The deformation, movement and breakup of a wall-attached droplet subject to Couette flow are systematically investigated using an enhanced lattice Boltzmann colour-gradient model, which accounts for not only the viscoelasticity (described by the Oldroyd-B constitutive equation) of either droplet (V/N) or matrix fluid (N/V) but also the surface wettability. We first focus on the steady-state deformation of a sliding droplet for varying values of capillary number ( $Ca$ ), Weissenberg number ( $Wi$ ) and solvent viscosity ratio ( $\beta$ ). Results show that the relative wetting area $A_r$ in the N/V system is increased by either increasing $Ca$ , or by increasing $Wi$ or decreasing $\beta$ , where the former is attributed to the increased viscous force and the latter to the enhanced elastic effects. In the V/N system, however, $A_r$ is restrained by the droplet elasticity, especially at higher $Wi$ or lower $\beta$ , and the inhibiting effect strengthens with an increase of $Ca$ . Decreasing $\beta$ always reduces droplet deformation when either fluid is viscoelastic. The steady-state droplet motion is quantified by the contact-line capillary number $Ca_{cl}$ , and a force balance is established to successfully predict the variations of $Ca_{cl}/Ca$ with $\beta$ for each two-phase viscosity ratio in both N/V and V/N systems. The droplet breakup is then studied for varying $Wi$ . The critical capillary number of droplet breakup monotonically increases with $Wi$ in the N/V system, while it first increases, then decreases and finally reaches a plateau in the V/N system.

Prediction of molecular parameters and material functions from the macroscopic viscoelastic properties of complex fluids are of great significance for molecular and formulation design in fundamental research as well as various industrial applications. A general learning method for computing molecular parameters of a viscoelastic constitutive model by solving an inverse problem is proposed. The accuracy, convergence and robustness of a deep neural network (DNN)-based numerical solver have been validated by considering the Rolie-Poly model for modeling the linear and non-linear steady rheometric properties of entangled polymer solutions in a wide range of concentrations. The results show that as long as the DNN could be trained with a sufficiently high accuracy, the DNN-based numerical solver would rapidly converge to its solution in solving an inverse problem. The solution is robust against small white noise disturbances to the input stress data. However, if the input stress significantly deviates from the original stress, the DNN-based solver could readily converge to a different solution. Hence, the resolution of the numerical solver for inversely computing molecular parameters is demonstrated. Moreover, the molecular parameters computed by the DNN-based numerical solver not only reproduce accurately the steady viscoelastic stress of completely monodisperse linear lambda DNA solutions over a wide range of shear rates and various concentrations, but also predict a power law concentration scaling with a nearly same scaling exponent as those estimated from experimental results.

The native extracellular matrix is highly dynamic with continuous mutual feedback between cells being responsible for many important cell function regulators. However, establishing bidirectional interaction between complex adaptive microenvironments and cells remains elusive. Herein an adaptive biomaterial based on lysozyme monolayers self-assembled at a perfluorocarbon FC40-water interface is reported. The dynamic adaptivity of interfacially assembled protein nanosheets is modulated independently of bulk mechanical properties by covalent crosslinking. This provides a scenario to establish bidirectional interactions of cells with liquid interfaces of varying dynamic adaptivity. This is found that growth and multipotency of human mesenchymal stromal cells (hMSCs) are enhanced at the highly adaptive fluid interface. The multipotency retention of hMSCs is mediated by low cell contractility and metabolomic activity involving the continuous mutual feedback between the cells and materials. Consequently, an understanding of the cells' response to dynamic adaptivity has substantial implications for regenerative medicine and tissue engineering.

The concentration dependence of linear viscoelastic properties of polymer solutions is a well-studied topic in polymer physics. Dynamic scaling theories allow qualitative predictions of polymer solution rheology, but quantitative predictions are still limited to model polymers. Meanwhile, the scaling properties of non-model polymer solutions must be determined experimentally. In present paper, the time–concentration superposition (TCS) of experimental data is shown to be a robust procedure for studying the concentration scaling properties of binary and ternary polymer solutions. TCS can not only identify whether power law scaling may exist or not, and over which concentration range, but also unambiguously estimate the concentration scaling exponents of linear viscoelastic properties for a range of non-model polymer solutions.

Terrain is a vital element in construction of virtual scene in the digital era. Despite considerable progress has been made in Generative Adversarial Network (GAN) based terrain modeling methods, their quality and controllability still cannot meet up the requirements of many emerging industries. The present work proposes a novel disentangled generative model, named as StyleTerrain, for achieving controllable high-quality terrain generation. It introduces disentangled representation learning into GAN-based terrain modeling methods for the first time. The model has been evaluated quantitatively. The results show a significantly short perceptual path length and the effectiveness of the disentanglement mechanism in controllable terrain generation, indicating that latent space disentanglement is a promising future direction for achieving generation controllability in GAN-based terrain modeling methods.

Enormous advances in physics of complex fluids/soft matter over last decades have rapidly transformed traditional industrial sectors in foods, personal care products, pharmaceuticals, paints, lubricants, ceramics, polymers, liquid crystals, high performance fibers, oil exploration and production into a digital era of formulation design and precision control over processing conditions from molecular viewpoint, and fertilizing a new industrial revolution. Development of high performance viscoelastic fluid solvers is of great significance for large scale digital manufacturing. In the present work, a portable and extensible scientific computing (PETSc) toolbox has been successfully integrated into the popular OpenFOAM CFD toolbox for carrying out large scale parallel computing of Turbulent Drag Reduction (TDR) and Elastic Turbulence (ET) in the isotropic turbulence flow. Its scalability has been evaluated and compared with the scalability of the OpenFOAM based viscoelastic fluid solvers. The results show that there are significant improvements.

Concentration scaling on linear viscoelastic properties of cellular suspensions has been studied by rheometric characterisation of Phormidium suspensions and human blood in a wide range of volume fraction under small amplitude oscillatory shear experiments. The rheometric characterisation results are analysed by the time-concentration superposition (TCS) principle and show a power law scaling of characteristic relaxation time, plateau modulus and the zero-shear viscosity over the concentration ranges studied. The results show that the concentration effect of Phormidium suspensions on their elasticity is much stronger than that of human blood due to its strong cellular interactions and a high aspect ratio. For human blood, no obvious phase transition could be observed over the range of hematocrits studied here and with respect to a high-frequency dynamic regime, only one concentration scaling exponent could be identified. For Phormidium suspensions with respect to a low-frequency dynamic regime, three concentration scaling exponents in the volume fraction Region I (0.36≤ϕ/ϕref≤0.46), Region II (0.59≤ϕ/ϕref≤2.89) and Region III (3.11≤ϕ/ϕref≤3.44) are identified. The image observation shows that the network formation of Phormidium suspensions occurs as the volume fraction is increased from Region I to Region II; the sol-gel transition takes place from Region II to Region III. In combination with analysis of other nanoscale suspensions and liquid crystalline polymer solutions reported in the literature, it is revealed that such a power law concentration scaling exponent depends on colloidal or molecular interactions mediated with solvent and is sensitive to the equilibrium phase behaviour of complex fluids. The TCS principle is an unambiguous tool to give a quantitative estimation.

A great progress has been made over the last decades in studying concentration scaling on rheometric properties of monodisperse polymer solutions.However,the effects of polydisperse polymer solutions on such a concentration scaling remain elusive.In this work,rheometric properties of industrially relevant polydisperse and high molecular weight polyacrylamide(PAAm)aqueous solution have been studied.The results show a concentration scaling of the characteristic relaxation time,the plateau modulus and the zero-shear viscosity across a concentration range from 10c* to 250c*.The time-concentration superposition principle is validated and extended in the data analysis of the terminal dynamic regime.The concentration scaling exponent of their shifting factors is significantly smaller than the results of monodisperse polymer solutions in good and θ solvents reported in the literature.The steady shear viscosity and shear stress of 18M PAAm aqueous solutions with relatively lower concentration(≤35c*)could also be superimposed into a master curve with the shear-thinning exponent of 0.73±0.03 and 0.27±0.03,respectively,over a wide range of shear rates in about six orders of magnitudes.However,for 18M PAAm aqueous solutions with higher concentration(≥48c*)in an intermediate shear thinning regime,the scaling exponent shows a pronounced concentration dependence.The shear thinning exponent of steady shear viscosity varies from 0.73 to 0.57 as concentration is increased,and then increases from 0.57 to 0.90 from sufficiently high shear rate.Further increasing shear rate,the shear-thinning exponent of 18M PAAm aqueous solutions at all concentrations converges to the lower bounded value observed in the relatively less concentrated(≤35c*)18M PAAm aqueous solutions,i.e.,0.73±0.02 for shear viscosity and 0.27±0.02 for steady shear stress,respectively.It reveals that the concentration effects of polydisperse polymer solutions could be greatly reduced by the dynamic"molecular individualism"in strong shear flow.

We introduce a “Rheo-chip” prototypical rheometer which is able to characterise model fluids under oscillatory flow at frequencies f up to 80 Hz and nominal strain up to 350, with sample consumption of less than 1 mL, and with minimum inertial effects. Experiments carried out with deionized (DI) water demonstrate that the amplitude of the measured pressure drop ΔPM falls below the Newtonian prediction at f≥ 3 Hz. By introducing a simple model which assumes a linear dependence between the back force and the dead volume within the fluid chambers, the frequency response of both ΔPM and of the phase delay could be modeled more efficiently. Such effects need to be taken into account when using this type of technology for characterising the frequency response of non-Newtonian fluids.

High-concentration (>100 g/L) solutions of monoclonal antibodies (mAbs) are typically characterized by anomalously large solution viscosity and shear thinning behavior for strain rates ≥103 s-1. Here, the link between protein-protein interactions (PPIs) and the rheology of concentrated solutions of COE-03 and COE-19 mAbs is studied by means of static and dynamic light scattering and microfluidic rheometry. By comparing the experimental data with predictions based on the Baxter sticky hard-sphere model, we surprisingly find a connection between the observed shear thinning and the predicted percolation threshold. The longest shear relaxation time of mAbs was much larger than that of model sticky hard spheres within the same region of the phase diagram, which is attributed to the anisotropy of the mAb PPIs. Our results suggest that not only the strength but also the patchiness of short-range attractive PPIs should be explicitly accounted for by theoretical approaches aimed at predicting the shear rate-dependent viscosity of dense mAb solutions.

Polyvinyl alcohol- (PVA-) based aerogels have attracted widespread attention owing to their low cost, eco-friendliness, and low density. However, the applications of PVA-based aerogels are limited by their flammability. In this study, a flame retardant, ammonium polyphosphate (APP), and a biopolymer, chitosan (CS), were added to polyvinyl alcohol (PVA), and the polymer was further crosslinked using boric acid (H3BO3). In the PVA aerogels, the negatively charged APP and positively charged CS formed a polyelectrolyte complex (PEC) through ionic interaction. Cone calorimetry and vertical burning tests (UL-94) indicated that the PVA composite aerogels have excellent flame retardancy; they could decrease the heat release rate, total heat release rate, and carbon dioxide (CO2) generation. Both PVA/H3BO3 and APP-CS in the composite aerogel could be burned to carbon, and the foamed char layer could act together to impart the PVA composite aerogels with good flame retardancy. Further, the decrease in the temperature at the backside of the aerogels with increasing APP-CS content, as determined by the flame-spraying experiment, indicated that the PVA-based aerogels with APP-CS can also serve as thermal insulation materials. This work provides an effective and promising method for the preparation of PVA-based aerogels with good flame retardancy and thermal insulation property for construction materials.

Nickel-based superalloys are one of the most industrially important families of metallic alloys at present. Selective Laser Melting (SLM), as one of the additive manufacturing technologies for directly forming complex metal parts, has been applied in the production of Inconel 718 components. Based on the more reasonable and comprehensive equivalent processing models (vaporization heat loss, equivalent physical parameters) for the nickel-based superalloy SLM process, an SLM molten pool dynamic behavior prediction model on the workpiece scale was established. Related equivalent processing models were customized by secondary development with the software Fluent. In order to verify the feasibility of the SLM molten pool dynamics model, the SLM single-pass employed to form the Inconel 718 alloy process was calculated. The simulated and experimental solidified track dimensions were in good agreement. Then, the influences of different process parameters (laser power, scanning speed) on the SLM formation of the Inconel 718 alloy were calculated and analyzed. The simulation and experimental solidified track widths were well-matched, and the result showed that, as a rule, the solidified track width increased linearly with the laser power and decreased linearly with the scanning speed. This paper will help lay the foundation for a subsequent numerical simulation study of the thermal-melt-stress evolution process of an SLM workpiece.

We have characterised the flow of semi-dilute PAAm solutions (3.3c* <= c <= 16.6c*) through a threedimensional cross-slot device (width to depth aspect ratio 2: 1) over a range of Weissenberg (0.13 <= Wi <= 88.5) and Elasticity (1.5 <= El <= 58.4) numbers by means of micro-particle imaging velocimetry (mu-PIV) and pressure drop measurements. The flow regimes are mapped into a Wi Re diagram. At intermediate Wi (12 <= Wi <= 45) we observe the formation of lip vortices in the inlet channels. At higher Wi (Wi >= 45) we observe the onset of an asymmetric flow regime, which occurs at a much higher Weissenberg number than previously reported in the literature. Increasing El in the asymmetric flow regime results in flow patterns that are markedly more time-dependent and unstable. The extensional rates measured along the centreline of the outlet channels are much lower than the corresponding nominal values. By means of an improved version of the numerical method that was used in our previous works, we have linked the measured velocity field with the "local Deborah number" field to quantify the spatial distribution of the deformation rate underwent by the polymer chains at high Wi flows near the stagnation point of the cross slot device. We measured the extensional viscosity and Trouton ratios of our polymer solutions over a range of 1 <= Wi <= 30. This work is of significance for the development of extensional rheometers for measuring the properties of low-viscosity fluids such as inks, blood, silk fibroin and protein solutions. (C) 2017 Elsevier B.V. All rights reserved.

This paper proposes an efficient and stable numerical method for modeling catheterization during endovascular surgeries. The guidewire‐catheter combination is treated as an elastic rod, which has very large resistance against twisting about its medial axis. A torsion free assumption is made, and the physical behavior of the rod is predominately governed by stretching and bending energies. This simplification greatly reduces the computational complexity and makes the model more stable, while the simulation results are still realistic enough for its application in endovascular surgeries. A contact handling algorithm that directly makes use of the volume data of the relevant tissues is proposed to simulate the interaction between the guidewire‐catheter combination and the aortic wall. During each simulation step, the penetration depth of each vertex in contact with the aortic wall is calculated using moving least squares surfaces, and the contact is then resolved in a position‐based manner. A comprehensive quantitative evaluation of the rod model is performed to validate its accuracy. Finally, the proposed approach is applied in a prototype system for simulation of endovascular aneurysm repair surgeries. Its efficiency and effectiveness are demonstrated in a real‐time interactive catheterization simulation. Copyright © 2016 John Wiley & Sons, Ltd.

This paper presents an interactive simulation system for surgical procedures of endovascular aneurysm repair. It extracts anatomical structure of clinic interest from patient‐specific X‐ray computed tomography or magnetic resonance imaging data by image segmentation techniques, and then reconstructs surface triangular meshes of these anatomical structures from the volumetric data. The core of the system is an interactive computer‐based simulation module. It consists of a physical modeling unit, a collision detection unit, a visualization unit, and a control unit. The integration of these units together makes it possible for users to interact with the system in real time, performing virtual catheterization, angiography, and stent graft deployment under a user‐specified rendering mode. The prototype system can be used as a cost‐efficient tool for surgical planning with patient‐specific anatomical geometry and for practice of surgical procedures before actual operation. Copyright © 2016 John Wiley & Sons, Ltd.

Computational methods based on Cartesian mesh are popular in simulating fluid flow with moving boundaries of complex geometry. In this paper, a sharp-interface Cartesian grid method is proposed for simulating viscoelastic fluid flow. We implement a finite volume numerical scheme with an improved Rhie-Chow interpolation on the open-source toolbox OpenFOAM. In the benchmark test of flow past a stationary cylinder, the velocity for Newtonian fluid flow is found to be second-order accurate with linear/bi-linear fitting functions for local reconstruction and third-order accurate with quadratic fitting functions. Only first-order accuracy is achieved with current solver for the Oldroyd-B fluid flows due to the difficulty in handling the extra stress near the boundary. However, our sharp-interface Cartesian grid method has been verified to correctly predict the extra stress on the surface of the cylinder. Simulation results of confined Oldroyd-B fluid flow past a pair of cylinders are also reported. A comparison between the proposed sharp-interface Cartesian grid method and a smoothed-interface immersed boundary method is carried out with respect to accuracy and efficiency. (C) 2016 Elsevier B.V. All rights reserved.

SummaryRhie–Chow interpolation is a commonly used method in CFD calculations on a co‐located mesh in order to suppress non‐physical pressure oscillations arising from chequerboard effects. A fully parallelized smoothed‐interface immersed boundary method on a co‐located grid is described in this paper. We discuss the necessity of modifications to the original Rhie–Chow interpolation in order to deal with a locally refined mesh. Numerical simulation with the modified scheme of Choi shows that numerical dissipation due to Rhie–Chow interpolation introduces significant errors at the immersed boundary. To address this issue, we develop an improved Rhie–Chow interpolation scheme that is shown to increase the accuracy in resolving the flow near the immersed boundary. We compare our improved scheme with the modified scheme of Choi by parallel simulations of benchmark flows: (i) flow past a stationary cylinder; (ii) flow past an oscillating cylinder; and (iii) flow past a stationary elliptical cylinder, where Reynolds numbers are tested in the range 10–200. Our improved scheme is significantly more accurate and compares favourably with a staggered grid algorithm. We also develop a scheme to compute the boundary force for the direct‐forcing immersed boundary method efficiently. Copyright © 2016 John Wiley & Sons, Ltd.

Flow instabilities of non-Newtonian fluids severely hamper the quality of products during various chemical processes, such as fibre spinning, extrusion, and film blowing. The origin of extrusion instability has been studied over many decades. However, no consensus has been reached among the research community so far. In this paper, the possible cause of extrusion instabilities is explored using the finitely extensible nonlinear elastic conformation-dependent (FENE-CD) model with a nonmonotonic constitutive curve. Many well-documented experimental phenomena are reproduced in our simulations, and it could be concluded that the nonmonotonic constitutive curve plays an essential role in extrusion instabilities. In addition, the results imply that the die exit singularity may generate or magnify oscillations.

Followed by our previous study, an OpenFOAM-based viscoelastic flow solver has been further validated through simulation of viscoelastic flow past a cylinder. The drag coefficients calculated by the Oldroyd-B model under the creeping flow in a range of Weissenberg (Wi) number are in good agreements with those reported in the literature. Using the linear Phan-Thien Tanner (L-PTT) model, time-dependent two-dimensional simulations of flow past cylinder have been carried out in a range of Wi number and Reynolds (Re) number, and revealed interesting cooperative effects of inertia and elasticity on the structural evolution of the wake behind the cylinder. The details of parallel computing strategy are analysed and discussed. The codes are evaluated for large scale parallel simulation of two-dimensional and three-dimensional contraction flow as well as two-dimensional flow past a cylinder. The key bottlenecks, which affect the scalability of parallel computing, are discussed. (C) 2014 Elsevier B.V. All rights reserved.

Nonlinear flows of polyacrylamide (PAAm) (\(M_{\text{w}} = 5.7 \times 10^{6}\,{\text{g}}/{\text{mol}}\)) aqueous solutions through a micro-fabricated, hyperbolic contraction geometry with high Hencky strain (\(\varepsilon_{{\text{H}}} = 3.7\)) have been characterized by micro-particle image velocimetry (\(\mu \)-PIV). Various flow dynamics regimes in a range of Weissenberg number (Wi) and Reynolds number (Re) are presented in a Wi–Re diagram. The symmetric corner vortices are only observed in the flow of low concentration PAAm solution (\(c/c^{*}=3.3\)). In a higher concentration (\(c/c^{*}=8.3\)), PAAm solution exhibits chaotic-like flow patterns in the strong nonlinear flow regime (\(Wi>350\)). Extensional deformation in nonlinear flows of Wi up to 860 has been analyzed. Furthermore, the local stretch experienced by the polymer chain in complex flow is systematically quantified and linked to the corresponding velocity vector fields, which are valuable for understanding the highly nonlinear flow phenomena.