Cette thèse est consacrée aux études expérimentales et numériques du comportement mécanique et poromécanique et de l’évolution de la perméabilité du grès en prenant en compte l’anisotropie du matériau. Après une analyse par la microscopie électronique à balayage (MEB) et les rayons X, les échantillons sont utilisés pour réaliser des essais de compression hydrostatique et de compression triaxiale sous différentes pressions de confinement. Les évolutions des coefficients de Biot et de la perméabilité sont mesurées respectivement et étudiées en prenant en compte le comportement mécanique. Un modèle élastoplastique couplé à l’endommagement en se basant sur l'approche discrète est proposé et appliqué aux grés secs. Les essais en compression sont simulés, l’évolution et la distribution de la variable d’endommagement et de l’écrouissage plastique sont analysées. Le modèle proposé est validé de nouveau par les simulations des essais réalisés (y compris le comportement mécanique, les coefficients de Biot et la perméabilité) sur des échantillons saturés. Une très bonne concordance est obtenue entre les prédictions et les données expérimentales. Enfin, on développe un modèle anisotropique poroplastique couplé avec l’endommagement afin de décrire les propriétés poromécaniques du grès saturé. Le modèle proposé est appliqué pour décrire le comportement du matériau dans les essais triaxiaux en condition non-drainée, et dans les essais triaxiaux en appliquant une pression interstitielle. En général, la aussi nous obtenons une bonne concordance entre modélisation et expérimentation. / This thesis presents the laboratory and numerical investigations on anisotropic mechanical, poromechanical and fluid transport behavior of sandstone. After the X-ray and SEM tests, the samples were stressed under triaxial loading to study the initial and stress-induced mechanical behavior. The evolution of anisotropic Biot’s coefficients and axial permeability are also investigated and related to mechanical behavior. A plastic damage model is presented based on discrete approach. The proposed model is applied to simulate the mechanical behavior of dry sandstone under different loading conditions, the evolution and distribution of damage variable and plastic hardening variable are also discussed. Furthermore, the proposed model is applied to simulate the previous experimental results (including mechanical behavior, Biot's coefficients and permeability) of saturated sandstones. The comparisons between the numerical result and test data show a good performance of the present model. Finally, an anisotropic poroplastic damage model is developed to describe the poromechanical behavior of saturated sandstone. The comparisons between numerical simulation and experimental data is given for the triaxial compression tests under drained and undrained condition, the tests of strain response to pore pressure increment is also simulated, a good accordance is obtained.

A six-degree-ofreedom piecewise simulation of aircraft motion is developed in SIMULINK. Using a mathematical model of fixed-wing aircraft, the simulation is used to observe the longitudinal and lateral-directional motions of the aircraft following a pilot input. The mathematical model is in state-space form and uses aircraft stability and control derivatives calculated from the aircraft geometric and aerodynamic characteristics. The simulation takes into account the changed speed and altitude due to pilot input and demonstrates the non-linearity of the aircraft motion due to change in speed and altitude. The results from the simulation are compared with the known results to validate the mathematical model used. The simulation is carried out for a number of airspeed and altitude combinations to examine the effect of changing speed and altitude on the aircraft dynamic response.

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Hoi Wai-leung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 62-63). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.5 / Chapter 2 --- Preminilaries --- p.8 / Chapter 2.1 --- Gauss and Jacobi Sums --- p.8 / Chapter 2.2 --- Basic Properties of Characters and Jacobi Sums --- p.10 / Chapter 2.3 --- Characters on Ok/Q --- p.11 / Chapter 2.4 --- Bernoulli Numbers and Bernoulli Polynomials --- p.15 / Chapter 2.5 --- Evaluation of Bp-1(k)-Bp-1 (mod p) --- p.16 / Chapter 2.5.1 --- "k = 2,3,4,6" --- p.16 / Chapter 2.5.2 --- "k = 5,8,10,12" --- p.17 / Chapter 3 --- The Main Result --- p.19 / Chapter 3.1 --- p-adic Gamma Functions and Gross-Koblitz Formula --- p.19 / Chapter 3.2 --- The Sum Σ - j(modp) --- p.22 / Chapter 3.3 --- The Main Theorem --- p.23 / Chapter 4 --- Evaluation of J(xk-r： Xk-s) (mod Q2) --- p.29 / Chapter 4.1 --- Basic Result --- p.29 / Chapter 4.2 --- Results for k = 8 --- p.30 / Chapter 4.3 --- Results for k = 12 --- p.32 / Chapter 4.4 --- "Results for k = 10,5" --- p.35 / Chapter 5 --- Evaluation of Binomial Coefficients --- p.41 / Chapter 5.1 --- Results for k = 8 --- p.41 / Chapter 5.2 --- Results for k = 12 --- p.44 / Chapter 5.3 --- Results for k = 10 --- p.49 / Chapter 5.4 --- Numerical Examples --- p.54 / Chapter 5.4.1 --- k = 8 --- p.54 / Chapter 5.4.2 --- k = 10 --- p.56 / Chapter 5.4.3 --- k = 12 --- p.58 / Bibliography --- p.61

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Due to the complexity of body-shape, the investigation of hydrodynamic forces on mooring lines, especially those comprised of chain segments, has not been conducted to a sufficient degree to properly characterize the hydrodynamic damping effect of mooring lines on the global motions of a moored offshore platform. In the present study, an experimental investigation of the hydrodynamic characteristics of various mooring elements is implemented through free and forced oscillation tests. Since no direct measurement capability for distributed hydrodynamic forces acting on mooring line segments such as chain and wire rope is available yet, an indirect measurement technique is introduced. The technique is based on the fact that hydrodynamic forces acting on a body oscillating in still water and on a stationary body in an oscillatory flow are equivalent except for the additional inertia force, the so-called Froude-Krylov force, present in the latter condition. The time-dependent displacement of a slender body moving in calm water is acquired through optical tracking with a high speed camera. The distributed hydrodynamic measurements are then used to obtain the force by solving the equation of motion with the boundary condition provided from tension measurements. Morison’s equation is employed along with Fourier analysis to separate the inertia and drag components out of the total fluid force. Given the experimentally-derived information on hydrodynamic behavior, the resistance provided by a mooring line to a floating structure is briefly studied in terms of damping and restoring force in a coupled dynamic system.

Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus reducing the damping capability. Furthermore, existing predictive models are too restrictive. Single frequency, unidirectional load and centered circular orbit experiments were conducted on a revamped SFD test rig. The damper journal is 1" in length and 5" in diameter, with nominal clearance of 5 mils (0.127 mm). The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice discharge ports to prevent air ingestion. The discharge end is fully sealed with a wave-spring that pushes a seal ring into contact with the SFD journal. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and amplitude of motion dependent, albeit decreasing rapidly as the motion parameters increase. Identified force coefficients, damping and added mass, for the squeeze film damper alone agree very well with predictions based on the full film, short length SFD model.