Solid Motion Research Articles

Microscopic theory of ionic motion in solids

Drag and diffusion of mobile ions in solids are of interest for both purely theoretical and applied scientific communities. This article proposes a theoretical description of ion drag in solids that can be used to estimate ionic conductivities in crystals, and forms a basis for the rational design of solid electrolyte materials. Starting with a general solid-state Hamiltonian, we employ the nonequilibrium path integral formalism to develop a microscopic theory of ionic transport in solids in the presence of thermal fluctuations. As required by the fluctuation-dissipation theorem, we obtain a relation between the variance of the random force and friction. Because of the crystalline nature of the system, however, the two quantities are tensorial. We use the drag tensor to write down the formula for ionic mobility, determined by the potential profile generated by the crystal's ions.

Manure drying optimization

Horse manure is a poor feedstock whose energetic content is comparable to that of herbaceous biomass. However, it can be effectively burnt provided that it is previously desiccated, being its moisture content very high (60% wb).This work reports an experimental investigation to identify optimal conditions for horse manure drying in a bench-scale direct heating rotary drier, to be sequentially combined with its combustion. The relative impact of the variables affecting the drying rate is assessed by an extensive sensitivity analysis which addresses both the role of solid motion and the drying fluid.Results show that the effectiveness of the gas-solid contact has a remarkable effect on the moisture release rate, and the drying air temperature is the controlling parameter. Tests using flue gases as drying medium confirm that they can be profitably used, without significant loss of drying capacity, suggesting that combined drying and combustion is a viable option. Setting a target residual moisture at 30% wb, by sensitivity analysis the time required could be cut to 12 min, for a reference quantity of 1.2 kg, with a maximum moisture removal capacity of 70 (kg/h)/m3.

Study on the aggregate motion for gas–liquid–solid agitated tank reactors design using radioactive particle tracking

This work provides a detailed study on the agitation rate influence on the solid motion within a pilot-scale slurry tank containing nickel oxide particle agglomerates suspended in iso-octane by the action of an axial impeller and slight bubbling nitrogen gas. The behaviour of a tracer particle representing solid aggregates is determined from radioactive particle tracking measurements with a spatial accuracy of ∼2 mm. An increase in the overall space occupied by the tracer is observed with increasing stirring speed. The instantaneous velocities, calculated by time differentiation of successive tracer positions, are significantly higher than the dynamic error. A measure based on the Reynolds stress as the turbulence level estimator is reliably mapped in three dimensions from the ensemble-averaged correlation matrix of the Lagrangian tracer velocity, enabling studying the influence of agitation on the turbulence levels distribution. This study offers an improved understanding of three-phase stirred reactors, which efficiencies are heavily coupled to complex fluid mechanics, especially in a turbulent flow. The axisymmetry is broken due to the presence of baffles. Incrementing the agitation intensity reduces the axial coherence of the thrust on the solid phase, raising turbulence levels, especially nearby the impeller tip.

Investigation on gas–solid flow regimes in a novel multistage fluidized bed

Abstract Gas–solid flow regime in a novel multistage circulating fluidized bed is investigated in this study. Pressure fluctuations are first sampled from gas–solid flow systems and then are analyzed through frequency and time-frequency domain methods including power spectrum and Hilbert–Huang transform. According to the flow characteristics obtained from pressure fluctuations, it is found that the gas–solid motions in the multistage circulating fluidized bed exhibit two dominant motion peaks in low and high frequencies. Moreover, gas-cluster motions become intensive for the multistage circulating fluidized bed in comparison with the fast bed. Unlike the traditional methods, the fuzzy C-means clustering method is introduced to objectively identify flow regime in the multistage circulating fluidized bed on the basis of the flow characteristics extracted from bubbling, turbulent, fast, and multistage fluidized beds. The identification accuracy of fuzzy C-means clustering method is first verified. The identification results show that the flow regime in the multistage circulating fluidized bed is in the scope of fast flow regime under examined conditions. Moreover, the results indicate that the consistency of flow regime between two enlarged sections exists. In addition, the transition onset of fast flow regime in the multistage circulating fluidized bed is higher than that in the fast bed.

P72: Fully Coupled Computational Simulation of the Syncardia Total Artificial Heart May Optimize Clinical Performance

Background: The Syncardia Total Artificial Heart (TAH) is used as a bridge to transplant for patients with biventricular heart failure and currently the only FDA approved TAH. There is a dearth in studies investigating its mechanics, hemodynamics, and optimal performance. Previous studies have provided limited characterization of Syncardia’s dynamics with respect to platelet activation but did not fully realize a complete dynamic coupled solution. Thus, there is a knowledge gap with regards to understanding the operational capacity and performance characteristics of the TAH. The objective of this study is to characterize the hemodynamic performance of the Syncardia TAH to optimize operational parameters and further understand why the device is an effective bridge to transplant. Methods: COMSOL Multiphysics (COMSOL Inc.) was used to conduct fully coupled fluid-structure interaction simulations of the device in standard operation. The computational model contained a blood fluid volume within Syncardia’s housing assembly (ventricle), segmented polyurethane solution (SPUS) diaphragm chamber filled with air, and SynHall valves in the mitral and aortic positions. These components’ coupled physics allow for the cohesive motion of the blood volume, diaphragm, and valves by solving the fluid Navier-Stokes and solid motion equations. Results: Figure 1C is flow patterning representative of the left ventricular diastolic filling with the development of the ventricular vortex present within diastole. Negative pressure collapses and deforms the diaphragm as shown in Figure 1D to drive filling during diastole. Figure 1E shows regional stress on the SynHall mitral valve during diastole. Conclusions: We utilized a fully coupled model of the Syncardia to study hemodynamic properties including vorticity and shear stress spatial and temporal distributions. Future work will be to perform failure mode analysis to identify parameters that are associated with thrombosis as well as optimize clinical operational parameters including device setting and associated clinical management.

Parallel GPU-accelerated adaptive mesh refinement on two-dimensional phase-field lattice Boltzmann simulation of dendrite growth

Simulations of dendritic solidification involving melt convection and solid motion usually require a considerably higher computational domain than the dendrite size, whose computational efficiency with a uniform mesh is extremely low. In this study, to accelerate those two-dimensional simulations using the phase-field and lattice Boltzmann (PF-LB) methods, we developed a parallel computing method with multiple graphics processing units (GPUs) for the adaptive mesh refinement (AMR) method with dynamic load balancing (parallel-GPU AMR). It was confirmed that parallel-GPU AMR simulations were faster than those with the uniform mesh when the number of grid points in the adaptive mesh was around 40% or less than those in the uniform mesh. We also demonstrate that the developed parallel-GPU AMR can greatly accelerate the PF-LB simulations of dendrite growth with melt convection and solid motion.

On the mechanism of pattern transformations in soft granular crystals

Tunable nonlinear characteristics of granular crystals can be potentially useful to a wide range of applications. Several diatomic two-dimensional granular crystals are reported showing compression-driven pattern transformations, but their underlying mechanisms are not explained. In this study, we investigate the veiled underlying mechanisms of compression-driven pattern transformations in 2-D soft granular crystals. In order to adopt a linear perturbation approach, we employ a simplified mass–spring model derived from the granular contact network and perform a series of numerical analyses including quasi-static analysis and microscopic/macroscopic instability analyses. The results show that the pattern transformation of the considered granular crystals are closely relating to instability. Furthermore, the effects of Young’s modulus and radius on the pattern transformations are studied by using the mass–spring model. We confirm the significance of instabilities in pattern transformations and the effectiveness of the simple mass–spring model by performing the corresponding finite element analyses where granular particles are modeled by continuum elements. In motions of continuum solids, instability is well known to serve as a symmetry-breaking mechanism. This study demonstrates that instability also plays a critical role to break the symmetry of deformed patterns in granular crystals.

Toward a Lattice Boltzmann Method for Solids—Application to Static Equilibrium of Isotropic Materials

This work presents a novel method for simulating the behavior of solid objects with the Lattice Boltzmann Method (LBM). To introduce and validate our proposed framework, comparative studies are performed for computing the static equilibrium of isotropic materials. Remembering that the LBM has strong theoretical foundations in the Boltzmann equation; this latter is firstly adjusted to solid motions, through its Boltzmann-Vlasov special case. This is indeed the case when combined with a suitable mean-field external force term to set a reliable solid framework. Secondly, a library is built and plugged on the top of the well-known Parallel Lattice Boltzmann Solver (PaLaBoS) library. Numerical implementations based on the previous equation of motion for solids are led in a non-intrusive manner so as to present results with an easy and flawless reproducibility. A newly designed Lattice Boltzmann Method for Solids (LBMS) is exhibited through a few key algorithms, showing the overall operation plus the major improvements. Efficiency, robustness and accuracy of the proposed approach are illustrated and contrasted with a commercial Finite Element Analysis (FEA) software. The obtained results reveal considerable potential concerning static and further dynamic simulations involving solid constitutive laws within the LBM formalism.

Multi-fidelity modeling to predict the rheological properties of a suspension of fibers using neural networks and Gaussian processes

Unveiling the rheological properties of fiber suspensions is of paramount interest to many industrial applications. There are multiple factors, such as fiber aspect ratio and volume fraction, that play a significant role in altering the rheological behavior of suspensions. Three-dimensional (3D) numerical simulations of coupled differential equations of the suspension of fibers are computationally expensive and time-consuming. Machine learning algorithms can be trained on the available data and make predictions for the cases where no numerical data are available. However, some widely used machine learning surrogates, such as neural networks, require a relatively large training dataset to produce accurate predictions. Multi-fidelity models, which combine high-fidelity data from numerical simulations and less expensive lower fidelity data from resources such as simplified constitutive equations, can pave the way for more accurate predictions. Here, we focus on neural networks and the Gaussian processes with two levels of fidelity, i.e., high and low fidelity networks, to predict the steady-state rheological properties, and compare them to the single-fidelity network. High-fidelity data are obtained from direct numerical simulations based on an immersed boundary method to couple the fluid and solid motion. The low-fidelity data are produced by using constitutive equations. Multiple neural networks and the Gaussian process structures are used for the hyperparameter tuning purpose. Results indicate that with the best choice of hyperparameters, both the multi-fidelity Gaussian processes and neural networks are capable of making predictions with a high level of accuracy with neural networks demonstrating marginally better performance.

Gas-Solid Interface Interactions Based on Molecular Dynamics Simulations

Gas-solid interface interaction as the key point and difficult point of dilute gas flow, understanding the mechanism of it, to have a clearer understanding of the gas molecules in the solid near-wall surface motion law. This paper combines the molecular dynamics method and particle beam method to simulate the interaction between argon molecules and solid platinum wall surface, to study the scattering law after the collision between gas molecules and solid surface at different incidence angles and the mechanism of energy conversion between them, the results show that the tangential kinetic energy is lost after the collision between gas molecules and wall surface, while the change of normal kinetic energy is determined by the magnitude of the incident velocity; the incident velocity is small, the reflected tangential velocity distribution basically fits the Maxwell reflection distribution when the incident velocity reaches a high speed, and the reflected tangential velocity distribution appears head-and-shoulder or even bimodal distribution, which is helpful for future research on the tangential momentum adaptation coefficient of the scattering nucleus model.

Evaluation of the effects of land-use change and increasing deforestation in the Sapanca Basin on total suspended solids (TSS) movement with predictive models

Evaluation of the effects of land-use change and increasing deforestation in the Sapanca Basin on total suspended solids (TSS) movement with predictive models

Dynamic water potential waves in unsaturated soils

Quantitative descriptions of the temporal and spatial variations of volumetric water content and total water potential in unsaturated soils have for more than nine decades focused on diffusive mechanisms as represented by the Richards equation (Richards, 1931). However, recent laboratory studies (Lo et al., 2017) have revealed short-time transient behavior of water in non-deforming unsaturated soils that is distinctly oscillatory, not diffusive. In this paper, we establish a theoretical framework to generalize the Richards equation in a systematic way to account for non-diffusive mechanisms giving rise to oscillatory behavior in the water content and total water potential. A partial differential equation is developed, with the total water potential as the dependent variable, based on the coupling of mass and linear momentum balance within the continuum theory of mixtures. This new differential equation becomes equivalent to the Richards equation when non-diffusive mechanisms can be neglected, but when this condition is not met, the governing equation describes damped propagating wave behavior of the total water potential. This dynamic wave differs from a poroelastic wave in respect to solid framework motions and wave speed, as well as time and length scales. For a rigid, homogeneous unsaturated soil, the governing equation reduces to the telegraph equation, which can be solved analytically. An inherent feature of our approach is the appearance of natural time and length scales characteristic of total water potential waves. Consideration of these natural scales for three representative soils of differing texture helps to prescribe more precisely the domain of applicability of the Richards equation.

Immersed body motion: near-bottom added mass effects

The presence of a solid boundary can cause a substantial increase in added mass due to a solid body movement in the fluid. If the body is very close to the boundary, the added mass increases at an even greater rate. The added mass can be of considerable importance in many dams and hydropower, water/ocean, civil and mechanical engineering problems; furthermore, it has an important effect on the dynamics of the vibrating body in the fluid. The principal aim of this paper is to define a novel model to properly evaluate the near-bottom effects of the added mass and to investigate the instantaneous pressure field due to a body movement that changes the thickness of a compressible thin fluid film close to a solid boundary. The body movement can be due to the application of an external force according to Newton's law. This phenomenon is studied theoretically in this paper, and a hydrodynamic model able to compute the instantaneous pressure field in the thin fluid film is drawn out. The fluid film thickness variation, producing compression and decompression waves, tends to reduce the mean body displacement due to external forces, but it generates both high-frequency fluctuations in body force and in body displacements. For the first time, this novel study provides the near-bottom added mass and justifies the strong body accelerations measured in the laboratory experiments that have not been evidenced in the theoretical studies in the known literature.

Review of Cases of Integrability in Dynamics of Lower- and Multidimensional Rigid Body in a Nonconservative Field of Forces

Study of the dynamics of a multidimensional solid depends on the force-field structure. As reference results, we consider the equations of motion of low-dimensional solids in the field of a medium-drag force. Then it becomes possible to generalize the dynamic part of equations to the case of the motion of a solid, which is multidimensional in a similarly constructed force field, and to obtain the full list of transcendental first integrals. The obtained results are of importance in the sense that there is a nonconservative moment in the system, whereas it is the potential force field that was used previously.

Cellular automata-lattice Boltzmann simulation of multi-dendrite motion under convection based on dynamic grid technology

A cellular automata-lattice Boltzmann coupling model with dynamic grids for simulating the preferential growth and movement of multiple dendrites under convection of binary alloy melt. In this model, dendritic growth is computed using the cellular automata method, and flow of the melt is computed using the lattice Boltzmann method, and the motion of the dendrite is described by solving the equation of motion. To deal with the motion of the dendrite, each dendrite is given a local dynamic grid, which can move with the motion of the dendrite. The correctness of this model in dealing with the motion of solids in fluids by simulating the settlement of a cylinder in a vertical channel. Then, dendrites of three different preferred growth directions grow under pure diffusion are simulated to prove that the model can also solve the grid dependence of dendritic growth in the Cartesian grid. Finally, this model is used to stimulate the growth of a single dendrite under Couette flow, and the settlement of multiple dendrites under gravity, and the growing motion of multiple dendrites under Poiseuille flow. The simulation results show that the dendritic morphology can be well maintained when this model is used to deal with dendritic movement, and the melt convection and motion will promote the dendritic growth in the direction of motion.

Fully-resolved simulations of an ellipsoidal particle settling in a Bingham fluid

Despite many particle shapes and motion patterns that can be present in viscoplastic settling, the scientific studies are mostly limited to spherical particles and cases in which the solid body motion is purely vertical or rotational. Here we tackle the problem of an ellipsoidal particle settling in Bingham fluid through fully-resolved simulations. Oblate and prolate spheroids of varied aspect ratios and initial orientations are analyzed. We use the Lattice Boltzmann Method (LBM), in which the Bingham constitutive equation is solved exactly. We employ the Immersed Boundary Method (IBM) to delineate the particle boundaries and enforce the no-slip condition over them. For the case of creeping flow around a settling ellipsoid, we benchmark results of the critical yield number for oblate and prolate spheroids against augmented Lagrangian method (ALM) data and provide values for different aspect ratios and initial orientations. Then, we analyze the dynamics of prolate and oblate spheroids settling in Bingham fluid at an inertial flow. We present the evolution of trajectory, orientation, angular momentum, Reynolds number, and drift angle for various aspect ratios and initial orientations.

A three-dimensional hybrid immersed smoothed point interpolation method for fluid-structure interactions

A three-dimensional hybrid immersed smoothed point interpolation method (3D HIS-PIM) has been developed to handle fluid-structure interactions (FSI) with simple geometries. Incompressible viscous fluid is solved by semi-implicit characteristic-based split method with standard Galerkin discretization, smoothed point interpolation method is employed to solve the motion and deformation of nonlinear solids based on gradient smoothing technique, and the virtual fluid is introduced into the entire solid domain to calculate the FSI force. The proposed method can avoid the fluid mesh adjustments, and allows the use of four-node tetrahedral elements for both fluid and solid domains to simplify the pre-processing for mesh generations. The FSI force condition is imposed with a hybrid force, which uses a form of body force for pressure term and boundary force for shear force. The boundary force accords with the physical law and the body force can ensure the numerical stability. The proposed method works well for FSI problems with moving or largely deformable solids, and can achieve more accurate results using a hybrid force than the fully body force in the original method. A large range of mesh size ratios between fluid and solid meshes is allowed due to the treatment of FSI boundary conditions.

Study of Solid Hydrogen Pellet Speed in a Gas Gun–Type Injector

Based on the ideal gas gun theory (IGT) approximation, an analytical study of solid hydrogen pellet motion in a gas gun–type pellet injector has been performed. A parametric investigation has been conducted to study the pellet speed dependence on the gun characteristics and the propellant conditions. The calculations have been verified by applying various experimental data reported from the literature. Experimental results are within 70% to 90% of the ideal IGT and are in line with global predictions. Calculations indicate that the speed of the pellet has a strong dependence on the propellant pressure and its mass, and a weak dependence on the length of the gun barrel. In addition, the effects of shock waves due to the sudden opening of the propellant valve and some nonideal effects, such as the effect of friction at the propellant pellet–wall interface, have been studied. The results of the calculations have been verified by applying them to the experimental results.

Multi-phase field lattice Boltzmann model of columnar-to-equiaxed transition in entire welding molten pool

Columnar-to-equiaxed transition (CET) often occurs during the solidification of the weld. Moving molten pool and strong fluidity are two notable characteristics in this process. The former causes the deflective epitaxial growth of columnar dendrites, while the latter makes the equiaxed dendrites grow asymmetrically and continuously move, collide and coalesce in the melt. This paper proposed a multi-phase field lattice Boltzmann model to simulate the CET in the entire molten pool. The model can characterize the polycrystalline growth, compute the fluid flow, and simulate the solid motion, collision, and coalescence. It also combined the transient growth condition model and the continuous nucleation model to reproduce the moving molten pool and define heterogeneous nucleation respectively. It further combined the initial grain structure of the base metal to provide a more realistic condition for epitaxial growth. The proposed model was verified by simulating the pure motion of dendrite in lid-driven flow, the free fall of single dendrite in static flow, and the single-dendrite growths in lid-driven and channel flow. The CET in the entire molten pool was simulated under different conditions, including considering or ignoring the fluid flow and gravity, the columnar and equiaxed dendrites growing simultaneously or sequentially. In these simulations, settlement, collision, and coalescence of equiaxed dendrites were reproduced successfully. Clear asymmetric growth, dendrite aggregation effect, and solute vortex were found. Significant differences in the size, symmetry, dendrite spacing, dendrite morphology, and solute distribution were found when the melt flow was considered or ignored. The dense equiaxed dendrite belt was found in the later stage of CET. They gathered in front of columnar dendrites and dominated the following solidification. The typical mixed structure that consists of columnar and equiaxed grains was obtained after complete solidification.

Curvature-Mediated Forces on Elastic Inclusions in Fluid Interfaces.

Heterogeneous fluid interfaces often include two-dimensional solid domains that mechanically respond to changes in interfacial curvature. While this response is well-characterized for rigid inclusions, the influence of solid-like elasticity remains essentially unexplored. Here, we show that an initially flat, elastic inclusion embedded in a curved, fluid interface will exhibit qualitatively distinct behavior depending on its size and stiffness. Small, stiff inclusions are limited by bending and experience forces directed up gradients of Gaussian curvature, in keeping with prior findings for rigid discoids. By contrast, larger and softer inclusions are driven down gradients of squared Gaussian curvature in order to minimize the elastic penalty for stretching. Our calculations of the force on a solid inclusion are shown to collapse onto a universal curve spanning the bending- and stretching-limited regimes. From these results, we make predictions for the curvature-directed motion of deformable solids embedded within a model interface of variable Gaussian curvature.