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Predicting the coefficient of friction in a sliding contact by applying machine learning to acoustic emission data

Friction 2024年第6期12卷 1299-1321页

作者： Robert GUTIERREZ Tianshi FANG Robert MAINWARING tom reddyhoff Tribology Group Department of Mechanical EngineeringImperial College LondonExhibition RoadLondon SW72AZUK Shell Global Solutions(US)Inc.Shell Technology Center Houston 3333 Highway 6 SouthHoustonTX 77082USA Shell International Petroleum Company Limited Shell CentreYork RoadLondon SE17NAUK

It is increasingly important to monitor sliding interfaces within machines,since this is where both energy is lost,and failures occur.Acoustic emission(AE)techniques offer a way to monitor contacts remotely without requiring transparent or electrically conductive materials.However,acoustic data from sliding contacts is notoriously complex and difficult to interpret.Herein,we simultaneously measure coefficient of friction(with a conventional force transducer)and acoustic emission(with a piezoelectric sensor and high acquisition rate digitizer)produced by a steel‒steel rubbing contact.Acquired data is then used to train machine learning(ML)algorithms(e.g.,Gaussian process regression(GPR)and support vector machine(SVM))to correlated acoustic emission with friction.ML training requires the dense AE data to first be reduced in size and a range of processing techniques are assessed for this(e.g.,down-sampling,averaging,fast Fourier transforms(FFTs),histograms).Next,fresh,unseen AE data is given to the trained model and the resulting friction predictions are compared with the directly measured friction.There is excellent agreement between the measured and predicted friction when the GPR model is used on AE histogram data,with root mean square(RMS)errors as low as 0.03 and Pearson correlation coefficients reaching 0.8.Moreover,predictions remain accurate despite changes in test conditions such as normal load,reciprocating frequency,and stroke length.This paves the way for remote,acoustic measurements of friction in inaccessible locations within machinery to increase mechanical efficiency and avoid costly failure/needless maintenance.

关键词： acoustic emission condition monitoring friction machine learning Gaussian process regression support vector machine

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A finite-element-aided ultrasonic method for measuring central oil-film thickness in a roller-raceway tribo-pair

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Friction 2022年第6期10卷 944-962页

作者： Pan DOU Tonghai WU Zhaopeng LUO Peiping YANG Zhongxiao PENG Min YU tom reddyhoff Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System Xi'an Jiaotong UniversityXi'an 710049China Dongfang Electric Machinery Co. Ltd.Deyang 618000China School of Mechanical and Manufacturing Engineering University of New South WalesSydney 2052Australia Department of Mechanical Engineering Imperial College LondonLondon SW72AZUK

Roller bearings support heavy loads by riding on an ultra-thin oil film(between the roller and raceway),the thickness of which is critical as it reflects the lubrication performance.Ultrasonic interfacial reflection,which facilitates the non-destructive measurement of oil-film thickness,has been widely studied.However,insufficient spatial resolution around the rolling line contact zone remains a barrier despite the use of miniature piezoelectric transducers.In this study,a finite-element-aided method is utilized to simulate wave propagation through a three-layered structure of roller-oil-raceway under elastohydrodynamic lubrication(EHL)with nonlinear characteristics of the i)deformed curvature of the cylindrical roller and ii)nonuniform distribution of the fluid bulk modulus along the circumference of the oil layer being considered.A load and speed-dependent look-up table is then developed to establish an accurate relationship between the overall reflection coefficient(directly measured by an embedded ultrasonic transducer)and objective variable of the central oil-film thickness.The proposed finite-element-aided method is verified experimentally in a rollerraceway test rig with the ultrasonically measured oil-flm thickness corresponding to the values calculated using the EHLtheory.

关键词： ultrasonic measurement central oil-film thickness rolling line contact ray model finite-element-ISSN 2223-7690 CN10-1237/TH aided method

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Rigid–flexible hybrid surfaces for water-repelling and abrasionresisting

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Friction 2023年第4期11卷 635-646页

作者： Songtao HU Weifeng HUANG Jinbang LI tom reddyhoff Xiaobao CAO Xi SHI Zhike PENG Andrew DEMELLO Daniele DINI State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong UniversityShanghai 200240China State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China School of Mechanical Engineering and Mechanics Ningbo UniversityNingbo 315211China Department of Mechanical Engineering Imperial College LondonLondon SW72AZUK Department of Chemistry and Applied Biosciences ETH ZurichZurich 8093Switzerland School of Mechanical Engineering Ningxia UniversityYinchuan 750021China

Droplets impacting solid superhydrophobic surfaces is appealing not only because of scientific interests but also for technological applications such as water-repelling.Recent studies have designed artificial surfaces in a rigid–flexible hybrid mode to combine asymmetric redistribution and structural oscillation water-repelling principles,resolving strict impacting positioning;however,this is limited by weak mechanical durability.Here we propose a rigid–flexible hybrid surface(RFS)design as a matrix of concave flexible trampolines barred by convex rigid stripes.Such a surface exhibits a 20.1%contact time reduction via the structural oscillation of flexible trampolines,and even to break through the theoretical inertial-capillary limit via the asymmetric redistribution induced by rigid stripes.Moreover,the surface is shown to retain the above water-repelling after 1,000 abrasion cycles against oilstones under a normal load as high as 0.2 N·mm−1.This is the first demonstration of RFSs for synchronous waterproof and wearproof,approaching real-world applications of liquid-repelling.

关键词： surface droplet impact hydrophobic abrasion

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Pneumatic programmable superrepellent surfaces

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Droplet 2022年第1期1卷 48-55页

作者： Songtao Hu Xiaobao Cao tom reddyhoff Xijia Ding Xi Shi Daniele Dini Andrew J.deMello Zhike Peng Zuankai Wang School of Mechanical Engineering State Key Laboratory of Mechanical System and VibrationShanghai Jiao Tong UniversityShanghaiChina Guangzhou Laboratory GuangzhouChina Department of Mechanical Engineering Imperial College LondonLondonUK Department of Chemistry and Applied Biosciences ETH ZurichZurichSwitzerland Department of Mechanical Engineering City University of Hong KongHong KongChina

Morphological transformation of surface structures is widely manifested in nature and highly preferred for many applications such as wetting interaction;however,in situ tuning of artificial morphologies independent of smart responsive materials remains elusive.Here,with the aid of microfluidics,we develop a pneumatic programmable superrepellent surface by tailoring conventional wetting materials(e.g.,polydimethylsiloxane)with embedded flexible chambers connecting a microfluidic system,thus realizing a morphological transformation for enhanced liquid repellency based on a nature‐inspired rigid‐flexible hybrid principle(i.e.,triggering symmetry breaking and oscillator coupling mechanisms).The enhancement degree can be in situ tuned within around 300 ms owing to pneumatically controllable chamber morphologies.We also demonstrate that the surface can be freely programmed to achieve elaborated morphological pathways and gradients for preferred droplet manipulation such as directional rolling and bouncing.Our study highlights the potential of an in situ morphological transformation to realize tunable wettability and provides a programmable level of droplet control by intellectualizing conventional wetting materials.

关键词： transformation connecting breaking

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Liquid superlubricity of lubricants containing hydroxyl groups and their aqueous solution under rolling/sliding conditions

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Friction 2024年第1期12卷 164-173页

作者： tomáš POLÁČEK Petr ŠPERKA Ivan KŘUPKA Faculty of Mechanical Engineering Brno University of TechnologyBrno 61669Czech Republic

Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.

关键词： macroscale superlubricity super low traction water-based lubricants elastohydrodynamic lubrication(EHL) film thickness

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The first record of a Konservat-Lagerstätten in which early post-settlement stages of fossil archaeobalanids(Cirripedia:Balanomorpha)are preserved

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Integrative Zoology 2024年第2期19卷 200-223页

作者： tomáš KOCÍ Rok GAŠPARIC John BUCKERIDGE Martina KOCOVÁ VESELSKÁ Aleš ŠOSTER Ivancická581 PragueCzech Republic Palaeontological Department Natural History MuseumNational MuseumPragueCzech Republic Oertijdmuseum Bosscheweg 80Boxtel5293 WBThe Netherlands Institute for Palaeobiology and Evolution Novi TrgKamnikSlovenia Earth and Oceanic Systems Group RMIT UniversityMelbourneAustralia Museums Victoria CarltonVictoriaAustralia Department of Paleobiology and Paleoecology Institute of Geology of the Czech Academy of SciencesPragueCzech Republic Institute of Geology and Palaeontology Charles UniversityPragueCzech Republic Faculty of Natural Sciences and Engineering University of LjubljanaLjubljanaSlovenia

A diverse sessile barnacle fauna from a Miocene shallow-water deposit at Dolnja Stara vas in Slovenia is described.It includes the first descriptions of early post settlement juveniles of Actinobalanus sloveniensis attached to mangrove leaves.These represent three distinct growth phases,the earliest being interpreted as being less than 24 h post settlement,the others being 1 to 2 days post settlement.An assessment of their taphonomy is provided.Associated adult balanomorphs are attached to a variety of organic substrates,including mangrove leaves and branches,fragments of the conifers?Taxodioxylon,Carapoxylon,pine cones,molluscs,and cetacean bones.The barnacles include A.sloveniensis,Amphibalanus venustus,and Perforatus perforatus—many with opercula retained within the shells.A.venustus retains some of the original shell color.This is the second record of barnacle–plant associations from the Central Paratethys from Kamnik and Trbovlje.The paleoecology and paleogeography of the site are discussed.

关键词： acorn barnacles barnacle metamorphosis epibiont paleoecology taxonomy

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Porphyrinic Acceptors forFullerene-Free MolecularPhotovoltaics

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CCS Chemistry 2024年第2期6卷 276-296页

作者： Jorge Labella Juan Laforga-Martin tomás Torres Department of Organic Chemistry Universidad Aut´onoma de Madrid28049 Madrid Institute for Advanced Research in Chemical Sciences Universidad Aut´onoma de MadridMadrid IMDEA—Nanociencia 28049 Madrid

Over the past few years,the development of nonfullerene acceptors(NFAs)has become a prominent focus in both organic and perovskite solar cell(OSCs and PSCs,respectively)research fields.In this context,porphyrinoids,compounds structurally related to porphyrins,have emerged as promising solar cell candidates.In contrast to the widely used fullerene acceptors,porphyrinoids exhibit strong,broad absorption properties across the UV–vis/NIR spectrum,which can be easily tuned through chemical modifications.Furthermore,they can be prepared and derivatized using cost-effective and straightforward methodologies,allowing for convenient adjustments in thin-film morphology,processability,supramolecular organization,and energy levels.Additionally,these compounds offer higher thermal and photochemical stability,resulting in longer device lifetimes compared to their fullerene-based counterparts.In this review,we outline the utilization of porphyrinoids as NFAs in OSCs and PSCs,discussing essential aspects such as design guidelines,molecular properties,and device configuration.Our goal is to inspire and further promote the development of n-type porphyrinoids,which have not yet fully unleashed their potential.

关键词： fullerene-free molecular photovoltaics nonfullerene acceptors porphyrinic acceptors n-type porphyrinoids organic and perovskite solar cells

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Hydrochar and synthetic natural gas co-production for a full circular economy implementation via hydrothermal carbonization and methanation:An economic approach

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Journal of Environmental Sciences 2024年第6期140卷 69-78页

作者： Judith González-Arias Guillermo Torres-Sempere Miriam González-Castaño Francisco MBaena-Moreno tomás RReina Inorganic Chemistry Department and Materials Sciences Institute University of Seville-CSICSevilleSpain Materials Sciences Institute(ICMSE) CSIC-University of SevilleSevilleSpain Department of Chemistry and Chemical Engineering Chalmers University of TechnologyGothenburgSE 41296Sweden

Herein we study the economic performance of hydrochar and synthetic natural gas coproduction from olive tree pruning.The process entails a combination of hydrothermal carbonization and methanation.In a previous work,we evidenced that standalone hydrochar production via HTC results unprofitable.Hence,we propose a step forward on the process design by implementing a methanation,adding value to the gas effluent in an attempt to boost the overall process techno-economic aspects.Three different plant capacities were analyzed(312.5,625 and 1250 kg/hr).The baseline scenarios showed that,under the current circumstances,our circular economy strategy in unprofitable.An analysis of the revenues shows that hydrochar selling price have a high impact on NPV and subsidies for renewable coal production could help to boost the profitability of the process.On the contrary,the analysis for natural gas prices reveals that prices 8 times higher than the current ones in Spain must be achieved to reach profitability.This seems unlikely even under the presence of a strong subsidy scheme.The costs analysis suggests that a remarkable electricity cost reduction or electricity consumption of the HTC stage could be a potential strategy to reach profitability scenarios.Furthermore,significant reduction of green hydrogen production costs is deemed instrumental to improve the economic performance of the process.These results show the formidable techno-economic challenge that our society faces in the path towards circular economy societies.

关键词： Hydrothermal carbonization CO_(2)waste valorization Methanation Profitability analysis

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Granger causal representation learning for groups of time series

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Science China(Information Sciences) 2024年第5期67卷 56-68页

作者： Ruichu CAI Yunjin WU Xiaokai HUANG Wei CHEN tom Z.J.FU Zhifeng HAO School of Computer Science Guangdong University of Technology Peng Cheng Laboratory College of Science Shantou University

Discovering causality from multivariate time series is an important but challenging problem.Most existing methods focus on estimating the Granger causal structures among multivariate time series,while ignoring the prior knowledge of these time series, e.g., the group of the time series. Focusing on discovering the Granger causal structures among groups of time series, we propose a Granger causal representation learning method to solve this problem. First, we use the multiset canonical correlation analysis method to learn the Granger causal representation of each group of time series. Then, we model the Granger causal relationships among the learned Granger causal representations using a recurrent neural network with temporal information. Finally, we formulate the above two stages into one unified optimization problem, which is efficiently solved using the augmented Lagrangian method. We conduct extensive experiments on synthetic and real-world datasets to validate the correctness and effectiveness of the proposed method.

关键词： Granger causal discovery Granger causal representation learning time series data recurrent neural network multiset canonical correlation analysis

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2024 Wheelchair Compendium of Physical Activities:An update of activity codes and energy expenditure values

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Journal of Sport and Health Science 2024年第1期13卷 18-23页

作者： Scott A.Conger Stephen D.Herrmann Erik A.Willis tom E.Nightingale Joseph R.Sherman Barbara E.Ainsworth Department of Kinesiology Boise State UniversityBoiseID 83725USA Kansas Center for Metabolism and Obesity Research The University of Kansas Medical CenterKansas CityKS 66160USA Center for Health Promotion and Disease Prevention University of North Carolina at Chapel HillChapel HillNC 27599USA School of Sport Exercise and Rehabilitation SciencesUniversity of BirminghamBirmingham AL B152TTUK Centre for Trauma Sciences Research University of BirminghamEdgbastonBirmingham AL B152TTUK College of Health Solutions Arizona State UniversityPhoenixAZ 85003USA School of Exercise and Health Shanghai University of SportShanghai 200438China

Purpose:This paper presents an update of the 2011 Wheelchair Compendium of Physical Activities designed for wheelchair users and is referred to as the 2024 Wheelchair Compendium.The Wheelchair Compendium aims to curate existing knowledge of the energy expenditure for wheelchair physical activities(PAs).Methods:A systematic review of the published energy expenditure of PA for wheelchair users was completed between 2011 and May 2023.We added these data to the 2011 Wheelchair Compendium data that was compiled previously in a systematic review through 2011.Results:A total of 47 studies were included,and 124 different wheelchair PA reported energy expenditure values ranging from 0.8 metabolic equivalents for wheelchair users(filing papers,light effort)to 11.8 metabolic equivalents for wheelchair users(Nordic sit skiing).Conclusion:In introducing the updated 2024 Wheelchair Compendium,we hope to bridge the resource gap and challenge the prevailing narratives that inadvertently exclude wheelchair users from physical fitness and health PAs.

关键词： Disability Exercise MET Mobility

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