Drazen Fabris

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This thesis involves the modeling of self-sustained oscillations in the flow past a rectangular cavity. The emphasis is on developing low-dimensional models that are suitable for analysis using tools from dynamical systems and control theory. Two-dimensional direct numerical simulations are performed, and indicate the presence of a “wake mode,” which has(More)
Experiments using active control to reduce oscillations in the flow past a rectangular cavity have uncovered surprising phenomena: in the controlled system, often new frequencies of oscillation appear, and often the main frequency of oscillation is split into two sideband frequencies. The goal of this paper is to explain these effects using physics-based(More)
Based on extensive experimental information, a model is developed that takes into account heat transport through the entire carbon nanofiber interconnect test structure and breakdown location. This electrothermal transport model elucidates observed current capacity behavior, and predicts variations in contact location with the support material. The(More)
To elucidate the observed current capacity behavior, a model is developed that takes into account heat transport through the entire carbon nanofiber interconnect test structure and breakdown location. The model also includes variations in contact location with the support material. The resulting predicted heat dissipation and current capacity are completely(More)
In a carbon nanofiber CNF -metal system such as a bridge between two gold electrodes, passing high current current stressing reduces the total resistance of the system CNF resistance RCNF plus contact resistance Rc by orders of magnitude. The role of current stressing is modeled as a reduction in the interfacial tunneling gap with transport characteristics(More)
To study the reliability of carbon nanofibers (CNFs) under high-current stress, electrical measurements of CNF breakdown are performed for four configurations: (a) suspended, (b) supported, (c) suspended with tungsten deposited onto the CNFelectrode contact, and (d) supported with tungsten deposition. Supported CNF has enhanced current capacity, consistent(More)
A joint experimental and computational methodology is developed and applied to investigate a vortex ring impinging normally on a wall. The method uses digital particle image velocimetry to make planar flow measurements, which are then used to initialize a second-order finite difference calculation. The experiment and the simulation are compared at later(More)
The flow field around a sphere falling at its terminal velocity in a column of viscoelastic non-shear-thinning fluid is experimentally measured with digital particle image velocimetry. The working fluid is an extensively characterized, monodisperse, polystyrene based Boger fluid. The sphere radius relative to the radius of the column of fluid is small(More)
An experimental investigation of acoustic mode noise suppression was conducted in a cavity using a digital controller with a linear control algorithm. The control algorithm was based on flow field physics similar to the Rossiter model for acoustic resonance. Details of the controller and results from its implementation are presented in the companion paper(More)