Finite element for the analysis of rotor-dynamic systems that include gyroscopic effects

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents new finite element formulations for the analysis of rotor-dynamic systems that include the effects of gyroscopic influence. Euler-Bernoulli finite elements have been created for both shaft and propeller descriptions. In addition to the gyroscopic effects, centrifugal stiffening has been considered for the propeller elements. The principle of virtual work has been used to determine the equations of motion and formulate element matrices. The proposed element matrices have been incorporated in the VIBRATIO suite of vibration analysis software in order to test the formulations. The software uses an innovative hybrid modelling technique that enables the user to analyse various dynamic problems including rotating beam elements with rigid body attachments. A model of a ship's drive shaft has been created in VIBRATIO for comparison against a verified ANSYS model. Results for forced vibration shaft analysis show excellent correlation between VIBRATIO's Euler shaft formulation and ANSYS's Timoshenko formulation. Incremental analyses of propeller systems using the novel gyroscopic formulation show gyroscopic effects of flexible blade attachments, and also the changing mode shapes and frequencies due to centrifugal stiffening. Results show gyroscopic and centrifugal stiffening effects must not be ignored for an accurate propeller analysis.This work was financially supported by Brunel University

Development of a dynamic model for vibration during turning operation and numerical studies

Turning operation is a very popular process in producing round parts. Vibration and chatter noise are major issues during turning operation and also for other machining processes. Some of the effects of vibration and chatter are short tool life span, tool damage, inaccurate dimension, poor surface finish and unacceptable noise. The basic dynamic model of turning operation should include a rotating work piece excited by a force that moves in the longitudinal direction. Dynamic interaction between a rotating work piece and moving cutting forces can excite vibration and chatter noise under certain conditions. This is a very complicated dynamic problem. Vibration and chatter in machining is one example of moving load problems as the cutter travels along the rotating work-piece. These moving cutting forces depend on a number of factors and regenerative chatter is the widely accepted mechanism and model of cutting forces which then introduce time delays in a dynamic model. In this investigation, the work piece is modelled as a rotating Rayleigh beam and the cutting force as a moving load with time delay based on the regenerative mechanism. The mathematical model developed considers work piece and cutting tools both as a flexible. Without doubt, this dynamic model of vibration of work piece in turning operation is more realistic than previous ones as the dynamic model has multiple-degrees-of-freedom and considers the vibration of the cutter with regenerative chatter. It is found that the cutting force model of regenerative chatter which introduces time delay in a dynamic model leads to interesting dynamic behaviour in the vibration of rotating beams and a sufficient number of modes must be included to sufficiently represent the dynamic behaviour. The effects of depth of cut, cutting speed and rotational speed on the vibration and chatter occurrence are obtained and examined. Simulated numerical examples are presented. These three different parameters are vital and definitely influence the dynamic response of deflection in the y and z directions. The depth of cut is seen to be the most influential on the magnitude of the deflection. In addition, higher cutting speed combined with high depth of cut promotes chatter and produces a beating phenomenon whereas rotational speeds have a moderate influence on the dynamic response. Furthermore, several turning experiments are conducted that demonstrate vibration and chatter in the machining operations. There is fairly good qualitative agreement between the numerical results and the experimental ones

MODEL UPDATING AND STRUCTURAL HEALTH MONITORING OF HORIZONTAL AXIS WIND TURBINES VIA ADVANCED SPINNING FINITE ELEMENTS AND STOCHASTIC SUBSPACE IDENTIFICATION METHODS

Wind energy has been one of the most growing sectors of the nation’s renewable energy portfolio for the past decade, and the same tendency is being projected for the upcoming years given the aggressive governmental policies for the reduction of fossil fuel dependency. Great technological expectation and outstanding commercial penetration has shown the so called Horizontal Axis Wind Turbines (HAWT) technologies. Given its great acceptance, size evolution of wind turbines over time has increased exponentially. However, safety and economical concerns have emerged as a result of the newly design tendencies for massive scale wind turbine structures presenting high slenderness ratios and complex shapes, typically located in remote areas (e.g. offshore wind farms). In this regard, safety operation requires not only having first-hand information regarding actual structural dynamic conditions under aerodynamic action, but also a deep understanding of the environmental factors in which these multibody rotating structures operate. Given the cyclo-stochastic patterns of the wind loading exerting pressure on a HAWT, a probabilistic framework is appropriate to characterize the risk of failure in terms of resistance and serviceability conditions, at any given time. Furthermore, sources of uncertainty such as material imperfections, buffeting and flutter, aeroelastic damping, gyroscopic effects, turbulence, among others, have pleaded for the use of a more sophisticated mathematical framework that could properly handle all these sources of indetermination. The attainable modeling complexity that arises as a result of these characterizations demands a data-driven experimental validation methodology to calibrate and corroborate the model. For this aim, System Identification (SI) techniques offer a spectrum of well-established numerical methods appropriated for stationary, deterministic, and data-driven numerical schemes, capable of predicting actual dynamic states (eigenrealizations) of traditional time-invariant dynamic systems. As a consequence, it is proposed a modified data-driven SI metric based on the so called Subspace Realization Theory, now adapted for stochastic non-stationary and timevarying systems, as is the case of HAWT’s complex aerodynamics. Simultaneously, this investigation explores the characterization of the turbine loading and response envelopes for critical failure modes of the structural components the wind turbine is made of. In the long run, both aerodynamic framework (theoretical model) and system identification (experimental model) will be merged in a numerical engine formulated as a search algorithm for model updating, also known as Adaptive Simulated Annealing (ASA) process. This iterative engine is based on a set of function minimizations computed by a metric called Modal Assurance Criterion (MAC). In summary, the Thesis is composed of four major parts: (1) development of an analytical aerodynamic framework that predicts interacted wind-structure stochastic loads on wind turbine components; (2) development of a novel tapered-swept-corved Spinning Finite Element (SFE) that includes dampedgyroscopic effects and axial-flexural-torsional coupling; (3) a novel data-driven structural health monitoring (SHM) algorithm via stochastic subspace identification methods; and (4) a numerical search (optimization) engine based on ASA and MAC capable of updating the SFE aerodynamic model

Full-scale monitoring of the wind-induced response of vertical slender structures, with fixed and rotating masses

Nowadays, structural monitoring is gaining more and more attention in the field of wind engineering. On the wake of these developments, the thesis develops and applies a comprehensive structural monitoring procedure tailored for the validation and investigation in full-scale of the wind-induced response of vertical slender structures, with fixed and rotating masses. All the main aspects of the monitoring practice are discussed, regarding the number, location and type of the sensors, the acquisition and the transmission of the full-scale data, as well as the management of the experimental database by following an encoded scheme. In addition, the thesis highlights a number of issues typical of the monitoring activity that are not addressed in literature, providing inspiration to solve them. The defined procedure finds application in two monitoring campaigns launched by the Wind Engineering group at the University of Genoa: one slender structure with fixed masses (a light tower) and one slender structure with rotating masses (a small vertical axis wind turbine). As regards the light tower, a reference calculation model of the wind-induced response of poles and towers is selected from literature and is validated in full-scale. The input parameters needed for the application of the model are identified from experimental surveys, intersecting wind tunnel tests and dynamic identification techniques. The results highlight the goodness of the selected model and the large uncertainties associated to the input parameters. As regards the wind turbine, the full-scale data are used to investigate the contribution of the rotating parts to the dynamic behavior. In addition, the fatigue damage of the supporting tower is calculated under stationary and non-stationary excitation due to wind, turbine rotation, emergency stop and start. The results highlight the importance of the detail modeling, the fundamental role played by the non-stationary conditions and the errors committed when using conventional models of the load

Aeronautical Engineering: A continuing bibliography with indexes, supplement 108

This bibliography lists 517 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1979

Finite element for the analysis of rotor-dynamic systems that include gyroscopic effects

This thesis presents new finite element formulations for the analysis of rotor-dynamic systems that include the effects of gyroscopic influence. Euler-Bernoulli finite elements have been created for both shaft and propeller descriptions. In addition to the gyroscopic effects, centrifugal stiffening has been considered for the propeller elements. The principle of virtual work has been used to determine the equations of motion and formulate element matrices. The proposed element matrices have been incorporated in the VIBRATIO suite of vibration analysis software in order to test the formulations. The software uses an innovative hybrid modelling technique that enables the user to analyse various dynamic problems including rotating beam elements with rigid body attachments. A model of a ship's drive shaft has been created in VIBRATIO for comparison against a verified ANSYS model. Results for forced vibration shaft analysis show excellent correlation between VIBRATIO's Euler shaft formulation and ANSYS's Timoshenko formulation. Incremental analyses of propeller systems using the novel gyroscopic formulation show gyroscopic effects of flexible blade attachments, and also the changing mode shapes and frequencies due to centrifugal stiffening. Results show gyroscopic and centrifugal stiffening effects must not be ignored for an accurate propeller analysis.EThOS - Electronic Theses Online ServiceBrunel UniversityGBUnited Kingdo

Aeronautical Engineering: A special bibliography with indexes, supplement 56

This bibliography lists 439 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1975

Aeronautical Engineering: A special bibliography with indexes, supplement 75, October 1976

This bibliography lists 300 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1976

Aeronautical Engineering: A special bibliography with indexes, supplement 87

This bibliography lists 368 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1977