A Comparative Performance Evaluation of Extended AANF with Different Parameter Estimation Techniques for Renewable Energy Integration

This paper presents real time performance evaluation of three phase extension of an amplitude adaptive notch filter (AANF) for online estimation of frequency, amplitude, and sequence components of the input grid voltage signal. The performance of an extended AANF is compared with conventional synchronous reference frame-phase lock loop (SRF-PLL), enhanced phase lock loop (EPLL), and existing adaptive notch filter (ANF). Comparative analysis has been carried out based on their ability in extracting frequency and amplitude of input grid voltage signal under balanced and unbalanced voltage sag/swell, frequency shift and distorted grid condition. Three phase AANF method provides high degree of accuracy than SRF-PLL, EPLL, and ANF in extracting appropriate signal information for unbalanced and harmonically distorted grid condition. The important feature of this method is its amplitude adaptability, which improves its speed of response and accuracy when grid signal is of variable amplitude. OPAL-RT’s (OP4500) real time controller with an in-built Xilinx Kintex-7 FPGA processor is used for real time implementation. Experimental results validate fast and accurate performance of an extended AANF in extracting frequency, amplitude, and sequence components of the utility grid voltage signal, which can be further used for performance improvement of grid connected renewable energy systems, custom power devices, and flexible ac transmission systems (FACTS) devices.     

A novel mechanical cleavage method for synthesizing few-layer graphenes

A novel method to synthesize few layer graphene from bulk graphite by mechanical cleavage is presented here. The method involves the use of an ultrasharp single crystal diamond wedge to cleave a highly ordered pyrolytic graphite sample to generate the graphene layers. Cleaving is aided by the use of ultrasonic oscillations along the wedge. Characterization of the obtained layers shows that the process is able to synthesize graphene layers with an area of a few micrometers. Application of oscillation enhances the quality of the layers produced with the layers having a reduced crystallite size as determined from the Raman spectrum. Interesting edge structures are observed that needs further investigation.     

Experimental investigation of transverse vibration-assisted orthogonal cutting of AL-2024

In the conventional use of vibration-assisted machining the vibratory motion is applied to the tool either linearly along the direction of the cutting velocity or elliptically in the plane containing the cutting velocity and surface normal. In contrast to this, this study investigates vibrations that are applied along the cutting edge and perpendicular to the cutting velocity. Such a vibratory motion is expected to provide a small sawing action that will enhance the ductile fracture occurring ahead of the cutting tool as the chip separates from the bulk work material. This enhancement in fracture will then contribute to reducing the chip thickness and cutting forces. Also, the sawing action reduces the imprint left behind by the cutting tool leading to a better surface finish. To confirm these predictions orthogonal cutting with the assistance of transverse vibrations applied to the cutting tool are performed on Al-2024 tubes using a carbide cutting tool. Experiments are performed at different conditions of cutting speeds, feeds and amplitudes of vibration at a fixed vibration frequency of 40 kHz. Cutting forces, chip thickness, and surface finishes are measured and compared with similar cutting conditions without application of vibration. In general, a reduction in cutting forces and feed forces is observed when transverse vibrations are applied. Chip thickness is also reduced and surface finish is improved upon application of vibration. Some explanations are offered to support these results.     

Development of a Centrifugal Oil Lubricator for Long-Term Lubrication of Spacecraft Attitude Control Systems—Design and Theory

Spacecraft, irrespective of their mission's purpose, contain a number of moving mechanical assemblies such as momentum/reaction wheels, control moment gyros, solar array drives, etc. Most problems encountered with these moving systems are related to tribology and, specifically, lubrication. Lubrication problems result from the loss of lubricant from the working zone by evaporation, surface migration, etc. Therefore, to ensure long-term uninterrupted performance of these systems, an efficient lubricant replenishment system is essential. This article describes the development of a novel lubricant supply system that can supply lubricant for more than 30 years at a controlled rate of few micrograms/hour. A mathematical model of a such lubrication system is developed to predict its useful life and performance. In addition, a computational fluid dynamics (CFD) simulation study of the lubricator is carried out and the results are used to verify and refine the theoretical model. Finally, the refined model is used to predict the performance of the lubricator for a period of 30 years.     

Development of a Lubrication System for Momentum Wheels Used in Spacecrafts

The success of any satellite mission largely depends upon the performance of the attitude control systems such as gyroscopes and momentum/reaction wheels. The required life and performance quality of these rotating mechanisms are ensured by the selection of bearings and its lubrication. The design and development of lubrication system to meet the long-term uninterrupted performance is a challenging task before the tribologists. This article describes the developmental study of a lubrication system for long-term requirements of momentum/reaction wheels. The developed system is compact and can be placed inside the bearing unit assembly. It works on centrifugal force and able to supply lubricant continuously at a very low rate of few micrograms per hour for many years. Further, the system can be tuned for any flow rate depending on the requirement.     

Multi-criteria decision making techniques for compliant polishing tool selection

The International Journal of Advanced Manufacturing Technology - Precision devices require surface finish of a few nanometers. The choice of compliant coated abrasive tools used in manufacturing...