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Jumping droplets

Droplet 2024年第2期3卷 3-33页

作者： Jonathan B.Boreyko department of mechanical engineering Virginia TechBlacksburgVirginiaUSA

When microdroplets with quasi-spherical contact angles coalesce together on a low-adhesion substrate,the capillary-inertial expansion of the liquid bridge induces a dramatic out-of-plane jumping event due to symmetry *** the onset of merging,droplet jumping initiates after a capillary-inertial time scale of t_(ci)∼1–100μs with characteristic jumping speeds of order v_(j)∼0.1m/*** coalescenceinduced jumping-droplet effect is most commonly observed among a population of growing dew droplets on a superhydrophobic condenser,but can also occur by colliding deposited droplets together or during droplet sliding on fog *** this review,we cover the historical development of capillary-inertial jumping droplets,summarize the decade-long effort to rationalize the ultra-low energy conversion efficiency and critical droplet size of the phenomenon,and then present 15 variations on a theme of ***-inertial jumping droplets are not only a visceral illustration of the surprising power of surface tension at the microscale but they also have the potential to enhance phase-change heat transfer,enable selfcleaning surfaces,combat frost formation,harvest energy,and govern the rate of disease spread for wheat crops.

关键词： capillary illustration rational

Development of a 3D model for particle-wall collision and induced rotation and its influence on particle trajectories

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Particuology 2024年第11期94卷 211-228页

作者： Cairen Miranda John Palmore Jr. department of mechanical engineering Virginia TechBlacksburg24060VAUSA department of mechanical engineering University of WashingtonSeattle98195WAUSA

The present research focuses on improving the prediction of rotating particle *** particle-surface collision models do not accurately predict the particle rebound when taking rotation into *** data,such as the studies by Gorham and Kharaz(2000),Buck,Tang,Heinrich,Deen and Kuipers(2017),and Dong and Moys(2006)show that the Tsuji,Oshima and Morikawa(1985)model is inaccurate due to the incorrect tangential coefficient of restitution ***,Kuipers,Mohd Salleh,Stein,and Seville(2001)introduced a similar model to the work by Tsuji et al.(1985)which includes a tangential coefficient of restitution but is only in two dimensions and does not consider out of plane *** work re-derives the particle collision model from the impulse equations for binary collisions in 3D while considering rotating *** derived equations in this work compares well to experimental particle-surface impact *** implications of this model are seen by investigating erosion due to particle collision in a simple pipe *** is shown that Tsuji et al.(1985)over predicts the *** small differences in particle trajectories between the present model and the Tsuji et al.(1985)model will grow in complex flows with multiple close range particle impacts leading to inaccurate erosion predictions which will negatively impact the design of turbomachinery and pneumatic pipes.

关键词： Particle collisions CFD Rotation Three dimensional

Two and three dimensional modeling of fluidized bed with multiple jets in a DEM-CFD framework

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Particuology 2014年第5期12卷 19-28页

作者： Surya Deb Danesh K.Tafti Randolph Hall(1141) Department of Mechanical EngineeringVirginia TechBlacksburgVA 24061USA

Fluidized beds with multiple jets have widespread industrial applications. The objective of this paper is to investigate the jet interactions and hydrodynamics of a fluidized bed with multiple jets. Discrete element modeling coupled with in-house CFD code GenlDLEST has been used to simulate a bed with nine jets. The results are compared with published experiments. Mono dispersed particles of size 550 ~m are used with 1.4 times the minimum fluidization velocity of the particles. Both two and three dimensional computations have been performed. To the best of our knowledge, the results presented in this paper are the first full 3D simulations of a fluidized bed performed with multiple jets. Discrepancies between the experiment and simulations are discussed in the context of the dimensionality of the simulations. The 2D solid fraction profile compares well with the experiment close to the distributor plate. At higher heights, the 2D simulation over-predicts the solid fraction profiles near the walls. The 3D simulation on the other hand is better able to capture the solid fraction profile higher up in the bed compared to that near the distributor plate. Similarly, the normalized particle velocities and the particle fluxes compare well with the experiment closer to the distributor plate for the 2D simulation and the freeboard for the 3D simulation, respectively. A lower expanded bed height is predicted in the 2D simulation compared to the 3D simulation and the experiment. The results obtained from DEM computations show that a 2D simulation can be used to capture essential jetting trends near the distributor plate regions, whereas a full scale 3D simulation is needed to capture the bubbles near the freeboard regions. These serve as validations for the experiment and help us understand the complex jet interaction and solid circulation patterns in a multiple jet fluidized bed system.

关键词： Discrete element modeling Fluidized beds Solid fraction Bed height Grid zone Multiple jets Particle flux

Physics-constrained deep learning for data assimilation of subsurface transport

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Energy and AI 2021年第1期3卷 104-114页

作者： Haiyi Wu Rui Qiao department of mechanical engineering Virginia TechBlacksburgVA 24061USA

Data assimilation of subsurface transport is important in many energy and environmental applications,but its solution is typically *** this work,we build physics-constrained deep learning models to predict the full-scale hydraulic conductivity,hydraulic head,and concentration fields in porous media from sparse measure-ment of these *** model is developed based on convolutional neural networks with the encoding-decoding *** model is trained by minimizing a loss function that incorporates residuals of governing equations of subsurface transport instead of using labeled *** trained,the model predicts the unknown conductivity,hydraulic head,and concentration fields with an average relative errorlable at 12.2%of the grid points in the porous *** model has a robust predictive performance for porous media with different conductivities and transport under different Péclet number(0.5

关键词： Physics-constrained deep learning Data assimilation Subsurface transport Convolutional encoder-decoder

An efficient analytical homogenization technique for mechanical-hygrothermal responses of unidirectional composites with applications to optimization and multiscale analyses

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Chinese Journal of Aeronautics 2019年第2期32卷 382-395页

作者： Guannan WANG mechanical engineering department Texas Tech University

The elasticity-based Locally Exact Homogenization Theory(LEHT) is extended to study the mechanical-hygrothermal behaviors of unidirectionally-reinforced composites. Based on the framework developed previously, thermal and moisture effects are incorporated into the LEHT to study the homogenized and localized responses of heterogeneous materials, which are validated using available analytical and numerical techniques. The LEHT programs are then encapsulated as subroutines with Input/Output(I/O) interfaces, to be readily applied in different computational scenarios. In order to illustrate the efficiency of the LEHT, the theory is firstly coupled to the Particle Swarm Optimization(PSO) algorithm in order to minimize the axial thermal expansion mismatch in hexagonal and square fiber arrays by tailoring the fiber volume fraction. The LEHT is then implemented into the lamination theory to study fabrication-induced residual stresses arising during the cool-down process which introduces local laminate stresses owing to thermo-mechanical property mismatch between plies. Both of these applications illustrate the efficiency and accuracy of the LEHT in generating effective properties and local stress distributions, making the theory a golden standard in validating other analytical or numerical techniques as well as a reliable tool in composite design and practice for professionals and non-professionals alike.

关键词： Coefficients of moisture expansion Coefficients of thermal expansion Elasticity-based locally exact homogenization theory mechanical-hygrothermal behavior Multiscale laminate analysis Particle swarm optimization

Antitangling and manufacturable Fog Harps for high‐efficiency water harvesting

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Droplet 2023年第4期2卷 38-44页

作者： Jimmy K.Kaindu Kevin R.Murphy Nicholas G.Kowalski Alexandra N.Jones Matthew Davis Fleming Brook S.Kennedy Jonathan B.Boreyko department of mechanical engineering Virginia TechBlacksburgVirginiaUSA department of Biomedical engineering and Mechanics Virginia TechBlacksburgVirginiaUSA School of Architecture and Design Virginia TechBlacksburgVirginiaUSA Samscreen Inc. ConklinNew YorkUSA

Fog Harps harvest substantially more water than conventional mesh‐based ***,to date,all large‐scale Fog Harps have been impractically hand‐wound at low wire tensions and suffer from elastocapillary wire ***,we develop large‐scale and high‐tension Fog Harps that are manufacturable and *** Fog Harps retain the record‐setting fog harvesting efficiency(η≈17%)of their optimized scale‐model counterparts,while uniquely enabling practical real‐life *** was achieved by adapting the industrial process for making harp screens,a pre‐existing technology used for screening solid *** critical tension required to minimize wire tangling was rationalized by an improved elastocapillary tangling model.

关键词： harvesting capillary rational

A technical survey on tire-road friction estimation

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Friction 2017年第2期5卷 123-146页

作者： Seyedmeysam KHALEGHIAN Anahita EMAMI Saied TAHERI Center for Tire Research(CenTiRe) Department of Mechanical Engineering Virginia Tech Blacksburg VA 24061 United States department of Biomedical engineering and Mechanics Virginia Tech Blacksburg VA 24061 United States

Lack of driver's knowledge about the abrupt changes in pavement's friction and poor performance of the vehicle's stability,traction,and ABS controllers on the low friction surfaces are the most important factors affecting car *** to its direct relation to vehicle stability,accurate estimation of tire-road friction is of interest to all vehicle and tire *** studies have been conducted in this field and researchers have used different tools and have proposed different *** literature survey introduces different approaches,which have been widely used to estimate the friction or other related parameters,and covers the recent literature that contains these *** emphasize of this review paper is on the algorithms and studies,which are more popular and have been repeated several *** focus has been divided into two main groups:experiment-based and model-based *** of these main groups has several sub-categories,which are explained in the next few *** summary tables are provided in which the overall feature of each approach is reviewed that gives the reader the general picture of different algorithms,which are widely used in friction estimation studies.

关键词： tire-road friction friction estimation model-based approach experiment-based approach

Improving the off-resonance energy harvesting performance using dynamic magnetic preloading

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Acta Mechanica Sinica 2020年第3期36卷 624-634页

作者： Feng Qian Shengxi Zhou Lei Zuo department of mechanical engineering Virginia TechBlacksburgVA 24061USA School of Aeronautics Northwestern Polytechnical UniversityXi'an 710072China

Piezoelectric stack transducers in d33 mode have a much higher mechanical-to-electric energy conversion efficiency compared with d3l mode piezoelectric ***,multilayered piezoelectric stacks usually operate in off-resonance due to the higher stiffness and thereby have a lower power output under low-frequency *** paper proposes to apply the dynamic magnetic pre-loading to a piezoelectric stack transducer to significantly increase the power *** energy harvesting system consists of a multilayered piezoelectric stack with a compliant force amplification frame,a proof mass,and two magnets configured in *** static force-displacement relationship of the magnets is identified from experiments and extended to a dynamic model capable of characterizing the dynamic magnetic *** electromechanical model is developed based on the theoretical derivation and the experimentally identified parameters to predict the voltage outputs under different resistive *** analytical solutions are derived by using the harmonic balance method and show good agreements with the numerical and experimental *** performance of the system is examined and compared with that of the harvester without magnetic *** influences of the distance between the two magnets and the electrical resistive loads on the power output are *** indicate the energy harvesting system with magnetic pre-loading can produce over thousand times more power than the system without magnetic pre-loading at the base excitation of 3 Hz and 0.5 m/s……2,far below the resonance at 243 Hz.

关键词： Energy harvesting Piezoelectric Off-resonance Harmonic balance analysis Magnetic interaction

A laser extinction based sensor for simultaneous droplet size and vapor measurement

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Particuology 2012年第1期10卷 9-16页

作者： Xueqiang Sun David J. Ewing Lin Ma College of Automatic Control and mechanical engineering Kunming University Kunming 650214 China department of Aerospace and Ocean engineering Virginia Tech Blacksburg VA 24063 USA

Multiphase flows involving liquid droplets in association with gas flow occur in many industrial and sci- entific applications. Recent work has demonstrated the feasibility of using optical techniques based on laser extinction to simultaneously measure vapor concentration and temperature and droplet size and loading. This work introduces the theoretical background for the optimal design of such laser extinction techniques, termed WMLE （wavelength-multiplexed laser extinction）. This paper focuses on the devel- opment of WMLE and presents a systematic methodology to guide the selection of suitable wavelengths and optimize the performance of WMLE for specific applications. WMLE utilizing wavelengths from 0.5 to 10 ixm is illustrated for droplet size and vapor concentration measurements in an example of water spray, and is found to enable unique and sensitive Sauter mean diameter measurement in the range of ~1-15 ~m along with accurate vapor detection. A vapor detection strategy based on differential absorp- tion is developed to extend accurate measurement to a significantly wider range of droplet loading and vapor concentration as compared to strategies based on direct fixed-wavelength absorption. Expected performance of the sensor is modeled for an evaporating spray. This work is expected to lay the ground- work for implementing optical sensors based on WMLE in a variety of research and industrial applications involving multi-phase flows.

关键词： Wavelength-multiplexed laser extinctionDropletMeasurementLaserExtinctionAbsorptionSpectroscopy