Dissertations / Theses on the topic 'Low winds'
To see the other types of publications on this topic, follow the link: Low winds.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Low winds.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Anderson, Bruce T. "Investigation of summertime low-level winds over the Gulf of California and the Southwestern United States /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035918.
2
Dahmer, Marc R. Market Patrick S. "Investigating near-surface wind fields as influenced by low-level jet occurrences in Missouri." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6555.
Abstract:
The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on November 13, 2009). Thesis advisor: Dr. Patrick S. Market Includes bibliographical references.
3
Steinhoff, Daniel Frederick. "Cyclogenesis Near the Adélie Coast and Influence of the Low-level Wind Regime." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204812781.
4
Sridharan, S. "Investigation of middle atmospheric winds, waves and tides from low latitudes." Thesis, IIG, 2002. http://localhost:8080/xmlui/handle/123456789/1604.
Abstract:
A Thesis submitted to the Moanonmaniam Sundaranar University, Tirunelveli, in partial fulfilment of the requirements for the Ph.D. degree under the guidance of Dr. S. Gurubaran, Equatorial Geophysical Research Laboratory, Tirunelveli and Dr. N. Arunachalam, M.S. University, Tirunelveli
5
Sridharan, S. "Investigation of middle atmospheric winds, waves and tides from low latitudes." Thesis, Indian Institute of Geomagnetism, Mumbai, 2002. http://localhost:8080/xmlui/handle/123456789/221.
6
Simon, M. N., I. Pascucci, S. Edwards, W. Feng, U. Gorti, D. Hollenbach, E. Rigliaco, and J. T. Keane. "TRACING SLOW WINDS FROM T TAURI STARS VIA LOW-VELOCITY FORBIDDEN LINE EMISSION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622166.
Abstract:
Using Keck/HIRES spectra (Delta v similar to 7 km s(-1)) we analyze forbidden lines of [O I] 6300 angstrom, [O I] 5577 angstrom. and [S II] 6731 angstrom. from 33 T Tauri stars covering a range of disk evolutionary stages. After removing a high-velocity component (HVC) associated with microjets, we study the properties of the low-velocity component (LVC). The LVC can be attributed to slow disk winds that could be magnetically (magnetohydrodynamic) or thermally (photoevaporative) driven. Both of these winds play an important role in the evolution and dispersal of protoplanetary material. LVC emission is seen in all 30 stars with detected [O. I] but only in two out of eight with detected [S. II], so our analysis is largely based on the properties of the [O. I] LVC. The LVC itself is resolved into broad (BC) and narrow (NC) kinematic components. Both components are found over a wide range of accretion rates and their luminosity is correlated with the accretion luminosity, but the NC is proportionately stronger than the BC in transition disks. The full width at half maximum of both the BC and NC correlates with disk inclination, consistent with Keplerian broadening from radii of 0.05 to 0.5 au and 0.5 to 5 au, respectively. The velocity centroids of the BC suggest formation in an MHD disk wind, with the largest blueshifts found in sources with closer to face-on orientations. The velocity centroids of the NC, however, show no dependence on disk inclination. The origin of this component is less clear and the evidence for photoevaporation is not conclusive.
7
Koleiny, Ali Fox Neil I. "An investigation into the contribution of the low-level jet (LLJ) to the available wind resource in Missouri." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6574.
Abstract:
The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on November 18, 2009). Thesis advisor: Dr. Neil I. Fox. Includes bibliographical references.
8
Davila, Ricardo Cruz. "A Study of Magnetic Activity Effects on the Thermospheric Winds in the Low Latitude Ionosphere." DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/6808.
Abstract:
The purpose of this thesis is to examine the effects of magnetic activity on the low latitude F-region thermospheric winds. The F-region (120-1600 km) is a partially ionized medium where O+ and O are the major ion and neutral species, respectively. The thermospheric winds at these altitudes are driven primarily by pressure gradient forces resulting from the solar heating during the day and cooling at night. For this study, we use measured Fabry-Perot Interferometer (FPD winds at Arequipa (16.5°S, 71.5°W) and measured FPI and Incoherent Scatter Radar (ISR) winds at Arecibo (18.6°N, 66.8°W).
Previous wind studies at Arequipa and Arecibo concentrated on the climatological wind patterns highlighting solar cycle effects and seasonal variations; however, these studies did not address the effects of magnetically disturbed conditions on the seasonal averaged winds. To properly investigate storm time effects on the neutral winds, we must first investigate solar cycle effects on the seasonal averages during magnetically quiet (Kp < 3) conditions. This study will include a detailed analysis of solar cycle effects on the seasonally averaged winds for Arequipa and Arecibo. In addition to the wind averages, we used cubic splines to fit the average wind profiles and to provide better comparisons with modeled results. We also performed a study on the airglow emission heights using both Jicamarca and Arecibo electron density profiles. This established the height which we will use to compare our experimental data with the model winds.
To investigate magnetic activity effects on the FPI and ISR winds, we used three magnetic activity cases which cover all storm time scenarios. These magnetic activity cases are the extended quiet, short-term disturbed, and extended disturbed conditions. The first case, the extended quiet, is the condition where the previous and short term magnetic activity is quiet (12 hour Kp ≤ 3 and the Kp ≤ 3). The short-term disturbed case is defined for the condition where the previous magnetic activity is quiet (12 hour Kp ≤ 3) and then becomes disturbed (Kp ≤ 3). Last, we considered the case where previous and short-term magnetic activity are disturbed (12 hour Kp ≤ 3 and the Kp ≤ 3).
Our last objective is to use our data to validate the predictions from the Thermosphere/Ionosphere General Circulation model (TIGCM93) and the Horizontal Wind Model (HWM93). This study should further our understanding of the physical processes which produce the low latitude quiet and disturbed winds. The TIGCM93 is a first principal model and the HWM93 is an empirical model based on ground-based and satellite measurements. The main advantage of using the TIGCM93 is the ease of studying the dynamics of ionospheric phenomena by simply changing various model inputs, while the HWM93 allows us a comparison between our experimental wind data sets with the established climatology of the winds over Arequipa and Arecibo.
9
Wannberg, Veronica Elaine. "Quantitative Uncertainty of Chemical Plume Transport in Low Wind Speeds Using Measured Field Data and Stochastic Modeling." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2570.pdf.
10
Wos, Kenneth A. Davidson Kenneth L. "A climatology of polar low occurrences in the Nordic Seas and an examination of katabatic winds as a triggering mechanism." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School; Available from the National Technical Information Service, 1992. http://edocs.nps.edu/npspubs/scholarly/theses/1992/Dec/92Dec_Wos.pdf.
11
Wos, Kenneth A. "A climatology of polar low occurrences in the Nordic Seas and an examination of katabatic winds as a triggering mechanism." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23831.
Abstract:
This study examines polar low formation frequency, origin region and storm tracks in the entire Nordic Sea region for a complete polar low season and identifies the prevailing synoptic situation common to polar low formation. The number of polar lows detected through TIROS-N satellite imagery between September 1988 and May 1989 was significantly greater than one would expect from previous studies. Many polar lows were detected over the land areas of Greenland, Iceland and Svalbard away from a direct surface heat source. The storms detected over Greenland generally formed at the outflows of glacial valleys. To determine probable formation areas, polar lows were linearly backtracked along the reciprocal of their storm tracks. A significant number were backtracked to glacier outflows. These formation locations suggest a katabatic influence on storm formation, possibly due to vortex stretching, or the enhancement and distortion of an over-ice or over-land boundary layer baroclinic zone. Katabatic flows were examined by analyzing one month of regional surface synoptic observations and NOGAP 1000 mb height gradients. To develop aids to enhance polar low forecasting, monthly mean 1000 and 500 mb fields for chart times closest to polar low detection, or time backtracked to Northern, Central and Southern Greenland, were calculated from archived NOGAPS 12 hourly analyses and compared to the monthly averaged climatology fields of height and temperature
12
Planella, Morató Jesús. "Intermittency of turbulence in natural waters: patchiness in the thermocline of a lake under low winds and small-scale intermittency in the bottom boundary layer of a tidal flow." Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/320432.
Abstract:
Turbulence intermittency influences so many processes in natural waters on a wide range of scales. This work analyzes intermittency, both internal and external, by considering two cases: the thermocline of a small lake under low winds and the bottom boundary layer of a tidal flow.
External intermittency in Lake Banyoles is studied based on patches. Variability of their sizes and turbulent scales is described using probability models, which are consistent with marine turbulence results. Dynamics of mixing depends on the phase of the dominant internal seiche. Episodic and powerful wind gusts generate large patches in the lake's interior.
Internal intermittency is analyzed based the analysis of tidal flow data. Scaling exponents of structure functions and moments of the dissipation rate fit to multifractal model. For energetic episodes intermittency parameters approach the values expected for fully developed turbulence. They increase with decreasing of Reynolds numbers, which is associated with underdeveloped turbulence.El comportament intermitent de la turbulència afecta molts processos en els sistemes aquàtics. Aquest treball estudia la intermitència interna i externa en dos casos particulars: la termoclina d'un estany sota vents fluixos i la capa de fons d'un corrent de marea. La intermitència externa a l'estany de Banyoles s'analitza estudiant la variabilitat de mides i escales turbulentes dels claps, que s'ajusten bé als models de probabilitat obtinguts també en turbulència marina. La dinàmica de barreja depèn de la fase de la seca interna dominant a l'estany. Els claps grans generats a l'interior s'han relacionat amb cops de vent episòdics forts. La intermitència interna s'analitza en un corrent de marea (funcions d'estructura i moments de la dissipació). Els exponents d'escalatge s'ajusten a models multifractals, amb paràmetres propers als de turbulència completament desenvolupada per a episodis energètics. Aquests augmenten quan el nombre de Reynolds disminueix, possiblement degut a turbulència no completament desenvolupada.
13
Zelenke, Brian Christopher. "An empirical statistical model relating winds and ocean surface currents : implications for short-term current forecasts." Thesis, Connect to the title online, 2005. http://hdl.handle.net/1957/2166.
14
Calderon, Dario. "Plunging low aspect ratio wings in low Reynolds number flows." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616645.
Abstract:
A growing desire exists to develop Micro Air Vehicles (MA Vs) that fall within a 15cm span. Their small scale and low operating flight speeds encourage a low Reynolds Number (Re) regime, in the order of Re - 104 - 105 . Wings under these conditions are highly susceptible to separated flows, posing a significant challenge for the MA V. Natural flyers are able to confront these issues through flapping flight, which has inspired an entire research field on the aerodynamics of oscillating wings. While the number of parameters that govern the problem is exhaustive, studies are required to explain the contribution of each and any phenomena that may ensue. This lends itself to a canonical approach. This thesis presents an experimental study on various wing geometries, undergoing a small amplitude oscillation in the form of a pure plunge. The focus lies on understanding the three-dimensional effects of oscillating a finite wing with a positive geometric angle of attack, to encourage greater lift than that achieved from an unforced wing. This expands on the current research which predominantly focuses on the thrust generating capabilities of a 'flapping' airfoil. Force measurements, hot-film measurements, Particle Image Velocimetry (PIV) and volumetric velocimetry, are used to examine the performance and flow topology that ensues from actuating the various wings. The study presents time-averaged force measurements as a function of Strouhal number (non-dimensionalised plunge frequency) for the various low aspect ratio wings. It is shown that while the finite nature of these wings suppresses lift, significant improvements are nonetheless possible. For example, a semi Aspect Ratio = 2 NACA0012 rectangular wing, is able to achieve 180% more lift than the unforced wing. A phenomenon arises in which peaks are observed in the time-averaged lift curve, for various rectangular and delta wing planforms. This suggests optimal lift conditions at particular Strouhal numbers. In a similar manner to a 2D airfoil the oscillating wing stimulates the formation of both leading and trailing-edge vortices. The trajectory and timing of these vortices, in relation to the plunge cycle, appear to be significantly affected by Strouhal number. At particular frequencies, the vortices interact in such a way that their induced flow generates a significant region of low velocity, recirculating flow near the wing. The size of the recirculating region closely correlates with the shape of the time-averaged lift curve, agreeing well with points of troughs and peaks when this region is maximised and minimised, respectively. It is thought that these Wing/vortex and vortex/vortex interactions contribute to the selection of optimal frequencies, and therefore determine optimal lift for the oscillating wing.
15
Sathaye, Sagar Sanjeev. "Lift distributions on low aspect ratio wings at low Reynolds numbers." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0427104-091112.
Abstract:
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: Low Reynolds Number; Micro Air Vehicle; Low Aspect Ratio; Spanwise pressure measurements; Spanwise Lift Distributions. Includes bibliographical references (p. 84-85).
16
Frith, Steven Pierre. "Flapless control for low aspect ratio wings." Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577239.
17
Rullan, Jose Miguel. "The Aerodynamics of Low Sweep Delta Wings." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/29386.
Abstract:
The aerodynamics of wings with moderately swept wings continues to be a challenging and important problem due to the current and future use in military aircraft. And yet, there is very little work devoted to the understanding of the aerodynamics of such wings. The problem is that such wings may be able to sustain attached flow next to broken-down delta-wing vortices, or stall like two-dimensional wings, while shedding vortices with generators parallel to their leading edge. To address this situation we studied the flow field over diamond-shaped planforms and sharp-edged finite wings. Possible mechanisms for flow control were identified and tested. We explored the aerodynamics of swept leading edges with no control. We presented velocity and vorticity distributions along planes normal and parallel to the free stream for wings with diamond shaped planform and sharp leading edges. We also presented pressure distributions over the suction side of the wing. Results indicated that in the inboard part of the wing, an attached vortex can be sustained, reminiscent of delta-wing type of a tip vortex, but further in the outboard region 2-D stall dominated even at 13° AOA and total stall at 21° AOA. To explore the unsteady flow field and the effectiveness of leading-edge control of the flow over a diamond-planform wing at 13° AOA, we employed Particle Image Velocimetry (PIV) at a Reynolds number of 43,000 in a water tunnel. Our results indicated that two-D-like vortices were periodically generated and shed. At the same time, an underline feature of the flow, a leading edge vortex was periodically activated, penetrating the separated flow, eventually emerging downstream of the trailing edge of the wing. To study the motion and its control at higher Reynolds numbers, namely 1.3 x 106 we conducted experiments in a wind tunnel. Three control mechanisms were employed, an oscillating mini-flap, a pulsed jet and spanwise continuous blowing. A finite wing with parallel leading and trailing edges and a rectangular tip was swept by 0°, 20°, and 40° and the pulsed jet employed as is control mechanism. A wing with a diamond-shaped-planform, with a leading edge sweep of 42°, was tested with the mini-flap. Surface pressure distributions were obtained and the control flow results were contrasted with the no-control cases. Our results indicated flow control was very effective at 20° sweep, but less so at 40° or 42°. It was found that steady spanwise blowing is much more effective at the higher sweep angle.Ph. D.
18
Tregidgo, Luke. "Low aspect-ratio rigid, flexible and membrane wings at low Reynolds numbers." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577740.
Abstract:
The interest in developing small, payload-carrying Micro Air Vehicles (MAVs) with a maximum linear dimension of six inches or below is as strong as ever, with both military and civilian bodies interested in the remote sensing capabilities such a vehicle would provide. However significant challenges remain in developing such aircraft and the research presented here addresses specific issues in the field of fluid-structure interactions for flexible wings. Wind tunnel tests were conducted on rectangular, aspect-ratio-two, rigid and flexible wings (including membrane wings) in an open-jet, closed-loop facility at the University of Bath. The chord Reynolds number for the experiments was in the range 34,000≤Rec≤69,000. Measurements of force, deformation and flow velocities were taken using a variety of techniques including Digital Image Correlation (DIC) and Particle Image Velocimetry (PIV). The key findings were that flexible wings experience different eigenmode vibrations and amplitudes. This was shown to be dependent on the incidence angle of the wing to the incoming flow. Through measurements of the flow-field it was further shown that as the incidence angle increased, the behaviour of the separated shear-layer was responsible for the changes in structural mode. There was a further change as the flow became fully separated and dominated by bluff-body vortex shedding. Dynamic pitching of the wings, to simulate gust encounters, highlighted the complex nature of the fluid-structure interactions. Time lags between the flow features and structural response suggested hysteresis effects also play a role. Tests conducted on free-to-roll wings demonstrated that self-excited ‘wing rock’ oscillations are possible for this configuration of wing at incidence angles either side of stall. These oscillations were driven by dynamic differences in the strength and position of the two tip vortices. When subjected to forced pitching manoeuvres, synchronisation of the roll phase and frequency were observed. Given the right combination of pitch frequency and amplitude, this offered a method of attenuating the self-excited rolling motion.
19
Marchenko, S. V. "Wind inhomogeneities in low-Z environment : observations." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1776/.
Abstract:
We discuss the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is $sim 1/5 Z_odot$. We were able to detect and follow numerous small-scale wind-embedded inhomogeneities in all observed stars. The general properties of the moving features, such as their velocity dispersions, emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.
20
Harvey, Scott A. "Low-speed wind tunnel flow quality determination." Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5584.
Abstract:
Approved for public release; distribution is unlimited.lected points. Incorporated instrumentation includes pressure transducers attached to a pitot-static tube, wall static pressure taps, and a pressure rake; a hotwire anemometry system, and a linear traverse system. These were integrated with a data acquisition (DAQ) processor with analog to digital conversion and digital I/O boards, and controlled using in-house developed LabVIEW software. Testing showed a maximum axial velocity of 38 m/s, which is 84% of the tunnel?s rated speed. The 2-D flow uniformity was within ±7% by pressure rake, and ±3% with a turbulence intensity ?0.11% at full speed using a CTA, affirming the tunnel?s viability as a demonstration platform. Spectral density plots in the boundary layer exhibit typical behavior of fully developed equilibrium turbulent flow with an intertial sub-range present. Future testing of a flat-plate wake for drag modification is planned.
21
Usui, Michiko. "AEROMECHANICS OF LOW REYNOLDS NUMBER INFLATABLE/RIGIDIZABLE WINGS." UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_theses/321.
Abstract:
Use of an inflatable/rigidizable wing is explored for Mars airplane designs. The BIG BLUE (Baseline Inflatable-wing Glider Balloon Launched Unmanned airplane Experiment) project was developed at the University of Kentucky, with an objective to demonstrate feasibility of this technology with a flight-test of an high-altitude glider with inflatable/rigidizable wings. The focus of this thesis research was to design and analyze the wing for this project. The wings are stowed in the fuselage, inflate during ascent, and rigidize with exposure to UV light. The design of wings was evaluated by using aerodynamic and finite element software and wind tunnel testing. The profile is chosen based upon aerodynamic results and consideration of manufacturability of the inflatable wing structures. Flow over prototypes of inflatable/rigidizable and ideal shaped wings were also examined in the wind tunnel. Flow visualization, lift and drag measurements, and wake survey testing methods were performed. Results from the wind tunnel testing are presented along with suggestions in improving the inflatable/rigidizable wings aerodynamic efficiency and use on a low Reynolds number platform. In addition, high altitude wing deployment tests and low altitude flight tests of the inflatable/rigidizable wing were conducted.
22
Keeli, Anupama. "Low frequency transmission for remote power generating systems." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41190.
Abstract:
The goal of this Masters Thesis research is to evaluate alternative transmission systems from remote wind farms to the main grid using low-frequency AC technology. Low frequency means a frequency lower than nominal frequency (60/50Hz). The low-frequency AC network can be connected to the power grid at major substations via cyclo-converters that provide a low-cost interconnection and synchronization with the main grid. Cyclo-converter technology is utilized to minimize costs which result in systems of 20/16.66 Hz (for 60/50Hz systems respectively). Low frequency transmission has the potential to provide an attractive solution in terms of economics and technical merits.
23
Alam, Muhammad Mahbubul. "Wind-driven rotodynamic pumps for low-lift applications." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359007.
24
Prevezer, Tanya. "Wind pressure fluctuations on a low-rise building." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287236.
25
Wang, Shuai. "The low-level wind structure of tropical cyclones." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/44564.
Abstract:
The main effects of tropical cyclones include high winds, extensive storm surges, and widespread flooding. These main effects are all closely related to the low-level wind structure, the height of which is about 2 km from the underlying surface. A physically based analytic model (λ model) is presented to describe the low-level wind structure of tropical cyclones in terms of one intensity measure, one size measure, and the storm meridional position. The λ model provides an accurate fit of the near-surface azimuthal wind field simulated with an idealized full-physics numerical model. This numerical model is further applied to investigate the tropical cyclone low-level wind structure evolution during the mature stage with observations. Three basic features at the mature stage are observed: the outward expansion of eyewall, the reduction of intensity and the increase of tangential wind in the outer spiral bands. Model simulations show that the outer circulation expansion is accompanied by the outward migration of diabatic heating at mid-level in the eyewall. The outward movement of eyewall is caused by the opposing angular momentum transports. Consequently, the intensity decays due to the angular momentum conservation and cyclostrophic adjustment, which is captured in a new analytic pressure-wind relationship derived from the λ model. To investigate the relationship between the tropical cyclone damage and low-level wind structure, the λ model is used to reconstruct the historical wind structure of hurricanes that allows us, for the first time, to calculate the correlation of damage with the integrated wind profile of all hurricanes at landfall since 1988. We find that those metrics, which include the horizontal wind structure, rather than just maximum intensity, are better correlated with the hurricane cost. The vertical wind shear over the main development region of hurricanes plays a more dominant role than the sea surface temperature in controlling these metrics and therefore also ultimately the cost of hurricanes.
26
Feldman, Michael A. "Efficient Low-Speed Flight in a Wind Field." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36527.
Abstract:
A new software tool was needed for flight planning of a high altitude, low speed unmanned aerial vehicle which would be flying in winds close to the actual airspeed of the vehicle. An energy modeled NLP formulation was used to obtain results for a variety of missions and wind profiles. The energy constraint derived included terms due to the wind field and the performance index was a weighted combination of the amount of fuel used and the final time. With no emphasis on time and with no winds the vehicle was found to fly at maximum lift to drag velocity, Vmd. When flying in tail winds the velocity was less than Vmd, while flying in head winds the velocity was higher than Vmd. A family of solutions was found with varying times of flight and varying fuel amounts consumed which will aid the operator in choosing a flight plan depending on a desired landing time. At certain parts of the flight, the turning terms in the energy constraint equation were found to be significant. An analysis of a simpler vertical plane cruise optimal control problem was used to explain some of the characteristics of the vertical plane NLP results.Master of Science
27
Carrion, Marina. "Low mach number CFD for wind turbine analysis." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2005639/.
Abstract:
To maximise the amount of energy extracted from wind turbines, the rotor diameter has increased, reaching values of 160m in some cases. Large scale wind turbines are working at high Reynolds numbers and a wide range of flow conditions, with virtually incompressible flow present at the root and mildly compressible near the blade tips, where the Mach numbers can reach locally 0.48 for the largest wind turbines employed to date. In traditional aerodynamics, most CFD methods were designed to cope with high Mach number flows and consequently solve the compressible Navier-Stokes equations. This is the case of the Helicopter Multi-Block (HMB2) CFD method from Liverpool University. The present PhD thesis aims to provide an all-Mach-number capability to the HMB2 method, by implementing modified Roe schemes to account for low-Mach flows. For 2D cases, the modified Roe schemes showed great improvement in the convergence and the quality of the solution, when compared with the Original Roe and Osher schemes, and the Low-Mach Roe scheme showed the best performance. With the low-Mach capability included in the compressible solver, both MEXICO and NREL Annex XX experiments were simulated. A detailed analysis of the velocity field behind the MEXICO rotor was performed, where the low-Mach scheme (LM-Roe) showed less sensitivity on the grid size than the Osher scheme. Accurate prediction of wind turbine wake breakdown is also important for the performance analysis of the turbines and their optimal positioning within tightly-spaced wind farms. Using a fine mesh able to preserve the vortices up to 8R downstream the MEXICO rotor plane, the instabilities on the wake leading to vortex pairing were captured. FFTs of the axial velocity component enabled to identify the main harmonics in the wake. In the stable region, the wake was a perfect spiral and the main frequency was the bladepassing one. An approximate exponential growth was then observed and in the region where instabilities were present, higher frequencies dominated, leading an oscillatory pattern. Simple wake models were also investigated and a combination between a kinematic model to account for the wake initial expansion and a field model to account for the far wake decay was proposed, showing good agreement with the CFD solution. With the correct set of constants, it was proved that this simple model can be used to approximate the behaviour of wind turbine wakes with minimal computational cost. Another consequence of the increased size of wind turbines is that their stiffness lowers and aeroelasticity therefore plays an important role, since the blades can suffer great deformations. To account for the blade deformations, a tightly coupled CFD-CSD method was employed to analyse the MEXICO and NREL Annex XX wind turbines. For the latter, the tower and nacelle were considered as stiff bodies and the blades were allowed to deform. As a result of the aeroelastic calculations, the blades showed deformation in bending (towards the tower). The maximum deflections were present after the blades had passed in front of the tower, and maximum amplitudes of 0.59%R, at 20m/s were observed.
28
Erten, Huseyin. "The production of low alcohol wines by aerobic yeasts." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/702.
29
Gresham, Nicholas T. "Free-to-roll oscillations of low aspect ratio wings." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538123.
30
Abtahi, Ali A. "Aspect ratio effects on wings at low Reynolds numbers." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/52330.
Abstract:
In this study the primary objective was to determine the effect of aspect ratio in particular and in general the effect of three dimensionality on the flow around wings at low Reynolds numbers. It was seen that the effects observed at high Reynolds number are also present in this Re range. There is the usual increase in lift slope and this increase can even be predicted with reasonable accuracy using Prandtl's lifting line theory. In addition to the change in lift slope the zero lift angle of attack was also influenced by the aspect ratio.
Through flow visualization it was ascertained that the wingtips have a rather restricted effect on the laminar separation bubble. The disappearance of the bubble extends only for a small distance inboard from the tips.
The size of the hysteresis loop and the Reynolds number at which hysteresis starts was found to be influenced by the aspect ratio.
The momentum deficit method was used to validate the data obtained by the strain gauge method and there was adequate agreement between the values found through the two methods.
From the measurements of pressure done around the airfoil contour one could determine both the location of the laminar separation bubble and the regions were flow is separated. The pressure taps themselves were found to influence measurements somewhat in certain regions of angle of attack and Reynolds number.
In the future it would be beneficial to continue strain gauge measurements on this airfoil with flaps and control surfaces to determine their effect on the formation of the laminar separation bubble. Also measurements on other shapes would give more insight into the phenomena occurring here. The effects of turbulence and noise will have to be investigated in detail to determine what performance to expect from an actual aircraft. Finally detailed measurements on boundary layer stability and its effect on the occurrence of reattachment should be studied in detail to gain insight into the reasons for the presence of a hysteresis loop in stall at these Reynolds numbers.Ph. D.
31
Borujerdi, Javad. "Numerical evaluation of low-slope roofs for wind uplift." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26588.
Abstract:
This dissertation contributes to an ongoing research project at the National Research Council Canada in the evaluation of roofing systems for wind uplift design. Accomplishments are grouped in two tasks. Task one provides development of a knowledge-based design module for the estimation of wind load distribution on roofs. Task two, numerical modeling using finite element methods and experiments to investigate the performance of roofing systems subjected to wind uplift loads.
For the Task one, all the data of wind uplift pressure distribution on roof configurations from open literature, including studies using wind tunnel boundary layer and full-scale measurements, are reviewed.
For the Task two, various mechanically attached single-ply roofing systems were numerically modeled based on the Finite Element program with the capability of non-linear analysis. Experiments were also carried out and data obtained from the Dynamic Roofing Facility was used for benchmarking the developed model. Since, there is no consensus on table size for evaluation of roofing system in various test procedures, the validated model was further used to investigate the effect of table size. (Abstract shortened by UMI.)
32
Kumaresannair, Suresh Kumar. "Simulation of fluctuating wind pressures on low building roofs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/NQ39782.pdf.
33
Balaramudu, Vasanth Kumar. "Tornado-induced wind loads on a low-rise building." [Ames, Iowa : Iowa State University], 2007.
34
Pietrzak, J. D. "Low frequency response of coastal waters to wind forcing." Thesis, Swansea University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638531.
Abstract:
The low frequency flow dynamics of the N.W. Aegean Sea, are investigated using a barotropic shelf circulation model, and by analysis of data from current meters deployed in Thermaikos Gulf. The performance of Groves (1955) and Lanczos-cosine filters is assessed to provide optimal low-pass filtering for the current meter records. The Lanczos-cosine filter is found to be the most effective in the present study. Time series and spectral analysis are applied to the filtered current meter records and to concurrent meteorological data. The results of these analyses show significant inputs of low frequency energy at periods of 2-4 days, 6-8 days and 20-26 days. An anomalous energy band exists that is uncorrelated with the wind and which is absent from one current meter record. The results from a depth-integrated momentum balance suggest that these bands are related to direct meteorological forcing. The 2-4 day band is related to 3-dimensional coastal water processes. The 6-8 day band is described in terms of internal Kelvin waves and the 20-26 day band is related to continental shelf waves. The anomalous band with 11-13 day period is associated with freshwater forcing from rivers. The low frequency shelf circulation of the Aegean Sea is modelled analytically. Solutions to the two-dimensional vorticity equation written in terms of stream functions are sought within a circular basin with exponential cross-shelf topography. The dispersion relations for the propagation of free waves is given. Introduction of the ageostrophic approximation allows solution to the wind-forced vorticity equation wherein, parameter separation leads to a wave equation soluble by the method of characteristics. The separation parameter is determined from the associated Sturm-Liouville equation. The damped wave problem is also solved. The model predicts the propagation of continental shelf waves, with periods of 20-26 days around the Aegean Sea.
35
Claudepierre, Seth G. "Solar wind driving of magnetospheric ultra-low frequency pulsations." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315834.
Abstract:
Thesis (Ph.D.)--University of Colorado at Boulder, 2008.Source: Dissertation Abstracts International, Volume: 69-07, Section: B, page: 4214. Advisers: Scot R. Elkington; Keith Julien. Includes supplementary digital materials.
36
Jones, Robin. "Aerodynamics of biplane and tandem wings at low Reynolds numbers." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.693328.
Abstract:
Overcoming the difficulties associated with low Reynolds number flows has recently become a primary goal for aerodynamicists due to the growing importance of micro air vehicles (MAVs). The limiting size requirement of a six-inch wing span for MAVs combined with their inherent tendency to suffer stall due to gusts makes this significantly more challenging. The use of two-wing configurations, inspired by historical aircraft, could prove to be an effective method of overcoming this limitation. This thesis is primarily concerned with the fundamental aerodynamics associated with biplane and tandem wing configurations at a low Reynolds number using experimental evidence. Experiments were performed at a Reynolds number, based on wing chord, of Re = 10^5 in a return-circuit open-jet wind tunnel. The wing models were rectangular flat planform wings with a semi-aspect ratio of two. The effects of streamwise and crosswise wing separation, spanwise wing flexibility, angle of attack and decalage (the relative incidence of two wings) are considered. Experiments considering the effects of streamwise and transverse wing separation in rigid wings without decalage revealed that at post-stall angles of attack, lift performance improves and stall is delayed significantly for many two-wing configurations. For a given angle of attack, there are optimal transverse wing separations for which total lift coefficient is maximised. Particle image velocimetry (PIV) measurements reveal five characteristic flow regimes. The aerodynamic characteristics of two-wing configurations depend heavily on the nature of the accelerated inter-wing flow. This accelerated flow has a profound influence on the separated shear layers emanating from the leading and trailing edges of both wings. Unsteady forces intensify for certain two-wing configurations. High flow unsteadiness and large lift fluctuations are associated with either a switching between stalled and unstalled states over the trailing-wing's suction surface or a switching between merged and distinct wing wakes. Combinations of spanwise flexible wings with rigid wings for two streamwise wing separations, ΔX/c = 0.5 and 1.5, at an angle of attack of 30° were investigated with force measurements. The selected data compare rigid-leading rigid-trailing (R-R) wing configurations with flexible-leading rigid-trailing (F-R) wing configurations for ΔX/c = 1.5 (α = 30°). The transverse wing separation was varied systematically from -1.5 to 1.5 chord lengths. PIV, Digital Image Correlation (DIC) and hot-wire measurements were performed to further investigate the nature of these two cases. For the F-R case, transverse wing separations between 0.0 and 0.4 chord lengths exhibit increased lift coefficients relative to the R-R case; the main benefit in lift generation is for the trailing-wing. For the F-R configuration, spanwise deformation of the leading-flexible wing shifts the impingement point of the trailing-edge shear layer on the trailing-wing thus affecting lift generation. DIC measurements show that the presence of the rigid-trailing wing has a profound influence on the flow-induced vibrations of the leading-flexible wing. These flow induced vibrations reach the greatest amplitude at a transverse separation of 0.32 chord lengths, matching the largest unsteady forces. Hot-wire velocity spectra measurements reveal that cases producing increased unsteady forces possess distinct inter-wing velocity fluctuations which are coupled with the wing vibrations. The results demonstrate that the time-averaged forces and unsteady fluid-structure interactions are strongly determined by the crosswise wing separation and the spanwise flexibility of the leading-wing in tandem configurations. To investigate the effects of decalage (differing wing angle), experiments were performed for three cases in the stalled regime. Force measurements demonstrate that the use of decalage can strongly enhance the lift characteristics of two-wing configurations in the stalled regime. PIV measurements show that performance relies heavily on the augmentation of downwash and the occurrence of a secondary trailing edge recirculation region. Configurations producing enhanced aerodynamic and power efficiency are associated with reduced recirculation regions and increased downwash. Configurations yielding enhanced lift characteristics are associated with increased downwash as well as significant entrainment of the wake over the upper/leading wing due to the accelerated inter-wing flow. The stall of the upper/leading wing is consistently coupled with a secondary recirculation region due to the upper/leading wing's trailing edge shear layer. A significant transverse wing separation dependence occurs for a fixed leading wing incidence of 25° and trailing wing incidence of -10°. A very sharp discontinuity in time-average force coefficients between ΔY/c = -0.75 and -0.6 occurs for this case and a similar discontinuity is observed for a trailing wing incidence of -5°. Flow fields reveal a sensitive flow regime transition which is highly dependent on the transverse wing separation. Three configurations with increased unsteadiness were identified in the force data; instantaneous PIV measurements reveal subtle and intermittent inter-wing flows encroaching through the wake. Significant unsteady forces are only found to occur in the considered configurations (with decalage) when the wings' wakes are merged.
37
Pitt, Ford Charles William. "Unsteady aerodynamic forces on accelerating wings at low Reynolds numbers." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608219.
38
Sangpanich, Umarin. "Optimization of wind-solar energy systems using low wind speed turbines to improve rural electrification." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18944.
Abstract:
Electricity is significant in improving the quality of life for people in rural and remote areas in developing countries. There are two main options for Rural Electrification (RE), namely grid extension and stand-alone systems. The governments and developers face the challenges of their limitations, namely technical, economic and environmental effects of each RE choice. This thesis intends to improve RE by focusing on renewable energy technologies, namely Wind Turbine (WT) and Photovoltaic (PV) systems. They have been developed and applied to RE because they are simple and environmentally friendly. They can be installed as separate units and they are sustainable alternative energy solutions. Installation, cost and performance are crucial issues of WT and PV applications, and are based on the terrain and climate where the renewable are installed. The efficiency of WTs and PV modules has increased, while their cost has declined continuously. However, a PV system still has installatio n costs around two times more expensive per watt than WTs. Most WTs using current technology can be financially worthwhile for high wind speed areas, having wind speeds greater than 6.4 m/s at 10 m hub height, but most rural areas have wind speeds of less than 6 m/s at the same height. Therefore, Low Wind Speed Turbines (LWSTs) have evolved, by increasing rotor diameter and while maintaining similar generator capacity. This is to reduce Levelized Cost of Energy (LCOE) for WTs in low wind speed areas. This thesis proposes simple cost models, namely the Sum-component cost model and the Total-cost model in order to calculate the LCOE of LWSTs. In addition, novel aspects of this thesis are that the optimization processes of stand-alone hybrid WT-PV systems and hybrid WT-PV systems using batteries at peak demand in remote area power systems provide simple, fast and flexible methods, by applying Multi-objective Evolutionary Algorithm (MOEA). The MOEA can analyze complex objective problems a nd provide an accurate multi-objective method. Results from relevant case studies show that the cost models and the optimization processes proposed are novel and are valuable tools for analysis and design, including the approaches for improving the system reliability and for estimating the Initial Capital Cost (ICC) of WTs having different rated wind speeds. The proposed algorithms are generic and can be utilized for other energy planning problems.
39
Joseph, Liselle AnnMarie. "Transition Detection for Low Speed Wind Tunnel Testing Using Infrared Thermography." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78145.
Abstract:
Transition is an important phenomenon in large scale, commercial, wind tunnel testing at low speeds because it is an excellent indicator of an airfoil performance. It is difficult to estimate transition through numerical techniques because of the complex nature of viscous flow. Therefore experimental techniques can be essential. Over the transition region the rate of heat transfer shows significant increases which can be detected using infrared thermography. This technique has been used predominantly at high speeds, on small models made of insulated materials, and for short test runs. Large scale testing has not been widely undertaken because the high sensitivity of transition to external factors makes it difficult to detect.
The present study records the process undertaken to develop, implement and validate a transition detection system for continual use in the Virginia Tech Stability Wind Tunnel: a low speed, commercial wind tunnel where large, aluminium models are tested. The final system developed comprises of two high resolution FLIR A655sc infrared cameras; four 63.5-mm diameter circular windows; aluminium models covered in 0.8-mm silicone rubber insulation and a top layer of ConTact© paper; and a series of 25.4-mm wide rubber silicone fiberglass insulated heaters mounted inside the model and controlled externally by experimenters. This system produces images or videos of the model and the associated transition location, which is later extracted through image processing methods to give a final transition location in percentage chord.
The system was validated using two DU96-W-180 airfoils of different chord lengths in the Virginia Tech Stability Wind Tunnel, each tested two months apart. The system proved to be robust and efficient, while not affecting the airfoil performance or any other system in use in the wind tunnel. Transition results produced by the system were compared to measurements obtained from pressure data and stethoscope tests as well as the numerical predictions of XFOIL. The transition results from all four methods showed excellent agreement with each other for the two models, for at least two Reynolds numbers and for several angles of attack on both suction and pressure side of the model. The agreement of data obtained under such different conditions and at different times suggests that the infrared thermography system efficiently and accurately detects transition for large aluminium models at low speeds.Master of Science
40
Gough, Tim. "Low Reynolds number turbulent boundary layers and wakes." Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360949.
41
Schmidt, Sarah Ruth. "Computational and wind tunnel studies of shelterbelts for reduction of wind flow and wind-induced loads on low-rise buildings." [Ames, Iowa : Iowa State University], 2008.
42
Ames, Richard Gene. "On the flowfield and forces generated by a rectangular wing undergoing moderate reduced frequency flapping at low reynolds number." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12468.
43
Sehn, Kevin. "Aerodynamic mitigation of extreme wind loading on low-rise buildings." [Ames, Iowa : Iowa State University], 2008.
44
Janajreh, Isam Mustafa II. "Wavelet Analysis of Extreme Wind Loads on Low-Rise Structures." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30414.
Abstract:
Over the past thirty years, extensive research has been conducted with the objective of reducing wind damage to structures. Wind tunnel simulations of wind loads have been the major source of building codes. However, a simple comparison of pressure coefficients measured in wind tunnel simulations with full-scale measurements show that the simulations, in general, underpredict extreme negative pressure coefficients. One obvious reason is the lack of consensus on wind tunnel simulation parameters.
The wind in the atmospheric surface layer is highly turbulent. In simulating wind loads on structures, one needs to simulate the turbulent character besides satisfying geometric and dynamic similitudes. Some turbulence parameters that have been considered in many simulations include, turbulence intensities, integral length scales, surface roughness, and frequency spectrum. One problem with these parameters is that they are time varying in the atmospheric boundary layer and their averaged value, usually considered in the wind tunnel simulations, cannot be used to simulate pressure peaks.
In this work, we show how wavelet analysis and time-scale representation can be used to establish an intermittency factor that characterizes energetic turbulence events in the atmospheric flows. Moreover, we relate these events to the occurrence of extreme negative peak pressures.Ph. D.
45
Saha, Nilanjan. "Gap Size Effect on Low Reynolds Number Wind Tunnel Experiments." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35938.
Abstract:
A system was designed to measure the effect of gap size on semi-span low Reynolds number wind tunnel experiments. The lift forces on NACA 1412, NACA 2412 and NACA 4412 half wings were measured using a strain gauge balance at chord Reynolds numbers of 100,000 and 200,000 and three different gap sizes including sealed gap. Pressure distributions on both airfoil top and bottom surfaces in the chord-wise direction near the gap were recorded for these airfoils. Also recorded was the span wise pressure distribution on both the airfoil surfaces at the quarter chord section. The results revealed that the presence of the gap, however small, affects the measurements. These effects were mainly observed in drop of lift and change in zero lift angle of attack and change in stall angle for the airfoil. The size of the gap is not linearly related to these changes, which also depend on the camber of the airfoil. These changes occur due to the flow through the gap from the lower surface to the upper surface of the model. The wing/end plate gap effect reduces along the span but is not fully restricted to the base of the model and the model behaves more like a full three-dimensional wing than a semi-span model. This study was made possible with the support of Department of Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University under the supervision of Dr. James MarchmanMaster of Science
46
Standridge, Zachary Dakotah. "Design and Development of Low-cost Multi-function UAV Suitable for Production and Operation in Low Resource Environments." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/83877.
Abstract:
A new flying wing design has been developed at the Unmanned Systems Lab (USL) at Virginia Tech to serve delivery and remote sensing applications in the developing world. The fully autonomous unmanned aerial vehicle (UAV), named EcoSoar, was designed with the goal of creating a business opportunity for local entrepreneurs in low-resource communities. The system was developed in such a way that local fabrication, operation, and maintenance of the aircraft are all possible. In order to present a competitive financial model for sustained drone services, EcoSoar is made with reliable low-cost materials and electronics. This paper lays out the rapid prototyping and flight experiment efforts that went into polishing the design, test results from an EcoSoar centered drone workshop in Kasungu, Malawi, and finally a range optimization study with flight test validation.Master of Science
47
Hu, Tianxiang. "Attenuation of self-induced roll oscillations of low-aspect-ratio wings." Thesis, University of Bath, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619294.
Abstract:
Micro Air Vehicles are currently receiving growing interest because of their broad applications in many fields. However, in MA V flight tests, the onset of unwanted large-amplitude roll oscillations for various designs has been reported, which has eventually led to difficulties in flight control and such undesirable selfinduced roll oscillations were investigated in the current study. More specifically, a common low-aspect-ratio wing, an AR = 2 rectangular flat plate, was researched, with the aim being to attenuate the self-induced roll oscillation of low-aspect-ratio wings by applying various flow control techniques. These flow control techniques were applied using in three completely different approaches using three different flow control techniques, i) global active excitation, ii) local active excitation and iii) passive flow control. The global active excitation was achieved by using external acoustic forcing and it is found that the self-induced roll oscillations of AR = 2 flat plate wing can be completely suppressed as well as the onset of the roll oscillations delayed using this method. Similar results were also obtained for wings with airfoil profiles of NACA0012 and SD7003-085-88. In addition, the velocity measurements indicated that acoustic excitation could restore a symmetric vortex flow over the free-to-roll wings and thus eliminate the self-induced roll oscillations. Frequency spectral study revealed that acoustic excitation could energize the shear layer instabilities and result in reattachment or a smaller separated flow region over the suction surface of the wings, thereby, attenuating the roll oscillations.
48
Disotell, Kevin James. "Low-Frequency Flow Oscillations on Stalled Wings Exhibiting Cellular Separation Topology." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449162356.
49
Jeyaratnam, Jonathan Jehan. "On the low speed longitudinal stability of hypersonic waveriders." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/22456.
Abstract:
The development of hypersonic civilian transport aircraft requires solutions to a number of challenging problems in the areas of aerothermodynamics, control, aeroelasticity, propulsion and others encountered at high Mach number flight. The desire for good aerodynamic performance at high Mach numbers results in slender vehicle designs called waveriders. The stability and handling of waverider shapes at the low speeds at the take-off and landing phases of flight is not well studied. This thesis covers static and dynamic CFD simulations of the Hexafly-Int glider which have been used to obtain longitudinal stability derivatives at low speeds. Complementary static and free-to-pitch dynamic wind tunnel testing, are used to validate the CFD computations. A final chapter on the optimisation of waverider designs including low speed longitudinal stability is presented to show the impacts of this additional requirement on the hypersonic design space. The static wind tunnel testing has identified stability issues relating to the location of the centre of gravity. The design centre of gravity which is suitable for the Hexafly-Int vehicle at Mach 7.2 is found to be too far aft which results in instability at low speeds. In addition, the dynamic testing in the wind tunnel shows that the pitch damping is inadequate at low speeds. The CFD simulations agree well with the wind tunnel test results validating the use of CFD tools for determining dynamic stability derivatives of this class of slender vehicle in the design process. To alleviate the low speed stability issue of hypersonic vehicles, a waverider shape optimisation study has been carried out to understand what shapes will produce better low speed stability behaviour. These shapes are found to produce lower aerodynamic efficiency at high speeds which suggests that a design compromise between low speed stability and high speed performance is required at the outset of hypersonic waverider design.
50
Burton, Melissa Deanne. "Effects of low frequency wind-induced building motion on occupant comfort." online access from Digital Dissertation Consortium, 2006. http://libweb.cityu.edu.hk/cgi-bin/er/db/ddcdiss.pl?3268726.