Fluid Viscous Forces Research Articles

Low Order Continuum-Based Liquid Sloshing Formulation for Vehicle System Dynamics

The objective of this investigation is to develop a low order continuum-based liquid sloshing model that can be successfully integrated with multibody system (MBS) algorithms. The liquid sloshing model proposed in this investigation allows for capturing the effect of the distributed inertia and viscosity of the fluid. The fluid viscous forces are defined using the Navier–Stokes equations. In order to demonstrate the use of the approach presented in this study, the assumption of an incompressible Newtonian fluid is considered with a total Lagrangian approach. Fluid properties such as the incompressibility condition are formulated using a penalty method. The low order model that captures the effect of the distributed fluid inertia on the vehicle dynamics is developed in this investigation using the floating frame reference (FFR) formulation. The use of this approach allows for developing an inertia-variant fluid model that accounts for the dynamic coupling between different modes of the fluid displacements. The matrix of position vector gradients and its derivative are formulated using the FFR kinematic description. The position and velocity gradient tensors are used to define the Navier–Stokes stress forces. The proposed liquid sloshing model is integrated with a MBS railroad vehicle model in which the rail/wheel interaction is formulated using a 3D elastic contact formulation that allows for the wheel/rail separation. Several simulation scenarios are used to examine the effect of the distributed liquid inertia on the motion of the railroad vehicle. The results, obtained using the sloshing model, are compared with the results obtained using a rigid body vehicle model. The comparative numerical study presented in this investigation shows that the effect of the sloshing tends to increase the possibility of wheel/rail separation as the forward velocity increases, thereby increasing the possibility of derailments at these relatively high speeds.

A theoritical study on spin coating technique

A comprehensive theory of the spin coating technique has been reviewed and the basic principles and parameters controlling the process are clearly highlighted, which include spin speed, spin time, acceleration and fume exhaust. The process generally involves four stages: a dispense stage, substrate acceleration stage, a stage of substrate spinning at a constant rate and fluid viscous forces dominate fluid thinning behaviour and a stage of substrate spinning at a constant rate and solvent evaporation dominates the coating thinning behaviour. The study also considered some common thin film defects associated with this technique, which include comet, striation, chucks marks environmental sensitivity and edge effect and possible remedies.

The Influence of Collar on Surge Pressure Caused by the Drilling Fluid Viscous Force under Pumping Condition

The study of surge pressure is of significant importance for the safety of drilling process because field practice shows that the surge pressure caused by fluid viscous force can cause a great damage to the drilling operation. The accurate calculation of surge pressure is directly related to the safety of the drilling process. However, the existing surge pressure models rarely take the impact of the collar into consideration and thus will inevitably affect the precision of the surge pressure calculation. In this study, based on the pumping condition, a steady-state calculation model for surge pressure caused by drilling fluid viscous force is developed considering the presence of collar. In the end a case study is presented to demonstrate the importance of collar during the calculation of surge pressure.

Lateral migration of an elastic capsule by optical force in a uniform flow

The lateral migration of an elastic capsule under an optical force in a uniform flow was studied to show the separation characteristics according to the elastic properties in the cross-type optical separator. The initially spherical capsule was moved through the fluid flow using a laser beam with a Gaussian distribution focused along the direction normal to the flow device surface. To simulate such a system, a penalty immersed boundary method was adopted to enable fluid-membrane coupling, and a dynamic ray tracing method was applied to the optical force calculation. The effects of the elastic properties of the capsule membrane (the surface Young's modulus and the bending modulus) on the lateral migration were studied. By increasing the surface Young's modulus, the capsule deformed less and the migration distance increased; however, buckling occurred in the capsule with a high surface Young's modulus. Buckling could be suppressed by increasing the bending rigidity. The effects of the flow velocity and the laser beam power were also examined. In the simulation, the S number, i.e., the ratio of the optical force to the viscous force, was adjusted by decreasing the flow velocity or increasing the laser beam power. The migration distance increased as the S number increased, and a constant lateral migration distance was obtained for a rigid particle for a given S number. An elastic capsule under conditions intermediate between a fixed flow velocity and a fixed laser beam power, however, did not yield a constant lateral migration distance due to the extent of the deformation in the different situations. To predict the lateral migration distance of an elastic capsule, a nondimensional parameter, S_{e}, was defined to include the effects of the optical force, the elastic force, and the fluid viscous force. A unified tendency of the lateral migration distance with S_{e} was obtained for capsules with intermediate elasticity, by varying either the flow velocity or the laser beam power.

Inertia Effects in an Externally Pressurized Thrust Bearing Using Herschel - Bulkley Lubricants

The combined effects of fluid inertia and viscous forces of a Herschel-Bulkley lubricant in an externally pressurized thrust bearing with circular geometry have been analyzed theoretically. Although the researchers of the past, laid out a foundation for the hydrodynamic lubrication, modern researchers intend to use non-Newtonian fluids characterized by a yield-value, such as Bingham, Casson and Herschel-Bulkley fluids as lubricants. More over, Tribologists emphasize a fact that in order to analyze the performance of the bearings adequately, it is necessary to consider the combined effects of fluid inertia and viscous forces of non-Newtonian lubricants. Therefore, in this research article, the combined effects of fluid inertia and viscous forces have been investigated theoretically in an externally pressurized thrust bearing with circular geometry using Herschel-Bulkley fluid as lubricant. The shape and extent of the core, along the radius, have been determined numerically for various values of the Herschel-Bulkley number and the power-law index. Using the appropriate boundary conditions, the velocity distributions in the flow and the core regions have been obtained. By considering the equilibrium of an element of the core in the fluid, the modified pressure gradient has been evaluated and thereby the film pressure and the load capacity of the bearing have been obtained numerically for different values of Reynolds number, Herschel-Bulkley number and power-law index. The effects of the inertia forces and the non-Newtonian characteristics of the lubricant, on the bearing performances have also been discussed.

Flow Resistance of Inertial Debris Flows

AbstractThis work deals with the evaluation of the most suitable expression for the motion resistance of a debris flow. In particular, it focuses on inertial debris flows, i.e., granular-fluid mixtures in which the particle inertia dominates both the fluid viscous force and turbulence; it provides, through an order-of-magnitude analysis, the criterion to be satisfied for a debris flow to be considered inertial and shows that most of real-scale debris flows match this description. The analytical relation between flow depth, depth-averaged velocity, and tangent of the angle of inclination of the free surface is then used in steady, uniform flow conditions to approximate the flow resistance in depth-averaged mathematical models of debris flows. That resistance formula is tested against experimental results on the longitudinal profile of steady, fully saturated waves of water and gravel over both rigid and erodible beds, and against field measurements of real events. The notable agreement, especially in compa...

Magnetically Actuated Artificial Cilia: The Effect of Fluid Inertia

Natural cilia are hairlike microtubule-based structures that are able to move fluid on the micrometer scale using asymmetric motion. In this article, we follow a biomimetic approach to design artificial cilia lining the inner surfaces of microfluidic channels with the goal of propelling fluid. The artificial cilia consist of polymer films filled with superparamagnetic nanoparticles, which can mimic the motion of natural cilia when subjected to a rotating magnetic field. To obtain the magnetic field and associated magnetization local to the cilia, we solve the Maxwell equations, from which the magnetic body moments and forces can be deduced. To obtain the ciliary motion, we solve the dynamic equations of motion, which are then fully coupled to the Navier-Stokes equations that describe the fluid flow around the cilia, thus taking full account of fluid inertial forces. The dimensionless parameters that govern the deformation behavior of the cilia and the associated fluid flow are arrived at using the principle of virtual work. The physical response of the cilia and the fluid flow for different combinations of elastic, fluid viscous, and inertia forces are identified.

The effect of fluid viscosity, habitat temperature, and body size on the flow disturbance of Euchaeta

Lay AbstractCopepods are small marine invertebrates that are one of the most abundant multicellular organisms on Earth. They serve as an important link in the marine food chain between small oceanic plant life, called phytoplankton, and larger organisms such as fish. As with all organisms, they must adapt to the surrounding fluid environment. Since copepods are small, they inhabit an aquatic flow regime that provides a balance of inertial and fluid viscous forces on the organism. The flow created by copepods controls, to a large degree, the interaction with prey, predators, and other individuals of the same species. Hence, examination of the flow disturbances created during cruise and escape behaviors provides insight into the method and consequences of propulsion in this unique flow environment. The genus Euchaeta includes species that inhabit ocean waters at different latitudes extending from the subtropics to the poles. The body shapes of these species are very similar, with the primary difference being much larger body size in colder waters. Thus, Euchaeta species provide a natural experiment to study adaptation to fluid property variation between habitats. Here, variation in body size, swimming and escape speeds, or viscosity has direct consequences on the hydrodynamic disturbance created by organism motion. We expected that body size and viscosity would work in opposite directions in shaping the spatial and temporal properties of the hydrodynamic disturbances generated by these copepod species. The results reveal an intriguing interplay between body size and the fluid environment that alters planktonic interactions, including the ability to prey on food items and the ability to escape from predators, in a complex manner. The complex interaction for the genus Euchaeta partially explains species adaptations to the local environmental conditions.

Viscous Force Model Analysis of Magnetic Viscous Effect in Magnetic Fluid

From the perspective of microscopic mechanism to study the origin and the macroscopic behavior of the magnetic viscosity characteristics need to discuss the magnetic viscosity effects of the magnetic fluid dynamics, and the magnetic viscous forces in the magnetic fluid dynamics equations is the root cause of the magnetic viscosity effects. In the paper, the common expressions of first-order viscous force and quatratic viscous force of the magnetic fluid are derived from combining the magnetic fluid viscosity expression forms under different concentrations together, while based on the molecular circulation theory and electromagnetic dynamics principle, the quatratic magnetic viscous force model of magnetic fluid is derived from the basic relationship between the magnetic relaxation process. Furthermore the coefficient correction model of the quatratic viscous force is given when the solid particles of magnetic fluid present the formation of chain. Finally it shows the magnetic fluid viscous force model and a clear description of the external magnetic field influence on the magnetic fluid viscosity changes.

Analytical Solution of Collisional Sheet Flows

This work focuses on the sediment transport that is dominated by collisional exchange of momentum between particles and can be identified as the transition regime between bed-load and suspended-load transport. Idealizing the particles as inelastic frictional spheres and accounting for the role of the interstitial fluid on particle collisions, three regions characterize such flows: a diffuse collisional layer neighboring the free surface, in which a simple trapezium rule is employed to solve a boundary-value problem based on the kinetic theory; a dense, algebraic layer, in which there is an algebraic balance between production and dissipation of particle fluctuation energy, the concentration is approximately constant, and correlated motion between the particles exists; and a macroviscous layer, close to the erodible bed, in which the collisions are inelastic and the fluid viscous force dominates the momentum exchange. Using boundary conditions of no-slip and yielding at the erodible bed and vanishing of th...

Effect of the natural state of an elastic cellular membrane on tank-treading and tumbling motions of a single red blood cell

A two-dimensional computer simulation model was proposed for tank-treading and tumbling motions of an elastic biconcave red blood cell (RBC) under steady shear flow. The RBC model consisted of an outer cellular membrane and an inner fluid; the membrane's elastic properties were modeled by springs for stretch/compression and bending to consider the membrane's natural state in a practical manner. Membrane deformation was coupled with incompressible viscous flow of the inner and outer fluids of the RBC using a particle method. The proposed simulation model was capable of reproducing tank-treading and tumbling motions of an RBC along with rotational oscillation, which is the transition between the two motions. In simulations using the same initial RBC shape with different natural states of the RBC membrane, only tank-treading motion was exhibited in the case of a uniform natural state of the membrane, and a nonuniform natural state was necessary to generate the rotational oscillation and tumbling motion. Simulation results corresponded to published data from experimental and computational studies. In the range of simulation parameters considered, the relative membrane elastic force versus fluid viscous force was approximately 1 at the transition when the natural state nonuniformity was taken into account in estimating the membrane elastic force. A combination of natural state nonuniformity and elastic spring constant determined that change in the RBC deformation at the transition is that from a large compressive deformation to no deformation, such as rigid body.

Transient Fluid Forces on a Rigid Circular Cylinder Subjected to Small Amplitude Motions

The present paper treats the transient fluid forces experienced by a rigid circular cylinder moving along a radial line in a fluid initially at rest. The body is subjected to a rapid displacement of relatively small amplitude in relation to its radius. Both infinite and cylindrically confined fluid domains are considered. Furthermore, non-negligible amplitude motions of the inner cylinder, and viscous and compressible fluid effects are addressed, successively. Different analytical methods and models are used to tackle each of these issues. For motions of non-negligible amplitude of the inner cylinder, a potential flow is assumed and the model, formulated as a two-dimensional boundary perturbation problem, is solved using a regular expansion up to second order. Subsequently, viscous and compressible effects are handled by assuming infinitesimal amplitude motions. The viscous fluid forces are formulated by solving a singular perturbation problem of the first order. Compressible fluid forces are then determined from the wave equation. A nonlinear formulation is obtained for the non-negligible amplitude motion. The viscous and compressible fluid forces, formulated in terms of convolution products, are linked to fluid history effects induced by wave propagation phenomena in the fluid domain. These models are expressed with dimensionless parameters and illustrated for a specific motion imposed on the inner cylinder. The different analytical models permit coverage of a broad range of motions. Hence, for a given geometry and imposed displacement, the appropriate fluid model can be identified and the resulting fluid forces rapidly estimated. The limits of these formulations are also discussed.

Low volume fraction rimming flow in a rotating horizontal cylinder

An experimental study was carried out to examine how uniform rimming flow is established for a very small volume fraction of aqueous Newtonian solutions in a partially filled rotating horizontal cylinder. There exists a certain critical volume fraction (Vc) for each solution, where the rotational speed required to achieve uniform rimming flow takes a minimum value. Counterintuitively, it takes greater rotation speeds for both larger and smaller volume fractions than this. Axial instabilities are observed for liquid volume fractions above or below this critical value. For V>Vc the defects are mainly of shark-teeth and turbulent types, while for V<Vc, fingers and rings are formed. The critical volume fraction increases with increasing fluid viscosity. Reducing surface tension increases the minimum rotational speed for V>Vc, but has very little effect for V<Vc. The lowest volume fraction for rimming flow found in the present study is 0.25%. The dimensionless minimum rotational speed Ω to achieve rimming flow is presented as a function of the dimensionless liquid volume fraction ϕ. The competing effects of fluid inertia and viscous force on rimming flow are demonstrated from a dimensionless plot of Ω versus ϕ.

Rheology of concentrated granular suspensions undergoing squeeze flow

This paper reports experimental and modeling work on biaxial extension of three highly filled microcrystalline cellulose suspensions employing squeeze flow with lubricated plates. The squeeze flow data explored both the initial compaction of the material before yield and subsequent flow rate dependant behavior. A Herschel-Bulkley model proved inadequate for describing the suspensions’ behavior across the range of strain rate studied as the consistency coefficient exhibited a strong shear-thinning characteristic depending on the strain rate at the onset of flow. This observation is interpreted here as a result of increasing fluid viscous forces, enhancing lubrication between the particles within the suspension as described by Coussot and Ancey [Phys. Rev. 59, 4445–4457 (1999)]. A modified form of the Herschel-Bulkley model is proposed which incorporates this behavior. Pure biaxial extensional strain was only achieved at intermediate squeezing velocities: wall shear effects were observed at high deformation...

Experimental study on tensioned‐web slot coating

AbstractTensioned‐web slot coating (TWSC) technology was developed in the early 1980s and was considered an efficient method for thin liquid film coating. An experimental study was carried out to investigate the effects of several key parameters on the minimum wet thickness of TWSC. The experiment was performed on a pilot coater with dilute Newtonian poly(vinyl) alcohol (PVA) solutions as test fluids coating on polyethylene‐terephthalate (PET) substrates. It was found that the minimum wet thickness for TWSC was between 0.5 and 1.5 μm, which is much lower than that obtained using conventional slot die coating. The minimum wet thickness was proportional to the tension number TN, which is defined as the ratio of fluid viscous force over web tension. Furthermore, on the basis of the experimental data, two additional dimensionless groups: dimensionless pressure PN and dimensionless surface tension LN were found to be relevant to the performance of TWSC. A universal correlation involving these dimensionless groups as well as the die geometry was used to predict the minimum wet thickness of TWSC. POLYM. ENG. SCI., 47:841–851, 2007. © 2007 Society of Plastics Engineers

エアーウエイブEHDポンプにおける液流の可視化計測

In this work, an AW (Air Wave) type EHD pump was examined, where the electrode system consists of a wire electrode in gas-phase and a partially immersed plate electrode inclined to the gas-liquid interface. This type of non-intrusive/non-moving component pump is normally used for the transport of hazardous liquid from containers or for the cleanup of spilled hazardous liquids. The EHD liquid pumping phenomenon was generated on the inclined plate electrode surface near the gas-liquid interface exposed to gas-phase corona discharges. The measurements of liquid flow towards the plate electrode surface were conducted by PIV. The fundamental characteristics of the two-phase EHD pump such as time-averaged liquid pumping flow rate, time-averaged current and internal liquid flow distribution for DC applied voltage were experimentally investigated in detail. The pumping performance was characterized by corona discharge induced dielectric EHD and conductive EHD, fluid viscous and gravity forces in terms of dimensionless parameters.

Endothelial cells exposed to erythrocytes under shear stress: An in vitro study

After injury and vascular replacement, endothelial cell recovery is limited and could lead to thrombosis. Seeding small diameter vascular prosthesis with endothelial cells has been proposed to fulfil cell lining and improve surface hemocompatibility. However, detachment of seeded cells occurs following implantation. Previous in vitro studies have looked at the fluid shear stress as a major cause of cell detachment. To our knowledge, the role of erythrocyte collisions has not been investigated. The present in vitro study aims at investigating whether endothelial cell adhesion depends on (i) the presence of erythrocytes in flow and (ii) the latent culture period (1, 24 and 48 h) between seeding and exposure to flow. Endothelial cells were exposed to culture media containing different erythrocyte concentrations using a steady laminar flow of 1350 ml min -1 in a parallel plate flow chamber. Endothelial cell morphology in dynamic conditions was quantified and compared to that in static conditions. The projected area of cells were mostly found smaller under dynamic than static conditions, particularly at a wall shear stress of 23 dyn cm -2. Cells from the 1 h latent culture period were oriented parallel to the flow axis and were more elongated than under static conditions. Conversely, endothelial cell shape was slightly modified when either the latent period or the wall shear stress was increased. Disparate orientation was observed on confluent endothelial cells (24–48 h latent period) exposed to shear stress with or without erythrocytes. Increasing fluid viscous forces due to erythrocytes play a critical role on the behaviour of freshly seeded endothelial cells upon exposure to blood flow.

Interaction between airway lining fluid forces and parenchymal tethering during pulmonary airway reopening.

In this study, our goal is to identify the interaction between airway lining fluid viscous and surface forces and parenchymal tethering forces during pulmonary airway reopening. The type of closure we modeled occurs when the airway walls and surrounding parenchyma collapse and are held in apposition by the lining fluid. We mimicked this system with a polyethylene tube coated with a Newtonian lining fluid supported by open-cell foam. Reopening occurs when a finger of air travels through the collapsed region. We measured the airway pressure (Paw) required to open the airway at a constant velocity (U). Increasing the foam stiffness (K), lining fluid viscosity (mu), and surface tension (gamma) results in an increase in Paw. Furthermore, increasing the downstream suction pressure (Pds), through tethering, causes an equivalent reduction in Paw. The upstream radius is the primary length scale, and fluid forces are represented by the capillary number: Ca = microU/gamma. On the basis of these results, we predicted the likelihood that tethering would begin to reopen collapsed airways in various disease states. This analysis showed that the ratio of tethering to fluid forces determines airway patency, which is defined as follows: lambda = PTrans/(gamma/R), where PTrans = Paw-Pds and R is airway radius. Finally, lung volume-dependent surface tension appears to be necessary to stabilize the lung.

Actuation of sloshing modulated force and moment on liquid container driven by jitter accelerations associated with siew motion in microgravity

The mathematical formulation of sloshing dynamics for a partially liquid filled dewar container driven by the gravity jitter acceleration associated with slew motion is studied. Explicit mathematical expressions to manage jitter acceleration associated with slew motion which is acting on the fluid systems in microgravity are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame container bound coordinate and the solution of time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions The numerical computation of fluid viscous stress forces and moment fluctuations exerted on the dewar container driven by jitter acceleration associated with slew motion is investigated.

Viscous expander

To make a small refrigerator with high efficiency, small refrigeration power and a low vibration level at low temperatures, an expander is introduced and theoretically investigated. This expander uses fluid viscous forces to drag a rotor, thus causing it to rotate and produce work, and therefore to generate refrigeration power. Analyses of the dynamic and thermodynamic processes of fluid flow in the expander have been carried out. Analytical expressions of output power with adiabatic expansion efficiency in terms of the geometric and hydrodynamic parameters are derived from viscous theory. The effects of the geometric and thermodynamic parameters of the performance of the expander are discussed. As an example, 41.5% of adiabatic efficiency and 6.2 W of output power are achieved with the expander at 20 K, according to our calculations. Calculations show that the expander would be a promising machine for use in a small refrigerator because of its high efficiency and small flow rate.