34 research outputs found

    InP membrane photonics for large-scale integration

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    InP membrane photonics for large-scale integration

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    Small scale desalination technologies: A comprehensive review

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    In recent decades, problems related to fresh water has become a very important issue for humans. Small-scale desalination (SSD) systems, besides large-scale desalination (LSD) systems, fulfil an important role in meeting freshwater demand by eliminating the cost of transmission and have the advantage of treating water on-site. In this study, for the first time, a comprehensive review of previous studies has been carried out on SSD systems (less than 25 m3/d water production). These systems are powered using renewable, non-renewable or hybrid sources of energy, incorporating different treatment technologies such as: reverse osmosis (RO); electro dialysis (ED); capacitive deionization (CDI); membrane desalination (MD); humidification–dehumidification processes (HDH); multi-effect desalination (MED); and hybrid technologies, including a combination of RO-UF, RO-ED and RO-MED. The advantages and drawbacks of the systems that operate using fossil fuels and renewable energy (RE) systems have been studied, considering membrane, evaporation and salinity features. Among these, solar-based desalination systems are the most popular. Accordingly, numerous studies on RO, ED, MD, HDH and MED technologies for solar-SSD systems have been compared in terms of their freshwater productivity, energy consumption and cost of produced water. Attention has also been paid to SSD systems powered via wind, geothermal, tidal and hybrid energies. It has been determined that the RO system holds the largest market share in both non-renewable (25 %) and renewable energy (40 %) systems. In addition, a comparison of low-cost SSD and LSD systems shows that SSD systems are economically competitive with LSD systems. The outlook for the future shows that the use of SSD systems powered using non-renewable energy is likely to decrease, except in areas where energy costs are very low. In addition, the use of solar-SSD systems is likely to increase, where systems that operate solely on wind or geothermal energy will be replaced by hybrid renewable energy systems

    Rotorcraft Flight Simulation Model Fidelity Improvement and Assessment - Final report of NATO STO AVT-296 Research Task Group

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    Rotorcraft flight dynamics simulation models require high levels of fidelity to be suitable as prime items in support of life cycle practices, particularly vehicle and control design and development, and system and trainer certification. On the civil side, both the FAA (US) and EASA (Europe) have documented criteria (metrics and practices) for assessing model and simulator fidelity as compared to flight-test data, although these have not been updated for several decades. On the military side, the related practices in NATO nations are not harmonised and often only developed for specific applications. Methods to update the models for improved fidelity are mostly ad hoc and lack a rational and methodical approach. Modern rotorcraft System Identification (SID) and inverse simulation methods have been developed in recent years that provide new approaches well suited to pilot-in-the-loop fidelity assessment and systematic techniques for updating simulation models to achieve the needed level of fidelity. To coordinate efforts and improve the knowledge in this area, STO Applied Vehicle Technology Panel Research Task Group (STO AVT-296 RTG) was constituted to evaluate update methods used by member nations to find best practices and suitability for different applications including advanced rotorcraft configurations. This report presents the findings of the AVT-296 RTG. An overview of previous rotorcraft simulation fidelity Working Groups is presented, followed by a review of the metrics that have been used in previous studies to quantify the fidelity of a flight model or the overall perceptual fidelity of a simulator. The theoretical foundations of the seven different update methods and a description of the eight flight databases (Bell 412, UH-60, IRIS+, EC135, CH-47, AW139, AW109, and X2, provided by the National Research Council of Canada, US Army, Airbus Helicopters, Boeing, Leonardo Helicopter Division, and Sikorsky) used by the RTG is presented. Both time- and frequency-domain fidelity assessment methods are considered, including those in current use by simulator qualification authorities and those used in the research community. Case studies are used to show the application, utility, and limitations of the update and assessment methods to the flight-test data. The work of the RTG has shown that time- and frequency-domain SID based metrics are suitable for use for assessing the model fidelity across a wide range of rotorcraft configurations. Gain and time delay update methods work well for well-developed flight dynamics models and can be used for flight control system design, but do not provide physical insights into the sources of errors in a model. Deriving stability and control derivatives from flight-test data using SID and nonlinear simulation models using perturbation extraction methods provides insight into the missing dynamics of the simulation model, which can subsequently be updated using additional forces and moments to significantly improve the fidelity of the model and can be used to update models for flight simulation training application methods. Reduced order model and physics-based correction methods provide large benefits when extrapolating to other flight conditions but does require detailed flight-test data. SID can quickly provide accurate point models, if detailed flight-test data are available, which can be ‘stitched’ together to produce models suitable for real-time piloted simulation and control design applications. However, the dependency on flight-test data means that this method is not suitable for early aircraft development activities. This documentation of rotorcraft simulation fidelity assessment and model update strategies will benefit NATO nations by allowing for common, agreed-upon best practices and recommendations, ensuring each country’s flight dynamics and simulation models are of the highest calibre possible. The collaboration between industry, academia, and government laboratories has been key to the success of this RTG; this cooperation model should be adopted in future research activities. As industries strive to achieve greater efficiency and safety in their products, the fidelity of simulation should match commercial aspirations to ensure that the ‘right first time’ ethos is fully embedded into industrial best practices. Militaries will be able to use the methods and metrics presented to set criteria that will underpin the use of modelling and simulation in certification to accelerate development and acquisition and reduce the cost of new aircraft systems, e.g., advanced high-speed rotorcraft and legacy system upgrades. The criteria may also set standards for training devices used to support the expansion of synthetic environments for training to offset the high costs of flight hours. This RTG has identified that current flight training simulator standards could be updated to use the flight model and perceptual fidelity metrics presented in this report to ensure that models are not ‘over-tuned’ and a more rigorous method of subjective simulator assessment is adopted

    Analysis of double elastic steel wind driven magneto-electric vibration energy harvesting system

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    [[abstract]]This research proposes an energy harvesting system that collects the downward airflow from a helicopter or a multi-axis unmanned rotary-wing aircraft and uses this wind force to drive the magnet to rotate, generating repulsive force, which causes the double elastic steel system to slap each other and vibrate periodically in order to generate more electricity than the traditional energy harvesting system. The design concept of the vibration mechanism in this study is to allow the elastic steel carrying the magnet to slap another elastic steel carrying the piezoelectric patch to form a set of double elastic steel vibration energy harvesting (DES VEH) systems. The theoretical DES VEH mechanism of this research is composed of a pair of cantilever beams, with magnets attached to the free end of one beam, and PZT attached to the other beam. This study analyzes the single beam system first. The MOMS method is applied to analyze the frequency response of this nonlinear system theoretically, then combines the piezoelectric patch and the magneto-electric coupling device with this nonlinear elastic beam to analyze the benefits of the system’s converted electrical energy. In the theoretical study of the DES VEH system, the slapping force between the two elastic beams was considered as a concentrated load on each of the beams. Furthermore, both SES and DES VEH systems are studied and correlated. Finally, the experimental data and theoretical results are compared to verify the feasibility and correctness of the theory. It is proven that this DES VEH system can not only obtain the electric energy from the traditional SES VEH system but also obtain the extra electric energy of the steel vibration subjected to the slapping force, which generates optimal power to the greatest extent.[[notice]]補正完

    Application of fibre optic sensing systems to measure rotor blade structural dynamics

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    This paper compares two fibre optic sensing techniques for vibration characterisation: (a) optical fibre Bragg grating (FBG) strain gauges and (b) a novel direct fibre optic shape sensing (DFOSS) approach based on differential interferometric strain measurements between multiple fibres within the same fibre arrangement. Operational mode shapes and frequency measurements of an Airbus Helicopters H135 bearingless main rotor blade (5.1 m radius) were acquired during a series of ground vibration tests undertaken in a controlled laboratory environment. Data recorded by the fibre optic instrumentation systems were validated using commercially available accelerometers and compared against a baseline finite element model. Both fibre optic sensing systems proved capable of identifying the natural frequencies of the blade in the frequency range of interest (0–100 Hz). The data from the FBG sensors exhibited a dependency on their position relative to the neutral axes of the blade, which meant that full characterisation of the flapping and lagging modes required careful consideration of sensor location in the chordwise direction. The DFOSS system was able to identify all structural dynamics, despite being located on the neutral axis in the lagging direction, due to its sensitivity to angle changes, rather than strain, and its biaxial measurement capability. The DFOSS system also allowed the operational mode shapes of the blade to be determined directly, without the requirement for strain transfer from the blade to the sensor and without the requirement for a model of the underlying structure. The accuracy of obtained natural frequencies and operational mode shapes is assessed, demonstrating the potential of the use of both fibre optic sensing systems for determining blade structural dynamics

    CMOS Active Gate Driver for Closed-Loop dv/dt Control of Wide Bandgap Power Transistors

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    Wide bandgap (WBG) power transistors such as SiC MOSFETs and GaN HEMTs are a real breakthrough in power electronics. These power semiconductor devices have lower conduction and switching losses than their Silicon competitors. However, the fast switching transients can be an issue in terms of Electromagnetic Interferences (EMI). Consequently, one must slow down the switching speeds of WBG transistors to comply with EMI limitations, which reduces their advantages in terms of higher switching frequencies and lower total losses. In this work, an active gate driver is proposed to control the switching speed of wide bandgap semiconductor power transistors. An innovative closed-loop control circuit makes it possible to adjust separately the dv/dt and di/dt during the switching sequences. Overall, the dv/dt values can be reduced to comply with system-level limits of EMI, with less switching losses than existing methods. The proposed method is thoroughly investigated, with analytic and numerical models to assess the key performances: feedback loop bandwidth, optimal circuit design, area consumption. Selected and optimal designs are implemented in two integrated circuits in CMOS technology which demonstrate delay times below the nanosecond. With such performances, it has been shown experimentally that it is possible to actively control switching speeds higher than 100 V/ns under voltages of 400 V
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