has been performed and the converter operation is validated for square-wave and quasi-square-wave modes under steady-state and transient conditions.
33
Lock, Wai Lek Willy. "Effects of radio wave propagation in urbanized areas on UAV-GCS command and control." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FLock.pdf.
Abstract:
Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2003.Thesis advisor(s): David C. Jenn, Jeffrey B. Knorr. Includes bibliographical references (p. 85-87). Also available online.
34
Plumley, Ryan W. "Conceptual Assessment of an Oblique Flying Wing Aircraft Including Control and Trim Characteristics." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/31417.
Abstract:
A method was developed to assist with the understanding of a unique configuration and investigate some of its stability and control attributes. Oblique wing aircraft concepts are a design option that is well understood, but has yet to be used in a production aircraft. Risk involved in choosing such a design can be averted through additional knowledge early in the concept evaluation phase.
Analysis tools commonly used in early conceptual level analysis were evaluated for applicability to a non-standard aircraft design such as an oblique flying wing. Many tools used in early analyses make assumptions that are incompatible with the slewed wing configuration of the vehicle.
Using a simplified set of tools, an investigation of a unique configuration was done as well as showing that the aircraft could be trimmed at given conditions. Wave drag was investigated to determine benefits for an oblique flying wing. This form of drag was reduced by the distribution of volume afforded by the slewing of the aircraftâ s wing. Once a reasonable concept was developed, aerodynamic conditions were investigated for static stability of the aircraft. Longitudinal and lateral trim were established simultaneously due to its asymmetric nature.Master of Science
35
Rosette, Keith Andrew. "Investigation of a compact acoustic source array for the active control of aircraft engine fan noise." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-12302008-063020/.
36
Bramberger, Martina [Verfasser], and Markus [Akademischer Betreuer] Rapp. "Mountain wave impact on flight conditions of high-flying aircraft / Martina Bramberger ; Betreuer: Markus Rapp." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1188564285/34.
37
Waddington, Michael Jon. "Development of an Interactive Wave Drag Capability for the OpenVSP Parametric Geometry Tool." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1435.
Abstract:
Minimizing wave drag is critical to successful and efficient transonic and supersonic flight. Area-ruling is the process of managing the cross-sectional area of an aircraft to lessen the wave drag experienced in flight. Effectively calculating the necessary areas for a given aircraft can be difficult, and existing tools for conducting a wave drag analysis often carry limitations in both functionality and availability.
In this work, the author utilized an existing parametric geometry tool named OpenVSP to create an interactive design tool for approximating zero-lift wave drag. Here, the wave drag calculation methodology used in industry for decades is combined with the powerful geometry engine of OpenVSP, which was recently heavily upgraded at the start of 2015. Various visual aids allow users of this OpenVSP wave drag tool to interact with area and wave drag results and develop intuition for supersonic aircraft design using the area rule approach. OpenVSP allows geometry changes to be made quickly, enabling rapid reanalysis by the wave drag tool for expeditious comparison of results across the design space.
38
Borgoltz, Aurelien. "Modifications of Coherent Structures in Fan Blade Wakes for Broadband Noise Reduction." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29619.
Abstract:
The effects of trailing edge flow control on the wakes of a linear cascade of idealized fan blades was investigated experiments with a view to the likely effects on broadband aircraft engine interaction noise. Single and three-component hotwire velocity measurements were made downstream of the cascade for a chord Reynolds number of 390,000 and a Mach number of 0.07. Measurements of the two-point velocity correlation were used extensively to evaluate the impact of various flow control strategies on the organization of the coherent structures of the wakes and their potential to generate noise.
A baseline flow was established by measuring the wake downstream of unmodified GE-Rotor-B blades. Four sets of serrated trailing edge blades (with two different serration sizes and with two trailing edge cambers) and three sets of blades with trailing edge blowing (a simple rectangular slot, rectangular slot with Kuethe-vane vortex generators, and rectangular slot with serrated lips) were tested.
The serrated trailing edges introduce corrugations into the wake, increase the wake decay and width as well as turbulence levels (possibly because of the blunt trailing edge created at the serration valley). The serrated trailing edges also increase the turbulence scales in the direction perpendicular to the plane of the wake because of the injection of streamwise vorticity. In almost all cases the serrations reduce the spanwise and streamwise turbulence scales. Serrations do not, however, affect the apparent time scale of quasi-periodic structures in the wake, and this appears to limit the potential of this trailing edge treatment to reduce broadband noise. The analysis of the characteristic eddies (obtained from proper orthogonal decomposition combined with linear estimation) revealed that the serrations do not change the qualitative form of the eddies.
Trailing edge blowing was found to significantly decrease the wake deficit and width as well as the turbulence levels at all blowing rates. Blowing through the simple rectangular slot, at mass flow rates between 1.4 and 2.0% of the total passage through flow, was shown to significantly affect the size, the organization and the strength of the coherent structures. For small blowing rates the strong spanwise eddies near the trailing edge actually appear to be enhanced. For larger blowing rates, however, the turbulent scales are reduced in all directions. The addition of Kuethe vanes on the suction side of the blowing blade results in a low momentum region just downstream of the vanes that may result from flow separation there. This further enhances the shedding and increases the blowing rate needed to overcome it. The serrated blowing blades show the greatest potential to reduce broadband noise as they reduce the turbulence levels and scales without creating potentially detrimental structures.
While no acoustic measurements were made, analysis of hypothetical perpendicular and parallel interactions of blades with these wakes has made possible to characterize for the first time the impact of the changes in the eddy structure of these wakes on their potential to generate broadband noise. The serrated trailing edges (especially the larger serrations) actually increase the potential of the wake to generate broadband noise (a direct consequence in the overall increase in turbulence scale and intensity). In contrast, every trailing edge blowing configuration was found to produce large reductions in the potential noise (a maximum of 6dB reduction was obtained at 2.0% blowing). The addition of Kuethe vanes on the suction side of the blowing blades significantly reduced the efficiency of the simple blowing configuration (a result of the increased coherency associated with the shedding of streamwise vorticity by the vanes). The serrated blowing configuration was found to yield reductions similar to the simple blowing configuration.Ph. D.
39
Pundarika, G. "Experimental And Theoretical Studies On Jet Acoustics." Thesis, Indian Institute of Science, 2001. https://etd.iisc.ac.in/handle/2005/250.
Abstract:
A systematic research on aeroacoustics conducted around the world for the last few decades has revealed various inherent characteristics of the jet noise radiation. However, a lot more needs to be done for the theoretical as well as experimental predictions of various jet noise features based on actual flow details. The work reported in the present thesis is an attempt in this direction.
A critical study of existing literature on jet noise shows that none of the general wave equations lends itself easily for predictions of all the jet noise features. It is shown that while LighthilPs classical acoustic analogy approach, with some reasonable approximations, can be used to yield most of the information needed by the engineers, the convected wave equations of Phillips and Lilley are required to study the acoustic radiation in what has come to be known as "Refraction valley" or "Cone of relative silence".
The characteristics of the sound field of underexpanded cold jet impingement flows were studied by measuring the noise emanating from two convergent nozzles of throat diameter 2.5 mm and 5 mm each and a convergent - divergent nozzle of exit diameter of 6.49 mm, when the jet impinges on a flat plate kept perpendicular to the direction of the jet. The measurements were conducted upstream of the nozzle over an extensive envelope of jet operating conditions such as chamber stagnation pressure, mass flow rate through the nozzle and diameter of the nozzle.
The source strength at the jet boundary was obtained by measuring acoustic pressure amplitude close to the jet contour assuming it as locally cylindrical. Particular attention was focussed on backward projection of the sound field on to a cylindrical surface. This is the application of acoustic holography to study the sound radiation in the audio frequency region. With the help of FFT and software developed for this purpose, the theoretical predictions using data from several cylindrical surfaces were compared.
A detailed analysis of noise radiation from a cold sonic and supersonic free jet was also carried out. The experimental work involved the measurement of noise field from a 2.5 mm, 5 mm convergent and a convergent - divergent nozzle of exit diameter of 6.49 mm and area ratio 1.687 for designed Mach number of two.
The experimental setup consisted essentially of a pressure chamber made of mild steel, designed to withstand 50 bar pressure. This chamber is a cylinder with dia 0.421 m and length 0.85 m. The nozzles were made of mild steel. Compressed air approximately at room temperature is supplied to the nozzle via a control valve.
The measuring and recording instruments consists of B & K Microphones, Preamplifiers, Conditioning amplifier and a Mediator, which measure a Sound Pressure Level at a point. The nozzles were operated at pressure ratio upto 25 bar. The noise signal was processed through 12 channel data acquisition system. Acoustic pressure and SPL were" calculated using theoretical relations and software developed. Using this software Fast Fourier Transformations of raw signal was obtained from 20 Hz to 20 kHz. Also constant SPL contour graphs were obtained.
Source strength distribution at the jet boundary has been obtained by the principle of acoustic holography. Experimental values are closely matching with the results obtained by acoustic holography. The percentage error for acoustic pressure and SPL were less than 12%. The experimental results were used to obtain the source distribution in terms of gross jet parameters.
40
Pundarika, G. "Experimental And Theoretical Studies On Jet Acoustics." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/250.
Abstract:
A systematic research on aeroacoustics conducted around the world for the last few decades has revealed various inherent characteristics of the jet noise radiation. However, a lot more needs to be done for the theoretical as well as experimental predictions of various jet noise features based on actual flow details. The work reported in the present thesis is an attempt in this direction.
A critical study of existing literature on jet noise shows that none of the general wave equations lends itself easily for predictions of all the jet noise features. It is shown that while LighthilPs classical acoustic analogy approach, with some reasonable approximations, can be used to yield most of the information needed by the engineers, the convected wave equations of Phillips and Lilley are required to study the acoustic radiation in what has come to be known as "Refraction valley" or "Cone of relative silence".
The characteristics of the sound field of underexpanded cold jet impingement flows were studied by measuring the noise emanating from two convergent nozzles of throat diameter 2.5 mm and 5 mm each and a convergent - divergent nozzle of exit diameter of 6.49 mm, when the jet impinges on a flat plate kept perpendicular to the direction of the jet. The measurements were conducted upstream of the nozzle over an extensive envelope of jet operating conditions such as chamber stagnation pressure, mass flow rate through the nozzle and diameter of the nozzle.
The source strength at the jet boundary was obtained by measuring acoustic pressure amplitude close to the jet contour assuming it as locally cylindrical. Particular attention was focussed on backward projection of the sound field on to a cylindrical surface. This is the application of acoustic holography to study the sound radiation in the audio frequency region. With the help of FFT and software developed for this purpose, the theoretical predictions using data from several cylindrical surfaces were compared.
A detailed analysis of noise radiation from a cold sonic and supersonic free jet was also carried out. The experimental work involved the measurement of noise field from a 2.5 mm, 5 mm convergent and a convergent - divergent nozzle of exit diameter of 6.49 mm and area ratio 1.687 for designed Mach number of two.
The experimental setup consisted essentially of a pressure chamber made of mild steel, designed to withstand 50 bar pressure. This chamber is a cylinder with dia 0.421 m and length 0.85 m. The nozzles were made of mild steel. Compressed air approximately at room temperature is supplied to the nozzle via a control valve.
The measuring and recording instruments consists of B & K Microphones, Preamplifiers, Conditioning amplifier and a Mediator, which measure a Sound Pressure Level at a point. The nozzles were operated at pressure ratio upto 25 bar. The noise signal was processed through 12 channel data acquisition system. Acoustic pressure and SPL were" calculated using theoretical relations and software developed. Using this software Fast Fourier Transformations of raw signal was obtained from 20 Hz to 20 kHz. Also constant SPL contour graphs were obtained.
Source strength distribution at the jet boundary has been obtained by the principle of acoustic holography. Experimental values are closely matching with the results obtained by acoustic holography. The percentage error for acoustic pressure and SPL were less than 12%. The experimental results were used to obtain the source distribution in terms of gross jet parameters.
41
Poh, Seng Cheong Telly. "Simulations of diversity techniques for urban UAV data links." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FPoh.pdf.
42
Judt, Falko. "Convectively-Generated Potential Vorticity in Rainbands and Secondary Eyewall Formation in Hurricanes." Scholarly Repository, 2009. http://scholarlyrepository.miami.edu/oa_theses/214.
Abstract:
Concentric eyewall formation and eyewall replacement cycles are intrinsic processes that determine the intensity of a tropical cyclone, as opposed to purely environmental factors such as wind shear or the ocean heat content. Although extensive research has been done in this area, there is not a single widely accepted theory on the formation of secondary eyewall structures. Many previous studies focused on dynamic processes in the inner core of a tropical cyclone that would precede and ultimately lead to the formation of a secondary eyewall. Hurricanes Katrina and Rita in 2005 were frequently sampled by research aircraft which gathered a copious amount of data. During this time, Rita developed a secondary eyewall which eventually replaced the original eyewall. This thesis will investigate the formation of a secondary eyewall with particular emphasis on the rainband region, as observations show that an outer principal rainband transformed into the secondary ring. A high resolution, full physics model (MM5) initialized with global model forecast fields correctly predicted the secondary eyewall formation in Rita. The model output will be used to investigate both Katrina and Rita in terms of their PV generation characteristics since PV and vorticity maxima correlate well with wind maxima that accompany the eyewall and rainbands. Furthermore, dynamical processes such as vortex Rossby wave (VRW) activity in the inner core region will be analyzed. Comparison of the differences in the two storms might shed some light on dynamics that can lead to structure changes. Comparison of the model data with aircraft observation is used to validate the results. Doppler radar derived wind fields will be used to calculate the vertical vorticity. The vorticity field is closely related to PV and thus a manifestation of the PV generation process in the rainband. The investigation has shown that Rita?s principal rainband features higher PV generation rates at radii beyond 80 km. Both the azimuthal component and the projection of asymmetric PV generated by convection onto the azimuthal mean connected with the principal band are hypothesized to be of importance for the formation of the secondary eyewall. VRW were found not to be important for the initial formation of the ring but might enhance convective activity once the outer eyewall contracts.
43
Kincová, Daniela. "Zavedení a provoz supersonického business jetu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-232021.
Abstract:
Tato práce se zabývá problematikou zavedení a provozu nadzvukových business jetů. V dnešní době se v civilní letecké přepravě, po ukončení provozu Concordu, žádná nadzvuková letadla nevyskytují. V dnešní době existuje mnoho projektů a organizací, které se zabývají znovuzavedením nadzvukových letounů do civilního letectví a soustředí se převážně na business jety. Hlavní otázkou je, zda je vůbec vhodné, či rozumné se k tomu typu dopravy znovu vracet. Existuje hodně problémů, které toto komplikují. Tyto letouny způsobují příliš velký hluk, mají obrovskou spotřebu paliva a musí řešit nadměrné emise, létají ve vysokých výškách ve kterých může docházet k problémům s přetlakováním kabiny, navigací, radioaktivním zářením apod. Navíc zákaz supersonických letů nad pevninou letové cesty omezuje a prodlužuje. Současně vznikající projekty navíc nedosahují tak velkého doletu jako klasické moderní bussjety, což způsobuje, že se nadzvukové business jety se na delších tratích stávají neefektivní. I přes tyto problémy, je víceméně jisté, že k zavedení nadzvukových business jetů dojde během následujících 10 - 15 let, i kdyby to měla být jen otázka jisté prestiže velmi bohatých lidí.
44
"Simulation of turbulent aircraft wake vortex flows and their impact on the signals returned by a coherent Doppler LIDAR system." Université catholique de Louvain, 2008. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-02182008-162330/.
45
Poletika, Nicole Marie. ""Wake up! Sign up! Look up!" : organizing and redefining civil defense through the Ground Observer Corps, 1949-1959." Thesis, 2013. http://hdl.handle.net/1805/4081.
Abstract:
Indiana University-Purdue University Indianapolis (IUPUI)In the early 1950s, President Dwight Eisenhower encouraged citizens to “Wake Up! Sign Up! Look Up!” to the Soviet atomic threat by joining the Ground Observer Corps (GOC). Established by the United States Air Force (USAF), the GOC involved civilian volunteers surveying the skies for Soviet aircraft via watchtowers, alerting the Air Force if they suspected threatening aircraft. This thesis examines the 1950s response to the longstanding problem posed by the invention of any new weapon: how to adapt defensive technology to meet the potential threat. In the case of the early Cold War period, the GOC was the USAF’s best, albeit faulty, defense option against a weapon that did not discriminate between soldiers and citizens and rendered traditional ground troops useless. After the Korean War, Air Force officials promoted the GOC for its espousal of volunteerism and individualism. Encouraged to take ownership of the program, observers appropriated the GOC for their personal and community needs, comprised of social gatherings and policing activities, thus greatly expanding the USAF’s original objectives.
46
Pereira, da Silva Carlos Manuel Baptista. "Lamb wave based structural health monitoring of aircraft structures." Thesis, 2010. http://hdl.handle.net/1828/3630.
Abstract:
Structural Health Monitoring (SHM) through adequate damage detection and prediction of the remaining useful life of structures is a major area of interest in the aerospace community, where the growing maintenance costs can reduce the operational life of flight vehicles. The objective of a SHM system with an advanced diagnostic capability is to gradually replace current schedule-based maintenance tasks, where components are inspected following a pre-established number of cycles using condition-based maintenance, or are maintained prior to attaining an insufficient remaining useful life, based on specified confidence bounds. The research challenge is to obtain a reliable method for determining damage existence and respective location during its initial growth state as a component of an early warning system.
In this thesis, an SHM system based on Lamb waves is proposed. A damage detection algorithm based on the comparison between the damaged structural state and a reference state has been developed. The detection algorithm, based on discrete signals correlation, was tested and improved by incorporating statistical methods and domain division techniques. Two SHM system architectures, namely the sensor network and phased array system were designed, implemented and tested.
A visualization method based on the superposition of solutions obtained from a test set was implemented. Tests executed with multiple damage, representing surface and through-the-thickness holes and cracks were performed. The proposed SHM systems using Lamb waves were able to reliably detect holes of 1 mm holes in aluminum and 1.5 mm in composite plates with great confidence.Graduate
47
Chang, Ting-Hao, and 張廷豪. "Decay of the Viscous Vortex-Wakes behind a Large Aircraft." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/35509791797719052956.
Abstract:
碩士國立成功大學
航空太空工程學系
87
The wingtip trailing vortexes generated by a large aircraft are known to be stable and persistent for several miles. Since tip vortexes would cause hazardous problems in airworthiness, the prediction of the descent and decay of the vortex motion is an important factor in determining safe separation between aircrafts during landing and take-off, or flight encounter in air. The objective of this research employs the finite volume method to simulate flow fields including both wing flow and its tip vortexes. A three-dimensional full Navier-Stokes equations solver, CFD-2000 flow analysis system, is used to calculate the steady, low-speed Newtonian viscous flow over a rectangular wing with NACA 0012 sections. The vortex wake flows are simulated by turbulent and laminar flow, respectively. In this thesis, the vortex center and vortex core radius are defined by velocity and by vorticity distribution on every cross flow section in the vortex wake. The descent of the vortex center and vortex span, the growth of the vortex radii and the decay of the vortex strength of the vortex are also discussed. The results show that the descent of the vortex center and vortex span in the turbulent case are slower than those in the laminar case. Besides, from the results of more intensive diffusion of the turbulent vortex wakes near the trailing edge of the wing, the vortex strength decays faster in this flow region, but it reaches the same strength as laminar case far downstream of the wake.
48
(8028554), Yiming Wang. "PROPAGATION OF EN-ROUTE AIRCRAFT NOISE." Thesis, 2019.
Abstract:
The prediction of the noise generated by en-route aircraft is gradually gaining in importance as the number of aircraft increases over the last few decades. While the studies of outdoor sound propagation have been focused on near ground propagation, the case when the sound source is high above the ground has not attracted much attention. At the same time there has been a lack of high-quality aircraft acoustic validation data sets that contain detailed acoustic, meteorology, and source-receiver position data. The DISCOVER-AQ data set, which was collected by Volpe in support of the Federal Aviation Administration (FAA), has greatly helped with studying the directivity and the Doppler effect in the comparison between simulation results and measurements. To provide a more accurate prediction of en-route aircraft noise, we derived the analytic asymptotic solution of the sound field above a non-locally reacting ground due to a moving point source and a line source using the methods of the steepest descent and a Lorentz transform. The model predicts a much more accurate result for sound field above "soft" grounds, such as a snow-covered ground and sand-covered ground. At the same time, we derived a fast numerical algorithm based on Levin’s collocation for the prediction of the sound field in the presence of a temperature gradient, which can be applied to a wide range of acoustic problems involving integration. The achievements recorded in this thesis can be used to predict the sound field generated by aircraft, trains, and vehicles with a subsonic moving speed. In addition,
the model can be used for detection and design of moving sound source.
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Ajith, V. "Wave Propagation in Healthy and Defective Composite Structures under Deterministic and Non-Deterministic Framework." Thesis, 2012. http://etd.iisc.ac.in/handle/2005/3253.
Abstract:
Composite structures provide opportunities for weight reduction, material tailoring and integrating control surfaces with embedded transducers, which are not possible in conventional metallic structures. As a result there is a substantial increase in the use of composite materials in aerospace and other major industries, which has necessitated the need for structural health monitoring(SHM) of aerospace structures. In the context of SHM of aircraft structures, there are many areas, which are still not explored and need deep investigation. Among these, one of the major areas is the development of efficient damage models for complex composite structures, like stiffened structures, box-type structures, which are the building blocks of an aircraft wing structure. Quantification of the defect due to porosity and especially the methods for identifying the porous regions in a composite structure is another such area, which demands extensive research. In aircraft structures, it is not advisable for the structures, to have high porosity content, since it can initiate common defects in composites such as, delamination, matrix cracks etc.. In fact, there is need for a high frequency analysis to detect defects in such complex structures and also to detect damages, where the change in the stiffness due to the damage is very small. Lamb wave propagation based method is one of the efficient high frequency wave based method for damage detection and are extensively used for detecting small damages, which is essentially needed in aircraft industry. However, in order, to develop an efficient Lamb wave based SHM system, we also need an efficient computational wave propagation model. Developing an efficient computational wave propagation model for complex structures is still a challenging area. One of the major difficulty is its computational expense, when the analysis is performed using conventional FEM. However, for 1D And 2D composite structures, frequency domain spectral finite element method (SFEM), which are very effective in sensing small stiffness changes due to a defect in a structure, is one of the efficient tool for developing computationally efficient and accurate wave based damage models. In this work, we extend the efficiency of SFEM in developing damage models, for detecting damages in built-up composite structures and porous composite structure. Finally, in reality, the nature of variability of the material properties in a composite structure, created a variety of structural problems, in which the uncertainties in different parameters play a major part. Uncertainties can be due to the lack of good knowledge of material properties or due to the change in the load and support condition with the change in environmental variables such as temperature, humidity and pressure. The modeling technique is also one of the major sources of uncertainty, in the analysis of composites. In fact, when the variations are large, we can find in the literatures available that the probabilistic models are advantageous than the deterministic ones. Further, without performing a proper uncertain wave propagation analysis, to characterize the effect of uncertainty in different parameters, it is difficult to maintain the reliability of the results predicted by SFEM based damage models. Hence, in this work, we also study the effect of uncertainty in different structural parameters on the performance of the damage models, based on the models developed in the present work.
First, two SFEM based models, one based on the method of assembling 2D spectral elements and the other based on the concept of coupling 2D and 1D spectral elements, are developed to perform high frequency wave propagation analysis of some of the commonly used built-up composite structures. The SFEM model developed using the plate-beam coupling approach is then used to model wave propagation in a multiple stiffened structure and also to model the stiffened structures with different cross sections such as T-section, I-section and hat section.
Next, the wave propagation in a porous laminated composite beam is modeled using SFEM, based on the modified rule of mixture approach. Here, the material properties of the composite is obtained from the modified rule of mixture model, which are then used in SFEM to develop a new model for solving wave propagation problems in porous laminated composite beam. The influence of the porosity content on the parameters such as wave number, group speed and also the effect of variation in theses parameters on the time responses are studied first. Next, the effect of the length of the porous region (in the propagation direction) and the frequency of loading, on the time responses, is studied. The change in the time responses with the change in the porosity of the structure is used as a parameter to find the porosity content in a composite beam.
The SFEM models developed in this study is then used in the context of wave based damage detection, in the next study. First ,the actual measured response from a structure and the numerically obtained response from a SFEM model for porous laminated composite beam are used for the estimation of porosity, by solving a nonlinear optimization problem. The damage force indicator (DFI) technique is used to locate the porous region in a beam and also to find its length, using the measured wave propagation responses. DFI is derived from the dynamic stiffness matrix of the healthy structure along with the nodal displacements of the damaged structure. Next, a wave propagation based method is developed for modeling damage in stiffened composite structures, using SFEM, to locate and quantify the damage due to a crack and skin-stiffener debonding. The method of wave scattering and DFI technique are used to quantify the damage in the stiffened structure.
In the uncertain wave propagation analysis, a study on the uncertainty in material parameters on the wave propagation responses in a healthy metallic beam structure is performed first. Both modulus of elasticity and density are considered uncertain and the analysis is performed using Monte-Carlo simulation (MCS) under the environment of SFEM. The randomness in the material properties are characterized by three different distributions namely normal, Weibul and extreme value distribution and their effect on wave propagation, in beam is investigated. Even a study is performed on the usage of different beam theories and their uncertain responses due to dynamic impulse load.
A study is also conducted to analyze the wave propagation response In a composite structure in an uncertain environment using Neumann expansion blended with Monte-Carlo simulation (NE-MCS) under the environment of SFEM. Neumann expansion method accelerates the MCS, which is required for composites as there are many number of uncertain variables. The effect of the parameters like, fiber orientation, lay-up sequence, number of layers and the layer thickness on the uncertain responses due to dynamic impulse load, is thoroughly analyzed.
Finally, a probabilistic sensitivity analysis is performed to estimate the sensitivity of uncertain material and fabrication parameters, on the SFEM based damage models for a porous laminated composite beam. MCS is coupled with SFEM, for the uncertain wave propagation analysis and the Kullback-Leibler relative entropy is used as the measure of sensitivity. The sensitivity of different input variables on the wave number, group speed and the values of DFI, are mainly considered in this study.
The thesis, written in nine chapters, presents a unified document on wave propagation in healthy and defective composite structure subjected to both deterministic and highly uncertain environment.
50
Ajith, V. "Wave Propagation in Healthy and Defective Composite Structures under Deterministic and Non-Deterministic Framework." Thesis, 2012. http://hdl.handle.net/2005/3253.
Abstract:
Composite structures provide opportunities for weight reduction, material tailoring and integrating control surfaces with embedded transducers, which are not possible in conventional metallic structures. As a result there is a substantial increase in the use of composite materials in aerospace and other major industries, which has necessitated the need for structural health monitoring(SHM) of aerospace structures. In the context of SHM of aircraft structures, there are many areas, which are still not explored and need deep investigation. Among these, one of the major areas is the development of efficient damage models for complex composite structures, like stiffened structures, box-type structures, which are the building blocks of an aircraft wing structure. Quantification of the defect due to porosity and especially the methods for identifying the porous regions in a composite structure is another such area, which demands extensive research. In aircraft structures, it is not advisable for the structures, to have high porosity content, since it can initiate common defects in composites such as, delamination, matrix cracks etc.. In fact, there is need for a high frequency analysis to detect defects in such complex structures and also to detect damages, where the change in the stiffness due to the damage is very small. Lamb wave propagation based method is one of the efficient high frequency wave based method for damage detection and are extensively used for detecting small damages, which is essentially needed in aircraft industry. However, in order, to develop an efficient Lamb wave based SHM system, we also need an efficient computational wave propagation model. Developing an efficient computational wave propagation model for complex structures is still a challenging area. One of the major difficulty is its computational expense, when the analysis is performed using conventional FEM. However, for 1D And 2D composite structures, frequency domain spectral finite element method (SFEM), which are very effective in sensing small stiffness changes due to a defect in a structure, is one of the efficient tool for developing computationally efficient and accurate wave based damage models. In this work, we extend the efficiency of SFEM in developing damage models, for detecting damages in built-up composite structures and porous composite structure. Finally, in reality, the nature of variability of the material properties in a composite structure, created a variety of structural problems, in which the uncertainties in different parameters play a major part. Uncertainties can be due to the lack of good knowledge of material properties or due to the change in the load and support condition with the change in environmental variables such as temperature, humidity and pressure. The modeling technique is also one of the major sources of uncertainty, in the analysis of composites. In fact, when the variations are large, we can find in the literatures available that the probabilistic models are advantageous than the deterministic ones. Further, without performing a proper uncertain wave propagation analysis, to characterize the effect of uncertainty in different parameters, it is difficult to maintain the reliability of the results predicted by SFEM based damage models. Hence, in this work, we also study the effect of uncertainty in different structural parameters on the performance of the damage models, based on the models developed in the present work.
First, two SFEM based models, one based on the method of assembling 2D spectral elements and the other based on the concept of coupling 2D and 1D spectral elements, are developed to perform high frequency wave propagation analysis of some of the commonly used built-up composite structures. The SFEM model developed using the plate-beam coupling approach is then used to model wave propagation in a multiple stiffened structure and also to model the stiffened structures with different cross sections such as T-section, I-section and hat section.
Next, the wave propagation in a porous laminated composite beam is modeled using SFEM, based on the modified rule of mixture approach. Here, the material properties of the composite is obtained from the modified rule of mixture model, which are then used in SFEM to develop a new model for solving wave propagation problems in porous laminated composite beam. The influence of the porosity content on the parameters such as wave number, group speed and also the effect of variation in theses parameters on the time responses are studied first. Next, the effect of the length of the porous region (in the propagation direction) and the frequency of loading, on the time responses, is studied. The change in the time responses with the change in the porosity of the structure is used as a parameter to find the porosity content in a composite beam.
The SFEM models developed in this study is then used in the context of wave based damage detection, in the next study. First ,the actual measured response from a structure and the numerically obtained response from a SFEM model for porous laminated composite beam are used for the estimation of porosity, by solving a nonlinear optimization problem. The damage force indicator (DFI) technique is used to locate the porous region in a beam and also to find its length, using the measured wave propagation responses. DFI is derived from the dynamic stiffness matrix of the healthy structure along with the nodal displacements of the damaged structure. Next, a wave propagation based method is developed for modeling damage in stiffened composite structures, using SFEM, to locate and quantify the damage due to a crack and skin-stiffener debonding. The method of wave scattering and DFI technique are used to quantify the damage in the stiffened structure.
In the uncertain wave propagation analysis, a study on the uncertainty in material parameters on the wave propagation responses in a healthy metallic beam structure is performed first. Both modulus of elasticity and density are considered uncertain and the analysis is performed using Monte-Carlo simulation (MCS) under the environment of SFEM. The randomness in the material properties are characterized by three different distributions namely normal, Weibul and extreme value distribution and their effect on wave propagation, in beam is investigated. Even a study is performed on the usage of different beam theories and their uncertain responses due to dynamic impulse load.
A study is also conducted to analyze the wave propagation response In a composite structure in an uncertain environment using Neumann expansion blended with Monte-Carlo simulation (NE-MCS) under the environment of SFEM. Neumann expansion method accelerates the MCS, which is required for composites as there are many number of uncertain variables. The effect of the parameters like, fiber orientation, lay-up sequence, number of layers and the layer thickness on the uncertain responses due to dynamic impulse load, is thoroughly analyzed.
Finally, a probabilistic sensitivity analysis is performed to estimate the sensitivity of uncertain material and fabrication parameters, on the SFEM based damage models for a porous laminated composite beam. MCS is coupled with SFEM, for the uncertain wave propagation analysis and the Kullback-Leibler relative entropy is used as the measure of sensitivity. The sensitivity of different input variables on the wave number, group speed and the values of DFI, are mainly considered in this study.
The thesis, written in nine chapters, presents a unified document on wave propagation in healthy and defective composite structure subjected to both deterministic and highly uncertain environment.