Thesis (M.S.)--University of Colorado, 1998. / Includes bibliographical references (leaves 45-46). Also available full text via Internet in .pdf format. Adobe Acrobat Reader required.

Thesis (M.S.)--California Polytechnic State University, 2010. / Title from PDF title page; viewed on June 10, 2010. Major professor: Xi Wu, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Mechanical Engineering." "May 14, 2010." Includes bibliographical references (p. 46-47).

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis - Technische hogeschool Delft. / Bibliography: p. 108.

M.Ing. / Variable liquid resistors are utilised in the rotor circuit, to control mine winders using slipring induction machines. These liquid resistors have a number of disadvantages, therefore a new drive technology is required to replace liquid controllers. A number of machine drives are discussed and a comparative study is made. A 22kW resistively loaded buck chopper in the rotor, is used as a case study. Full design details and procedures are given for the chopper. These designs are verified by simulations and experimental results. A current control was designed and implemented for the buck chopper in the rotor, using a PI controller and pulse width modulation. The 22kW resistively loaded buck chopper operated exceptionally well and it is evident that it could be a viable method for replacing liquid controllers. The oscillation generated in the hoist cables are discussed and a possible counter acting acceleration method of removing these oscillations is described. A rotating oscillation system was designed and constructed for experimental purposes. From the tests undertaken on the experimental system, it was evident that by the implementation of the counter action process, it is possible to remove the oscillations in the hoist ropes.

Interest in high speed rotorcraft has directed attention toward the slowed-rotor, high advance ratio compound autogyro concept. The behavior of partially unloaded rotors, autorotating at high advance ratio is not well understood and numerous technical issues must be resolved before the vehicle can be realized. The necessity for a reduction in rotor speed with increasing flight speed results in high advance ratio operation. Further, rotor speed changes also affect the rotor dynamics and the associated hub moments generated by cyclic flapping. The result is rotor characteristics that vary widely depending on advance ratio. In the present work, rotor behavior is characterized in terms of issues relevant to the control system conceptual design and the rotor impact on the intrinsic vehicle flight dynamics characteristics. In this research, non-linear models, including the rotor speed degree of freedom, were created and analyzed with FLIGHTLABTM rotorcraft modeling software. Performance analysis for rotors trimmed to autorotate with zero average hub pitching and rolling moments indicates reduced rotor thrust is achieved primarily through rotor speed reduction at lower shaft incidence angle, and imposing hub moment trim constraints results in a thrust increment sign reversal with collective pitch angle above advance ratio . Swashplate control perturbations from trim indicate an increase in control sensitivities with advance ratio, and advance ratio dependent control cross coupling. Rotor speed response to swashplate control perturbations from trim results in non-linear behavior that is advance ratio dependent, and which stems from cyclic flapping behavior at high advance ratio. Rotor control strategies were developed including the use of variable shaft incidence to achieve rotor speed control with hub moment suppression achieved through cyclic control. Flight dynamics characteristics resulting from the coupling of the rotor and airframe were predicted in flight using a baseline airframe with conventional fixed-wing controls. Results predicted by linearization of the non-linear models were compared with system identification results using the non-linear simulation as surrogate flight test data. Low frequency rotor response is shown to couple with the vehicle motion for short period and roll mode response to airframe control inputs. The rotor speed mode is shown to couple with short period and long period vehicle modes as the rotor torque balance is sensitive to vehicle speed and attitude changes.

\Yith the current develop111ent in computer technology and Computational Fluid D)'n<'tlllics techniques, t.he si11utlation within axial flow compressors becomes 1110re and 1110re pract.ical and beneficial to the compressor designs. Due to the insufficient capabilit)' of today's COll1put.ers for three-dimensional unsteady flow 1110delling of 111Ult i~Llg(' axial flow compressors, sophisticated models of steady state flow and perfor111ance 1110delling of the C0111prcssors deserve to be thoroughly investigated. In l1utltistage C0111pressor sinlulations with steady state methods, frame of reference is fixed on blades and the c0111putational domains for rotors and stators haye relati\'e rotation. One of the difficulties in such simulations is how to pass information across the interfaces between blade rows without losing continuity. Two 111ajor stead)' state modelling approaches, a mixing plane approach based on Denton's circu111ferentially non-uniform mixing plane model and a deterministic stress approach based on Adamczyk's average passage model, are investigated and compared with each other through the flow predictions of the third stage of Cranfield Low Speed Research Compressor at peak efficiency operating condition. In the deterministic stress approach, overlapped solution domains are introduced to calculate deterministic stresses in order to 'close' the time-averaged governing equation system and the influence of the downstream blade row of the blade row under investigation has to be imposed through the simulation of bodyforce and blade blockage effect of the downstream blade row. An effective method of simulating bodyforce and blade blockage effect has been developed and proven to be simple in programming. ConYentionally, boundary conditions are specified in CFD calculations based on experimental data or other empirical calculations. By taking advantage of the special flow features in rear stages of multistage axial flow compressors where each rear stage behaves like a repeating stage of its neighbouring stages in terms of flow pattern at the inlet and the exit of these stages, a repeating stage model has been developed aiming at significantly simplifying the boundary conditions when simulating rear stages of a multistage axial flow compressor with only mass flow rate and stage exit average static pressure required as global input. A computer simulation system 1'/ STurbo3D has been developed to investigate a11d assess different steady state simulation models within multistage compressor environment. It has been proven that with the mixing plane model M STurbo3D is able to predict flows in multistage low speed axial flow compressors with acceptable accuracy. Application of the repeating stage model to the third stage of LS RC shows that the prediction with this model has equivalent accuracy to the prediction with the conventional boundary setting, and proves that the repeating stage model is an effective alternative to the expensive complete compressor simulation. The deterministic stress model provides more information of rotor-stator interaction and slightly better performance prediction than the mixing plane model, but the benefits of the model is not significant when applied to low speed axial flow compressors.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Vita. / Includes bibliographical references. / Ph.D.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Vita. / Includes bibliographical references. / by Michael P. Scully. / Ph.D.

The torque associated with overcoming the losses on a rotating disc is of particular importance to the designers of gas turbine engines. Not only does this represent a reduction in useful work, but it also gives rise to unwanted heating of metal surfaces and the adjacent fluid. This research presents a numerical study on the effect of rotor-mounted bolts on the moment coefficient and flow structure within a rotor–stator cavity under conditions representative of modern gas turbine engine design. Steady-state, two-dimensional and three-dimensional, computational fluid dynamics simulations are obtained using the FLUENT commercial code with a standard (k–ω) turbulence model. The model is firstly validated against experimental data and then used to study the effects of presence of rotormounted hexagonal bolts in the rotor-stator cavity under investigation using different dimensionless flow parameters. Also investigated were the effects of changing the number and size of rotor-mounted bolts on the flow structure and amount of losses for two test cases; one corresponding a throughflow dominated condition and the other corresponding a rotationally dominated one. The simulation results showed that decreasing the throughflow rate reduces the area of the wake region causing the wakes to become more circumferential in their path around the bolts. Also it was found that increasing the number and diameter of bolts respectively reduces and increases the area of the wake region. For N>18 a separation bubble forms above the bolt which its length increases with increasing the number of bolts. The total moment coefficient of all bolts in the system increases with increasing the number of bolts. However, the rate of this increase reduces by mounting more bolts. While increasing the diameter of the bolts consistently increases the moment and drag coefficients for the rotationally dominated condition, for the throughflow dominated case an increase and a reduction was observed for respectively the moment and drag coefficients.