Search results for "Pressure"
showing 10 items of 4493 documents
Impeller optimization in crossflow hydraulic turbines
2021
Crossflow turbines represent a valuable choice for energy recovery in aqueducts, due to their constructive simplicity and good efficiency under variable head jump conditions. Several experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines have already been proposed, but all of them assume that structural safety is fully compatible with the sought after geometry. We show first, with reference to a specific study case, that the geometry of the most efficient impeller would lead shortly, using blades with a traditional circular profile made with standard material, to their mechanical failure. A methodology for fully coupled fluid dynamic and mechanical …
A gradient-based decomposition approach to optimize pressure path and counterpunch action in Y-shaped tube hydroforming operations
2008
International audience; In tube hydroforming, the concurrent actions of pressurized fluid and mechanical feeding allows obtaining tube shapes characterized by complex geometries such as different diameters sections and/or bulged zones. Main process parameters are material feeding history (i.e., the punches velocity history), internal pressure path during the process, and (in T- or Y-shaped tube hydroforming) counterpunch action. What is crucial, in such processes, is the proper design of operative parameters aimed to avoid defects (for instance underfilling or ductile fractures). Actually, the design of tube hydroforming operations is mainly aimed to prevent bursting or buckling occurrence …
Optimal design of an electro-hydraulic valve for heavy-duty vehicle clutch actuator with certain constraints
2016
Abstract The main objective of this paper is to investigate the sensitivity analysis and optimal design of a proportional solenoid valve (PSV) operated pressure reducing valve (PRV) for heavy-duty automatic transmission clutch actuators. The nonlinear electro-hydraulic valve model is developed based on fluid dynamics. In order to implement the sensitivity analysis and optimization for the PRV, the PSV model is validated by comparing the results with data obtained from a real test-bench. The sensitivity of the PSV pressure response with regard to the structural parameters is investigated by using Sobol׳s method. Finally, simulations and experimental investigations are performed on the optimi…
Self-sustained coherent phonon generation in optomechanical cavities
2016
Optical forces can set tiny objects in states of mechanical self-sustained oscillation, spontaneously generating periodic signals by extracting power from steady sources. Miniaturized self-sustained coherent phonon sources are interesting for applications such as mass-force sensing, intra-chip metrology and intra-chip time-keeping among others. In this paper, we review several mechanisms and techniques that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical cavities, namely stimulated emission, dynamical back-action, forward stimulated Brillouin scattering and self-pulsing.
Changes of colour and carotenoids contents during high intensity pulsed electric field treatment in orange juices
2005
Abstract Liquid chromatography (LC) was the method chosen to evaluate the effects of high intensity pulsed electric fields (HIPEF), with different electric field intensities (25, 30, 35 and 40 kV/cm) and different treatment times (30–340 μs), on orange juice cis / trans carotenoid contents. In parallel, a conventional heat treatment (90 °C, 20 s) was applied to the orange juice in order to compare the effect on the carotenoid contents. HIPEF processing of orange juice is an alternative to the thermal treatment of pasteurization, provided that it is kept refrigerated, because, when the most extreme conditions of this kind of treatment are applied, the decrease in the concentration of caroten…
High-pressure NMR spectroscopy: An in situ tool to study tin-catalyzed synthesis of organic carbonates from carbon dioxide and alcohols. Part 2 [1]
2015
Dialkoxide diorganotin(IV) complexes are known to readily react with carbon dioxide under pressure and they are considered as suitable catalyst precursor models for the direct synthesis of organic carbonates. To gain a better understanding of CO2 insertion processes with Sn-OR bonds, the reactivity of n-Bu2Sn(OCH(CH3)(2))(2) (2) was investigated using high-pressure NMR (HP-NMR) spectroscopy. In deuterated solvents (isopropanol-d(8) and toluene-d(8)) under 50 bar of CO2 pressure at 80 degrees C, Sn-119{H-1} NMR experiments revealed the exclusive formation of an unprecedented tetraorganodistannoxane species, characterized as the bis[diisopropycarbonatotetrabutyldistannoxane] complex, {[n-Bu2S…
Challenge Demands and Resilience
2022
Abstract. This study investigates the relationship of challenge demands (i. e., time pressure, job complexity) on employee resilience. We provide insights into potential pathways (i. e., learning, cognitive irritation) for how challenge stressors influence employee resilience. We employed a two-wave, time-lagged design to examine the influences of challenge stressors and explanatory pathways on employee resilience 2 months later. The data from 359 participants (52.1 % male) were analyzed using a Bayesian time-lagged path model. Results indicate that time pressure and job complexity are negatively related to employee resilience via cognitive irritation. In contrast, we found a positive, ind…
Affective responses to work process and outcomes in virtual teams
2005
PurposeTo analyze the direct and combined effects of the communication media and time pressure in group work on the affective responses of team members while performing intellective tasksDesign/methodology/approachA laboratory experiment was carried out with 124 subjects working in 31 groups. The task performed by the groups was an intellective one. A 2 × 3 factorial design with three media (face‐to‐face, video‐conference, and e‐mail) and time pressure (with and without time pressure) was used to determine the direct and combined effects of these two variables on group members' satisfaction with the process and with the results, and on members' commitment with the decision.FindingsResults s…
Feeling interrupted-Being responsive: How online messages relate to affect at work
2017
Being constantly connected to others via e‐mail and other online messages is increasingly typical for many employees. In this paper, we develop and test a model that specifies how interruptions by online messages relate to negative and positive affect. We hypothesize that perceived interruptions by online messages predict state negative affect via time pressure and that perceived interruptions predict state positive affect via responsiveness to these online messages and perceived task accomplishment. A daily survey study with 174 employees (a total of 811 day‐level observations) provided support for our hypotheses at the between‐person and within‐person level. In addition, perceived interru…
Time and Performance Pressure
2018
Abstract. Time pressure and performance pressure are among the most crucial job demands of today’s workforce. However, the literature on psychological stress barely distinguishes between these constructs. Therefore, we aimed to examine time pressure and performance pressure as two qualitatively different job demands in terms of unique moderators for both demands. We investigated whether time control would moderate the relationship between time pressure and both emotional exhaustion and work engagement. As a vulnerability factor for dealing with performance pressure, we investigated perfectionism. The cross-sectional data of 167 employees showed that time control was a significant moderator…