scholarly journals Theoretical Model and Experimental Research on Friction and Torque Characteristics of Hydro-viscous Drive in Mixed Friction Stage

2019 ◽  
Vol 32 (1) ◽  
Author(s):  
Hongwei Cui ◽  
Qiliang Wang ◽  
Zisheng Lian ◽  
Long Li
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Friction Torque ◽  
Wear Testing ◽  
Contact Friction ◽  
Stress Model ◽  
Oil Film ◽  
Average Shear Stress ◽  
Mixed Friction ◽  
Average Shear

Abstract The hydro-viscous drive (HVD) has been widely used in fan transmission in vehicles, fans, and scraper conveyors for step-less speed regulation or soft starting. In the mixed friction stage, the contact, friction, and torque characteristics of friction pairs are very complex and change at any time. The characteristics of the frictional and hydrodynamic lubrication states were studied in order to calculate and predict the friction and torque characteristics of the friction pairs in the mixed friction stage. The fluid torque was calculated by applying the average shear stress model and the load-carrying capacity of asperity was determined on the basis of the fractal contact theory. In addition, the contact friction coefficient of the friction pairs was taken into consideration and measured by using the MM1000-III friction and wear testing machine. The asperity friction torque and total torque in the mixed friction stage were obtained and finally, the test rig for the torque characteristics was set up. The results show that the contribution to the total torque is shared by the oil film and the asperity friction. The friction coefficient decreases sharply at first and then increases with a change in the relative rotational speed, following the Stribeck curve closely, and the contact frictional coefficient slowly decreases with increase in the pressure between the friction pairs. The torque between the friction pairs is provided by the asperity friction, and the torque due to the oil film reduces to zero. When the thickness of the oil film is small, a major contribution to the total torque is due to the asperity friction. The total torque also increases with the decrease in the film thickness ratio. Therefore, by theoretical analysis and experimental verification, the torque of the friction pairs in the mixed friction stage can be accurately calculated using the average shear stress model and asperity friction torque model.

scholarly journals Numerical Study of Fluid Dynamics in Suspension Culture of iPS Cells

2019 ◽  
Vol 17 (1) ◽  
pp. 73 ◽  
Author(s):  
Masaki Yano ◽  
Takuya Yamamoto ◽  
Yasunori Okano ◽  
Toshiyuki Kanamori ◽  
Mashiro Kino–oka
Keyword(s):  
Shear Stress ◽  
Suspension Culture ◽  
Numerical Study ◽  
Maximum Shear Stress ◽  
Ips Cells ◽  
Stirred Tanks ◽  
Average Shear Stress ◽  
Average Shear ◽  
Orbital Shaking ◽  
Induced Pluripotent

In a suspension culture of iPS cells, the shear stress generated during mixing is expected to promote differentiation of induced pluripotent stem (iPS) cells. The stress on the cells can be controlled by rotational rate and shape of impeller. However, it is difficult to optimize these operative parameters by experiments. Therefore, we have developed a numerical model to obtain the average and the maximum shear stress in two kinds of stirred tanks and an orbital shaking cylindrical container. The present results showed that the shear stress strongly depended on the type of mixing and lesser extent on the shape of the impeller. The average shear stress is larger in the shaking mode than that in the stirring mode. In contrast, the maximum shear stress is much smaller in the shaking than the stirring. These results suggest that stirring and shaking should be selectively used depending on the application

scholarly journals Effects of Nanoparticle Enhanced Lubricant Films in Thermal Design of Plain Journal Bearings at High Reynolds Numbers

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1353 ◽  
Author(s):  
Abdollahzadeh Jamalabadi ◽  
Alamian ◽  
Yan ◽  
Li ◽  
Leveneur ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Rise ◽  
Rotational Speed ◽  
Volume Fraction ◽  
Journal Bearings ◽  
Thermal Design ◽  
Average Shear Stress ◽  
Average Shear ◽  
Dissipation Power

Performance investigation of oil journal bearings is of particular importance given the growing use of them as a support for rotary components in a wide range of industrial machines. Frictional forces and shear stresses, which are proportionate to the velocity of lubricating layers at different points in the bearing space, provide the basis for changing temperature conditions. Various factors such as rotational velocity increase, slip width reduction, and small heat transfer coefficient of lubricant cause intensification of lubricant temperature changes. In the present study, with using computational fluid dynamic (CFD) thermohydrodynamic (THD) numerical simulations, the effect of nanoparticles on the performance features of plain journal bearings is evaluated. Particularly, 3D simulation of a journal bearing is implemented using CFD which considerably improves the accuracy of results, coupled with conjugate heat transfer model for metal parts of bearings. Reynolds equation model is used to calculate the oil-film pressure developed in hydrodynamic journal bearings by applying the nano-based lubricants. The configuration of thrust bearing consists of six pads in this study. In order to reduce the modeling complexity and computational cost and because of the symmetrical geometry of the pads, simulation of a single pad is considered instead of the entire domain. In this study, TiO2 nanoparticle with different volume fraction percentages are used. The parameters that are changed to evaluate the performance of the bearing include volume fraction percentage of the nanoparticle, type of lubricant, and rotational speed. Based on the results, for all different lubricant types, the dissipation power, average shear stress, and temperature rise are increased with augmenting the rotational speed. By increasing the rotational speed from 500 to 1500 rpm, the average shear stress increases by more than 100%, 120%, and 130% for DTE 26, DTE 25, and DTE 24 lubricant types, respectively. Moreover, by increasing the rotational speed from 500 to 1500 rpm, the dissipation power, and temperature rise are increased around 600% and 800%, respectively. Furthermore, increasing nanoparticles volume fraction from 0% to 10%, increases all parameters by approximately 10% for all lubricant types and in all rotational speeds.

Model-Based Shear Stress Gradient in Realistic Vascular Flows and Its Relation to Arterial Macromolecular Permeability

2003 ◽  
Author(s):  
Jeffrey A. LaMack ◽  
Heather A. Himburg ◽  
Xue-Mei Li ◽  
Morton H. Friedman
Keyword(s):  
Shear Stress ◽  
Fluid Dynamic ◽  
Stress Gradient ◽  
Blue Dye ◽  
Infrarenal Aorta ◽  
Flow Measurements ◽  
Average Shear Stress ◽  
Average Shear ◽  
Time Average ◽  
Shear Stress Gradient

Evans blue dye (EBD) was injected into the carotid arteries of three anesthetized pigs and allowed to circulate for 90 minutes. At the conclusion of the 90-minute period, the animals were sacrificed and injection casts of the infrarenal aorta and iliac-femoral arteries were prepared. The casts with their surrounding arteries were removed and immersed in fixative. After fixation, the EBD-stained vessels were separated from the casts, which were used to construct computational meshes for simulation of the flow fields and wall shear stress distributions that had existed in the casted regions during the experiments. The inlet flow waves and flow partitions were based on flow measurements performed during each experiment. Based on a conceptual model of the relation between shear stress nonuniformity and permeability increase, the spatial and angular variation of the gradient of the time-average shear stress at the walls of the external iliac arteries was found from the computational fluid dynamic simulations for each experiment. Using affine transformations, the gradient and time-average shear stress results, and the EBD optical density distributions, were mapped to a common template, allowing pixel-by-pixel correlations of the hemodynamic stress parameters and local permeability. The results suggest that both shear stress gradient and time-average shear play a role in determining vascular permeability to macromolecules.

scholarly journals Effect of Polypropylene Modification by Impregnation with Oil on Its Wear and Friction Coefficient at Variable Load and Various Friction Rates

2017 ◽  
Vol 2017 ◽  
pp. 1-19 ◽  
Author(s):  
Paweł Sędłak ◽  
Beata Białobrzeska ◽  
Tomasz Stawicki ◽  
Piotr Kostencki
Keyword(s):  
Friction Coefficient ◽  
Sliding Friction ◽  
Wear Test ◽  
Friction Torque ◽  
Engine Oil ◽  
Wear Testing ◽  
Wear Behaviour ◽  
Linear Wear ◽  
Variable Load ◽  
Fatigue Wear

Laboratorial two-body wear testing was carried out in order to assess effects of polypropylene modification by impregnating it with oils on friction coefficient and wear in comparison to those parameters of unmodified polypropylene, Teflon, and polyamide during operation under conditions of sliding friction without lubrication. Wear behaviour of the tested specimens was investigated using ASTM G77-98 standard wear test equipment. Recording program made it possible to visualise and record the following parameters: rotational speed and load, linear wear, friction coefficient, temperature of the specimen, and ambient temperature. In addition, wear mechanisms of the analysed materials were determined with use of scanning electron microscopy. In the case of the remaining tested polymers, the most important mechanism of wear was adhesion (PP, PTFE, PA 6.6, and PA MoS2), microcutting (PTFE, PA 6.6, and PA MoS2), fatigue wear (PTFE), forming “roll-shaped particles” combined with plastic deformation (PA 6.6 and PA MoS2), and thermal wear (PP). Impregnation of polypropylene with engine oil, gear oil, or RME results in significant reduction of friction coefficient and thus of friction torque, in relation to not only unmodified polypropylene but also the examined polyamide and Teflon.

Analytical and numerical modelling of Newtonian and non-Newtonian liquid in a rotational cross-flow MBR

2012 ◽  
Vol 66 (11) ◽  
pp. 2318-2327 ◽  
Author(s):  
T. R. Bentzen ◽  
N. Ratkovich ◽  
S. Madsen ◽  
J. C. Jensen ◽  
S. N. Bak ◽  
...  
Keyword(s):  
Shear Stress ◽  
Laser Doppler Anemometry ◽  
Membrane Surface ◽  
Empirical Relationship ◽  
Tangential Velocity ◽  
Cross Flow ◽  
Weighted Average ◽  
Newtonian Liquid ◽  
Average Shear Stress ◽  
Average Shear

Fouling is the main bottleneck of the widespread use of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid cross-flow velocity. In rotational cross-flow MBR systems, this is attained by the spinning of, for example, impellers. Validation of the CFD (computational fluid dynamics) model was made against laser Doppler anemometry (LDA) tangential velocity measurements (error less than 8%) using water as a fluid. The shear stress over the membrane surface was inferred from the CFD simulations for water. However, activated sludge (AS) is a non-Newtonian liquid, for which the CFD model was modified incorporating the non-Newtonian behaviour of AS. Shear stress and area-weighted average shear stress relationships were made giving error less that 8% compared with the CFD results. An empirical relationship for the area-weighted average shear stress was developed for water and AS as a function of the angular velocity and the total suspended solids concentration. These relationships can be linked to the energy consumption of this type of systems.

Failure Pressure in Corroded Pipelines Based on Equivalent Solutions for Undamaged Pipe

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
M. Bony ◽  
J. L. Alamilla ◽  
R. Vai ◽  
E. Flores
Keyword(s):  
Shear Stress ◽  
Numerical Simulations ◽  
Wall Thickness ◽  
Yield Criteria ◽  
Failure Pressure ◽  
Average Shear Stress ◽  
Average Shear ◽  
Thin Walled ◽  
Von Mises

Simple and accurate approaches to predict failure pressures in corroded pipelines are outlined in this work. It is shown that failure pressures for corroded pipelines can be predicted from the solution for undamaged pipelines using an equivalent wall thickness. Three different yield criteria (Tresca, ASSY (average shear stress yield), and von Mises) are reviewed in the light of reported experimental burst pressures. At first, failure pressures for cylindrical vessels with an infinitely long groove are studied by means of numerical simulations. The effect of groove size (depth and width) over the pipeline performance is quantified through a model. Finally, the scheme is extended to estimate the failure pressure of thin walled vessels with irregular finite defects.

scholarly journals Tribological Properties of V-Shaped Surface Texture under Oil Lubrication Condition

2019 ◽  
Vol 37 (2) ◽  
pp. 401-406
Author(s):  
Yuanbo Wu ◽  
Xuefeng Yang ◽  
Shouren Wang ◽  
Jian Cheng ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Tribological Properties ◽  
Turbulence Intensity ◽  
Friction And Wear ◽  
Testing Machine ◽  
Wear Testing ◽  
Oil Lubrication ◽  
Oil Film ◽  
Texture Model ◽  
The Stability

In order to study the tribological properties of V-shaped texture under oil lubrication conditions, the loading force and speed are selected as the influencing factors, each factor selected six levels. Experimental study on friction and wear of V-shaped texture with ring arrangement is finished by MMG-10 Multifunctional Friction and Wear Testing Machine, and the data of the experimental results are analyzed by using Matlab. The results show that there is a near linear relationship between the friction coefficient and the loading force and velocity. The relationship between the friction coefficient and the loading force and velocity can be expressed by a functional equation. The loading force has a greater influence on the friction coefficient than the speed. The SEM images of the post-test specimens show that the main weared zone of the V-shaped texture is the tip part. Create a single V-shaped texture model with Solidworks and use CFD to divide the mesh into the Fluent solution. According to the pressure distribution cloud diagram and the turbulence intensity cloud diagram, the stability of the oil film is improved due to the enhanced fluidity of the oil film and the small change in the oil pressure. The tip portion is also the region with a large turbulence intensity value. The improvement of the stability of the oil film is the key to reduce the friction coefficient of the V-shaped texture when the loading force increases.

scholarly journals COMPUTATIONAL STUDY OF GEOMETRIC EFFECTS OF BOTTOM WALL MICROGROOVES ON CELL DOCKING INSIDE MICROFLUIDIC DEVICES

2021 ◽  
pp. 2150017
Author(s):  
SINA AHANDOUST ◽  
MARYAM SAADATMAND
Keyword(s):  
Shear Stress ◽  
Cell Surface ◽  
Drag Force ◽  
Fluid Velocity ◽  
Cell Movement ◽  
Microfluidic Devices ◽  
Cell Detachment ◽  
Average Shear Stress ◽  
Average Shear ◽  
Recirculation Area

Cells docking inside microfluidic devices is effective in studying cell biology, cell-based biosensing, as well as drug screening. Furthermore, single cell and regularly cells docking inside the microstructure of microfluidic systems are advantageous in different analyses of single cells exposed to equal drug concentration and mechanical stimulus. In this study, we investigated bottom wall microgrooves with semicircular and rectangular geometries with different sizes which are suitable for single cell docking along the length of the microgroove in [Formula: see text]-direction and numerous cells docking regularly in one line inside the microgroove in a 3D microchannel. We used computational fluid dynamics to analyze the fluid recirculation area inside different microgrooves. The height of recirculation area in the bottom of microgroove could affect the cell’s attachment, and also materials delivery to attached cells, so the height of recirculation area may have optimum value. In addition, we analyzed the fluid drag force on cell movement toward the microgroove. This parameter was proportional to the fluid velocities in [Formula: see text] and [Formula: see text] directions in different microgrooves geometries. In different microgrooves’ geometries the fluid velocity in [Formula: see text]-direction did not change, but the fluid velocity in [Formula: see text]-direction decreased inside the microgroove. Therefore, the cell movement time inside the microgroove increased, and also the drag force in [Formula: see text]-direction could push the cells toward the bottom due to the lower drag force in [Formula: see text]-direction. The percentages of negative shear stress and average shear stress on the adhered cell surface were also calculated. The lower average shear stress, and negative shear stress around 50% on the cell surface were against cell detachment from the substrate. The results indicated that at the constant fluid inlet velocity and microchannel height, microgroove geometry and ratio of cell size to the microgroove size play pivotal roles in the cell initial adhesion to the substrate as well as the cell detachment.

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