Prediction of cavity growth rate during underground coal gasification using multiple regression analysis

During underground coal gasification （UCG）, whereby coal is converted to syngas in situ, a cavity is formed in the coal seam. The cavity growth rate （CGR） or the moving rate of the gasification face is affected by controllable （operation pressure, gasification time, geometry of UCG panel） and uncontrollable （coal seam properties） factors. The CGR is usually predicted by mathematical models and laboratory experiments, which are time consuming, cumbersome and expensive. In this paper, a new simple model for CGR is developed using non-linear regression analysis, based on data from 1 l UCG field trials. The empirical model compares satisfactorily with Perkins model and can reliably predict CGR.

Thermal Analysis of Implant-Defined Vertical Cavity Surface Emitting Laser Array

A three-dimensional electrical-thermal coupling model based on the finite element method is applied to study thermal properties of implant-defined vertical cavity surface emitting laser （VCSEL） arrays. Several parameters including inter-element spacing, scales, injected current density and substrate temperature are considered. The actual temperatures obtained through experiment are in excellent agreement with the calculated results, which proves the accuracy of the model. Due to the serious thermal problem, it is essential to design arrays of low self-heating. The analysis can provide a foundation for designing VCSEL arrays in the future.

Beam Steering Analysis in Optically Phased Vertical Cavity Surface Emitting Laser Array

Beam steering in implant defined coherently coupled vertical cavity surface emitting laser （VCSEL） arrays is simulated using the FDTD solution software. Angular deflection dependent on relative phase differences among elements, inter-element spacing, element size and emitted wavelength is analyzed detailedly and systematically. We design and fabricate 1×2 implant defined VCSEL arrays for optimum beam steering performance. Electroni- cally controlled beam steering with a maximum deflection angle of 1.6° is successfully achieved in the 1 × 2 VCSEL arrays. The percentage of the power in the central lobe is above 39% when steering. The results show that the steering is controllable. Compared with other beam steering methods, the fabrication process is simple and of low cost.

Benchmark solutions of large-strain cavity contraction for deep tunnel convergence in geomaterials

To provide precise prediction of tunnelling-induced deformation of the surrounding geomaterials,a framework for derivation of rigorous large-strain solutions of unified spherical and cylindrical cavity contraction is presented for description of confinement-convergence responses for deep tunnels in geomaterials.Considering the tunnelling-induced large deformation,logarithmic strains are adopted for cavity contraction analyses in linearly elastic,non-associated Mohr-Coulomb,and brittle Hoek-Brown media.Compared with approximate solutions,the approximation error indicates the importance of release of small-strain restrictions for estimating tunnel convergence profiles,especially in terms of the scenarios with high stress condition and stiffness degradation under large deformation.The ground reaction curve is therefore predicted to describe the volume loss and stress relaxation around the tunnel walls.The stiffness of circular lining is calculated from the geometry and equivalent modulus of the supporting structure,and a lining installation factor is thus introduced to indicate the time of lining installation based on the prediction of spherical cavity contraction around the tunnel opening face.This study also provides a general approach for solutions using other sophisticated geomaterial models,and serves as benchmarks for analytical developments in consideration of nonlinear large-deformation behaviour and for numerical analyses of underground excavation.

Safety Analysis of Flow Parameters in a Rotor-stator Cavity

In order to ensure the safety of engine life limited parts （ELLP） according to airworthiness regulations, a numerical approach integrating one-way fluid structure interaction （FSI） and probabilistic risk assessment （PRA） is developed, by which the variation of flow parameters in a rotor-stator cavity on the safety of gas turbine disks is investigated. The results indicate that the flow parameters affect the probability of fracture of a gas turbine disk since they can change the distribution of stress and temperature of the disk. The failure probability of the disk rises with increasing rotation Reynolds number and Chebyshev number, but descends with increasing inlet Reynolds number. In addition, a sampling based sensitivity analysis with finite difference method is conducted to determine the sensitivities of the safety with respect to the flow parameters. The sensitivity estimates show that the rotation Reynolds number is the dominant variable in safety analysis of a rotor-stator cavity among the flow parameters.