1,721,003 research outputs found
Simulation approaches for the study of the oil flow rate distribution in lubricating systems with rotating shafts
No full textThis study addresses the issue of predicting the distribution of lubricant flow through the outlets of a rotating
shaft used in vehicle power transmission. A typical geometry with closely spaced rows of holes, suitable for the
lubrication of multi-disk clutches, was considered. Both lumped parameter and computational fluid dynamics
approaches were applied and compared. The test rig for model validation was designed with a variable speed shaft
featuring an axial oil inlet and three equally spaced pairs of radial outlet holes. The main characteristic of the
experimental facility is the possibility to selectively measure the flow rates through each outlet. It was found that the
three-dimensional model based on the multiple reference frame approach provides a reliable prediction of how the
flow rate is distributed. Generally, the flow rate is lower through the outlet closest to the inlet and is maximum at the
farthest exit. The flow distribution is minimally affected by the shaft speed. The influence of geometric parameters
on making the flow distribution more uniform was studied. It was found that a better flow balance is obtained with
a low ratio between the diameter of the radial holes and that of the axial channel. The results obtained offer bestpractice
guidelines for accurately simulating comparable systems, in order to optimize reliability of the mechanical
transmission and energy efficiency of the flow generation uni
Laboratory characterization aimed at analyzing the performance of diamond wires for marble cutting
No full textOver the years the diamond wire has got many improvements and optimizations, thanks to which one of the greatest revolutions in the stone industry took place. However, its use is still the cause of injuries, sometimes fatal, following the opening of the loop during cutting, with consequent whiplash and high-speed projection of its elements. The present work is focused on the study of some possible causes of diamond wire breakage, from those known, including slipping of the support cable from the junction clamp and cable break near the clamp, to that, observed in quarries of the Carrara Basin during on-site analyzes, of breaking the same junction clamp.
To help improving the safety level in the quarries, tensile tests were carried out at the “Marmotest s.a.s” laboratories of Carrara and DISEG of the Politecnico di Torino on wire elements, in detail junction clamps, pressing devices and support cable, supplied by the ‘Megadiamant Srl’ manufacturer of diamond wires, reproducing configurations and technological choices observed on site and assessing compliance with the European reference standard UNI EN 13236:2016 (“Safety Requirements for superabrasive products”). 100% of pressing devices and more than 90% of junction clamps subjected to slip tests have respected the limit value imposed by the reference standard.
For the latter, three factors mainly contribute to the slip resistance: the type of material, the length of the junction clamps and their thickness. Despite the research carried out, no technical documents are available regarding the chemical composition of the materials with which the joints are made but, in general, the clamps marketed as copper (or, more properly, copper steel) and annealed steel have provided greater extraction resistances than those in steel. Furthermore, the slip resistance is linked to the length of the clamp by direct proportionality, and its thickness by inverse proportionality. The water for cooling the diamond wire during cutting may not be used correctly or be limited byenvironmental problems. For this reason, the study of the slip resistance of copper and steel clamps has been extended, including the variation of their properties to temperature increase. Finally, the deterioration of the mechanical characteristics
of the diamond wire following the cutting was measured by performing tensile tests on used elements
Combined speed control and centralized power supply for hybrid energy-efficient mobile hydraulics
Full text linkImproving energy efficiency in mobile hydraulics is paramount and feasible via machine electrification, but all actuators' power in standard systems must flow through the electric motors, which is unfeasible for medium-to-high power applications. Therefore, this paper leverages the idea of splitting the transferred power between the hydraulic and electric domains to save energy while downsizing the electric motors. A novel layout of a hybrid excavator is presented, validated using high-fidelity simulations, and compared to the state-of-the-art, load-sensing machine. The results show the expected system's functioning and efficiency benefits (fuel savings close to 28% compared to the original excavator). Almost 60% of the energy is transferred to the actuators hydraulically minimizing the power rating of the electric machines in favor of the system's cost and compactness. Future research will focus on controlling the hybrid system to maximize energy savings and make it easily applicable to different fluid power machines
Effect of desmethyldiazepam and chlordesmethyldiazepam on 3',5'-cyclic guanosine monophosphate levels in rat cerebellum.
No full textDownsizing the electric machines of energy-efficient electro-hydraulic drives for mobile hydraulics
Full text linkThe poor energy efficiency of state-of-the-art mobile hydraulics affects the carbon dioxide released into the atmosphere and the operating costs. These crucial factors require urgent improvements that can be addressed by the electrification of fluid power. This approach has already generated electro-hydraulic drives that remove flow throttling and enable energy recovery. However, the entire power managed by the actuators of conventional systems must pass through the electric machines. This characteristic is unfeasible for medium-to-high power applications since they need electric motors and electronics with high power ratings and large onboard generation of electricity. Thus, this paper applies to a hydraulic excavator’s boom the idea of splitting the power being transferred to/from the actuator between the hydraulic and electric domains (i.e., a centralized hydraulic power supply is involved). The objective is downsizing the power rating of the boom’s electric components while maintaining the highpower output of the hydraulic actuator. The results show the expected behavior of the hybrid excavator in terms of motion control, but only 57% of the boom’s peak power is now exchanged electrically. The resulting electric machine with 61% downsizing favors the system’s cost and compactness supporting the electrification process that is aligned with the low-carbon economy
Energy analysis of a hybrid electro-hydraulic system for efficient mobile hydraulics
Full text linkEnergy efficiency plays a significant role in mobile hydraulics due to the high amount of carbon dioxide and pollutants being released into the atmosphere. Efficiency improvements are urgently needed, so the electrification of mobile hydraulics represents a fantastic opportunity in this regard. This approach leads to electro-hydraulic systems that remove functional flow throttling in control valves and enable energy recovery. Fuels savings were already demonstrated in simulation, but the literature does not offer entire energy analyses of these electro-hydraulic solutions. This limitation prevents complete system-level comprehension and does not give enough insight to pinpoint areas for further efficiency improvements. Thus, this paper focuses on a hybrid system for excavators based on electro-hydraulic drives that is compared against the original valve-controlled layout. The objective is to quantify the energy flows insight the excavator during relevant operations and highlight the resulting energy losses. The outcomes confirm that electro-hydraulic solutions are suitable for a low-carbon economy. They indicate hydraulic actuators, speed-controlled pumps, and electric motors as the critical components for further energy efficiency enhancement excluding the combustion engine
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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