Viscous System Research Articles

Design of Passive Viscous Fluid Control Systems for Nonlinear Structures Based on Active Control

ABSTARCTA practical procedure is developed for the design of passive control systems using viscous fluid dampers for nonlinear structures. The design methodology takes advantage of the modification of the damping, strength, and stiffness properties of the structure to achieve the desired relative displacement and absolute acceleration response. For this purpose, a study of poles in the complex plane is used to determine the required changes in the dynamic properties of nonlinear structures. Furthermore, a relatively simple relation between the ductility demands of highly damped single- and multiple-degree-of-freedom (SDF and MDF respectively) systems is established to reduce the computational burden of the proposed design method.

Global Classical Solutions of Three Dimensional Viscous MHD System Without Magnetic Diffusion on Periodic Boxes

In this paper, we study the global existence of classical solutions to the three dimensional incompressible viscous magneto-hydrodynamical system without magnetic diffusion on periodic boxes, i.e., with periodic boundary conditions. We work in Eulerian coordinate and employ a time-weighted energy estimate to prove the global existence result, under the assumptions that the initial magnetic field is close enough to an equilibrium state and the initial data have some symmetries.

Glycerosomes: Investigation of role of 1,2-dimyristoyl-sn-glycero-3-phosphatidycholine (DMPC) on the assembling and skin delivery performances

Glycerosomes were formulated using 1,2-dimyristoyl-sn-glycero-3-phosphatidycholine (DMPC), diclofenac sodium salt and 10, 20 or 30% glycerol in the water phase, while corresponding liposomes were prepared with the same amount of DMPC and diclofenac, without glycerol. The aim of the present work was to evaluate the effect of the used phospholipid on vesicle features and ability to favour diclofenac skin deposition by comparing these results with those found in previous works performed using hydrogenated soy phosphatidylcholine (P90H) and dipalmitoylphosphatidylcholine (DPPC). Liposomes and glycerosomes were multilamellar, liposomes being smaller (72±6nm). Interactions among glycerol, phospholipids and drug led to the formation of a non-rigid bilayer structure and a variation of the main transition temperature, which shifted to lower temperature. The addition of glycerol led to the formation of more viscous systems (from ∼2.5mPa/s for basic liposomes to ∼5mPa/s for glycerosomes), which improved spread ability of the formulations on the skin.Results obtained in vitro were promising using glycerosomes, irrespective of the amount of glycerol used: the amount of drug, which accumulated into and permeated through the different skin strata, was high and comparable with that obtained using P90H, suggesting that glycerosomes may represent an efficient carrier for both local effect or systemic absorption.

Boundary conditions and Schwarz waveform relaxation method for linear viscous Shallow Water equations in hydrodynamics

We propose in the present work an extension of the Schwarz waveform relaxation method to the case of viscous shallow water system with advection term. We first show the difficulties that arise when approximating the Dirichlet to Neumann operators if we consider an asymptotic analysis based on large Reynolds number regime and a small domain aspect ratio. Therefore we focus on the design of a Schwarz algorithm with Robin like boundary conditions. We prove the well-posedness and the convergence of the algorithm.

Computational fluid dynamics modeling of viscous liquid flow characteristics and end effect in rotating packed bed

Processing viscous fluid system in industrial applications is one of the challenges in process intensification. In this work, a two-dimensional CFD model was developed to reveal viscous liquid flow characteristics in the injection zone, inner cavity, packing zone and outer cavity of rotating packed bed (RPB). The CFD results agreed well with the published experimental data. The transition of the liquid flow pattern in RPB was discussed with operating conditions. The liquid viscosity showed no significant influence on the liquid holdup and the average diameter of droplets in RPB. In addition, the liquid holdup and droplet diameter decreased as rotational speed increased, and increased as liquid flow rate increased. Based on the simulated results of residence time distribution along radial direction, the end effect zone of RPB was specified, and a novel way was proposed to quantify the thickness of end effect zone. Results showed that the viscosity had great influence on the end effect zone, which had guiding significance for practical operations and configuration optimization.

Effect of CePO4 nanostructures in transparent PMMA/castor-oil based PU IPNs on thermal stability, optical and mechanical properties

Interpenetrating polymer networks (IPNs) based on PMMA/castor-oil based PU/cerium phosphate nanoparticles (CePO4) constitute an important type of materials to modulate the stiffness and confers ductile behavior to PMMA. A comparison of CePO4 dispersion into different ratios of PMMA/PU IPNs between sonication method and the classic magnetic stirring during the sequential polymerization synthesis was done through structural, optical, thermal, morphological and mechanical analysis. The results demonstrated that sonication is the adequate method to disperse CePO4 in low viscous systems such as PMMA/PU 70/30 and 60/40 wt.%, while magnetic stirring favors the dispersion in high viscous systems (PMMA/PU 50/50 wt.%). Thanks to the physical interaction, the good compatibility/miscibility between PMMA/PU and CePO4 is reached. The obtained experimental results indicated that the luminescent CePO4 nanoparticles, in addition to improve the structural properties and the Young’s modulus, can reduce voids in the networks.

Choice between series and parallel connections of hysteretic system and viscous damper for seismic protection of structures

SummarySupplemental viscous damping devices are generally envisioned to be connected in parallel to the inelastic parent structure or hysteretic damping devices. This gives rise to higher base shear, and often greater ductility demand of the hysteretic system. The series connection of the viscous and hysteretic system (the inelastic structure or a damper) is an alternative approach. In this paper, comparisons between the series and parallel connections of the hysteretic system and viscous dampers are done through response spectra analyses of single degree of freedom structures. Ductility demand of the hysteretic system and the total base shear are chosen as the response quantities. For the series model, a semi‐implicit solution scheme for classical Maxwell model is modified to include the inelasticity of the time‐independent hysteretic spring. It is observed that the series connection of the 2 dampers gives lower base shear than does the parallel connection. For long‐period and low‐damping structures, the ductility demand of the hysteretic system in series connection is higher than that in parallel connection. Increasing the viscous damping in series connection reduces the ductility demand substantially, lower than that obtained in parallel connection. Practical methods for implementing the series and parallel connections, in line with roof isolation, are also suggested.

Effect of Liquid Viscosity on Mass Transfer Area and Liquid Film Mass Transfer Coefficient for GT-OPTIMPAK 250Y

The viscosity of amine solutions used for post-combustion CO2 capture is significantly greater than water. The effect of liquid viscosity (μL) on both the effective mass transfer area (ae) and the liquid film mass transfer coefficient (kL) of packings is required to predict mass transfer rate and design the absorber and stripper. Existing correlations are mostly based on water so they do not represent the viscosity of amine solvents. In this work, ae and kL were measured in a packed column (0.43 m inner diameter) with 3 meters of GT-OPTIMPAK 250Y. Liquid viscosities of 65, 15, 4, and 1 cP were obtained by adding 85, 65, 44, and 0wt % glycerol to water. The ae was determined by reactive absorption of ambient CO2 into 0.1M sodium hydroxide solution with the absorption rate (kg’) calculated from a kinetic model specific to the viscous system. The kL was determined by air stripping toluene from the liquid. Liquid viscosity does not show significant effect on ae over the range of μL investigated. The total dependence of kL on μL is -0.73 for the packing examined. The variance of μL is the greatest that can be found in open literature with larger scale equipment, and the result with this packing is believed to be qualitatively representative of other structured packings.

Boundary layer problem and zero viscosity-diffusion limit of the incompressible magnetohydrodynamic system with no-slip boundary conditions

The purpose of this paper is to study the boundary layer problem and zero viscosity-diffusion limit of the initial boundary value problem for the incompressible viscous and diffusive magnetohydrodynamic (MHD) system with (no-slip characteristic) Dirichlet boundary conditions and to prove that the corresponding Prandtl's type boundary layer are stable with respect to small viscosity-diffusion coefficients. The main difficulty here comes from Dirichlet boundary conditions for the velocity and magnetic field. Firstly, we identify a non-trivial class of initial data for which we can establish the uniform stability of the Prandtl's type boundary layers and prove rigorously the solution of incompressible viscous-diffusion MHD system converges strongly to the sum of the solution to the ideal MHD system and the approximating solution to Prandtl's type boundary layer equation by using the elaborate energy methods and the special structure of the solution to ideal MHD system with the initial data we identify here, which yields that there exists the cancellation between the boundary layer of the velocity and that of the magnetic field. Secondly, for general initial data, we obtain zero viscosity-diffusion limit of the incompressible viscous and diffusive MHD system with the different horizontal and vertical viscosities and magnetic diffusions, when they go to zero with the different speeds, and, we prove rigorously the convergence of the incompressible viscous and diffusion MHD system to the ideal MHD system or the anisotropic MHD system by constructing the exact boundary layers and using the elaborate energy methods. We also mention that these results obtained here should be the first rigorous ones on the stability of Prandtl's type boundary layer for the incompressible viscous and diffusion MHD system with no-slip characteristic boundary condition.

A novel pH-responsive hydrogel-based on calcium alginate engineered by the previous formation of polyelectrolyte complexes (PECs) intended to vaginal administration

This work aimed to develop a calcium alginate hydrogel as a pH responsive delivery system for polymyxin B (PMX) sustained-release through the vaginal route. Two samples of sodium alginate from different suppliers were characterized. The molecular weight and M/G ratio determined were, approximately, 107 KDa and 1.93 for alginate_S and 32 KDa and 1.36 for alginate_V. Polymer rheological investigations were further performed through the preparation of hydrogels. Alginate_V was selected for subsequent incorporation of PMX due to the acquisition of pseudoplastic viscous system able to acquiring a differential structure in simulated vaginal microenvironment (pH 4.5). The PMX-loaded hydrogel (hydrogel_PMX) was engineered based on polyelectrolyte complexes (PECs) formation between alginate and PMX followed by crosslinking with calcium chloride. This system exhibited a morphology with variable pore sizes, ranging from 100 to 200 μm and adequate syringeability. The hydrogel liquid uptake ability in an acid environment was minimized by the previous PECs formation. In vitro tests evidenced the hydrogels mucoadhesiveness. PMX release was pH-dependent and the system was able to sustain the release up to 6 days. A burst release was observed at pH 7.4 and drug release was driven by an anomalous transport, as determined by the Korsmeyer–Peppas model. At pH 4.5, drug release correlated with Weibull model and drug transport was driven by Fickian diffusion. The calcium alginate hydrogels engineered by the previous formation of PECs showed to be a promising platform for sustained release of cationic drugs through vaginal administration.

The Influence of Impeller Combination on the Gas-Liquid Dispersion Performance of a Coaxial Mixer in Viscous Fluids

Abstract As a kind of mixer with wide adaptability, coaxial mixer has a wide-application in the process industry. With the help of experiment and numerical simulation, the gas-liquid dispersion performance of four impeller combinations in viscous system was studied in terms of the global gas holdup, local gas holdup, local bubble size and liquid phase flow field. Wall-scraping anchor is the common outer impeller of the four impeller combinations, and the four inner impellers are Rushton turbine, six-straight-blade turbine (SBT), 45° six-pitched-blade turbine pumping downwards (PBTD) and 45° six-pitched-blade turbine pumping upwards (PBTU). The experimental results indicate that the global gas holdup of the Rushton impeller combination is the highest among the four impeller combinations and that of PBTU is the lowest. The local gas holdup of Rushton and PBTU combinations are all high, but the gas distribution with the Rushton combinations is more uniform. Besides, the local bubble size of the four impeller combinations has the same tendency with the local gas holdup. Under the same conditions, the flow field and distribution of gas holdup of the four impeller combinations in stirred tank were simulated numerically. Compared with the experimental results, the simulation results show a good agreement on the value and distribution of local gas holdup. Among the four coaxial mixers, the Rushton impeller combination is more suitable for gas-liquid dispersion.

Dynamics of Reversed Urban Breeze Circulation

Abstract The urban breeze circulation (UBC) is a thermally forced mesoscale circulation that is characterized by low-level inward flow toward the urban center, updrafts near the urban center, upper-level outward flows, and weak downdrafts outside the urban area. Previous numerical modeling studies indicate that in the early morning the direction of the UBC can be reversed. Here, the dynamics of a reversed UBC is studied in the context of the response of the atmosphere to specified thermal forcing, which represents diurnally varying urban heating. For this, a linearized, two-dimensional, hydrostatic, Boussinesq airflow system in a rotating frame with specified thermal forcing is solved using the Fourier transform method. The occurrence of a reversed UBC in the early morning is confirmed. The Coriolis parameter affects the strength and vertical structure of the UBC, whose role is similar to that of the coefficient of Rayleigh friction and Newtonian cooling. The occurrence condition, strength, and vertical structure of a reversed UBC are examined. The Coriolis force as well as urban heating alters the occurrence time of the reversed UBC. For a strongly viscous system, a reversed UBC occurs only in high latitudes with low occurrence possibility. A simple oscillation-type model for the horizontal velocity is constructed to get some dynamical insights into a reversed UBC. The analysis results also show that the Coriolis force alters the occurrence time of the reversed UBC.

Boundary layer problems in the vanishing viscosity-diffusion\\ limits for the incompressible MHD system

In this paper, we study boundary layer problem for the incompressible magneto-hydrodynamical (MHD) system in the presence of physical boundaries with the standard Dirichlet boundary conditions with small generic viscosity and diffusion coefficients. We identify a non-trivial class of initial data for which we can establish the uniform stability of the Prandtls type boundary layers and prove rigorously that the solutions to the viscous and diffusive incompressible MHD system converges strongly to the superposition of the solution to the ideal MHD system with a Prandtls type boundary layer corrector. One of the main difficulties is to deal with the effect of the difference between viscosity and diffusion coefficients and to control the singular boundary layers resulting from the Dirichlet boundary conditions for both the viscosity and the magnetic fields. One key derivation here is that for the class of initial data we identify here, there exist cancelations between the boundary layers of the velocity field and that of the magnetic fields so that one can use an elaborate energy method to take advantage of this special structure. In addition, in the case of fixed positive viscosity, we also establish the stability of diffusive boundary layer for the magnetic field and convergence of solutions in the limit of zero magnetic diffusion for general initial data.

Influence of fluid and operating parameters on the recovery factors and gas oil ratio in high viscous reservoirs under foamy solution gas drive

Foamy oil flow behavior is reported in several high viscous reservoirs in the world, wherein reduction of pressure was noticed to be the main factor of such characteristics. It is also believed to be a significant recovery mechanism in numerous high viscous heavy oil reservoirs that have revealed higher recovery factors when compared with the fluid flow using ordinary Darcy equation. This research investigates the effects of number of factors that influence the oil recovery trends, as well as the production rates in high viscous reservoirs under foamy solution gas drive behavior. The factors investigated comprised of refined mineral oil versus crude oil, saturation pressure, oil viscosity, drawdown pressure, flow direction, solution gas, pressure depletion rate and gas oil ratio (GOR). Live oil-gas system is prepared by blending a mixture of dead oil with gases such as CO2, ethane and methane. Each high viscous live oil system was completely characterized by evaluating fluid parameters and operating parameters. The significant outcome of the depletion tests confirms that the decreasing pressure depletion rate result in lower performance. At the similar rate of pressure depletion, higher oil recovery was obtained with methane saturated oil compared to either ethane/CO2 systems, even though it had the lowest solution GOR. At saturation pressure of 500psi, the solution GOR was 9.1m3/m3, 28m3/m3 and 33m3/m3 with methane, CO2 and ethane gas respectively, whereas solution GOR of methane saturated with crude oil were found to be 11m3/m3. Both mineral and crude oil systems displayed similar decline in the oil recovery performance with decreasing pressure depletion rate. In high depletion rate tests, the recovery factor was 26.1%, 23.7% and 19.6% with respect to methane, ethane and CO2 respectively, whereas in slow depletion runs, the recovery factor declined from 13.1% with methane to 5.5% with CO2.

Global existence of strong solution for viscous shallow water system with large initial data on the irrotational part

We are interested in studying the Cauchy problem for the viscous shallow-water system in dimension N≥2, we show the existence of global strong solutions with large initial data on the irrotational part of the velocity for the scaling of the equations. More precisely our smallness assumption on the initial data is supercritical for the scaling of the equations. It allows us to give a first kind of answer to the problem of the existence of global strong solution with large initial energy data in dimension N=2. To do this, we introduce the notion of quasi-solutions which consists in solving the pressureless viscous shallow water system. We can obtain such solutions at least for irrotational data which are subject to regularizing effects both on the velocity and on the density. This smoothing effect is purely nonlinear and is crucial in order to build solution of the viscous shallow water system as perturbations of the “quasi-solutions”. Indeed the pressure term can be considered as a remainder term which becomes small in high frequencies for the scaling of the equations. To finish we prove the existence of global strong solution with large initial data when N≥2 provided that the Mach number is sufficiently large.

Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization

In the last decade nuclear spin hyperpolarization methods, especially Dynamic Nuclear Polarization (DNP), have provided unprecedented possibilities for various NMR techniques by increasing the sensitivity by several orders of magnitude. Recently, in-situ DNP-enhanced Fast Field Cycling (FFC) relaxometry was shown to provide appreciable NMR signal enhancements in liquids and viscous systems. In this work, a measurement protocol for DNP-enhanced NMR studies is introduced which enables the selective detection of nuclear spin hyperpolarized by either Overhauser effect or solid effect DNP. Based on field-cycled DNP and relaxation studies it is shown that these methods allow for the independent measurement of polymer and solvent nuclear spins in a concentrated solution of high molecular weight polybutadiene in benzene doped with α,γ-bisdiphenylene-β-phenylallyl radical. Appreciable NMR signal enhancements of about 10-fold were obtained for both constituents. Moreover, qualitative information about the dynamics of the radical and solvent was obtained. Selective DNP-enhanced FFC relaxometry is applied for the measurement of the 1H nuclear magnetic relaxation dispersion of both constituents with improved precision. The introduced method is expected to greatly facilitate NMR studies of complex systems with multiple overlapping signal contributions that cannot be distinguished by standard methods.

Modulations of viscous fluid conduit periodic waves

Modulated periodic interfacial waves along a conduit of viscous liquid are explored using nonlinear wave modulation theory and numerical methods. Large-amplitude periodic-wave modulation (Whitham) theory does not require integrability of the underlying model equation, yet often either integrable equations are studied or the full extent of Whitham theory is not developed. Periodic wave solutions of the nonlinear, dispersive, non-integrable conduit equation are characterized by their wavenumber and amplitude. In the weakly nonlinear regime, both the defocusing and focusing variants of the nonlinear Schrödinger (NLS) equation are derived, depending on the carrier wavenumber. Dark and bright envelope solitons are found to persist in long-time numerical solutions of the conduit equation, providing numerical evidence for the existence of strongly nonlinear, large-amplitude envelope solitons. Due to non-convex dispersion, modulational instability for periodic waves above a critical wavenumber is predicted and observed. In the large-amplitude regime, structural properties of the Whitham modulation equations are computed, including strict hyperbolicity, genuine nonlinearity and linear degeneracy. Bifurcating from the NLS critical wavenumber at zero amplitude is an amplitude-dependent elliptic region for the Whitham equations within which a maximally unstable periodic wave is identified. The viscous fluid conduit system is a mathematically tractable, experimentally viable model system for wide-ranging nonlinear, dispersive wave dynamics.

Contrasting the Influence of Cationic Amino Acids on the Viscosity and Stability of a Highly Concentrated Monoclonal Antibody.

To explain the effects of cationic amino acids and other co-solutes on the viscosity, stability and protein-protein interactions (PPI) of highly concentrated (≥200mg/ml) monoclonal antibody (mAb) solutions to advance subcutaneous injection. The viscosities of ≥200mg/ml mAb1 solutions with various co-solutes and pH were measured by capillary rheometry in some cases up to 70,000s-1. The viscosities are analyzed in terms of dilute PPI characterized by diffusion interaction parameters (k D ) from dynamic light scattering (DLS). MAb stability was measured by turbidity and size exclusion chromatography (SEC) after 4weeks of 40°C storage. Viscosity reductions were achieved by reducing the pH, or adding histidine, arginine, imidazole or camphorsulfonic acid, each of which contains a hydrophobic moiety. The addition of inorganic electrolytes or neutral osmolytes only weakly affected viscosity. Systems with reduced viscosities also tended to be Newtonian, while more viscous systems were shear thinning. Viscosity reduction down to 20cP at 220mg/ml mAb1 was achieved with co-solutes that are both charged and contain a hydrophobic interaction domain for sufficient binding to the protein surface. These reductions are related to the DLS diffusion interaction parameter, k D , only after normalization to remove the effect of charge screening. Shear rate profiles demonstrate that select co-solutes reduce protein network formation.

수동형 댐퍼를 장착한 구조물의 동적응답기반 신뢰성 해석 - 제2편: 시스템 파괴확률 산정

This study proposes a multi-scale dynamic system reliability analysis of control system as a method of quantitative evaluation of its performance in probabilistic terms. In this second paper, we discuss the control effect of the viscous damper on the seismic performance of the structure-level failure. Since the failure of one structural member does not necessarily cause the collapse of the structural system, we need to consider a set of failure scenarios of the structural system and compute the sum of the failure probabilities of the failure scenarios where the statistical dependence between the failure scenarios should be taken into account. Therefore, this computation requires additional system reliability analysis. As a result, the proposed approach takes a hierarchial framework where the failure probability of a structural member is computed using a lower-scale system reliability with the union set of time-sequential member failures and their statistical dependence, and the failure probability of the structural system is again computed using a higher-scale system reliability with the member failure probabilities obtained by the lower-scale system reliability and their statistical dependence. Numerical results demonstrate that the proposed approach can provide an accurate and stable reliability assessment of the control performance of the viscous damper system on the system failure. Also, the parametric study of damper capacity on the seismic performance has been performed to demonstrate the applicability of the proposed approach through the probabilistic assessment of the seismic performance improvement of the damper system.

Electron hydrodynamics dilemma: Whirlpools or no whirlpools

In highly viscous electron systems such as, for example, high quality graphene above liquid nitrogen temperature, a linear response to applied electric current becomes essentially nonlocal, which can give rise to a number of new and counterintuitive phenomena including negative nonlocal resistance and current whirlpools. It has also been shown that, although both effects originate from high electron viscosity, a negative voltage drop does not principally require current backflow. In this work, we study the role of geometry on viscous flow and show that confinement effects and relative positions of injector and collector contacts play a pivotal role in the occurrence of whirlpools. Certain geometries may exhibit backflow at arbitrarily small values of the electron viscosity, whereas others require a specific threshold value for whirlpools to emerge.