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Experimental study was conducted to investigate fluidelastic instability in finned tube bundles with normal and parallel triangular arrays. Three arrays of each geometry type were studied experimentally: two arrays with serrated, helically wound finned tubes of different fin densities, and a bare tube array with the same base diameter as the finned tubes. The finned tubes under consideration were commercial finned tubes typically used in the fossil and process industries. For the purpose of the present investigation, the concept of "effective diameter" of a finned tube, as used to predict the vortex shedding, was used to compare the finned tube results with the existing bare tube world data and some theoretical predictions for fluidelastic instability. The finned tube arrays in this study have the same tube pitch and have been scaled to have the same mass ratio and tuned to have the same natural frequency. A low speed wind tunnel, Betz micro manometer and HP 35670a dynamic signal analyzer were employed to conduct the experiments. Experimental results for the triangular arrays show that the fin's structure strongly influences the fluidelastic stability of finned tube bundles and the fin pitch is demonstrated to reduce the difference in the fluidelastic instability between the tube arrangements as the fin density increases. The results also suggest that there might be an optimum fin pitch value at which the threshold reduced velocity for a finned tube array is much higher than the one for its corresponding bare tube array, due to the influence of fin geometry. In the appendix, an analytical model produces a new correlation of critical reduced velocity against mass damping parameter to predict the fluidelastic instability of tube bundles. Its predictions are in reasonable agreement with the experimental data. Since negative damping is one of the mechanisms of fluidelastic instability of a tube array, "Lift effect" was applied to explain the negative damping in an inviscid flow. An experiment is suggested to test the relationship between the pitch flow velocity and a tube velocity dependent "lift effect". Accordingly, two duct structure designs are suggested which may alleviate the negative damping by using the energy of oncoming flow to reduce the "lift effect" on the tubes. / Thesis / Master of Applied Science (MASc)

Over the past decades, phased arrays have played a significant role in the development of modern radar and communication systems. The availability of printed circuit technology and ease of integration with microwave components, as well as the development of low profile and low weight approaches, have also played an important role in their conformal adaptation. However, fabrication costs remain prohibitive for many emergent platforms, including 5G base stations and autonomous vehicles, when compared to a conventional mechanically steered passive array. Therefore, cost reductions in the fabrication and integration of modern phased arrays are essential to their adaptation for many upcoming commercial applications. Indeed, although phased array design methods are well-understood, even for wideband and wide-angle scanning applications, their fabrication is still based on high-cost, low-yield printed circuit technology. With this in mind, this dissertation focuses on a new planar aperture topology and low-cost techniques for phased array methodologies. The first part of the thesis presents new fabrication advancements using commercially available multi-layered printed circuit technologies. We discuss methods for low cost fabrication while still maintaining performance and design constraints for planar array apertures. The second part of the dissertation presents a novel Integrated Planar Array (IPA) at S-Band and discusses dramatic cost reductions for multi-function radar applications. Performance and cost benefits are presented, and fabrication techniques to exploit an emerging class of high-speed digital laminates are discussed. These are compatible with high-volume, high-yield production, while reducing aperture cost by 75% when compared to conventional approaches. Performance of a planar array employing a pin-fed dual-polarized antenna element with active VSWR Overall, this dissertation addresses several manufacturing and performance challenges in realizing affordable planar phased arrays using low cost fabrication without performance compromise. As commercial interest in phased array technology is anticipated to grow, the proposed approaches for phased array design and fabrication will enable quick turnaround times for mainstream adoption.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

abstract: Exhaustive testing is generally infeasible except in the smallest of systems. Research has shown that testing the interactions among fewer (up to 6) components is generally sufficient while retaining the capability to detect up to 99% of defects. This leads to a substantial decrease in the number of tests. Covering arrays are combinatorial objects that guarantee that every interaction is tested at least once. In the absence of direct constructions, forming small covering arrays is generally an expensive computational task. Algorithms to generate covering arrays have been extensively studied yet no single algorithm provides the smallest solution. More recently research has been directed towards a new technique called post-optimization. These algorithms take an existing covering array and attempt to reduce its size. This thesis presents a new idea for post-optimization by representing covering arrays as graphs. Some properties of these graphs are established and the results are contrasted with existing post-optimization algorithms. The idea is then generalized to close variants of covering arrays with surprising results which in some cases reduce the size by 30%. Applications of the method to generation and test prioritization are studied and some interesting results are reported. / Dissertation/Thesis / Masters Thesis Computer Science 2015

The design of antenna arrays involves, amongst others, the selection of the array elements and geometry, as well as the element excitations. The feeding network to obtain the desired excitations can become quite complex, and hence expensive. One possible alternative would be to make use of micros trip wire-grid antenna arrays. These arrays are composed of staggered interconnected rectangular loops of dimensions a half¬wavelength by a wavelength (in the presence of the dielectric). It is because the short sides are considered to be discrete elements fed via micros trip transmission lines, that these antennas are viewed as arrays. While considerable success has been achieved in the design of these antennas, published work has been either of an entirely experimental nature or based on approximate (albeit clever) network models which do not allow for fine control of the array element excitations or off-centre-frequency computations generally. It is the purpose of this thesis to perform an almost rigorous numerical analysis of these arrays in order to accurately predict their element excitations. Models used to study microstrip antennas range from simplified ones, such as transmission-line models up to more sophisticated and accurate integral-equation models. The mixed-potential integral equation formulation is one of these accurate models which allows for the analysis of arbitrarily shaped microstrip antennas with any combination of frequency and dielectric thickness. The model treats the antenna as a single entity so that physical effects such as radiation, surface waves, mutual coupling and losses are automatically included. According to this formulation, the microstrip antenna is modelled by an integral equation which is solved using the method of moments. By far the most demanding part of the integral equation analysis is its actual numerical implementation. For this reason a complete description of the numerical implementation of the formulation is given in this thesis. To verify the accuracy of the implementation, rectangular microstrip patch antennas were analysed and surface current distributions were shown to compare favourably with published results. The formulation is then applied to the analysis of micros trip wire-grid antenna arrays which makes it possible to accurately predict surface current distributions on these arrays. Radiation patterns are determined directly from computed current distributions in the presence of the dielectric substrate and groundplane, and are essentially exact except for finite groundplane effects. To verify theoretically predicted results for wire-grid antenna arrays, several arrays were fabricated and actual radiation patterns were measured. Good correspondence between measured and predicted co-polar radiation patterns was found, while the overall cross¬polarization behaviour in cases with large groundplanes could also be predicted. The fact that numerical experimentation can be performed on wire-grid antenna arrays to examine element excitations, means that it is now possible to carefully design for some desired aperture distribution. / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

No / The performances of two different angle of arrival estimation algorithms, phase interferometry and covariance based super resolution, and two different mutual coupling compensation methods, conventional and received mutual impedance, have been compared. Two different scenarios have been explored, firstly with a single source transmitter, and then with dual source transmitters. Different powers levels were used to estimate the performance of these algorithms in a multipath/multisource environment over a perfect ground plane. The results show greater accuracy using the covariance based technique, and also support the use of the received mutual impedance method for coupling compensation.