查看更多>>摘要：In the era of the Internet of Things(IoT),the provision of sustainable power to distributed,mobile,and low-power-consumption electronic devices is a critical challenge.To overcome this challenge,the triboelectric nanogenerator(TENG),a highly efficient high-entropy mechanical energy harvesting device,was developed in 2012.This device enables the direct conversion of irregular and low-frequency mechanical energy into pulsed alternating current(AC)signals.However,the incompatibility of most electronic devices with AC signals necessitates rectifier circuits or generators that deliver direct current(DC)signals.In recent years,DC-TENGs have undergone extensive development,achieving significant milestones in various application fields while also facing crucial challenges that require solutions.In this review,three categories of DC-TENG devices with distinct operating mechanisms are comprehensively explored:multiphase coupling,mechanical rectification,and air breakdown.Their typical structures and working mechanisms are thoroughly discussed,and specific output performance limitations,along with corre-sponding optimization strategies,are identified.Furthermore,the applications of DC-TENGs in various scenarios are sum-marized.Finally,the challenges faced by DC-TENGs and potential solutions are analyzed to guide further advancements in this technology.
查看更多>>摘要：The need for very-high-cycle fatigue(VHCF)testing up to 1010 cycles of aviation gas turbine engine blade materials under combined mechanical loads and complex environments has encouraged the development of VHCF testing instrumentation and technology.This article begins with a comprehensive review of the existing available techniques that enable VHCF testing.Recent advances in ultrasonic fatigue testing(UFT)techniques are highlighted,containing their new capabilities and methods for single load,multiaxial load,variable amplitude fatigue,and combined cycle fatigue.New techniques for conducting UFT in high-temperature,humid environments,and corrosive environments are summarized.These developments in mechanical loading and environmental building techniques provide the possibility of laboratory construction for real service conditions of blade materials.New techniques that can be used for in situ monitoring of VHCF damage are summarized.Key issues in the UFT field are presented,and countermeasures are collated.Finally,the existing problems and future trends in the field are briefly described.
查看更多>>摘要：In this study,a structure-optimized two-phase microchannel heat sink with sintered submicron nucleation sites was developed and tested.The copper-based microchannels had a rectangular cross-section with an equivalent hydraulic diameter of 222 pm.The subcooled flow boiling characteristics were comprehensively compared between pure HFE-7100 and a non-azeotropic,immiscible binary mixture of HFE-7100 and water,considering heating areas of 1 and 5 cm.The total heating power input to the test section were 100-1500 and 250-3000 W for a 1 and 5 cm2 heat source,respectively,with a flow rate ranging from 50 to 150 L/h.Compared to pure HFE-7100,the non-azeotropic immiscible binary mixture of HFE-7100/water in the sintered porous microchannels exhibited a much higher overall heat transfer coefficient and lower power consumption.To maintain the junction temperature of a high power electronic chip below 85℃,the proposed supercapillary microchannel heat sink could effectively dissipate the heat flux of 1275 W/cm2 over 1 cm2 heat source and 500 W/cm2 over 5 cm2 heat source.In addition,the volume ratio of the binary mixture strongly influence the two-phase flow heat transfer characteristics.An optimal volume ratio exist in terms of the thermal resistance-pumping power minimization(HFE-7100:water=2:8 is recommended in this study).The findings of this investigation on the flow boiling properties of non-azeotropic immiscible mixtures help fill a gap in the related field.
查看更多>>摘要：Based on constructal theory,a rectangular parallel phase change microchannel model in a three-dimensional electronic device(TDED)is established with R134a as the cooling fluid.Based on the minimization of a complex function(CF)composed of linear weighting sum of maximum temperature difference and pumping power consumption,constructal design of the TDED is conducted first;and then,maximum temperature difference and pumping power consumption are minimized by non-dominated sorting genetic algorithm-Ⅱ methods.The results reveal that there exist an optimal mass flow rate(0.0012 kg/s)and a quadratic optimal aspect ratio(AR)(0.39)of the microchannel which lead to quadratic minimum CF(0.817).Compared with the original value,the CF after optimization is reduced by 18.34％.Reducing the inlet temperature of cooling fluid and microchannel number appropriately can help to enhance the overall performance of TDED.By using the artificial neural network and genetic algorithms in the toolboxes of Matlab software,the optimal AR gained in the Pareto solution set is located between 0.2-0.45.The smallest deviation index among three discussed strategies is 0.346,and the corresponding optimal AR is 0.413,which is selected as the optimal design strategy of the microchannel in the TDED under multiple requirements.The findings in this study can serve as theoretical guides for thermal designs of electronic devices.
查看更多>>摘要：In our daily lives,low-frequency kinetic energy primarily manifests as vibrations.However,effective harnessing of low-frequency kinetic energy remains a formidable challenge.This paper proposes a rope-driven rotor that rotates around an axis and consists of an ultra-high-molecular-weight polyethylene(UHMWPE)wire wrapped around a metal shaft.The rotor can convert ultra-low frequency vibration/linear motion into rapid rotation by pressing the top at low frequencies and driving the rope for a quick release.The harvester can generate up to 36.25 mW power using a 0.1-mm-diameter UHMWPE wire as the rotor when periodically pressed down to 20 mm at a frequency of 1 Hz.A simple power generation floor is assembled,generating 28.58-mW power with a matching load at a frequency of 1.5 Hz.Moreover,the harvester can increase the charging voltage of a 0.47-F supercapacitor from 0 to 6.8 V within 10 min.In addition,the harvester can harvest energy through a light finger press motion,and the energy obtained can also support the continuous operation of multiple electronic devices concurrently.This study introduces an effective method for harvesting ultra-low frequency energy and has great prospects in the field of power generation floor and human movement energy harvesting.
查看更多>>摘要：We present a numerically stable one-point quadrature rule for the stiffness matrix and mass matrix of the three-dimensional numerical manifold method(3D NMM).The rule simplifies the integration over irregularly shaped manifold elements and overcomes locking issues,and it does not cause spurious modes in modal analysis.The essential idea is to transfer the integral over a manifold element to a few moments to the element center,thereby deriving a one-point integration rule by the moments and making modifications to avoid locking issues.For the stiffness matrix,after the virtual work is decomposed into moments,higher-order moments are modified to overcome locking issues in nearly incompressible and bending-dominated conditions.For the mass matrix,the consistent and lumped types are derived by moments.In particular,the lumped type has the clear advantage of simplicity.The proposed method is naturally suitable for 3D NMM meshes automatically generated from a regular grid.Numerical tests justify the accuracy improvements and the stability of the proposed procedure.
查看更多>>摘要：Rhenium separation from molybdenum in molybdenite minerals and waste leachate has become an emerging challenge.Ad-dressing this challenge,we prepared a set of protein-based alkylamine/alkylammonium salts complexes as extractants for selective uptake of rhenium from molybdenum,where the protein component turned into the insoluble amyloid-like structure when its internal disulfide bonds were reduced,namely phase-transition process.Among them,the phase-transited lysozyme and methyletrioctyleammonium chloride complex(PTL-N263)exhibited the most efficient adsorption at the alkaline condition for the electrostatic interaction between negatively charged metal ions with positively charged center(R4N+)in N263,where negatively charged protein residues hindered the ion exchange of Cl-in N263 for larger size Mo species(Mo7O246-)than smaller size Re species(ReO4-).The adsorption follows the Freundlich model and pseudo-second-order kinetics,which exhibits top-level adsorption performance with a maximum adsorption capacity of 124 mg/g and a separation factor(βRe/Mo)of 2.78 × 103 for Re.The adsorption capacity per unit area(57.2 mg/(g m2))is 1.6-41 times higher than previously reported adsorbents,and the cost for adsorbing 1 g of Re(Ⅶ)is $1.07,indicating its industrial capability.This adsorption strategy can be applied to separating Re from Mo in binary solutions and industrial wastewater with other competing ions.
查看更多>>摘要：The glass-forming ability(GFA)is of great significance for the development of novel functional metal-based metallic glasses.In this study,seven popular machine learning(ML)algorithms were employed to design novel M-based(M=Fe,Co,Ni,Ti,Zr,and rare earth metal(RE))and X-component(X=2,3,4,5,6,and＞6)alloys with excellent GFA.A GFA containing 6957 data points with structural analysis was established.Feature engineering was used to analyze the importance and correlation of features.ML algorithms were utilized for GFA prediction,revealing that Xtreme Gradient Boosting Trees exhibited the strongest predictive capability,achieving a high accuracy of 94.0％,a true positive rate of 97.6％,and a root mean squared error of 0.3705 across the entire dataset.Subsequently,the GFA of ternary to hexahydroxy alloys based on Fe,Co,Ni,Zr,Ti,and Y was predicted using all possible compositions generated through Python.Finally,a series of alloys with good GFA was successfully designed and prepared.The present work suggests that the proposed ML method can be utilized to design novel multiple-M-based amorphous alloys with high GFA.
查看更多>>摘要：The 6-8 wt％yttria-stabilized zirconia with a tetragonal structure(t'-YSZ)is extensively employed in thermal barrier coatings.The exceptional fracture toughness of t'-YSZ can be attributed to its distinctive ferroelastic toughening mechanism.Micro-structure and interface tension play a critical role in ferroelastic variant switching at the micro-and nano-scale.This paper presents an original thermodynamically consistent phase field(PF)theory for analyzing ferroelastic variant switching at the micro-and nano-scale of t'-YSZ.The theory incorporates strain gradient elasticity using higher-order elastic energy and interface tension tensor via geometric nonlinearity to represent biaxial tension resulting from interface energy.Subsequently,a mixed-type formulation is employed to implement the higher-order theory through the finite element method.For an interface in equilibrium,the effects of strain gradient elasticity result in a more uniform distribution of stresses,whereas the presence of interface tension tensor significantly amplifies the stress magnitude at the interface.The introduction of an interface tension tensor increases the maximum value of stress at the interface by a factor of 4 to 10.The nucleation and evolution of variants at a pre-existing crack tip in a mono-phase t'-YSZ have also been studied.The strain gradient elasticity is capable of capturing the size effect of ferroelastic variant switching associated with microstructures in experiments.Specifically,when the grain size approaches that of the specimen,the critical load required for variant switching at the crack tip increases,resulting in greater dissipation of elastic energy during ferroelastic variant switching.Moreover,the interface tension accelerates the evolution of variants.The presented framework exhibits significant potential in modeling ferroelastic variant switching at the micro-and nano-scale.
查看更多>>摘要：Accurate aerodynamic distribution perception and real-time flight state evaluation are crucial for flight safety,e.g.,stall detection.However,the observations are usually sparse due to limitations in sensor mounting space and cost,and a re-construction technology is urgently required.Herein,a machine learning-assisted assimilation method based on sparse ob-servations has been proposed.Different from the traditional reconstruction methods focusing on boundary condition correction,the proposed method formulates the flow field pressure distribution as a linear superposition of flow field modes,thereby forming a real-time reconstruction pattern that combines offline modal extraction using computational fluid dynamics(CFD)with real-time determination of modal weights using a neural network.In this study,CFD simulations were conducted under 800 different operating conditions for common modal extraction and model training.The weights of these modes were determined online based on merely five observations for reconstructing the full pressure field.A pressure reconstruction with a relative error of 6.1％and a mean square error of 0.003 was achieved within the prescribed condition range.The computational cost was just 2 ms for each reconstruction run,significantly faster than the 20 min required by the classical reconstruction ensemble transform Kalman filter.It also showed that the method maintains almost the same accuracy amidst 1.5％measurement noise.As practical examples,shock waves and the change of lift coefficient were analyzed using the proposed method,providing remarkable evidence for the capability of the method in supporting stall detection.These validate the method's effectiveness and explore its potential in real-time and accurate monitoring of an aircraft.
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