Dissertations / Theses on the topic 'Ground effect'
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1
Read, Gillian Margaret. "Extreme ground effect." Title page, contents and summary only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phr284.pdf.
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2
Cai, Jielong. "Changes in Propeller Performance Due to Ground and Partial Ground Proximity." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1588164898961792.
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3
Doig, Graham Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Compressible ground effect aerodynamics." Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44696.
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The aerodynamics of bodies in compressible ground effect flowfields from low-subsonic to supersonic Mach numbers have been investigated numerically and experimentally. A study of existing literature indicated that compressible ground effect has been addressed sporadically in various contexts, without being researched in any comprehensive detail. One of the reasons for this is the difficulty involved in performing experiments which accurately simulate the flows in question with regards to ground boundary conditions. To maximise the relevance of the research to appropriate real-world scenarios, multiple bodies were examined within the confines of their own specific flow regimes. These were: an inverted T026 wing in the low-to-medium subsonic regime, a lifting RAE 2822 aerofoil and ONERA M6 wing in the transonic regime, and a NATO military projectile at supersonic Mach numbers. Two primary aims were pursued. Firstly, experimental issues surrounding compressible ground effect flows were addressed. Potential problems were found in the practice of matching incompressible Computational Fluid Dynamics (CFD) simulations to wind tunnel experiments for the inverted wing at low freestream Mach numbers (<0.3), where the inverted wing was found to experience significant compressible effects even at Mach 0.15. The approach of matching full-scale CFD simulations to scale model testing at an identical Reynolds number but higher Mach number was analysed and found to be prone to significant error. An exploration was also conducted of appropriate ways to conduct experimental tests at transonic and supersonic Mach numbers, resulting in the recommendation of a symmetry (image) method as an effective means of approximating a moving ground boundary in a small-scale blowdown wind tunnel. Issues of scale with regards to Reynolds number persisted in the transonic regime, but with careful use of CFD as a complement to experiments, discrepancies were quantified with confidence. The second primary aim was to use CFD to gain a broader understanding of the ways in which density changes in the flowfield affect the aerodynamic performance of the bodies in question, in particular when a shock wave reflects from the ground plane to interact again with the body or its wake. The numerical approach was extensively verified and validated against existing and new experimental data. The lifting aerofoil and wing were investigated over a range of mid-to-high subsonic Mach numbers (1>M???>0.5), ground clearances and angles of incidence. The presence of the ground was found to affect the critical Mach number, and the aerodynamic characteristics of the bodies across all Mach numbers and clearances proved to be highly sensitive to ground proximity, with a step change in any variable often causing a considerable change to the lift, moment and drag coefficients. At the lowest ground clearances in both two and three dimensional studies, the aerodynamic efficiency was generally found to be less than that of unbounded (no ground) flight for shock-dominated flowfields at freestream Mach numbers greater than 0.7. In the fully-supersonic regime, where shocks tend to be steady and oblique, a supersonic spinning NATO projectile travelling at Mach 2.4 was simulated at several ground clearances. The shocks produced by the body reflected from the ground plane and interacted with the far wake, the near wake, and/or the body itself depending on the ground clearance. The influence of these wave reflections on the three-dimensional flowfield, and their resultant effects on the aerodynamic coefficients, was determined. The normal and drag forces acting on the projectile increased in exponential fashion once the reflections impinged on the projectile body again one or more times (at a height/diameter ground clearance h/d<1). The pitching moment of the projectile changed sign as ground clearance was reduced, adding to the complexity of the trajectory which would ensue.
4
Purvis, Richard. "Rotor blades and ground effect." Thesis, University College London (University of London), 2002. https://ueaeprints.uea.ac.uk/20790/.
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This thesis uses numerical, asymptotic and flow structural techniques to examine various aspects of rotor blade flows and ground effect. It explores two- and three-dimensional flows, generally concentrating upon regimes that have a degree of relevance to typical rotor blade flows. Chapter 2 considers, as a first step towards understanding a general rotor blade system in ground effect, a finite rotating disc near horizontal ground. More specifically, it concentrates on determining the layer shape beyond the disc rim that, due to the presence of the ground, cannot remain flat without violating a pressure condition across it. Chapter 3 examines the flow past many blades in ground effect using both a numerical approach and considering various limits of interest to illuminate some of the important features such as enhanced lift and sheltering effects. Chapter 4 then extends this by exploring the many blade limit, whereby the flow develops a periodic structure once sufficiently many blades have been passed. We then move on to three-dimensional configurations. Chapter 5 takes the previous work further by considering the interactive case that arises after a very large number of blades have been passed, generating a pressure-displacement interaction in the boundary layer. We examine the case of three-dimensional blades, considering the full triple deck problem and then the short blade limit, investigating the flow structure for this physically relevant case. Chapter 6 considers the flow past a three-dimensional hump on a blade of a rotor, examining the flow structure and solution and tentatively using this to propose a description of the flow past the trailing corner of a typical rotor blade. Finally Chapter 7 returns to ground effect, exploring the flow past a single, three-dimensional blade near the ground. It uses a compact difference technique to examine the flow solution for a particular blade shape and investigates the idea of change-over points, where the effective leading edge becomes a trailing edge switching the boundary conditions, these points being generally unknown in advance
5
Kusmarwanto, I. "Ground effect on a rotor wake." Thesis, Cranfield University, 1985. http://dspace.lib.cranfield.ac.uk/handle/1826/4545.
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The effect of the ground on a rotor wake in
forward flight has been investigated experimentally in the
working section of an 8ft x Oft straight-through wind
tunnel. A three bladed fully articulated rotor with a
solidity ratio of 0.07 and diameter of 1.06m, powered by
a hydraulic motor, has been tested at a height of 0.47 rotor
diameter above a solid ground board which has an elliptical
leading edge.
Tests have been run at various low advance ratios
(<0.1) with two collective pitch settings.
A three-element hot wire anemometer probe has
been used to measure the average value of the three
components of velocity simultaneously in the forward half
(advancing side) of the rotor wake and in the main stream
surrounding it.
The rotor wake and the ground vortices have been
visualized by smoke. Surface flow patterns on the ground
board have located the interaction region between the rotor
wake and the oncoming flow on the ground board.
Theoretical estimates of the flowfield based on
Heyson's vortex cylinder model (Ref. 2) are compared with the
experimental results.
Both experimental results and theoretical estimates
show that the ground-induced interference is an upwash and
a decrease in forward velocity. The upwash interference'
opposes the vertical flow through the rotor, and have large
effects on the rotor performance in producing thrust. The
streamwise interference decelerates the mainstream and
becomes more noticeable as the wake boundary is approached.
6
Jones, Marvin Alan. "Mechanisms in wing-in-ground effect aerodynamics." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343624.
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An aircraft in low-level flight experiences a large increase in lift and a marked reduction in drag, compared with flight at altitude. This phenomenon is termed the 'wing-in-ground' effect. In these circumstances a region of high pressure is created beneath the aerofoil, and a pressure difference is set up between its upper and lower surfaces. A pressure difference is not permitted at the trailing edge and therefore a mechanism must exist, which allows the pressures above and below to adjust themselves to produce a continuous pressure field in the wake. It is the study of this mechanism and its role in the aerodynamics of low-level flight that forms the basis of our investigation
7
Pulla, Devi Prasad. "A study of helicopter aerodynamics in ground effect." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149869712.
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Molina, Juan. "Aerodynamics of an oscillating wing in ground effect." Thesis, University of Southampton, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582653.
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This research intends to provide new insight into the aerodynamics of wings in ground effect under dynamic motion. This work represents a new step forward in the field of race car aerodynamics, in which steady aerodynamics are well understood. As the first comprehensive study on oscillating wings in ground effect, several modes of oscillation were studied numerically, including heaving, pitching and combined motion of an airfoil and heaving of a wing fitted with endplates. A wide range of reduced frequencies were tested for the simulations at different ride heights, which showed appreciable differences with respect to a stationary wing. The flowfield around the airfoil was obtained by solving the Reynolds-Averaged Navier- Stokes equations, while Detached Eddy Simulation was used for the wing. A dynamic mesh model was implemented to adapt the grid to the wing motion. The results showed other aerodynamic mechanisms in addition to the ground effect, namely the effective incidence and added mass. Stall can be postponed to lower ride heights by increasing the frequency of heaving, while a pitching airfoil can stall below the static stall incidence when placed close to the ground. A stability analysis showed that flutter can occur at low frequencies in heaving motion but increasing the frequency always stabilises the motion. The behaviour of the vortex formed on the inboard face of the endplate is altered by the heaving motion and has an important effect on the downforce generation. Vortex breakdown can be induced or suppressed depending on the frequency and effective incidence. At high frequencies, these vortices interact with counter-rotating trailing edge vortices to form vortex loops that transform into omega vortices in the wake. Additional experiments for a stationary wing serve to qualitatively validate and complement the reference cases.
9
Roberts, L. S. "Boundary-layer transition on wings in ground effect." Thesis, Cranfield University, 2017. http://dspace.lib.cranfield.ac.uk/handle/1826/12789.
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The competitiveness of a high-performance racing car is extremely reliant on aerodynamics. Due to the current economic climate, track testing is often forsaken and the majority of aerodynamic development carried out using sub-scale wind tunnel testing and computational simulations. It is important, therefore, that experimental and computational approaches represent real-world conditions as closely as possible. Although racing cars travel at much higher speeds than typical passenger cars, in comparison to aircrafts they still operate at relatively low Reynolds numbers and, consequently, laminar and transitional phenomena are evident. Despite this, the bulk of relevant literature available for racing-car aerodynamics is undertaken with little regard to the influence of Reynolds number, and in the case of computational studies, the omission of laminar and transitional phenomena all together. The present work has demonstrated, using a super-scale two- dimensional wind-tunnel model, that laminar and transition flow phenomenon are important at Reynolds numbers equivalent to a full-scale racing car. Moreover, the influence of these aspects increased as the wing’s ground clearance reduced; meaning that in ground effect they are even more important. Further experiments with three-dimensional models of varying complexity, from a simple single-element wing to a highly complex F1-specification wing, showed that laminar phenomena are important for F1 applications as well as for lower-downforce capability racing cars. A transition-sensitive eddy-viscosity turbulence model, k-kL-w, was used to simulate inverted wings operating in ground effect. It was shown that that laminar and transitional flow states could be simulated easily inside a commercial solver, and that the model offered a substantial improvement over the classical fully-turbulent k-w SST in terms of both force coefficient prediction and surface-flow structures. This experiments and computational simulations described in this thesis show the Reynolds number sensitivity of, and importance of laminar phenomenon on, wings operating in ground effect. It has been shown that laminar boundary layers are an important aspect of the flow characteristics of wings in ground effect, at both full-scale and model-scale Reynolds numbers. As such, it is recommended that future studies incorporate laminar and transitional phenomena.
10
Igue, Roberto T. "Experimental Investigation of a lift augmented ground effect platform." Wright-Patterson AFB, OH : Air Force Institute of Technology, 2005. http://handle.dtic.mil/100.2/ADA440437.
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11
McDarby, John Michael. "Modelling of turbulent rotor-blade flow and ground effect." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444821/.
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Rotor blade flows occur in numerous physical systems from helicopters to fans, and from propellers to food mixers. Many previous studies have concentrated on the laminar flow generated by a set of rotors but in many practical cases the flow is turbulent, a setting in which previous research appears to be mainly experimental or purely numerical. The thesis examines turbulent rotor flow as its prime feature, before moving on to the impact of the ground and side structures on the flow. Whilst there exists a wide variety of rotor blade flows in industry, the present research is motivated by the application to helicopters. Using asymptotic analysis and computational methods the thesis first examines the turbulent boundary layer on a flat plate with a moving surface and, second, a rotating disc. Analytical and numerical predictions are then derived and compared with previous results. Asymmetry about the axis of rotation is introduced next and the problem of a rotating cut-disc is studied as an approximation to a set of rotors. A numerical solution is obtained and is supported by analytical results. Blade inclination and thickness are then incorporated into the three-dimensional case, with asymmetric blade shape being analyzed as if in two dimensions only. The influence of ground effect is examined firstly through the use of an image potential in the two-dimensional asymmetric blade shape problem and secondly in the axisymmetric case of flow between a stationary and a rotating disc. A numerical solution is determined and compared with existing research, whilst an analytical solution is produced for large radii. The flow between a stationary disc and a rotating cut disc is then briefly discussed before, finally, the possible extension of this thesis to the problem of turbulent jets is examined.
12
Law, Rachel Hoi-chee. "Effect of existing building on tunneling-induced ground movements." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74406.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 113-115).
The goal of this thesis is to assess the influence of an existing structure on tunneling-induced ground movements. This is accomplished through 2D numerical simulations that are compared with similar prior studies reported by Potts and Addenbrooke (1997). The current study uses the Plaxis finite element code together with the Hardening Soil (HS and HSS) family of constitutive models in order to represent the undrained shear behavior of clay. Input parameters of the HS and HSS models were calibrated for the case of London Clay and compared with results of Potts and Addenbrooke (1997) who used a non-linear elastic model (PJ model). Results have clearly indicated that the choice of soil model has an important influence on the prediction of greenfield ground settlement. The HSS model with the selected set of stiffness parameters provides a reasonable fit with the PJ model and matches closely the greenfield settlement trough expected from empirical models. Numerical analyses are carried out to evaluate the effects of the self-weight, and equivalent elastic bending and axial stiffness of a surface building on tunneling-induced ground movements. For the case of a weightless building, design modification factors for bending and axial stiffness are consistent with results promulgated in Potts and Addenbrooke (1997). For the self-weight scenario, the current analyses indicated that neglecting this factor in the analyses can result in nonconservative estimate of modification factors for deflection ratio and horizontal strain. It is therefore suggested that the effect of building weight cannot be neglected when the boundary effect of building stiffness on the ground is used as a tool to reduce the estimated values of greenfield settlement trough or deflection ratio and horizontal strain of existing buildings in a building damage assessment.
by Rachel Hoi-chee Law.
M.Eng.
13
Mahon, Stephen Alexander. "The aerodynamics of multi-element wings in ground effect." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/47619/.
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14
Ehirim, Obinna Hyacinth. "Aerodynamics and performance enhancement of a ground-effect diffuser." Thesis, Cranfield University, 2018. http://dspace.lib.cranfield.ac.uk/handle/1826/13211.
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This study involved experimental and equivalent computational investigations into the automobile-type 3―D flow physics of a diffuser bluff body in ground-effect and novel passive flow-control methods applied to the diffuser flow to enhance the diffuser’s aerodynamic performance. The bluff body used in this study is an Ahmed-like body employed in an inverted position with the slanted section together with the addition of side plates along both sides forming the ramped diffuser section. The first part of the study confirmed reported observations from previous studies that the downforce generated by the diffuser in proximity to a ground plane is influenced by the peak suction at the diffuser inlet and subsequent static pressure-recovery towards the diffuser exit. Also, when the bluff body ride height is gradually reduced from high to low, the diffuser flow as indicated by its force curve and surface flow features undergoes four distinct flow regimes (types A to D). The types A and B regimes are reasonably symmetrical, made up of two low-pressure core longitudinal vortices travelling along both sides of the diffuser length and they increase downforce and drag with reducing ride height. However, below the ride heights of the type B regime, types C and D regimes are asymmetrical because of the breakdown of one vortex; consequently a significant loss in downforce and drag occurs. The second part of the study involved the use ― near the diffuser exit ― of a convex bump on the diffuser ramp surface and an inverted wing between the diffuser side plates as passive flow control devices. The modification of the diffuser geometry with these devices employed individually or in combination, induced a second-stage pressure-drop and recovery near the diffuser exit. This behaviour was due to the radial pressure gradient induced on the diffuser flow by the suction surface ii curvature of the passive devices. As a result of this aerodynamic phenomenon, the diffuser generated across the flow regimes additional downforce, and a marginal increase in drag due to the profile drag induced by the devices.
15
Mirghasemi, Seyed Alireza. "Fractional Order Controller for Quadcopter Subjected to Ground Effect." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39252.
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Although the concept of fractional calculus was known for centuries, it was not considered in engineering due to the lack of implementation tools and acceptable performance of integer order models and control. However, recently, engineers and researchers started to investigate the potentially high performance of fractional calculus in various fields among which are acoustics, conservation of mass, diffusion equation and specifically in this thesis control theory. The intention of this thesis is to analyze the relative performance of fractional versus integer order PID controller for a quadcopter. Initially, the dynamics of the quadcopter is presented with additional consideration of the ground effect and torque saturation. Then, are introduced the concept of fractional calculus and the mathematical tools to be used for modeling fractional order controller. Finally, the performance of the fractional order controller is evaluated by comparing it to an integer order controller.
16
Caporaletti, Paola. "Tunnelling in layered ground and its effects on pre-existing masonry structures." Doctoral thesis, La Sapienza, 2005. http://hdl.handle.net/11573/917015.
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The research described in this dissertation concerns the soil movements
due to tunnelling in two layers ground condition and its effects on pre-existing
historical structures. In this introductory chapter the objectives and background of
the work are presented, followed by an overview of the methodology used to
investigate the problem and an outline of the following chapters.
17
Pouloupatis, Panayiotis. "Determination of the thermal characteristic of the ground in Cyprus and their effect on ground heat exchangers." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/10982.
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Since the ancient years, human beings were using holes and caves to protect themselves from weather conditions making it the first known form of exploiting ground’s heat, known as Geothermal Energy. Nowadays, geothermal energy is mainly used for electricity production, space heating and cooling, Ground Coupled Heat Pump (GCHP) applications, and many other purposes depending on the morphology of the ground and its temperature. This study presents results of investigations into the evaluation of the thermal properties of the ground in Cyprus. The main objectives were i) to determine the thermal characteristics of the ground in Cyprus, ii) investigate how they affect the sizing and positioning of Ground Heat Exchangers (GHE) and iii) present the results for various ground depths, including a temperature map of the island, as a guide for engineers and specifiers of GCHPs. It was concluded that there is a potential for the efficient exploitation of the thermal properties of the ground in Cyprus for geothermal applications leading to significant savings in power and money as well. Six new boreholes were drilled and two existing ones were used for the investigation and determination of i) the temperature of the ground at various depths, ii) its thermal conductivity, iii) its specific heat and iv) its density. The thermal conductivity was determined by carrying out experiments using the line source method and was found to vary in the range between 1.35 and 2.1 W/mK. It was also observed that the thermal conductivity is strongly affected by the degree of saturation of the ground. The temperature of the undisturbed ground in the 8 borehole locations was recorded monthly for a period of 1 year. The investigations showed that the surface zone reaches a depth of 0.25 m and the shallow zone 7 to 8 m. The undisturbed ground temperature in the deep zone was measured to be in the range of 18.3 °C to 23.6 °C and is strongly dependent on the soil type. Since the ground temperature is a vital parameter in ground thermal applications, the temperature of the ground in locations that no information is available was predicted using Artificial Neural Networks and the temperature map of the island at depths of 20 m, 50 m and 100 m was generated. Data obtained at the location of each borehole were used for the training of the network. Data for the sizing of GHEs based on the ground properties of Cyprus were presented in an easily accessible form so that they can be used as a guide for preliminary system sizing calculations. With the aid of Computational Fluid Dynamics (CFD) software the capacity of the GHEs in each location and the optimum distance between them was estimated. Additionally, the long term temperature variation of the ground was investigated. For the first time since a limited study in the 1970’s, a research focusing on the determination and presentation of the thermal properties of the ground in Cyprus has been carried out. Additionally, the use of Artificial Neural Networks (ANNs) is an innovative approach for the prediction of data at locations where no information is available. The publication of this information not only contributes to knowledge locally but also internationally as it enables comparison with other countries with similar climatic conditions to be carried out.
18
Zhou, Jian Mei. "Effect of nonlinear soil modeling on ground response at Macau." Thesis, University of Macau, 2010. http://umaclib3.umac.mo/record=b2182936.
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Phillips, Catriona. "Computational study of rotorcraft aerodynamics in ground effect and brownout." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1783/.
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When helicopters operate close to the ground in desert conditions, the rotor wake can entrain large amounts of dust into the flow field surrounding the aircraft. This entrainment of dust can result in the potentially dangerous condition known as brownout where the pilot loses situational awareness. Understanding the physics that governs the entrainment of dust from the ground may eventually allow the condition of brownout to be avoided completely. To enable the formation of dust clouds around helicopters to be investigated, Brown's Vorticity Transport Model~(VTM) has been enhanced to include the ability to model the entrainment of dust from the ground and the transport of this dust once in the flow field. Comparison of the predictions of the VTM with experimental results has shown the VTM to be capable of capturing the general characteristics of the dust clouds. Close examination of the formation of the dust clouds revealed that the general physics that governs the entrainment process is the same for different rotors and a universal model of this process is described. Differences in the size and density of the dust clouds that form around different rotors result from differences in the overall behaviour of the wakes that are generated. The design of a rotor can have a significant effect on the size and density of the dust cloud that is produced. The tip vortices have been identified as the main cause of the changes to the dust cloud. However, the behaviour of these tip vortices, when the rotor is operating in ground effect, is dependent on the rotor design and also on the advance ratio of the rotor. Thus, to determine the size and density of the dust cloud that would form around any particular rotor, the behaviour of the wake of that rotor must first be known.
20
Han, Wu M. Eng Massachusetts Institute of Technology. "Effect of ground motion frequency on non-structural seismic damage." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99622.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (page 88).
The need for economic consideration in structural design triggered the emergence of performance-based design to minimize material waste while achieving better performance. The displacement measurements of structures are significant to structural damage evaluation, and most seismic design methods consider the effect of peak ground acceleration, while the frequency content of seismic activities remains largely unexplored. In order to better understand the impact of low magnitude seismic activities on non-structural damage, we develop an assessment method for a specific site by comparing structural response with frequency content analysis on corresponding seismic activities. A method of analyzing frequency content of seismic activities at San Francisco is presented. By computing Discrete Fourier Transforms, time history seismic data is transformed from time domain to frequency domain. We apply structural response analysis on a representative residential/office/mixed-use building to evaluate seismic performance. We scale earthquakes with respect to the natural frequency of the target structure, and structural response simulations are performed based on scaled earthquakes. We utilize linear analysis in structural response simulations with constant damping ratio. The applicability of linear analysis as well as varying damping ratio requires further justification. A comparison between frequency content analysis and structural response is presented. The frequency content analysis provides an amplitude distribution for each seismic activity, and the magnitude of structural response is influenced by the amplitude distribution for corresponding seismic activities.
by Wu Han.
M. Eng.
21
Schembri-Puglisevich, Lara. "Large eddy simulation for automotive vortical flows in ground effect." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12555.
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Large Eddy Simulation (LES) is carried out using the Rolls-Royce Hydra CFD code in order to investigate and give further insight into highly turbulent, unsteady flow structures for automotive applications. LES resolves time dependent eddies that are modelled in the steady-state by Reynolds-Averaged Navier-Stokes (RANS) turbulence models. A standard Smagorinsky subgrid scale model is used to model the energy transfer between large and subgrid scales. Since Hydra is an unstructured algorithm, a variety of unstructured hexahedral, tetrahedral and hybrid grids are used for the different cases investigated. Due to the computational requirements of LES, the cases in this study replicate and analyse generic flow problems through simplified geometry, rather than modelling accurate race car geometry which would lead to infeasible calculations. The first case investigates the flow around a diffuser-equipped bluff body at an experimental Reynolds number of 1.01 times 10 to the power 6 based on model height and inlet velocity. LES is carried out on unstructured hexahedral grids of 10 million and 20 million nodes, with the latter showing improved surface pressure when compared to the experiments. Comparisons of velocity and vorticity between the LES and experiments at the diffuser exit plane show a good level of agreement. Flow visualisation of the vortices in the diffuser region and behind the model from the mean and instantaneous flow attempts to explain the relation or otherwise between the two. The main weakness of the simulation was the late laminar to turbulent transition in the underbody region. The size of the domain and high experimental Reynolds number make this case very challenging. After the challenges faced by the diffuser-equipped bluff body, the underbody region is isolated so that increased grid refinement can be achieved in this region and the calculation is run at a Reynolds number of 220, 000, reducing the computational requirement from the previous case. A vortex generator mounted onto a flat underbody at an onset angle to the flow is modelled to generate vortices that extend along the length of the underbody and its interaction with the ground is analysed. Since the vortex generator resembles a slender wing with an incidence to the flow, a delta wing study is presented as a preliminary step since literature on automotive vortex generators in ground effect is scarce. Results from the delta wing study which is run at an experimental Reynolds number of 1.56 times 10 to the power 6 are in very good agreement with previous experiments and Detached Eddy Simulation (DES) studies, giving improved detail and understanding. Axial velocity and vorticity contours at several chordwise stations show that the leading edge vortices are predicted very well by a 20 million node tetrahedral grid. Sub-structures that originate from the leading edge of the wing and form around the core of the leading edge vortex are also captured. Large Eddy Simulation for the flow around an underbody vortex generator over a smooth ground and a rough ground is presented. A hexahedral grid of 40 million nodes is used for the smooth ground case, whilst a 48 million node hybrid grid was generated for the rough ground case so that the detailed geometry near the ground could be captured by tetrahedral cells. The geometry for the rough surface is modelled by scanning a tarmac surface to capture the cavities and protrusions in the ground. This is the first time that a rough surface representing a tarmac road has been computed in a CFD simulation, so that its effect on vortex decay can be studied. Flow visualisation of the instantaneous flow has shown strong interaction with the ground and the results from this study have given an initial understanding in this area.
22
Fohring, Dora. "The effect of scintillation on ground-based exoplanet transit photometry." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/10954/.
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In this thesis, the effect of scintillation arising from atmospheric optical turbulence on exoplanet transit and secondary eclipse photometry is examined. Atmospheric scintillation arises from the propagation of phase aberrations resulting from wavefront perturbations due to optical turbulence high in the atmosphere. Scintillation causes intensity variations of astronomical targets, which is a problem in exoplanet transit photometry, where the measurement of a decrease in brightness of 1% or less is required. For this reason, ground-based telescopes have inferior photometric precision compared to their space-based counterparts, despite having the advantage of a reduced cost. In contrast with previous work on the detection limits of fast photometry, which is obtained for an atmosphere averaged over time, the actual scintillation noise can vary considerably from night to night depending on the magnitude of the high-altitude turbulence. From simulation of turbulent layers, the regimes where scintillation is the dominant source of noise on photometry are presented. These are shown to be in good agreement with the analytical, layer based, equations for scintillation. Through Bayesian analysis, the relationship between the errors on the light and the uncertainties on the astrophysical parameters are examined. The errors on the light curve arising from scintillation linearly increase the scatter on the astrophysical parameters with a gradient in the range of 0.68 -0.80. The noise due to the photometry aperture is investigated. It is found that for short exposure in times in good seeing, speckle noise contributes to noise in photometry for aperture sizes of up to approximately 2.3xFWHM. The results from simultaneous turbulence profiling and time-series photometry are presented. It is found that turbulence profiling can be used to accurately predict the amount of scintillation noise present in photometric observations. An investigation of the secondary eclipse of WASP-12b on the William Herschel Telescope (WHT) is performed, resulting in a high quality z’-band light curve for WASP-12b consistent with a carbon-rich model and with no evidence for strong thermal inversion.
23
Ockfen, Alex Earle. "Viscous modeling of ground effect aerodynamics of airfoil and jet." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/a_ockfen_112408.pdf.
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Thesis (M.S. in mechanical engineering)--Washington State University, December 2008.Title from PDF title page (viewed on Dec. 31, 2008). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 149-154).
24
Zerihan, Jonathan. "An investigation into the aerodynamics of wings in ground effect." Thesis, University of Southampton, 2001. https://eprints.soton.ac.uk/426058/.
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The aerodynamics of wings in ground effect has been studied using experimental and computational methods. Wind tunnel tests were used to quantify the effect of the ground on the aerodynamic performance of a wing, with the suction surface nearest to the ground. Features of the flowfield around the wing were investigated using Laser Doppler Anemometry and Particle Image Velocimetry to map the wake at the centre of the wing, and the state of the tip vortex. Initially, a single element configuration was used, both under transition free and transition fixed conditions. The application of Gurney flaps was then examined. The experimental study was completed using a double element configuration. The performance is discussed together with the flowfield results. Wind Tunnel testing was performed at a Reynolds number of approximately 0.75x10(6) based on the chord of the double element wing. The application of a computational technique has been examined using a Reynolds averaged Navier Stokes solver. Trends in the aerodynamic performance of a single element aerofoil in ground effect were predicted well using a Spalart-Allmaras turbulence model.
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Adhynugraha, Muhammad Ilham. "Longitudinal dynamics of wing in ground effect craft in waves." Thesis, Cranfield University, 2017. http://dspace.lib.cranfield.ac.uk/handle/1826/13095.
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An assessment of the longitudinal motion of a hybrid configuration called the aerodynamically alleviated marine vehicle (AAMV) with the presence of waves, is demonstrated in the thesis. The development of this type of vehicle requires a mathematical framework to characterise its dynamics with the influence of external forces due to the waves’ motion. An overview of the effect of waves towards the models of dynamics developed for wing in ground effect (WIGE) craft and high-speed marine vehicles (planing craft) is carried out. However, the overview only leads to a finding that the longitudinal stability of a lifting surface over wavy ground effect is not entirely established. Taking this fact into account, the analysis of the model is proposed for a WIGE craft configuration. A simplification is adopted considering heave motion only in the modelling of oscillation. The simplification is made to thoroughly capture the effect of oscillation toward dynamic stability of the vehicle. To support the model verification, a numerical simulation followed by a semi-empirical design method was adopted to produce aerodynamic data, both in two-dimensional and three-dimensional domains, respectively. The results show that the combination of underpinning parameters, i.e. ride height, frequency and amplitude of oscillation, remarkably influence the aerodynamics. The characteristics in aerodynamics affect the production of stability derivatives and eventually stability behaviour of the chosen configuration. Some patterns in the results are identified but there also some data that show the peculiarity. Thus further investigation is needed.
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Standingford, David William Fin. "Optimal lifting surfaces, including end plates, ground effect & thickness /." Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phs785.pdf.
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Walter, Daniel James, and Daniel james walter@gmail com. "Study of aerofoils at high angle of attack in ground effect." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080110.145138.
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Aerodynamic devices, such as wings, are used in higher levels of motorsport (Formula-1 etc.) to increase the contact force between the road and tyres (i.e. to generate downforce). This in turn increases the performance envelope of the race car. However the extra downforce increases aerodynamic drag which (apart from when braking) is generally detrimental to lap-times. The drag acts to slow the vehicle, and hinders the effect of available drive power and reduces fuel economy. Wings, in automotive use, are not constrained by the same parameters as aircraft, and thus higher angles of attack can be safely reached, although at a higher cost in drag. Variable geometry aerodynamic devices have been used in many forms of motorsport in the past offering the ability to change the relative values of downforce and drag. These have invariably been banned, generally due to safety reasons. The use of active aerodynamics is currently legal in both Formula SAE (engineering compet ition for university students to design, build and race an open-wheel race car) and production vehicles. A number of passenger car companies are beginning to incorporate active aerodynamic devices in their designs. In this research the effect of ground proximity on the lift, drag and moment coefficients of inverted, two-dimensional aerofoils was investigated. The purpose of the study was to examine the effect ground proximity on aerofoils post stall, in an effort to evaluate the use of active aerodynamics to increase the performance of a race car. The aerofoils were tested at angles of attack ranging from 0° - 135°. The tests were performed at a Reynolds number of 2.16 x 105 based on chord length. Forces were calculated via the use of pressure taps along the centreline of the aerofoils. The RMIT Industrial Wind Tunnel (IWT) was used for the testing. Normally 3m wide and 2m high, an extra contraction was installed and the section was reduced to form a width of 295mm. The wing was mounted between walls to simulate 2-D flow. The IWT was chosen as it would allow enough height to reduce blockage effect caused by the aerofoils when at high angles of incidence. The walls of the tunnel were pressure tapped to allow monitoring of the pressure gradient along the tunnel. The results show a delay in the stall of the aerofoils tested with reduced ground clearance. Two of the aerofoils tested showed a decrease in Cl with decreasing ground clearance; the third showed an increase. The Cd of the aerofoils post-stall decreased with reduced ground clearance. Decreasing ground clearance was found to reduce pitch moment variation of the aerofoils with varied angle of attack. The results were used in a simulation of a typical Formula SAE race car.
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Al-Hammoud, Abdullah. "Effect of joint design on vehicle bodyshell stiffness." Thesis, Loughborough University, 1985. https://dspace.lboro.ac.uk/2134/10336.
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The work presented in this thesis is an investigation into vehicle bodyshell structural joints, with the aim of improving their stiffness. The bodyshell joint is defined to be an area or sub-structure containing the intersection of beam-type members, the behaviour of which may be defined by a matrix determined experimentally or analytically by using the finite element method. An actual bodyshell was tested on a suitably designed rig and the primary displacement modes affecting the steady state and vibration response of a bodyshell were identified and the relevant stiffness measured by using a special transducer. The joint rotational displacements were measured in these modes and the relative importance of the joints obtained. The joints were then modified by the addition of stiffening plates and the effect on the various stiffnesses noted. To assist the analyst, a similar study was performed on the effectiveness of the panels, such as roof, floor and rear quarter. A finite element beam model was established for the bodyshell and modified until a good approximation was achieved with respect to the experiments. Some practical modification of three selected joints cut from the bodyshell was done in order to improve their stiffness. A theoretical study of the influence of spot welding size and spacing on the stiffness of two plates was made. A finite element model of an actual body joint was established and the effect on stiffness of various modifications was observed.
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Ganesh, Balakrishnan. "Unsteady aerodynamics of rotorcraft at low advance ratios in ground effect." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-03072006-145825/.
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Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2006.Narayanan Komerath, Committee Chair ; Lakshmi Sankar, Committee Member ; JVR Prasad, Committee Member ; Mark Costello, Committee Member ; A. Terrence Conlisk Jr., Committee Member.
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Senior, Andrea Elizabeth. "The aerodynamics of a diffuser equipped bluff body in ground effect." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/47113/.
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An investigation of the flow physics of a diffuser equipped bluff body in ground effect has been undertaken. Situated at the rear of a racing car undertray, the diffuser is an important component and the least understood part of the vehicle. Diffuser performance can change dramatically with vehicle ride height. This includes a significant loss in performance at low ride heights which can also be a serious vehicle safety issue. An increased understanding of the diffuser behaviour in ground effect is required to assist design improvements. An accurate experimental database of the flow field is necessary both to aid this understanding and also to provide information against which the continuing development of computational simulations may be assessed. The present research is two-fold; experimental and computational. Model tests were conducted on a generic 3D bluff body equipped with a fixed angle diffuser representative of current racing car diffusers. Extensive experimental tests in wind tunnels equipped with moving belts included mean forces, surface pressures, oilflow visualisation, laser doppler anemometry and particle image velocimetry. The 3D diffuser flow field has been measured for the first time and the results are used to analyse the behaviour of the diffuser in ground effect. Complementary RANS simulations provide valuable insight into the modelling requirements. It is known that the diffuser generates down-force by accelerating air underneath the model through the channel formed by the model underside and the ground. The diffuser flow is characterised by a counter rotating vortex pair. The present research presents a new understanding of the diffuser flow field and the mechanisms causing its behaviour in ground effect. It has been found that the behaviour of the vortices alters according to the model ride height and the pressure gradient inside the diffuser. Additional down-force is generated due to the low pressure zones associated with these vortices. At relatively large ground clearances, the vortices are coherent and strong with a high axial speed core. At these heights the down-force experienced by the model increases with reducing model ride height. This behaviour is terminated at lower ground clearances by the advent of a plateau in the down-force curve and the occurrence of breakdown in the vortices inside the diffuser. The vortex breakdown results in large, diffusive and weak vortices. Maximum down-force on the model occurs at the lowest ride height of this type of flow at the end of the plateau. A sharp reduction in the down-force occurs thereafter, due to the complete breakdown of one of the vortices. The resulting asymmetric flow consists of a single coherent vortex to one side of the flow and significant flow reversal at the other side. At very low ride heights the vortices are asymmetric and weak Down-force reduction is believed to occur as a result of the steep pressure gradient inside the diffuser which advances the vortex breakdown inside the diffuser upstream as the model ride height is reduced. At the point of down-force reduction one of the vortices breaks down completely. At very low ride heights the boundary layers at the model underside and at the moving ground are believed to merge to restrict flow through the diffuser inlet. The experimental database is comprehensive and provides the necessary tool for validation of computational modelling. A computational simulation of the flow at a high ride height successfully predicts force and surface pressure coefficients and the main flow features.
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Raikhola, Sagar Singh. "EFFECT OF DIFFERENT BASELINE CORRECTION METHODS ON THE GROUND ACCELERATION SIGNAL." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2526.
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The main objective of this study is to compare the effect of different baseline correction methods on the ground acceleration signal and on the seismic response of structures. Three for strong ground motion processing methods, namely, Chiu, Akkar and EERL methods were selected in this study. For each method, a MATLAB code was written, and used in processing ground motions recorded at Belmont, IL and Gorkha, Nepal. The processed acceleration, velocity and displacement time histories obtained from the MATLAB Code were compared to the time histories provided on the USGS website. Next, the effect of each method on the response spectra was examined for five different damping ratios. A numerical integration scheme called the state-space method was used in computing the time-domain response. Finally, to get an understanding of how the processed accelerations will affect a real structure, a four-story steel frame was modeled using RISA 3D software. The response of the frame was computed using time-history analysis and the resulting story displacements were compared, and implications for structures with different natural periods were discussed
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Fairbanks, Bonnie Marie Dobson F. Stephen. "Vigilance in Columbian ground squirrels the effects of kinship and mechanisms of the group-size effect /." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2005%20Fall/Thesis/FAIRBANKS_BONNIE_53.pdf.
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Archila, Manuel. "Nonlinear response of high-rise buildings: effect of directionality of ground motions." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/33949.
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The response of high-rise buildings to strong ground shaking depends on ground motion parameters namely: intensity, frequency content, duration and horizontal ground motion directionality. The latter has been a concern to engineers for several decades in seismic design. The prediction of the direction where ground motion will hit the building is rendered difficult because in many regions faults are not mapped to a great extent, and for regions were fault locations are known accurate prediction of ground motion directionality is impeded because ground motions have unique wave propagation characteristics along its path. The purpose of this study was to evaluate the influence of ground motion directionality on the nonlinear dynamic response of a high-rise building.
The influence of ground motion directionality was evaluated for a building case study. The building was 44 storey, and resembled general features of structural configuration commonly provided to reinforced concrete high-rise in Vancouver city. The nonlinear time history analysis (NLTHA) method was used to estimate seismic response of the building model to bi-directional ground shaking. This method was systematically applied for 40 ground motion component angles of incidence, which accounted for different ground motion directionalities ranging from 0 to 360 degrees. A suite of 3 pairs of horizontal ground motion representative of seismic hazard 2% in 50 years in Vancouver was considered for analysis.
The ground motion directionality had significant effect over the calculated building seismic response. In some scenarios at critical angle of incidence the calculated floor displacements and interstorey drifts were 4 times as large as the displacements and drifts calculated for ground motion at 0 degrees angle of incidence. The largest building response envelope was obtained for several critical angles of incidence of the ground motion components. Critical angles of incidence were distributed over the entire building’s height.
The relevance of ground motion directionality for seismic design of high-rise buildings was clearly demonstrated. The NLTHA used in conventional design practice still ignores ground motion directionality. It is concluded there is a need to develop the tools engineers can readily use to consider ground motion directionality in seismic design of modern high-rise buildings.
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Xin, Hong. "Development and validation of a generalized ground effect model for lifting rotors." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/11880.
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Chierico, Paul Stephen. "An Investigation into Ground Effect for an Underwater Biologically Inspired Flapping Foil." Thesis, University of Rhode Island, 2014. http://hdl.handle.net/10945/44417.
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CIVINSThe topic that was investigated was whether there is a lift and thrust benefit to flapping an underwater, biologically inspired three dimensional foil near the solid bottom surface (so that it was in ground effect). The experimental method used a dual canister device that allowed actuation in roll and pitch, with force sensors attached to the pitch shaft, in order to record the forces produced by the foil as it flapped. The dual canister was towed on a carriage at a constant speed in a large tow tank that had been configured to have a long run of constant, deep water depth, a very short transition period, and then another long run of constant, shallow water depth. Due to this configuration, in one run the foil was able to encounter freestream conditions and ground effect conditions. The results proved in all sixteen experimental cases for varying Strouhal number and maximum angle of attack that the mean lift coefficient near the bottom was larger than that in the freestream. A potentially useful data point, for which the mean thrust coefficient had a positive change from flapping near bottom as compared to the freestream, was found to have a change in maximum instantaneous lift force of 14%. This would give a large enough change in signal strength that it could be used as a parameter on a future underwater vehicle to control altitude above the ground. The benefit to flapping in ground effect was equivalent to a larger than 1° pitch bias difference at a zero mean lift coefficient. Additionally, there was a thrust benefit seen to flapping in ground effect, but only under certain kinematics. Though not as dramatic as the benefit in lift, there was still an 8% difference in the mean thrust coefficient observed between flapping near the bottom and flapping in the freestream, for the case where the largest change in mean thrust coefficient was observed. This could equate to a large savings in battery life, and hence a longer endurance for a vehicle taking advantage of the thrust benefit seen by flapping in ground effect. While this work remains preliminary in nature, it shows that much more useful work remains to be done to explore the benefit induced by flapping a foil close to a hard surface ground.
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Nishino, Takafumi. "Dynamics and stability of flow past a circular cylinder in ground effect." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/49931/.
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A combined experimental, computational and theoretical study is presented on the dynamics and stability characteristics of turbulent flow past a circular cylinder placed near and parallel to a moving ground. The study consists of four main parts: (i) wind tunnel experiment, (ii) numerical simulation, (iii) linear stability analysis, and (iv) proper orthogonal decomposition (POD) analysis. The main focus of the study is on the cessation of large-scale, von Karman-type vortex shedding in 'ground effect', i.e., the cessation observed when the cylinder comes close to the ground. The experiments, performed at upper-subcritical Reynolds numbers of 0.4 and 1.0 x 105, show that the cessation of von Karman-type vortex shedding and an attendant critical drag reduction of the cylinder (equipped with end-plates) occurs at the gap-to-diameter ratio h/d of around 0.35, at which point the flow through the gap between the cylinder and the ground is till not blocked at all due to the ground moving at the same speed as the free stream. It is subsequently shown that detached-eddy simulations (DES) can correctly reproduce these critical phenomena, whereas unsteady RANS simulations predict them at much smaller h/d of between 0.1 and 0.2, despite the fact that the unsteady RANS simulations are 'overly dissipative' compared with the DES. The linear stability analysis of analytical wake profiles then provides a possible explanation for the above experimental and computational results; that is, the cessation of the von Karman-type vortex shedding in ground effect may also be largely explained by the change of inviscid instability characteristics in the near wake region from 'absolutely unstable' to 'convectively unstable', in analogy with the case for a cylinder equipped with a backward splitter plate in a free stream. Finally, the near wake structure of the cylinder in ground effect is further investigated with the POD analysis. The results show that about 60% of the total kinetic energy in the near wake region (in the time-averaged sense) is contained only in the first three POD modes even when the energetically dominant, von Karman-type vortex shedding becomes intermittent at h/d = 0.4. It is also shown that both shedding and non-shedding states at this gap ratio can roughly be reproduced from the combination of these three POD modes.
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Pavlenko, Vasily. "Ground motion variability and its effect on the probabilistic seismic hazard analysis." Thesis, University of Pretoria, 2016. http://hdl.handle.net/2263/60850.
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The majority of injuries and casualties during earthquakes occur as a result of partial or complete
collapse of buildings. The assessment of possible seismic ground motions for the purposes
of earthquake-resistant design can be performed by following the deterministic or probabilistic
methodology.
Chapter 1 presents an overview of the current practice in seismic hazard analysis with emphasis
on PSHA. At present, the Cornell-McGuire method prevails in PSHA studies. Despite significant
development and modifications, this method has several controversial aspects. Absence of
an upper bound of the seismic hazard curve is one of the most disputable aspects of the method,
as it leads to unrealistic ground motion estimates for very low probabilities of exceedance. This
problem stems from using the unbounded log-normal distribution in the modelling of the ground
motion variability.
The main objective of the study was to investigate this variability and suggest a more realistic
probability distribution which would allow accounting for the finiteness of the ground motion
induced by earthquake. Chapter 2 introduces the procedure that is suitable for studying the ground
motion variability. Given the data sample, this procedure allows selecting the most plausible
probability distribution from a set of candidate models. Chapter 3 demonstrates the application
of this procedure to PGA data recorded in Japan. This analysis demonstrated the superiority of
the GEVD in the vast majority of considered examples. Estimates of the shape parameter of
the GEVD were negative in every considered example, indicating the presence of a finite upper
bound of PGA. Therefore, the GEVD provides a model that is more realistic for the scatter of the
logarithm of PGA, and the application of this model leads to a bounded seismic hazard curve.
In connection with a revival of interest in seismic intensity as an analogue for physical ground
motion parameters, the problem of accounting for anisotropy in the attenuation of MMI is considered
in Chapter 4. A set of four equations that could account for this anisotropy was proposed
and the applicability of these equations was demonstrated by modelling the isoseismal maps of
two well-recorded seismic events that have occurred in South Africa. The results demonstrated
that, in general, the new equations were superior to the isotropic attenuation equation, especially
as regards to the pronounced anisotropy.
As several different PSHA methods exist, it is important to know how the results of application
of these methods corresponded to each other. Chapter 5 presents the comparative study
of three major PSHA methods, namely, the Cornell-McGuire method, the Parametric-Historic
method, and the method based on Monte Carlo simulations. Two regions in Russia were selected
for comparison, and the PGA estimates were compared for return periods of 475 and 2475 years.
The results indicated that the choice of a particular method for conducting PSHA has relatively little
effect on the hazard estimates when the same seismic source model was used in the calculations.
The considered PSHA methods would provide closely related results for areas of moderate seismic
activity; however, the difference among the results would apparently increase with increasing
seismic activity.Thesis (PhD)--University of Pretoria, 2016.
Physics
PhD
Unrestricted
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Fernández, Prats Rafael. "Hydrodynamics of pitching foils: flexibility and ground effects." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/296444.
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En termes de propulsió la rigidesa flexural i l'efecte terra en una placa rectangular en piteig pur han estat investigats. Velocimetria per imatges per partícules, mesures de forces i moments amb una cèl·lula de carga de 6 eixos, mesures de velocitat i adquisició d'imatges de la cinemàtica de la placa han estat realitzades per estudiar els patrons de flux i les forces hidrodinàmiques en plaques de diferent flexibilitat.
La presència de la paret va millorar la velocitat de creuer fins a un 25% i l'empenta fins a un 45% per angles escombrats de 160 i 240 graus. El mecanisme físic sota aquest efecte és discutit estudiant els camps de vorticitat produïts per l'estela de l'aleta bioinspirada en un rajiforme.
Les forces hidrodinàmiques linkejades a les tècniques de visualització, van permetre calcular eficiències i camps de vorticitat promitjats en fase. Aquestes dades van revelar com l'angle escombrat de la placa juga un paper fonamental en la distribució de moment en l'estela d'una placa rígida per incrementar la propulsió.
En termes de rigidesa flexural, l'òptima flexibilitat va ser determinada amb una placa semi-flexible amb una eficiència d'un 69% amb un angle d'atac de 72 graus.En términos de propulsión la rigidez flexural y el efecto suelo en una placa rectangular en puro picheo han sido investigados. Velocimetría de imágenes por partículas, medidas de fuerzas y momentos con una célula de carga de 6 ejes, medidas de velocidad y adquisiciones de imágenes de la cinemática de la placa han sido realizadas para estudiar los patrones de flujo y las fuerzas hidrodinámicas en placas con diferentes flexibilidad. La presencia de la pared mejoró la velocidad de crucero hasta en un 25% y el empuje hasta un 45% para ángulos barridos de 160 y 240 grados. El mecanismo físico bajo este efecto es discutido estudiando los campos de vorticidad producidos por la estela de la aleta bioinspirada en un rajiforme. Las fuerzas hidrodinámicas linkadas a las técnicas de visualización, permitieron calcular eficiencias y campos de vorticidad promediados en fase. Estos datos revelaron como el ángulo barrido de la placa juega un papel fundamental en la distribución de momento en la estela de un foil rígido para incrementar la propulsión. En términos de rigidez flexural la óptima flexibilidad fue determinada con la placa semi-flexible con una eficiencia de un 69% con un ángulo de ataque de 72 grados.
The roles of the chordwise flexural stiffness and ground effect in a rectangular plate undergoing in pure pitching motion have been investigated. Digital Particle image velocimetry (DPIV), load measurement with a 6-axes balance, measurements of the swimming speed and image acquisition of the kinematics of the foil have been done to study the flow patterns and hydrodynamics forces around the flapping flexible plates. The presence of the wall enhances the cruising velocity in some cases up to 25% and the thrust by a 45% , for swept angles of 160 and 240°. The physical mechanisms underlying of this effect are discussed by studying the vorticity dynamics in the wake of the foil. Experimental data of the hydrodynamic forces and moments allowed to obtain the efficiencies of the flapping propulsion. These load measurements were linked to the wakes of the flapping foils in order to reveal configurations with higher thrust. The momentum distribution in the wake of the foil has allowed the physical explanation for the cases with highest thrust production capacity. In terms of flexural stiffness, the optimum flexibility has been determined with the semi − flexible plate up to 69% of efficiency under a swept angle of 72 degrees for Re = O(10^4) tested in the investigation.
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Adam, Fatima. "Quantification of the effect of air traffic on terminal precinct ground traffic and the corresponding ground traffic effect on kerbside and parking infrastructure requirements at O.R. Tambo International Airport." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/9991.
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The sharp increase in travel demand at ORTIA in recent years has been translated into frequent parking supply and kerbside pick-up/drop-of bay shortages, particularly during peak periods. This often results in long delays and increased frustration among those using these facilities. In an attempt to solve the terminal precinct congestion problems currently experienced at O.R.Tambo International Airport (ORTIA), a need exists to understand parking and kerbside drop-off/pick-up bay demand, so that infrastructure investment corresponds to this demand.
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Smith, Justin L. "Computational analysis of airfoils in ground effect for use as a design tool." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5291.
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Thesis (M.S.)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains viii, 59 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 51-52).
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Nathan, Nita Darshini. "The rotor wake in ground effect and its investigation in a wind tunnel." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1821/.
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Rotorcraft operating in ground effect have been known to experience beneficial performance effects as well as operational difficulties during low speed forward flight. While these have been attributed to the formation of the ground induced wake, limited experimental investigations of the wake have been conducted. Difficulties in re-creating representative forward flight ground boundary conditions in wind tunnels have meant a lack of quantitative information on the ground effect wake. This research is based on experimentally investigating the ground effect wakes of rotors in forward flight, to detail the fluid mechanics associated with the ground effect wake and to identify the influence of rotor parameters and ground boundary conditions on the formation of the ground effect wake. Particle Image Velocimetry (PIV) tests were conducted on wide regions of the ground effect wake produced by a rotor model in a wind tunnel fitted with a moving ground. Results from this research showed the ground effect wake to consist of a flow separation boundary and a region of recirculation, formed by the rotor tip vortex system trailing along the ground plane. Unsteadiness of the wake was seen to result in a constantly evolving wake, and this was observed to affect the classification of the ground effect flow regimes. Flow visualisation experiments conducted on the brownout phenomenon showed the ground effect wake features to influence the dust pick-up and transport mechanisms involved in the dust cloud formation. Experimental testing showed rotor parameters such as collective angles, rotor trim settings, rotor ground distance and root cut-out ratios to cause insignificant changes to the fluid mechanics of the ground effect wake, affecting only the location of the wake features. Effects of ground boundary conditions on the ground effect wake fluid mechanics were observed to be most significant, affecting both the location and detailed structure of the wake features. Results from this research show that ground effect experimental testing can be conducted in the wind tunnel environment and highlight the importance of accurately representing the ground boundary conditions during ground effect experimental testing.
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Moore, Nicholas John. "An experimental investigation into wing in ground effect over flat and wavy surfaces." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419402.
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Black, Sean C. E. "The effect of abrasive properties on the surface integrity of ground ferrous materials." Thesis, Liverpool John Moores University, 1996. http://researchonline.ljmu.ac.uk/5100/.
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The effect of the thermal properties of alumina and CBN abrasives on workpiece temperatures in grinding was investigated. A review of the literature revealed a lack of knowledge of the thermal properties of CBN limiting the accuracy of theoretical predictions of the heat conduction in CBN grinding. A grain contact analysis was developed to predict the energy partitioning between the workpiece and wheel. The analysis takes into account two dimensional transient heat transfer in the grain and maintains temperature compatibility at the grain wear flatworkpiece interface. The proportion of the total grinding energy entering the workpiece, termed the partition ratio, was estimated by correlating measured temperature distributions with theoretical distributions. The partition ratios when grinding with CBN were substantially lower than grinding with alumina wheels for a range of ferrous materials. The lower partition ratios with CBN grinding were attributed to the higher thermal conductivity of the CBN abrasive. The effective thermal conductivity of alumina and CBN grains were quantified by correlating the theoretical partitioning model with the measured results. The effective thermal conductivity of CBN was found to be considerably lower than the reported theoretical value albeit much higher than the effective thermal conductivity of alumina. A model to predict the background temperature in grinding was proposed based on the experimental findings. The thermal model takes into account a triangular heat flux distribution in the grinding zone, the real length of contact and experimentally validated grain thermal properties. The input parameters to the thermal model were specified. To avoid temper colours on the workpiece surface the maximum background temperature must not exceed 450 to 500deg. C. for commonly used ferrous materials.
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Heyder-Bruckner, Jacques. "The aerodynamics of an inverted wing and a rotating wheel in ground effect." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/207263/.
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This study investigates the aerodynamics of nil inverted wing in ground effect, a race car wheel and the interaction between the two components, using numerical and experimental methods. The wheels were located behind the wing at flU overlap and gap of 20mm, and the wing ride height. iu the vertical direction was the primary variable. Models of 50% scale were used , giving a Reynolds number of 5.8 x 105 based on the wing chord . The Detached-Eddy Simulation model was validated against wind tunnel measurements including PIV, surface pressures and forces , where it was found to outperform a Reynolds averaged Navier-Stokes approach which used the Spalart-Allmaras turbulence model. It accurately predicted the wing vortex breakdown at low ride heights, which is of the bubble type with a spiralling tail, and the wake of the wheel. A mesh sensitivity study revealed that a finer mesh increased the amount of structures captured with the DES model, improving its accuracy.
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Bleischwitz, Robert. "Fluid-structure interactions of membrane wings in free-flight and in ground-effect." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397261/.
Full textAbstract:
Currently, there is a growing demand to improve the aerodynamic performance of Micro-Air-Vehicles for extended mission time, higher payload capacity and improved agility. Their wings have to operate within a challenging Reynolds number regime of Re =10(4)-10(5) which is known for its low energy content in the boundary layer, causing early flow separation and loss in lift production. Flexible wings, inspired from bats, could potentially exploit given flow separations by forming lift carrying shedding structures close to the upper wing surface. The aspect-ratio is one key parameter which modifies these vortex formations and their ability to couple with the membrane. However, vortex related lift production comes at a price of increased drag and limitation in aerodynamic efficiency. Membrane wings in ground-effect could combine ground-effect related efficiency enhancement with flexibility related stall improvements. Therefore, two separate wind tunnel experiments are conducted to understand the impact of aspect-ratio and ground-effect on the fluid-structure interaction of membrane wings. Multiple high-speed recordings involve lift, drag and pitch moment measurements with a load-cell, membrane deformation measurements with photogrammetry and digital image correlation (DIC)and flow measurements with planar/stereo particle image velocimetry (PIV). Next to time-averaged quantities, reduced order models are used to group predominant flow and membrane dynamics. Synchronised fluid-membrane coupling of flexible membrane wings allows to exploit separated flow conditions to provide further lift enhancement from vortical flow formations. An exemplary membrane wing at [alpha] = 25(o) shows similar vortex-shedding to a rigid at-plate at [alpha] = 15(o), but comes with 50 % more lift production. Higher aspect-ratios are found to exploit the benefits of wing flexibility to a larger extend, showing a gain in peak-lift of up to 60% for an aspect-ratio of 2 and 31% for an aspect-ratio of 1 (in reference to rigid at-plates). Membrane wings extend their performance window in ground-effect conditions by delaying ground-effect induced premature flow separation by [DELTA alpha] = 5(o). In addition, membrane wings in ground-effect are found to be up to 30% more efficiency than rigid at-plates.
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Kim, Changmin. "Effect of Iron on Residual Nitrite Level in Ground Pork and Model Systems." DigitalCommons@USU, 1985. https://digitalcommons.usu.edu/etd/5302.
Full textAbstract:
The effects of iron, temperature, and presence of botulinal spores or sodium ascorbate on depletion of nitrite level were determined in meat and model systems. Higher temperature and presence of botulinal spores definitely increased nitrite depletion in a meat system. Added hemoglobin also significantly increased nitrite depletion, while ferrous iron and ferric iron did not significantly decrease nitrite level in a meat system. High temperature and presence of sodium ascorbate increased nitrite depletion in a model system. Only ferrous iron significantly decreased nitrite level in the absence of ascorbate, while ferric iron, heme iron, and ferritin iron did not decrease nitrite level in the absence of ascorbate. Ferrous iron, ferric iron, and heme iron decreased nitrite level in the presence of ascorbate, while ferritin iron did not decrease nitrite level in a model system.
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Eberhart, Gina M. "Modeling of Ground Effect Benefits for Multi-Rotor Small Unmanned Aerial Systems at Hover." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1502802483367365.
Full text
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Mondal, Partha. "Wing in Ground Effect." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/2848.
Full textAbstract:
The thesis presents a two pronged approach for predicting aerodynamics of air- foils/wings in the vicinity of the ground. The first approach is effectively a model for ground effect studies, employing an inexpensive Discrete Vortex Method for the 2D pre- dictions and the well known Numerical lifting line theory for the 3D predictions. The second one pertains to the dynamic ground effect analysis which employs the state of the art moving mesh methodology based time accurate CFD. In that sense, the thesis deals with two ends of spectrum in the ground effect analysis; one, a model to be used in the concept design phase and the other an advanced CFD tool for analysis.
The proposed model for ground effect studies is based on the well known Discrete Vortex Method (DVM). An important aspect of this method is that it employs what is referred to as the Generalized Kutta Joukowski Theorem (GKJ), meant for interaction problems with multiple vortices, for predicting the lift (and drag) within a potential flow framework. After ascertaining the correctness of using the GKJ theorem for lift prediction for airfoils in ground effect, a modified DVM is presented as a model for ground effect predictions. As per this model, knowing the free stream lift and drag (either from an ex- periment or from a RANS computation) the aerodynamics of the section in ground effect can be predicted. The model is effectively built by constraining the DVM to produce the reference lift/drag in the free stream. The accuracy of the model, particularly for the more relevant high lift sections used during take-off and landing, is systematically estab- lished for a number of test cases. Knowing the sectional ground effect, the extension to 3D analysis is very simple and this is achieved through the well known Numerical Lifting Line theory. The efficacy of the proposed method for the 3D applications is demonstrated using a high lift wing in ground effect. It is worth noting that the proposed model predicts the lift and drag very accurately, practically at no computational cost as compared to modern RANS based CFD tools requiring over 40 or 50 million volumes at a high computational cost and intense human intervention for generating the grids for every ground clearance.
The other aspect of the thesis pertains to what is referred to as the Dynamic Ground Effect. Normally the CFD computations mimic the ground effect experiments in simulat- ing the ground effect. These simulations do not maintain geometric similarity with the actual landing or take-off sequence of the aircrafts and this can only be achieved when the simulations are dynamic. Dynamics is also important in case of combat aircrafts (particularly their naval versions) with an aggressive landing and take-off. The dynamic ground effect simulations also provides a framework for simulating varied gust conditions. This dynamic simulation of the ground effect is accomplished using a novel sinking grid methodology, which allows the grids to sink in the ground as the aircraft approaches the ground along the glide path. These simulations make use of the state of the art, time accurate moving grid methods and therefore can be computationally expensive. Never- theless, the utility of such computations in terms of their ability to produce continuous data has been highlighted in the thesis. In that sense, these dynamic computations will be cheaper as compared to the static simulations to produce data at the same level of resolution.
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Mondal, Partha. "Wing in Ground Effect." Thesis, 2013. http://etd.iisc.ernet.in/handle/2005/2848.
Full textAbstract:
The thesis presents a two pronged approach for predicting aerodynamics of air- foils/wings in the vicinity of the ground. The first approach is effectively a model for ground effect studies, employing an inexpensive Discrete Vortex Method for the 2D pre- dictions and the well known Numerical lifting line theory for the 3D predictions. The second one pertains to the dynamic ground effect analysis which employs the state of the art moving mesh methodology based time accurate CFD. In that sense, the thesis deals with two ends of spectrum in the ground effect analysis; one, a model to be used in the concept design phase and the other an advanced CFD tool for analysis.
The proposed model for ground effect studies is based on the well known Discrete Vortex Method (DVM). An important aspect of this method is that it employs what is referred to as the Generalized Kutta Joukowski Theorem (GKJ), meant for interaction problems with multiple vortices, for predicting the lift (and drag) within a potential flow framework. After ascertaining the correctness of using the GKJ theorem for lift prediction for airfoils in ground effect, a modified DVM is presented as a model for ground effect predictions. As per this model, knowing the free stream lift and drag (either from an ex- periment or from a RANS computation) the aerodynamics of the section in ground effect can be predicted. The model is effectively built by constraining the DVM to produce the reference lift/drag in the free stream. The accuracy of the model, particularly for the more relevant high lift sections used during take-off and landing, is systematically estab- lished for a number of test cases. Knowing the sectional ground effect, the extension to 3D analysis is very simple and this is achieved through the well known Numerical Lifting Line theory. The efficacy of the proposed method for the 3D applications is demonstrated using a high lift wing in ground effect. It is worth noting that the proposed model predicts the lift and drag very accurately, practically at no computational cost as compared to modern RANS based CFD tools requiring over 40 or 50 million volumes at a high computational cost and intense human intervention for generating the grids for every ground clearance.
The other aspect of the thesis pertains to what is referred to as the Dynamic Ground Effect. Normally the CFD computations mimic the ground effect experiments in simulat- ing the ground effect. These simulations do not maintain geometric similarity with the actual landing or take-off sequence of the aircrafts and this can only be achieved when the simulations are dynamic. Dynamics is also important in case of combat aircrafts (particularly their naval versions) with an aggressive landing and take-off. The dynamic ground effect simulations also provides a framework for simulating varied gust conditions. This dynamic simulation of the ground effect is accomplished using a novel sinking grid methodology, which allows the grids to sink in the ground as the aircraft approaches the ground along the glide path. These simulations make use of the state of the art, time accurate moving grid methods and therefore can be computationally expensive. Never- theless, the utility of such computations in terms of their ability to produce continuous data has been highlighted in the thesis. In that sense, these dynamic computations will be cheaper as compared to the static simulations to produce data at the same level of resolution.
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Chen, Hen-Chung, and 陳恆權. "Ground Effect of 3D Subsonic Flying Vehicle." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/20365210365714526486.
Full textAbstract:
碩士國立成功大學
航空太空工程學系
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The objective of the present research is to study the ground effect of a low-flying three-dimensional subsonic vehicle. Morino''s panel method and the method of image were used as the analysis tool. The ground effect can be decomposed into steady and unsteady parts using the superposition principle. The steady ground effect is attributed to the height of a flying vehicle in the proximity over a flat ground. It was found in the steady flow numerical study that, as the height reduces, the lift increases and the pitching moment decreases with the pressure center moves ahead. The unsteady disturbances, however, come from the combined contribution due to the height and the surface wave movement. Moreover, this wave-induced unsteady disturbances can be thought as a modification of the downwash distribution over the body surface, whose strength is found to be in proportion to the product of the amplitude and the convective speed of the wave. Only the theoretical formulation was done presently for the unsteady ground effect, and the related numerical investigation will be performed in the future.