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Numerical simulations of steady and unsteady viscous flows are presented by adopting two different numerical methodologies: the Smoothed Particle Hydrodynamics formulation implemented in the open-source code DualSPHysics and an in-house lattice Boltzmann code based on a concise central-moments scheme. Both methods employ a weakly compressible assumption to simulate incompressible flow, which means the fluid is assumed barotropic and the density and pressure are related through an equation of state. The accuracy of the two approaches is evaluated against well-defined and consolidated benchmark tests. Advantages and disadvantages of the two methodologies are discussed and substantiated by quantitative comparisons that focus on accuracy and efficacy of the two methodologies against other well-established computational methods. Overall, both formulations proposed herein are able to capture the relevant flow physics with a good level of accuracy when compared to other more affirmed techniques. Remarkably, this is observed in spite of the proposed two methods lacking key strategies commonly used in grid-based methods, such as adaptive mesh refinement.

The viscosity of different concentrations of sunflower oil + DMF and corn oil + DMF solvents in the presence of potassium iodide was measured at temperatures of 303.15–323.15 K in steps of 5.0 K. The viscosity increased with the increase in the concentration of potassium iodide and oil, while an increase in temperature decreased the viscosity. The change in the viscosity was used to evaluate the structural changes and electrostatic interactions produced by the addition of potassium iodide to the oil + DMF solvent. The structure-breaking or structure-promoting behavior of potassium iodide was evaluated by applying the Jones–Dole, Vand, and Breslau–Miller equations. The increase in viscosity B-coefficients with the temperature confirmed the structure-breaking behavior of potassium iodide in the oil + DMF solvent. The ionic B-coefficients were evaluated by subjecting the experimental data to the mathematical approximations available in the literature. The Moulik and Einstein relations were also found applicable to the viscosity of the oil + DMF solvent while deviations were observed from the Thomas relation. The thermodynamic parameters of the viscous flow also supported the obtained results about the ionic interactions.

We study the asymptotic spatial behavior of the vorticity field, $$\omega (x,t)$$ , associated to a time-periodic Navier–Stokes flow past a body, $${\mathscr {B}}$$ , in the class of weak solutions satisfying a Serrin-like condition. We show that, outside the wake region, $${\mathcal {R}}$$ , $$\omega $$ decays pointwise at an exponential rate, uniformly in time. Moreover, denoting by $${\bar{\omega }}$$ its time-average over a period and by $$\omega _P:=\omega -{\bar{\omega }}$$ its purely periodic component, we prove that inside $${\mathcal {R}}$$ , $${\bar{\omega }}$$ has the same algebraic decay as that known for the associated steady-state problem, whereas $$\omega _P$$ decays even faster, uniformly in time. This implies, in particular, that “sufficiently far” from $${\mathscr {B}}$$ , $$\omega (x,t)$$ behaves like the vorticity field of the corresponding steady-state problem.

Densities, $$\rho$$, and kinematic viscosities, $$\nu$$, have been determined at atmospheric pressure and at 293.15–303.15 K for binary mixtures formed by methanol and one linear polyether of the type CH3–O–(CH2CH2O)n–CH3 (n = 2, 3, 4). Measurements on $$\rho$$ and $$\nu$$ were carried out, respectively, using an Anton Paar DMA 602 vibrating-tube densimeter and an Ubbelohde viscosimeter. The $$\rho$$ values were used to compute excess molar volumes, $$V_{{\text{m}}}^{{\text{E}}}$$, and, together with the $$\nu$$ results, dynamic viscosities ($$\eta$$). Deviations from linear dependence on mole fraction for viscosity, $$\Delta \eta$$, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are the: Grunberg–Nissan, Hind, Frenkel, Katti–Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The $$V_{{\text{m}}}^{{\text{E}}}$$ values are large and negative and contrast with the positive excess molar enthalpies, $$H_{{\text{m}}}^{{\text{E}}}$$, available in the literature, for these systems. This indicates that structural effects are dominant. The $$\Delta \eta$$ results are positive and correlate well with the difference in volumes of the mixture compounds, confirming the importance of structural effects. The temperature dependences of $$\eta$$ and of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies, $$\Delta G^{*}$$, of viscous flow. It is demonstrated that $$\Delta G^{*}$$ is essentially determined by enthalpic effects. Methanol + CH3–O–(CH2CH2O)n–CH3 mixtures have been treated in the framework of the ERAS model. Results for $$H_{{\text{m}}}^{{\text{E}}}$$ are acceptable, while the composition dependence of the $$V_{{\text{m}}}^{{\text{E}}}$$ curves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.

In the production of steel parts employing metal injection molding (MIM), powders with particles within 22 μm are commonly used. Such powders are very expensive and inevitably increase the cost of finished parts. To reduce the production cost of MIM parts, a new composition of the BMSTU 42CrMo4 feedstock with particles within 50 μm, like in additive processes, is proposed. The rheological and mechanical characteristics of the new feedstock were determined and compared with those of the BASF Catamold 42CrMo4 feedstock. The viscous flow and melt flow index of the BMSTU 42CrMo4 feedstock were similar to those of the Catamold 42CrMo4 feedstock. The tensile strength was 70% of that for Catamold 42CrMo4. Surface roughness Ra equaled 1.85–2.22 μm and hardness varied in the range 144–220 HV1, indicating that coarser powders can be used in the MIM process.

Viscous flow between two sinusoidally deforming curved concentric tubes is mathematically investigated for the first time. Exact solutions are computed to analyse the flow between these two tubes and graphical outcomes are included for a thorough analysis of the solutions. The present article has prime applications in endoscopy as a novel peristaltic endoscope is introduced first time for a curved sinusoidal tube. This curved nature of outer sinusoidal tube with a flexible peristaltic endoscope placed inside it covers the topic of practical applications like endoscopy of human organs having curved shapes and the maintenance of complex machineries that involve complex curve structures. The usage of a flexible peristaltic endoscope inside a curved sinusoidal tube makes the process of catheterization more comfortable.

The viscous flow and sintering of porous materials that contain 2D defects are analyzed. The analysis relies on the rheological theory of sintering developed by Valerii Skorokhod and on the extended continuum powder model. The behavior of porous materials is considered for the sintering process combined with uniaxial tension. In particular, neutral sintering is addressed and an indirect method to determine the effective Laplace pressure is discussed.

A CFD solver naoe-FOAM-SJTU (The abbreviation naoe stands for naval architecture and ocean engineering) is developed based on the open source platform OpenFOAM with the purpose of simulating various marine hydrodynamic problems. In the present paper, self-developed modules, i.e., wave generation and absorption, 6 degrees of freedom motion, mooring system, dynamic overset grid, fluid-structure interaction, unsteady actuator line model, implemented on the open source platform OpenFOAM are introduced to illustrate the development of the marine hydrodynamics CFD solver. Furthermore, extensive simulations of marine hydrodynamic problems using the developed modules are conducted and validated by available experimental data. It has been proved that the CFD solver naoe-FOAM-SJTU is suitable and reliable in predicting the complex viscous flow around ship and offshore structures. Efficiency and accuracy need to be focused in the future development of the present CFD solver.

Ignited by and based on the studies (Liu in Math Probl Eng 2008:754262, 2008; J Eng Math 89(1):1–11, 2014) on viscous flows generated by two infinite-breadth plates moving in opposite directions, which are also named as extended Stokes’ problems, a finite-breadth case of Newtonian flow is examined in present study. Solutions of both cases of infinite-depth and finite-depth flows are separately derived. Main mathematical methods including integral transforms in time and spatial domains are applied to acquire the exact solution of flow velocity. Based on the derived solutions, evolution of velocity profiles in time as well as in space, and velocity gradient are examined. Solutions derived in past studies for the infinite-breadth cases are verified to be limiting cases of present results. Present study not only provides mathematical methods for analyzing viscous flow driven by moving boundaries, but also can be applied to examine many practical applications such as flows in mechanical manufacturing, flows induced by faulting, and even heat-transfer problems.

Telehelic oligodimethylsiloxanes containing 4-carboxypyrrolidone fragments were synthesized by the reactions of oligodimethylsiloxanes bearing terminal 3-aminopropyl groups with itaconic acid. The thermal and rheological properties of the obtained polymers were studied. The activation energies of viscous flow of the oligomers obtained and the previously synthesized oligodimethylsiloxanes containing terminal fragments of undecenoic or benzoic acid are compared.

In the setting of steady wind-driven oceanic currents in a non-equatorial two-layer ocean with constant eddy viscosity in the lower layer and a general continuous eddy viscosity profile in the upper layer, we derive a formula for the change of the surface deflection angle due to a perturbation (in the upper layer) of a given eddy viscosity profile for which the solution to the problem is known. This extends and generalizes previous results for perturbations of a constant eddy viscosity. The perturbation analysis is performed using a recent reformulation of the linear second-order governing equations for Ekman-type flows as a nonlinear first-order Riccati-type equation.

Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications., Comment: 19 pages, 7 figures. Regular article contributed to the Topical Issue of the European Physical Journal E entitled "Physics of Motile Active Matter" edited by Gerhard Gompper, Clemens Bechinger, Holger Stark, and Roland G. Winkler

In this paper, we present a hybrid grid generation approach for viscous flow simulations by marching a surface triangulation on viscous walls along certain directions. Focuses are on the computing strategies used to determine the marching directions and distances since these strategies determine the quality of the resulting elements and the reliability of the meshing procedure to a large extent. With respect to marching direction, three strategies featured with different levels of efficiencies and robustness performance are combined to compute the initial normals at front nodes to balance the trade-off between efficiency and robustness. A novel weighted strategy is used in the normal smoothing scheme, which evidently reduce the possibility of early stop of front generation at complex corners. With respect to marching distances, the distance settings at concave and/or convex corners are locally adjusted to smooth the front shape at first; a further adjustment is then conducted for front nodes in the neighbourhood of gaps between opposite viscous boundaries. These efforts, plus other special treatments such as multi-normal generation and fast detection of local/global intersection, as a whole enable the setup of a hybrid mesher that could generate qualitied viscous grids for geometries with industry-level complexities.

A truly three-dimensional (3D) gas-kinetic flux solver for simulation of incompressible and compressible viscous flows is presented in this work. By local reconstruction of continuous Boltzmann equation, the inviscid and viscous fluxes across the cell interface are evaluated simultaneously in the solver. Different from conventional gas-kinetic scheme, in the present work, the distribution function at cell interface is computed in a straightforward way. As an extension of our previous work (Sun et al., Journal of Computational Physics, 300 (2015) 492–519), the non-equilibrium distribution function is calculated by the difference of equilibrium distribution functions between the cell interface and its surrounding points. As a result, the distribution function at cell interface can be simply calculated and the formulations for computing the conservative flow variables and fluxes can be given explicitly. To validate the proposed flux solver, several incompressible and compressible viscous flows are simulated. Numerical results show that the current scheme can provide accurate numerical results for three-dimensional incompressible and compressible viscous flows.

This paper explores the energy-saving advantages of the burst-and-glide swimming and compares it with the normal self-swimming for a thunniform swimmer. The virtual swimmer allows us to perform controlled numerical experiments by varying the swinging tail number and the duty cycle while keeping the other parameters fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the swimmer. The user-defined functions and the dynamic mesh technology are used to simulate the burst-and-glide swimming. The results show that with the increase of the swinging tail number or the duty cycle, the swimming velocity, the power and the efficiency all increase, but the velocity-power ratio decreases somewhat. Therefore, choosing smaller swinging tail number and duty cycle is beneficial in reducing the power and increasing the velocity-power ratio, and thus to obtain the same velocity, less power is consumed. And to swim the same distance, the energy can significantly be saved. The power consumption, the efficiency and the velocity-power ratio in the burst-and-glide case are 43.9%, 40.6% and 1.15 times of those in the normal swimming case, respectively. The flow structures clearly show the evolution process around the fish in the burst-and-glide swimming. The findings can be used to reasonably plan the swimming action and to take the advantage of the external flow field energy for the fishlike robot, to be more efficient and energy-saving.

The hydrodynamic analysis of multi-floating bodies is important and widely used in marine engineering. In this study, we systematically simulated the wave diffraction problem of a fixed vertical four-cylinder structure in regular waves in the time domain in a viscous numerical wave tank. The hydrodynamic interaction of waves with a bottom-mounted structure consisting of four vertical cylinders arranged at the corners of a square shows a complicated interference phenomenon. In this paper, we illustrate and analyze the run-up around the structure and the corresponding wave forces. To investigate the viscous effect on the near-trapping phenomenon, we pay particular attention to investigating the waves near-trapped inside the four-cylinder structure, and make a comparative study of the viscous- and inviscid-flow solutions with the experimental measurements. The results show that the maximum wave elevation occurs on the inner side of the leeside cylinder, and that the wave elevations on the outer side of the cylinders are lower than those on the inner side. We can conclude that viscosity has an obvious damping effect on wave elevations inside the structure. The cylinders show a tendency to drift apart from each other when the near-trapping phenomenon occurs.

Accurate experimental isobaric densities and viscosities data between 288.15 and 318.15 K at 5 K intervals for five binary liquid mixtures of endo-dicyclopentadiene with 2,2-dimethylbutane, 3-methylpentane, n-hexane, n-heptane and 2,2,4-trimethylpentane are reported. Excess molar volume, $$V_{\text{m}}^{\text{E}}$$ , viscosity deviation, Δη, excess Gibbs energy of activation of viscous flow, G*E, have been calculated from these data and fitted by the Redlich–Kister-type equation. Prigogine–Flory–Patterson theory, Eyring–NRTL, Eyring–UNIQUAC, Eyring–Wilson, NRTL, UNIQUAC and Heil models have been applied to the binary systems.

Grunberg–Nissan parameter (d1) and the Gibbs free energy of activation of viscous flow (G*E) have been calculated with the help of density and viscosity data for sixteen binary systems at different temperatures and presented graphically. The system combinations of terpenoids + hexane, aliphatic alcohols (C1–C4) + nitromethane, polyethers + alcohol and N-methylacetamide + solvents such as 2-methoxy ethanol and water have been interpreted on the basis of molecular interaction study. Density and viscosity data necessary for calculation of above mentioned parameters for the binary mixtures are taken from literature. The results are discussed in terms of strength of interaction between the component molecules. The trend of graph is unique and leads to reliable conclusions.

Research efforts have been done to determine the limit of validity of Darcy’s Law in various fields of engineering where viscous conditions of flow are likely exceeded. In geotechnical and geological engineering, the application of centrifuge modeling for studying flow through porous materials is complex because the seepage velocity scales proportionally to centrifuge gravity, resulting in greater potential for exceeding the limit of viscous flow. This limit is usually estimated based on Forchheimer’s Law and the concept of critical Reynolds number, Rcritic, but its interpretation remains ambiguous. This study provides new insights and establishes a connection between different theoretical approaches available in the literature. Centrifuge permeability tests were conducted at different gravitational levels for different materials. Effects of the characteristics of the porous media and centrifuge acceleration on the flow behavior were evaluated. Results show that parameters of Forchheimer’s Law remain constant regardless of the centrifuge acceleration. Values of Rcritic were obtained in a range from 0.2 to 11 depending on the characteristics of material. The interpretation of the limit of validity of Darcy’s Law was analyzed based on different definitions of Reynolds number and the Forchheimer number, and critical velocities of flow and hydraulic gradients were estimated.

Toward Lions open question in Lions (1996) concerning the propagation ofregularity for density patch, we prove that the boundary regularity of the 3-D density patchpersists by time evolution for inhomogeneous incompressible viscous flows, with the initial densitygiven by $(1-\eta)~\bf{1}_{\Om_0}+~\bf{1}_{\Om_0^c}$for some small enough constant $\eta$ and some $W^{k+2,p}$ domain $\Om_0$, $p\in]3,\infty[$,and with the initial velocity satisfying some smallness conditionand appropriate conormal regularities.

The present study experimentally investigates the effect of Cr2O3 on the viscosity of molten slags. The viscosities of CaO-SiO2-10 pct Al2O3-Cr2O3 quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr2O3 content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr2O3 could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr2O3, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr2O3.

The present investigation deals with the flow of a viscous fluid in an inclined deformable porous layer bounded by rigid plates. The lower and upper moving plates are maintained at constant different temperatures. A heat source of strength $$Q_0 $$ is introduced in the porous layer. The coupled phenomenon of the fluid movement and solid deformation in the porous layer has been considered. An exact solution of governing equations has been obtained in closed form. The expressions for the fluid velocity, solid displacement and temperature distribution are obtained. The influence of pertinent parameters on flow quantities is discussed. In the inclined deformable porous medium, it is observed that the fluid velocity and temperature decreases with increasing viscous drag $$\delta $$ . But the solid displacement increases with increasing viscous drag $$\delta $$ . A table of comparison is made for flux in the present work and that of flux observed by Nield et al. (Transp Porous Media 56:351–367, 2004) for viscous flow in a horizontal undeformable porous medium. One of the important observations is that the volume flow rate is less for deformable porous media when compared with undeformable (rigid) porous media. The present result coincides with the findings of Nield et al. (2004). The results obtained for the present flow characteristics reveal many interesting behaviors that warrant further study of viscous fluid flow in an inclined deformable porous media.

Thermodynamic activation parameters, enthalpies (ΔH ‡), entropies (ΔS ‡) and Gibbs energies (ΔG ‡) for viscous flow of the systems tert-butanol (TB)+n-butylamine (NBA), TB+di-n-butylamine (DBA) and TB+tri-n-butylamine (TBA) have been calculated from measured density and viscosity data at temperatures ranging from 303.l5 to 323.15 K over the composition range 0 ≤ x 2 ≤ 1, where x 2 is the mole fraction of TB. For all systems, the corresponding excess properties ΔH ‡E, ΔS ‡E and ΔG ‡E have been determined, which are negative in the whole range of composition. The observed negative excess activation properties have been accounted for in terms of dispersive forces and H-bonding. The derived properties are well represented by fourth degree polynomial equations whereas the excess properties could be fitted to third degree Redlich–Kister polynomial equations. Furthermore, the viscosities have been predicted by using the UNIFAC–VISCO model, Grunberg–Nissan model and McAllister three-body interaction model. The UNIFAC–VISCO model and Grunberg–Nissan model do not show good agreement with the experimental data, whereas the McAllister three-body interaction model shows excellent agreement for all three systems, with small average absolute percent deviations (AAD% = 0.6–2.3). The DFT-B3LYP method with the 6-311 G (d, p) basis set has been employed for the optimization of the geometry and calculation of the total energies of the pure compounds and their binary complexes.

Scattering between electrons in the material graphene can cause these particles to flow like a viscous liquid. Such flow, which has previously been detected using measurements of electrical resistance, has now been visualized. Viscous flow of electrons seen in an electrical conductor.

The oxidation behavior of ZrB2–SiC composites in air was studied at 1650 °C. Diffusion-controlled oxidation kinetics were found for the composites studied. A parabolic rate constant of 1.2 × 10−8 g2 cm−4 s−1 was measured for ZrB2–10 % SiC composite. A transition in the oxidation kinetics was observed for ZrB2–30 % SiC composite with the initial parabolic rate constant being 1.3 × 10−8 g2 cm−4 s−1. After exposure for 60 min, the parabolic rate constant was found to be 0.3 × 10−8 g2 cm−4 s−1. A single ZrO2-rich oxide layer was found in the oxide scale structure of ZrB2–10 % SiC composite. On the other hand, three-layer oxide structures, namely SiO2-rich top layer, followed by ZrO2-rich oxide scale and SiC-depleted layer, were found for ZrB2–30 % SiC composite. The outer layer in the oxide scale structure of ZrB2–SiC composite was tapered with enhanced oxidation at the corners of the sample. Vortex formation during the viscous flow of B2O3–SiO2–ZrO2 liquid near the corners on the surface was proposed as the root cause for enhanced oxidation at the corners of the sample.

In the present study, an open source CFD tool, OpenFOAM has been extended and applied to investigate roll motion of a 2-D rectangular barge induced by nonlinear regular waves in viscous flow. Comparisons among the present OpenFOAM results with published potential-flow solutions and experimental data have indicated that the newly extended OpenFOAM model is very capable of accurate modelling of wave interaction with freely rolling structures. The wave-induced roll motions, hydrodynamic forces on the barge, velocities and vorticity flow fields in the vicinity of the structure in the presence of waves have been investigated to reveal the real physics involved in the wave induced roll motion of a 2-D floating structure. Parametric analysis has been carried out to examine the effect of structure dimension and body draft on the roll motion.

A numerical method based on fast multipole summation scheme is used to calculate hydrodynamic interactions in random suspensions of non-colloidal hard-sphere particles. The calculation is carried out for suspensions of 1,024 particles randomly placed in periodic unit cell to determine hydrodynamic transport properties such as permeability of a viscous flow through porous medium, effective viscosity of suspension, and sedimentation velocity of the suspended particles. The particle volume fraction o ranges from 0.01 to 0.25. Effect of particle number N on the transport properties was examined through the numerical calculations with N=64-1,024. It is shown that sedimentation velocity increases with N approaching an estimate for infinite N, and the finite N effect is negligible in effective viscosity and permeability problems. The present scheme is quite useful for obtaining a statistically-averaged quantity for random suspensions. As an example, ensemble-averaged velocity when position of one particle is fixed is numerically obtained in sedimentation problem. The numerical results are shown to be in excellent agreement with theoretical prediction.

An investigation has been conducted to quantify the effect of waterway geometry on the form and magnitude of forces and moment experienced by a berthed ship due to a passing ship. By using the dynamic mesh technique and solving the unsteady RANS equations in conjunction with a RNG k-e turbulence model, numerical simulation of the three-dimensional unsteady viscous flow around a passing ship and a berthed ship in different waterway geometries is conducted, and the hydrodynamic forces and moment acting on the berthed ship are calculated. The proposed method is verified by comparing the numerical results with existing empirical curves and a selection of results from model scale experiments. The calculated interaction forces and moment are presented for six different waterway geometries. The magnitude of the peak values and the form of the forces and moment on the berthed ship for different cases are investigated to assess the effect of the waterway geometry. The results of present study can provide certain guidance on safe maneuvering of a ship passing by a berthed ship.

We present numerical simulations of the April 27, 1975, landslide event in the northern extreme of Kitimat Arm, British Columbia. The event caused a tsunami with an estimated wave height of 8.2 m at Kitimat First Nations Settlement and 6.1 m at Clio Bay, at the northern and southern ends of Kitimat Arm, respectively. We use the nonhydrostatic model NHWAVE to perform a series of numerical experiments with different slide configurations and with two approaches to modeling the slide motion: a solid slide with motion controlled by a basal Coulomb friction and a depth-integrated numerical slide based on Newtonian viscous flow. Numerical tests show that both models are capable of reproducing observations of the event if an adequate representation of slide geometry is used. We further show that comparable results are obtained using estimates of either Coulomb friction angle or slide viscosity that are within reasonable ranges of values found in previous literature.

The rheological properties of melts of nonfunctional hyperbranched polycarbosilane polymers differed in regularity of the structure and chain length between the branch points were studied for the first time. Unlike melts of linear polymers, the studied hyperbranched systems are Newtonian fluids, and the viscosity and activation energy of their viscous flow depend substantially on the molecular parameters and regularity of the molecular structure.

Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate with a torsion spring acting about the pivot at the leading-edge of the plate, which is called a lumped-torsional-flexibility model. When the leading-edge is forced to take a vertical oscillation, the plate pitches passively due to the fluid-plate interaction. Based on our numerical simulations, various fundamental mechanisms dictating the propulsive performance, including the forces on the plate, power consumption, propulsive efficiency and vortical structures, have been studied. It is found that the torsional flexibility of the passively pitching plate can improve the propulsive performance. The results obtained in this study provide some physical insights into the understanding of the propulsive behaviors of swimming and flying animals.

An unsymmetrical diglycolamide namely N,N, didodecyl-N′,N′-dioctyl diglycolamide developed in our laboratory is evaluated for its hydrodynamic suitability by determining the changes in its physical properties such as density and viscosity as a function of temperature and compared with those of tri n-butyl phosphate and N,N,N′,N′-tetraoctyl diglycolamide. The effect of irradiation on density, viscosity and interfacial tension, up to a dose of 1000 kGy are also measured. In addition, the activation energy for the viscous flow (E vis) were obtained for these pure solvents and their binary mixtures with n-dodecane in the temperature range 20–65 °C using the Andrade’s equation.

Measuring yielding in cohesive suspensions is often hampered by slip at measurement surfaces. This paper presents creep data for strongly flocculated suspensions obtained using vane-in-cup tools with differing cup-to-vane diameter ratios. The three suspensions were titania and alumina aggregated at their isoelectric points and polymer-flocculated alumina. The aim was to find the diameter ratio where slip or premature yielding at the cup wall had no effect on the transient behaviour. The large diameter ratio results showed readily understandable material behaviour comprising linear viscoelasticity at low stresses, strain-softening close to yielding, time-dependent yield across a range of stresses and then viscous flow. Tests in small ratio geometries however showed more complex responses. Effects attributed to the cup wall included delayed softening, slip, multiple yielding and stick–slip events, and unsteady flow. The conclusion was that cups have to be relatively large to eliminate wall artefacts. A diameter ratio of three was sufficient in practice, although the minimum ratio must be material dependent.

Atomic-force thermodilatometry is used to investigate the change in the morphology of two-dimensional ensembles of iron metal-oxide nanoparticles obtained by reactive evaporation and subsequent programmable low-temperature (20–160°C) annealing. It is shown that when ensembles of nanoparticles are annealed, thermal shrinkage occurs (up to 25% of the volume) due to dehydration, oxidation and possible coalescence and spreading by a viscous flow mechanism.

The paper overviews experimental and theoretical studies focusing on the sintering of cermet and ceramic bodies conducted and published from 1922 to 1967. Special attention is paid to the generation and evolution of new ideas, elements of the physical theory of sintering, and attempts to use the entire wealth of knowledge in solid-state physics and physical mechanics available in a given time period. Analysis of the accumulated knowledge on sintering phenomena and the actual contribution of individual researchers to this process may promote further improvement of the physical theory of sintering and its advance to applied problems of powder materials. The key role of theoretical physicists, Frenkel, Herring, and Lifshits, in resolving the most complex problems of sintering science is emphasized.

The prediction of a ship’s resistance especially the viscous wave-making resistance is an important issue in CFD applications. In this paper, the resistances of six ships from hull 1 to hull 6 with different hull forms advancing in still water are numerically studied using the solver naoe-FOAM-SJTU, which was developed based on the open source code package OpenFOAM. Different components of the resistances are computed and compared while considering two speed conditions (12 kn and 16 kn). The resistance of hull 3 is the smallest while that of hull 5 is the largest at the same speed. The results show hull 3 is a good reference for the design of similar ships, which can provide some valuable guidelines for hull form optimization.

A novel concept of self-repairable glass useful as seals in solid oxide fuel cells (SOFCs) is proposed, developed, and used for making metal-glass–ceramic seals for enhancing reliability and life. In this concept, cracks created during SOFC operation are repaired by the crack healing process driven by the viscous flow of the glass. An approach for studying the kinetics of crack healing in glasses responsible for the self-repair is described and used to study the crack healing behavior. The cracks are created by a microindenter, and the progression of healing of cracks thus created on a silicate glass surface is experimentally determined at different annealing temperatures and times. Sequential changes in the crack morphology during thermal healing are also studied to identify the three stages of crack healing process. A crack healing model, based on the relationship among crack length, time, temperature, glass viscosity, and its flow behavior is developed in order to describe and predict the time required for self-repair on a glass surface. The predictions from the developed model is then compared with the experimental data and found to be in good agreement. These results also demonstrated the relative importance of the different stages of crack healing on the overall healing or self-repair behavior.

A new slender-body theory for viscous flow, based on the concepts of dimensional reduction and hyperviscous regularization, is presented. The geometry of flat, elongated, or point-like rigid bodies immersed in a viscous fluid is approximated by lower-dimensional objects, and a hyperviscous term is added to the flow equation. The hyperviscosity is given by the product of the ordinary viscosity with the square of a length that is shown to play the role of effective thickness of any lower-dimensional object. Explicit solutions of simple problems illustrate how the proposed method is able to represent with good approximation both the velocity field and the drag forces generated by rigid motions of the immersed bodies, in analogy with classical slender-body theories. This approach has the potential to open up the way to more effective computational techniques, since the complexity of the geometry can be significantly reduced. This, however, is achieved at the expense of involving higher-order derivatives of the velocity field. Importantly, both the dimensional reduction and the hyperviscous regularization, combined with suitable numerical schemes, can be used also in situations where inertia is not negligible., 12 pages

The rheological properties of a series of epoxy-diane and epoxy-novolac oligomers and active diluents were studied in a wide temperature range. The activation energies of their viscous flow in the regions of low and high temperatures were calculated. In a series of active diluents, the efficiency of decreasing viscosity of their mixtures with epoxy oligomers correlates with the glass transition temperature of the diluent.

A model has been developed that enables the viscosities of the fully liquid slag in the multi-component Al2O3-CaO-FeO-Fe2O3-MgO-Na2O-SiO2 system to be predicted within experimental uncertainties over a wide range of compositions and temperatures. The Eyring equation is used to express viscosity as a function of temperature and composition. The model links the activation and pre-exponential energy terms in the viscosity expression to the slag internal structure through the concentrations of various Si0.5O, \( {\text{Me}}^{n + }_{2/n} {\text{O}} \) , and \( {\text{Me}}^{n + }_{ 1/n} {\text{Si}}_{0. 2 5} {\text{O}} \) viscous flow structural units (SUs). The concentrations of these SUs are derived from a quasi-chemical thermodynamic model of the liquid slag using the thermodynamic computer package FactSage. The model describes a number of slag viscosity features including the charge compensation effect specific for the Al2O3-containing systems. The predictive capability of the model is enhanced by the physical aspects of the model parameters—the correlation with other physicochemical properties as well as experimental viscosity data is used to determine model parameters. The present series of two papers outlines (a) recent significant improvements introduced into the model formalism and (b) application of the model to the Al2O3-CaO-MgO-SiO2 system, review of experimental viscosity data, and optimization of the corresponding model parameters for this system.

Express methods are proposed for determination of physico-chemical properties of multi-component hydrocarbon systems based on principles correlating physicochemical and optical properties of substances, i.e., based on spectrum-property and color-property correlations. Statistical processing of data acquired indicates that the proposed express methods are in no way inferior to conventional investigatory methods in accuracy.

Stresses on blood cellular constituents induced by blood flow can be represented by a continuum approach down to the μm level; however, the molecular mechanisms of thrombosis and platelet activation and aggregation are on the order of nm. The coupling of the disparate length and time scales between molecular and macroscopic transport phenomena represents a major computational challenge. In order to bridge the gap between macroscopic flow scales and the cellular scales with the goal of depicting and predicting flow induced thrombogenicity, multi-scale approaches based on particle methods are better suited. We present a top-scale model to describe bulk flow of platelet suspensions: we employ dissipative particle dynamics to model viscous flow dynamics and present a novel and general no-slip boundary condition that allows the description of three-dimensional viscous flows through complex geometries. Dissipative phenomena associated with boundary layers and recirculation zones are observed and favorably compared to benchmark viscous flow solutions (Poiseuille and Couette flows). Platelets in suspension, modeled as coarse-grained finite-sized ensembles of bound particles constituting an enclosed deformable membrane with flat ellipsoid shape, show self-orbiting motions in shear flows consistent with Jeffery's orbits, and are transported with the flow, flipping and colliding with the walls and interacting with other platelets.

To improve the performance of Si solar cells after firing, it is necessary to control the thickness of the glass layers between the Ag and Si, and the formation of Ag when it recrystallizes into the Si emitter, both of which decisively influence the performance of the cell. In this study, the effect of the physical properties of the frits on the contacts between Ag and Si is verified. Interfaces of Ag electrodes/glass layers/Ag recrystallized into n + emitter are formed when using high-fluidity frits. On the other hand, as the viscous flow of the frits slows as the temperature increases, an interface structure formed of Ag/thin glass/SiN x layers results, with the formation of Ag nanoprecipitates in the glass layers. Our results suggest that the viscous behavior of frits under increasing temperatures leads to the formation of distinct interfaces between Ag electrodes and Si.

New experimental data for the viscosity of molten lithium nitrate from its melting point up to about 700 K are reported. The measurements were taken, for the first time, with an oscillating-cup viscometer with an estimated uncertainty of 3 %. The obtained data were compared with previous works. It was concluded that there are still large discrepancies between different sets of data. Our data follow the Arrhenius behavior with an activation energy for viscous flow of $$E_{\eta } \hbox {= 19.3}$$ $$\hbox {kJ}{\cdot }\hbox {mol}^{-1}$$ , slightly higher than previous recommendations.

The presence of the compensation effect of dynamic viscosity for multicomponent systems produced in different ways (physical mixing, chemical reactions) is established. The growth in the entropy term ΔS as part of the preexponent of the Frenkel equation is accompanied by the change in the activation energy E a of viscous flow. An analysis of the available results shows that this phenomenon is universal in character for hydrocarbon systems.

Viscous flow in a tube is basic in fluid mechanics. However, there are cases where the tube is filled with a porous medium, such as those in filters, catalytic reactors or matrix-filled biological pores. In these cases the appropriate governing equation is the DarcyBrinkman equation, where both the resistance of the matrix and the bounding walls are taken into account [1, 2]. There are many articles on the flow in a straight tube filled with a porous medium, notably Refs. [3– 10]. This paper considers the flow in a curved tube filled with a porous medium. Previous literature include the works of Avramenko and Kuznetsov [11, 12] who solved analytically for the flow in a curved channel and a curved rectangular tube. Full numerical solution was also done for a helically coiled tube [13]. We shall introduce a Ritz method to treat the flow through a porous medium in a general curved tube, then apply the method to a curved tube of elliptic cross section. The Ritz method and its convergence have been known in elasticity (e.g. [14]), but its applications

The diffusion coefficients and viscosity of four Al1–x Zr x (x = 0.4, 0.5. 0.6, and 0.67) alloys are predicted by ab initio molecular dynamic simulations via the Einstein and Darken equations. It is observed that the addition of Zr to Al reduces the self-diffusion coefficient of Al drastically, whereas the addition of Al to Zr has little effect on the self-diffusion coefficient of Zr. The interdiffusion coefficient and viscosity are predicted with both being close to those of pure Al extrapolated to high temperatures. Based on the analysis of atomic structures, the observations are attributed to clustering in liquid so that the migration of Al and Zr are correlated strongly and viscous flow is affected by Al-Al bonding between clusters.

Precise measurements of viscosities and densities of solutions of Et4NBF4 in propylene carbonate are reported in wide range of concentrations from 0.01 to 0.8 mol⋅kg−1 at 283.15, 298.15, 308.15 and 313.15 K. The viscosity data have been analyzed by the Jones–Dole equation for dilute solutions as well as by the Angell equation for concentrated solutions. The activation parameters have been evaluated using the transition-state treatments of Eyring and Feakins. The contributions of volumetric and energetic terms for viscous flow of the Et4NBF4 in propylene carbonate are evaluated.

The paper develops a comprehensive approach for the servo-fluid-elastic modeling of electromagnetically levitated secondary adaptive mirrors. The system modeling includes the mirror structural dynamics model, its interaction with the fluid film interposed between the mirror and its reference backplate and disturbances due to local air turbulence. The accuracy of the proposed fluid dynamic model is assessed by comparing it with a significant sample of high fidelity 3D Navier---Stokes analyses. The simulation tool is then used to demonstrate the effectiveness and robustness of a recently proposed control, based on a system dynamics cancellation and an iterated steady state feedforward contribution. The simulations clearly highlights the improvements achievable implementing the new control scheme.

An analysis is presented for the steady non-linear viscous flow of an incompressible viscous fluid over a horizontal surface of variable temperature with a power-law velocity under the influences of suction/blowing, viscous dissipation and thermal radiation. Numerical results are illustrated by means of tables and graphs. The governing partial differential equations are converted into nonlinear ordinary differential equations by a similarity transformation. The effects of the stretching parameter n, suction/blowing parameter b, Prandtl number ¿, Eckert number E c(E c *) and radiation parameter N R are discussed. Two cases are studied, namely, (i) Prescribed surface temperature (PST case) and, (ii) Prescribed heat flux at the sheet (PHF case). © 2011 Springer Science+Business Media B.V.