No abstract

Switched reluctance machines (SRMs) are of great interest because of their simplicity, low-cost, reliability, robustness, fault-tolerance and extended-speed constant-power operation. However, conventional SRMs suffer from high torque ripples. There exist several methods, which have been proposed to reduce torque ripples. One of the proposed methods is to change the geometric structure of the machine. However, analysis of the state-of-the-art designs show that, despite achieving favourable results in applications, the moulding pins of the machines are normally neglected. A motor that gives positive results may get affected negatively by its random moulding during its manufacturing. In this paper, mitigation of torque ripples in short-pitched SRMs (SPSRMs) and fully-pitched SRMs (FPSRMs) are investigated. Three-phase SPSRM and FPSRM are chosen for this study and the effects of the geometric points of moulding pins in the machines are studied comparatively. Maxwell 2D program is used for the analysis and two different models are compared for both SPSRM and FPSRM. The obtained results show that the torque ripples of the two machines are lower when moulding pins are closer to the rotor position. It is reduced by 2.56% at 10 Amps in the proposed SPSRM and 12% at 6 Amps in the proposed FPSRM. It is also observed that the applied method is more effective in reducing torque ripples of FPSRMs than SPSRMs.

[1] Wave, current, acoustic backscatter and suspended sediment concentration measurements (both single-point and vertical profiles estimated by conversion of acoustic backscatter data) are used to investigate wave-current-cohesive sediment interaction on the muddy Atchafalaya inner shelf. During an energetic storm, we propose that bed state follows a cycle of dilation due to fluidization, erosion, deposition with fluid mud formation and consolidation. A one-dimensional-vertical cohesive sediment transport model is calibrated using current and concentration profiles to estimate the physical parameters that could not be measured directly, e.g., bottom stresses. Estimated bed position and computed bottom stresses suggest that the critical erosion threshold is in the range of 0.3 Pa to 0.5 Pa. The study site is impacted by a sediment-laden fresh water plume coming from the Atchafalaya River mouth. Bed density evolution during the storm is estimated from vertical sediment exchange between the water column and the bed excluding the duration of passage of a sediment-carrying water front. The values are in the range of 1,030 kg/m 3 to 1,200 kg/m 3 and indicate that the bed density increases during the erosion phase and decreases during deposition. At the end of the storm, it shows a steady increasing trend during hindered settling and exceeds the space-filling value during consolidation. Both the critical erosion shear stress and bed density values are consistent with the results of laboratory tests on samples from the experimental site.

The flocculation of cohesive sediment in the presence of waves is investigated using high-resolution field observations and a newly-developed flocculation model based on artificial neural networks. Vertical profiles of suspended sediment concentration and turbulent intensity are estimated using measurements of current profile and acoustic backscatter. The vertical distribution of floc size is estimated using an artificial neural network (ANN) that is trained and validated using floc size measurements at one vertical level. Data analysis suggests a linear correlation between suspended sediment concentration and turbulence intensity. Observations and numerical simulations show that floc size is inversely related to sediment concentration, turbulence intensity and water temperature. The numerical results indicate that floc growth is supported by low concentration and low turbulence. In the vertical direction, mean size of flocs decreases toward the bottom, suggesting floc breakage due to increasing turbulence intensity toward the bed. A significant decrease in turbulent shear could occur within the bottom few-cm, related to increased damping of turbulence by sediment induced density stratification. The results of the numerical simulations presented here are consistent with the concept of a cohesive sediment particle undergoing aggregation-fragmentation processes, and suggest that the ANN can be a precise tool to study flocculation processes.

2017-08-30T02:06:41