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Laboratory sciences and disease diagnostics need accelerated medical tests, ease of testing for patients, and lower diagnostic costs. In this respect, one of the most innovative methods is paper-based microfluidic analysis tools, called micro-PAD. Since the chemical-based micro-PADs need sufficient blood to show an accurate blood test, the shape of the micro-PADs, the blood quantity, and the droplet flow to reach the end of the microchannels are important. Therefore, this research showed the liquid droplet motion on a heterogeneous (hydrophobic and hydrophilic) surface using the lattice Boltzmann method, and two star-shaped micro-PADs were modeled to investigate the effect of the droplet size and the droplet deflection from the center of the micro-PAD on liquid flow in microchannels. Based on the obtained results, fluid behavior was similar in two patterns (ten-pointed pattern and four-pointed pattern). This study compared the effects of parallel, convergent, and divergent channels in a four-pointed pattern on fluid velocity. The off-center error of the droplet was considered at the initial moment. The obtained results confirmed the direct relationship between the increased deviation of the center and the lack of uniformity in the fluid penetration. The present simulation results were validated against the laboratory data. [ABSTRACT FROM AUTHOR]

Uncertainty quantification is becoming a key tool to ensure that numerical models can be sufficiently trusted to be used in domains such as medical device design. Demonstration of how input parameters impact the quantities of interest generated by any numerical model is essential to understanding the limits of its reliability. With the lattice Boltzmann method now a widely used approach for computational fluid dynamics, building greater understanding of its numerical uncertainty characteristics will support its further use in science and industry. In this study we apply an in-depth uncertainty quantification study of the lattice Boltzmann method in a canonical bifurcating geometry that is representative of the vascular junctions present in arterial and venous domains. These campaigns examine how quantities of interest—pressure and velocity along the central axes of the bifurcation—are influenced by the algorithmic parameters of the lattice Boltzmann method and the parameters controlling the values imposed at inlet velocity and outlet pressure boundary conditions. We also conduct a similar campaign on a set of personalised vessels to further illustrate the application of these techniques. Our work provides insights into how input parameters and boundary conditions impact the velocity and pressure distributions calculated in a simulation and can guide the choices of such values when applied to vascular studies of patient specific geometries. We observe that, from an algorithmic perspective, the number of time steps and the size of the grid spacing are the most influential parameters. When considering the influence of boundary conditions, we note that the magnitude of the inlet velocity and the mean pressure applied within sinusoidal pressure outlets have the greatest impact on output quantities of interest. We also observe that, when comparing the magnitude of variation imposed in the input parameters with that observed in the output quantities, this variability is particularly magnified when the input velocity is altered. This study also demonstrates how open-source toolkits for validation, verification and uncertainty quantification can be applied to numerical models deployed on high-performance computers without the need for modifying the simulation code itself. Such an ability is key to the more widespread adoption of the analysis of uncertainty in numerical models by significantly reducing the complexity of their execution and analysis. [ABSTRACT FROM AUTHOR]

A mathematical model of myocardial perfusion based on the lattice Boltzmann method (LBM) is proposed and its applicability is investigated in both healthy and diseased cases. The myocardium is conceptualized as a porous material in which the transport and mass transfer of a contrast agent in blood flow is studied. The results of myocardial perfusion obtained using LBM in 1D and 2D are confronted with previously reported results in the literature and the results obtained using the mixed‐hybrid finite element method. Since LBM is not suitable for simulating flow in heterogeneous porous media, a simplified and computationally efficient 1D‐analog approach to 2D diseased case is proposed and its applicability discussed. [ABSTRACT FROM AUTHOR]

During deep-sea mining, heavy metal pollutants can cause contamination in the marine environment. In this paper, the multiphasic coupling model is established to describe the heavy metal migration process during deep-sea mining, which takes the effects of the convection–diffusion, adsorption–desorption, and sedimentation–resuspension of heavy metals in the aquatic environment into full consideration. Due to the advantages of the Lattice Boltzmann method, it is adopted to numerically solve the multiphasic coupling model and achieve the simulation of the heavy metal migration process during deep-sea mining. In addition, taking cadmium as an example, the concentration variations are discussed and analyzed in detail. Based on the established model and Lattice Boltzmann method, the concentration distribution of heavy metals can be accurately described to provide the reasonable bases for the evaluation of marine environmental protection. [ABSTRACT FROM AUTHOR]

A neutrally buoyant circular particle motion in a double lid-driven cavity flow (LDCF) is investigated by immersed moving boundary based lattice Boltzmann method, where the top and bottom walls move with constant velocities. To understand the mechanism of particle motion in double LDCF, the influence of the moving wall velocity ratio u w r , initial position, particle size, and Reynolds number on the trajectory and limit circle of the neutrally buoyant circular particle motion in double LDCF is systematically studied. The results show that the trajectory of the particle is obviously different with different afore impactors. As u w r varies, the limit circle is changed accordingly. The limit circle of the particle motion is insensitive to the initial position with negative moving wall velocity ratio except for the initial location of the particle at the center of the cavity with u w r = -1, where the particle is stationary all the time. When moving wall velocity ratio becomes positive, due to the more complex fluid structure or vortices in cavity, some interesting limit circle modes of particle motion are observed. When particle size increases, the confinement of cavity is enhanced. The limit circle shrinks to the center of the cavity, and it can be greatly changed with different particle size for u w r > 0. With the increment of Reynolds number, the flow is strengthened, and the influence domain and the strength of the secondary vortices are enhanced, where the limit circle of particle motion is pushed away from the secondary vortices generated in cavity. However, the limit circle mode of particle motion is insensitive to the Reynolds number varied from 500 to 5000. [ABSTRACT FROM AUTHOR]

Identifying the yarn end from the package surface is integral to the textile process. Using the automatic method based on negative pressure adsorption instead of the traditional manual method to capture the yarn end is an excellent solution to the time-consuming and inefficient problems caused by the latter. To clarify the influence of process parameters on the process of the yarn end being adsorbed to break away from the package surface by the suction nozzle, this paper first establishes a kinetic model of the yarn attached to the package surface. Next, the air-yarn interaction is solved using the momentum exchanged-based immersed boundary-lattice Boltzmann method (IB-LBM). Then, the effect of the distance between the suction nozzle and the package, the rotational speed of the package, and the airflow velocity in the suction nozzle duct on the movement of the yarn end with the airflow field are studied. Further, the regression model for the depth of the yarn end sucked into the suction nozzle duct when the package turns through a fixed angle is solved. Finally, with the goal of a high success rate, large distance, high efficiency, and energy saving, a multi-parameter optimization is performed using the Central Composite Design-based response surface methodology. The work has been proven effective through experimental validation and practical production applications. It provides a theoretical basis for the automatic process of yarn-end-capturing from the package in the textile field. • The kinetic model of the yarn end being adsorbed to break away from the package surface by airflow is established. • The air-yarn interaction is solved using the momentum exchanged-based immersed boundary-lattice Boltzmann method (IB-LBM). • The effects of several process parameters on the movement of the yarn end with the airflow field are studied emphatically. • Multi-parameter and multi-objective optimization are performed by the Central Composite Design-based response surface method. [ABSTRACT FROM AUTHOR]

A three-dimensional multicomponent multiphase (MCMP) thermally coupled lattice Boltzmann model (LBM) was developed to investigate the effect of water content on the effective thermal conductivity (ETC) of the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEMFC). A stochastic model was then used to reconstruct the 3D GDLs, and the effects of the material conditions on the heat and mass transfer characteristics were examined in detail. The results showed that the more the liquid water was saturated, the higher the estimated ETC of the GDL. When the wettability of the carbon fiber was constant, the distribution of liquid water played a more critical role in predicting the ETC. [ABSTRACT FROM AUTHOR]

In this work, the droplet impact and rebound behaviors on a flat substrate are comprehensively investigated by using the consistent and conservative phase-field based lattice Boltzmann method, which is robust for the multiphase flow problems with the large density ratios and long-time dynamics. The dynamic behavior of the droplet considered here is governed by five key factors: the contact angle, droplet size, the Bond number, the Reynolds number and the density ratio. The effects of these parameters on the barycenter motion trajectory, contact time, the maximum spreading factor and rebound height are studied, and the results show that the Bond number and the density ratio play the critical roles in the droplet morphology when it impacts the substrate. After the impact process, there are three typical patterns: fragmentation, deposition and rebound, which are mainly controlled by the wettability, the size of droplet and the Bond number. In the rebound process, we focus on the rebound height and the number of rebound, and also give the distribution of pressure inside the droplet and the evolution of pressure before fragmentation. Finally, it is also found that under some certain conditions, the air density has a positive effect on the droplet rebound behavior and a large density ratio of 6400 can be achieved. [ABSTRACT FROM AUTHOR]

This research employed the pseudopotential multi-relaxation times lattice Boltzmann method to investigate the impact process of a droplet on solid surfaces, focusing on the influence of surface wettability for three different Reynolds numbers Re = 100, 200, and 500). Initially, the impact process is studied on both hydrophobic and hydrophilic surfaces, revealing distinct behaviors characterized by spreading and recoiling stages. Subsequently, the investigation extends to a mixed wettability wall, offering insights into the droplet's density behaviors. Through this study, we demonstrate that the wettability of the surface plays a crucial role in determining the contact dynamics with the impacting droplet. Notably, the average velocity of the droplet exhibits a monotonic increase with higher wettability. Furthermore, the droplet profile responds to variations in the Reynolds number, though droplet deformation remains relatively limited even when the interaction with the wetting surface intensifies. Our findings shed light on the complex interplay between wettability, droplet dynamics, and surface interactions during impact processes. • The Pseudopotential multi-relaxation times lattice Boltzmann method to analyze the impact of droplets on surfaces is used. • The process of spreading droplets on hydrophobic and hydrophilic surfaces and a mixed wettability surface is investigated. • The behavior of the droplet with Reynolds number on the wetting surface is studied. [ABSTRACT FROM AUTHOR]

Thermodynamic consistency is a key factor in heat and mass transfer simulation. A modified lattice Boltzmann pseudopotential model with the ability to simulate multiphase and multicomponent flow with a large density and viscosity ratio is proposed. Relative to a model using the exact difference method, a better thermodynamic consistency is obtained through introducing an improved external force term, a multi-relaxation-time collision operator, and a scaling coefficient k of the equation of state. The coefficient of scale k = 0.1 is preferred due to its better thermodynamic consistency, lower spurious current and a smaller surface tension. The inter-particle interaction strength has little influence over the thermodynamic consistency due to its limited contributions to the surface tension. With the model, the bubble dissolution under pressure is investigated and Henry's law is validated. • A lattice Boltzmann pseudopotential multiphase-multicomponent model is developed. • Improved source term achieves thermodynamic consistency with large density ratio. • Effect of the inter- and intra-particle forces on the surface tension is investigated. [ABSTRACT FROM AUTHOR]

This study unveils a numerical paradigm that amalgamates the partially saturated lattice Boltzmann method (PSLBM) with the non‐isothermal quantitative phase‐field (PF) model. This innovative integration equips us with a prognostic tool ready to elucidate the progression and motion of solid‐air dendritic growth in the presence of both natural and forced convection. The PSLBM is employed to compute the flow of the solution and the interaction forces between the fluid and solid dendrites. Concurrently, the PF model is utilized to simulate the formation of solid‐air dendrites. The reliability of calculating of interaction forces between the fluid and solid was confirmed through a numerical case study involving fluid flow around a stationary cylinder. The results indicate that this model is applicable for simulating the growth and evolution of single/multiple solid‐air dendrites under the influence of convection, whether they are stationary or in motion. The promotion of the upstream side dendritic arms and the inhibition of the downstream dendritic arms increase with the intensification of natural convection. As the initial undercooling is raised, the capacity of natural convection to reshape dendritic morphology gradually diminishes. With the enhancement of forced convection intensity, due to alterations in the flow pattern, the downstream dendritic arms do not consistently exhibit growth suppression. The motion of solid‐air dendrites induced by forced convection counteracts the influence of convection, resulting in slightly faster growth of the downstream dendritic arms compared to the upstream arms. Simultaneously, it fosters the formation of secondary dendritic branches in the upstream zone. [ABSTRACT FROM AUTHOR]

A numerical method for describing droplet-driven particle motion at low Weber numbers in fluids is proposed. A coupling strategy combining the Shan–Chen (SC) model and the smoothed profile method (SPM) is employed. The proposed scheme correctly resolves the momentum transfer between solid particles and fluid phases, while effectively controlling the wetting condition. An interaction zone where three phases coexist is introduced to solve the contradiction between the SC model and SPM (i.e. whether fluid particles are allowed at the solid nodes). In the interaction zone, partial solid particles are entrapped in the fluids owing to the coexistence of solid and fluid particles, causing solid particles to exchange momentum with fluid particles. Furthermore, the interaction forces between fluid and solid particles near the solid surface are considered at nodes near pure solid particles within this region. Based on the proposed scheme, the interactions between freely moving particles and freely moving droplets were investigated, along with the effects of wettability (Gads) and volume forces (Fp*) on particle–droplet interactions. When a liquid droplet comes into contact with a solid particle, the adhesion force between the droplet and the solid surface promotes the movement of solid particles toward the droplet. When a double emulsion comes into contact with solid particles, the adhesion force between the emulsion film and solid surface causes the double emulsion to break at the connecting point, and the volume force of the emulsion film Fd* causes the solid particles to penetrate the emulsion. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method is employed in the current study to simulate the heat transfer characteristics of sinusoidal-temperature-distributed heat sources at the bottom of a square cavity under various conditions, including different amplitudes, phase angles, initial positions, and angular velocities. Additionally, a machine learning-based model is developed to accurately predict the Nusselt number in such a sinusoidal temperature distribution of heat source at the bottom of a square cavity. The results indicate that (1) in the phase angle range from 0 to π, Nu basically shows a decreasing trend with an increase in phase angle. The decline in Nu at an accelerated rate is consistently observed when the phase angle reaches 4π/16. The corresponding Nu decreases as the amplitude increases at the same phase angle. (2) The initial position of the sinusoidal-temperature-distributed heat source Lc significantly impacts the convective heat transfer in the cavity. Moreover, the decline in Nu was further exacerbated when Lc reached 7/16. (3) The optimal overall heat transfer effect was achieved when the angular velocity of the non-uniform heat source reached π. As the angular velocity increases, the local Nu in the square cavity exhibits a gradual and oscillatory decline. Notably, it is observed that Nu at odd multiples of π surpasses that at even multiples of π. Furthermore, the current work integrates LBM with machine learning, enabling the development of a precise and efficient prediction model for simulating Nu under specific operational conditions. This research provides valuable insights into the application of machine learning in the field of heat transfer. [ABSTRACT FROM AUTHOR]

The generalized Zakharov equation is a widely used and crucial model in plasma physics, which helps to understand wave particle interactions and nonlinear wave propagation in plasma. The solitary wave solution of this equation provides insights into phenomena such as electron and ion acoustic waves, as well as magnetic field disturbances in plasma. The numerical simulation of solitary wave solutions to the generalized Zakharov equation is an interesting problem worth studying. This is crucial for plasma-based technology, as well as for understanding nonlinear wave propagation in plasma physics and other fields. In this study, a numerical investigation of the generalized Zakharov equation using the lattice Boltzmann method has been conducted. The lattice Boltzmann method is a new modeling and simulating method at the mesoscale. A lattice Boltzmann model was constructed by performing Taylor expansion, Chapman–Enskog expansion, and time multiscale expansion on the lattice Boltzmann equation. By defining the moments of the equilibrium distribution function appropriately, the macroscopic equation can be restored. Furthermore, the numerical experiments for the equation are carried out with the parameter lattice size m = 100 , time step Δ t = 0.001 , and space step size Δ x = 0.4 . The solitary wave solution of the equation is numerically simulated. Numerical results under different parameter values are compared, and the convergence and effectiveness of the model are numerically verified. It is obtained that the model is convergent in time and space, and the convergence orders are all 2.24881. The effectiveness of our model was also verified by comparing the numerical results of different numerical methods. The lattice Boltzmann method demonstrates advantages in both accuracy and CPU time. The results indicate that the lattice Boltzmann method is a good tool for computing the generalized Zakharov equation. [ABSTRACT FROM AUTHOR]

Improving the water removal capacity is critical to the application of metal foam flow fields (MFFF) in proton exchange membrane fuel cells. In this study, the complete growth, detachment, and removal processes of liquid water in MFFF is numerically investigated by using an improved pseudopotential lattice Boltzmann model, with a particular interest in understanding the effects of structural parameters (porosity and pore density) and wettability of MFFF on the water removal performance. Three flow patterns are identified in the simulations, including droplet , coalescent slug , and unseparated slug , among which the droplet flow pattern is most effective for water removal. Either a lower porosity or a higher contact angle enlarges the range for droplet flow and accelerates water discharge. In hydrophobic MFFF, liquid water prefers to transport within the pore structures, and an optimal pore density is observed due to the competition between the gas drag and the ligament resistance. In contrast, in hydrophilic MFFF, liquid water prefers to move along the ligament structures, and a smaller pore density is favored since the ligament resistance becomes the prevailing factor. By optimizing the structural parameters and wettability, the water removal time for droplet flow is reduced by 52.1% compared to the benchmark case. • Water transport process in MFFF is investigated by using an improved LB model. • The flow patterns are identified as droplet, coalescent slug, and unseparated slug. • Droplet flow pattern is most effective in water removal and favors low porosity. • An optimal pore density is observed for hydrophobic MFFF. • The increase in MFFF contact angle promotes liquid water removal as droplets. [ABSTRACT FROM AUTHOR]

The emphasis of this study is the numerical analysis via D2Q9-based Lattice Boltzmann Method of free convection MHD non-Darcy flow in hybrid nanofluid (TiO2/Cu–water) occupying a differentially heated square enclosure. A key novelty of the work is the inclusion of a response surface methodology (RSM)-based sensitivity analysis. The current investigation has been done considering the variation in Rayleigh number (103 ≤ Ra ≤ 106), Darcy number (0.0001 ≤ Da ≤ 0.1), and Hartmann number (0 ≤ Ha ≤ 50). From RSM, high Darcy parameter, low volumetric fraction, and low Hartmann number are identified as the optimum functioning conditions for heat transfer rates. [ABSTRACT FROM AUTHOR]

AbstractThe manifold microchannel (MMC) has garnered significant interest owing to its inherent advantages of low pressure drop and high heat dissipation capability. In this article, the lattice Boltzmann method was used to numerically study the effect of Reynolds number (20≤Re≤240) and microchannel height (Hch) on the flow and heat transfer characteristics of the MMC with the heat source at the bottom of microchannels. The flow distribution, heat transfer uniformity, and pressure drop were analyzed. The results showed that the increase of Re increased the total average Nusselt number (Nu) and also made the flow distribution and the heat transfer distribution more uneven. Poiseuille number (Po) was not a constant but increased with the increase of Re. Decreasing Hch increased the total average Nu and improved flow distribution uniformity, but also increased Po. Based on our investigation, at a low Re, lowering Hch improved the uniformity of heat transfer distribution. However, at a high Re, the reduction of the heat transfer distribution non-uniformity required a reduction in Hch until the flow distribution became significantly more uniform. Moreover, we found that there are two power law relationships between the total average Nu and Re, and the powers were independent of Hch. We established two correlations by taking the total average Nu as a function of Re and Hch to better express their relationships. The dependence of the total average Nu on Re was Nu∝Re0.3929 at Re = 20–80 and Nu∝Re0.5558 at Re = 90–240. [ABSTRACT FROM AUTHOR]

Wall-modeled large eddy simulation (WMLES) is considered to be a powerful method in high Reynolds number wall-bounded fluid dynamics calculations. However, little research on aero-acoustic simulation by lattice Boltzmann method (LBM) combined with LES considering wall model has been found. Moreover, the discussion of the dominant geometric parameters of the wall model, which is dedicated to curved boundary modeling and based on a non-fitted Cartesian mesh, is rarely addressed. This paper proposes a WMLES algorithm based on a hierarchical Cartesian mesh and utilizing LBM, including the treatment of dominant geometric parameters. Firstly, based on the Green's formula, a strategy for obtaining detection point positions is developed using the mathematical formulas to solve the boundary free parameters, such as the normal direction of the curved surface and the distance from the lattice point to the solid-fluid boundary in the given direction. Secondly, a new wall model adapted to non-fitted Cartesian mesh is proposed to improve the precision of pressure fluctuation calculation. This model applies an interpolation bounce-back (IBB) scheme where slip velocity is estimated by an implicit wall function proposed by Spalart, and the eddy viscosity is reconstructed in the near-wall region. Finally, to enhance the accuracy of pressure fluctuation propagation, an appropriate transition zone treatment method of a multi-domain scheme with spatio-temporal second-order is applied and validated with a point source case. The aforementioned algorithms are implemented in a self-developed LBM code and validated through a three-element airfoil 30P30N benchmark, demonstrating their effectiveness and high accuracy in acoustic calculations. [ABSTRACT FROM AUTHOR]

Nanofluid is a particle suspension composed of liquid and nanoparticles, and has great potential to enhance mass transfer. Most previous studies have only considered the effect of the Brownian motion of nanoparticles on mass transfer. In this study, the two-dimensional Lattice Boltzmann method (LBM) combined with the cell automation (CA) probabilistic model is proposed to investigate the mass transfer of CO 2 in nanofluids. The model predictions were in good agreement with experimental data, validating the developed mass transfer model. The simulation results indicated that the Brownian motion and grazing effect enhanced the mass transfer in nanofluids, and should be considered simultaneously. Comparing with the pure water, adding 0.1 wt% SiO 2 nanoparticles increased the absorption rate up to 58.3 %, and the effective diffusion coefficients reached 5.41 × 10−9 m2s−1. In addition, changing the physical parameters directly affected the Brownian motion and grazing effect, and changed the effective diffusion coefficient of CO 2 in the nanofluid. The effective diffusion coefficient decreased with an increase in particle size and increased with an increase in fluid temperature. [Display omitted] • The LBM combined with the CA was proposed to investigate the mass transfer of CO 2 in nanofluids. • In our developed model, the nanoparticles can move independently in the solution and absorb CO 2. • The effect of nanoparticles's Brownian motion and grazing effect on mass transfer were both considered. • The effects of different physical parameters on mass transfer in nanofluids were analyzed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the utilization of artificial neural networks (ANNs) in learning models that address the nonlinear anisotropic flow and hysteresis retention behavior of deformable porous materials. Herein, the micro‐geometries of various networks of porous Bentheimer Sandstones subjected to several degrees of strain from the literature are considered. For the generation of the database required for the training, validation, and testing of the machine learning (ML) models, single‐phase and biphasic lattice Boltzmann (LB) simulations are performed. The anisotropic nature of the intrinsic permeability is investigated for the single‐phase LB simulations. Thereafter, the database contains the computed average fluid velocities versus the pressure gradients. In this database, the range of applied fluid pressure gradients includes Darcy as well as non‐Darcy flows. The generated output from the single‐phase flow simulations is implemented in a feed‐forward neural network, representing a path‐independent informed graph‐based model. Concerning the two‐phase LB simulations, the Shan‐Chen multiphase LB model is used to generate the retention curves of the cyclic drying/wetting processes in the deformed porous networks. Consequently, two different ML path‐dependent approaches, that is, 1D convolutional neural network and the recurrent neural network, are used to model the biphasic flow through the deformable porous materials. A comparison in terms of accuracy and speed of training between the two approaches is presented. Conclusively, the outcomes of the papers show the capability of the ML models in representing constitutive relations for permeability and hysteretic retention curves accurately and efficiently. [ABSTRACT FROM AUTHOR]

Background Objective Methods Results Conclusions Given the varying vulnerability of the rostral and caudal regions of the hippocampus to neuropathology in the Alzheimer's disease (AD) continuum, accurately assessing structural changes in these subregions is crucial for early AD detection. The development of reliable and robust automatic segmentation methods for hippocampal subregions (HS) is of utmost importance.Our aim is to propose and validate a HS segmentation model that is both training‐free and highly generalizable. This method should exhibit comparable accuracy and efficiency to state‐of‐the‐art techniques. The segmented HS can serve as a biomarker for studying the progression of AD.We utilized the functional magnetic resonance imaging of the Brain's Integrated Registration and Segmentation Tool (FIRST) to segment the entire hippocampus. By intersecting the segmentation results with the Brainnetome (BN) atlas, we obtained coarse segmentation of the four HS regions. This coarse segmentation was then employed as a shape prior term in the lattice Boltzmann (LB) model, as well as for initializing contours. Additionally, image gradients and local gray levels were integrated into the external force terms of the LB model to refine the coarse segmentation results. We assessed the segmentation accuracy of the model using the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset and evaluated the potential of the segmentation results as AD biomarkers on both the ADNI and Xuanwu datasets.The median Dice similarity coefficients (DSC) for the left caudal, right caudal, left rostral, and right rostral hippocampus were 0.87, 0.88, 0.88, and 0.89, respectively. The proportion of segmentation results with a DSC exceeding 0.8 was 77%, 78%, 77%, and 94% for the respective regions. In terms of volume, the correlation coefficients between the segmentation results of the four HS regions and the gold standard were 0.95, 0.93, 0.96, and 0.96, respectively. Regarding asymmetry, the correlation coefficient between the segmentation result's right caudal minus left caudal and the corresponding gold standard was 0.91, while for right rostral minus left rostral, it was 0.93. Over time, we observed a decline in the volumes of the four HS regions and the total hippocampal volume of mild cognitive impairment (MCI) converters. Analysis of inter‐group differences revealed that, except for the right rostral region in the ADNI dataset, the p‐values for the four HS regions in the normal controls (NC), MCI, and AD groups from both datasets were all below 0.05. The right caudal hippocampal volume demonstrated correlation coefficients of 0.47 and 0.43 with the mini‐mental state examination (MMSE) and Montreal cognitive assessment (MoCA), respectively. Similarly, the left rostral hippocampal volume showed correlation coefficients of 0.50 and 0.58 with MMSE and MoCA, respectively.Our framework allows for direct application to different brain magnetic resonance (MR) datasets without the need for training. It eliminates the requirement for complex image preprocessing steps while achieving segmentation accuracy comparable to deep learning (DL) methods even with small sample sizes. Compared to traditional active contour models (ACM) and atlas‐based methods, our approach exhibits significant speed advantages. The segmented HS regions hold promise as potential biomarkers for studying the progression of AD. [ABSTRACT FROM AUTHOR]

Compound droplets have received increasing attention due to their applications in many several areas, including medicine and materials. Previous works mostly focused on compound droplets on planar surfaces and, as such, the effects of curved walls have not been studied thoroughly. In this paper, the influence of the properties of curved solid wall (including the shape, curvature, and contact angle) on the wetting behavior of compound droplets is explored. The axisymmetric lattice Boltzmann method, based on the conservative phase field formulation for ternary fluids, was used to numerically study the wetting and spreading of a compound droplet of the Janus type on various curved solid walls at large density ratios, focusing on whether the separation of compound droplets occurs. Several types of wall geometries were considered, including a planar wall, a concave wall with constant curvature, and a convex wall with fixed or variable curvature (specifically, a prolate or oblate spheroid). The effects of surface wettability, interfacial angles, and the density ratio (of droplet to ambient fluid) on the wetting process were also explored. In general, it was found that, under otherwise identical conditions, droplet separation tends to happen more likely on more hydrophilic walls, under larger interfacial angles (measured inside the droplet), and at larger density ratios. On convex walls, a larger radius of curvature of the surface near the droplet was found to be helpful to split the Janus droplet. On concave walls, as the radius of curvature increases from a small value, the possibility to observe droplet separation first increases and then decreases. Several phase diagrams on whether droplet separation occurs during the spreading process were produced for different kinds of walls to illustrate the influences of various factors. [ABSTRACT FROM AUTHOR]

Recently, Murthy et al. (Commun Comput Phys 2:23, 2017. http://dx.doi.org/10.4208/cicp.OA-2016-0259) and Escande et al. (Lattice Boltzmann method for wave propagation in elastic solids with a regular lattice: theoretical analysis and validation, 2020. arXiv.doi:1048550/ARXIV.2009.06404. arXiv:2009.06404) adopted the Lattice Boltzmann Method (LBM) to model the linear elastodynamic behaviour of isotropic solids. The LBM is attractive as an elastodynamic solver because it can be parallelised readily and lends itself to finely discretised simulations of dynamic effects in continua, allowing transient phenomena such as wave propagation to be modeled efficiently. This work proposes simple local boundary rules which approximate the behaviour of Dirichlet and Neumann boundary conditions with an LBM for elastic solids. The boundary rules are shown to be consistent with the target boundary values in the first order. An empirical convergence study is performed for the transient tension loading of a rectangular plate, with a Finite Element (FE) simulation being used as a reference. Additionally, we compare results produced by the LBM for the sudden loading of a stationary crack with an analytical solution from Freund (Dynamic fracture mechanics. Cambridge Monographs on Mechanics. Cambridge University Press, Cambridge, 1990. https://doi.org/10.1017/CBO9780511546761). [ABSTRACT FROM AUTHOR]

Hydrodynamic lubrication is widely used between two relatively moving objects, and the effect of fluid flow state and temperature distribution on lubrication performance in wedge-shaped gaps is a popular topic to study. In this paper, the incompressible double-distribution lattice Boltzmann method (LBM) is applied to study the effect of micro convex surface texture on micro lubrication and heat transfer in wedge-shaped channels. By comparing this model with the analytical solution of an infinitely wide wedge slider, the maximum pressure calculated by LBM is 0.1081 MPa, and the maximum pressure calculated by the Reynolds equation is 0.1079 MPa. The error of the maximum pressure is 1.11%, and the Reynolds equation result is slightly smaller. The reason is that the Reynolds equation ignores the influence of fluid inertia force on oil film pressure. The results indicate that the application of LBM can be used to study lubrication problems. Compared with the Reynolds equation, LBM can calculate the velocity field and pressure field in the film thickness direction, and can also observe precise flow field details such as vortices. Three micro convex texture shapes were established to study the effects of different convex textures on micro lubrication and oil film temperature distribution, and the velocity distribution, temperature distribution and oil film pressure along the oil film thickness direction were given. Under the same conditions, comparing the oil film pressure with and without surface texture, the results show that the maximum oil film pressure with surface texture 3 is increased by about 4.34% compared with that without surface texture. The slightly convex texture can increase the hydrodynamic lubrication effect and obtain greater load-bearing capacity, helping to reduce the possibility of contact friction. The results show that the convex surface texture can improve the hydrodynamic lubrication performance, increase the load carrying capacity and reduce the possibility of contact friction, and the convex surface texture can influence the temperature distribution of the oil film. At 3.6 mm in the slider length direction and 7.5 μm in the oil film thickness direction, the temperature of surface texture 1 is 402.64 K, the temperature of surface texture 2 is 403.31 K, and the temperature of surface texture 3 is 403.99 K. The presence of vortices is captured at a high convergence ratio. [ABSTRACT FROM AUTHOR]

The microstructure plays a crucial role in determining the properties of metallic materials, in terms of both their strength and functionality in various conditions. In the context of the formation of microstructure, phase transformations that occur in materials are highly significant. These are processes during which the structure of a material undergoes changes, most commonly as a result of variations in temperature, pressure, or chemical composition. The study of phase transformations is a broad and rapidly evolving research area that encompasses both experimental investigations and modeling studies. A foundational understanding of carbon diffusion and phase transformations in materials science is essential for comprehending the behavior of materials under different conditions. This understanding forms the basis for the development and optimization of materials with desired properties. The aim of this paper is to create a three-dimensional model for carbon diffusion in the context of modeling diffusional phase transformations occurring in carbon steels. The proposed model relies on the utilization of the LBM (Lattice Boltzmann Method) and CUDA architecture. The resultant carbon diffusion model is intricately linked with a microstructure evolution model grounded in FCA (Frontal Cellular Automata). This manuscript provides a concise overview of the LBM and the FCA method. It outlines the structure of the developed three-dimensional model for carbon diffusion, details its correlation with the microstructure evolution model, and presents the developed algorithm for simulating carbon diffusion. Demonstrative examples of simulation results, illustrating the growth of the emerging phase and affected by various model parameters within particular planes of the 3D calculation domain, are also presented. [ABSTRACT FROM AUTHOR]

In this study, the behavior of bubbles and droplets during boiling and condensation processes on a wettable horizontal plate with variable density (qw) is investigated using pseudopotential lattice Boltzmann model for multiphase flow. The analysis focuses on the complete life cycle of bubbles and droplets, from their appearance to their disappearance under the effect of gravity. The main objectives of this study are to analyze the propagation of bubbles or droplets on the horizontal surface (l*) and to study their evolution as a function of time, characterized by h*, for different values of the wetting surface density. To ensure the reliability of our model in simulating these phenomena, the hydrodynamic effect and Laplace's law were. This combination of approaches demonstrated a good compromise between our results and the references, confirming the model's reliability. Furthermore, we present results that showcase the density behaviors for different wetting surfaces, allowing us to analyze droplet behavior on the horizontal plate. It was observed that for large values of qw, significant droplet spreading occurred, and this process took time to subside. Conversely, for small values of qw, spreading was minimal, enabling rapid droplet detachment. Interestingly, in the case of boiling, the observed behaviors were reversed compared to condensation. Moreover, the heat flux analysis for the single-density case provided insights into the temperature behavior around bubbles during the nucleation process and droplets during the droplet condensation process, while maintaining a fixed density value on average. These findings contribute to a better understanding of the thermal dynamics associated with boiling and condensation phenomena. [ABSTRACT FROM AUTHOR]

Lattice Boltzmann method (LBM) is a powerful fluid flow solver. Using this method to solve other PDEs might be a difficult task. The first challenge is to find a suitable local equilibrium distribution function (EDF) capable of recovering the desired PDE. The next difficulty arises from the explicit nature of LBM. The conditional stability of the LBM algorithm affects the numerical solution accuracy. Damped Kuramoto–Sivashinsky (DKS) equation is a fourth–order PDE that recently challenged many numerical methods' abilities. This equation is highly sensitive to a parameter that causes three states of solutions in a small interval of freedom. In this paper, we challenged LBM to solve the two–dimensional DKS equation by finding EDF using the Chapman–Enskog analysis up to the fourth–order. Also, the von Neumann analysis and a simple genetic algorithm are applied to find reliable values for the free parameters. Furthermore, a modification on image-based ghost node method is proposed for implementation of the boundary conditions in the complex geometries. [ABSTRACT FROM AUTHOR]

The catalyst layer (CL) structure has a great impact on proton exchange membrane fuel cell (PEMFC) performance. In this study, the microporous structure of a cathode CL is reconstructed via a stochastic algorithm. Subsequently, the lattice Boltzmann method (LBM) is used to investigate the influence of the CL structure regarding carbon carrier and platinum (Pt) particle sizes and ionomer thickness on oxygen reduction reaction (ORR) processes within the cathode CL. The LBM simulation results indicate that an increased carbon carrier size promotes oxygen transport through the CL pores owing to the decreased tortuosity of the porous CL but reduces the overall ORR rate. A larger Pt particle size leads to a reduction in the number of reaction sites but shortens the ionomer thickness for oxygen diffusion to the reaction sites. The oxygen transport resistance through the ionomer increases with increasing ionomer thickness and thus degrades the overall ORR rate. However, an excessively small ionomer thickness leads to the exposure and shedding of Pt, thereby reducing the number of reaction sites. The findings here demonstrate that proper design of the carbon carrier and Pt particle sizes and ionomer thickness are essential for achieving a CL with high oxygen transport performance and overall ORR rate. • Increasing carbon size promotes oxygen transport through pores but reduces ORR rate. • Larger Pt size causes reduced active sites but favors oxygen transport through ionomer. • Increasing ionomer thickness declines oxygen transport within both pores and ionomer. • ORR rate is determined by the interaction between oxygen transport and active sites. [ABSTRACT FROM AUTHOR]

In order to investigate the characteristics of wall heat flow density distribution in the process of side-by-side double droplets impinging on the high temperature wall covered with liquid film, the effects of droplet spacing, impact velocity and liquid phase viscosity coefficient on the instantaneous wall heat flow density distribution at different moments were investigated based on the lattice Boltzmann pseudopotential model with hydrothermal coupling double distribution functions. The results show that the diffusion and dive of low-temperature droplets lead to an increase in the temperature gradient between the wall and liquid film in the impact zone and the central jet zone, causing a sharp increase in the heat flow density of the wall in the impact zone and the central jet zone. The heat transfer in the impact zone is mainly in the form of convective heat transfer, and the heat transfer in the static zone is mainly in the form of diffusive heat transfer due to the effect of velocity discontinuity at the liquid crown. The increase of double droplets impact velocity leads to the deepening of droplet dive and expansion, and the convective heat transfer inside the liquid film is enhanced. The increase of double droplets spacing causes the expansion space of the liquid crown inside the liquid film to increase, resulting in the increasing area of high heat flow density region on the transient wall surface, which is conducive to heat dissipation. In addition, the larger viscosity coefficient of the liquid phase increases the viscous dissipation during the droplet impact with the liquid film, which reduces the dive of the low-temperature droplet and the convection intensity of the liquid film flow field in the impact area, and leads to the reduction of the peak heat flow density at the wall surface. [ABSTRACT FROM AUTHOR]

The simulation of seismic wavefields holds paramount significance in understanding subsurface structures and seismic events. The lattice Boltzmann method (LBM) provides a computational framework adept at capturing detailed wave interactions, offering a new approach to improve seismic wavefield simulations. Our study involves a novel comparative analysis of wavefields using different lattice Boltzmann models, focusing on how relaxation times, discrete velocity models, and collision operators affect simulation accuracy and efficiency. We explore the impacts of distinct relaxation times and evaluate their effects on wave propagation speed and fidelity. By incorporating four discrete velocity models of LBM, we innovatively investigate the trade-off between spatial resolution and computational complexity. Additionally, we delve into the implications of employing three collision operators—single relaxation time (SRT), two relaxation times (TRT), and multiple relaxation times (MRT). By comparing their accuracy and stability, we provide insights into selecting the most suitable collision operator for capturing complex wave interactions. Our research provides a comprehensive framework to optimize the LBM parameters, enhancing both accuracy and efficiency in seismic wave simulations, and offers valuable insights to benefit wave simulation across diverse disciplines. [ABSTRACT FROM AUTHOR]

This study presents a novel approach inspired by the hexagonal honeycomb structure found in nature, leveraging image processing algorithms to precisely define complex geometries in thermal systems. Hexagonal phase change material containers and thermally conductive fins were meticulously delineated, mirroring the intricate real-world designs of honeycombs. This innovative methodology not only streamlines setup processes but also enhances our understanding of melting dynamics within enclosures, highlighting the potential benefits of biomimetic design principles in engineering applications. Two distinct honeycomb structures were employed to investigate their impact on the melting process within cavities subject to heating from the left wall, with the remaining walls treated as adiabatic surfaces. The incorporation of a thermally conductive fin system within the enclosure significantly reduced the time required for a complete phase change, emphasizing the profound influence of fin systems on thermal design and performance. This enhancement in heat transfer dynamics makes fin systems advantageous for applications prioritizing precise temperature control and expedited phase change processes. Furthermore, the critical role of the fin system design was emphasized, influencing both the onset and location of the final point of melting. This underscores the importance of tailoring fin systems to specific applications to optimize their performance. Our study highlights the significant impact of the Rayleigh (Ra) number on the melting time in a cavity without fins, revealing a decrease from 6 to 0.4 as the Ra increased from 102 to 105; the introduction of a fin system uniformly reduced the melting time to Ste.Fo = 0.5, indicating fins' universal effectiveness in optimizing thermal dynamics and expediting the melting process. Moreover, the cavity angle was found to significantly affect the fluid fraction diagram in unfanned cavities but had minimal impact when fins were present, highlighting the stabilizing role of fins in mitigating gravitational effects during melting processes. These insights expand our understanding of cavity geometry and fin interactions in heat transfer, offering potential for enhanced thermal system designs in various engineering applications. Decreasing thermal conductivity (λ) by increasing the fin thickness can halve the melting time, but the accompanying disadvantages include a heavier system and reduced energy storage due to less phase change material, necessitating a careful balance in decision-making. [ABSTRACT FROM AUTHOR]

As a powerful tool to investigate turbulent flows laden with finite-size particles, the lattice Boltzmann method (LBM)'s capability to contribute to a particle-resolved simulation of particle-laden homogeneous shear turbulence (HST) has yet to be realized. To capture the turbulence-particle interactions more accurately, the interpolated-bounce-back schemes combined with the momentum-exchange method that possesses second-order accuracy are adopted to treat the no-slip condition on particle surfaces and compute the hydrodynamic force/torque. However, this choice brings extra difficulties in enforcing the shear periodic boundaries due to the absence of fluid information in solid regions. The present study resolves these difficulties by designing a scheme to construct the distribution functions in the particle gaps based on the lubrication theory and an algorithm for the "refilling" process near the shear periodic boundaries. With these developments, a direct numerical simulation of particle-laden HST is achieved with LBM. The turbulence modulation effects induced by particles are briefly discussed. [ABSTRACT FROM AUTHOR]

The presence of cracks in the gas diffusion layer (GDL) can have a significant impact on the flow of two phases within Proton Exchange Membrane Fuel Cells (PEMFCs). This study focuses on investigating the transport process of two-phases flow in a GDL sample using both experimental and numerical methods. The porous structure of a hydrophobic carbon paper, serving as the macro-porous substrate (MPS) of the GDL, is examined using synchrotron radiation X-ray phase contrast Computed Tomography (CT). A 3-D model with various crack geometries is then created, and a Lattice Boltzmann Method (LBM) simulation is employed to analyze the flow behavior within the GDL model. The findings reveal that the water intrusion mode in the MPS primarily depends on its hydrophobic nature, but the width and depth of the cracks also significantly influence both the rate and path of water intrusion. Increasing the crack width from 7 μm to 28 μm results in a 30% increment in water intrusion rate, while the intrusion path remains unchanged. However, when the crack width reaches 42 μm, the crack itself becomes the primary path for water intrusion, doubling the intrusion rate. Furthermore, an increase in crack depth leads to a higher invasion rate of the liquid phase, consequently increasing the liquid storage volume within the GDL. This research provides a novel approach for analyzing cracked GDLs and demonstrates the potential to optimize the water management process of PEMFCs through GDL microstructure design. • A 3D model of gas diffusion layer (GDL) in PEMFC is obtained via Synchrotron X-ray phase contrast CT. • Lattice Boltzmann Method is applied to investigate GDL cracking phenomenon. • The two-phase transport process in the cracked GDL is analyzed. • The effect of the crack geometric features on the GDL performance is investigated. [ABSTRACT FROM AUTHOR]

The proposed method simulates the growth and collapse mechanisms of lasers or sparks cavitation bubbles based on a double-distributed pseudo-potential thermal lattice Boltzmann method, which gives a high-temperature spot equal to or larger than the critical temperature of the fluid. This technique offers valuable insights into both the hydro- and the thermodynamics evolution of near-wall bulk bubbles. Our findings indicate that the dimensionless bubble-wall distance and the maximum radius share a correlative relationship, expressible via a piecewise function. The critical radius required for bubble inception exhibits a direct correlation with surface tension. We also observe a power-law relationship between surface tension and the maximum radius: lower surface tension results in increased deformation and a larger jet volume. The simulation results reveal the significant influence of initial input temperature on the pressure dynamics within the gas nucleus, leading to varied surface expansion velocities. However, this factor only marginally affects the surface wall expansion velocities. An increased input temperature results in intensified collapse mechanisms. Nevertheless, the elevated temperature during the initial collapse may cause an increase in pressure within the remaining bubble components, potentially leading to oscillations in the bubble radius. • A segmental relationship between bubble-wall distance and maximum radius is delineated. • A mathematical relationship, governed by a power-law, between surface tension and maximum radius is elucidated. • An extensive analysis of the influence of initial input temperature on bubble pressure dynamics is presented. • A comprehensive examination of the effect of initial input temperature on surface expansion velocities is conducted. [ABSTRACT FROM AUTHOR]

The 2-phase flow systems with bubbles exist in various industrial processes and involve complex phase interface changes, but the bubble movement through orifice plates accompanied by liquid flow in channels has not been fully studied. The phase field lattice Boltzmann model has advantages in simulating complex interface, and is suitable for studying the movement of bubble 2-phase flow through microchannels in orifice plates, and analyzing the effects of factors such as the We number, the relative bubble size and the orifice surface wettability on the dynamic characteristics of bubbles. The numerical results show that, with the increase of the We number, the surface tension of the bubble would decrease, which makes the bubble more likely to be torn and its peak velocity decrease when it passes through the orifice structure. There are 2 critical diameter ratios in the studied parameter range, which divide the bubble movement into 3 forms through the orifice, and the critical diameter ratio decreases with the We number. In addition, with the increase of the contact angle, the adsorption capacity of gas on the surface of the orifice plate would improve, and the contact area between the bubble and the orifice plate surface would increase, which would cause the bubble mass passing through the orifice plate to decrease and the bubble speed passing through the orifice plate to increase. [ABSTRACT FROM AUTHOR]

A randomly distributed cavity model was constructed for 3D metal foam composite phase change materials (PCMs), and the multi-relaxation time lattice Boltzmann method was used to explore the cavity effects with different volume fractions, distribution locations, and thermal conductivity ratios of metal foam to PCM at the cavity scale. The results show that, with the increase of the cavity volume fraction, the heat transfer rate and latent heat storage capacity of composite PCMs would decrease. At a Fourier number of 0.7, compared to the case without cavity, the heat storage decreases respectively by 3.2%, 9.0%, and 13.0% for a cavity volume fraction of 2.4%, 7.6%, and 11.7%, respectively. The significant hindering effect on the melting process of composite PCMs occurs in the case of cavities with a volume fraction of 3% and concentrated near the high-temperature wall. The cavities act as an adiabatic layer, extending the complete melting time of composite PCMs by 6.1%. To weaken the cavity effect, the metal foam skeleton with a thermal conductivity ratio of more than 100 can be selected to improve its leading role in heat transfer. [ABSTRACT FROM AUTHOR]

In this work, a lattice Boltzmann method (LBM) for studying microchannel gas flow is developed in the multi-flow regime. In the LBM, by comparing previous studies' results on effective viscosity in multi-flow regimes, the values of the rarefaction factor applicable to multi-flow regions were determined, and the relationship between relaxation time and Kn number with the rarefaction factor is given. The Kn number is introduced into the second-order slip boundary condition together with the combined bounce-back/specular-reflection (CBBSR) scheme to capture the gas flow in the multi-flow regime. Sensitivity analysis of the dimensionless flow rate to adjustable parameters using the Taguchi method was carried out, and the values of adjustable parameters were determined based on the results of the sensitivity analysis. The results show that the dimensionless flow rate is more sensitive to j than h. Numerical simulations of Poiseuille flow and pulsating flow in a microchannel with second-order slip boundary conditions are carried out to validate the method. The results show that the velocity profile and dimensionless flow rate simulated by the present numerical simulation method in this work are found in the multi-flow regime, and the phenomenon of annular velocity profile in the microchannel is reflected in the phases. [ABSTRACT FROM AUTHOR]

An innovative coupling numerical algorithm is proposed in the current paper, the front-tracking method–lattice Boltzmann method–machine learning (FTM-LBM-ML) method, to precisely capture fluid flow phase interfaces at the mesoscale and accurately simulate dynamic processes. This method combines the distinctive abilities of the FTM to accurately capture phase interfaces and the advantages of the LBM for easy handling of mesoscopic multi-component flow fields. Taking a single vacuole rising as an example, the input and output sets of the machine learning model are constructed using the FTM's flow field, such as the velocity and position data from phase interface markers. Such datasets are used to train the Bayesian-Regularized Back Propagation Neural Network (BRBPNN) machine learning model to establish the corresponding relationship between the phase interface velocity and the position. Finally, the trained BRBPNN neural network is utilized within the multi-relaxation LBM pseudo potential model flow field to predict the phase interface position, which is compared with the FTM simulation. It was observed that the BRBPNN-predicted interface within the LBM exhibits a high degree of consistency with the FTM-predicted interface position, showing that the BRBPNN model is feasible and satisfies the accuracy requirements of the FT-LB coupling model. [ABSTRACT FROM AUTHOR]

Understanding, predicting and controlling the motion of the solid particles in the square cavity with obstacles are important. This work performs a lattice Boltzmann study on the motion of a neutrally buoyant circular particle in a lid-driven square cavity with a semicircular obstacle, where the effects of Reynolds numbers and initial positions of the circular particle on the motion of the circular particle are investigated. The motion of the circular particle is affected significantly by the semicircular obstacle, which is quite different from the case without obstacles. With the increase of the Reynolds number, the motion of the circular particle is divided into three stages. At low Reynolds numbers (5 0 0 ≤ Re ≤ 8 0 0), similar to the case without obstacles, no matter where the initial position of the circular particle is, the limit cycle of the circular particle is the same. Beyond a critical Reynolds number (between 800 and 900), the limit cycle of the circular particle is dependent on the initial position of the circular particle obviously, which is attributed to the opposing centrifugal and wall-repulsion forces. [ABSTRACT FROM AUTHOR]

In this work, we propose a non-orthogonal multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) for the two-dimensional (2D) incompressible Navier-Stokes equations in vorticity-stream function formulation. In this method, the vorticity and the streamfunction equations are calculated by two separate LB equations, which are constructed by using the non-orthogonal transformation matrix. Most importantly, to eliminate the residual term that may appear in the recovered vorticity equation, the convection term is handled as a source term in the LB equation rather than being directly recovered by the evolution equation. In addition, due to the convection term in our method is computed with a local scheme, it retains the parallel feature of the standard LBM. We then test the accuracy and the stability of the present LBM by considering various benchmark examples. The results show that the present method has a second-order convergence rate in space. Our numerical results indicate that the present LBM is a good candidate for solving streamfunction-vorticity formulation. • A MRT LBM is proposed for vorticity-streamfunction formulation. • The present model is constructed with a simple non-orthogonal matrix. • The convection term in vorticity equation is treated as a source in the LBE. [ABSTRACT FROM AUTHOR]

To understand the relationship between topography and wetting, it is not enough to study the contact angle. Indeed, the liquid-solid interface plays an important role in wetting. However, data such as the total triple line length, the wetting area and the anchoring depth are inaccessible or difficult to obtain experimentally. This work proposes to overcome the experimental limitations by using a numerical approach to characterize the wetting behavior on textured surfaces. The wetting behavior of an anisotropic textured surface was compared for both experimental and numerical approaches. The experimental wetting is characterized by sessile drop experiments. The simulations were performed by applying the pseudo-potential Lattice-Boltzmann method. The numerical approach was then used to predict the wetting behavior of different materials. The simulations capture both the wetting state and the contact angle, in accordance with the experimental observation. Without making any assumptions about the interfacial shape and anchoring, the simulation allows to characterize the liquid-solid interface by quantifying the total length of the triple line and the wetting area. Simultaneously, the simulations enable the characterization of impregnation within textures for complex mixed regimes. [ABSTRACT FROM AUTHOR]

Aim: The aim of the article is to qualitatively assess the usability of a mathematical flow model for visualizing the flow in aortic bifurcation treated with stents. Methodology: Nine examinations of aortic bifurcations were conducted using a 4D Flow sequence. Patients without stents, patients with a stent in one branch, and patients with stents in both branches of the aortic bifurcation were examined. 4D Flow data were used to prepare a visualization of the velocity field. Flow simulations were performed based on the segmented bifurcation and measured flow data, including areas where flow measurements were affected by artifacts. Measured and simulated velocity fields were visually compared. Results: For patients without stents, the simulated flow contributed to eliminating small inaccuracies in the measured field. In patients with stents, the simulated data were more consistent than the measured data and provided additional insight into the situation within the stents. Discussion: Simulated velocity fields must inherently adhere to the laws of physics, allowing for the correction of measured data in regions where measurements are compromised. Depending on the accuracy of the segmentation, it may also offer new diagnostic information. However, the obtained results are solely qualitative and will need quantitative validation. Conclusion: The mathematical flow model can aid in quantitative assessment of flow in the vascular locations treated with stents where the direct MR measurement of blood flow fails. [ABSTRACT FROM AUTHOR]

In tsunami inundations or slope disasters of heavy rain, a lot of floating debris or driftwood logs are included in the flows. The damage to structures from solid body impacts is more severe than the damage from the water pressure. In order to study free-surface flows that include floating debris, developing a high-accurate simulation code of free-surface flows with high performance for large-scale computations is desired. We propose the single-phase free-surface flow model based on the cumulant lattice Boltzmann method coupled with a particle-based rigid body simulation. The discrete element method calculates the contact interaction between solids. An octree-based AMR (Adaptive Mesh Refinement) method is introduced to improve computational accuracy and time-to-solution. High-resolution grids are assigned near the free surfaces and solid boundaries. We conducted two kinds of tsunami flow experiments in the 15 and 70m water tanks at Hachinohe Institute of Technology and Kobe University to validate the accuracy of the proposed model. The simulation results have shown good agreement with the experiments for the drifting speed, the number of trapped wood pieces, and the stacked angles. [ABSTRACT FROM AUTHOR]

In this paper we propose a mesoscale model for polar fluids and numerically investigate its validity by considering well known benchmark cases: the steady and unsteady Poiseuille and the low Reynolds lid-driven cavity flow. Analytical and numerical results are compared with our numerical results and a very good agreement is found. Then we consider not yet investigated high Reynolds lid-driven cavity flow cases, obtaining consistent and interesting results, which encourage to apply the proposed model to more complex cases. [ABSTRACT FROM AUTHOR]

A diffuse interface-lattice Boltzmann model is proposed for modeling conjugate heat transfer problems with imperfect interfaces. According to the continuity condition of heat flux and jump condition of temperature across the imperfect interface, a unified sharp interface equation of the temperature field with a singular source term in the composite media domain is established. Then a diffuse interface equation is obtained by making a smoothed approximation of the unified sharp interface equation. The novel diffuse interface equation is restructured into a second-order heat diffusion equation with an anisotropic diffusion coefficient tensor. To numerically solve the second-order anisotropic diffusion equation, a multiple-relaxation-time (MRT) lattice Boltzmann (LB) scheme is employed. Several numerical simulations of benchmark test examples with analytical solutions are carried out to demonstrate the accuracy of the present model, including the steady-state heat diffusion in a two-layer medium with a flat interface, steady heat diffusion in a square domain with a curved interface and unsteady-state temperature diffusion with two-layer media. The numerical results show that the phenomenon of temperature jump across the imperfect interface can be successfully and correctly captured. Moreover, as an example of practical application, the new proposed diffuse interface model is utilized to predict the effective thermal conductivity of porous media with thermal contact resistance at pore scale. The variation law of the effective thermal conductivity is obtained for each parameter by studying the effects of thermal conductivity ratios of the dual-component material, the shape and volume fraction of blocks in the material, the interfacial thermal conductance coefficient, and the number of blocks on the effective thermal conductivity. Both uniform and random pore structures are considered. The previous theoretical equations strongly support the validity of the present model. [ABSTRACT FROM AUTHOR]

Building geometrical features have a significant effect on the local wind environment. The presented study investigated the impact of building perforation design geometrical features on mean wind speed around the vicinity of the building and the indoor environment for generic midrise buildings. The study focused on purpose-built perforation designs for wind permeability in naturally ventilated buildings. A lattice Boltzmann method simulation was conducted to evaluate the impact of perforation profile and draft angle. The influence of wind conditions such as wind speed and wind direction was taken into account in the study. The results indicated that the geometrical features of the perforation design can significantly affect the mean wind speed around the building vicinity and inside the building. The surrounding mean wind speed showed 6.75% and 7.25% differences from the baseline model for square and circular perforation profiles, respectively. The change in the perforation profile draft angle led to a 6.2% change in the mean wind speed. The major wind speed changes occurred in the indoor space. This finding can be used when selecting and designing building perforations for better natural ventilation performance, air quality, and wind comfort. [ABSTRACT FROM AUTHOR]

The paper presents a three-dimensional numerical study of the acoustic streaming induced by the dissipation of ultrasounds during their propagation in the air. The waves are generated by a circular acoustic source positioned at the center of the left wall of a parallelepipedic cavity. The simulations are performed with the lattice Boltzmann method associated with the D3Q19 multiple relaxation time model. A validation of this model is first performed by comparing the numerical and analytical acoustic intensities along the central axis of the acoustic source. The main objective of this study is to use two different methods to calculate the acoustic streaming flow. The first method is the direct calculation of the mean velocity fields as the mean values of the instantaneous velocities. The second method is an indirect technique, which first calculates the acoustic streaming force and then injects this force into the numerical code to produce the streaming. A comparison between the results obtained by the two methods was carried out and a good agreement was found between them. These different investigations, rather new in three-dimensional configurations, have allowed us to discuss the advantages and limitations of the lattice Boltzmann approach to simulate real situations of wave propagation and acoustic streaming. [ABSTRACT FROM AUTHOR]

Despite the advances in microscale modelling capabilities, physically observed non-zero Knudsen number (Kn) effects still elude the lattice Boltzmann method (LBM). This article details various Regularized LBM (RLBM) strategies used to model microscale flows and presents a thorough analysis on their applicability for the force-driven Poiseuille flow problem. In particular, we compare the formulations of eight schemes: Projected RLBM (P-RLBM), standard and Galilean Invariant Filtered Collision RLBM, Kn-dependant P-RLBM, Recursively Regularized LBM (R-RLBM), Hybrid R-RLBM, Central-Moment RLBM, and Onsager-Regularized LBM. We demonstrate, at different Kn with discrete Maxwell's diffuse kinetic wall boundary conditions, the numerical equivalence of the considered RLBM schemes for hard sphere molecules on the D2Q9 lattice. Thereafter, we include a Kn-dependant wall-modified mean-free-path and extend the characterization onto higher-order D2Q17, D2Q21 and Q2Q25-Zero-One-Three, Q2Q49-Zero-One-Two-Three lattices. The study indicates that RLBM schemes are Navier-Stokes solvers which fail to entirely capture all the non-equilibrium phenomenon of slip/transition regime flows. [ABSTRACT FROM AUTHOR]