Rheological Model Research Articles

Designing Advanced Drug Delivery Systems: Core-Shell Alginate Particles through Electro-Fluid Dynamic Atomization.

Innovations in drug delivery systems are crucial for enhancing therapeutic efficiency. Our research presents a novel approach based on using electro-fluid dynamic atomization (EFDA) to fabricate core-shell monophasic particles (CSMp) from sodium alginate blends of varying molecular weights. This study explores the morphological characteristics of these particles in relation to material properties and process conditions, highlighting their potential in drug delivery applications. A key aspect of our work is the development of a mathematical model that simulates the release kinetics of small molecules, specifically sodium diclofenac. By assessing the diffusion properties of different molecules and gel formulations through transport and rheological models, we have created a predictive tool for evaluating the efficiency of these particles in drug delivery. Our findings underscore two critical, independent parameters for optimizing drug release: the external shell thickness and the diffusivity ratios within the dual layers. This allows for precise control over the timing and intensity of the release profile. This study advances our understanding of EFDA in the fabrication of CSMp and offers promising avenues for enhancing drug delivery systems by tailoring release profiles through particle characteristic manipulation.

The Slump Flow of Cementitious Pastes: Simulation vs. Experiments.

Understanding the transient properties of cementitious pastes is crucial for construction materials engineering. Computational modeling, particularly through Computational Fluid Dynamics (CFD), offers a promising avenue to enhance our understanding of these properties. However, there are several numerical uncertainties that affect the accuracy of the simulations using CFD. This study focuses on evaluating the accuracy of CFD simulations in replicating slump flow tests for cementitious pastes by determining the impact of the numerical setup on the simulation accuracy and evaluates the transient, viscosity-dependent flows for different viscous pastes. Rheological input parameters were sourced from rheometric tests and Herschel-Bulkley regression of flow curves. We assessed spatial and temporal convergence and compared two regularization methods for the rheological model. Our findings reveal that temporal and spatial refinements significantly affected the final test results. Adjustments in simulation setups effectively reduced computational errors to less than four percent compared to experimental outcomes. The Papanastasiou regularization was found to be more accurate than the bi-viscosity model. Employing a slice geometry, rather than a full three-dimensional cone mesh, led to accurate results with decreased computational costs. The analysis of transient flow properties revealed the effect of the paste viscosity on the time- and shear-dependent flow progress. The study provides an enhanced understanding of transient flow patterns in cementitious pastes and presents a refined CFD model for simulating slump flow tests. These advancements contribute to improving the accuracy and efficiency of computational analyses in the field of cement and concrete flow, offering a benchmark for prospective analysis of transient flow cases.

Establishment of dynamic prediction model on morphology development of polypropylene/polyamide 6 blends under in-situ fibrillation flow

In this work, the morphology development of polypropylene (PP)/polyamide 6 (PA6) blends was thoroughly investigated under in-situ fibrillation process, including shear mixing flow and uniaxial elongational flow. By establishing rheological constitutive model based on Trouton Rules, the shear and elongational rheological characteristic parameters of PP and PA6 were obtained for the establishment of the prediction model. In the shear mixing process, different screw speed was applied to evaluate the effects of the shear flow on PA6 original particle size in PP/PA6 blends. In the uniaxial stretching process, the elongational flow field characteristics were obtained through solving dynamic equation with Fourth-order Runge-Kutta method. And the evolution of PA6 droplets in obtained elongational flow field characteristics was analyzed by combining SEM results of PP/PA6 in situ fibrillar composites and theorical parameters of the deformation and breakup of the droplets (the reduced capillary number Ca*). Finally, based on force balance theory, the dynamic model of morphology development of PA6 dispersed phase in PP matrix was defined under the whole in situ fibrillation process. By comparing with experimental values, it was found that the established model was supposed to be able to predict the phase morphology development of polymer droplets well when the original particle size was smaller, and when the original particle size was larger, the coalescence between the droplets should be further considered.

Time-dependent behavior of reinforcement rock unit anchored by energy-absorbing bolt for large deformation control in tunneling

The energy-absorbing bolt is designed to counteract both burst-prone and squeezing rock conditions in rock excavation. In this paper, the mechanical contribution of energy-absorbing bolts installed systematically around tunnels excavated in rock masses was investigated based on the assumptions of the reinforced rock unit (RRU) model. The time-dependent behavior of rock with a large deformation problem was simulated using a Nishihara model, while that of an energy-absorbing bolt was simplified by a rheological model connecting a Hookean elastic element and a Saint-Venant element in series. The mechanical model of RRU anchored by an energy-absorbing bolt was established by connecting the rock mass model and the energy-absorbing bolt model in a parallel combination. The closed-form solution presented the time-dependent behavior of RRU under an instantaneously applied tension stress and an linearly increasing load, respectively. The results showed the reinforcement could reduce the time-dependent deformation of the reinforced region of tunnels significantly. A preliminary estimate of NPR-bolt reinforcement for large-deformation controls in the Muzhailing tunnel was carried out using the proposed model. The results showed that the NPR cables could have critical effects in controlling the large deformation of the tunnel.

Calibration of Thixotropic and Viscoelastic Shear-Thinning Fluids Using Pipe Rheometer Measurements

Some non-Newtonian fluids have time-dependent rheological properties like a shear stress that depends on the shear history or a stress overshoot that is a function of the resting time, when fluid movement is started. The rheological properties of such complex fluids may not stay constant while they are used in an industrial process, and it is therefore desirable to measure these properties frequently and with a simple and robust device like a pipe rheometer. This paper investigated how the time-dependent rheological properties of a thixotropic and viscoelastic shear-thinning fluid can be extracted from differential pressure measurements obtained at different flowrates along a circular pipe section. The method consists in modeling the flow of a thixotropic version of a Quemada fluid and solving the inverse problem in order to find the model parameters using the measurements made in steady-state conditions. Also, a Maxwell linear viscoelastic model was used to reproduce the stress overshoot observed when starting circulation after a resting period. The pipe rheometer was designed to have the proper features necessary to exhibit the thixotropic and viscoelastic effects that were needed to calibrate the rheological model parameters. The accuracy of rheological measurements depends on understanding the effects that can influence the observations and on a proper design that takes advantage of these side effects instead of attempting to eliminate them.

Stress Evolution of the Main Himalayan Thrust Fault Induced by the Mw 7.8 Gorkha Earthquake

ABSTRACT The Mw 7.8 Gorkha earthquake that occurred in 2015 is the largest thrust event in the middle of the main Himalayan thrust fault zone (MHT) in the past 81 yr. Its impact on the regional tectonic stress state and future seismic risks is a significant scientific issue worthy of in-depth analyses. In this study, we inverted the planar fault-slip model (the planar model), the flat-ramp fault-slip model (the flat-ramp model) and the double flat-ramp fault-slip model (the double flat-ramp model) to analyze the effect of the fault geometry, based on the steepest descent method (SDM) and the layered earth model. Compared with the flat-ramp model, the planar model exhibits a wider slip distribution in the down-dip direction of the main rupture zone, whereas the double flat-ramp model shows a larger coseismic slip on the middle ramp at the depth of 7.5–11.5 km. Those slip differences produce larger stress shadow areas in the above models, but for a blind thrust event induced by a low-dip thrust fault, this does not significantly change the distribution mode of coseismic Coulomb stress change (ΔCFS) in the three models. Namely, there is an obvious stress release in the main rupture but an obvious stress loading in the up-dip and down-dip directions of the main rupture zone. Based on the Burgers rheological model, we calculated the postseismic viscoelastic Coulomb stress change (V−ΔCFS) and the cumulative Coulomb stress change (C−ΔCFS) induced by the Gorkha earthquake in the flat-ramp model and comparatively analyzed the evolution pattern of coseismic and postseismic stresses. Our results indicate that the variation trend of postseismic stress in the lithosphere is opposite to that of the coseismic ΔCFS. The postseismic viscoelastic relaxation promotes the slip of the flat-ramp structure at the depth of 10–25 km, and the stress unloads in the shallow and deep part simultaneously. As a blind thrust event, the coseismic ΔCFS still plays a dominant role in the shallow part after 50 yr, whereas the loading C−ΔCFS in the deep part of the MHT is greatly weakened by the postseismic V−ΔCFS. Seismic risks still exist in the unruptured area on the west side of the mainshock and the shallow Main Frontal thrust.

Development and rheological modeling of dietary fiber and policosanol plant-based bigels for potential food applications

Bigels are composite materials made by two phases with different polarities (i.e., an oleogel and a hydrogel) mixed between them without the addition of emulsifiers. Owing to their versatile rheological properties, they can be used for designing new products for food industry, or for cosmetics and pharmaceutical applications. In the past, different models have been proposed to relate their rheological properties to single phases characteristics and volume fraction. This paper proposes the rheological characterization and modeling of bigels prepared with citrus fiber particle gels (as the aqueous phase) and policosanol-based oleogels by investigating the effects of the ratio between rheological properties of phases and of the dispersed phase volume fraction. Both components (i.e., citrus fiber and policosanol) exhibit interesting properties for preparing plant-based healthy foodstuffs. Rheological characterization was carried out revealing that O/W bigels were formed at low fractions of oleogel added to gelled suspension whereas, at higher fractions, a transition through a matrix-in-matrix systems and, finally, a phase inversion occurred. The trend of phase angle at 1 Hz with oleogel volume fraction was used as a criterion to highlight the phase transition, as confirmed by confocal microscopy. Two models were proposed for predicting the rheological behavior of samples with both phase arrangements.

Modelling of fluid mud flow based on a three-dimensional hydrodynamic model : incorporating a 3D rheological model

Modeling fluid mud in estuaries and coastal areas is a complicated task due to its non-Newtonian characteristics. A continuous modeling approach was adopted to investigate the laminar flow of fluid mud, with a three-dimensional (3D) form of the Herschel–Bulkley rheological model introduced into the finite volume coastal ocean model (FVCOM) to calculate the apparent viscosity of fluid mud. The model was validated against two flume experiments for the laminar flow of fluid mud. The results showed that the developed model was capable of accurately reflecting the continuous distribution of velocity and density from the near-bottom to the upper water column. Based on the validated model, the difference between the 3D rheological model and a 1DV rheological model on the simulation results was assessed. The study found the results of the 1DV model and the 3D model show obvious differences. This illustrates the significant effect of apparent viscosity in horizontal direction taken into account by the 3D rheological model.

Decreased erythrocyte aggregation in Glenn and Fontan: univentricular circulation as a rheologic disease model.

In the Fontan palliation for single ventricle heart disease (SVHD), pulmonary blood flow is non-pulsatile/passive, low velocity, and low shear, making viscous power loss a critical determinant of cardiac output. The rheologic properties of blood in SVHD patients are essential for understanding and modulating their limited cardiac output and they have not been systematically studied. We hypothesize that viscosity is decreased in single ventricle circulation. We evaluated whole blood viscosity, red blood cell (RBC) aggregation, and RBC deformability to evaluate changes in healthy children and SVHD patients. We altered suspending media to understand cellular and plasma differences contributing to rheologic differences. Whole blood viscosity was similar between SVHD and healthy at their native hematocrits, while viscosity was lower at equivalent hematocrits for SVHD patients. RBC deformability is increased, and RBC aggregation is decreased in SVHD patients. Suspending SVHD RBCs in healthy plasma resulted in increased RBC aggregation and suspending healthy RBCs in SVHD plasma resulted in lower RBC aggregation. Hematocrit corrected blood viscosity is lower in SVHD vs. healthy due to decreased RBC aggregation and higher RBC deformability, a viscous adaptation of blood in patients whose cardiac output is dependent on minimizing viscous power loss. Patients with single ventricle circulation have decreased red blood cell aggregation and increased red blood cell deformability, both of which result in a decrease in blood viscosity across a large shear rate range. Since the unique Fontan circulation has very low-shear and low velocity flow in the pulmonary arteries, blood viscosity plays an increased role in vascular resistance, therefore this work is the first to describe a novel mechanism to target pulmonary vascular resistance as a modifiable risk factor. This is a novel, modifiable risk factor in this patient population.

Numerical investigation into effects of rheological properties on grout flow in rock fracture using Herschel-Bulkley model

Grouting is an essential technique for reducing the hydraulic conductivity and enhancing the strength of rock mass used in the Dongzhuang hydro-junction project. The rheological properties of grout are not to be disregarded during grouting. In this study, a numerical grouting model is established by combining a modified Herschel–Bulkley (HB) rheology model with the level set method. The effects of rheological parameters (power-law index n, consistency coefficient k, and yield stress τ0) on distribution pattern and flow characteristics of the grout are investigated. The HB model is more effective and precise than the Bingham model for predicting rheological characteristics. Numerical results indicated that distribution pattern and grout volume are primarily determined by n. A low shear rate inhibits the horizontal distribution and reduces the filling capacity of the grout, thus resulting in minimal deposition in the fracture. Grouts with a higher n and k require higher pressure to distribute around the fracture. The reduction in water volume in the fracture is calculated to provide comprehensive understanding into the sealing efficiency of the grout by varying the rheological parameters. This study provides valuable guidance regarding the different rheological parameter of grout in fractures, in addition to a novel concept for the optimal design of grouting distribution.

Smoothed particle hydrodynamics approach for modelling submerged granular flows and the induced water wave generation

In this study, we develop a Smoothed Particle Hydrodynamics (SPH) 2D-model for simulating fully submerged granular flows and their arising water waves. The granular particles are characterised by a non-Newtonian flow pattern, following a Casson constitutive law, generalised by applying the infinitesimal strain theory to avoid numerical singularities inherited from the original law. The implementation of this rheological model on the weakly compressible viscous Navier-Stokes equations enables the simultaneous modelling of the motion of granular flows and their resulting water waves, establishing a monolithic representation of fluid-structure coupling. The novelty of this model lies in the numerical continuity of the generalised rheological model based mainly on the yield stress criterion, which is computed purely from the mechanical properties of granular materials, including internal friction, cohesion, and viscosity coefficients. The proposed SPH model is validated through two benchmarks available in the literature, representing a submarine landslide along an inclined plane and an immersed granular column collapse. The outcomes of our study illustrate the effectiveness of the proposed model in accurately predicting the motions of submerged granular masses and their resulting water waves, which is crucial for accurately predicting the behaviour of underwater landslides and other natural hazards.

Rheological model of cement-based material slurry with different water-cement ratio and temperature

PurposeThe purpose of this paper is to obtain a constitutive model of cement-based material in the rheological stage, which owns the different water-cement ratio (w/c) and temperature and have a significant impact on the workability of concrete materials.Design/methodology/approachIt is introduced a modified Arrhenius equation into the Herschel–Bulkley model, which is widely applied in rheological analysis and constructed an ordinary differential equation (ODE) of w/c from the Navier–Stokes equation. By solving the ODE, an approximate constitutive relation of cement-based materials included w/c and temperature is derived. Compared with the experimental results, the present model is validated.FindingsThe shear stress and shear rate curves with different w/c and temperature are simulated by the present method, and the present model can be applied to analyze the changes of apparent viscosity in cement-based material slurry as the w/c and temperature varying.Originality/valueThis work gives a mathematical model, which can effectively approximate the shear stress–shear rate relation with different w/c and temperature in the rheological stage of cement-based material.

Exploring the interplay between thermo-oxidative degradation and asphalt aging in thermoplastic polyurethane-modified asphalt: Mechanisms, properties, and performance evolution

The aging behavior of thermoplastic polyurethane-modified asphalt (TPUMA) is intricate and the mechanisms of its thermal degradation are not well understood. This study examines the viscoelastic, chemical and morphological characteristics of thermoplastic polyurethane modified asphalt (TPUMA) under different aging conditions (RTFOT/PAV). The rheological master curve model of the S parameter was used to analyze the fitting effect on TPUMA, with SBS (styrene–butadiene–styrene) modified asphalt serving as the control group. The relationship between the phase angle plateau area and polymer aging degradation was elucidated. This study investigates the impact of polymer degradation on the high-temperature rheological behavior and medium-temperature fatigue properties of asphalt through temperature sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Fourier transform infrared spectrometer (FTIR) and confocal laser scanning microscopy (CLSM) are used to qualitatively and quantitatively analyze the chemical composition and morphological evolution of TPUMA during thermal-oxidative degradation. The findings suggest that TPUMA's performance changes in the aging environment is result from the dual coupling effect of polymer degradation and asphalt oxidative hardening. The closely arranged isocyanate (-NCO) and polar component molecular chains in asphalt slow down its oxidation speed, which enhances the aging and deformation resistance of TPUMA. The successful blending of TPU and asphalt was confirmed, and the degradation degree of the polymer was quantitatively characterized by the percentage of the degraded area. The results provide insights to better understand the interplay between TPU degradation and asphalt oxidation.

Effect of thermal-oxidative and mechanical degradation of recycled LDPE on foaming

In this study, we investigated the effect of recycling process on the molecular structure, viscoelasticity and foaming behavior of low density polyethylene (LDPE). A series of LDPE samples with different recycling process was prepared by multiple extrusion using a twin-screw extruder. The molecular weight distribution (MWD) was characterized by gel permeation chromatography (GPC). Wider MWD indicated the generation of higher molecular weight products. Small-amplitude oscillation rheology showed reduced loss factors, indicating that the chain entanglement was more difficult to relax. Moreover, nonlinear viscoelasticity was investigated using elongational rheology and molecular stress function (MSF) model. The results showed a steeper strain hardening exhibited in recycled LDPE. The correlated parameter β in the MSF model indicated that the recycling did not significantly change the branches regularity in LDPE, while the increasing [Formula: see text], the other correlated parameter, indicated that the chain entanglement was enhanced, which was corresponded to the improvement of high molecular weight component. The foaming results revealed that the recycled LDPE had finer cellular structure and higher nucleation density. Moreover, despite adding PP and active CaCO3 to simulate the impurities, the foamability loss of these mixed samples was well restricted and still valuable. Recycled LDPE is instead better than its corresponding virgin one in foaming performance, exhibiting the application potential for further developments.

On the Application of Non-Linear Rheological Models In Longitudinal Fracture Analysis of Beams Made of Functionally Graded Materials

On the Application of Non-Linear Rheological Models In Longitudinal Fracture Analysis of Beams Made of Functionally Graded Materials

Analysis of Methodology for Selecting Rheological Model of Cement Slurry for Determining Technological Parameters of Well Casing

Analysis of Methodology for Selecting Rheological Model of Cement Slurry for Determining Technological Parameters of Well Casing

VARIATIONAL PRINCIPLE FOR A FRACTAL LUBRICATION PROBLEM

Micro/nanoscale lubrication must take into account the fractal profile of the shaft and bearing surfaces. A new fractal rheological model is proposed to describe the properties of the non-Newtonian fluid, and a fractal variational principle is established by the semi-inverse method, and finally the Lagrange multipliers can be found in the obtained variational formulation. This work provides a new fractal approach to nano/micro lubrication.

Движение слоя сыпучей среды по рабочим органам вибрационных конвейеров

Theoretical studies of vibrational transportation of bulk material are presented. The dependence of the vibration transportation speed on the frequency and amplitude of oscillations is investigated, as well as the methodology for selecting the optimal law of oscillations of the load-bearing surface of the working element. The differences between the movement of a single layer of real bulk material along the working element of a vibratory conveyor and the movement of a material particle on a vibrating surface are considered. The formula forvibration displacement speed is modified by introducing a correction coefficient that takes into account the air permeability of the material. The necessity of studying the process of vibration transportation based on an elastic-viscous-plastic rheological model of the moving vibratory layer of bulk cargo is justified.

Scraper factors investigation on Al2O3 paste flow based on marine predators algorithm-bidirectional gated recurrent unit pseudo-lattice Boltzmann method for stereolithography molding

The coating process is an essential part of stereolithography technology to mold alumina paste, achieved using a scraper. The characteristics of the scraper (geometry and roughness) are investigated to discover the potential influence mechanism on the coating process. To complete the analysis, the bidirectional gated recurrent unit (BiGRU) optimized by the marine predator algorithm (MPA) is proposed to provide a predicted model for the rheological data instead of the traditional fitting by using the known rheological equations. Then, a pseudo-lattice Boltzmann (pseudo-LB) method is proposed to conduct the coating flow simulation without a specific rheological equation, where the predicted rheological model is applied to obtain the relaxation time for each iteration. Based on the above MPA-BiGRU pseudo-LB method, three geometries and different roughnesses are explored for the coating process. The results indicate that the rectangle geometry suits the large coating speed, and the trapezium geometry is recommended for conditions with the small coating speed. The roughness significantly affects the coating process with the rectangle geometry, and the smoother scraper generates a minor disturbance. However, it is almost ineffective in the cases with trapezium geometry.

A rheological model for spheroids including extra-cellular matrix

Abstract The rheology of spheroids has been studied intensively recently and it was shown that the presence of the Extra-Cellular Matrix (ECM) can have significant effects on the overall behaviour of these biological systems. Collagen I can indeed be a proxy between cells and bring new intriguing effects, as its content increases. To investigate these effects further, a two-phase emulsion model is proposed including interactions between cells and the ECM. Starting with the single cell and collagen individual viscoelastic properties, the model can be tested against previously obtained data for spheroids. The model has interesting features and capabilities for it covers a variety of behaviours and uses fitting parameters such as collagen and cell concentration, as well as adhesion energy. It is shown that the final intercellular collagen content can be large as compared to the initial one, and that this increase in collagen content induces a larger packing of cells, together with a larger adhesion energy.