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Journal articles on the topic 'Slow rotating bearings'
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1
Morales-Espejel, G. E., P. M. Lugt, H. R. Pasaribu, and H. Cen. "Film thickness in grease lubricated slow rotating rolling bearings." Tribology International 74 (June 2014): 7–19. http://dx.doi.org/10.1016/j.triboint.2014.01.023.
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Jamaludin, N., D. Mba, and R. H. Bannister. "Condition monitoring of slow-speed rolling element bearings using stress waves." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 215, no. 4 (November 1, 2001): 245–71. http://dx.doi.org/10.1177/095440890121500401.
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Condition monitoring of rolling element bearings through the use of vibration analysis is an established technique for detecting early stages of component degradation. However, this success is not mirrored at rotational speeds below 16r/min. At such speeds the energy generated from bearing defects might not show as an obvious change in signature and thus becomes undetectable using conventional vibration measuring equipment. This paper presents an investigation into the applicability of stress wave analysis for detecting early stages of bearing damage at a rotational speed of 1.12r/min (0.0187 Hz). Furthermore, it reviews work undertaken in monitoring bearings rotating at speeds below 16r/min.
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Elforjani, Mohamed. "Diagnosis and prognosis of slow speed bearing behavior under grease starvation condition." Structural Health Monitoring 17, no. 3 (April 28, 2017): 532–48. http://dx.doi.org/10.1177/1475921717704620.
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The monitoring and diagnosis of rolling element bearings with acoustic emission and vibration measurements has evolved as one of the much used techniques for condition monitoring and diagnosis of rotating machinery. Furthermore, recent developments indicate the drive toward integration of diagnosis and prognosis algorithms in future integrated machine health management systems. With this in mind, this article is an experimental study of slow speed bearings in a starved lubricated contact. It investigates the influence of grease starvation conditions on detection and monitoring natural defect initiation and propagation using acoustic emission approach. The experiments are also aimed at a comparison of results acquired by acoustic emission and vibration diagnosis on full-scale axial bearing. In addition to this, the article concentrates on the estimation of the remaining useful life for bearings while in operation. To implement this, a multilayer artificial neural network model has been proposed to correlate the selected acoustic emission features with corresponding bearing wear throughout laboratory experiments. Experiments confirm that the obtained results were promising and selecting this appropriate signal processing technique can significantly affect the defect identification.
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Nienhaus, K., F. D. Boos, K. Garate, and R. Baltes. "Development of Acoustic Emission (AE) based defect parameters for slow rotating roller bearings." Journal of Physics: Conference Series 364 (May 28, 2012): 012034. http://dx.doi.org/10.1088/1742-6596/364/1/012034.
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Belfiore, Nicola Pio, Carlo Costa, Rosanna Pileggi, Fabio Botta, and Claudio Guarnaschelli. "An accelerated test stand to assess wear in offshore wind turbines rolling bearings." Wind Engineering 42, no. 2 (February 16, 2018): 136–40. http://dx.doi.org/10.1177/0309524x18756963.
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Rolling bearings are universally adopted to serve as revolute joints in almost all mechanisms or machines, because they offer a convenient solution to the problem of minimizing friction and, simultaneously, providing a large load-carrying capacity at any kinematic regime, including slow or alternate rotations. However, in offshore wind turbines not only they reach large dimensions but also they move within strong electromagnetic fields created by the turbine generators. For example, considering the last amplification stadium epicyclic gearbox, they may serve to sustain elements rotating around floating shafts (planetary) which also move around a fixed principal shaft (solar). This article illustrates an original experimental test bench that simulates sliding and rolling contacts through which a test current is flowing. Unexpected and interesting results disclose how this particular field is challenging and how more investigations are still required to achieve an adequate and complete interpretation. The understanding of this phenomenon could give rise to modification to the composition and the microstructure of rollers and rings employed in offshore wind turbines.
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Chiementin, Xavier, Fabrice Bolaers, and Jean-Paul Dron. "Early Detection of Fatigue Damage on Rolling Element Bearings Using Adapted Wavelet." Journal of Vibration and Acoustics 129, no. 4 (March 19, 2007): 495–506. http://dx.doi.org/10.1115/1.2748475.
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Among the advanced techniques of the predictive maintenance, the vibratory analysis proves to be very effective, in particular, for monitoring rotating components such as the bearings. Their damage creates cyclic efforts which are at the origin of the processing of vibratory measurements. This processing can be made by temporal methods, frequential methods, or by time-scale methods using the wavelets for 2 decades. The wavelet transform is a very effective processing, however, the difficulties of application and interpretation of the results slow down their employment. The determination of the parameters of the wavelets makes its use all the more difficult. Moreover, the use of these time-scale methods is very expensive in time computation. This paper proposes a wavelet adapted to the mechanical shock response of a structure with n degrees of freedom. In addition, we developed a procedure for analysis of signals by this wavelet which makes it possible to accelerate the process and to improve detection in the case of disturbed signals. This methodology is compared with the traditional time-scale methods and is implemented to detect defects of different sizes on outer rings and inner rings of ball bearings.
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Qiu, Li Jun, Jia Yang, and Su Ying Xu. "The Analysis and Design of Turbocharger Thrust Bearing." Advanced Materials Research 308-310 (August 2011): 1333–36. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.1333.
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Turbocharger turbine shaft thrust bearing is the role of high-speed rotating turbine to withstand the axial force generated by the turbine shaft and a part of the axial position. Fixed on the intermediate thrust bearing on the two sides and both sides of the ring, respectively, relative sliding. Sliding contact surface produces a condition of dynamic pressure oil film structure and shape of the oil wedge. Bearing the sides of the structural design of the oil wedge slot and forming a design to solve the main content. Bearing thrust bearing stiffness and rotation in the process of stress state and the smooth line is to improve the bearing life. Rotating turbine shaft to ensure the accuracy of key factors. Method of lubricating oil to the oil and oil Xie in the shape and precision bearings to ensure the prerequisite conditions and service life.
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Liu, Jiao, Zheng Lin Liu, Xiang Kun Meng, and Xing Xin Liang. "Study on the Performance of Water Lubricated Stern Tube Bearing Based on Fluent." Applied Mechanics and Materials 496-500 (January 2014): 692–96. http://dx.doi.org/10.4028/www.scientific.net/amm.496-500.692.
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Apply FLUENT software to establish the water lubricated rubber stern tube bearing CFD model,study temperature and pressure distribution of the bearings at different speeds of rotation. It plays an important role in improving the performance of ship water lubricated stern tube bearing and security, reliability of propulsion system. The simulation results show that increasing the shaft speed in a certain range can reduce water film temperature, the effect is obvious especially at slow entrance velocity of bearings. Both high and low pressure ranges in the middle of bearings are enlarged with the increase of speed.
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Gębura, Andrzej. "Investigation Of Tribologic Processes in Bearing Nodes with the Use of the Fam-C And Fdm-A Methods – The Model With Elevated Passive Resistance." Research Works of Air Force Institute of Technology 35, no. 1 (December 1, 2014): 115–25. http://dx.doi.org/10.1515/afit-2015-0008.
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Abstract The paper discloses selected results of application of the FAM-C (a.c. generator) and FDM-A (d.c. generator) methods for comprehensive troubleshooting of bearing nodes in single-spool turbojet engines. A.c. generators provide information about slow-changing processes and, consequently, that information makes it possible to monitor radial and axial clearance of bearings as well as misalignment of shafts. On the other hand, the information transmitted by d.c. generators refers to fast-changing processes and is suitable to monitor dynamic properties of antifriction bearings: variations in the Q factor of bearings, slip factor of mating antifriction surfaces, rates of bearing cage rotation against its journal, etc. Nearly ten years of observations and data collection from a numerous set of engines during their operation have made it possible to classify processes associated with wear of bearings and categorize them into four phenomenological models. This paper is devoted to the model of elevated passive resistance
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Barkova, N. A., A. V. Barkov, V. V. Fedorishchev, and D. V. Grishchenko. "Bearing diagnostics of slow speed industrial rotating equipment by shock pulses." IOP Conference Series: Materials Science and Engineering 643 (November 13, 2019): 012026. http://dx.doi.org/10.1088/1757-899x/643/1/012026.
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Caesarendra, Wahyu, Mahardhika Pratama, Buyung Kosasih, Tegoeh Tjahjowidodo, and Adam Glowacz. "Parsimonious Network Based on a Fuzzy Inference System (PANFIS) for Time Series Feature Prediction of Low Speed Slew Bearing Prognosis." Applied Sciences 8, no. 12 (December 17, 2018): 2656. http://dx.doi.org/10.3390/app8122656.
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In recent years, the utilization of rotating parts, e.g., bearings and gears, has been continuously supporting the manufacturing line to produce a consistent output quality. Due to their critical role, the breakdown of these components might significantly impact the production rate. Prognosis, which is an approach that predicts the machine failure, has attracted significant interest in the last few decades. In this paper, the prognostic approaches are described briefly and advanced predictive analytics, namely a parsimonious network based on a fuzzy inference system (PANFIS), is proposed and tested for low speed slew bearing data. PANFIS differs itself from conventional prognostic approaches, supporting online lifelong prognostics without the requirement of a retraining or reconfiguration phase. The PANFIS method is applied to normal-to-failure bearing vibration data collected for 139 days to predict the time-domain features of vibration slew bearing signals. The performance of the proposed method is compared to some established methods, such as ANFIS, eTS, and Simp_eTS. From the results, it is suggested that PANFIS offers an outstanding performance compared to those methods.
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Allmaier, Hannes, and David E. Sander. "Piston-Pin Rotation and Lubrication." Lubricants 8, no. 3 (March 10, 2020): 30. http://dx.doi.org/10.3390/lubricants8030030.
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The rotational dynamics and lubrication of the piston pin of a Gasoline engine are investigated in this work. The clearance plays an essential role for the lubrication and dynamics of the piston pin. To obtain a realistic clearance, as a first step, a thermoelastic simulation is conducted for the aluminum piston for the full-load firing operation by considering the heat flow from combustion into the piston top and suitable thermal boundary conditions for the piston rings, piston skirt, and piston void. The result from this thermoelastic simulation is a noncircular and strongly enlarged clearance. In the second step, the calculated temperature field of the piston and the piston-pin clearance are used in the simulation of the piston-pin journal bearings. For this journal bearing simulation, a highly advanced and extensively validated method is used that also realistically describes mixed lubrication. By using this approach, the piston-pin rotation and lubrication are investigated for several different operating conditions from part load to full load for different engine speeds. It is found that the piston pin rotates mostly at very slow rotational speeds and even changes its rotational direction between different operating conditions. Several influencing effects on this dynamic behaviour (e.g., clearance and pin surface roughness) are investigated to see how the lubrication of this crucial part can be improved.
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Lovell, M. R., M. M. Khonsari, and R. D. Marangoni. "The Response of Balls Undergoing Oscillatory Motion: Crossing From Boundary to Mixed Lubrication Regimes." Journal of Tribology 115, no. 2 (April 1, 1993): 261–66. http://dx.doi.org/10.1115/1.2921000.
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There are many applications where determining the response of a slowly oscillating ball bearing becomes crucial. Many instrument pointing mechanisms, in particular those used for aerospace applications, contain ball bearings which sinusoidally oscillate at very slow rates over small angles. Prediction of the frictional response of these bearings is essential to designers, as the friction torque which they develop is an important factor for controlling space instruments. The friction torque associated with the motion of sinusoidally oscillating ball bearings has been found to trace out hysteresis loops. These loops can be separated into two regions: the steady rolling region and the pre-rolling region. The steady rolling friction torque, Ts, characterizes the steady rolling region, while the rest slope, σ, characterizes the pre-rolling region. The speed of a ball bearing in sinusoidal motion varies from rest to a maximum velocity, changing velocity at instantaneous increments. It is found that while moving toward this maximum velocity, a bearing may cross from boundary to mixed lubrication regimes. As a result, the prediction and interpretation of σ and Ts in sinusoidal oscillating systems becomes more difficult than their counterparts in constant rate systems, which ordinarily operate in only one lubrication regime. To establish the velocity boundaries associated with the onset of different lubrication regimes, a series of experiments were conducted at a constant rotation rate. Starting at the ultra-low-speed of .01 deg/s, the angular velocity was gradually increased to 72 deg/s. In this velocity range, the balls traveled from boundary lubrication, crossing the mixed lubrication regime, into the elastohydrodynamic lubrication regime. Sinusoidal hysteresis curves were also generated experimentally and characterized. The rest slope and steady rolling friction torque were investigated in both rolling regions using two different lubricants.
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Aye, S. A., and P. S. Heyns. "Acoustic Emission-Based Prognostics of Slow Rotating Bearing Using Bayesian Techniques Under Dependent and Independent Samples." Applied Artificial Intelligence 29, no. 6 (June 18, 2015): 563–96. http://dx.doi.org/10.1080/08839514.2015.1038432.
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Hakhamaneshi, Manouchehr, Bruce L. Kutter, Andreas G. Gavras, Sivapalan Gajan, Angelos Tsatsis, Weian Liu, Keshab Sharma, et al. "Database of rocking shallow foundation performance: Slow-cyclic and monotonic loading." Earthquake Spectra 36, no. 3 (March 16, 2020): 1585–606. http://dx.doi.org/10.1177/8755293020906564.
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Many physical model tests have examined the performance of rocking foundations during cyclic and seismic loading. These tests varied in model size, testing equipment, superstructure properties, footing shape, supporting soil environment, and loading protocol. “FoRCy, Foundation Rocking database of Cyclic and Monotonic Loading” is a new database (published at https://datacenterhub.org/ ), summarizing the results of monotonic and slow-cyclic loading tests of rocking foundations. The database consists of columns identifying testing equipment and facility, soil, superstructure, and system properties, as well as loading protocol and results. The database contains 456 records (rows), each one being unique in either model configuration or loading amplitude. To illustrate its value, this article shows correlations between (1) settlement, rotation, and factor of safety with respect to bearing capacity and (2) moment and cumulative rotation for shallow footings. Data indicate that the rotation required to mobilize the moment capacity is surprisingly constant (about 0.01 radians) for a wide range of experiments.
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Elforjani, M., and D. Mba. "Detecting the onset, propagation and location of non-artificial defects in a slow rotating thrust bearing with acoustic emission." Insight - Non-Destructive Testing and Condition Monitoring 50, no. 5 (May 2008): 264–68. http://dx.doi.org/10.1784/insi.2008.50.5.264.
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Ullrich, Michel, Maik Wolf, Mathias Rudolph, and Wolfgang Diller. "Shaft Integrated Electromagnetic Energy Harvester with Gravitational Torque." Designs 4, no. 2 (June 23, 2020): 16. http://dx.doi.org/10.3390/designs4020016.
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This paper presents the development of an electromagnetic energy harvester for electrical supply of a sensor unit integrated on the rotating inner ring of a rolling bearing. This energy harvester is of special interest for condition monitoring tasks on rotating shafts. A sensory monitor on the inner ring can detect wear conditions at an early stage. The harvester works without mechanical and energetic contact to surrounding components by utilizing the rotational energy of the shaft. The functionality of the Energy Harvester is enabled by the inertia principle, which is caused by an asymmetrical mass distribution. We provide simulations to validate the designs. This work includes simulation studies on the electrical power output of the harvester. Therefore, the necessary simulation of the magnetic problems is realized in a substitute simulation environment. The harvester design enables existing machines to be equipped with the harvester to provide an energy supply on rotating shafts. This clamp connection enables shaft mounting independent of location without mechanical work on the shaft. With an electrical power of up to 163.6 m W, at 3600 rpm, the harvester is used as an energy supply, which enables sensor-based monitoring of slow wear processes.
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Panagiotidou, Andriani I., George Gazetas, and Nikos Gerolymos. "Pushover and Seismic Response of Foundations on Stiff Clay: Analysis with P-Delta Effects." Earthquake Spectra 28, no. 4 (November 2012): 1589–618. http://dx.doi.org/10.1193/1.4000084.
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Finite-element analyses are performed for the response to lateral monotonic, slow-cyclic, and seismic loading of rigid footings carrying tall slender structures and supported on stiff clay. The response involves mainly footing rotation under the action of overturning moments from the horizontal external force on—or the developing inertia at—the mass of the structure, as well as from the aggravating contribution of its weight (P-delta effect). Emphasis is given to the conditions for collapse of the soil-foundation-structure system. Two interconnected mechanisms of nonlinearity are considered: detachment from the soil with subsequent uplifting of the foundation (geometric nonlinearity) and formation of bearing-capacity failure surfaces (material inelasticity). The relation between monotonic behavior (static “pushover”), slow-cyclic behavior, and seismic response is explored parametrically. We show that with “light” structures uplifting is the dominant mechanism that may lead to collapse by dynamic instability (overturning), whereas “very heavy” structures mobilize soil failure mechanisms, leading to accumulation of settlement, residual rotation, and ultimately collapse.
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Zhang, Qiang, TianMin Wu, Chen Chen, Shaul Mukamel, and Wei Zhuang. "Molecular mechanism of water reorientational slowing down in concentrated ionic solutions." Proceedings of the National Academy of Sciences 114, no. 38 (September 5, 2017): 10023–28. http://dx.doi.org/10.1073/pnas.1707453114.
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Water dynamics in concentrated ionic solutions plays an important role in a number of material and energy conversion processes such as the charge transfer at the electrolyte–electrode interface in aqueous rechargeable ion batteries. One long-standing puzzle is that all electrolytes, regardless of their “structure-making/breaking” nature, make water rotate slower at high concentrations. To understand this effect, we present a theoretical simulation study of the reorientational motion of water molecules in different ionic solutions. Using an extended Ivanov model, water rotation is decomposed into contributions from large-amplitude angular jumps and a slower frame motion which was studied in a coarse-grained manner. Bearing a certain resemblance to water rotation near large biological molecules, the general deceleration is found to be largely due to the coupling of the slow, collective component of water rotation with the motion of large hydrated ion clusters ubiquitously existing in the concentrated ionic solutions. This finding is at variance with the intuitive expectation that the slowing down is caused by the change in fast, single-molecular water hydrogen bond switching adjacent to the ions.
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Koike, Hitonobu, Edson Costa Santos, Katsuyuki Kida, Takashi Honda, and Justyna Rozwadowska. "Effect of Repeated Induction Heating on Fatigue Crack Propagation in SAE 52100 Bearing Steel." Advanced Materials Research 217-218 (March 2011): 1266–71. http://dx.doi.org/10.4028/www.scientific.net/amr.217-218.1266.
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Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications when high wear and fatigue resistance are required. Refining the microstructure of steel improves its mechanical properties (e.g. toughness). In this work SAE 52100 specimens were exposed to repeated induction heating process and rotation bending tests were performed using single- and repeatedly heat-treated material in order to investigate the influence of this cyclic heat treatment on the mechanical properties of SAE 52100. In an attempt to determine the effect of the repeated induction heating and quenching on the material, we focused our observations on the internal fatigue “fisheye" cracks. It was noted that crack propagation was successfully halted by the refined microstructure in heat affected zone, therefore it can be concluded that repeated induction heating and quenching processes help to slow down the propagation of fisheye cracks in SAE52100 steel bars.
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Saeed, Nasser A., and Mostafa Eissa. "Bifurcation Analysis of a Transversely Cracked Nonlinear Jeffcott Rotor System at Different Resonance Cases." June 2019 24, no. 2 (June 2019): 284–302. http://dx.doi.org/10.20855/ijav.2019.24.21309.
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This work focuses on the dynamical behaviour and bifurcations of a vertically supported Jeffcott rotor system having a transverse crack and nonlinear stiffness characteristics at the primary, sub-harmonic, and super-harmonic resonance cases. The nonlinear restoring force due to the bearing-clearance, the crack breathing, the disc eccentricity, and the orientation angle between the crack and imbalance direction are considered in the system model. The equations governing the system motion are derived and solved analytically by applying the Multiple Scales Perturbation Technique (MSPT). The slow-flow modulating equations are obtained and the spinning speed response curve is plotted. The whirling orbit and amplitude spectrum are constructed in the three considered resonance cases. The acquired results provide a better understanding of the main reasons of the super- and sub-harmonic resonance excitations. In additions, we concluded that the suitable resonance case that can be used for early detections of the cracks in the rotating shafts is the sub-harmonic resonance case. Finally, the obtained results are confirmed numerically and compared with the work published in the literature
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Li, Lijuan, Richard E. Perrier, Donald R. Eaton, and Michael J. McGlinchey. "The reactions of nitrosoarenes with cationic cyclohexadienyl complexes of iron tricarbonyl: an ESR study." Canadian Journal of Chemistry 67, no. 11 (November 1, 1989): 1868–77. http://dx.doi.org/10.1139/v89-290.
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The reactions of nitrosoarenes with the (cyclohexadienyl)Fe(CO)3 cation have been investigated by using electron spin resonance spectroscopy. The radicals produced are nitroxides of the type (OC)3Fe(C6H7)(Ar)N—O• but, in some cases, disproportionation and loss of the metal carbonyl fragment leads to the corresponding C6H5(Ar)N—O• radical. With bulky nitrosoarenes, such as C6Me5NO, isomers are observed in which the aryl ring rotation is slow on the ESR time scale. The analogous reactions with the cyclohexadienyl cation derived from the B ring of (ergosteryl acetate)Fe(CO)3 lead to initial attack not at one of the termini of the delocalized system but rather at the central carbon, i.e., at C-7. Subsequent hydrogen migration leads to the (5,7-diene)Fe(CO)3 complex bearing the arylnitroxide at the 7-position. The mechanisms of these reactions are discussed. Keywords: nitrosoarenes, iron cations, ESR.
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Rakhmanov, S. R. "Elaboration of a lubrication system for universal spindle hinges of rolling mills." Ferrous Metallurgy. Bulletin of Scientific , Technical and Economic Information 77, no. 9 (September 21, 2021): 1047–53. http://dx.doi.org/10.32339/0135-5910-2021-9-1047-1053.
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The experience of running drives of most of heavy-duty rolling mills shows that the designs of universal spindles with blade hinges under conditions of increased alternating loads are most acceptable comparing with other spindles types. Open friction surfaces are the drawbacks of these types of spindles, which complicate the matter of continuous supply of lubrication. Perfected effective system of forced lubrication of rolling mill spindles hinges proposed. The facility for their lubrication has a bearing support of balancing design, spindle, in radial holes of which spring-loaded plungers are installed in a diametrically opposite order. Besides, the facility has suction valves and force valves installed in the spindle axial holes, connecting with the radial ones. A methodology proposed to select the eccentricity of the internal cylindrical surface of the bearing support of the spindle hinge, the axis of which is located eccentrically relative the spindle rotation axis. A calculating scheme and a mathematical model of the process of lubrication supply into joints of rolling mill spindle hinge elaborated. A differential equation of lubrication motion in the conical slot of the hinge between a blade and insertions drawn up. Parameters of hydrodynamic motion of lubrication in the conical slot established. Modes of the lubrication motion in the conical slot between roller blade and hinge insertion determined. Based on experience of operation of friction couple bronze-steel, a lubrication for rolling mills universal spindles proposed. To improve the operation characteristics of hinges based on the friction couple bronze-steel, a thick lubrication having antifriction properties namely based on oils with additives ИП-10, КП-10 and ДФ-11 proposed. Dependence of pressure distribution along the length of the hinge conical slot presented for various lubrications of low viscosity (ИП-10 + ДФ-11) and high viscosity (КП-10 + ДФ-11). The quality effect of the speed of roller blade movable wall on distribution of speeds of lubrication layer motion over the height of the hinge conical slot for comparatively low and comparatively high boundary speeds demonstrated.
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Sharma, Keshab, and Lijun Deng. "Field testing of rocking foundations in cohesive soil: cyclic performance and footing mechanical response." Canadian Geotechnical Journal 57, no. 6 (June 2020): 828–39. http://dx.doi.org/10.1139/cgj-2018-0734.
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This paper presents a field test program of a large-scale soil–footing-structure system designed with a rocking foundation in a cohesive soil to examine the behaviour of the system and to provide case histories for possible performance-based seismic design of foundations. The rocking system was subjected to slow cyclic loadings at various drift ratios up to 7%. Twenty-four tests were conducted for foundations with varying initial factors of safety against the bearing failure, loading directions, rotation amplitudes, and embedment. A geotechnical investigation was carried out to determine soil properties before and after the experiments. The system performance indices, such as damping, stiffness, settlement, and re-centering capability, were quantified and compared with the published literature. Field test results showed that the strength and unit weight of soils at footing edges were increased due to rocking, for the present cohesive soil. The rocking moment capacity increased slightly with the increasing soil strength. An empirical equation for the secant stiffness was developed. The rocking system on the cohesive soil exhibited superior performance in terms of small residual settlement and large re-centering capability. Footing’s mechanical response was quantified using strain gauge readings. The footing remained elastic in tension; the transient soil–footing contact areas were estimated with strain gauges, and they agreed very well with the measured or calculated contact areas.
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Jones, M. G., E. Papastergis, V. Pandya, L. Leisman, A. J. Romanowsky, L. Y. A. Yung, R. S. Somerville, and E. A. K. Adams. "Contribution of HI-bearing ultra-diffuse galaxies to the cosmic number density of galaxies." Astronomy & Astrophysics 614 (June 2018): A21. http://dx.doi.org/10.1051/0004-6361/201732409.
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We estimate the cosmic number density of the recently identified class of HI-bearing ultra-diffuse sources (HUDs) based on the completeness limits of the ALFALFA survey. These objects have HI masses approximately in the range 8.5 < logMHI∕M⊙ < 9.5, average r-band surface brightnesses fainter than 24 mag arcsec−2, half-light radii greater than 1.5 kpc, and are separated from neighbours by at least 350 kpc. In this work we demonstrate that they contribute at most ~6% of the population of HI-bearing dwarfs detected by ALFALFA (with similar HI masses), have a total cosmic number density of (1.5 ± 0.6) × 10−3 Mpc−3, and an HI mass density of (6.0 ± 0.8) × 105 M⊙ Mpc−3. We estimate that this is similar to the total cosmic number density of ultra-diffuse galaxies (UDGs) in groups and clusters, and conclude that the relation between the number of UDGs hosted in a halo and the halo mass must have a break below M200 ~ 1012 M⊙ in order to account for the abundance of HUDs in the field. The distribution of the velocity widths of HUDs rises steeply towards low values, indicating a preference for slow rotation rates compared to the global HI-rich dwarf population. These objects were already included in previous measurements of the HI mass function, but have been absent from measurements of the galaxy stellar mass function owing to their low surface brightness. However, we estimate that due to their low number density the inclusion of HUDs would constitute a correction of less than 1%. Comparison with the Santa Cruz semi-analytic model shows that it produces HI-rich central UDGs that have similar colours to HUDs, but that these UDGs are currently produced in a much greater number. While previous results from this sample have favoured formation scenarios where HUDs form in high spin-parameter halos, comparisons with recent results which invoke that formation mechanism reveal that this model produces an order of magnitude more field UDGs than we observe in the HUD population, and these have an occurrence rate (relative to other dwarfs) that is approximately double what we observe. In addition, the colours of HUDs are bluer than predicted, although we suspect this is due to a systematic problem in reproducing the star formation histories of low-mass galaxies rather than being specific to the ultra-diffuse nature of these sources.
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Popescu, Florin Dumitru, Sorin Mihai Radu, Krzysztof Kotwica, Andrei Andraș, and Ildiko Kertesz (Brînaș). "Simulation of the Time Response of the ERc 1400-30/7 Bucket Wheel Excavator’s Boom during the Excavation Process." Sustainability 11, no. 16 (August 12, 2019): 4357. http://dx.doi.org/10.3390/su11164357.
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The sustainability of lignite production requires, among other factors, cost reduction, high efficiency, as well as the increase of the production capacity. In order to rationalize and increase the efficiency of lignite mines, the optimization of the production process is necessary. In this respect, equipment revitalization and modernization is a key issue. This paper deals with the analysis of the time response of the boom structure of a bucket wheel excavator (BWE) during operation. For this, we propose a virtual model of the boom, on which a variable-in-time force generated by the bucket wheel acts. The kinematic drive chain of the bucket wheel and the conveyor belt, which are also vibration generators, were simulated only by the static load produced on the excavator’s boom. Thus, it is possible to highlight the time response of the load-bearing structure (the boom) of the bucket wheel to the action of forces resulting from the cutting of the face under pretensioning conditions. The forces generated by the excavation process have high values and a slow variation over time, depending on the bucket wheel’s rotation speed and the number of buckets installed on the wheel. The dynamic time response simulation was performed considering the global damping variation as dependent on frequency. The simulation was done for both the excavation of a homogeneous material and for the case of the sudden appearance of a hard material inclusion (boulder) during homogenous material cutting.
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Oravec, Milan, Pavol Lipovský, Miroslav Šmelko, Pavel Adamčík, Mirosław Witoś, and Jerzy Kwaśniewski. "Low-Frequency Magnetic Fields in Diagnostics of Low-Speed Electrical and Mechanical Systems." Sustainability 13, no. 16 (August 16, 2021): 9197. http://dx.doi.org/10.3390/su13169197.
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The magnetic field created by technical devices is a source of information. This information could be used in contactless diagnostics and predictive maintenance or for resolving problems along with standard NDT (nondestructive testing) methods, especially if we consider large, slow-speed devices, such as electromotors, transmissions, or generators. Identification of causalities of device failure processes with near magnetic field is one of the suitable NDT methods improving sustainability of systems. The measurements presented in the article were performed with the VEMA 04 fluxgate vector magnetometer with the DC-250 Hz bandwidth and 2 nT sensitivity. Postprocessing of the results was performed in the means of standard methods of discrete Fourier Transform, spectrogram creation and Wavelet Transform. The article presents data gathered during the measurement of a pair of extraction fans with power of 140 kW each and maximum revolutions up to 740 rev/min controlled by frequency converters and a single semi-Kaplan water power plant with 400 kW peak power at 1005 rev/min maximum generator speed. The measurements were performed before and after repairs of one of the ventilators in the ventilation system at 60% and 100% of maximal output power. The rotating magnetic fields of the fan electromotor stator, fan rotor revolutions, rotor slip frequency and ball-bearing frequencies were identified in frequency spectrums in the distance of 700 mm from fan electromotor axis in both cases. During the measurements on the semi-Kaplan turbine, the changes in states of mechanical and electrical components of the machine were monitored in the magnetic fields with increase of the power in the range of 0–95%, before and after phasing to the electrical grid. Standard processing methods, Discrete Fourier Transform, spectrograms and Discrete Wavelet Transform were used. In the spectrograms of the measured magnetic fields, the 1st–4th harmonics of the turbine shaft, generator shaft and also their side frequencies were identified. Significant changes of magnetic fields in time were identified in the area of 60–95% power. With the help of the Wavelet, transform intervals were identified where it is desirable to operate the turbine. The analyses of magnetic fields measurements performed on the power plant were compared with vibro-diagnostic principles.
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Wang, Jin, Krzysztof S. Bankiewicz, Robert J. Plunkett, and Edward H. Oldfield. "Intrastriatal implantation of interleukin-1." Journal of Neurosurgery 80, no. 3 (March 1994): 484–90. http://dx.doi.org/10.3171/jns.1994.80.3.0484.
Full textAbstract:
✓ Intrastriatal implantation with dopaminergic or nondopaminergic tissue can elicit behavioral recovery in parkinsonian animals. Because in these animals, especially in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned monkeys, there are still considerable numbers of dopaminergic neurons left in the mesencephalon, implantation-induced trophic effects on host residual dopaminergic neurons have been suggested as a mechanism underlying the behavioral recovery. Gliosis around the graft is a universal finding in any implantation procedure and is probably mediated by interleukin-1 (IL-1); in addition, activated astrocytes secrete several neurotrophic factors in vitro. Therefore, the authors postulated that trophic effects from IL-1-induced gliosis may be a “final common pathway” for recovery in parkinsonian animals after implantation. Hemiparkinsonism was induced in rats by injection of 6-hydroxydopamine either directly into the substantia nigra or into the median forebrain bundle. The substantia nigra-lesioned rats showed complete depletion of dopaminergic neurons in the substantia nigra but sparing of those in the ventral tegmental area, whereas the median forebrain bundle-lesioned animals had depletion of dopaminergic cells in the substantia nigra and the ventral tegmental area. Polymer pellets containing either slow-released IL-1 alpha and beta or placebo pellets were implanted in the caudate nucleus on the lesioned side in both groups. The rats' rotational response to amphetamine was tested weekly for 8 weeks. Selective substantia nigra-lesioned rats with implantation of IL-1 pellets had a 45% reduction in amphetamine-induced rotation, whereas placebo-implanted substantia nigra-lesioned rats had a 14% reduction in rotation. In the median forebrain bundle-lesioned group, neither IL-1 nor placebo implantation elicited any effect on turning. Immunohistochemical staining for glial fibrillary acidic protein was markedly increased surrounding the IL-1 pellets compared to the placebo pellets. In the selective substantia nigra-lesioned rats with IL-1 pellets implanted in the caudate nucleus, a considerable number of tyrosine hydroxylase immunoreactive (TH-IR) fibers were observed in the medial and middle portions of the caudate nucleus. Fewer TH-IR fibers were seen in the rats with placebo-bearing pellets. These results suggest that neurotrophic activities mediated by IL-1 and reactive astrocytes might be a common path through which tissue trauma and some tissue transplants exert their beneficial effects in parkinsonian animals. Furthermore, most of the sprouted dopaminergic fibers induced by IL-1 in the caudate nucleus come from dopaminergic neurons in the ventral tegmental area.
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Howard, Samuel A., and Luis San Andrés. "A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings." Journal of Engineering for Gas Turbines and Power 133, no. 2 (October 29, 2010). http://dx.doi.org/10.1115/1.4001997.
Full textAbstract:
Gas foil bearings offer several advantages over traditional bearing types that make them attractive for use in high-speed turbomachinery. They can operate at very high temperatures, require no lubrication supply (oil pumps, seals, etc.), exhibit very long life with no maintenance, and once operating airborne, have very low power loss. The use of gas foil bearings in high-speed turbomachinery has been accelerating in recent years although the pace has been slow. One of the contributing factors to the slow growth has been a lack of analysis tools, benchmarked to measurements, to predict gas foil bearing behavior in rotating machinery. To address this shortcoming, NASA Glenn Research Center (GRC) has supported the development of analytical tools to predict gas foil bearing performance. One of the codes has the capability to predict rotordynamic coefficients, power loss, film thickness, structural deformation, and more. The current paper presents an assessment of the predictive capability of the code named XLGFBTH©. A test rig at GRC is used as a simulated case study to compare rotordynamic analysis using output from the code to actual rotor response as measured in the test rig. The test rig rotor is supported on two gas foil journal bearings manufactured at GRC with all pertinent geometry disclosed. The resulting comparison shows that the rotordynamic coefficients calculated using XLGFBTH© represent the dynamics of the system reasonably well especially as they pertain to predicting critical speeds.
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Walker, Cody, and Jamie Coble. "Wind Turbine Bearing Fault Detection Using Adaptive Resampling and Order Tracking." International Journal of Prognostics and Health Management 9, no. 2 (November 20, 2020). http://dx.doi.org/10.36001/ijphm.2018.v9i2.2735.
Full textAbstract:
Wind energy is growing increasingly popular in the United States, so it is imperative to make it as cost competitive as possible. Operations and Maintenance (O&M) make up 20-25% of the total cost of onshore wind projects. Unplanned maintenance contributes approximately 75% of the total maintenance costs (WWEA, 2012). Condition-based maintenance strategies intend to maximize the uptime by reducing to the amounts of unplanned maintenance. This should result in an overall decrease in the cost of maintenance. Wind turbines produce an interesting challenge, because their main shaft rotation is both slow and nonstationary. Through the use of adaptive resampling and order tracking, both of these challenges were combated as the bearing fault was identified in the order spectrum then tracked as it progressed. The fault was identified as an outer race defect on the main bearing that initiated sometime during or before installation. The total energy in the order spectrum around the bearing fault rate was identified as a potential front-runner for a prognostic parameter. This paper presents a case study application to operational wind turbine bearing data to demonstrate the ease and intuitiveness of combining adaptive resampling and order tracking to diagnose faults for slow, nonstationary bearings. Prognosis of remaining useful life is proposed with features extracted from the order spectrum, but additional data are needed to develop and demonstrate this analysis.
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Kejian, Jiang, Zhu Changsheng, and Tang Ming. "A Uniform Control Method for Imbalance Compensation and Automation Balancing in Active Magnetic Bearing-Rotor Systems." Journal of Dynamic Systems, Measurement, and Control 134, no. 2 (December 29, 2011). http://dx.doi.org/10.1115/1.4005279.
Full textAbstract:
The undesired synchronous vibration due to rotor mass imbalance is a main disturbance source in all rotating machinery including active magnetic bearing (AMB)-rotor systems. In the AMB-rotor system, imbalance compensation, which causes the AMB actuators to spin a rotor about its geometric axis, and automation balancing, which spins a rotor about its inertial axis, are two kinds of common control aim for the rotor imbalance control. In this study, the internal relation between the imbalance compensation and the automation balancing is analyzed and a uniform control method is proposed. With the identical control algorithm, the proposed control method can realize the automation balancing or the imbalance compensation, respectively, by switching the controller’s junction position in the original control loop. The proposed control method does not depend on the dynamic plant model, because its algorithm is based on the real-time identification for the Fourier coefficient of the rotor imbalance disturbance. In this paper, the process of identification algorithm is given in detail and all the possible junction forms of the controller are illustrated. By the simulations, the identification performances of the control algorithm are compared in the conditions with three variable factors, including the signal noise ratio (SNR), the imbalance phase and the identification delay time. The noise level has considerable influence on the identification precision, but the imbalance phase has little. To prolong the identification delay time will be of benefit to improve the identification precision but slow down the identification process. Experiments, which are carried out on an AMB-rigid rotor test rig, indicate that by switching the junction position of the controller in control loop, both kinds of rotor imbalance control can achieve the good effectiveness.
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Pier, Benoît, and Peter J. Schmid. "Optimal energy growth in pulsatile channel and pipe flows." Journal of Fluid Mechanics 926 (September 6, 2021). http://dx.doi.org/10.1017/jfm.2021.702.
Full textAbstract:
Pulsatile channel and pipe flows constitute a fundamental flow configuration with significant bearing on many applications in the engineering and medical sciences. Rotating machinery, hydraulic pumps or cardiovascular systems are dominated by time-periodic flows, and their stability characteristics play an important role in their efficient and proper operation. While previous work has mainly concentrated on the modal, harmonic response to an oscillatory or pulsatile base flow, this study employs a direct–adjoint optimisation technique to assess short-term instabilities, identify transient energy-amplification mechanisms and determine their prevalence within a wide parameter space. At low pulsation amplitudes, the transient dynamics is found to be similar to that resulting from the equivalent steady parabolic flow profile, and the oscillating flow component appears to have only a weak effect. After a critical pulsation amplitude is surpassed, linear transient growth is shown to increase exponentially with the pulsation amplitude and to occur mainly during the slow part of the pulsation cycle. In this latter regime, a detailed analysis of the energy transfer mechanisms demonstrates that the huge linear transient growth factors are the result of an optimal combination of Orr mechanism and intracyclic normal-mode growth during half a pulsation cycle. Two-dimensional sinuous perturbations are favoured in channel flow, while pipe flow is dominated by helical perturbations. An extensive parameter study is presented that tracks these flow features across variations in the pulsation amplitude, Reynolds and Womersley numbers, perturbation wavenumbers and imposed time horizon.