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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Boundary-Layer Stability and Transition on a Flared Cone in a Mach 6 Quiet Wind Tunnel

Hofferth, Jerrod William 16 December 2013 (has links)
A key remaining challenge in the design of hypersonic vehicles is the incomplete understanding of the process of boundary-layer transition. Turbulent heating rates are substantially higher than those for a laminar boundary layer, and large uncertainties in transition prediction therefore demand conservative, inefficient designs for thermal protection systems. It is only through close collaboration between theory, experiment, and computation that the state of the art can be advanced, but experiments relevant to flight require ground-test facilities with very low disturbance levels. To enable this work, a unique Mach 6 low-disturbance wind tunnel, previously of NASA Langley Research Center, is established within a new pressure-vacuum blow-down infrastructure at Texas A&M. A 40-second run time at constant conditions enables detailed measurements for comparison with computation. The freestream environment is extensively characterized, with a large region of low-disturbance flow found to be reliably present for unit Reynolds numbers Re < 11×10^6 m-1. Experiments are performed on a 5º half-angle flared cone model at Re = 10×10^6 m-1 and zero angle of attack. For the study of the second-mode instability, well-resolved boundary-layer profiles of mean and fluctuating mass flux are acquired at several axial locations using hot-wire probes with a bandwidth of 330 kHz. The second mode instability is observed to undergo significant growth between 250 and 310 kHz. Mode shapes of the disturbance agree well with those predicted from linear parabolized stability equation (LPSE) computations. A 17% (40 kHz) disagreement is observed in the frequency for most-amplified growth between experiment and LPSE. Possible sources of the disagreement are discussed, and the effect of small misalignments of the model is quantified experimentally. A focused schlieren deflectometer with high bandwidth (1 MHz) and high signal-to-noise ratio is employed to complement the hot-wire work. The second-mode fundamental at 250 kHz is observed, as well as additional harmonic content not discernible in the hot-wire measurements at two and three times the fundamental. A bispectral analysis shows that after sufficient amplification of the second mode, several nonlinear mechanisms become significant, including ones involving the third harmonic, which have not hitherto been reported in the literature.
142

Identifikace podmínek nestability v makromodelech finančních cyklů / Identifying the Conditions of Instability in Macromodels of Financial Cycles

Zenáhlík, Aleš January 2017 (has links)
The purpose of this thesis is to construct an endogenous macroeconomic model explaining the cause of financial cycles and systemic instability based on the financial instability hypothesis (FIH) published by Hyman Minsky (1982). FIH maintains that capitalist financial systems have an inherent disposition to fi- nancial instability because periods of economic prosperity encourage borrowers and lenders to be increasingly reckless which in turn lead to the formation of financial bubbles. The problem is approached by employing an adaptive ex- pectations model based on stylized facts from Kaldor's and Kalecki's models with addition of behavioral equations implemented in an attempt to simulate market expectations. JEL Classification E02, E11, E32 Keywords Instability, Macromodel, Cycles Author's e-mail ales.z@hotmail.com Supervisor's e-mail jaromir.baxa@fsv.cuni.cz
143

Lending Sociodynamics and Drivers of the Financial Business Cycle

J. Hawkins, Raymond, Kuang, Hengyu January 2017 (has links)
We extend sociodynamic modeling of the financial business cycle to the Euro Area and Japan. Using an opinion-formation model and machine learning techniques we find stable model estimation of the financial business cycle using central bank lending surveys and a few selected macroeconomic variables. We find that banks have asymmetric response to good and bad economic information, and that banks adapt to their peers' opinions when changing lending policies.
144

Linear Simulations of the Cylindrical Richtmyer-Meshkov Instability in Hydrodynamics and MHD

Gao, Song 05 1900 (has links)
The Richtmyer-Meshkov instability occurs when density-stratified interfaces are impulsively accelerated, typically by a shock wave. We present a numerical method to simulate the Richtmyer-Meshkov instability in cylindrical geometry. The ideal MHD equations are linearized about a time-dependent base state to yield linear partial differential equations governing the perturbed quantities. Convergence tests demonstrate that second order accuracy is achieved for smooth flows, and the order of accuracy is between first and second order for flows with discontinuities. Numerical results are presented for cases of interfaces with positive Atwood number and purely azimuthal perturbations. In hydrodynamics, the Richtmyer-Meshkov instability growth of perturbations is followed by a Rayleigh-Taylor growth phase. In MHD, numerical results indicate that the perturbations can be suppressed for sufficiently large perturbation wavenumbers and magnetic fields.
145

Flow-induced Vibration of Double Wall Carbon Nanotubes Conveying Pulsating Fluid.

Alnujaie, Ali H. 25 June 2019 (has links)
No description available.
146

Study of impulsive magnetic reconnection due to resistive tearing mode with the effect of viscosity and dynamic flow in fusion plasmas / 核融合プラズマにおける粘性と動的流れの影響を受けた抵抗性ティアリングモードによる突発的磁気リコネクションに関する研究

AHMAD, ALI 23 March 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19091号 / エネ博第315号 / 新制||エネ||64(附属図書館) / 32042 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 岸本 泰明, 教授 前川 孝, 教授 中村 祐司 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM
147

The Effects of Abdominal Training on Postural Control, Lower Extremity Kinematics, Kinetics, and Muscle Activation

Gage, Matthew J. 04 August 2009 (has links) (PDF)
Context: Abdominal training may decrease the risk of lower extremity injuries through improved balance and postural control. Objective: To determine the effect of an eight-week abdominal-training program on center of pressure, lower extremity joint angles, and abdominal muscle activation during a single-leg drop landing. The effects of abdominal training on abdominal muscle thickness was assessed. Design: A cohort research design. Setting: Research laboratory. Other Participants: Sixty healthy physically active college-aged students participated. They were divided into three groups: Control, Chronic ankle instability (CAI), and Healthy. Nineteen Control (age = 22.0 ± 2.72 yrs, mass = 74.1 ± 13.8 kg, height = 172.6 ± 11.3 cm, BMI = 24.8 ± 3.1 %), 21 CAI (age = 22.1 ± 2.3 yrs, mass = 77.6 ± 14.0 kg, height = 175.4 ± 12.3 cm, BMI = 25.1 ± 2.6 %), and 20 healthy (age = 22.9 ± 3.4 yrs, mass = 70.9 ± 15.6 kg, height = 172.2 ± 8.9 cm, BMI = 23.7 ± 3.3 %). Subjects in the CAI group had a history of CAI and functional ankle instability (FAI). The Ankle Instability Index and the Functional Ankle Ability Measure were used to self-report CAI and FAI respectively. Interventions: The CAI and Healthy groups participated in an eight-week abdominal-training program while the Control group maintained their normal activities of daily living and level of physical activity. Main Outcome Measures: Abdominal muscle thickness was measured biweekly throughout the study. Center of pressure excursion, muscle activation, vertical ground reaction force, and lower extremity joint angles were measured during a single-leg drop landing, pre- and postabdominal training. Results: Muscle thickness at rest increased in the rectus abdominis and external oblique muscles follow training. Eight weeks of abdominal training decreased vertical ground reaction forces and muscle activation down the lower kinetic chain. Center of pressure excursion and velocity were increased following training. Conclusions: Eight-weeks of abdominal training increased abdominal muscle thickness. Training improved neuromuscular efficiency throughout the kinetic chain and may have improved dynamic postural control. Our data also suggest CAI subjects may utilize both feedforward and feedback mechanisms to maintain postural control.
148

Prediction of Combustion Instabilities in a Non-Compact Flame via a Wave-Based Reduced Order Network Model

Hunter, Riley 22 August 2022 (has links)
No description available.
149

Characteristics of the nonlinear hysteresis loop for rotor-bearing instability

Guo, Jenq-Shan January 1995 (has links)
No description available.
150

Causes of Combustion Instabilities with Passive and Active Methods of Control for practical application to Gas Turbine Engines

Cornwell, Michael 19 September 2011 (has links)
No description available.

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