Transitions in the erosive wear behavior of a glass-ceramic

The mechanisms of material removal were investigated during the erosive wear of a glass-ceramic. The effects of erodent particle shape, velocity and angle were studied. Single impacts and incremental erosion tests were performed, to study the development of surface features and to elucidate the mechanisms of material removal. It was found that transitions in mechanism occurred which depended on the particle shape, impact velocity and impact angle. The mechanisms of material removal, for erosion by silica sand, changed from fine scale fracture and plastic processes below a transition point to large-scale cracking of the surface above. Spherical glass beads caused wear dominated by fatigue, with a very strong dependence of wear rate on the impact conditions. This work indicates that laboratory erosion testing of glass-ceramic and other brittle materials should reflect the conditions present in practice, and that account must be taken of possible changes in wear mechanisms.

RANS-URANS in axial compressor, a design methodology

Turbomachinery flows are inherently unsteady. Until now during the design process, unsteadiness has been neglected, with resort merely to steady numerical simulations. Despite the assumption involved, the results obtained with steady simulations have been used with success. One of the questions arising in recent years is can unsteady simulations be used to improve the design of turbomachines? In this work the numerical simulation of a multi-stage axial compressor is carried out. Comparison of Reynolds averaged Navier-Stokes (RANS) and unsteady Reynolds averaged Navier-Stokes (URANS) calculation shows that the unsteadiness affects pressure losses and the prediction of stall limit. The unsteady inflow due to the wake passing mainly modifies the losses and whirl angle near the endwalls. The computational cost of the fully unsteady compared with a steady simulation is about four times in terms of mesh dimension and two orders of magnitude as number of iterations. A mixed RANS-URANS solution has been proposed to give the designer the possibility to simulate an unsteady stage embedded in a steady-state simulation. This method has been applied to the simulation of a four-stage axial compressor rig. The mixed RANS-URANS approach has been developed using sliding and mixing planes as interface conditions. The rotor-stator interaction has been captured physically while reducing the computational time and mesh size.

Trench insulated gate bipolar transistor - a high power switching device

This paper presents a comprehensive theoretical study of the Trench Insulated Gate Bipolar Transistors (TIGBT). Specific physical and geometrical effects, such as the accumulation layer injection, increased channel density, increased channel charge and transversal electric field modulation are discussed. The potential advantages of the Trench IGBT over its conventional planar variant are highlighted. It is concluded that the Trench IGBT is one of the most promising structures in the area of high voltage MOS-controllable switching devices.

Dual-mode thin film bulk acoustic wave resonators for parallel sensing of temperature and mass loading.

Thin film bulk acoustic wave resonator (FBAR) devices supporting simultaneously multiple resonance modes have been designed for gravimetric sensing. The mechanism for dual-mode generation within a single device has been discussed, and theoretical calculations based on finite element analysis allowed the fabrication of FBARs whose resonance modes have opposite reactions to temperature changes; one of the modes exhibiting a positive frequency shift for a rise of temperature whilst the other mode exhibits a negative shift. Both modes exhibit negative frequency shift for a mass load and hence by monitoring simultaneously both modes it is possible to distinguish whether a change in the resonance frequency is due to a mass load or temperature variation (or a combination of both), avoiding false positive/negative responses in gravimetric sensing without the need of additional reference devices or complex electronics.

Dual-mode thin film bulk acoustic wave resonators for parallel sensing of temperature and mass loading

Thin film bulk acoustic wave resonator (FBAR) devices supporting simultaneously multiple resonance modes have been designed for gravimetric sensing. The mechanism for dual-mode generation within a single device has been discussed, and theoretical calculations based on finite element analysis allowed the fabrication of FBARs whose resonance modes have opposite reactions to temperature changes; one of the modes exhibiting a positive frequency shift for a rise of temperature whilst the other mode exhibits a negative shift. Both modes exhibit negative frequency shift for a mass load and hence by monitoring simultaneously both modes it is possible to distinguish whether a change in the resonance frequency is due to a mass load or temperature variation (or a combination of both), avoiding false positive/negative responses in gravimetric sensing without the need of additional reference devices or complex electronics. © 2012 Elsevier B.V.