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The Rotor System and Flying Qualities of PeriscoptersGupta, Suresh K. 04 1900 (has links)
<p> Prototypes of the recently developed periscopter, a flying platform tethered to a ground station, are presently extremely difficult to fly. Tests conducted by the Defence Research Board of Canada in Valcartier, Quebec, and by Westinghouse of Canada near Hamilton, have led to several crashes. Possible causes for the lack of flying qualities are: unbalanced aerodynamic forces and moments; inadequate controls; and poor inherent stability characteristics. </p> <p> In this investigation, the system of counter-rotating lifting rotors used in the present periscopters is examined with a view to improvement of the flying qualities. The aerodynamic theory of helicopter rotors is considered as a background. </p> <p> The blades of the present periscopter rotors neither flap nor feather. The feasibility of using either articulated (flapping) blades or rigid feathering blades is examined. It is found that flapping blades are not feasible mainly because of associated stability and control problems. Also the two counter-rotating rotors would tend to strike against each other. A rigid rotor system featuring feathering blades is found to be feasible. Such a system is therefore examined in detail by computing all relevant aerodynamic parameters. It is shown that the feathering system can provide all required control moments. Its introduction would therefore eliminate the present bail mechanism. </p> <p> An analysis of the stability characteristics of a periscopter featuring a rigid feathering rotor system is developed. However, when hovering in still air, such a periscopter is shown to be unstable. The possibility of rendering it stable by the use of rotor controls is demonstrated. No attempt is made to suggest a specific design for the control system to be used. </p> <p> The effect of various operational parameters on the flying qualities of the periscopter is investigated. </p> / Thesis / Master of Engineering (ME)
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STABILITY AND BIFURCATION DYNAMICS OF JOURNAL BEARING ROTOR SYSTEMSXu, Yeyin 01 September 2020 (has links) (PDF)
In this dissertation, the mechanical models of 2-DOF and 4-DOF nonlinear journal bearing rotor systems are established. A more accurate model of oil film forces is derived from Reynolds equations. The periodic motions in such nonlinear journal bearing systems are obtained through discrete mapping method. Such a semi-analytical method constructs an implicit discrete mapping structure for periodic motions by discretization of the continuous journal bearing rotor differential equations. Stable and unstable periodic solutions of periodic motions are obtained with prescribed accuracy. The bifurcation tree of periodic motions in rotor system without oil film forces is demonstrated through the route from period-1 motion to period-8 motion. Stable period-2 and unstable period-1 motion are presented for 2 DOF journal bearing rotor system. Possibly infinite periodic solutions are found in 4 DOF journal bearing rotor system. For the rotor systems, the stability and bifurcations of periodic motions are analyzed through eigenvalue analysis of the corresponding Jacobian matrix of the discretized nonlinear systems. The frequency amplitude characteristics of periodic motions in 2 DOF journal bearing system are presented for a good understanding of the nonlinear dynamics of journal bearing rotor system in frequency domain . The rich dynamics of the journal bearing systems are discovered. The numerical illustrations of stable periodic motions are brought out with the initial conditions from analytical prediction.
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Dynamické vlastnosti rotoru kmitajícího v tekutině / Dynamic behavior od rotor dynamics stystem vibrating in a liquidChlud, Michal January 2010 (has links)
This thesis deals with dynamic behavior of swirl turbine vibrating in a liquid. Primarily is studied decrease of natural frequencies of rotor due the interaction with fluid environment, namely for different levels of submerged rotor in fluid. After that follows the detection of natural frequencies of swirl turbine in operating speed. The problem is solved by computational modeling in ANSYS system. For this solution is used acoustic elements method. The results are compared with experiment.
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Rub-impact of coupled vibration of vertical rotor-stator system submerged in incompressible fluidSozinando, Desejo Filipeson 21 January 2020 (has links)
M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Fault diagnosis of a rotor system operating in a fluid is one of the most difficult aspects
of rotating machinery. Fluid in machinery plays a significant role in concealing the
allowable rubbing stress limit during the impact generated from the rotor-stator rub which
may progressively deteriorate the rotating system. Therefore, a numerical and
experimental investigation was performed to analyse the influence of the fluid during the
rotor-stator contact of a vertical rotor system partially submerged in an incompressible
inviscid fluid with a focus on detecting rubbing fault in the presence of axial load. The
theoretical model of lateral-torsional rotor consists of a 3-D rub-impact induced
parametric excitation, which was assimilated to operate as elastic vertical rotor system by
considering the transient vibration of a flexible axial force and energy of the vertical shaft
system. The model was established based on Jeffcott rotor, time-varying stiffness and the
rotor-stator fluid interaction. The Lagrangian principle was used to establish the
governing equation of motion. The hydrodynamic forces acting on the vertical rotor were
established and introduced into the system based on the Laplace form of the linearized
Navier–Stokes equations under lateral excitation yielding a highly nonlinear 5-DOF
system. To evaluate the dynamic response and ensure the accurate acquisition of rubbing
features in a fluid, the classical Fast Fourier Transform (FFT) and the vibration waveform
have been discretised and illustrated through the frequency components. Furthermore, for
effective extraction of some hidden features of rub, the nonlinear features embedded in
the vibration waveform have been discretised and illustrated through to the lateral
deformation of the rotor and the orbit patterns of the shaft. Qualitative numerical analysis
suitable for highly nonlinear and non-stationary signal Time-Frequency strategies,
Wavelet Synchrosqueezed Transform (WSST) and Instantaneous Frequency (IF)
technique were employed to successfully extract the frequency of oscillating modes and
the periodic frequency response of the faulted rotor system. It is demonstrated that the
coupled lateral-torsional vibration of the submerged vertical rotor system has the
potential to enhance the much-unwanted hidden frequencies of vibration that leads to
significant instability of the rotor system. In particular, the responses revealed the
existence of unstable regimes with respect to the lateral-torsional deflection as well as the
angular velocity. High harmonic peaks were also identified at the critical speed, which
can be considered as a monitoring index to detect the rubbing in rotating shafts in a fluid.
It was found that even at relatively slow rotating speed fluid elastic forces induced by the co-rotating flow surrounding the shaft significantly affect the transverse natural modes of
vibration of the shaft. Despite the interaction between the fluid and the rotor generates
self-excitation of low frequencies, obtained results indicated that the fluid-rotor
interaction reduces the dynamic vibration response of the faulted system running below
the second critical speed. It has been analytically demonstrated that the time-varying
stiffness induced is the principal cause of the frequency-modification feature of the
dynamic response of an unbalance-rub rotor system at the contact region. The model
investigated in this study has potential application for drill string-borehole shaft system
used in the oil industry.
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Dynamické vlastnosti rotoru kmitajícího v tekutině / Dynamic behavior od rotor dynamics system vibrating in a liquidKučera, Martin January 2009 (has links)
This thesis deals with dynamic behavior of rotor dynamics system vibrating in a liquid. Work is factually oriented on influence of the liquid to natural frequences of rotor of vortex turbine. There is described the creation of geometric and computational model of the system and the results of natural frequences and damping in dependence on environment are presen-ted. There are compared variations in natural frequences of the rotor system, which are caused of the interaction of the various level of the water environment. The step of integration are tested and compared for choise solving method. Problem is solved by computational simulation in commercial software ANSYS 11.0 There is used software tools Multiphysics/FSI.
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Metodika výpočtu kritických otáček elektrických strojů točivých / Methodology of calculation of critical speed of rotating electrical machinesSedláček, Jan January 2013 (has links)
This Master thesis describes the design of methodology for calculating the critical speed of rotating electric machines. The aim is to build finite element model of rotor system model, determine the natural frequencies to plot Campbell diagram and use this diagram to obtain the critical speeds. The Matlab software is used for this purpose and the Ansys software is used for verify the calculation.
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