Ahmad Al-Shyyab

Non-linear dynamic behaviour of compound planetary gear trains: Model formulation and semi-analytical solution

Abstract A discrete, non-linear, time-varying, torsional dynamic model of a multi-stage planetary train that is formed by any number of simple planetary stages is proposed in this study. Each planetary stage has a distinct fundamental mesh frequency and any number of planets spaced in any angular positions. The model allows the analysis of the gear train in all possible power flow configurations suitable for various gear drive ratios. It includes periodic variation of gear mesh stiffnesses as well as clearance (backlash) non-linearities that allow tooth separations. Equations of motion for the general case are formulated and solved semi-analytically using a hybrid harmonic balance method (HBM) in conjugate with inverse Fourier transform. Relative mesh displacements along lines of action of individual gear pairs were used as the continuation parameters to pass singular points and ill-conditioned equations in their proximity. At the end, a case study of a two-stage planetary train is used to demonstrate the effectiveness of the model and solution methods. The HBM solutions are compared to those obtained by a direct numerical integration method to assess their accuracy.

Strain-Concentration Factor of Circumferentially V-Notched Cylindrical Bars Under Static Tension

The FEM is used to study the effects of notch opening angle (β) and notch radius on the new strain-concentration factor (SNCF) for circumferentially V-notched cylindrical bars under static tension. The new SNCF has been defined under the triaxial stress state at the net section. Nevertheless, the conventional SNCF has been defined under uniaxial stress state. The new SNCF ( ) is constant in the elastic deformation. The range where this elastic value remains constant increases with increasing β and increasing notch radius (ρ o ). The effect of the notch opening angle on the elastic decreases with increasing ρ o . Particularly, the elastic of β = 120° is the minimum for all notch radii employed. The new SNCF increases from its elastic value to a peak value and then decreases with plastic deformation for notches with β = 120°. This peak value is the maximum . Nevertheless, for the notches with β o = 0.5 and 1mm. After that it increases to the maximum SNCF and then slightly decreases for further plastic deformation. The variations in with the ratio of tensile load to that at yielding at the notch root (P/P Y ) are nearly independent of stress-strain curve up to general yielding.

Transient Thermal Behavior of Hot–Mix Asphalt Pavement

A heat transfer model was developed to predict a transient thermal behavior of asphalt concrete during service life at different weather conditions. The developed model has the capability to predict the distribution of temperature field with respect to time within the Hot-Mix asphalt body based on surrounding environmental conditions. This will greatly help pavement engineers to select the suitable asphalt grade to achieve the best pavement performance and avoid pavement distresses might be caused due to extreme pavement temperatures. These distresses include fatigue cracks, rutting, and thermal cracking. The resulted model required data on asphalt mixture, incident radiation, surface, and ambient temperatures in addition to thermal properties of Hot-Mix asphalt including absorptivity, heat transfer coefficient, and the emissivity. A sensitivity analyses wasperformed to study the impact of a number of thermalenvironmental and pavement geometric parameters on predicted temperature responses. The results of analysis indicated that the incident radiation, absorptivity, and the heat transfer coefficient have the most significant effect on Hot-Mix asphalt temperature. Also, the emissivity has insignificant effect on surface temperature Hot-Mix asphalt.

Steady Hydrodynamics and Thermal Behaviors of Fluid Flows in Micro – Parallel Plates (Couette Flows)

The hydrodynamics and thermal behaviors of fluid in micro - Couette flows is investigated numerically. The model that combines both the continuum approach and the possibility of slip at the boundary is adopted in the study. The Effects of Knudsen number Kn, Brinkman number and the pressure gradient on the Couette microchannel hydrodynamics and thermal behaviors are investigated. It is found that as Kn increases the slip in the hydrodynamic and thermal boundary condition increases. Also, it is found that the slip velocity and the temperature jump at the boundaries increases as the Brinkman number and the pressure gradient increases.