Motion capture through inertial sensors is becoming popular, but its accuracy to describe kinematics during changes in walking speed is unknown. The aim of this study was to determine the accuracy of trunk speed extracted using an inertial motion system compared to a gold standard optical motion system, during steady walking and stationary periods. Eleven participants walked on pre-established paths marked on the floor. Between each lap, a 1-second stationary transition period at the initial position was included prior to the next lap. Resultant trunk speed during the walking and transition periods were extracted from an inertial (240 Hz sampling rate) and an optical system (120 Hz sampling rate) to calculate the agreement (Pearson's correlation coefficient) and relative root mean square errors between both systems. The agreement for the resultant trunk speed between the inertial system and the optical system was strong (0.67 < r ≤ 0.9) for both walking and transition periods. Moreover, relative root mean square error during the transition periods was greater in comparison to the walking periods (>40% across all paths). It was concluded that trunk speed extracted from inertial systems have fair accuracy during walking, but the accuracy was reduced in the transition periods.
Compressed air is crucial on an electric or electrified heavy-duty vehicle. The objective of this work was to experimentally determine the performance parameters of the first prototype of an electric-driven sliding-vane air compressor, specifically designed for electric and electrified heavy-duty vehicles, during the transient conditions of cold start-ups. The transient was analyzed for different thermostatic temperatures: 0 °C, −10 °C, −20 °C, and −30 °C. The air compressor unit was placed in a climatic chamber and connected to the electric grid, the water-cooling loop, and the compressed air measuring and controlling rig. The required start-up time was greater the lower the thermostatic temperature, ranging from 30 min at 0 °C to 221 min at −30 °C and depending largely on the volume of the lubricant oil filled initially. The volume flow rate of the compressed air was lower than nominal at the beginning, but it showed a step increase well beyond nominal when the oil reached 50 °C and then decreased gently towards nominal, while the input power kept steady at nominal after a short initial peak. These facts must be considered when estimating the time and the energy required by the air compressor unit to fill up the compressed air tanks of the vehicles.
The decarbonization of the residential sector is fundamental for energy transition. In this context, it is promising the introduction of hydrogen in natural gas networks in specific hydrogen districts. Accordingly, hydrogen meters are needed for accounting the fuel consumptions. The topic of this work is the development and construction of an experimental apparatus for testing safely hydrogen volume and flow meters up to 24 m3/h (referred to standard conditions) in controlled environmental conditions, between -25 and +55 °C (and beyond). The apparatus realized can test up to four volume and flow meters in a climatic chamber while processing air or pure hydrogen or methane. Methane-hydrogen mixtures can be tested connecting simply bottles with synthetic blends. The aim is to verify the measurement accuracy of the meters under test. A dedicated data analysis protocol featuring statistical process control is developed to monitor the stability of the system during the test. It exploits statistical indicators representing the autocorrelation, the normality of residuals of the mean value and the lag plot. The apparatus is realized, and it complies with the leakage limits set by indications in literature. A new ultrasonic domestic meter is tested in the apparatus. It has been developed by Pietro Fiorentini S.p.A. in the framework of the Hy4Heat project. Its error trends measured at all temperatures comply with the limit of 3.5% between 0.12 and 2 m3/h and 2% between 2 and 20 m3/h, as imposed by legislations.
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