In the pursuit of developing hypersonic cruise vehicles, unstart is a major roadblock to achieving stable flight. Unstart occurs when a sudden instability in the combustor of a vehicle’s propulsion system creates an instantaneous pressure rise that initiates a shock. This shock travels upstream out of the inlet of the vehicle, until it is ejected from the inlet and creates a standing shockwave that chokes the flow entering the vehicle, thereby greatly reducing its propulsive capability. In severe cases, this can lead to the loss of the vehicle. This thesis presents the results of a computational study of the dynamics of unstart near Mach 5 and presents some possible precursor signals that may indicate its presence in flight. Using SU2, an open-source CFD code developed at Stanford University, the Unsteady Reynolds-Averaged Navier-Stokes equations are used to develop a model for flow in a scramjet inlet-isolator geometry, both in the fully started state and during unstart. The results of these calculations were compared against experimental data collected by J. Wagner, at the University of Texas, Austin. In the present computations, unstart was initiated through the use of an artificial body force, which mimicked a moveable flap used in the experiments. Once the results of the code were validated against these experiments, a selection of parametric studies were conducted to determine how the design of the inlet-isolator by Wagner affected the flow, and thus how generalizable the results can be. In addition, precursor signals indicative of unstart were identified for further study and examined in the different parametric studies. It was found that a thick boundary layer is conducive to a stronger precursor signal and a slower unstart. In addition, an aspect ratio closer to 1:1 promotes flow mixing and reduces the unstart speed and strength. Moreover, an aspect ratio in this range reduces the precursor signal strength but, if a thick boundary layer is present, will smear the signal out over a larger area, potentially making it easier to detect. <br>

A numerical analysis was conducted to study the effects of geometrically scaling scramjet inlet-combustor isolators. Three-dimensional fully viscous numerical simulation of the flow inside constant area rectangular ducts, with a downstream back pressure condition, was analyzed using the SolidWorks Flow Simulation software. The baseline, or 1X, isolator configuration has a 1” x 2.67” cross section and 20” length. This baseline configuration was scaled up based on the 1X configuration mass flow to 10X and 100X configurations, with ten and one hundred times the mass flow rate, respectively. The isolator aspect ratio of 2.67 was held constant for all configurations. To provide for code validation, the Flow Simulation program was first used to analyze a converging-diverging channel and a wind tunnel nozzle. The channel case was compared with analytical theory and showed good agreement. The nozzle case was compared with AFRL experimental data and showed good agreement with the entrance and exit conditions (Pi0= 40 psia, Ti0= 530ºR, Pe= 18.86 psia, Te= 456ºR, respectively). While the boundary layer thickness remained constant, the boundary layer thickness with respect to the isolator height decreased as the scale increased. For all the isolator simulations, a shock train was expected to form inside the duct. However, the flow simulation failed to generate this flow pattern, due to improper sizing of the isolator and combustor for a 3-D model or having a low pressure ratio of 2.38. Instead, a single normal shock wave was established at the same relative location within the length of each duct, approximately 80% of the duct length from the isolator entrance. The shape of the shock changed as the scale increased from a normal shock wave, to a bifurcated shock wave, and to a normal shock train, respectively for the 1X, 10X, and 100X models.

The dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber is the focus of this thesis consisting of five papers A-E. Paper A presents results drawn from experiments on samples subjected to different constant shear strains over varying frequencies and magnetic fields. Main features observed are the existence of an amplitude dependence of the shear modulus referred to as the Fletcher-Gent effect for even small displacements, and the appearance of large MS effects. These results are subsequently used in Paper B and C to model two magneto-sensitive rubber isolators, serving to demonstrate how, effectively, by means of MS rubber, these can be readily improved. The first model calculates the transfer stiffness of a torsionally excited isolator, and the second one, the energy flow into the foundation for a bushing inserted between a vibrating mass and an infinite plate. In both examples, notable improvements in isolation are obtainable. Paper D presents a non-linear constitutive model of MS rubber in the audible frequency range. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. A very good agreement with experimental values is obtained. In Paper E, the magneto-sensitive rubber bushing stiffness for varying degrees of magnetization is predicted by incorporating the non-linear magneto-sensitive audio frequency rubber model developed in Paper D, into an effective engineering formula for the torsional stiffness of a rubber bushing. The results predict, and clearly display, the possibility of controlling over a large range through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness. / QC 20100816

This report is introduced with a presentation of fundamental electromagnetic theories, which have helped a lot in the achievement of methods for calculation and design of microstrip transmission lines and circulators. The used software for the work is also based on these theories. General considerations when designing microstrip solutions, such as different types of transmission lines and circulators, are then presented. Especially the design steps for microstrip lines, which have been used in this project, are described. Discontinuities, like bends of microstrip lines, are treated and simulated. There are also sections about power handling capability of microstrip transmission lines and different substrate materials. In the result part there are computed and simulated dimensions of the microstrip transmission lines used in the prototype system. Simulations of conceivable loads in the cavity illustrate quantitatively the reflection coefficient. Even practical measurements are made in a network analyzer and are presentedin this part. Suitable materials and dimensions for the final microwave feed transmission line system for high powers are then presented. Since circulators are included in the system a basic introduction to the design of these in stripline and microstrip techniques is also made. At last conclusions, examinations of the designed system and comparisons to the today’s systems are made.

In this study, seismic roof isolation solutions were investigated with a case study of Halkapinar Gymnasium, izmir. In the first part, seismic isolation was explanied and philosophy behind it was given. In the second part, existing seismic roof isolators, elastomeric bearing and viscous damper, were investigated with different support isolation combinations. In the third part, two more types of seismic isolators, lead rubber bearing and friction pendulum isolators, were also analyzed by using the same model and all results were compared with each other and that of non-isolated roof system. Furthermore, bilinear effect of the non-linear isolators were also studied. Finally, all results were compared with each other considering structure responses and effectiveness of the seismic isolators. It has been tried to find the most efficient seismic isolation solution for Halkapinar Gymnasium.

The experimental research presented in this dissertation aims to develop a new rubber&ndash / based seismic isolator type on the basis of the idea that the damping of a conventional annular elastomeric bearing (EB) can be increased by filling its central core with small diameter steel balls, which dissipate energy via friction inside the confined hole of the bearing during their movements under horizontal loads. The proposed bearing type is called &ldquo / Ball Rubber Bearing (BRB)&rdquo / . A large set of BRBs with different geometrical and material properties are manufactured and tested under reversed cyclic horizontal loading at different vertical compressive load levels. Effect of supplementary confinement in the central hole of the bearing to performance of BRB is studied by performing some additional tests. Test results are used to develop design equations for BRB. A detailed non-linear finite element model is developed to verify the test results. The proposed analytical model is determined to simulate the structural hysteretic behaviour of the bearings. In design of BRBs, the proposed design guideline can be used in conjunction with the proposed non-linear finite element analysis. Extensive test results indicate that steel balls do not only increase the energy dissipation capacity of the elastomeric bearing (EB) but also increase its horizontal and vertical stiffness. It is also observed that the energy dissipation capacity of a BRB does not degrade as the number of loading cycles increases, which indicates remarkably reliable seismic performance.

Rubber material used in seismic isolation systems has a tendency to stiffen in cold climate conditions. Structural responses of rubber based seismic isolation bearings are known to be temperature dependent. The main focus of this research is to investigate the temperature related behavior shifts at a certain type of a rubber based seismic isolation system. This research is a complementary study to a recent experimental study on a newly developed seismic isolator called &ldquo / Ball Rubber Bearing&rdquo / (BRB). BRBs can be easily manufactured as in the case of a standard rubber based bridge bearing and can provide adequate energy dissipation during an earthquake. However, structural response of BRBs at low temperatures has not been examined yet. In this research, behavior of BRBs exposed to different temperatures is examined under combined axial and cyclic lateral load. The performance of the specimens used in this study, &ldquo / Elastomeric Bearing&rdquo / (EB) and &ldquo / Ball Rubber Bearing&rdquo / (BRB) are compared with each other and also with previous researches conducted in this topic. The results indicated that BRBs show better performance at low temperatures in terms of energy dissipation compared to room temperature performance. Big size bearings have higher energy dissipation per cycle compared to small size bearings by reason of size effect. The higher damping percentage is observed at the small size bearings compared to big size bearings due to better confinement of the inner core. As a result of temperature records heat exchange is not detected in the rubber during cyclic loading.

<p>This report is introduced with a presentation of fundamental electromagnetic theories, which have helped a lot in the achievement of methods for calculation and design of microstrip transmission lines and circulators. The used software for the work is also based on these theories. </p><p>General considerations when designing microstrip solutions, such as different types of transmission lines and circulators, are then presented. Especially the design steps for microstrip lines, which have been used in this project, are described. Discontinuities, like bends of microstrip lines, are treated and simulated. There are also sections about power handling capability of microstrip transmission lines and different substrate materials. </p><p>In the result part there are computed and simulated dimensions of the microstrip transmission lines used in the prototype system. Simulations of conceivable loads in the cavity illustrate quantitatively the reflection coefficient. Even practical measurements are made in a network analyzer and are presentedin this part. </p><p>Suitable materials and dimensions for the final microwave feed transmission line system for high powers are then presented. Since circulators are included in the system a basic introduction to the design of these in stripline and microstrip techniques is also made. </p><p>At last conclusions, examinations of the designed system and comparisons to the today’s systems are made.</p>

A numerical analysis was conducted to study the effects of geometrically scaling scramjet inlet-combustor isolators. Three-dimensional fully viscous numerical simulation of the flow inside constant area rectangular ducts, with a downstream back pressure condition, was analyzed using the SolidWorks Flow Simulation software. The baseline, or 1X, isolator configuration has a 1” x 2.67” cross section and 20” length. This baseline configuration was scaled up based on the 1X configuration mass flow to 10X and 100X configurations, with ten and one hundred times the mass flow rate, respectively. The isolator aspect ratio of 2.67 was held constant for all configurations. To provide for code validation, the Flow Simulation program was first used to analyze a converging-diverging channel and a wind tunnel nozzle. The channel case was compared with analytical theory and showed good agreement. The nozzle case was compared with AFRL experimental data and showed good agreement with the entrance and exit conditions (Pi0= 40 psia, Ti0= 530ºR, Pe= 18.86 psia, Te= 456ºR, respectively). While the boundary layer thickness remained constant, the boundary layer thickness with respect to the isolator height decreased as the scale increased. For all the isolator simulations, a shock train was expected to form inside the duct. However, the flow simulation failed to generate this flow pattern, due to improper sizing of the isolator and combustor for a 3-D model or having a low pressure ratio of 2.38. Instead, a single normal shock wave was established at the same relative location within the length of each duct, approximately 80% of the duct length from the isolator entrance. The shape of the shock changed as the scale increased from a normal shock wave, to a bifurcated shock wave, and to a normal shock train, respectively for the 1X, 10X, and 100X models.

In dieser Arbeit wird vor allem der Einflu¨s eines quasiperiodischen Gitters und dessen Topologie auf die Lokalisierungseigenschaften der Eigenzust¨ande und die elektronische Zustandsdichte untersucht. Ausgehend vom Penrosegitter und dessen dreidimensionalen Analogons werden auch die quasiperiodischen Gitter aus anderen lokal isomorphen Klassen untersucht. Durch den Einbau von Phasonendefekten werden weiterhin Random-Tiling-Gitter konstruiert. Ferner wird untersucht, inwieweit ein quasiperiodisches Gitter den Metall-Isolator-¨Ubergang beeinflu¨st. Zwei- und dreidimensionale Quasigitter werden mit der Gridmethode nach de Bruijn konstruiert und ¨Random Tiling¨-Gitter durch den Einbau von Phasonendefekten erzeugt. Im Vertexmodell wird jeder Ecke eines Rhombus ein s-Atomorbital zugewiesen mit ausschlie¨slich N¨achster-Nachbar-Wechselwirkung entlang der Kanten. Aus den berechneten Eigenzust¨anden werden Zustandsdichten berechnet und deren Partizipationzahlen und R¨uckkehrwahrscheinlichkeiten bestimmt, um das Lokalisierungsverhalten zu untersuchen. Im Penrosegitter zeigen die Zustandsdichten eine hohe Entartung in der Bandmitte. Die entsprechenden Zust¨ande sind stark lokalisiert (¨confined states¨) und durch eine Energiel¨ucke von den anderen Energieniveaus getrennt. Die Zust¨ande an der Bandkante sind dagegen ausgedehnt. Durch die Phasonen werden die Zustandsdichte und das Lokalisierungsverhalten ver¨andert. Im Falle dreidimensionaler Quasigitter ist die Energiel¨ucke verschwunden, und man findet eine wesentlich kleinere Anzahl entarteter Zust¨ande in der Bandmitte. Die anderen Zust¨ande in der Bandmitte sind nicht lokalisiert.