One of the negative effects that a laser beam experiences as it propagates through the atmosphere is intensity fluctuations or scintillation. Because scintillation-- as it pertains to laser radar and laser satellite communication systems-- is the main subject of this research, the assumption of an optical element ( such as a Gaussian lens) along the propagation path in front of the detector is valid. The mathematical addition of optical elements to the propagation path is treated using the ABCD ray matrix method. The expression for scintillation is derived, analyzed, and numerically calculated for positions to the left and right of the image plane, which is behind the collecting lens of a receiver system. Simultaneously, the behavior of the scintillation is investigated when the aperture size of the lens is increased. The results are compared to the aperture averaging effect experienced when the beam is in the image plane. This is a per-unit scintillation decrease because the aperture averages it over the surface of the lens.

Processing and analysis routines giving normalized moments of optical intensity, structure functions of wind velocity and temperature, central moments, and various measures of the turbulence parameter, C2N, are presented. Rapid analog-to-digital data conversion and storage to implement this analysis using MINC 11/23 with RT11 operating system are discussed. Coding for file organization and implementation of processing routines on the VAX 11/750, VMS operating system are also discussed.

No description available.

No description available.

The distribution of lift between the wing and tail surfaces of a conventional aircraft is examined in order to determine the combination that would produce the minimum drag for a given lift. Further, the center of gravity (CG) position which gives the desired lift distribution and at the same time, maintains aircraft trim is determined. Furthermore, a classic set of non-linear equations of motion for longitudinal flight is reduced to a set of linear equations by linearization. The location of the CG of the aircraft is then changed and a linear feedback control law is used to retain the dynamic characteristic (flying qualities) of the airplane. The response of the aircraft to an external disturbance such as a gust (modeled with a stochastic process) is studied in terms of drag versus CG position. Finally, it is shown that the position of the CG for minimum drag should be determined with consideration of the expected atmospheric turbulence. / Master of Science

No description available.

No description available.

No description available.

Eight roughness configurations in Clemson boundary layer wind tunnel are presented. For these configurations, flow parameters such as turbulent intensities, integral length scales, large- and small- scale turbulence, and spectra of velocity components of the wind are obtained and studied to the simulated turbulence. At the same time, new analyzing tools, orthogonal wavelet techniques, are applied to provide additional information in time domain. This makes it possible to study the intermittency event, one important characteristic associated with pressure peak activities in turbulence. Three parameters, scale energy, intermittency factor and intermittency energy are defined. Variation of these quantities as a result of different configuration is discussed. Finally, the corresponding variations in measured pressure peaks in relation with the variations of configuration as well as with the intermittency parameters are investigated. The work here is of important significance for future wind tunnel and field data comparison, and this could help to find the best simulation among all configurations. / Master of Science

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Zhongquan Zheng / Windscreens are widely used in outdoor microphone measurement for acoustic sensing systems. In many cases of outdoor microphone applications, wind noise interferes with the signals. The performance of measurement microphones thus heavily depends on correct designs of windscreens that are used to maximize the signal to noise ratio of the sensing system. The purpose of the study is to investigate the wind noise reduction between the unscreened microphone and the screened microphone under different frequencies of incoming wind turbulence. In this study, a modified immersed boundary method using the distributed forcing term has been applied to simulate the flow/acoustic interaction between air and the porous medium. Because of the high accuracy requirement in the vicinity of the interface between air and the porous medium, spatial derivatives of flux need to be discretized using high order schemes. In this study, several different schemes have been tested in the vicinity of the interface including a second-order upwind scheme, a third-order upwind scheme, and a fifth-order Weighted Essentially Non-Oscillatory (WENO) scheme. Based on the test results, the fifth-order WENO scheme is selected for most of the simulation cases. The model equations for flow outside the windscreen are the Navier-Stokes equations; flow inside the windscreen (porous medium) uses the modified Zwikker-Kosten equation. The wind turbulence in this study is generated by two different ways. The first is to place different sizes of solid cylinders and spheres in the upstream of the microphone under two-dimensional and three-dimensional conditions. The second is to use a Quasi-Wavelet method to generate the background atmospheric turbulence to simulate the real physical phenomena. Both two-dimensional and three-dimensional simulations for the flow over the unscreened and the screened microphone are presented and discussed under both low Reynolds number and high Reynolds number flow conditions. The results show that the windscreen effect is significant and the wind noise reduction level between the unscreened and the screened microphone can reach around 20dB either for low Reynolds number cases or for high Reynolds number cases. For low Reynolds number cases, Low flow resistivity windscreens are more effective for low frequency turbulence; high flow resistivity windscreens are more effective for high frequency turbulence. For high Reynolds number cases, the medium flow resistivity windscreens perform better compared to low flow resistivity windscreens and high flow resistivity windscreens.