Herschel-Bulkley Model Research Articles

Physical parametric study of bacterial biofilm disruption and removal by jet impingement: A CFD investigation

Bacterial biofilm formation is one of the most critical challenges in industrial and health systems. It is the leading cause of nearly 80 % of clinical infections. Biofilms are usually evaluated from the physiological point of view as microbial cells enclosed in an extracellular polymer and represent a complex, dynamic bacterial community. Cohesive mechanical forces hold the bacteria within the biofilm together. These forces contribute to the biofilm's mechanical and structural stability, resulting in its viscoelastic properties. Studying the biofilm's mechanical properties as a viscoelastic matter can provide a better understanding of the biofilm's characteristics and the survival strategies of bacteria in the biofilm state of life. In the present study, a 2D-axisymmetric RANS-CFD simulation model using the Volume Of Fluid (VOF) method was developed to track changes in biofilm surface and ripple formation across six biofilm thicknesses ranging from 15 μm to 115 μm, two substrate geometries including flat and curved, and two substrate roughnesses of 0.4 μm and 0.9 μm height. A modified Herschel-Bulkley model was employed to capture the biofilm's non-Newtonian shear-thinning behavior under high-velocity gas jet impingement. The results revealed the importance of biofilm thickness, substrate geometries, and properties like roughness in biofilm's mechanical behavior. Higher thickness of biofilm resulted in smaller jet-impingement region and more significant ripples formation. Biofilm on curved substrates decreased in thickness more rapidly than those on flat substrates. The substrate's geometry impacted biofilm folding patterns, removal, and mechanical behavior. Selected substrate roughnesses did not create any resistance against the mechanical removal of biofilms. Here, we successfully captured biofilms' non-Newtonian and shear-thinning behavior with numerical simulations consistent with previously reported experimental results. This could benefit industrial and health systems by tackling biofilm-related challenges and developing more accurate and detailed models of biofilms to optimize tools for drug testing or screening and enhance the models for in-vitro and in-vivo analysis.

Research on the flow characteristics of blasthole stemming slurry in open-pit mining

The flow characteristics of blasthole stemming slurry (BSS), predominantly comprising yellow mud (YM), tail mud (TM), or drilling cuttings (DC), were systematically investigated. Various influencing factors, including slurry mass concentration, the addition of TM or DC, and the mass ratio of TM to YM (TM/YM) and DC to YM (DC/YM), were meticulously examined. Experiments were conducted to assess the fluidity, rheological properties, and bleeding rate of BSS samples, which were prepared by manipulating slurry mass concentration and the proportions of TM or DC. The results indicate that the rheological properties of BSS are suitably described by the Herschel-Bulkley model. A critical mass concentration was identified, beyond which the flowability of BSS rapidly deteriorates. Replacing YM with an equivalent amount of TM at a mass concentration of 59% increased the yield stress by 167.30%, while reducing the bleeding rate to 0 within the 53%–59% mass concentration range. Conversely, replacing YM with DC at a mass concentration of 62% reduced the yield stress by 63.96%, while increasing the 60-minute bleeding rate from 0% to 1.44%. Increasing the TM/YM ratio resulted in reduced fluidity, elevated yield stress, and a variable degree of shear thickening. The degree of shear thickening was highest when the TM/YM ratio was 1, with significant impacts on differential viscosity at higher shear rates. On the other hand, increasing the DC/YM ratio enhanced fluidity, decreased yield stress, and influenced the degree of shear thickening and differential viscosity, with the highest shear thickening and lowest differential viscosity observed at a DC/YM ratio of 3. The bleeding rate of BSS consistently rose with the increase in the DC/YM ratio.

Empirical Assessment of African Oil Bean Husk as a Fluid-Loss Control Agent in Oil-Based Drilling Mud

Efficiency of drilling mud is partly determined by filtrate loss. In this article, research on suitability of African oil bean husk (AOBH), as a fluid loss control additive for oil-based drilling mud (OBM) is presented. Dry AOBH of particle sizes 63µm, 125µm and 250µm were used. Fourier Transform Infrared Spectrophotometer (FTIR) and Phenom Prox model of the Scanning Electron Microscope energy dispersive X-ray spectroscopy (SEM-EDS) were used to determine morphology and chemical properties of AOBH. OBM samples were prepared using the various sizes of AOBH as fluid-loss control additives and Grel Alphatex as industrial grade additives. Power Law Model and Herschel-Bulkley Models were used to model rheology of samples. Results show that AOBH contains mainly asphaltic compounds, is eco-friendly and biodegradable. Results from mud tests show close values in performances of AOBH and industrial grade. Filter cake thickness was 2.1mm – 2.8mm for AOBH-additives mud, but 2.3mm for industrial-additives mud. Filtrate loss was 2.0ml – 3.4ml for AOBH-additives mud, but 2.3ml for industrial-additives mud. Apparent viscosity for AOBH-additives mud was 77.5 -92.0cp, but 99.0cp for industrial–additives mud. Plastic viscosity for AOBH-additives mud was 73.0 - 81.0cp, but 87.0cp for industrial-additives mud. Yield point for AOBH-additives mud was 9.0 – 22.0, but 24.0 for industrial-additives mud. Both models show that efficiency of the mud containing AOBH in cleaning hole increased as grain size of AOBH reduced.

Numerical modelling of flow performance of fresh concrete considering rheological characteristics

The flow performance of concrete has a significant impact on the workability during the fresh stage, as well as the mechanical strength and durability after hardening. In this study, a three-dimensional numerical model for fresh concrete is developed to investigate the flow properties, including flowability, passing ability, and filling ability, by means of L-box and V-funnel tests. Corresponding experiments are carried out to validate the reliability of the presented model. Moreover, parametric investigations are performed to analyse the influence of relevant factors. The results show that the model predictions based on the Herschel-Bulkley model are more accurate compared to the Bingham model, indicating that the role of nonlinear rheological characteristics in the flow performance of fresh concrete needs to be properly considered. Both tL and tV are positively correlated with the power-law exponent, yield stress, and consistency index of the concrete mixture, whereas they are negatively correlated with the apparent density. The findings of this study can provide a deeper understanding of the underlying mechanism behind the flow behaviour of fresh concrete from a rheological perspective.

Screening transparent model fluids to emulate the rheological properties of high solid anaerobic digestate of food waste

Due to the opacity of high solid anaerobic digestate, optical visualization techniques (e.g., particle image velocimetry) cannot be used directly for measuring the flow field inside high solid anaerobic digestion (HSAD) systems. This study mainly focused on selecting suitable surrogate fluids for optical visualization techniques by comparing the flow curves, thixotropic properties, viscoelastic behavior and creep recovery properties of HSAD digestate with a total solid from 10 % to 15 % (w/w) and transparent model fluids. Results indicated that the Bingham model outperformed the power-law model and Herschel-Bulkley model in describing the flow curves of HSAD digestate, xanthan gum and laponite. The digestate and xanthan gum had a similar thixotropic kinetic coefficient of 0.003 and 0.004, respectively. Besides, the digestate and xanthan gum had a similar modulus transformation trend with a power function whose power exponents were 0.17 and 0.19, respectively. In general, xanthan gum can be a suitable substitute for HSAD digestate with a total solid from 10 % to 15 %. The results can guide the implementation of optical visualization techniques to understand the flow pattern within HSAD systems, and improve the mass and heat transfer efficiency during food waste disposal processes.

Fine-Tuning Filter Cake Sealing Performance: The Role of Particle Size in Hematite Weighted Water-Based Drilling Fluid.

Three hematite grades with different particle sizes (i.e., large, medium, and small) were evaluated, and the selection criterion was median particle size. The investigation involves the following stages: rheology, filtration, and filter cake formation. Different rheological models including Bingham, Power law, Herschel-Bulkley, and Robertson-Stiff were implemented to find the optimum model for characterizing fluid behavior. The results showed that medium-sized hematite particles produced the highest filtration volume, filter cake thickness, and filter cake permeability. These results were confirmed when a varied pore distribution filtration medium was used. The NMR results showed the same trend where the highest reduction in core porosity was found when a medium-size particle distribution was used. There is a minimum alteration in the rheological behavior of the drilling fluid as the particle size was varied, and the drilling fluids showed a shear-thinning behavior and were best described by the Herschel-Bulkley model. Particle size ratio emerges as a key factor for controlling and enhancing the filtration properties and filter cake characteristics.

Production and characterisation of microfluidized olive powder

SummaryMicrofluidization has been gaining popularity as a size reduction process in recent years. In this study, microfluidization technique was used for olives to change the cell wall structure and decrease the size of oil droplets. Olive powders were produced from green, black and raw olives using freeze drying following microfluidization at 1200 bar. Antioxidant activity was not affected significantly for all powders while total phenolic content decreased for green and raw olive powders with microfluidization. Among all olive powders, the one raw olive gave the highest antioxidant activity and phenolic content. In microscopic analysis, Scanning Electron Microscope images revealed that microfluidization results in finer particles which are self‐encapsulated by trapping the oil droplets. Stability analysis through Turbi Scan and rheological measurements of the powder suspensions showed that microfluidization process enables more stable suspensions having higher water holding capacity. Herschel–Bulkley model was found for the flow behaviours of the olive powder suspensions.

Influence of organic acids on the viscosity and rheological behavior of guar gum solution

The present study aims to determine the influence of four edible organic acids (ascorbic, citric, malic, and tartaric) at two concentrations (0.5, and 1 %) on the viscosity and rheological behavior of guar gum dispersion (0.2 %, w/v). The finding of this study revealed that the apparent viscosity of guar gum dispersions reduced when the shear rate increased. Additionally, the apparent viscosity of the guar gum dispersions reduced as the organic acids concentration increased from 0 to 1 %. The highest decrease in viscosity was related to 1 % ascorbic acid and the lowest was related to 0.5 % malic acid. The rheological behavior of dispersions were successfully modeled using Power law, Bingham, Herschel-Bulkley, and Casson models, and the Power law model was the best one for describing the behavior of guar gum dispersions containing organic acids. The Power law model showed good performance with the maximum r-value (mean = 0.9988) and least sum of squared error (SSE) values (mean = 0.0021) and root mean square error (RMSE) values (mean = 0.0119) for all samples. The consistency coefficient (k-value) values of the samples (Power law and Herschel-Bulkley models) reduced as the acid percent was increased. The sample containing 1 % tartaric acid had the lowest k-value and the sample containing 0.5 % ascorbic acid had the highest k-value. The flow behavior index (n-value) (Power law and Herschel-Bulkley models) of the samples increased when the acid percent was increased. In summary, the use of guar gum in food products containing high concentrations of tartaric and ascorbic acids is not recommended.

The basic characteristics of paste backfill materials based on highly active mineral admixtures: Part I. Preliminary study on flow, mechanics, hydration and microscopic properties

The cost performance of backfill materials in coal mines has long limited the widespread use of backfill technology. Therefore, developing backfill materials that are both cost-effective and high-performing is a pressing scientific issue that requires immediate attention. This study proposes replacing ordinary Portland cement (OPC) with highly active mineral admixtures, such as mineral powder and limestone powder, to prepare a green, low-cost, and high-performance coal mine backfill material. The use of mineral admixtures can improve the performance of the backfill material while reducing its environmental impact. The proposed approach is cost-effective and environmentally friendly. The study employed experimental tests and microscopic characterization methods, such as the slump test, hydration heat test, uniaxial compressive strength test, and microstructure test, to clarify the synergistic reaction mechanism of highly active mineral admixture-based paste backfill material (HAM-PBM). This clarification is helpful in regulating the macroscopic properties of hardened paste. The results show that: (1) The rheological properties of fresh HAM-PBM slurry are consistent with the Herschel-Bulkley model, and its fluidity meets the technical requirements for coal mine backfilling. The slump of fresh HAM-PBM slurry ranges from 140 to 145 mm, and the yield stress ranges from 3.188 to 12.819 Pa. (2) Highly active mineral admixtures significantly affect the early hydration process of HAM-PBM. The parameters of the hydration characteristics during the initial dissolution stage, acceleration stage, deceleration stage, and stabilization stage gradually decrease, while the duration of the induction stage gradually increases. This confirms that the early hydration activity of mineral powder (MP) and limestone powder (LF) is lower than that of OPC. (3) The uniaxial compressive strength (UCS) of the MP series exhibits an "anti-hook" change pattern, while the UCS of the LF series shows a decreasing change pattern. The microstructure, including the number of hydration products, microscopic density, and other characteristics, follows the same change pattern as the UCS. (4) Based on the synergistic reaction mechanism of hardened slurry, it is recommended that MP replace a maximum of 10 % of OPC and LF replace a maximum of 5 % of OPC. The need for composite replacement of OPC with MP and LF is clarified, resulting in a cost-effective coal mine backfill material. This study has contributed to the national "double carbon" policy and the low-cost backfilling application of coal mines.

Optimisation of Synchronous Grouting Mix Ratio for Shield Tunnels

During shield construction in underground spaces, synchronous grouting slurry is poured between the surrounding rock and tunnel lining to ensure stability. For synchronous grouting slurries, few studies have investigated the relationship between the rheological parameters and physical properties, grout-segregation mechanism, and anti-segregation performance. Therefore, we explored the relationships between the slurry rheological parameters, segregation rate, and bleeding rate. Cement, sand, fly ash, and bentonite were used to prepare the slurry, and the effects of different polycarboxylate water-reducing agents and dispersible latex powder dosages were studied. The rheological parameters of 16 groups of uniformly designed slurries were tested, and the data were fit using the Herschel–Bulkley model. The optimal mix ratio lowered the slurry segregation rate, and its rheological behaviour was consistent with the Herschel–Bulkley fluid characteristics. High-yield-shear-stress synchronous grouting slurries with high and low viscosity coefficients were less likely to bleed and segregate, respectively. The optimised slurry fluidity, 3 h bleeding rate, 24 h bleeding rate, segregation rate, coagulation time, and 28 days compressive strength were 257.5 mm, 0.71%, 0.36%, 3.1%, 6.7 h, and 2.61 MPa, respectively, which meet the requirements of a synchronous grouting slurry of shield tunnels for sufficiently preventing soil disturbance and deformation in areas surrounding underground construction sites.

Experimental study on the rheological behavior of superfine cement–sodium silicate slurry under seawater intrusion

Grouting is the effective method to prevent water inrush and reinforce fractured surrounding rocks in the construction of the submarine tunnel. The seawater intrusion will lead to obvious changes in the rheological properties of slurries, which can be adverse for the diffusion properties of slurries. This study aimed to identify the impact of seawater intrusion on the constitutive relationship of superfine cement–sodium silicate slurry (SC-S slurry). The chemical gelling time, viscosity, and rheological model of the slurry were studied. The concentrations of seawater ranged from 0% to 100%. The water–cement ratio ranged from 0.6 to 2.0. This study revealed that seawater significantly shortened the chemical gelling time of the slurry. The effect was more pronounced as the concentration of seawater increases. Furthermore, it was observed the rheological model of SC-S slurry will change from Bingham model to Herschel–Bulkley model with the increase in concentration of seawater. Rheological parameters that vary with time were also studied. The rheological constitutive models of slurry under seawater intrusion were established.

Multi-phase modelling of loose, unsaturated soil’s continuous motion using a three-phase Eulerian approach

This paper develops a numerical model for loose, unsaturated soil to represent its mixing and motion using Computational Fluid Dynamics. It was found that existing models are not suitable for loose, unsaturated soil. The Herschel–Bulkley model is more appropriate for sludge and mud-like materials, and the Kinetic Theory of Granular Flow is inapt because it lacks yield stress. To mitigate these shortcomings, a novel three-phase Eulerian model is proposed, which combines these two models with an air phase. Each phase includes a physical characteristic of loose, unsaturated soil: the Herschel–Bulkley phase includes yield stress, a solid phase includes granular behaviour, and the air fraction adds porosity. To identify the model’s parameters, density is measured, and a slump test is performed. The radial run-out of the slump test is used to determine the required yield stress in the model. Test simulations showed clear improvements over the existing models by combining yield stress and granular, lumpy behaviour successfully. Application of the new model to a 3D screw conveyor simulation showcases its ability to simulate continuous soil motion phenomena, such as avalanching caused by a recirculatory flow, soil spilling over the flight and soil flowing back to the previous pitch.

Study of Lactobacillus plantarum coated with Tremella polysaccharides to improve its intestinal adhesion.

The adhesion of probiotics to the intestine is crucial for their probiotic function. In previous studies, Tremella polysaccharides (TPS) (with sodium casein) have shown the potential to encapsulate probiotics and protect them in a simulated gastrointestinal tract. This study explored the effect of TPS (with sodium casein) on the adhesion of probiotics. Lactobacillus plantarum was coated with TPS and sodium casein in different proportions, and was freeze-dried. The rheological properties of the mixture of probiotics powder and mucin solution were determined by static and dynamic rheological analysis. Aqueous solutions of probiotic powder and mucin mixture exhibited pseudoplastic fluid rheological properties. The higher the proportion of TPS content, the higher the apparent viscosity and yield stress. The mixed bacterial powder and mucin fluid displayed thixotropy and was in accordance with the Herschel-Bulkley model. The TPS increased the bio-adhesive force of the probiotic powder and mucin. When using TPS as the only carbon source, the adhesion of L. plantarum to Caco-2 cells increased by 228% in comparison with glucose in vitro. Twelve adhesive proteins were also detected in the whole-cell proteome of L. plantarum. Among them, ten adhesive proteins occurred abundantly when grown with TPS as a carbon source. Tremella polysaccharides therefore possess probiotic properties and can promote the intestinal adhesion of L. plantarum. © 2024 Society of Chemical Industry.

Effect of ultrasound geometry on the production efficiency of damaged starch: Determining rheology parameters, and non-isothermal reaction kinetics

Present study investigates the effects of probe size geometry on thermodynamic kinetics, rheology, and microstructure of wheat and tapioca starch. Ultrasound treatment using different probe diameters (20 mm and 100 mm) significantly influenced the gelatinization process. Results showed reduced enthalpy (ΔH) and Gibbs energy (ΔG), indicating enhanced gelatinization efficiency. According to the results, using a 20 mm and 100 mm probe leads to a reduction of 52.7 % and 68.6 % in reaction enthalpy for wheat starch compared to native starch, respectively. Microstructure analysis revealed structural changes, with ultrasound treatment leading to granular fractures and a sheet-like structure with air bubbles. The rheological behavior of the starches is found to exhibit shear thinning behavior, with the Casson model providing the best fit for the experimental data. Moreover, rheology modeling using Herschel-Bulkley and power law models showed increased viscosity and shear stress in larger probes. Numerical simulation data demonstrated that probe size influenced ultrasonic pressure, sound pressure level, and thermal power dissipation density, affecting fluid motion and velocity field components. Moreover, the maximum dissipated power decreases from 8.43 to 0.655 mW/m3 with an increase in probe diameter from 20 to 100 mm. The average yield shear stress values are calculated as 3.36 and 3.14 for wheat and tapioca starches, respectively. The larger probe diameter leads to greater entropy increases, with tapioca starch showing a 4.72 % increase and wheat starch a 4.97 % increase, compared to 2.56 % and 3.11 %, respectively, with the smaller probe. Additionally, the Keller-Miksis model provided insights into bubble dynamics, revealing increased pressure and temperature with higher pressure amplitudes.

Synthesis of rGO/CoFe2O4 Composite and Its Magnetorheological Characteristics.

In this study, composite particles of rGO/CoFe2O4 were synthesized using a solvothermal method to fabricate a low-density magnetorheological (MR) material with enhanced sedimentation stability. The morphology and crystallographic features of rGO/CoFe2O4 were characterized via SEM, TEM, and XRD, and its magnetic properties were tested using VSM. The MR fluid was formulated by blending rGO/CoFe2O4 particles into silicone oil. Under different magnet strengths (H), a rotational rheometer was used to test its MR properties. Typical MR properties were observed, including shear stress, viscosity, storage/loss modulus, and dynamic yield stress (τdy) following the Herschel-Bulkley model reaching 200 Pa when H is 342 kA/m. Furthermore, the yield stress of the MR fluid follows a power law relation as H increases and the index changes from 2.0 (in the low H region) to 1.5 (in the high H region). Finally, its MR efficiency was calculated to be about 104% at H of 342 kA/m.

Study on operational temperature of magneto-rheological fluid and design dimensions of magneto-rheological damper for optimization

This study aims to restrict the upper limit for flow gap and effective length in magnetorheological (MR) damper for optimal performance. Initially, the sedimentation study of in-house MR fluid (25%) shows that an 8% reduction in the sedimentation ratio with the addition of additive and nonlinear Herschel-Bulkley (HB) model fit reflects a 32.5% decrease in average yield stress with increasing currents when the parallel plate gap is increased from 1 mm to 2 mm. Owing to this decrease in yield stress, further study is extended to fabricate two MR dampers with limit values (LV) of flow gap and effective length with a common magnetic outer cylinder. Testing results of MR dampers revealed a 72% reduction in damping force at 0.8 A current when the LV’s is increased from LV-1 to LV-2. Selecting LV-1 over LV-2 as the upper limit for any design optimization will give the MR damper optimal performance. At higher input parameters, amplitude has a 135% greater impact on damping force than frequency and current. It is also demonstrated that saturation magnetization depends on the applied magnetic field and input loading parameters. Finally, gravimetric analysis shows that the effectiveness of the MR fluid and magnetic particle starts to decline after 322 °C and 400 °C.

3D printing of rice starch incorporated peanut protein isolate paste: Rheological characterization and simulation of flow properties

This study investigates the viscosity and creep behavior of peanut protein isolate (PPI) paste incorporated with rice starch (RS) for potential applications in 3D printing. The change in flow properties during the 3D printing was also studied by numerical simulation. The paste exhibited shear-thinning behavior with yield stress. The pressure predicted from the Herschel-Bulkley model showed higher values than those derived from the Power-Law model. The PPI and RS levels had negligible influence on velocity and shear rate; however, they showed greater dependence on the inflow rate. The fractional element model described the creep data well (R2 > 0.9). The addition of PPI resulted in increased viscosity, simulated pressure, and mean extrusion force, with similar effects observed for RS, except at higher PPI levels. Furthermore, the 3D-printed objects revealed that deformations were pronounced at low concentrations of PPI and RS, while resolution suffered when employing higher concentrations of PPI and RS. Industrial relevanceUsing peanut protein isolate, a plant-based high protein ingredient in 3D printing, reduces energy consumption, thereby reducing carbon footprints, offers improved functional properties, and diversifies dietary options by offering an alternative protein source from peanuts. The printing is influenced by the rheological properties of food ink. Thus, knowing the rheological properties of food ink can help researchers and industries to prepare food inks with desired properties. The observations of numerical simulation of this work have the potential to offer practical insights for designing 3D printing systems. In summary, this work has the potential to aid in improving and developing food ink for 3D printing, hence enhancing the performance of extrusion-based 3D food printers.

The Optimization Study of Rheological Characteristics of Wind Power Grease Based on Gel-State.

The gel-state grease plays a vital and indispensable role in the long-term operation of wind turbines. To reduce carbon emissions and increase the reliability of wind turbines, this paper takes the gel-state Mobil SHC 461WT grease as the study object. Firstly, the rheological properties of the gel-state Mobil SHC 461WT grease were investigated using the Anton Paar MCR302 rotational rheometer. Secondly, the rheological characteristics of three different gel states of the Mobil SHC 461WT grease (additive content of 0.1% of RFM3000, SK3115, and PV611, respectively, in the gel-state Mobil SHC 461WT grease) were optimized under the same conditions. Finally, according to the experimental results and the Herschel-Bulkley (H-B) model, the RFM3000 additive has the best effect on improving the rheological characteristics of the gel-state Mobil SHC 461WT grease. This research provides a new idea and direction for the technological advancement of the gel-state grease industry.

Dual-stage theoretical model of magnetorheological dampers and experimental verification

The theoretical model for predicting the damping characteristics of magnetorheological dampers (MRDs) not only facilitates the optimization of MRD parameters, but also provides assistance for the theoretical design of MRDs. However, some existing models have limitations in fully characterizing the damping characteristics of MRDs. In this paper, the working stage of MRDs was categorized into yield and pre-yield stages based on whether the internal magnetorheological fluid attains the dynamic shear yield state or not, and the Herschel–Bulkley model with pre-yield viscosity (HBPV) and improved polynomial model (IPOL) were employed to respectively characterize the yield and pre-yield stages of MRDs. Subsequently, the HBPV-IPOL model was proposed to characterize the complete damping characteristics of MRDs in low-frequency vibration conditions, with considering the local loss effect of the fluid in the model. To accurately characterize the magnetic induction intensity in the MRD damping channel, employing the steady-state finite element method for magnetic field analysis; on this basis, dividing the damping channel to investigate the variation trends of the magnetic induction intensity in different regions. Simultaneously, the zero-field region hypothesis was proposed to quantitatively consider the influence of minute magnetic induction intensity in the traditional zero-field regions on the damping characteristics of MRDs. Finally, integrating the impact trends of currents in different regions, and employing the HBPV model to determine the impact magnitude of each region within the damping channel on the damping characteristics of the MRD in the yield stage. In the pre-yield stage, polynomial curves were fitted to experimental damping force–velocity curves, and the obtained polynomials were employed to predict the damping characteristics. Extensive experiments have been conducted on MRD samples to assess the predictive performance of the model on MRD damping characteristics under sinusoidal displacement excitation vibration conditions with different excitation currents, vibration frequencies and vibration amplitudes.

NUMERICAL SIMULATION OF BLOOD FLOW THROUGH NORMAL AND STENOTIC CAROTID ARTERY

The carotid artery sinus is often the site of vascular diseases such as atherosclerosis, which may induce cerebral stroke. Individual differences in the carotid artery can lead to different possibilities for atherosclerosis, and the different hemodynamics of the carotid artery with stenosis can help to reveal the occurrence of atherosclerosis. In this work, the hemodynamics in the patient-specific carotid bifurcation are studied by using the modified Herschel–Bulkley model. Calculations show that the helical flow is presented in the healthy carotid sinus and disappears in the stenosed carotid sinus. The disappearance of helical flow in the carotid artery enhances the risk of atherosclerosis. The atherosclerotic lesion is more prone to occur in the distal portion of the carotid sinus than in the proximal portion where the oscillatory shear index (OSI) is also high. The presence of stenosis makes the atherosclerotic lesion develop toward the proximal portion. The disappearance of helical flow in the carotid artery is an important risk signal for the occurrence of atherosclerosis.