Development of variable speed horizontal axis wind turbines has resulted in a need for an analysis code with a rotor speed degree-of-freedom. This study develops a five degree-of-freedom time domain computer code that evaluates blade and rotor, mean and cyclic loads with nonlinear aerodynamics together with atmospheric turbulence as a forcing function. Verification of the model is made by comparison of loads predictions between ESI-80 wind turbine data and analytical solutions. Results show good agreement for mean and cyclic loads and teeter angle excursions. A single-blade point turbulence simulation model is optimized using a three-blade point turbulence simulation model. The optimum point is the 80% radius location, although a multiplying factor is needed to make conservative fatigue cycle predictions of blade bending. ESI-80 start-up and shutdown scenarios are examined, prediction trends matched ESI-80 data. Three generator models are investigated. Results show that generator torque cycles are reduced and yearly energy capture increased by 24% when a variable speed generator is implemented. / Graduation date: 1991

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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In this thesis a mathematical model for the combined effects of vortex-induced oscillation and galloping of a square section cylinder in cross flow is examined. The model equations are obtained by simply combining Parkinson and Smith's Quasi-Steady Model for galloping with the Hartlen-Currie model for vortex-induced vibration, which is essentially the same model used by Bouclin in the hydrodynamic case. The semi-empirical model is solved using three popular approximate analytical methods, and the methods of solution are evaluated. The solution of the model is compared with recent experimental data. The methods of solution used are the Method of Van Der Pol, (also called the method of Harmonic Balance), the Method of Multiple Scales, and some results from the Hopf Bifurcation Theory. The Method of Multiple Scales provides the most useful solutions, getting good results even with just the ༠(1) terms, although the next-order terms are necessary for the solution in the resonance regions. The phenomenon of subharmonic resonance, observed in recent experiments, is also observed in the solution of the model equations. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Significant advances in understanding early stages of transitional flows have been achieved by studying secondary instabilities in selected prototype flows. These secondary instabilities can be modeled as parametric instabilities of the nearly periodic flow that consists of the prototype velocity profile and a superposed finite-amplitude TS-wave (wavelength λ). The generally three dimensional secondary instabilities are governed by a linearized system of partial differential equations with periodic coefficients which are reduced to an algebraic eigenvalue problem through the application of a spectral collocation method Following Floquet theory, previous analysis looked for subharmonic (wavelength 2 λ) and fundamental (wavelength λ) types of solutions. We extend the Floquet theory to solutions having arbitrary wavelengths, hence including the previous solutions as special cases. Modes with wavelength in between the subharmonic and fundamental values are called detuned modes. Detuned modes lead to combination resonance which has been observed in controlled transition experiments. Knowledge of the bandwidth of amplified detuned or (combination) modes is very important for clarification of the selectivity of the early stages of transition with respect to initial disturbances. We have selected two flows: the Blasius boundary layer flow and the hyperbolic-tangent free-shear flow as prototypes of wall bounded Hows and unbounded Hows, respectively. In the Blasius flow we have concentrated on studying detuned modes. We found the growth rates of modes slightly detuned from the subharmonic wavelength to be almost as large as the growth rate of the subharmonic itself. This result is consistent with both the broadband spectra centered at subharmonic frequency observed in the "biased" experiment of Kachanov & Levchenko, wherein only the TS frequency was introduced, and with the large band-width of resonance in the "controlled" experiments, wherein a TS wave and the detuned modes were introduced simultaneously. In the free-shear flow, our goals were three-fold. The first was to investigate whether the Floquet analysis based on the shape assumption for TS waves would provide results consistent with results for the stability of Stuart vortices. Second, we aimed at revealing the effect of viscosity on these results. Finally, we wanted to evaluate a group of spectral methods for the numerical treatment of the flow in an unbounded domain. We have made a detailed analysis of subharmonic, fundamental, and detuned modes. Results display the basically inviscid, convective character of the secondary instabilities, and their broadband nature in the streamwise and spanwise directions. In the inviscid limit, and for neutral TS waves, a detailed comparison is made with the closely related study on stability of Stuart vortices by Pierrehumbert & Widnall. Good quantitative agreement is obtained. For a wide range of Reynolds numbers and amplitudes of the 2-D primary wave, results reveal that the most unstable subharmonic modes are two-dimensional (vortex pairing). On the other hand, the most unstable fundamental modes are three-dimensional, with short spanwise wavelengths. Detuned modes have characteristics in between, being most unstable in the two-dimensional or three-dimensional form depending on the detuning value. Comparisons of our results for a superposed TS wave of constant amplitude with results obtained by numerical simulations suggested that the growth of the TS wave may have a significant effect on the secondary disturbance growth. To check this hypothesis, we have developed a numerical method that accounts for small variations in the TS amplitude. However, the results indicate that the discrepancies are due to other yet concealed effects. / Ph. D. / incomplete_metadata

Kwok Chun-yin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves [121]-122). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Experimental data --- p.7 / Chapter 2.1 --- Turbulent Convection using Helium --- p.7 / Chapter 2.2 --- Turbulent Convection using water --- p.8 / Chapter 3 --- Probability Distribution and Scaling behavior --- p.9 / Chapter 3.1 --- PDF of YT --- p.9 / Chapter 3.1.1 --- Helium Convection --- p.10 / Chapter 3.1.2 --- Water Convection --- p.26 / Chapter 3.1.3 --- Comparison between helium data and Water data --- p.34 / Chapter 3.2 --- T -dependence of the moments of XT --- p.39 / Chapter 3.2.1 --- Helium Convection --- p.39 / Chapter 3.2.2 --- Water Convection --- p.47 / Chapter 4 --- Hierarchical Moment Relation --- p.50 / Chapter 4.1 --- Method of Analysis --- p.50 / Chapter 4.2 --- Results and Discussion --- p.53 / Chapter 4.2.1 --- Helium Convection --- p.53 / Chapter 4.2.2 --- Water Convection --- p.81 / Chapter 5 --- Discussion and Conclusion --- p.95 / Chapter 5.1 --- Passive Scalar --- p.96 / Chapter 5.2 --- Comparison between Turbulent Convection and Passive Scalar --- p.99 / Chapter 5.3 --- Scaling behavior for length scale above and below the Bolgiano scale for turbulent convection using Helium gas --- p.100 / Chapter 5.4 --- Conclusions --- p.107 / Chapter A --- The lognormal model --- p.108 / Chapter B --- Definition of XT --- p.110 / Chapter C --- Reasons for analysis of (xTp) for p≤ 12 --- p.112 / Chapter D --- Functional form of μp implied by the hierarchical relation --- p.119 / Bibliography --- p.122

Lo Ka Fai / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves [67]-68). / Text in English; abstracts in English and Chinese. / Lo Ka Fai / Abstract --- p.ii / Acknowledgements --- p.iii / List of Figures --- p.v / List of Tables --- p.ix / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- The First Problem: Heat Transfer and Large-scale Flow --- p.7 / Chapter 2.1 --- Circulating flow --- p.8 / Chapter 2.2 --- Shear flow --- p.10 / Chapter 3 --- Results and Discussions --- p.13 / Chapter 3.1 --- Circulating flow --- p.13 / Chapter 3.2 --- Shear flow --- p.17 / Chapter 4 --- The second problem: Intermittency --- p.22 / Chapter 5 --- Method of Analysis --- p.25 / Chapter 6 --- Results and discussions --- p.29 / Chapter 6.1 --- C=0.01 --- p.29 / Chapter 6.2 --- "C=0.05, 0.1 and 0.5" --- p.41 / Chapter 7 --- Conclusions --- p.60 / Chapter A --- Linear Scaling Exponents --- p.62 / Chapter B --- The Formula of and the Hierarchy --- p.64 / Bibliography --- p.66

by Pang Cheuk Sum. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Text in English; abstract also in Chinese. / by Pang Cheuk Sum. / Contents --- p.i / List of Figures --- p.iii / List of Tables --- p.v / Abstract --- p.vi / Acknowledgement --- p.viii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- The Problem --- p.7 / Chapter 2.1 --- Model of random advection --- p.7 / Chapter 2.2 --- Model without large scale flow --- p.8 / Chapter 2.3 --- "Model with, large-scale mean circulating flow" --- p.11 / Chapter 3 --- Reviews of the previous studies --- p.16 / Chapter 3.1 --- Review of previous studies on one-point scalar statistics --- p.16 / Chapter 3.2 --- Review of previous study on scalar difference --- p.18 / Chapter 4 --- Effects of a large-scale flow on one-point statistics --- p.20 / Chapter 4.1 --- Effects on mean scalar profile --- p.20 / Chapter 4.2 --- Effects on rms fluctuation --- p.23 / Chapter 4.3 --- Effects on probability density function --- p.26 / Chapter 5 --- Study of scalar difference --- p.34 / Chapter 5.1 --- Scalar difference at the center of lattice --- p.34 / Chapter 5.1.1 --- Probability density function --- p.34 / Chapter 5.1.2 --- Structure function --- p.43 / Chapter 5.1.3 --- Conditional averages --- p.52 / Chapter 5.1.4 --- Structure function at other position --- p.55 / Chapter 5.2 --- Effects of large-scale flow --- p.57 / Chapter 6 --- Summary --- p.65 / Chapter 6.1 --- Effects of a large-scale flow on passive scalar --- p.65 / Chapter 6.2 --- Statistics of scalar difference --- p.66 / Chapter A --- Simulation parameters --- p.67 / Chapter B --- Normalization of Probability Density Function --- p.68 / Bibliography --- p.69