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1
Labardi, M., P. Tripathi, S. Capaccioli, and R. Casalini. "Intermittent-contact local dielectric spectroscopy of nanostructured interfaces." Nanotechnology 33, no. 21 (February 28, 2022): 210002. http://dx.doi.org/10.1088/1361-6528/ac52be.
Анотація:
Abstract Local dielectric spectroscopy (LDS) is a scanning probe method, based on dynamic-mode atomic force microscopy (AFM), to discriminate dielectric properties at surfaces with nanometer-scale lateral resolution. Until now a sub-10 nm resolution for LDS has not been documented, that would give access to the length scale of fundamental physical phenomena such as the cooperativity length related to structural arrest in glass formers (2–3 nm). In this work, LDS performed by a peculiar variant of intermittent-contact mode of AFM, named constant-excitation frequency modulation, was introduced and extensively explored in order to assess its best resolution capability. Dependence of resolution and contrast of dielectric imaging and spectroscopy on operation parameters like probe oscillation amplitude and free amplitude, the resulting frequency shift, and probe/surface distance-regulation feedback gain, were explored. By using thin films of a diblock copolymer of polystyrene (PS) and polymethylmethacrylate (PMMA), exhibiting phase separation on the nanometer scale, lateral resolution of at least 3 nm was demonstrated in both dielectric imaging and localized spectroscopy, by operating with optimized parameters. The interface within lamellar PS/PMMA was mapped, with a best width in the range between 1 and 3 nm. Changes of characteristic time of the secondary (β) relaxation process of PMMA could be tracked across the interface with PS.
2
Peng, Wei, James Kiely, and Yiao-Tee Hsia. "Wear Analysis of Head-Disk Interface During Contact." Journal of Tribology 127, no. 1 (January 1, 2005): 171–79. http://dx.doi.org/10.1115/1.1843832.
Анотація:
To achieve a higher storage density in a hard disk drive, the fly height of the air bearing slider, as part of the magnetic spacing, has to be minimized. At an ultralow fly height, the intermittent–continuous contact at the head–disk interface (HDI) is unavoidable and directly affects the mechanical and magnetic performance of the hard disk drive, and is of great interest. The HDI wear has a nonlinear and time-varying nature due to the change of contact force and roughness. To predict the HDI wear evolution, an iterative model of Coupled Head And Disk (CHAD) wear, is developed based on the contact mechanics. In this model, a composite transient wear coefficient is adopted and multiple phases of the wear evolution are established. A comprehensive contact stiffness is derived to characterize the contact at the HDI. The abrasive and adhesive wear is calculated based on the extended Archard’s wear law. The plastic and elastic contact areas are calculated with a three-dimensional (3D) sliding contact model. Based on the CHAD wear model, for the first time, the coupling between head and disk wear evolutions is thoroughly investigated. Accelerated wear tests have also been performed to verify the disk wear effect on the slider wear. A wear coefficient drop with time is observed during the tests and it is attributed to a wear mechanism shift from abrasive to adhesive wear. A shift in the type of contact from plastic to elastic accounts for the wear mechanism change.
3
Lotfi, Mohammad, Saeid Amini, and Hossein Ashrafi. "Theoretical and numerical modeling of tool–chip friction in ultrasonic-assisted turning." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 4 (November 15, 2018): 824–38. http://dx.doi.org/10.1177/0954408918812271.
Анотація:
Decrease of friction in tool–chip contact zone is a key subject in metal cutting operation. Therefore, effect of ultrasonic vibration in this area is analyzed by using experimental and simulation methods. In this study, a theoretical model is firstly developed based on the shear friction model, and then sticking–sliding contact zones plus their contact lengths are defined in order to simulate conventional and ultrasonic-assisted turning. Accordingly, shear angle, sticky length, and cutting forces were measured in experiments as input parameters for the calculation of friction coefficients. As a result, intermittent contact of vibrated tool decreases the time of thermal conduction in tool–chip interface, resulting in a significant reduction in friction coefficient and contact length, particularly, in sticky region.
4
Maeno, Takashi, and David B. Bogy. "Effect of the Rotor/Stator Interface Condition Including Contact Type, Geometry, and Material on the Performance of Ultrasonic Motor." Journal of Tribology 116, no. 4 (October 1, 1994): 726–32. http://dx.doi.org/10.1115/1.2927326.
Анотація:
The purpose of this paper is to show the dynamic contact characteristics and the motor performance of several types of ultrasonic motors. First, we compare the performance of “intermittent” and “traveling” contact type ultrasonic motors by using the locally deforming rotor model. We show that the motor performances are the same when the shape of the stator’s amplitude, and the rotor’s interpenetration are the same. Then, we show that the performance of these two types of motors are different according to the effects of inertia and actual three dimensional displacement by using the FE (finite element) analysis. Finally, the effects of the teeth and a surface layer at the contact interface on the performance of the ultrasonic motor, including T-N (torque-speed) characteristics and friction loss, are analyzed.
5
Polycarpou, A. A., and A. Soom. "A Two-Component Mixed Friction Model for a Lubricated Line Contact." Journal of Tribology 118, no. 1 (January 1, 1996): 183–89. http://dx.doi.org/10.1115/1.2837076.
Анотація:
A two-component, two-dimensional friction model for a lubricated line contact, operating in boundary and mixed lubrication regimes, is developed. The friction is explicitly decomposed into the solid and the fluid shear components. The solid component is due to the asperity interactions and the fluid shear arises from the lubricant present at the interface. The friction model includes the sliding velocity, the instantaneous separation of the sliding bodies, normal to the sliding direction, the normal load and fluid properties. The model is based on unsteady friction experiments carried out under constant normal loads and time-varying sliding velocities. The model is applied to quasi-steady sliding, unsteady continuous and intermittent sliding, including sticking and momentary reversals of motion. In each case it becomes possible to track the instantaneous fluid shear and solid friction components.
6
Annakodi, Vivek Anand, Ramachandra Arvind Singh, Subramanian Jayalakshmi, Yupeng Zhang, Muhammed Anaz Khan, Koppula Srinivas Rao, and Rajashekhara Shabadi. "Patterning SS304 Surface at Microscale to Reduce Wettability and Corrosion in Saline Water." Metals 12, no. 7 (July 3, 2022): 1137. http://dx.doi.org/10.3390/met12071137.
Анотація:
Stainless steel 304 (SS304) experiences corrosion when it is exposed to a saline atmosphere, which attains severity due to its high surface wettability. Topographical modification of metallic surfaces is an effective route to reduce wettability and thereby mitigate liquid-mediated corrosion. In this work, topographical modification of stainless steel 304 flat surface in the form of micropillars was done (pillar width: 100 μm, inter-pillar distance: 100 μm and height: 80 μm). Micropillars were fabricated by a chemical etching process. Wetting and corrosion of the micropillars was studied over long-time duration in comparison with flat surface, before and after intermittent and continuous exposures to saline water for 168 h. Wetting was characterized by measuring the static water contact angle on the test surfaces and their corrosion by electrochemical polarization tests (electrolyte: 3.5 wt.% sodium chloride solution). The relationship between the nature of wetting of the test surfaces and their corrosion was examined. Micropillars showed predominantly composite wetting over a long time, which imparted an effective resistance against corrosion over a long time to the SS304 surface. When compared to the flat surface, the corrosion rates of the micropillars were lower by two orders of magnitude, prior to and also upon long-time contact with the NaCl solution. Micropillars lowered corrosion due to composite wetting, i.e., solid-liquid-air interface that reduced the area that was in contact with the NaCl solution. The efficiency of corrosion inhibition (η) of micropillars was 88% before long-time contact, 84% after intermittent contact, and 77% after continuous contact with NaCl solution. Topographical modification in the form of micropillars that can impart composite wetting is an effective route to induce long-term anticorrosion ability to the SS304 surface.
7
Santhosh, B., S. Narayanan, and C. Padmanabhan. "Nonlinear Dynamics of Shrouded Turbine Blade System with Impact and Friction." Applied Mechanics and Materials 706 (December 2014): 81–92. http://dx.doi.org/10.4028/www.scientific.net/amm.706.81.
Анотація:
Dry friction dampers are passive devices used to reduce the resonant vibration amplitudes in turbine bladed systems. In shrouded turbine blade systems, in addition to the stick- slip motion induced by dry friction during the contact state in the tangential direction, the interface also undergoes intermittent separation in the normal direction. The problem can thus be treated as a combination of impact and friction. In this work, the dynamics of dry friction damped oscillators which are representative models of dry friction damped bladed system is investigated. A one dimensional contact model which is capable of modeling the interface under constant and variable normal load is used. The steady state periodic solutions are obtained by multi - harmonic balance method (MHBM). Frequency response plots are generated for different values of normal load using the arc length continuation procedure. The MHBM solutions are validated using numerical integration. A single degree of freedom (dof) model under constant normal load with constant and variable friction coefficients, a dry friction damped two dof system under constant normal load and a two dof system under variable normal load are investigated. In the presence of variable normal load, the system shows multivalued frequency response and jump phenomenon. The optimal value of the normal load which gives minimum resonant response is also obtained.
8
Tagawa, N., and M. Hashimoto. "Self-Loading Slider Dynamics for Noncontact Start Stop Operation With Negative Pressure Air-Lubricated Slider Bearing in Magnetic Disk Storage." Journal of Tribology 111, no. 4 (October 1, 1989): 698–702. http://dx.doi.org/10.1115/1.3261997.
Анотація:
This paper proposes self-loading flying head slider mechanisms to be used for information storage on magnetic disk media under noncontact start/stop mode conditions. The mechanisms consist of a zero-load negative pressure air-lubricated slider bearing, a slider suspension mechanism, and a twin-structure piezoelectric actuator as the head loading mechanism. Experimental research was carried out on fundamental flying characteristics for the slider. The dynamics of a self-loading/unloading negative pressure air-lubricated slider bearing were successfully studied in detail with a laser Doppler vibrometer. No intermittent contact between head and disk was observed in either the self-load or unload cases. A theoretical study on the self-loading phenomenon was carried out, and its conclusions were in good agreement with the experimental results. This suggests the feasibility of achieving a high head/disk interface reliability and, in particular, of overcoming problems regarding stiction and tribology between head and disk.
9
Sun, Haichao, Yunlai Shi, Qiang Wang, Xing Li, and Junhan Wang. "Modeling and Design Optimization of a New Piezoelectric Inchworm Actuator with Screw Clamping Mechanisms." Micromachines 13, no. 12 (November 22, 2022): 2038. http://dx.doi.org/10.3390/mi13122038.
Анотація:
A new piezoelectric inchworm actuator with screw clamping mechanisms has been developed recently for the wing folding mechanism of a small unmanned aircraft where the actuator power density is a great concern. Considering that the prototype actuator was designed just with engineering intuition and the performance optimization through experimental developments would take a vast amount of cost and time, a mathematical model was developed to investigate the actuator’s critical design parameters and optimize its presently undesirable performance. Based on the lumped parameter method reported previously, and taking full account of the detailed modeling of the complex actuator housing and the actual nonlinear behaviors from the high-force contact and friction occurring at the screw-nut interface, as well as the output performance of the main drive elements including the piezoelectric stack and hollow ultrasonic motors (HUSMs), this model was built and then was experimentally verified for its accuracy and availability. Finally, nine design parameters were studied for their individual effect on the actuator’s output using the proposed model. The simulation results indicate that the performance can be considerably improved by performing a slight modification to the prototype, and the dynamic modeling and parameter optimization methods used in this study can also serve as a useful reference for the design of similar piezoelectric inchworm actuators with intermittent clamping behaviors.
10
Annakodi, Vivek Anand, Ramachandra Arvind Singh, Subramanian Jayalakshmi, Yupeng Zhang, Koppula Srinivas Rao, and Rajashekhara Shabadi. "Anticorrosion Behaviour of SS304 Microgroove Surfaces in Saline Water." Metals 11, no. 10 (September 28, 2021): 1543. http://dx.doi.org/10.3390/met11101543.
Анотація:
The 304 Stainless Steel (SS304) is severely affected by salt water corrosion due to its high surface wettability. By reducing its surface wettability, its corrosion can be reduced. To achieve this, topographical modification of the steel surface is an effective route. In this work, SS304 flat surfaces were topographically modified into microgrooves (ridge width 250 μm to 500 μm, groove width 200 μm, width ratio = ridge width/groove width >1). Wire cut electrical discharge machining was used to fabricate the microgrooves. Long-term wetting characteristics and long-term corrosion behaviour of flat surface and microgrooves were studied. The influence of the nature of wetting of the tested surfaces on their corrosion behaviour was examined. The sessile drop method and potentiodynamic polarization tests in sodium chloride (3.5 wt. % NaCl) solution (intermittent and continuous exposures for 168 h) were studied to characterize their wetting and corrosion behaviours, respectively. Topographical modification imparted long-term hydrophobicity and, as a consequence, long-term anticorrosion ability of the steel surface. Micropatterning reduced the corrosion rate by two orders of magnitude due to reduction in interfacial contact area with the corrosive fluid via composite wetting, i.e., solid–liquid–air interface. Microgrooves showed corrosion inhibition efficiency ≥88%, upon long-term exposure to NaCl solution. By comparing the wetting and corrosion behaviours of the microgrooves with those of the previously studied microgrooves (ridge width/groove width <1), it was found that the surface roughness of their ridges strongly influences their wetting and corrosion properties.
11
Bekker, Eric Botha, Daniel J. Holland, and Aaron Timothy Marshall. "Electrical Resistive Tomography to Analyse the Flow Behaviour in Redox Flow Batteries." ECS Meeting Abstracts MA2022-01, no. 48 (July 7, 2022): 2016. http://dx.doi.org/10.1149/ma2022-01482016mtgabs.
Анотація:
Redox flow batteries (RFBs) are re-emerging as a safe, scalable, efficient and versatile means of large-scale energy storage. Growing adoption of renewable energy generation has ushered a new optimism regarding future reduction in fossil fuel dependency; limiting further harm dealt to the climate and wider environment. However, this momentum demands more efficient energy storage solutions to reconcile power demand and the intermittent nature of wind, solar and tidal energy generation [1]. Without proper storage, reliable back-up generation – largely provided by fossil fuels – will continue to be an unavoidable reality [2]. RFBs utilise the electrochemical properties of dissolved metal ions to store and release energy. Independent sizing of electrolyte storage tanks and flexible power delivery contributes to the flexibility of RFBs compared to alternative battery technologies [3]. RFB reactions occur at the electrode-electrolyte interface, and thus the mass transport at this interface is a critical factor in determining the overall RFB performance. Most RFBs use porous electrodes, with a popular choice of material being carbon felt (CF) due to its low cost, chemical stability and high conductivity [4], although the hydrophobic nature of some CF can cause poor electrode ‘wettability’- decreasing the contact area between the electrode and the electrolyte. Further, electrolyte depletion and asymmetric flow can lead to the presence of ‘dead spots’ where the interface is inactive. Many studies have been conducted on CF to improve the electrochemical performance, using surface treatments, compression and channel flow to improve active area, wettability, and species transport [5-7]. These each have direct impact on current density, pressure drop, overpotentials, and energy efficiency. While the flow of electrolyte in the RFB porous electrodes can be modelled using computational fluid dynamics (CFD) [8], and experimentally assessed using x-ray tomography [9,10] and some optical visualisation methods [11], there are limited experimental methods which can be used on entire RFB stacks. In this study, we explore the use of electrical resistive tomography (ERT) to probe the flow of electrolyte through RFB electrodes. ERT has the advantage that it can provide a non-intrusive means of investigating the hydrodynamics of the otherwise opaque cell stack. Measurements were performed using an array of electrodes place around the perimeter of an RFB electrode chamber which contained conventional carbon felt electrodes. Sensitivity maps were generated using the COMSOL Multiphysics platform and compared with experimental measurements. The flow distribution was evaluated by using injections of concentrated KCl solutions into the background electrolyte. Overall, ERT demonstrated promise as a technique for characterising real-time flow dynamics in RFB stacks and for future research into porous electrode and flow field modifications. References [1] Ambec, S., and Crampes, C., Electricity Provision with Intermittent Sources of Energy. Resource and Energy Economics, Elsevier, 2012. 34: p.320-331. [2] Wagner, F., Electricity by intermittent sources: An analysis based on the German situation 2012. The European Physical Journal Plus, Springer, 2014. 129: 20. [3] Wang, W., et al., Recent Progress in Redox Flow Battery Research and Development. Advanced Functional Materials, Wiley, 2013. 23: p. 970-986. [4] Gonzalez-Garcia, J., et al., Characterization of a carbon felt electrode: structural and physical properties. Journal of materials Chemistry, 1999. 9: p. 419-426. [5] Wang, Q., et al., Experimental study on the performance of a vanadium redox flow battery with non-uniformly compressed carbon felt electrode. Applied Energy, Elsevier, 2018. 213: p. 293-305. [6] Wang, S., et al., Nitrogen-Doped Carbon Nanotube/Graphite Felts as Advanced Electrode Materials for Vanadium Redox Flow Batteries. The Journal of Physical Chemistry Letters, ACS Publications, 2012. 3: p. 2164-2167. [7] Kim, K., et al., The effects of surface modification on carbon felt electrodes for use in vanadium redox flow batteries. Materials Chemistry and Physics, 2011. 131: p. 547-553. [8] Oh, k., et al., Three-dimensional, transient, non-isothermal model of all-vanadium redox flow batteries. Energy, Elsevier, 2015. 81: p. 3-14. [9] Eifert, L., et al., Synchrotron X-ray Radiography and Tomography of Vanadium Redox Flow Batteries—Cell Design, Electrolyte Flow Geometry, and Gas Bubble Formation. ChemSusChem, Wiley, 2020. 13: 3154-3165. [10] Trogadas, P., et al., X-ray micro-tomography as a diagnostic tool for the electrode degradation in vanadium redox flow batteries. Electrochemistry Communications, Elsevier, 2014. 48: p. 155-159 [11] Bhattarai, A., et al., Study of flow behaviour in all-vanadium redox flow battery using spatially resolved voltage distribution. Journal of Power Sources, Elsevier, 2017. 360: p. 443- 452.
12
Li, Yufeng, and Aric R. Kumaran. "The Determination of Flash Temperature in Intermittent Magnetic Head/Disk Contacts Using Magnetoresistive Heads: Part II—Experimental Investigation." Journal of Tribology 115, no. 1 (January 1, 1993): 179–84. http://dx.doi.org/10.1115/1.2920973.
Анотація:
The flash temperature during intermittent head/disk contacts was measured using specially fabricated magnetoresistive heads. Microasperities were intentionally created on disk substrates, and ZrO2 was sputtered on disc surfaces as overcoat. It was found that with a disk spinning speed of 20 m/s, flash temperature could reach 50 to 100°C for transient contact (head was moving in disk radial direction), but less than 40°C for dwell on track contact (head was stationary). The contact times were in the range from submicroseconds to several microseconds, contact widths on the order of several micrometers, and temperature sensitivity coefficients in the range from 0.15 to 0.7 for a 2.5–μ high magnetoresistive sensor.
13
Li, Yufeng, and Aric R. Kumaran. "The Determination of Flash Temperature in Intermittent Magnetic Head/Disk Contacts Using Magnetoresistive Heads: Part I—Model and Laser Simulation." Journal of Tribology 115, no. 1 (January 1, 1993): 170–78. http://dx.doi.org/10.1115/1.2920972.
Анотація:
The feasibility of using a magnetoresistive magnetic head to determine the flash temperature of intermittent magnetic head/disk contacts is investigated. A finite difference model is developed to study the effects of the magnetoresistive sensor height, the contact power intensity and the contact duration on the temperature response characteristics of the magnetoresistive sensor. A pulsed neody-minum:yttrium-aluminum-garnet laser is used as the heat source to simulate the contact and verify the model. The simulation results agree well with the theoretical model. Based on the theoretical model and laser simulation, a temperature sensitivity coefficient ζ is proposed to determine the surface temperature rise.
14
Ayala, Jose R. Ruiz, Kwangjin Lee, Mujibur Rahman, and J. R. Barber. "Effect of Intermittent Contact on the Stability of Thermoelastic Sliding Contact." Journal of Tribology 118, no. 1 (January 1, 1996): 102–8. http://dx.doi.org/10.1115/1.2837063.
Анотація:
In many sliding systems, the sliding surfaces are not coextensive, so that points on one surface experience alternating periods of contact and separation. This intermittent process can be expected to influence the sliding speed at which the system is susceptible to frictionally-induced thermoelastic instability (TEI). This question is explored in the context of a simple system consisting of a rotating thin-walled cylinder whose end face slides against a rigid surface. The results show that at low Fourier number—i.e., when the frequency of the process is high compared with the thermal transient of the system—only the time-averaged frictional heat input is important and the critical speed is an inverse linear function of the proportion of time in sliding contact. At higher Fourier number, lower critical speeds are obtained, but the dependence on Fourier number is relatively weak.
15
Barber, J. R., T. W. Beamond, J. R. Waring, and C. Pritchard. "Implications of Thermoelastic Instability for the Design of Brakes." Journal of Tribology 107, no. 2 (April 1, 1985): 206–10. http://dx.doi.org/10.1115/1.3261021.
Анотація:
Thermal distortion in brakes due to frictional heating causes localized contact and high temperatures (hot spots) with consequent thermal damage to the sliding components. This paper examines the effect of brake design and operating parameters on the maximum temperature reached. Previous solutions for steady-state sliding are reviewed and the effects of hot spots being in intermittent contact due to the geometric design of the brake are discussed. Approximate solutions for transient thermoelastic contact are extended to the case of uniform deceleration to determine the duration of the stop for which thermoelastic effects will be significant. If the stop is sufficiently slow for hot spots to develop, the temperatures will generally be high. However, high temperatures are also reached in sufficiently rapid stops due to the high rate of energy dissipation. An optimum is found between these extremes.
16
Li, Shiqi, and Tianyang Ma. "Dynamic performance fluctuation of solid-lubricated rotating mechanism for intermittent operation caused by launch vibration load." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, no. 4 (July 3, 2017): 401–14. http://dx.doi.org/10.1177/1350650117716371.
Анотація:
Space mechanism is the key to success of long-term space missions. The service life of solid-lubricated space mechanisms is affected by various mechanical loads before in-orbit operation, among which the load caused by the launch vibration is the most severe one. Dynamic performance is an indication of the operating state of solid-lubricated mechanisms. The fluctuation of dynamic performances caused by the load of launch vibration is an unanswered but important question. In this paper, the fluctuation of dynamic performances of solid-lubricated rotating mechanisms for intermittent operation was studied by means of experiments and theoretical analyses. One group of rotating mechanisms for intermittent operation with solid-lubricated ball bearings were subjected to sine sweep tests and random vibration tests, followed by continuous operation test. The dynamic performance of mechanisms was obtained throughout all tests. The other group of mechanisms were studied with continuous operation test only for comparing the effects of vibration on the dynamic performance of mechanisms. At the same time, the sample moments of the dynamic performance of mechanisms were calculated and analyzed. The contact stress in the vibration tests was calculated by the Hertz theory. The fluctuation of the dynamic performances of solid-lubricated rotating mechanisms for intermittent operation caused by the load of launch vibration was then concluded with further discussion.
17
Suzuki, M., and K. C. Ludema. "The Wear Process During the “Running-In” of Steel in Lubricated Sliding." Journal of Tribology 109, no. 4 (October 1, 1987): 587–91. http://dx.doi.org/10.1115/1.3261511.
Анотація:
Steel cylinders were slid against flat steel disks, using a liquid lubricant, in order to study the progression of events associated with “running-in.” It was found that, when using mineral oil, the electrical contact resistance varied over a small range of high values indicating no metallic contact, whereas with engine oil a high resistance with an intermittent negligible contact resistance was found. A surface film forms from the additives in the engine oil which produces lower wear, slightly higher friction, a retarded running-in, and a rougher surface finish in the direction of sliding than does the mineral oil. A film which is composed only of Fe3O4 is formed when mineral oil is used. In addition, the mineral oil lubricated surfaces develop a conforming waviness across the sliding tracks. The oxide must have enhanced this surface conformity since it was not seen in the surfaces lubricated with engine oil. The role of the oxide may be further seen in experiments in which wear debris that accumulated in the entrance region of specimen contact was removed at frequent intervals. Little conforming waviness was seen in the latter case, suggesting that oxide which gathered in the entrance region abraded grooves in the steel surfaces. After the oxides were dislodged the friction increased and the contact resistance decreased for a time, indicating that the oxide acted like a solid lubricant.
18
Narvaez Cubillos, Eider Alexander, Camilo Andrés Cortés Guerrero, and Cesar Leonardo Trujillo Rodríguez. "Topologies for Battery and Supercapacitor Interconnection in Residential Microgrids with Intermittent Generation." Ingeniería 25, no. 1 (March 12, 2020): 6–19. http://dx.doi.org/10.14483/23448393.15668.
Анотація:
Context:This paper presents a comparative study of the performance of three topologies for interconnecting Lithium ion batteries and supercapacitors in a hybrid energy storage system for use in electric residential microgrids with intermittent generation. The hybrid system’s main purpose is to prolong battery life, using the supercapacitor to handle the dynamic component of current from a pulsed current load. This work builds upon a preliminary simulation-based study, in which two semi-active topologies were compared and evaluated. Here, we add an active topology to the study and describe the operational benefits of each topology.
Method:For every topology in this study, a non-isolated half-bridge bidirectional DC converter was used, and a proportional–integral (PI) double-loop linear ACC control algorithm was designed for controlling the converters. In the active topology an additional optimisation-based real-time frequencydecoupling control strategy was employed.
Results:A parallel active topology allows better management of stored energy in the SC by supporting variation of SC terminal voltages with a DC converter as interface to the DC bus.
Conclusions: Semi-active topologies are easier to design and control, but the operational benefits of supercapacitors require voltage variation at the terminals. This variation is made possible with an active topology.
Acknowledgements: First author thanks Universidad Distrital Francisco Jos´e de Caldas for the financial support in his doctoral studies through the study commission contract N° 000101-2016.
19
Farhadi, Jafar, and Vahid Bazargan. "Marangoni flow and surfactant transport in evaporating sessile droplets: A lattice Boltzmann study." Physics of Fluids 34, no. 3 (March 2022): 032115. http://dx.doi.org/10.1063/5.0086141.
Анотація:
The circulatory Marangoni flow can alter the contact line deposition in evaporating colloidal droplets with pinned contact line. Marangoni flow can be induced by surfactants or thermal effects. Although both cases have been exclusively investigated, the combined effect of surfactant-induced and thermal Marangoni flows is still unknown. The lattice Boltzmann method is utilized to simulate droplet evaporation and corresponding Marangoni flow. Five equations for hydrodynamics, interface capturing, vapor concentration, temperature field, and surfactant transport are intrinsically coupled with each other. They are simultaneously solved in the lattice Boltzmann framework. A geometrical method is proposed to pin the contact line at the triple point. First, evaporation-induced and thermal Marangoni flows are successfully captured. By incorporating surfactant-induced effects, interesting flow patterns are observed. Considering the combined effect of surfactant and temperature gradient, maximum surfactant concentration and maximum temperature (local minima for surface tension) are found at the top and the edge of the droplet, respectively. The maximum surface tension is consequently located between them, and double-circulation flow is observed. If the thermal effect is eliminated, surfactant local concentrations intermittently converge to steady values so that the edge concentration becomes higher than the apex concentration. Until reaching the steady state, there are two patterns that the flow alternates between: one in the direction of the thermal Marangoni flow and the other in the opposite direction.
20
Partsch, Hugo. "Compression for the management of venous leg ulcers: which material do we have?" Phlebology: The Journal of Venous Disease 29, no. 1_suppl (May 2014): 140–45. http://dx.doi.org/10.1177/0268355514528129.
Анотація:
Compression therapy is the most important basic treatment modality in venous leg ulcers. The review focusses on the materials which are used: 1. Compression bandages, 2. Compression stockings, 3. Self-adjustable Velcro-devices, 4. Compression pumps, 5. Hybrid devices. Compression bandages, usually applied by trained staff, provide a wide spectrum of materials with different elastic properties. To make bandaging easier, safer and more effective, most modern bandages combine different material components. Self-management of venous ulcers has become feasible by introducing double compression stockings (“ulcer kits”) and self-adjustable Velcro devices. Compression pumps can be used as adjunctive measures, especially for patients with restricted mobility. The combination of sustained and intermittent compression (“hybrid device”) is a promising new tool. The interface pressure corresponding to the dosage of compression therapy determines the hemodynamic efficacy of each device. In order to reduce ambulatory venous hypertension compression pressures of more than 50 mm Hg in the upright position are desirable. At the same time pressure should be lower in the resting position in order to be tolerated. This prerequisite may be fulfilled by using inelastic, short stretch material including multicomponent bandages and cohesive surfaces, all characterized by high stiffness. Such materials do not give way when calf muscles contract during walking which leads to high peaks of interface pressure (“massaging effect”).
21
Lee, Kwangjin. "Frictionally Excited Thermoelastic Instability in Automotive Drum Brakes." Journal of Tribology 122, no. 4 (December 29, 1999): 849–55. http://dx.doi.org/10.1115/1.1286207.
Анотація:
Thermoelastic instability in automotive drum brake systems is investigated using a finite layer model with one-sided frictional heating. With realistic material properties of automotive brakes, the stability behavior of the one-sided heating mode is similar to that of the antisymmetric mode of two-sided heating but the critical speed of the former is higher than that of the latter. The effects of the friction coefficient and brake material properties on the critical speeds are examined and the most influential properties are found to be the coefficient of friction and the thermal expansion coefficient of drum materials. Vehicle tests were performed to observe the critical speeds of the drum brake systems with aluminum drum materials. Direct comparisons are made between the calculation and measurement for the critical speed and hot spot spacing. Good agreement is achieved when the critical speeds are calculated using the temperature-dependent friction material properties and the reduced coefficient of friction to account for the effect of intermittent contact. [S0742-4787(00)01503-4]
22
Hlava´cˇek, Miroslav. "Squeeze-Film Lubrication of the Human Ankle Joint Subjected to the Cyclic Loading Encountered in Walking." Journal of Tribology 127, no. 1 (January 1, 2005): 141–48. http://dx.doi.org/10.1115/1.1828076.
Анотація:
Squeeze-film lubrication of the human ankle joint during walking is numerically analyzed, the effect of surface sliding being neglected at this stage. Biphasic mixture models are considered for synovial fluid (an ideal and viscous fluid phases) and for articular cartilage (an ideal interstitial fluid and an elastic porous matrix). In the model, the ideal fluid phase passes through the articular surface and matrix pores. The cartilage matrix is considered both normal and pathological (with primary osteoarthrosis). Calculations show that water and small solutes of synovial fluid imbibe into the articular cartilage during the stance period, while the interstitial fluid of the cartilage exudes and enriches the lubricant during the swing period in a central part of the contact at each step. Soon after the onset of walking, repeatedly near the load culmination of each step, the synovial fluid should be turned into a synovial gel and, shortly after, changed back again into a fluid there. In the pathological case, the protective synovial gel layer is quickly depleted after several steps and the surfaces may come briefly into contact in each cycle. With normal cartilage, however, the protective intermittent gel film (formed briefly at each step) maintains its thickness for a longer time. Normal cartilage also behaves more favorably, when a long walk is broken and then resumed shortly afterwards. With normal articular cartilage, maintenance of a lubricating fluid film is much aided by the cyclic nature of the loading encountered in walking, compared with the steady loading in standing where the fluid film is quickly filtered out into a protective permanent gel film.
23
Pendlebury, R. E. "Unlubricated fretting wear of mild steel surfaces in air at room temperature: II electrical contact resistance measurements and the effect on wear of intermittent loading." Wear 118, no. 3 (August 1987): 341–64. http://dx.doi.org/10.1016/0043-1648(87)90077-9.
24
L'Antigua, Alex, Megan Flannagin, and George J. Nelson. "Capacity Fade and Impedance Evolution in Tin Phosphide Anodes for Sodium-Ion Batteries." ECS Meeting Abstracts MA2022-02, no. 4 (October 9, 2022): 397. http://dx.doi.org/10.1149/ma2022-024397mtgabs.
Анотація:
Sodium-ion batteries (SIBs) offer a potentially more cost effective and environmentally friendly alternative to Lithium-ion batteries for room temperature high density energy storage. To maintain the benefits of SIBs, earth abundance for all the batteries components is paramount. One promising earth abundant anode material for SIBs is tin phosphide (Sn4P3). Tin phosphides are able to retain a high specific capacity for an extended cycle life. Understanding the changes in electrochemistry within a battery as a result of cycling is crucial in the complete understanding of capacity fade mechanisms and subsequent improvement and implementation as an anode material. In this work, the main technique employed to gain this understanding is electrochemical impedance spectroscopy with distribution of relaxation times analysis (EIS-DRT). This mathematical approach to understanding traditional EIS datasets helps distinguish impedance contributions from the following processes: diffusion, counter electrodes, solid electrolyte Interfaces (SEI), and contact resistances. Tin phosphide active material was synthesized by mechanical milling, with material structure confirmed by X-ray diffraction (XRD). Half cells were assembled with sodium counter electrodes and cycled with intermittent EIS assessment. Capacity retention was tracked during cycling to assess electrode operation. EIS-DRT analysis was performed every 5 cycles and after the end of cycling across the anode’s voltage range (0.01-1.5 V vs Na/Na+). After cycling, cyclic voltammetry (CV) and XRD were employed to further understand changes in electrochemical activity and crystal structure associated with the end of cycle life. The evolution of impedance signatures across the initial five cycles exhibits significant shifting within the SEI and counter electrode peak at 1000 Hz. Impedance trends across the voltage range switched, in which lower voltages at higher levels of sodiation exhibit larger impedance contributions to the system. These trends are confirmed by a base understanding of SEI formation and sodiation trends. Relative impedance contributions from the diffusion process increase from pristine to cycled electrodes, with diffusion peaks at becoming the dominant impedance contribution as cycling progresses. Significant changes in DRT trends plateaued after the initial SEI formation over the first five cycles. Abrupt and early failure during cycling of a subset of the cells was marked by a plateau in the working electrode voltage, an increase in contact resistance within EIS-DRT plots and decreased electrochemical activity within CV. Visual post mortem checks correlated well with these findings, with an apparent delamination of the electorate coating from the current collector. Understanding the physical and electrochemical phenomenon within a battery though nondestructive in situ characterization is crucial to simplify work flows in battery testing.
25
Litvinov, Rustem I., Valeri Barsegov, Andrey Mekler, John W. Weisel та Joel S. Bennett. "The PLATELET INTEGRIN αIIbβ3 CHANGES FROM A LOWER- to A Higher-AFFINITY STATE DURING INTERACTION with FIBRINOGEN". Blood 118, № 21 (18 листопада 2011): 1130. http://dx.doi.org/10.1182/blood.v118.21.1130.1130.
Анотація:
Abstract Abstract 1130 The integrin αIIbβ3 (GPIIb-IIIa) plays an essential role in platelet adhesion and cohesion by binding to a number of adhesive ligands including fibrinogen, von Willebrand factor, fibronectin, and vitronectin. Following ligand binding, αIIbβ3-mediated intracellular signaling is thought to stabilize platelet adhesive interactions, cause platelet spreading, and initiate clot retraction. Here we investigated the time course of interactions between purified αIIbβ3 and its major ligand fibrinogen when both were firmly attached to apposed surfaces, mimicking αIIbβ3-mediated platelet adhesive interactions. To measure the mechanical resistance of individual αIIbβ3-fibrinogen complexes under a constant tensile force, we used a previously described optical trap force clamp system (Litvinov et al., Biophys. J., 2011, 100, 165). Briefly, we trapped a fibrinogen-coated microscopic bead in a focused laser beam and intermittently brought it into contact with an αIIbβ3-coated silica pedestal. Repeated touching and separation of the bead and pedestal occurred with a compressive force of 20 pN and a constant pulling force of 50 pN. When the duration of contact between interacting molecules on the bead and pedestal was varied from 0.1s to 2s, the probability of αIIbβ3-fibrinogen interaction was time-dependent. This enabled us to extract two-dimensional kinetic parameters, i.e., how fast the αIIbβ3-fibrinogen complex forms and dissociates at the interface without the application of an external tensile force (zero-force kinetics). To convert the kinetic parameters to absolute values, we determined the density of αIIbβ3 molecules on the pedestal surface capable of binding 125I-fibrinogen to be ≈3,000 molecules per μm2. We found that the reactive αIIbβ3 exists in at least two states that differ significantly in their on-rates (kon1 =8×10−5 and kon2 =5.6×10−4 μm2/s), off-rates (koff1 =1.56 and koff2 =1.70 1/s) and affinities (Kd1 =2×104 and Kd2 =3×103 1/μm2) for fibrinogen. In the absence of αIIbβ3 activators, the interacting molecules reached a stable equilibrium in which 85% of the complexes were in the lower affinity form. In the presence of the activator Mn2+, the proportion of lower affinity forms decreased to 60%. Mn2+ also changed the on-rates (kon1 =3.38×10−5 and kon2 =9.9×10−4 μm2/s), off-rates (koff1 =2.99 and koff2 =4.82 1/s) and affinities (Kd1 =9×104 and Kd2 =5×103 1/μm2). We then tested whether the ratio between the two integrin activation states and the mechanical stability of the αIIbβ3-fibrinogen complex depends on the duration of contact between the interacting surfaces. As the contact duration was prolonged from 0.1s to 2s, the αIIbβ3-fibrinogen bond lifetime increased from shorter lifetimes (<2s) corresponding to the low-affinity state to longer lifetimes (up to 50s) corresponding to the high-affinity state. Moreover, the rate of transition from low- to high-affinity increased ∼3-fold, whereas the reverse rate decreased 1.5–2-fold, resulting in an overall 6-fold increase in the equilibrium rate constant. This means that reversible conformational transitions of αIIbβ3 from low- to high affinity states occur during its interaction with fibrinogen with the equilibrium gradually shifting toward the higher affinity state as contact duration increases. Thus, the strength of αIIbβ3-fibrinogen interactions is time-dependent due to a progressive increase in the affinity of the αIIbβ3-fibrinogen complex during the course of the interaction. These results provide kinetic and thermodynamic characteristics of the adhesive interaction between αIIbβ3 and fibrinogen at the single-molecule level and provide evidence for a direct fibrinogen-induced change in αIIbβ3 conformation as a potential mechanism for the initiation of αIIbβ3-mediated outside-in signaling in platelets. Disclosures: No relevant conflicts of interest to declare.
26
Sasikumar S P, Varsha, Robert P. Lynch, Maria Al Hajji Safi, D. Noel Buckley, and Andrea Bourke. "(Invited) Effect of Electrochemical Treatment and pH on VIV/VV Electrode Kinetics." ECS Meeting Abstracts MA2022-02, no. 30 (October 9, 2022): 1099. http://dx.doi.org/10.1149/ma2022-02301099mtgabs.
Анотація:
Flow batteries are a promising technology for flexible large-scale energy storage systems to tackle the problem of intermittency with renewable energy sources. Several flow battery systems have been successfully developed and deployed to date, including all-vanadium, zinc-iron, zinc-bromine, and all-iron flow batteries.1 Among these, vanadium flow batteries (VFBs) have received a lot of attention in the large-scale energy storage sector due to their excellent characteristics such as long cycle life with almost zero electrode and electrolyte degradation, safe and non-flammable aqueous electrolytes, short response times, and the ability to operate at reasonable temperatures.2 The operation of flow batteries involves simultaneous oxidation and reduction reactions at the anodic and cathodic compartments. In the VFB, the redox couple at the anode is VII-VIII and at the cathode is VIV-VV. Voltage inefficiencies at the electrode-electrolyte interface are a source of concern for the operation of these systems.3 Electrode polarization, slow kinetics, and iR losses associated with contact and ionic resistances all contribute to battery voltage inefficiencies. It is widely acknowledged that the electrode material and pretreatments (chemical, thermal, and electrochemical) have significant impacts on the electrode kinetics and hence the performance of the VFB system.4 Investigation of the electrode kinetics is thus important in order to better understand and improve the performance of VFBs. Previous research from our group has shown that electrochemical treatments of carbon electrodes at different potentials significantly affect the electrode kinetics of VIV-VV and VII-VIII oxidation-reduction reactions. The electrode kinetics of VIV-VV are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. In contrast, the electrode kinetics of VII-VIII are enhanced by anodic treatment of the electrode and inhibited by cathodic treatment. Furthermore, the carbon electrode can be toggled repeatedly and reproducibly between the enhanced (activated) and the inhibited (deactivated) state.5,6,7 Other factors affecting the electrode activity include ageing of the electrode, the final treatment potential, the redox rest potential, and the treatment potential window.8 This previous research involves treatments in strong acid, low pH electrolytes. In this study, we investigate the electrochemical treatment of glassy carbon electrodes in electrolytes at a range of pH. The resulting electrode kinetics of the vanadium redox couples at each treatment potential are studied using electrochemical characterization techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Acknowledgements Varsha Sasikumar S P would like to thank the Irish Research Council (IRC) for providing funding for this research work. References Xinyou Ke et al., Chemical Society Reviews, 47, 8721-8743 (2018). R. Chalamala et al., Proceedings of the IEEE, 102(6), 976-999, (2014). A. H. Whitehead and M. Harrer, Journal of Power Sources, 230, 271–276 (2013). Ki Jae Kim, et al., Journal of Materials Chemistry A, 33(3), 16913-16933 (2015). A. Bourke et al., Journal of Electrochemical Society, 163, A5097 (2016). A. Bourke et al., Journal of Electrochemical Society, 162, A1547 (2015). M. A. Miller, et al., Journal of Electrochemical Society, 163, A2095-A2102, (2016). D. N. Buckley, et al., ECS Transactions, 98(9), 223-239 (2020).
27
Engelhardt, Hermann, and Barclay Kamb. "Basal hydraulic system of a West Antarctic ice stream: constraints from borehole observations." Journal of Glaciology 43, no. 144 (1997): 207–30. http://dx.doi.org/10.3189/s0022143000003166.
Анотація:
AbstractPressure and tracer measurements in boreholes drilled to the bottom of Ice Stream B, West Antarctica, are used to obtain information about the basal water conduit system in which high water pressures are developed.These high pressures presumably make possible the rapid movement of the ice stream. Pressure in the system is indicated by the borehole water level once connection to the conduit system is made. On initial connection, here also called “breakthrough” to the basal water system, the water level drops in a few minutes to an initial depth in the range 96–117 m below the surface. These water levels are near but mostly somewhat deeper than the floation level of about 100 m depth (water level at which basal water pressure and ice overburden pressure are equal), which is calculated from depth-density profiles and is measured in one borehole. The conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed; the thickness of the gap δ has to be about 2 mm to account for the water-level drop on breakthrough, and about 4 mm to fit the results of a salt-tracer experiment indicating downstream transport at a speed of 7.5 mm s−1. The above gap-conduit model is, however, ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole, and also by the large hole-to-hole variation in measured basal pressure, which if present in a gap-conduit system with δ = 2 or 4 mm would result in unacceptably large local water fluxes. An alternative model that avoids these objections, called the “gap opening” model, involves opening a gap as injection proceeds: starting with a thin film, the injection of water under pressure lifts the ice mass around the borehole, creating a gap 3 or 4mm wide at the ice/bed interface. Evaluated quantitatively, the gap-opening model accounts for the volume of water that the basal water system accepts on breakthrough, which obviates the gap-conduit model. In order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits, of which the most promising type is the “canal” conduit proposed theoretically by Walder and Fowler (1994): flat, low conduits incised into the till, ∼0.1 m deep and perhaps ∼1 m wide, with a flat ice roof. The basal water-pressure data suggest that the canals are spaced ∼50–300 m apart, much closer than R-tunnels would be. The deepest observed water level, 117 m, is the most likely to reflect the actual water pressure in the canals, corresponding to a basal effective pressure of 1.6 bar. In this interpretation, the shallower water levels are affected by loss of hydraulic head in the narrow passageway (s) that connect along the bed from borehole to canal(s). Once a borehole has frozen up and any passageways connecting with canals have become closed, a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till, given enough time for pressure equilibration. This pressure varies considerably with time, over the equivalent water-level range from 100 to 113 m. Basal pressure sensors 500 m apart report uncorrelated variations, whereas sensors in boreholes 25 m араrt report mostly (but not entirely) well-correlated variations, of unknown origin. In part of the record, remarkable anticorrelated variations are interspersed with positively correlated ones, and there are rare, abrupt excursions to extreme water levels as deep as 125 m and as shallow as 74 m. A diurnal pressure fluctuation, intermittently observed, may possibly be caused by the ocean tide in the Ross Sea. The lack of any observed variation in ice-stream motion, when large percentagewise variations in basal effective pressure were occurring according to our data, suggests that the observed pressure variations are sufficiently local, and so randomly variable from place to place, that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed.
28
Engelhardt, Hermann, and Barclay Kamb. "Basal hydraulic system of a West Antarctic ice stream: constraints from borehole observations." Journal of Glaciology 43, no. 144 (1997): 207–30. http://dx.doi.org/10.1017/s0022143000003166.
Анотація:
AbstractPressure and tracer measurements in boreholes drilled to the bottom of Ice Stream B, West Antarctica, are used to obtain information about the basal water conduit system in which high water pressures are developed.These high pressures presumably make possible the rapid movement of the ice stream. Pressure in the system is indicated by the borehole water level once connection to the conduit system is made. On initial connection, here also called “breakthrough” to the basal water system, the water level drops in a few minutes to an initial depth in the range 96–117 m below the surface. These water levels are near but mostly somewhat deeper than the floation level of about 100 m depth (water level at which basal water pressure and ice overburden pressure are equal), which is calculated from depth-density profiles and is measured in one borehole. The conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed; the thickness of the gap δ has to be about 2 mm to account for the water-level drop on breakthrough, and about 4 mm to fit the results of a salt-tracer experiment indicating downstream transport at a speed of 7.5 mm s−1. The above gap-conduit model is, however, ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole, and also by the large hole-to-hole variation in measured basal pressure, which if present in a gap-conduit system with δ = 2 or 4 mm would result in unacceptably large local water fluxes. An alternative model that avoids these objections, called the “gap opening” model, involves opening a gap as injection proceeds: starting with a thin film, the injection of water under pressure lifts the ice mass around the borehole, creating a gap 3 or 4mm wide at the ice/bed interface. Evaluated quantitatively, the gap-opening model accounts for the volume of water that the basal water system accepts on breakthrough, which obviates the gap-conduit model. In order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits, of which the most promising type is the “canal” conduit proposed theoretically by Walder and Fowler (1994): flat, low conduits incised into the till, ∼0.1 m deep and perhaps ∼1 m wide, with a flat ice roof. The basal water-pressure data suggest that the canals are spaced ∼50–300 m apart, much closer than R-tunnels would be. The deepest observed water level, 117 m, is the most likely to reflect the actual water pressure in the canals, corresponding to a basal effective pressure of 1.6 bar. In this interpretation, the shallower water levels are affected by loss of hydraulic head in the narrow passageway (s) that connect along the bed from borehole to canal(s). Once a borehole has frozen up and any passageways connecting with canals have become closed, a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till, given enough time for pressure equilibration. This pressure varies considerably with time, over the equivalent water-level range from 100 to 113 m. Basal pressure sensors 500 m apart report uncorrelated variations, whereas sensors in boreholes 25 m араrt report mostly (but not entirely) well-correlated variations, of unknown origin. In part of the record, remarkable anticorrelated variations are interspersed with positively correlated ones, and there are rare, abrupt excursions to extreme water levels as deep as 125 m and as shallow as 74 m. A diurnal pressure fluctuation, intermittently observed, may possibly be caused by the ocean tide in the Ross Sea. The lack of any observed variation in ice-stream motion, when large percentagewise variations in basal effective pressure were occurring according to our data, suggests that the observed pressure variations are sufficiently local, and so randomly variable from place to place, that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed.
29
Ma, Tianbao, Zhiwei Yu, Aisheng Song, Jiahao Zhao, Haibo Zhang, Hongliang Lu, Dandan Han, Xueyan Wang, and Wenzhong Wang. "Intermittent failure mechanism and stabilization of microscale electrical contact." Friction, March 16, 2022. http://dx.doi.org/10.1007/s40544-022-0613-x.
Анотація:
AbstractThe stability and lifetime of electrical contact pose a major challenge to the performance of microelectro-mechanical systems (MEMS), such as MEMS switches. The microscopic failure mechanism of electrical contact still remains largely unclear. Here conductive atomic force microscopy with hot switching mode was adopted to simulate the asperity-level contact condition in a MEMS switch. Strong variation and fluctuation of current and adhesion force were observed during 10,000 repetitive cycles, exhibiting an “intermittent failure” characteristic. This fluctuation of electrical contact properties was attributed to insulative carbonaceous contaminants repetitively formed and removed at the contact spot, corresponding to degradation and reestablishment of electrical contact. When contaminant film was formed, the contact interface became “metal/carbonaceous adsorbates/metal” instead of direct metal/metal contact, leading to degradation of the electrical contact state. Furthermore, a system of iridium/graphene on ruthenium (Ir/GrRu) was proposed to avoid direct metal/metal contact, which stabilized the current fluctuation and decreased interfacial adhesion significantly. The existence of graphene enabled less adsorption of carbonaceous contaminants in ambient air and enhanced mechanical protection against the repetitive hot switching actions. This work opens an avenue for design and fabrication of microscale electrical contact system, especially by utilizing two-dimensional materials.
30
Jung, Chulwoo, Akira Saito, and Bogdan I. Epureanu. "Detection of Cracks in Mistuned Bladed Disks Using Reduced-Order Models and Vibration Data." Journal of Vibration and Acoustics 134, no. 6 (October 29, 2012). http://dx.doi.org/10.1115/1.4007244.
Анотація:
A novel methodology to detect the presence of a crack and to predict the nonlinear forced response of mistuned turbine engine rotors with a cracked blade and mistuning is developed. The combined effects of the crack and mistuning are modeled. First, a hybrid-interface method based on component mode synthesis is employed to develop reduced-order models (ROMs) of the tuned system with a cracked blade. Constraint modes are added to model the displacements due to the intermittent contact between the crack surfaces. The degrees of freedom (DOFs) on the crack surfaces are retained as active DOFs so that the physical forces due to the contact/interaction (in the three-dimensional space) can be accurately modeled. Next, the presence of mistuning in the tuned system with a cracked blade is modeled. Component mode mistuning is used to account for mistuning present in the uncracked blades while the cracked blade is considered as a reference (with no mistuning). Next, the resulting (reduced-order) nonlinear equations of motion are solved by applying an alternating frequency/time-domain method. Using these efficient ROMs in a forced response analysis, it is found that the new modeling approach provides significant computational cost savings, while ensuring good accuracy relative to full-order finite element analyses. Furthermore, the effects of the cracked blade on the mistuned system are investigated and used to detect statistically the presence of a crack and to identify which blade of a full bladed disk is cracked. In particular, it is shown that cracks can be distinguished from mistuning.
31
Mitra, Mainak, and Bogdan I. Epureanu. "Dynamic Modeling and Projection-Based Reduction Methods for Bladed Disks With Nonlinear Frictional and Intermittent Contact Interfaces." Applied Mechanics Reviews 71, no. 5 (September 1, 2019). http://dx.doi.org/10.1115/1.4043083.
Анотація:
AbstractTurbine bladed disks or blisks, which constitute critical components of most modern turbomachinery, are known for their complex vibratory behavior. The nonlinear dynamics observed in most operational regimes of blisk with contact interfaces are dominated by one of two typical contact behaviors. Frictional contacts are dominated by Coulomb friction forces, while intermittent contacts are characterized by multiple separation events. Other factors such as the dispersion in material or geometric properties across blades, known as mistuning, also affect the dynamics significantly. Presently, probabilistic analysis is the widely accepted design methodology to account for mistuning, which is unknown prior to manufacture. Thus, reduced order modeling of these blisks is essential as high fidelity models are prohibitively expensive for such simulations. This paper provides a technical discussion of dynamic modeling and reviews projection-based techniques used for creation of reduced models of blisks with contacts.
32
Benabed, Yasmine, Maxime Rioux, Steeve Rousselot, Geoffroy Hautier, and Mickaël Dollé. "Assessing the Electrochemical Stability Window of NASICON-Type Solid Electrolytes." Frontiers in Energy Research 9 (May 27, 2021). http://dx.doi.org/10.3389/fenrg.2021.682008.
Анотація:
All-Solid-State Lithium Batteries (ASSLBs) are promising since they may enable the use of high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through solid electrolytes (SEs) stated large electrochemical stability window (ESW). Nevertheless, reported values for these ESWs are very divergent in the literature. Establishing a robust procedure to accurately determine SEs’ ESWs has therefore become crucial. Our work focuses on bringing together theoretical results and an original experimental set up to assess the electrochemical stability window of the two NASICON-type SEs Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP). Using first principles, we computed thermodynamic ESWs for LATP and LAGP and their decomposition products upon redox potentials. The experimental set-up consists of a sintered stack of a thin SE layer and a SE-Au composite electrode to allow a large contact surface between SE and conductive gold particles, which maximizes the redox currents. Using Potentiostatic Intermittent Titration Technique (PITT) measurements, we were able to accurately determine the ESW of LATP and LAGP solid electrolytes. They are found to be [2.65–4.6 V] and [1.85–4.9 V] for LATP and LAGP respectively. Finally, we attempted to characterize the decomposition products of both materials upon oxidation. The use of an O2 sensor coupled to the electrochemical setup enabled us to observe operando the production of O2 upon LAGP and LATP oxidations, in agreement with first-principles calculations. Transmission Electron Microscopy (TEM) allowed to observe the presence of an amorphous phase at the interface between the gold particles and LAGP after oxidation. Electrochemical Impedance Spectroscopy (EIS) measurements confirmed that the resulting phase increased the total resistance of LAGP. This work aims at providing a method for an accurate determination of ESWs, considered a key parameter to a successful material selection for ASSLBs.
33
San Andrés, Luis, José Baker, and Adolfo Delgado. "Measurements of Leakage and Power Loss in a Hybrid Brush Seal." Journal of Engineering for Gas Turbines and Power 131, no. 1 (October 10, 2008). http://dx.doi.org/10.1115/1.2967497.
Анотація:
Simplicity, low cost, and easy replacement make labyrinth seals the primary seal type in gas turbines. However, excessive leakage and potential for rotordynamic instability are well known issues. Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low pressure differentials. Hybrid brush seals (HBSs) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, which under rotor spinning lifts off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, thus lowering the operating temperature and thermal distortions and even eliminating bristle wear. The hybrid brush seal improves sealing, is more durable and reliable than conventional brush seals, and allows reverse shaft rotation without seal damage. This paper presents measurements of power loss and leakage in a HBS for increasing pressure differentials over a range of rotor speeds. The test HBS, Haynes-25 bristle pack (∼850 bristles∕cm) and 45 deg lay angle, is 166.4 mm in diameter and integrates 20-arcuate pads connected with thin electrical-discharge machined webs (EDM-webs) to the seal casing. The webs are designed with low radial stiffness to allow for rotor excursions and high axial stiffness to avoid pad pitching motions resulting from high pressure differentials across the seal. Measured drag power at low rotor speeds (<11 m∕s at 1300 rpm) decreases as the pressure differential across the seal increases. At a fixed rotor speed, a significant drop in drag torque (and drag power) ensues as the supply pressure increases, thus demonstrating that a gas film separates the rotor from the seal pads. Additionally, the operating temperature measured at the rotor/seal interface remains approximately constant (∼24°C) during tests with shaft rotation (power loss and drag torque measurements) under pressurized conditions, indicating that the rotor and seal pads are not in contact. Flow rate measurements at room temperature (25°C) show an improved sealing ability with a leakage reduction of about 36% when compared with a first generation shoed-brush seal. The HBS calculated effective clearance (∼50 μm) is approximately 70% smaller than the radial clearance (∼180 μm) of an ideal noncontacting seal with similar rotor diameter. Improved brush seal technology will increase the efficiency of gas turbines while also aiding to improve the engine stability and to reduce vibrations.
34
Alia, Shaun M., Kimberly S. Reeves, Haoran Yu, Jae Hyung Park, Nancy N. Kariuki, Kropf Jeremy, Deborah J. Myers, and David Cullen. "Electrolyzer Performance Loss from Accelerated Stress Tests and Corresponding Changes to Catalyst Layers and Interfaces." Journal of The Electrochemical Society, April 22, 2022. http://dx.doi.org/10.1149/1945-7111/ac697e.
Анотація:
Abstract Stress tests are developed for proton exchange membrane electrolyzers that utilize low catalyst loading, elevated potential, and frequent cycling with square- and triangle-waves to accelerate anode catalyst layer degradation during intermittent operation. Kinetics drive performance losses (ohmic/transport secondary) and are accompanied by decreasing exchange current density, decreasing cyclic voltammetric capacitance, and increasing polarization resistance. Decreased kinetics is likely due to a combination of iridium (Ir) migration into electrochemically inaccessible locations in the anode or membrane, Ir particle growth (supported by X-ray scattering), changes in the extent of the Ir oxidation state (supported by X-ray absorption spectroscopy), and anode catalyst layer reordering. Decreasing catalyst/transport layer contact and catalyst/membrane interfacial tearing may add contact resistances and account for increasing ohmic losses. Performance losses for low and moderate catalyst loading, as well as from accelerated and model wind/solar cycling protocols, were likewise dominated by kinetics but vary in severity. Accelerated cycling (1 cycle per minute) appears to reasonably accelerate relevant loss mechanisms and can be used to project electrolyzer lifetime from anode deterioration. Ongoing accelerated stress test development and studies into performance loss mechanisms will continue to be critical as electrolysis shifts to intermittent power and low-cost applications.
35
Viswanathan, Koushik, and Srinivasan Chandrasekar. "Fifty years of Schallamach waves: from rubber friction to nanoscale fracture." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 380, no. 2232 (August 2022). http://dx.doi.org/10.1098/rsta.2021.0339.
Анотація:
The question of how soft polymers slide against hard surfaces is of significant scientific interest, given its practical implications. Specifically, such systems commonly show interesting stick–slip dynamics, wherein the interface moves intermittently despite uniform remote loading. The year 2021 marked the 50th anniversary of the publication of a seminal paper by Adolf Schallamach ( Wear , 1971), which first revealed an intimate link between stick–slip and moving detachment waves, now called Schallamach waves. We place Schallamach’s results in a broader context and review subsequent investigations of stick–slip, before discussing recent observations of solitary Schallamach waves. This variant is not observable in standard contacts so that a special cylindrical contact must be used to quantify its properties. The latter configuration also reveals the occurrence of a dual wave—the so-called separation pulse—that propagates in a direction opposite to Schallamach waves. We show how the dual wave and other, more general, Schallamach-type waves can be described using continuum theory and provide pointers for future research. In the process, fundamental analogues of Schallamach-type waves emerge in nanoscale mechanics and interface fracture. The result is an ongoing application of lessons learnt from Schallamach-type waves to better understand these latter phenomena. This article is part of the theme issue ‘Nanocracks in nature and industry’.
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Frezzato, Diego, Gianluca Stocco, Enrico Boscaro, Marco Ferraro, and Andrea Tapparo. "Diffusive model to assess the release of chemicals from a material under intermittent release conditions." Scientific Reports 12, no. 1 (March 2, 2022). http://dx.doi.org/10.1038/s41598-022-07144-0.
Анотація:
AbstractWe consider the archetype situation of a chemical species that diffuses in a material and irreversibly escapes through the interface. In our setup, the interface switches between two states corresponding to ‘release phase’ (absorbing boundary) during which the species is released to the exterior, and ‘pause phase’ (reflecting boundary) during which the species is not released and its concentration profile inside the material partially relaxes back to uniformity. By combining numerical solution of the diffusion equation and statistical analysis of the outcomes, we derive upper and lower bounds and an empirical approximation for the amount of species released up to a certain time, in which the only information about the release-pause alternation schedule is the number of release phases and the average duration of a release phase. The methodology is developed thinking especially to dermal exposure assessment in the case of a slab-like homogeneous material irreversibly releasing chemicals during a number of contacts. However, upon proper extensions, this approach might be useful for inspecting other situations that are encountered, for instance, when dealing with leakage of chemicals in environmental contexts and regulatory toxicology.
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Wallaschek, Jörg, Sebastian Willeke, and Lars Panning-von Scheidt. "Discussion of “Dynamic Modeling and Projection-Based Reduction Methods for Bladed Disks With Nonlinear Frictional and Intermittent Contact Interfaces” (Mitra, M., Epureanu, B. I., 2018, ASME Appl. Mech. Rev., 71(5), p. 050803)." Applied Mechanics Reviews 71, no. 5 (September 1, 2019). http://dx.doi.org/10.1115/1.4044933.
Анотація:
Abstract Mitra and Epureanu have written a very good and complete overview on nonlinear vibrations of turbine blades. Nonlinearities due to friction and contact mechanics are the main focus. Questions related to modeling and model reduction are particularly addressed. This paper begins with an investigation of the vibration behavior of cyclic linear structures, in which a variety of considerations about the occurrence of standing and propagating waves play an important role. Subsequently, several methods of model-order reduction are presented, where cyclic sectors of tuned bladed disks are assumed. The classification of the linear vibration modes according to their nodal diameters (NDs) is explained in detail. Large models with a high number of degrees-of-freedom (DOF) occurring in the field of turbomachinery dynamics lead to very high computational cost. In this context, the authors consider model-order reduction with projection-based methods to be of particular interest. They give an overview of modern projection-based methods and compare them with regard to their respective advantages and disadvantages in the context of bladed disks with nonlinear friction and intermittent contact.
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Masoudi, Ramin, Stephen Birkett, and John McPhee. "A Mechanistic Multibody Model for Simulating the Dynamics of a Vertical Piano Action." Journal of Computational and Nonlinear Dynamics 9, no. 3 (February 13, 2014). http://dx.doi.org/10.1115/1.4026157.
Анотація:
The theoretical framework for constructing a fully mechanistic multibody dynamic model of a vertical piano action is described, and its general validity is established. Equations of motion are derived symbolically using a graph-theoretic formulation. Model fidelity is increased by introducing several novel features: (i) a new contact model for representing the compression of the felt-lined interfaces between interacting parts, capable of capturing the intermittent loading and unloading of these contacts occurring through the key stroke, as well as providing smooth transitions between these states; (ii) models for two important components that are unique to the vertical action, the bridle strap and the butt spring; (iii) a sophisticated key pivot model that captures both the rotational motion and the vertical translation of the key as it can lift off the balance rail under some conditions; (iv) flexible beam models for backcheck wire and hammer shank so as to predict observed vibrations in the response accurately; and (v) coupling of the mechanism model to a flexible stiff string model for realistic hammer impact. For simulation, parameters were obtained by experimental testing and measurement of a physical prototype vertical action. Techniques are described for the virtual regulation of the model to ensure that initial conditions and pseudostatic response accurately represent the precise configuration and desired relationships between the parts during the key stroke. Two input force profiles were used for simulations, a forte pressed (hard) and piano pressed touch (soft), typical of those measured at the key surface when activated by a pianist. Simulated response to these quite different inputs is described, and compared to experimental observations obtained from a physical prototype.
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Yuan, Yanhui, and Shao Wang. "A Simplified Dynamic Model for the Analysis of the Slider Off-Track Motion Due to Head-Disk Interactions." Journal of Tribology 131, no. 2 (March 3, 2009). http://dx.doi.org/10.1115/1.3063808.
Анотація:
A five-degree-of-freedom model was developed for the analysis of the off-track motion of the magnetic head slider in a hard disk drive. The air bearing was integrated into the dynamic system by combining its stiffness and damping matrices with those of the suspension. Simulation was conducted for the slider in intermittent contact with circumferentially located bumps on a rotating magnetic disk. For a single bump, the excitation to the transverse displacement of the slider is close to that of an impulse. However, for multiple bumps in a sequence, the excitation gives an effect similar to that of a step force function. The maximum transverse displacement increases almost linearly with both the coefficient of friction and the skew angle. The average contact force is determined by the maximum contact force, the contact time ratio, and the shape factor of the contact force, which change with the bump spacing and the rotational speed of the disk. The steady-state transverse displacement is related to the average contact force. As the bump spacing decreases, the average contact force increases, resulting in a greater transverse displacement. Based on the system dynamic characteristics alone, changing the rotational speed of the disk has only a small impact on the average contact force and, thus, on the transverse displacement. At zero skew angle with the bump path close to a rear pad edge, significant transverse motion occurs because of the excited roll mode and the coupling between the roll angle and the transverse displacement. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, as verified by comparing the results of the transverse displacement from the 5DOF model to that from a 2DOF model of the transverse motions of the actuator arm and suspension. The effects of the roll angle on the transverse displacement through coupling were found to be responsible for the difference in the transverse displacements obtained from the two models.
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Orevi, Tomer, Søren J. Sørensen, and Nadav Kashtan. "Droplet size and surface hydrophobicity enhance bacterial plasmid transfer rates in microscopic surface wetness." ISME Communications 2, no. 1 (August 16, 2022). http://dx.doi.org/10.1038/s43705-022-00159-8.
Анотація:
AbstractConjugal plasmids constitute a major engine for horizontal gene transfer in bacteria, and are key drivers of the spread of antibiotic resistance, virulence, and metabolic functions. Bacteria in terrestrial habitats often inhabit surfaces that are not constantly water-saturated, where microscopic surface wetness (MSW), comprised of thin liquid films and microdroplets, permanently or intermittently occurs. How physical properties of microdroplets, and of the surfaces they reside on, affect plasmid transfer rates is not well understood. Here, building on microscopy-based microdroplet experiments, we examined the relation between droplet properties (size and spread) and plasmid transfer rates at single-cell and individual droplet resolution, using Pseudomonas putida as a model species. We show that transfer rates increase with droplet size, due to higher densities of cells on the surface in larger droplets, resulting from lower ratio between the area of the liquid-solid interface and droplet volumes. We further show that surface hydrophobicity promotes transfer rates via the same mechanism. Our results provide new insights into how physical properties of surfaces and MSW affect plasmid transfer rates, and more generally, microbial interactions mediated by cell-to-cell contact, with important implications for our understanding of the ecology and evolution of bacteria in unsaturated environments.
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Mitra, Mainak, and Bogdan I. Epureanu. "Closure to “Discussion of ‘Dynamic Modeling and Projection-Based Reduction Methods for Bladed Disks With Nonlinear Frictional and Intermittent Contact Interfaces’” (Wallaschek, J., Willeke, S., and Panning-von Scheidt, L., ASME Appl. Mech. Rev., 2019, 71(5), p. 055502)." Applied Mechanics Reviews 71, no. 5 (September 1, 2019). http://dx.doi.org/10.1115/1.4044803.