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structural parameter analysis and experimental study of micropumps with saw-tooth microchannel

SENSORS AND ACTUATORS A-PHYSICAL 2015年 234卷 195-205页

作者： Guan Yan-fang Liu Chun-bo Henan Univ Technol Coll Mech Engn Zhengzhou 450001 Peoples R China

The changing trends of vortex, pressure loss, microchannel efficiency and instantaneous flow rate along with Reynolds number are discussed based on the structural parameters of a saw-tooth microchannel that include diffuser angle, sectional width, length, taper angle and depth. Through finite element analysis it is shown that the nozzle flow is steadier than diffuser angle. The optimal range of diffuser angle is 5-9 degrees. The channel efficiency decreases with an increase of sectional width, and the optimal value is 0.04 mm according to the technology conditions. The pressure loss increases with increasing length. The channel performance is best when the taper angle is in the range 20-40 degrees. The channel efficiency increases with an increase of depth, but, with this increasing depth, the wall friction force increases, and the fabrication processing becomes more difficult. Finally, five micropump structures were designed and fabricated with deep reactive ion etching technology based on silicon wafers. The five micropumps were irreversibly sealed with polydimethylsiloxane (PDMS) on both sides using ultraviolet irradiation of the PDMS. For testing the flow rate and pressure of the five micropumps, a test-bed was established. The results show that the flow rate and pressure of one of the micropumps are maximal values under sine, square and triangular driving waves. This agrees well with the results of the structural parameter analysis. When the driving frequency is 200 Hz, the maximum flow and pressure are 63.6 mu l/min and 1.3 kPa respectively. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Micropump Vortex structural parameter Flow rate

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structural parameter Analyses on Rotor Airloads with New Type Blade-Tip Based on CFD/CSD Coupling Method

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Transactions of Nanjing University of Aeronautics and Astronautics 2016年第6期33卷 -页

作者： Wang Junyi Zhao Qijun Ma Li National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade *** CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous *** CSD module is developed based on Hamilton′s variational principles and moderate deflection beam *** deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade *** CFD and the CSD modules are verified *** the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight *** calculated results agree well with test ***,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are *** results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.

关键词： rotor airloads structural parameter computational fluid dynamics(CFD) computational structural dynamics(CSD) loose coupling method

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structural parameter study on stress intensity factors of interfacial crack in thermal barrier coatings

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CERAMICS INTERNATIONAL 2021年第10期47卷 14354-14365页

作者： Zhu, Yongqiang Yan, Bo Cai, Daoda Wu, Kaiwen Zhang, Xiaomin Chongqing Univ Coll Aerosp Engn Chongqing 400044 Peoples R China

Cracks on the wave-shaped interface between the top coating (TC) layer and the bonding coating (BC) layer of thermal barrier coatings (TBCs) are unavoidable during manufacture and operation, which may reduce the strength of the TBCs under thermal shock. A model with curved crack on the wave-shaped interface is established, and the influences of structural parameters, including the porosity, the distribution of pores and thickness of the TC layer, the interface roughness and position of crack tip on the wave-shaped interface, on the stress intensity factors (SIFs) of the cracks during thermal shock are numerically studied with the finite element method (FEM). According to the microstructure of the TBCs, the shape of a pore is assumed to be elliptical, and the pores are randomly distributed in the TC layer. A program is developed to automatically generate the distribution of pores. The variation laws of the stress intensity factors (SIFs), K-I and K-II, of the curved interfacial crack under various structural parameters are obtained and analyzed, which may provide an instruction for the design of the TBCs.

关键词： Thermal barrier coatings Interfacial crack structural parameter Stress intensity factor

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Testing for regularity and stochastic transitivity using the structural parameter of nested logit

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TRANSPORTATION RESEARCH PART B-METHODOLOGICAL 2016年 93卷 355-376页

作者： Batley, Richard Hess, Stephane Univ Leeds Inst Transport Studies Leeds LS2 9JT W Yorkshire England

We introduce regularity and stochastic transitivity as necessary and well-behaved conditions respectively, for the consistency of discrete choice preferences with the Random Utility Model (RUM). For the specific case of a three-alternative nested logit (NL) model, we synthesise these conditions in the form of a simple two-part test, and reconcile this test with the conventional zero-one bounds on the structural ('log sum') parameter within this model, i.e. 0 < theta <= 1, where theta denotes the structural parameter. We show that, whilst regularity supports the lower bound of zero, moderate and strong stochastic transitivity may, for some preference orderings, give rise to a lower bound greater than zero, i.e. impose a constraint l <= theta, where l > 0. On the other hand, we show that neither regularity nor stochastic transitivity constrain the upper bound at one. Therefore, if the conventional zero-one bounds are imposed in model estimation, preferences which violate regularity and/or stochastic transitivity may either go undetected (if the 'true' structural parameter is less than zero) and/or be unknowingly admitted (if the 'true' lower bound is greater than zero), and preferences which comply with regularity and stochastic transitivity may be excluded (if the 'true' upper bound is greater than one). Against this background, we show that imposition of the zero-one bounds may compromise model fit, inferences of willingness-to-pay, and forecasts of choice behaviour. Finally, we show that where the 'true' structural parameter is negative (thereby violating RUM - at least when choosing the 'best' alternative), positive starting values for the structural parameter in estimation may prevent the exposure of regularity and stochastic transitivity failures. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Regularity Stochastic transitivity Random Utility Model Nested logit structural parameter

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Proper accounting of mass transfer resistances in forward osmosis: Improving the accuracy of model predictions of structural parameter

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JOURNAL OF MEMBRANE SCIENCE 2015年 492卷 289-302页

作者： Bui, Nhu-Ngoc Arena, Jason T. McCutcheon, Jeffrey R. Univ Connecticut Dept Chem & Biomol Engn Ctr Environm Sci & Engn Storrs CT 06269 USA

This work demonstrates a more accurate method for calculating structural parameter (S) of asymmetric osmotic membranes using experimental data and a theoretical flux model which encapsulates all significant boundary layer phenomena. External boundary layer effects on the porous side of the membrane have been neglected in many current models. In these models, external concentration polarization (ECP) effects get combined with internal concentration polarization (ICP), resulting in inflated S values. In this study, we proposed a mathematical flux model in which ECP effects are accounted for, so that S can be more accurately measured. This model considered the in-series resistances for solute transport based on intrinsic properties of the membrane, as well as boundary layers at membrane surfaces and within the support layer. We therefore introduced new equations to define total resistance to solute transport and reflection coefficient of membranes in FO. The results indicate that ICP is less severe than previously predicted and that cross-flow velocity, temperature and concentration of the draw and the feed solutions impact both external and internal concentration polarization. Our calculations surprisingly show that changes in cross-flow velocity impact internal concentration polarization due to induced mixing within the support layer. Also, we suggest that it is critical to consider the "residence time" of solutes in the vicinity of the selective layer when determining the membrane selectivity. (C) 2015 Elsevier B.V. All rights reserved.

关键词： structural parameter Concentration polarization Reflection coefficient Membrane resistance Pressure retarded osmosis

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ELASTOPLASTIC MODEL OF ROCKS WITH A LINEAR structural parameter

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JOURNAL OF APPLIED MECHANICS AND TECHNICAL PHYSICS 2018年第2期59卷 332-340页

作者： Revuzhenko, A. F. Mikenina, O. A. Russian Acad Sci Min Inst Siberian Branch Novosibirsk 630091 Russia

A closed mathematical model is formulated, which takes into account elastoplastic strains and the medium capability of accumulating the energy of internal self-balanced stresses. Satisfaction of the diffeomorphism postulate (assumption of displacement field smoothness) is not required;as a result, the strains depend on the stresses and second derivatives of the stresses with respect to the coordinates. The model involves a linear structural parameter. Relations that take into account local bending of the elementary volumes of the medium are derived.

关键词： rocks elasticity plasticity self-balanced stresses structural parameter

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e-p curve-based structural parameter for assessing clayey soil structure disturbance

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BULLETIN OF ENGINEERING GEOLOGY AND THE ENVIRONMENT 2020年第8期79卷 4387-4398页

作者： Meng, Fanyan Chen, Renpeng Kang, Xin Li, Zhongchao Hunan Univ Coll Civil Engn Changsha 410082 Hunan Peoples R China Hunan Univ Minist Educ Key Lab Bldg Safety & Energy Efficiency Changsha 410082 Hunan Peoples R China Wuhan Municipal Construct Grp Co Ltd Wuhan 430024 Peoples R China

Additional void ratio and yield stress that can be easily determined by one-dimensional consolidation test are two representative parameters for the assessment of clayey soil structure. In this paper, a "structural parameter" that defined as the normalization of the integral of additional void ratio times effective vertical stress until yield stress was proposed to evaluate the disturbance induced by soil structure changes. By conducting oedometer tests on Hangzhou clay at various disturbed states, the compression index, yield stress, and structural parameter were obtained. The evolution of normalized additional void ratio during one-dimensional loading is presented to establish the soil structural indexing strategies for assessment of clay structure disturbances. Based on the laboratory investigations, a linear relationship between the normalized structural parameter and normalized yield additional void ratio was obtained. For a certain soil, specimens with the same initial void ratio but different disturbed state have a nearly constant void ratio when yielding. It is also found that soils with a higher plasticity index exhibit stronger structure and lower compressibility. In addition, quick direct shear tests were carried out to examine the undrained shear strength of soils at different disturbed states. The soil disturbance degree quantified from the undrained shear strength is found slightly higher than that from the structural parameter. This study can provide a reference for assessing the clayey soil structure.

关键词： Compression behavior Disturbance Structure structural parameter Structured clay

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Minimizing structural parameter of thin film composite forward osmosis membranes using polysulfone/halloysite nanotubes as membrane substrates

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DESALINATION 2016年 377卷 152-162页

作者： Ghanbari, M. Emadzadeh, D. Lau, W. J. Riazi, H. Almasi, D. Ismail, A. F. Univ Teknol Malaysia Adv Membrane Technol Res Ctr AMTEC Skudai 81310 Johor Malaysia Islamic Azad Univ Dept Chem Engn Gachsaran Branch Gachsaran Iran Univ Ottawa Ind Membrane Res Lab Dept Chem & Biol Engn Ottawa ON K1N 6N5 Canada Amirkabir Univ Technol Dept Polymer Engn & Color Technol Tehran Iran Univ Teknol Malaysia Fac Mech Engn Dept Mfg & Ind Engn Skudai 81310 Johor Malaysia

Novel forward osmosis (FO) is a membrane-based separation process with significant potentials for low energy desalination. While this technology offers various benefits, overcoming its low water flux performance caused by internal concentration polarization (ICP) of solutes in porous substrates remains a challenge. This study aims at addressing this issue by introducing hydrophilic halloysite nanotubes (HNTs) into substrate made of polysulfone (PSF). The thin film nanocomposite (TFN) membranes suitable for FO applications were prepared via interfacial polymerization on the top surface of PSF-HNT nanocomposite substrates. The results obtained from filtration experiments showed that the TFN membrane prepared with 0.5 wff. HNTs (TFN0.5 membrane) demonstrated the most satisfactory results by exhibiting high water permeability and low reverse solute flux. Furthermore, TFN0.5 membrane exhibited remarkably higher water flux than that of control TFC membrane in both FO (27.7 vs 13.3 L/m(2) h) and PRO (423 vs 26.0 L/m(2) h) configurations when they were tested with 10 mM NaCl as feed solution and 2 M NaCl as draw solution. This improvement can be ascribed to the fact that the structural parameter of TFN0.5 is much lower compared to control TFC membrane (0.37 vs 0.95 mm), leading to reduced ICP effect. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Thin film nanocomposite membrane Forward osmosis Halloysite nanotubes structural parameter Desalination

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A Theoretical Study on the Effect of structural parameter on Tensile Properties of Helical Auxetic Yarns

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FIBERS AND POLYMERS 2019年第8期20卷 1742-1748页

作者： Liu, Sai Gao, Yajie Chen, Xiaogang Du, Zhaoqun Donghua Univ Coll Text Minist Educ Key Lab Text Sci & Technol Shanghai 201620 Peoples R China Jiangxi Prov Ctr Qual Inspect & Supervis Prod Gongqingcheng 332020 Peoples R China Univ Manchester Sch Mat Manchester M13 9PL Lancs England

When auxetic yarns with helical wrapping structure are axially stretched, pressure and friction between the yarn components exist during the deformation. The tensile property of auxetic yarns not only depends on the materials of the two components, but also the structure of the yarns. Thus, the structuring effects on the tensile properties were studied by theoretical modelling with the series arrangement of a linear spring and a Newton dashpot. Besides, analysing the experimental results by the OriginPro 9 software, the effectiveness of theoretical model was validated and all the values of correlation coefficients were higher than 0.97. The relations between stress and strain were presented and it was expected to be used for predicting the tensile property of auxetic yarns with different helical angles.

关键词： Auxetic yarn Tensile property structural parameter Theoretical model

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Impact of surface porosity on water flux and structural parameter in forward osmosis

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DESALINATION 2018年 439卷 46-57页

作者： Lee, Woonghee Kang, Peter K. Kim, Albert S. Lee, Seockheon Korea Inst Sci & Technol Seoul 02792 South Korea Korea Univ Green Sch Grad Sch Energy & Environm Environm & Energy Dept 145 Anam Ro Seoul 02841 South Korea MIT 77 Massachusetts AveBldg 1 Cambridge MA 02139 USA Univ Hawaii Manoa Civil & Environm Engn 2540 Dole St Holmes 383 Honolulu HI 96822 USA

Improving water flux is a crucial objective of research in forward osmosis (FO) technology. A structural parameter is the property of the support layer of the membrane that determines the internal concentration polarization, which is determined by the bulk porosity, tortuosity, and thickness of the support layer. Surface porosity, i.e., porosity at the interface between the active and support layers, has recently been recognized as another critical factor in determining the water flux behavior and the structural parameter. In this study, the relative importance of the surface porosity, bulk porosity, and pore geometry of the support layer on water flux behavior is investigated using a recently developed pore-scale CFD simulator. To this end, various straight-like pore geometries with different combinations of surface and bulk porosities are studied. An increase in bulk porosity reduces internal concentration polarization, thereby increasing effective osmotic pressure. However, for the same magnitude of increase, an increase in surface porosity leads to a significantly larger increase in water flux. We show that water flux is most sensitive to surface porosity, and inconsistency in the structural parameter can be resolved by introducing surface porosity into the FO modeling framework.

关键词： Forward osmosis structural parameter Surface porosity Bulk porosity Pore geometry Water flux

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