Letteratura scientifica selezionata sul tema "Top-Bar effect"
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Articoli di riviste sul tema "Top-Bar effect"
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Skrodzka, Ewa B., Bogumił B. J. Linde e Antoni Krupa. "Effect of Bass Bar Tension on Modal Parameters of a Violin's Top Plate". Archives of Acoustics 39, n. 1 (1 marzo 2015): 145–49. http://dx.doi.org/10.2478/aoa-2014-0015.
Testo completoAbstract (sommario):
Abstract Experimental modal analysis of a violin with three different tensions of a bass bar has been performed. The bass bar tension is the only intentionally introduced modification of the instrument. The aim of the study was to find differences and similarities between top plate modal parameters determined by a bass bar perfectly fitting the shape of the top plate, the bass bar with a tension usually applied by luthiers (normal), and the tension higher than the normal value. In the modal analysis four signature modes are taken into account. Bass bar tension does not change the sequence of mode shapes. Changes in modal damping are insignificant. An increase in bass bar tension causes an increase in modal frequencies A0 and B(1+) and does not change the frequencies of modes CBR and B(1-).
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Reza Esfahani, M., M. Lachemi e M. Reza Kianoush. "Top-bar effect of steel bars in self-consolidating concrete (SCC)". Cement and Concrete Composites 30, n. 1 (gennaio 2008): 52–60. http://dx.doi.org/10.1016/j.cemconcomp.2007.05.012.
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von Grünau, Michael, Zeina Saikali e Jocelyn Faubert. "Processing Speed in the Motion-Induction Effect". Perception 24, n. 5 (maggio 1995): 477–90. http://dx.doi.org/10.1068/p240477.
Testo completoAbstract (sommario):
The motion-induction effect, where an illusory motion is perceived within a bar when it is shown next to a spot presented slightly earlier, was studied with respect to the idea that it is based on differential processing speeds between the two ends of the bar. First, by using just a bar with a luminance gradient, the existence of a motion illusion (gradient motion) within such a bar was demonstrated, presumably due to the different processing speeds of differential luminances. When such a bar was used in the motion-induction effect, it was shown to modulate, for short delays, the strength of the effect up or down, according to the direction of the gradient with respect to the position of the spot. When the same bar was used in the double-motion-induction effect (split priming), in which motion is usually away from the later spot, it totally determined the perceived direction of illusory motion, independently of gradient direction with respect to the later spot or the time between the two spots. These results demonstrate, on the one hand, that differential local processing speed is a likely mechanism to underlie the motion-induction effect. On the other hand, they also suggest the involvement of other more global (and perhaps top—down) processes.
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Wang, Yikuan, Abhijit Mukherjee e Arnaud Castel. "Detection of Top-Bar Effect in Reinforced Concrete Using Guided Ultrasonic Waves". Journal of Structural Engineering 147, n. 4 (aprile 2021): 04021032. http://dx.doi.org/10.1061/(asce)st.1943-541x.0002950.
Testo completo
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Zhao, Fang Ran, Jia Lin Cao e Ning Wang. "Analysis of Factors Influence on Void Underneath at Concrete Pavement Joints". Applied Mechanics and Materials 488-489 (gennaio 2014): 483–86. http://dx.doi.org/10.4028/www.scientific.net/amm.488-489.483.
Testo completoAbstract (sommario):
Three-dimensional finite element analysis was made on the transverse joint stress state of the concrete pavement slab with void underneath using ANSYS. The transfer effect of dowel bar was discussed with aircraft loaded in the joints. The influence rule of load transfer effect under different dowel bar spacing and dowel bar cross section dimension was compared. Based on the results of finite element analysis, this paper had carried on the experimental study on stress-transferring effect on concrete pavement joints with different location of the dowel bar. The influencing factors of pavement slab transverse joint with void underneath and the resistance of pavement damage on the joint was analyzed. Theoretical analysis showed that in order to reinforce the resistance capacity of local cavity on concrete pavement joint, the largest spacing of transverse dowel bar set shall not be more than 45cm, and the main factors influencing the resistance void ability on the joint are top reaction modulus, coefficient of cavity, the concrete elastic modulus and coefficient of transverse reinforcement.
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Minato, Kenichi, Tomoichiro Okamoto e Masasuke Takata. "Effect of Atmosphere on Zinc Oxide Crystal Growth by Electric Current Heating with Au Catalyst". Advanced Materials Research 11-12 (febbraio 2006): 269–72. http://dx.doi.org/10.4028/www.scientific.net/amr.11-12.269.
Testo completoAbstract (sommario):
We developed a new zinc oxide (ZnO) crystal growth method using Au combined with electric current heating. Au paste was placed on a ZnO ceramic bar. When a certain current flowed through the bar, the paste melted on the bar. Then crystals grew on the molten Au surface immediately. The shape of the crystals depended on the atmosphere during the growth. The whiskers with spherical top and the crystals consisting of a hexangular pyramidal base and needle head were grown on Au in air and Ar atmosphere, respectively. From cathodoluminescence at room temperature, the weak ultraviolet (UV) emission at approximately 3.2 eV and the strong visible emission at approximately 2.3 eV were observed from the whisker grown in air. The UV emission at approximately 3.3 eV dominated a spectrum from the pyramidal crystal grown in Ar atmosphere.
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Kim, Nam Yong, Dae-Cheol Ko, Yangjin Kim, Sang Wook Han, Il Yeong Oh e Young Hoon Moon. "Feasibility of Reduced Ingot Hot-Top Height for the Cost-Effective Forging of Heavy Steel Ingots". Materials 13, n. 13 (29 giugno 2020): 2916. http://dx.doi.org/10.3390/ma13132916.
Testo completoAbstract (sommario):
Feasibility studies have been performed on ingots with reduced hot-top heights for the cost-effective hot forging of heavy ingots. The quality of the heavy ingots is generally affected by internal voids, which have been known to be accompanied by inclusions and segregation. To guarantee the expected mechanical performance of the forged products, these voids should be closed and eliminated during the hot open die forging process. Hence, to effectively control the internal voids, the optimum hot-top height and forging schedules need to be determined. In order to improve the utilization ratio of ingots, the ingot hot-top height needs to be minimized. To investigate the effect of the reduced hot-top height on the forged products, shaft and bar products have been manufactured via hot forging of ingots having various hot-top heights. From the operational results, the present work suggests effective forging processes to produce acceptable shaft and bar products using ingots having reduced hot tops. The mechanical properties of shop-floor products manufactured from ingots with reduced hot tops have also been measured and compared with those of conventional ingot products.
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Reichardt, Elisabeth, Steffen Decker, Michel Dalstra, Prasad Nalabothu, Markus Steineck, Leandro Fernandez e Carlalberta Verna. "The Effect of Ligature Type on Lateral Tooth Movement during Orthodontic Treatment with Lingual Appliances—An In Vitro Study". Materials 15, n. 9 (7 maggio 2022): 3365. http://dx.doi.org/10.3390/ma15093365.
Testo completoAbstract (sommario):
(1) Background: One of the most challenging parts in lingual orthodontics is the control and correction of the tip of anterior teeth, due to the occlusal open vertical slot of the incisors in lingual systems. The presented experimental in-vitro study was performed to determine the maximal tipping moment of the anterior teeth between two types of lingual brackets, the Incognito™ Appliance System (Incognito, TOP-Service, Bad Essen, Germany) and Tip-Bar™ system (Incognito, TOP-Service, Bad Essen, Germany). Furthermore, twelve different ligation methods and two different ligature materials were investigated. (2) Methods: The measurement was performed by assessing the stiffness and ultimate strength of the ligature in a uniaxial material testing machine (Instron, Norwood, MA, USA) using a 0.025 × 0.018 inch stainless steel wire. (3) The results showed that the highest precision for control tipping of anterior teeth was determined for the 0.010 inch Stainless Steel Tie (Pelz and Partner). Furthermore, the Tip-Bar™ brackets increased the maximal moment by 33.8% for elastic and steel ligatures. (4) Conclusions: The lateral tooth movement is highly dependent on the type of ligature and applied material during orthodontic treatment with lingual appliances. The use of 0.010 inch steel ligatures and the Tip-Bar™ bracket design results in better alignment in the anterior teeth segment.
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Esfahani, M. Reza, M. Reza Kianoush e M. Lachemi. "Bond strength of glass fibre reinforced polymer reinforcing bars in normal and self-consolidating concrete". Canadian Journal of Civil Engineering 32, n. 3 (1 giugno 2005): 553–60. http://dx.doi.org/10.1139/l05-005.
Testo completoAbstract (sommario):
This paper presents the results of an experimental study on bond strength of reinforcing bars made of glass fibre reinforced polymers (GFRP) embedded in normal and self-consolidating concrete. The study included pull-out tests of 36 GFRP reinforcing bars embedded in concrete specimens. Different parameters such as type of concrete, bar location, and cover thickness were considered as variables in different specimens. The results showed that the type of bond failure was by splitting of concrete for all specimens. The bond strength of bottom GFRP reinforcing bars was almost the same for both normal concrete and self-consolidating concrete. For the top bars, however, the bond strength of self-consolidating concrete was less than that of normal concrete.Key words: bond strength, glass FRP, reinforcing bars, top-bar effect, self-consolidating concrete.
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Liu, Xiaochao, Wentao Li, Yunqian Zhen, Luanluan Jia, Yongzhe Li e Xianjun Pei. "Effect of Process Parameters on Weld Quality in Vortex- Friction Stir Welding of 6061-T6 Aluminum Alloy". Materials 16, n. 2 (16 gennaio 2023): 873. http://dx.doi.org/10.3390/ma16020873.
Testo completoAbstract (sommario):
Vortex- friction stir welding (VFSW) utilizes a stir bar made of an identical material to the workpiece to rub the workpiece’s top surface, which avoids the keyhole defect in conventional friction stir welding. It presents great potential in the repair field of aluminum alloys. In this study, the effect of stir bar diameter, rotation speed, and welding speed on the weld formation was investigated in the VFSW of 6061-T6 aluminum alloy. The weld macrostructure, penetration, and mechanical properties were characterized. The results show that a large diameter of the stir bar can enhance the vortex material flow, increase the heat input, and eliminate the incomplete-penetration defect. The increase in rotation speed within limits can enhance the weld penetration and the mechanical properties of the weld nugget zone (WNZ). However, too high a rotation speed reduces the weld penetration and weakens the mechanical properties of the WNZ. The increase in welding speed reduces the weld penetration but enhances the mechanical properties of the heat affected zone. The incomplete-penetration defect significantly weakens the ductility of the VFSW joint. It can be eliminated by enlarging the stir bar diameter and choosing a moderate rotation speed and a lower welding speed.
Tesi sul tema "Top-Bar effect"
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Nguyen, Thi Thu Trang. "Influence de l'effet de l'interface acier/béton (top-bar effect) sur la corrosion de structures en béton armé exposées en environnement de chlorures ou de carbonatation". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEI009.
Testo completoAbstract (sommario):
Le béton armé est connu l’un des matériaux les plus utilisés dans la construction. Néanmoins, après une période de mise en exploitation, il peut se corroder. Les chlorures et la carbonatation sont les principaux facteurs provoquant la corrosion des structures en béton armé. La thèse a pour objectif d’étudier le comportement à la corrosion du béton armé sous l’environnement de carbonatation ou des chlorures, correspondant à l'influence de l’effet de la qualité de l’interface acier/mortier (top-bar effet), du type de ciment ainsi que de la fissure transversale artificielle ou des fissures transversales induites par la charge mécanique.En général, la corrosion induite par la carbonatation est étudiée du point de vue de la corrosion uniforme. Le premier objectif de la thèse est de confirmer l’opinion de la corrosion par macro-cellule ou non uniforme dans la corrosion induite par la carbonatation. Selon les résultats expérimentaux, le taux de corrosion dans les armatures de béton carbonaté est susceptible d'être considéré du point de vue de la corrosion uniforme et macro-cellule, qui est fortement influencée par le rapport cathode/anode. De plus, l'application de CEM III utilisant des laitiers comme addition minérale a montré une réduction efficace de la corrosion non uniforme.La deuxième partie se concentre sur l'influence de l’effet de la qualité de l’interface acier/mortier (top-bar effet) sur le comportement de la corrosion dans le cas d'une corrosion induite par la carbonatation et de la présence d'une fissure induite par la charge mécanique. Le suivi du courant de corrosion par macro-cellule a été utilisée dans les essais expérimentaux. Puis la perte de masse ainsi que la cinétique de corrosion ont été calculée. La corrosion s'est développée principalement au niveau du pré-fissures. En raison de l’effet de la qualité de l’interface acier/mortier, les barres supérieures étaient plus corrodées que les barres inférieures. La valeur du courant de la corrosion mesurée sur les barres supérieures a été observée plus élevée que sur les barres inférieures. La perte de masse de l'acier calculée à partir de la mesure du suivi de courant ne correspond qu'à une petite partie de la perte de masse totale déterminée par la mesure gravimétrique. La corrosion uniforme semble être le phénomène principal.La dernière partie étudie l’effet de la qualité de l’interface acier/mortier (top-bar effet) dans des échantillons de béton fibré avec ou sans fissure artificielle sur la corrosion induite par les chlorures. Les barres supérieures sont plus corrodées que les barres inférieures et la partie supérieure de la barre supérieure présente une corrosion plus élevée que la partie inférieure. En présence de fissures artificielles, le ‘’top-bar effet’’ entraîne la propagation de la corrosion le long de la surface des barres d'acier. La corrosion se développe également le long de la barre supérieure lorsqu'il n'y a pas de fissure artificielle, dans un temps pas si différent du cas d'une fissure artificielle. Cela confirme que l'exposition de la surface supérieure et l’effet de la qualité de l’interface acier/mortier sont très préjudiciables à la corrosion. En comparant le comportement avec un béton sans fibres, il apparaît que l'ajout de fibres dans le béton armé entraîne une augmentation de la résistance à la fissuration induite par la corrosion.Dans chaque partie, les observations expérimentales sont couplées à des simulations numériques pour comparer et démontrer les résultats expérimentauxReinforced concrete is known one of the most popular materials applied in construction. Nevertheless after a period of time it can be corroded. Chloride and carbonation are the main factors causing to corrosion in reinforced concrete structure. The thesis aimed to study the corrosion behavior of reinforcement concrete under carbonation or chloride environment, corresponding to the influence of top-bar effect, the cement type as well as artificial transverse crack or load-induced cracks.In general carbonation induced corrosion is usually researched from the point of view that it generates uniform corrosion. The first objective of the thesis is to confirm the opinion of macro cell or non-uniform corrosion in carbonated induced corrosion. According to the results of experiments in this part, corrosion rate in carbonated concrete reinforcement is likely to consider from the point of view of both uniform and macro cell corrosion, which is highly influenced by the ratio cathode/anode. In addition the application of CEM III using slag as addictive exhibited reduction of non-uniform corrosion effectively.The second part focuses on the influence of top-bar effect on corrosion behavior in the case carbonation induced corrosion and presence of load induced crack. Macro cell corrosion current monitoring was utilized in the experiment following the loss of mass as well as corrosion kinetic was calculated. Corrosions mainly developed at the position of the pre-cracks. Due to the top-bar effect upper bars were more corroded than bottom bars. Current corrosion value of top bars was observed higher than bottom bars. Loss of steel mass calculated from macro cell current measurement corresponds to only to a small part of the total loss of mass determined by gravimetric measurement. Uniform corrosion appears to be the main phenomena.The last part investigates the effect of top-bar effect in fibers concrete samples with or without artificial crack on chloride induced corrosion. The top steel bars are more corroded than the bottom bars and the upper part of the top bar is recorded higher corrosion than the lower part. In presence of artificial crack the top casting effect results that corrosions spread along the surface of the steel bars. Corrosion also spread along the top bar when there is no artificial crack, in a time not so different from the case of artificial crack. It confirms that top surface exposure and top bar effect are highly prejudicial for corrosion. By comparing the behavior with concrete without fibers, it appears that the addition of fibers in reinforced concrete leads to an increase of resistance to corrosion induced cracking.For each part, experimental observations are coupled with numerical simulations to compare as well as demonstrate the experimental results
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Cogneras, E. "Production de paires de Top et effet de Nouvelle Physique. Calibration des jets légers avec le processus W en jet-jet. Mesure de la masse du Top". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2007. http://tel.archives-ouvertes.fr/tel-00178221.
Testo completoAbstract (sommario):
Depuis sa découverte en 1995 à Fermilab, le quark Top fait l'objet d'une grande attention. Il complète la troisième famille de quarks du Modèle Standard de la physique des particules, et la mesure de ses propriétés contraint fortement ce modèle. Il constitue également une voie d'accès privilégiée à la nouvelle physique attendue à une énergie de l'ordre du TeV. Ce travail de thèse, réalisé auprès du détecteur ATLAS du LHC, présente les méthodes mises en œuvre afin de mesurer précisément la masse du quark Top dans le canal lepton+jets. Différentes stratégies d'analyse sont présentées en fonction des performances du détecteur, notamment sa capacité d'identification des jets beaux. La mesure précise de la masse du Top passe par une connaissance approfondie de l'échelle d'énergie des jets. Ce document propose une stratégie d'étalonnage des jets légers qui s'appuie sur la contrainte de la masse du boson W, et montre qu'une précision de l'ordre du GeV/c² sur la mesure de la masse du Top est tout à fait possible. Une évaluation du potentiel de découverte de résonances ttbar, prévues dans le cadre de modèles au-delà du Modèle Standard, est également menée.
Capitoli di libri sul tema "Top-Bar effect"
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Trezos, Konstantinos G., Ioannis P. Sfikas, Myron S. Palmos e Ellas K. Sotiropoulou. "Top-Bar Effect in Self-Compacting Concrete Elements". In Design, Production and Placement of Self-Consolidating Concrete, 355–66. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-90-481-9664-7_30.
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Yung, Yuk L., e William B. DeMore. "Venus". In Photochemistry of Planetary Atmospheres. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195105018.003.0011.
Testo completoAbstract (sommario):
Venus has been visited by a number of spacecraft. Those most important in advancing our understanding of the atmosphere include Mariner 10 (1974), Pioneer Venus (1978- 1992), and the series of Venera probes by the former USSR (1982-1986). The Pioneer Venus orbiter conducted more than a decade of monitoring of the upper atmosphere of Venus. The spacecraft data are supplemented by telescopic and satellite (in Earth orbit) observations. The astronomical data for Venus are summarized in table 8.1. Venus is a close but slightly smaller sibling of Earth. The radius is 6051 km, as compared to Earth's 6371 km. The mass is 4.87 x 1024 kg, a little less than Earth's 5.98 x 1024 kg. The gravity of Venus is 8.87 ms-2, as compared to Earth's 9.82 ms-2. The dynamical and orbital parameters of Venus are very different from those of Earth. The rotation of Venus is retrograde, with a period of 225 days. The planet has little obliquity, and its orbit is close to being circular. Thus there is little seasonal variation in insolation over a Cytherian year. Perhaps the greatest surprise about Venus is its dense, dry, and hot atmosphere of 92 bar (see figure 8.1). This is all the more surprising because the planet is completely covered by thick clouds. Figure 8.2 shows the altitude profiles of three modes of cloud particles in the middle atmosphere. The high albedo of Venus implies that the planet receives less energy from the sun than Earth despite its closer proximity to the sun. However, the surface of Venus is hot, with a temperature of 733 K, attributed to the greenhouse effect. The bulk of our knowledge of the atmosphere of Venus is derived from observations in the middle atmosphere (60-100 km altitude). At cloud-top levels (65 km), groundbased ultraviolet (UV) observations revealed a 4-5 day period, east-to-west circulation that is 60 times faster than the solid surface. The mechanism for generating this superrotation is not well understood. The net result of this rotation is that it gives the upper atmosphere an effective diurnal cycle of 4-5 days.
Atti di convegni sul tema "Top-Bar effect"
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"Effect of Admixture Combination on Top-Bar Effect of Highly Flowable and Self-Consolidating Concrete Mixtures". In SP-247: Self-Consolidating Concrete for Precast Prestressed Applications. American Concrete Institute, 2007. http://dx.doi.org/10.14359/18996.
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Dardalis, Dimitrios, Amiyo K. Basu, Matt J. Hall e Ronald D. Matthews. "Minimizing Boundary Friction in Diesel Engines Piston Assembly: Testing the Rotating Liner Engine Prototype Under Load". In ASME 2022 ICE Forward Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icef2022-88867.
Testo completoAbstract (sommario):
Abstract The Rotating Liner Engine (RLE) is a design concept where the cylinder liner of a heavy-duty Diesel engine rotates at about 2–4 m/s surface speed to eliminate the piston ring and skirt boundary friction near the top and bottom dead center. Based on prior testing results from our single cylinder RLE prototype (a converted four-cylinder Cummins ISB 3.9 Diesel) compared to a similar baseline, under idle conditions, the friction reduction is approximately 50 kPa (0.5 bar) in FMEP (friction mean effective pressure), which translates to about 40% for a complete engine. In this new set of experiments, we compare the RLE performance under load of up to about 7 bar IMEP (indicated mean effective pressure). It has been proven that the elimination of metallic contact between the compression rings and cylinder wall persists for up to 75 bar peak cylinder pressure and 1.5–2.3 m/s liner surface speed (283–426 rpm) for the 850–1280 rpm crankshaft speed. Additionally, the RLE FMEP is substantially reduced under load, which is a trend opposite to standard engines. Presumably, at idle the RLE cylinder and piston are cooler than the standard engine because the substantial heat dissipation by the metallic contact of the rings and skirts with the liner does not take place. Under load, however, the increased heat transfer from the combustion raises a piston and rotating cylinder temperatures, which reduces local lubricant viscosity and reduces mid-stroke viscous losses as well as rotating liner parasitic losses. Furthermore, based on higher speed baseline engine data, it appears that there is also a reduction in the hydrodynamic piston terms. The reason is attributed to the increased lubricant film thickness at mid-stroke, due to the combined effects of the liner rotation and the traditional wedge effects of the piston skirt and rings. This effect seems to more than compensate for the increase of the hydrodynamic parasitic friction of the liner rotation with engine speed (we currently have a constant 3:1 ratio of the crankshaft to liner speed). The combined fuel efficiency benefit is shown to exceed 10% for medium loads and speeds.
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De Salve, Mario, Mario Malandrone e Bruno Panella. "Gas Driven Circulation in an Adiabatic Air-Water Loop With Reference to Accelerator Driven Systems". In 10th International Conference on Nuclear Engineering. ASMEDC, 2002. http://dx.doi.org/10.1115/icone10-22546.
Testo completoAbstract (sommario):
In order to investigate the fluid dynamic mechanisms of the gas driven circulation, with reference to the accelerator driven systems (ADS), an experimental research with water driven by air injected at the inlet of the vertical riser in an adiabatic test rig has been carried out. The present experimental apparatus consists essentially of two vertical plexiglass pipes 3.8 m long, 0.08 m I.D., that are connected at the bottom by a horizontal pipe and at the top by a large open tank. The test rig is equipped with differential pressure transducers and two quick closing valves to measure the pressure drops and the average void fraction. The air flow rate ranges up to 5000 Nl/h, at 7 bar pressure, and the liquid flow rate can reach the value of more than 5 kg/s. The research aim is to investigate the effect of the superficial gas velocity on the superficial liquid velocity, on the void fraction and on the pressure drops, for a given geometry. The test data have been compared with some two-phase pressure drops and void fraction correlations. The geometry effect has been investigated too.
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Kim, Daejong, Prajwal Shetty e Donghyun Lee. "Imbalance Response of a Rotor Supported by Hybrid Air Foil Bearings". In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45576.
Testo completoAbstract (sommario):
Air foil bearings (AFB’s) are widely used in small to midsized turbomachinery. They are simple in construction, offer very low drag friction, and have very high reliability at high speed operations. This paper presents experimental imbalance response of a 4.84 kg rigid rotor (operating below bending critical speed) supported by two hybrid air foil bearings with 50 mm in diameter. The concept of “hybrid” in this paper utilizes the hydrostatic augmentation of the load capacity during the start up and shut down. The hybrid air foil bearings were designed with three top foils for enhanced stability. Imbalance responses in cylindrical mode are presented up to 44,000rpm with different supply pressures. As the supply pressure is increased from 2.67 to 4 bar, the bearing stiffness increases slightly, resulting in slightly larger vibration (and reduced damping ratio) during the trans-critical speed operation. Hydrodynamic instability was observed with whirl frequency ratios of about 0.17∼0.2 depending on the supply pressures. Tests were also conducted to investigate the effect of supply pressure on the rotordynamic stability. The test results show that the hybrid operation is very effective to suppress the subsynchronous vibrations at high speeds.
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Félix, Lorenzo Marzari, José Eduardo Ferreira da Fonseca, Carlos Fortis Kwietniewski, Marcelo Favaro Borges, Jefferson Haag e Giovanni Dalpiaz. "The Effect of Nickel on Fracture Toughness at Low Temperature for Hydrogen Pre-Charged Steel Samples". In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23274.
Testo completoAbstract (sommario):
Production of oil and gas in the Brazilian pre-salt will face several technical challenges. One of them that is a major concern is the presence of CO2 in high concentrations. Indeed, since the local regulatory agency requires increasingly stricter recommendations, it seems unlikely the possibility of simply release CO2 in the atmosphere. Besides that, as it happens since the 1970’s in USA, enhanced oil recovery (EOR) using CO2 might be a great opportunity and has to be considered. If that is the case, as soon as CO2 is separated from the oil in the top side, it has to be pressurized and transported through pipelines into the reservoir. The material of choice for that pipeline would be API 5L X65 since it is widely used and most available. The working pressure can reach up to 500 bar or more and it is an important issue to consider the fact that a suddenly depressurization due to a crack in the pipeline or a failure in a fastener or flange can promote a local abrupt decrease in temperature down to −60°C or even lower. That concern in addition to the fact that cathodic protection has to be used in the pipeline for corrosion control has the potential to produce embrittlement due to a combination of low temperature and hydrogen charging and ultimately lead to a catastrophic failure. The use of nickel to improve steel toughness has been used extensively and some grades or classes of nickel containing steels have been created for special applications. The aim of this work is to evaluate whether a nickel containing steel would be a more suitable material to manufacture high pressure CO2 transporting pipelines, taking in account a possible leak and the corresponding effect of a local and abrupt drop in temperature on the fracture toughness of the material. The effect of hydrogen due to cathodic protection on fracture toughness is also evaluated. The results indicated that under the experimental conditions and materials examined here the 9%wt nickel steel is not sensitive to low temperature and hydrogen, practically maintaining its original fracture toughness.
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Jatana, Gurneesh S., Flavio Dal Forno Chuahy e James Szybist. "Effect of Split-Injection Strategies on Engine Performance and Emissions under Cold-Start Operation". In WCX SAE World Congress Experience. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2023. http://dx.doi.org/10.4271/2023-01-0236.
Testo completoAbstract (sommario):
<div class="section abstract"><div class="htmlview paragraph">The recently concluded partnership for advancing combustion engines (PACE) was a US Department of Energy consortium involving multiple national laboratories focused on addressing key efficiency and emission barriers in light-duty engines. Generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior was a major pillar in this program. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon, and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster three-way catalyst light-off, and engine out emissions during that period. In this study, engine performance, emissions, and catalyst warmup potential were monitored while the engine was operated using a single direct injection (baseline case) as well as a two-way-equal-split direct injection strategy. These injection strategies were analyzed at a range of cold-start-operation relevant retarded spark timings of up to 25 degrees after top dead center of firing (dATDCf). A stoichiometric 2-bar NIMEP steady-state condition was used for all cases to simulate cold-start operation. Significant improvement in engine stability was observed with the two-way-split injection strategy at the retarded spark timings allowing for up to 2.5x increase in exhaust heat rate when engine operation is stability constrained. Similar fuel-loss-to-oil trends with exhaust heat rate were observed for both single and two-way-split injection strategies. However, the two-way split injection was observed to produce higher NOx emissions per unit exhaust heat rate. A single data point run with three-way-split direct injection at a very retarded spark-timing of 30 dATDCf pointed to further improvements in engine stability and reduction in fuel-loss-to-oil as compared to single injection strategy. Engine stability decreased as spark timing was initially retarded with a single injection but was observed to plateau and stabilize beyond spark timing of 10 dATDCf. For the two-way-split-injection strategy, retarding the start of injection (SOI) timing of the second injection led to a decrease in engine stability as well as an increase in soot emissions.</div></div>
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Soloiu, Valentin, Cesar E. Carapia, Richard Smith, Amanda Weaver, Levi Mckinney, David Mothershed, Drake Grall, Marcel Ilie e Mosfequr Rahman. "RCCI With High Reactivity S8-ULSD Blend and Low Reactivity N-Butanol". In ASME 2020 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icef2020-3010.
Testo completoAbstract (sommario):
Abstract A fuel blend consisting of 10% S8 by mass (a Fischer-Tropsch synthetic kerosene), and 90% ULSD (Ultra Low Sulfur Diesel) was investigated for their combustion characteristics and impact on emissions during RCCI (Reactivity Controlled Compression Ignition) combustion in a single cylinder experimental engine utilizing a 65% by mass n-butanol port fuel injection (PFI). RCCI is a dual fuel combustion strategy achieved with the introduction of a PFI fuel of the low-reactive n-butanol, and a direct injection (DI) of a high-reactivity blend (FT-BLEND) into an experimental diesel engine. The combustion analysis and emissions testing were conducted at 1500 RPM at an engine load of 5 bar IMEP (Indicated Mean Effective Pressure), and CA50 of 9° ATDC (After Top Dead Center); CDC (Conventional Diesel Combustion) and RCCI with 65Bu-35ULSD were utilized as the baseline for AHRR (Apparent Heat Release Rate), ringing and emissions comparisons. It was found during a preliminary investigation with a Constant Volume Combustion Chamber (CVCC) that the introduction of 10% by mass S8 into a mixture with 90% ULSD by mass only increased Derived Cetane Number (DCN) by 0.8, yet it was found to have a significant effect on the combustion characteristics of the fuel blend. This led to the change in injection timing necessary for maintaining 65Bu-35F-T BLEND RCCI at a CA50 of 5° ATDC (After Top Dead Center) to be shifted 3° closer to TDC, thus affecting the Ringing Intensity (RI), Pressure Rise Rate, and heat release of the blend all to decrease. CDC was conducted with a primary injection of 14° BTDC at a rail pressure of 800 bar, all RCCI testing was conducted with 65% PFI of n-butanol by mass and 35% DI, to prevent knock, with a rail pressure of 600 bar and a pilot injection of 60° BTDC for 0.35 ms. 65Bu-35ULSD RCCI was conducted with a primary injection at 6° BTDC with neat ULSD#2, the fuel 65Bu-35F-T BLEND in RCCI had a primary injection at 3° BTDC to maintain CA50 at 9° ATDC. 65Bu-35ULSD RCCI experienced a NOx and soot emissions decrease of 40.8% and 91.44% respectively in comparison to CDC. The fuel 65Bu-35F-T BLEND in RCCI exhibited an additional decrease of NOx and soot of 32.9 and 5.3%, in comparison to 65Bu-35ULSD RCCI for an overall decrease in emissions of 73.7% and 96.71% respectively. Ringing Intensity followed a similar trend with reductions in RI for 65Bu-35ULSD RCCI decreasing only by 6.2% whereas 65Bu-35F-T BLEND had a decrease in RI of 76.6%. Although emissions for both RCCI fuels experienced a decrease in NOx and soot in comparison to CDC, UHC and CO did increase as a result of RCCI. CO emissions for 65Bu-35ULSD RCCI and 65Bu-35F-T BLEND where increased from CDC by a factor of 5 and 4 respectively with UHC emissions rising from CDC by a factor of 3.4. The fuel 65Bu-35F-T BLEND had a higher combustion efficiency than 65Bu-35ULSD in RCCI at 91.2% due to lower CO emissions of the blend.
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Ebewele, Ehiremen, Daejong Kim e Jeongpill Ki. "Analytical Study on Hybrid Thrust Foil Bearing, Structural Characterization and Measurement of Static Performance". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-104282.
Testo completoAbstract (sommario):
Abstract This work presents a novel design of a hybrid thrust foil bearing (HTFB) with an outer diameter of 154mm, along with simulation and test results. The HTFB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. As a result, this bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HTFB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and external loads. The bearing performance was predicted at 40krpm, 3000N axial load, and 6 bar absolute hydrostatic pressure in both hydrodynamic and hybrid modes. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the minimum film thickness compared to hydrodynamic bearing due to the boost effect of hydrodynamic pressure in the main film. The preliminary experimental measurements on load capacity at zero speed agree with the prediction. Rotational tests were conducted at 10krpm, 15krpm and 20krpm. Ultimately, the novel HTFB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.
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Dempsey, Adam, Scott Curran, Robert Wagner e William Cannella. "Effect of Premixed Fuel Preparation for Partially Premixed Combustion With a Low Octane Gasoline on a Light-Duty Multi-Cylinder Compression Ignition Engine". In ASME 2014 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icef2014-5561.
Testo completoAbstract (sommario):
Gasoline compression ignition concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multi-cylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies has been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection strategy to create a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from −91° to −324° ATDC, which is just after the exhaust valve closes for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 L diesel engine with a variable geometry turbocharger, high pressure common rail injection system, wide included angle injectors, and variable swirl actuation was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection pressures. The gasoline used in this study has relatively high fuel reactivity with a research octane number of 68. The results of this experimental campaign indicate that the highest brake thermal efficiency and lowest emissions are achieved simultaneously with the earliest pilot injection timings (i.e., during the intake stroke).
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Maroteaux, Fadila, Salim SEBAI, Ezio Mancaruso, Salvatore Rossetti, Patrick Schembri, Katia Radja e Arnault Barichella. "Numerical and Experimental Analysis of Dual Fuel Hydrogen/Diesel Combustion at Varying Engine Speed on a Single Cylinder Engine". In Conference on Sustainable Mobility. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2024. http://dx.doi.org/10.4271/2024-24-0044.
Testo completoAbstract (sommario):
<div class="section abstract"><div class="htmlview paragraph">In this study, dual fuel combustion process has been investigated numerically and experimentally in a single cylinder research engine. Two engine speeds have been investigated (1500 and 2000 rpm) at fixed BMEP of 5 bar for both engine speeds. For each engine speed two operating points have tested with and without EGR (Exhaust Gas Recirculation). The hydrogen has been injected in the intake manifold in front of the tumble intake port inlet and a small amount of diesel fuel has been introduced directly in the cylinder through two injections strategy: one pilot injection occurring Before Top Dead Center (BTDC) and one main occurring around the Top Dead Center (TDC). The dual-fuel combustion model in GT-SUITE has been used first to calibrate the combustion model by using the Three Pressure Analysis (TPA) model. This step allows the calibration of the combustion model to predict in-cylinder combustion processes. Simulations have been performed at varying mass distribution of injected diesel fuel during pilot and main injections at fixed start of pilot injection (SOIp).</div><div class="htmlview paragraph">For both engine speeds it was found that the model predicts well the in-cylinder pressure traces, the ignition delays, the heat release rates and NOx emissions. The simulated results at varying mass distribution of injected diesel fuel between the pilot injection and the main injection, have shown that the distribution has no effect on the ignition delay times. This distribution mainly controls the combustion duration and NOx emissions. Indeed, when the amount of diesel pilot injection is increased the NOx emissions are increased by around two for all engine operations. As expected, when a small amount of EGR is used the NOx emissions are lower compared to the operations without EGR. This first step of parametric analysis of DF combustion shows that further investigations are required into the dual-fuel (H2 /diesel) combustion to optimize engine performances and emissions.</div></div>