Search

Underwater pulsed spark discharge has been widely used in industrial fields as a source of shock waves or acoustic waves, and numerical modeling of the discharge and pressure wave characteristics is necessary to improve the application performance. In this paper, a numerical model is proposed that couples the circuit equation, the mass and energy conservation equations, and a momentum conservation equation based on the Rankine–Hugoniot conditions. A tabulated wide range equation of state and conductivity data of water are used, and various physical processes during the plasma channel expansion are considered, including the energy flow and mass exchange between the channel and the surrounding water due to thermal radiation, evaporation, and condensation. The model self-consistently solves the circuit current and voltage, the plasma channel parameters including composition, temperature, conductivity, pressure, etc., and the pressure profile at a certain distance from the discharge channel. The calculated results show good consistency with the experimental measurements, and three sets of experimental results from other literature are tested to further verify the applicability and effectiveness of the model. [ABSTRACT FROM AUTHOR]

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum. [ABSTRACT FROM AUTHOR]

We report on viscous adhesion measurements conducted in sphere-plane geometry between a rigid sphere and soft surfaces submerged in silicone oils. Increasing the surface compliance leads to a decrease in the adhesive strength due to elastohydrodynamic deformation of the soft surface during debonding. The force-displacement and fluid film thickness-time data are compared to an elastohydrodynamic model that incorporates the force measuring spring and finds good agreement between the model and data. We calculate the pressure distribution in the fluid and find that, in contrast to debonding from rigid surfaces, the pressure drop is non-monotonic and includes the presence of stagnation points within the fluid film when a soft surface is present. In addition, viscous adhesion in the presence of a soft surface leads to a debonding process that occurs via a peeling front (located at a stagnation point), even in the absence of solid–solid contact. As a result of mass conservation, the elastohydrodynamic deformation of the soft surface during detachment leads to surfaces that come closer as the surfaces are separated. During detachment, there is a region with fluid drainage between the centerpoint and the stagnation point, while there is fluid infusion further out. Understanding and harnessing the coupling between lubrication pressure, elasticity, and surface interactions provides material design strategies for applications such as adhesives, coatings, microsensors, and biomaterials. [ABSTRACT FROM AUTHOR]

Cracks are a common rock microstructure and have a large effect on elastic properties during wave propagation. The fluid flow between a crack and its adjacent pore space can cause wave attenuation and dispersion. In this work, we introduce a crack connectivity parameter which is meant to improve the expression of local flow by weighting the contributions of fully connected and isolated cracks. We then update the analytical expression for frequency-dependent moduli by modifying the boundary conditions of the linearized Navier–Stokes equation and mass conservation equation. The proposed model contains the effect of cracks and stiff pores, in which the attenuation and dispersion are determined by squirt-flow and stiff-pore relaxations. The resulting model shows the squirt-flow relaxation frequency depends on not only the crack aspect ratio but also the crack connectivity. However, their contributions are different. The crack connectivity has little effect on the attenuation amplitude of shear modulus, but affects the attenuation amplitude of bulk modulus when multiple sets of cracks exist in the rock. The attenuation frequency band is also affected by the crack connectivity. As the crack connectivity deteriorates, the attenuation peak moves to low frequencies. In addition, by comparing the crack connectivity with the fluid viscosity coefficient, it is observed that the crack connectivity only affects the attenuation frequency band of cracks, whereas the fluid viscosity coefficient affects the attenuation frequency bands of cracks and stiff pores simultaneously. Thus, the introduction of crack connectivity is a supplement to the theoretical model of cracked fluid-saturated rocks. It helps understand the local fluid flow induced by seismic waves and provides a reasonable variation analysis of moduli and attenuation, especially for tight reservoirs. [ABSTRACT FROM AUTHOR]

The conservative Allen-Cahn equation satisfies three important physical properties, namely the mass conservation law, the energy dissipation law, and the maximum bound principle. However, very few numerical methods can preserve them at the same time. In this paper, we present a multi-physical structure-preserving method for the conservative Allen-Cahn equation with nonlocal constraint by combining the averaged vector field method in time and the central finite difference scheme in space, which can conserve all three properties simultaneously at the fully discrete level. We propose an efficient linear iteration algorithm to solve the presented nonlinear scheme and prove that the iteration satisfies the maximum bound principle and a contraction mapping property in the discrete L ∞ norm. Furthermore, concise error estimates in the maximum norm are established on non-uniform time meshes. The theoretical findings of the proposed scheme are verified by several benchmark examples, where an adaptive time-stepping strategy is employed. [ABSTRACT FROM AUTHOR]

We present an efficient numerical method to approximate the flux variable for the Darcy flow model. An important feature of our new method is that the approximate solution for the flux variable is obtained without approximating the pressure at all. To accomplish this, we introduce a user‐defined parameter delta, which is typically chosen to be small so that it minimizes the negative effect resulting from the absence of the pressure, such as inaccuracy in both the flux approximation and the mass conservation. The resulting algebraic system is of significantly smaller degrees of freedom, compared to the one from the mixed finite element methods or least‐squares methods. We also interpret the proposed method as a single step iterate of the augmented Lagrangian Uzawa applied to solve the mixed finite element in a special setting. Lastly, the pressure recovery from the flux variable is discussed and an optimal‐order error estimate for the method is obtained. Several examples are provided to verify the proposed theory and algorithm, some of which are from more realistic models such as SPE10. [ABSTRACT FROM AUTHOR]

This work proposes the use of an array of yawed porous vanes to control the lateral bedload transport by locally steering bedform migration and maximize the amount of sediments redirected toward a potential sediment extraction system or bypass channel. A laboratory experiment was conducted in a quasifield-scale channel with an array of permeable vanes installed on one side, in live-bed conditions under bedload dominant regime, i.e., negligible suspended load. A baseline experiment without vanes was also performed for comparison. The evolution of migrating bedforms of different scales was tracked in space and time using a high-resolution, state-of-the-art laser scanning device. The bedload transport rate in the streamwise direction was first calculated using bedforms' geometry and migration velocity, and then spatially distributed over the entire monitored area using a new Eulerian-averaged grid-mapping method. This allowed us to introduce a new methodology to estimate the lateral bedload transport using control volume theory and applying mass conservation. Quantitative assessments of lateral bedload transport along the channel yield consistent results, suggesting that the vanes effectively move sediments laterally as intended. Under the investigated setup, the maximum lateral sediment transport rate ranges from 9% to 18% of the whole domain-averaged streamwise transport rate. The developed methodology also allowed to identify the location where sediment capture could be maximized for the given vane spatial distribution. Practical Applications: In river engineering, in-stream structures are used to control flow and sediment movement to prevent erosion, intake clogging, and habitat disruption. Submerged vanes are small, angled structures that are installed to redirect sediments toward a preferred direction by creating secondary flow circulations. This study tests experimentally an array of porous vanes in an open channel to measure and quantify the lateral displacement of sediment. Porous plates were selected to minimize local scour and anchoring requirements while directing flow, bedforms, and sediment laterally. The amount of sand moved laterally is measured by comparing the streamwise bedform transport within and outside of the vane array. The proposed vane array is part of a modular hydrosuction sediment bypass system being developed for low-head dams, which features inlets to collect coarse sediments and siphon them over the dam via a slurry conduit. The vane array is meant to be installed upstream of the collector to increase the lateral transport of coarse sediment toward the intake structures. Porous elements can potentially be replaced by vegetation and log structures for nature-based alternatives. [ABSTRACT FROM AUTHOR]

Existing nonlocal diffusion models are mainly classified into two categories: bond-based models, which involve a single-fold integral and usually simulate isotropic diffusion, and state-based models, which contain a double-fold integral and can additionally prototype anisotropic diffusion. While bond-based models exhibit more computational efficiency, they sometimes could be limited in modeling capabilities. In this paper, we successfully develop a novel bond-based nonlocal model for the diffusion process with matrix-valued coefficients in non-divergence form. Our approach incorporates the coefficients into a covariance matrix and employs the multivariate Gaussian function with truncation to define the kernel function, and subsequently model the nonlocal diffusion through the bond-based formulation. We establish the well-posedness of the proposed model along with deriving some of its properties on maximum principle and mass conservation. Furthermore, an efficient linear collocation scheme is designed for numerical solution of our model. Comprehensive experiments in two and three dimensions are conducted to showcase application of the proposed nonlocal model to both isotropic and anisotropic diffusion problems, and to demonstrate high-order accuracy and conditional δ -convergence of the proposed collocation scheme. [ABSTRACT FROM AUTHOR]

We propose two efficient energetic spectral-element methods in time for marching nonlinear gradient systems with the phase-field Allen–Cahn equation as an example: one fully implicit nonlinear method and one semi-implicit linear method. Different from other spectral methods in time using spectral Petrov-Galerkin or weighted Galerkin approximations, the presented implicit method employs an energetic variational Galerkin form that can maintain the mass conservation and energy dissipation property of the continuous dynamical system. Another advantage of this method is its superconvergence. A high-order extrapolation is adopted for the nonlinear term to get the semi-implicit method. The semi-implicit method does not have superconvergence, but can be improved by a few Picard-like iterations to recover the superconvergence of the implicit method. Numerical experiments verify that the method using Legendre elements of degree three outperforms the 4th-order implicit-explicit backward differentiation formula and the 4th-order exponential time difference Runge-Kutta method, which were known to have best performances in solving phase-field equations. In addition to the standard Allen–Cahn equation, we also apply the method to a conservative Allen–Cahn equation, in which the conservation of discrete total mass is verified. The applications of the proposed methods are not limited to phase-field Allen–Cahn equations. They are suitable for solving general, large-scale nonlinear dynamical systems. • Two energetic spectral-element schemes in time for parabolic systems. • Maintain mass conservation and energy dissipation. • Superconvergence of the implicit method proven without use of supercloseness. • Linear, energy stable and efficient semi-implicit method. • Semi-implicit scheme as iterative implicit solver excels existing methods. [ABSTRACT FROM AUTHOR]

We consider a nonconservative nonlinear Schrödinger equation (NCNLS) with time‐dependent coefficients, inspired by a water waves problem. This problem does not have mass or energy conservation, but instead mass and energy change in time under explicit balance laws. In this paper, we extend to the particular NCNLS two numerical schemes which are known to conserve energy and mass in the discrete level for the cubic nonlinear Schrödinger equation. Both schemes are second‐order accurate in time, and we prove that their extensions satisfy discrete versions of the mass and energy balance laws for the NCNLS. The first scheme is a relaxation scheme that is linearly implicit. The other scheme is a modified Delfour–Fortin–Payre scheme, and it is fully implicit. Numerical results show that both schemes capture robustly the correct values of mass and energy, even in strongly nonconservative problems. We finally compare the two numerical schemes and discuss their performance. [ABSTRACT FROM AUTHOR]

The multispecies Landau collision operator describes the two-particle, small scattering angle or grazing collisions in a plasma made up of different species of particles such as electrons and ions. Recently, a structure preserving deterministic particle method (Carrillo et al. in J. Comput. Phys. 7:100066, 2020) has been developed for the single species spatially homogeneous Landau equation. This method relies on a regularization of the Landau collision operator so that an approximate solution, which is a linear combination of Dirac delta distributions, is well-defined. Based on a weak form of the regularized Landau equation, the time dependent locations of the Dirac delta functions satisfy a system of ordinary differential equations. In this work, we extend this particle method to the multispecies case, and examine its conservation of mass, momentum, and energy, and decay of entropy properties. We show that the equilibrium distribution of the regularized multispecies Landau equation is a Maxwellian distribution, and state a critical condition on the regularization parameters that guarantees a species independent equilibrium temperature. A convergence study comparing an exact multispecies Bobylev-Krook-Wu (BKW) solution to the particle solution shows approximately 2nd order accuracy. Important physical properties such as conservation, decay of entropy, and equilibrium distribution of the particle method are demonstrated with several numerical examples. [ABSTRACT FROM AUTHOR]

In this article, we propose a split-step finite element method (FEM) for the two-dimensional nonlinear Schrödinger equation (NLS) with Riesz fractional derivatives in space. The space-fractional NLS is first spatially discretized by finite element scheme and the semi-discrete variational scheme is obtained. We prove that it maintains the mass and energy conservation laws. Then, we establish a fully discrete split-step finite element scheme for the considered problem, which avoids the iteration at each time layer, thereby significantly reducing computational cost. The discrete mass conservation property and error estimate of this split-step finite element scheme is derived. Finally, illustrative tests and the numerical simulation of dynamic of wave solutions are included to confirm its effectiveness and capability. [ABSTRACT FROM AUTHOR]

Urbanization forms one of the most drastic alterations of the environment and poses a major threat to wildlife. The human–induced modifications of the landscape may affect individual's fitness resulting in population declines. Research on how urbanization affects fitness traits has shown mixed results. However, studies typically contrasted data from a single species from few urban and non‐urban sites collected over short timeframes. Examining multiple species across a broad urbanization gradient enables a more robust comparison and understanding of how different species are impacted by urbanization‐knowledge crucial for generating population predictions, which are essential for conservation management. Here, we use data from a nation‐wide citizen science project to examine variation in survival and relative body mass and size (wing length) of common passerine birds, collected along an urbanization gradient in the Netherlands over an 8‐year period. Urbanization was measured as the distance from the city's border and the proportion of impervious surface area. Although the overall association between urbanization and survival was slightly negative, there was support for lower survival closer to the city in three species (chiffchaff Phylloscopus collybita, European robin Erithacus rubecula, European greenfinch Chloris chloris) and higher survival closer to the city in two (great tit Parus major and house sparrow Passer domesticus) of the 11 species examined. The contrasting survival successes among species suggest that ongoing urbanization may lead to shifts in community structure and loss of biodiversity. Impacts of urbanization on relative mass and size also exhibited varying effects, albeit less pronounced, and these effects were not correlated with the effects on survival. This implies that body mass and size cannot be used as indicators for urban‐associated patterns of survival. Our results further imply that effective conservation management targeting bird communities should involve a range of diverse actions, as focusing on single measures is unlikely to simultaneously impact multiple species due to the variation in responses to urbanization. [ABSTRACT FROM AUTHOR]

Unsteady-flow wind tunnels typically employ control louvers installed in the wind-tunnel circuit to produce rapid changes in the test-section flow velocity. For these wind tunnels, an open-return circuit is advantageous because of the lower mass of air that must be accelerated by the louver forcing. However, in addition to inertial effects, the wind-tunnel behavior is also affected by the interaction of the pressure disturbances from the louvers and their reflection from the open boundary conditions of the wind tunnel, resulting in a windspeed response that is nonintuitively related to the louver motion. In this paper, an experimental investigation into the unsteady behavior of a model-scale, open-return wind tunnel is described. An incompressible method of characteristics model for the wind tunnel is shown to successfully predict the wind-tunnel dynamic behavior, and an approach to produce controlled windspeed histories that compensates for the wind-tunnel response is demonstrated. [ABSTRACT FROM AUTHOR]

Icing is a popular research area in wind energy, and the icing problem of the supercooled droplet–ice crystal mixed-phase condition is one of the new challenges. A numerical method for analyzing the icing characteristics of wind turbine airfoil under mixed-phase conditions is presented. The control equations for the dynamics of supercooled droplets and ice crystals are formulated using the Lagrangian method. Equations for the conservation of mass and energy during the icing process involving supercooled droplets and ice crystals are constructed. The impact of erosion phenomena on the mixed-phase icing process is examined, and methodologies for solving the control equations are introduced. The numerical method is utilized for modeling mixed-phase icing under a range of conditions. The results of these simulations are then compared with data obtained from icing wind tunnel tests to assess the validity of the method. The influence of various mixed-phase conditions on ice shapes is studied. It is found that higher icing temperatures correspond to a larger icing range and amount. The increase in supercooled droplet content, ice crystal content, and ice crystal diameter all contribute to enhanced ice accretion. However, the effects of ice crystal content and diameter are relatively minor. [ABSTRACT FROM AUTHOR]

The global flows of cultivated seaweed were estimated for the year 2019 using a combination of literature review, assumptions, and simple conservation of mass calculations. Red seaweeds were found to be the largest contributors to the hydrocolloids industry, for both food and non‐food applications. Carrageenan‐containing species were found to be the largest contributors to both food (62%) and non‐food (55%) hydrocolloids and are the primary source for water gels, which make up 27% of non‐food hydrocolloids, followed by pet food (16%), toothpaste (6%), and others (6%). Carrageenan also accounts for almost all meat products, which make up 35% of the food hydrocolloid industry, and dairy products, which make up 26%. Agar‐containing seaweeds are used in confections (10% of food hydrocolloids), baking (9%), and other (2%) and make up 15% of non‐food hydrocolloids. Porphyra (nori) is cultivated for direct consumption and makes up 23% of direct food consumption. Cultivated brown seaweeds were found to comprise Laminaria/Saccharina for alginate production (30%), Laminaria/Saccharina for direct consumption (44%), and Undaria for direct consumption (16%). About half of the alginates produced make up 18% of food hydrocolloids, and the other half is used in non‐food hydrocolloids comprising technical grades (28% of non‐food) and animal feed (3%). The results are discussed in the context of emerging markets for seaweed and the potential for seaweeds as a substitute for staple foods, and the environmental impact of seaweed farming is explored through a review of life cycle assessment studies. [ABSTRACT FROM AUTHOR]

The frequency solutions of finite elements may significantly deteriorate as the mesh aspect ratios become large, which implies a severe element side-length discrepancy. In this work, an aspect ratio dependent lumped mass (ARLM) formulation is proposed for serendipity elements, i.e., the two-dimensional eight-node and three dimensional twenty-node quadratic elements for linear problems. In particular, a generalized parametric lumped mass matrix template taking into account the mesh aspect ratios is introduced to examine the frequency accuracy of serendipity elements. This generalized lumped mass matrix template completely meets the mass conservation and non-negativity requirements. Subsequently, analytical frequency error estimates are developed for serendipity elements, which clearly illustrate the relationship between the frequency accuracy and element aspect ratios. Accordingly, optimal mass parameters are obtained as the functions of element aspect ratios through solving a constrained optimization problem for frequency accuracy. It turns out that the resulting aspect ratio dependent lumped mass matrices yield much more accurate frequency solutions, in comparison to the diagonal scaling lumped mass (HRZ) matrices and the mid-node lumped mass (MNLM) matrices without consideration of the element aspect ratios, especially for finite element discretizations with severe element side-length discrepancy. The superior accuracy and robustness of the proposed ARLM over HRZ and MNLM are consistently demonstrated by numerical examples. [ABSTRACT FROM AUTHOR]

Since the fundamental works of Kachanov and Rabotnov, creep damage mechanics is an established field of research in solid mechanics. The starting point is the creep behavior of materials under moderate loads but elevated temperatures. The final stage of creep behavior is accompanied by damage and other microstructural changes such as embrittlement. In the present paper a detailed analysis of literature is given. A special focus is made on the different types of representation of damage by scalar, vectorial and tensorial variables. In addition, some Russian sources are presented which are not widely known yet. The survey is representative, but not complete - due to the large number of sources, it is not possible to provide a complete overview. Considering the huge number of parameters of tensorial damage variables which should be established experimentally in the second part of the paper a simple model for the high temperature creep and embrittlement in metals and alloys under conditions of the long-term usage is introduced. The model is an extension of R. Arutunyan's model developed in the 90th of the last century. The extension includes the consideration of a compressible medium, the introduction of the mass conservation law and true stress, and definition of the damage parameter as a relative change in the density of the material. The parameters are experimentally estimated and the comparison of simulations and experiments is given. [ABSTRACT FROM AUTHOR]

Throughout history, many scientists considered time as the result of changing the world and believed that time is not true. Among those who say that time is not true, Einstein is the only one who was able to mathematically explain the relativity of time in the field of geometry (space time) and present his equations in relativistic physics. Although Einstein, like other scientists, did not provide a clear definition of time, he presented the relativity of time well. He showed that time is not independent of space and bends along with space. Also, Einstein used the speed of light to convert mass into energy to introduce the law of mass–energy equivalence. Currently, basic laws such as conservation of mass, conservation of energy and equivalence of mass and energy have been presented. Recently, due to the importance of time in the development of science, especially in the field of water and chemistry, "timemass equivalence law" has also been presented (by the author). In this research, with the aim of expanding the relativity of time in the flows of mass and energy (not the field of motion and geometry), while presenting new definitions of "phenomenon", "time" and "specific speed of transformation", in addition to the theory of "mass equivalence law" "Time" was completed, the general equations of equivalence of energy time—and timemass were introduced. Then, to check the results more accurately, the general masstime equation (in this study, absorption kinetics) by performing surface absorption experiments of heavy metals (Fe + 2, Pb + 2, Zn + 2, Ni + 2, Cd + 2, Cu + 2)) was investigated by the adsorbents of green walnut shell (GWH) and its biochar (GWHB), and the results are tested in different ways. [ABSTRACT FROM AUTHOR]

The orchid Dendrobium moniliforme faces endangerment due to habitat loss and illegal harvesting, necessitating the development of an optimized artificial propagation system to aid conservation and reintroduction efforts. This study evaluated the effects of three plant growth media, namely Murashige and Skoog (MS), Hyponex, and Orchid Maintenance Medium (OMM) (P668), and various organic additives (apple homogenate, banana homogenate, and coconut water) on the in vitro seedling growth of D. moniliforme. The results reveal that, in early postgermination stages, seedlings achieve maximum growth in the Hyponex medium, with a fresh weight (92 mg) and root length (2.7 cm) approximately 20-fold greater than those in the MS medium and OMM. After 6 months, for seedlings grown in MS medium and OMM with banana (50 g·L−1), the mean fresh weights were 29 and 107 mg, respectively; however, the highest biomass was observed in seedlings grown in the Hyponex medium with coconut water (50 mL·L−1), exhibiting a mean fresh weight of 201 mg. This study highlights Hyponex medium with coconut water as the most effective combination for promoting D. moniliforme growth and identifies suitable organic supplements for the in vitro cultivation of seedlings from asymbiotic seed culture. This propagation system offers valuable technical support for the mass production and conservation of this epiphytic orchid. [ABSTRACT FROM AUTHOR]

The present study discusses flood hazard characteristics in the lower reaches of the West Rapti River based on the results obtained from field surveys and numerical computations using depth averaged 2-D numerical models for flood flow and associated sediment transportation. To evaluate the inundation process with sediment erosion and deposition in the floodplain, a new erosion term was introduced into the mass conservation equations for suspended sediment and bed sediment. The results obtained from numerical computations indicated that field data on the spatial distributions of depths for inundation, and sediment erosion and deposition can be evaluated by the numerical model. Thus, numerical predictions were performed for the inundated areas, and the accumulated volumes of sediment erosion/deposition for floods with return periods of 50, 100, and 200 years, as a step towards damage assessment and risk assessment due to floods with active sediment transportation in the floodplains. [ABSTRACT FROM AUTHOR]

As a typical metallurgical defect, macrosegregation seriously affects the internal quality of the continuous casting billet, and it cannot be solved by processes such as high-temperature diffusion and rolling. For continuous casting billet, the solidification shrinkage and thermal shrinkage of the microstructure directly affect the macrosegregation defect. In order to reveal the effects of solidification shrinkage and thermal shrinkage on the melt flow, microstructure distribution, and solute segregation, a multiphase solidification model based on the Eulerian–Eulerian approach was established in this work. The growth behaviors of the columnar dendrite trunk and the columnar dendrite tip were fully considered, as well as the nucleation, growth, free migration of equiaxed grains, and the columnar-to-equiaxed transition (CET). Besides, the corresponding relationship between the secondary dendrite arm spacing (SDAS) and the cooling rate has also been taken into account in the model, which makes the net mass transport source term of the mass conservation equations more accurate. The calculation results show that when no any shrinkage behavior is considered in the model, the melt flow velocity in front of the solidification end will gradually decrease until it is the same as the casting speed, and the segregation index at the billet center will gradually increase until it reaches the maximum value at the solidification end. Both thermal shrinkage and solidification shrinkage can generate a negative pressure zone in the billet center, sucking the poor-solute melt located the upstream of continuous casting strand flows towards the solidification end, and mixing with the enriched-solute melt before the solidification end, thereby inhibiting macrosegregation. However, compared with the solidification shrinkage, the effect of thermal shrinkage on reducing the positive segregation index in the billet center is limited. [ABSTRACT FROM AUTHOR]

We study the long time behavior of the generalized solution of the flow and thermal explosion model of the reactive real micropolar gas. The dynamics of the chemical reaction involved and the usual laws of conservation of mass, momentum, angular momentum, and energy generate a complex governing system of partial differential equations. The fluid is nonideal and non‐Newtonian. In this work, we prove that the problem can be solved in an infinite time domain and establish the asymptotic properties of the solution. Namely, we conclude that for certain parameter values, the solution stabilizes exponentially to a steady‐state solution, while for others the stabilization occurs but at power decay rate. At the end, we conducted a few numerical tests whereby we experimentally confirmed theoretical findings about long‐term behavior of the solution. [ABSTRACT FROM AUTHOR]

In this work, the Cattaneo–Christov double diffusion model is used to analyze the three-dimensional boundary layer flow of an upper-convected Maxwell fluid flowing over a bi-directional stretching surface. The model assumes that the fluid's diffusivity is concentration-dependent, whereas dynamic viscosity and thermal conductivity are temperature-dependent; and the model takes into account the influence of the magnetic field of uniform strength. The problem is formulated using the conservation rules of mass, momentum, and energy as well as the boundary layer approximation. The resulting nonlinear system is then numerically solved using the bvp4c procedure in MATLAB. The obtained results are set forth graphically to illustrate the variations of different parameters. It is contemplated that the increase in thermal relaxation parameter results in a drop in fluid temperature while there is an enhancement in the concentration profile. Also, the temperature field has a direct relationship with the temperature-dependent viscosity. This research has proven its utility in industries where there is a need to analyze fluid flow over surfaces that can stretch in two directions. [ABSTRACT FROM AUTHOR]

The creeping flow of a tangent hyperbolic liquid via a channel of porous walls is discussed in this article. For the formulation of problem, the laws of conservation of mass, momentum, and energy are used. A description of fluid leakage through channel walls is provided by Darcy's law. An analytical solution to the equations of motion is determined with appropriate physical approximations by applying the perturbation technique. Expressions for the hydrostatic pressure, velocity field, and temperature are found. The flow characteristics of tangent hyperbolic fluid are affected by the filtration coefficient and inlet pressure, which are also discussed. Graphs are used to discuss the effects of the inlet pressure, the Wiessenberg number, the magnetic field, the law index, the Brickman number, and the wall filtration parameter on the flow characteristics. The mean pressure difference is shown to be increased by the magnetic field. The derived data are used in a flat plate hemodialyzer to investigate the filtrate flow. The theoretical values for the hemodialyzer's mean pressure difference and filtration rate are computed using the derived solutions. A reasonable agreement is established between the calculated results and the experimental data. It is determined that the fluid flow in a flat plate hemodialyzer can be studied hydrodynamically using the model that is presented. A flat plate hemodialyzer's filtrate flow is examined by using the results that were obtained. [ABSTRACT FROM AUTHOR]

Recently, non-local configurations have been proposed by adding beyond nearest neighbour couplings among elements in lattices to obtain roton-like dispersion relations and phase and group velocities with opposite signs. Even though the introduction of non-local elastic links in metamaterials has unlocked unprecedented possibilities, literature models and prototypes seem neither to provide criteria to compare local and non-local lattices nor to discuss any related rules governing the transition between the two configurations. A physically reasonable principle that monoatomic one-dimensional chains must obey to pass from single- to multi-connected systems is here proposed through a mass conservation law for elastic springs thereby introducing a suitable real dimensionless parameter α to tune stiffness distribution. Therefore, the dispersion relations as a function of α and of the degree of non-locality P are derived analytically, demonstrating that the proposed principle can be rather interpreted as a general mechanical consistency condition to preserve proper dynamics, involving the spring-to-bead mass ratio. Finally, after discussing qualitative results and deriving some useful inequalities, numerical simulations and two-dimensional FFTs are performed for some paradigmatic examples to highlight key dynamics features exhibited by chains with finite length as the parameters α and P vary. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

The contradiction of high subducting plate rate (ranging from 4 to 9 cm/yr on Earth's surface) and low slab sinking rate (about 1 and 2 cm/yr in lower mantle) calls for significant slab deformation in the middle mantle. However, mechanisms that can account for both the deformation and the rate discrepancy have not been fully explored. Here, using 2‐D numerical models that incorporate grain size evolution, we propose a new slab deformation mode, slab segmentation and stacking, to accommodate the differential slab sinking rates. Our results show that the segmented slab due to faulting and grain‐size reduction may further break off and stack over itself as it encounters the high‐viscosity lower mantle. Stacked slabs slowly sink in the lower mantle, while periodic slab tearing hinders upward stress transmission, allowing shallow plates to subduct at a higher rate. This discovered mode also provides an alternative explanation for slab thickening in the lower mantle. Plain Language Summary: According to observations and analysis, the velocities of plates entering the trench are much higher than the slab sinking rate in the lower mantle. Inconsistent velocities at the slab's two ends must be accommodated by slab deformation or accumulation in the middle mantle to ensure mass conservation. We have considered three different deformation modes: slab buckling, horizontal deflection, segmentation and stacking. Compared to the diffusive plastic weakening in the mode of slab buckling, previous studies have shown that slab faulting and grain size evolution can induce stronger localized weakening within slabs. Our study goes a step further by finding that the segmented slab can break off and stack over itself periodically when it encounters the lower mantle. This allows the slab to deform more easily in the mantle transition zone, enabling the plate to subduct at a higher rate while keeping the lower‐mantle slab sinks at a low rate. We also find that this mode of slab deformation can equally well explain the thickening of the slab in the lower mantle. Key Points: The discrepancy between the subducting plate rate and lower mantle slab sinking rate calls for slab accumulations in the middle mantleSimple buckling explains the accumulation but is not sufficient to accommodate the rate discrepancyThe mode of slab segmenting, breaking off, and stacking is a possible solution to the slab accumulation and rate discrepancy [ABSTRACT FROM AUTHOR]

Existence, non-existence, and uniqueness of mass-conserving weak solutions to the continuous collision-induced nonlinear fragmentation equations are established for the collision kernels Φ satisfying Φ (x , y) = x λ 1 y λ 2 + y λ 1 x λ 2 , (x , y) ∈ (0 , ∞) 2 , with λ 1 ≤ λ 2 ≤ 1 , and non-integrable fragment daughter distributions. In particular, global existence of mass-conserving weak solutions is shown when 1 ≤ λ : = λ 1 + λ 2 ≤ 2 with λ 1 ≥ k 0 , the parameter k 0 ∈ (0 , 1) being related to the non-integrability of the fragment daughter distribution. The existence of at least one mass-conserving weak solution is also demonstrated when 2 k 0 ≤ λ < 1 with λ 1 ≥ k 0 but its maximal existence time is shown to be finite. Uniqueness is also established in both cases. The last result deals with the non-existence of mass-conserving weak solutions, even on a small time interval, for power law fragment daughter distribution when λ 1 < k 0. It is worth mentioning that the previous literature on the nonlinear fragmentation equation does not treat non-integrable fragment daughter distribution functions. [ABSTRACT FROM AUTHOR]

This paper presents a numerical comparison of finite-element methods resulting in local mass conservation at the element level for Poisson's problem, namely the primal hybrid and mixed methods. These formulations result in an indefinite system. Alternative formulations yielding a positive-definite system are obtained after hybridizing each method. The choice of approximation spaces yields methods with enhanced accuracy for the pressure variable, and results in systems with identical size and structure after static condensation. A regular pressure precision mixed formulation is also considered based on the classical RT k space. The simulations are accelerated using Open multi-processing (OMP) and Thread-Building Blocks (TBB) multithreading paradigms alongside either a coloring strategy or atomic operations ensuring a thread-safe execution. An additional parallel strategy is developed using C++ threads, which is based on the producer-consumer paradigm, and uses locks and semaphores as synchronization primitives. Numerical tests show the optimal parallel strategy for these finite-element formulations, and the computational performance of the methods are compared in terms of simulation time and approximation errors. Additional results are developed during the process. Numerical solvers often fail to find an accurate solution to the highly indefinite systems arising from finite-element formulations, and this paper documents a matrix ordering strategy to stabilize the resolution. A procedure to enable static condensation based on the introduction of piecewise constant functions that also fulfills Neumann's compatibility condition, and yet computes an average pressure per element is presented. • Numerical comparison of the mixed, primal hybrid, and other locally conservatives finite element methods. • Introduction of a twice hybridized primal hybrid method, yielding a positive definite matrix after static condensation. • Comparison of multi-threaded strategies and thread-safety mechanisms. • A numerical procedure to stabilize the linear system resolution for indefinite matrices is described. • A general procedure that enables static condensation and fulfills Neumann's compatibility condition. [ABSTRACT FROM AUTHOR]

Propeller-wing-flap systems are subject to complex aerodynamic interactions between each part of the system. Although the propeller-wing interaction in cruise conditions is well defined, the high-lift condition is relatively unexplored. Effective analysis of the complex aerodynamic relationship between propeller, wing, and flap is being impeded by a lack of understanding of the underlying mechanisms. In this paper, we therefore investigate the effects of a 2D jet impinging on a multisection airfoil. We quantify which factors that define a jet-wing-flap configuration dominate lift, drag, and moment responses. We further investigate interactions between these factors and discuss how they affect the flow. We find that the jet velocity ratio is by far the dominant factor in lift, drag, and moment responses, but it does not have strong interactions with other factors. The sensitivities of the multi-element airfoil do not change significantly when impinged upon by a jet, except when critical Mach numbers are exceeded. This strongly affects the aerodynamic response and dominant sensitivities. We furthermore conclude that the immersion of the flap is a key aspect when it comes to augmenting the lift by increasing the dynamic pressure in the flowfield. The conclusions from this paper can provide key insights for propeller-wing-flap flows. [ABSTRACT FROM AUTHOR]

A physical description is given of the formation of corrosion product deposits on the surfaces of pipelines of heat supply systems, and an investigation has been made into the effects of various factors on this process. An analysis has been made of the existing models of formation of corrosion deposites. A mathematical model has been developed for the formation of corrosion product deposites in the liquid's motion through pipelines of heat supply systems in the region of linear velocity of the growth of deposits at a constant temperature of the heat transfer agent. The model is based on equations of conservation of the mass of dissolved depolarizer and solid particles suspended in the solution. The parametric calculations performed on the basis of the developed mathematical model have shown a possibility for the existence of a maximum in the thickness of the corrosion product deposit layer through the pipe length. [ABSTRACT FROM AUTHOR]

Annual mass migrations of seabirds between their breeding and wintering grounds are critical for ensuring their survival and reproductive success. It is essential to comprehend their physical condition in order to identify the causes of death and to facilitate conservation efforts. This study focuses on evaluating the age, body condition index, and metabolites in liver and muscle (triglycerides, glycerol, glycogen, cholesterol, lactate, and glucose) of stranded Razorbills (n = 84) and Atlantic puffins (n = 11). The study was conducted along the Andalusian coast of Spain during the winter season of 2022–2023. The study examined the body condition of stranded individuals and their metabolic state to determine potential factors that may have caused their deaths. The study found that the majority of stranded individuals were juveniles. Both species exhibited low levels of carbohydrate (glucose and glycogen) in their tissues and high levels of lactate in their muscles. These findings could suggest that the individuals had undergone prolonged, strenuous exercise, demanding energy on anaerobic pathways, which may have been associated with migration. The study highlights the significance of adhering to standardized protocols when assessing the body condition of stranded seabirds. Doing so can help to identify causes of death and facilitate conservation efforts. A proposed index for body condition, which incorporates biometric measurements and individual physical condition, provides a comprehensive means of understanding the health of these unique species. This study underscores the importance of further research into the conservation measures and recommendations for protecting seabird populations. It is critical to comprehend the contributing factors of mass mortality incidents to work towards safeguarding these species and preserving their vital migration patterns. [ABSTRACT FROM AUTHOR]

In this paper, we propose two momentum-preserving finite difference schemes for solving one-dimensional Camassa–Holm equation with periodic boundary conditions. A two-level nonlinear difference scheme and a three-level linearized difference scheme are constructed by using the method of order reduction. For nonlinear scheme, we combine mid-point rule and a specific difference operator, which ensures that our obtained scheme is of second-order convergence in both temporal and spatial directions. For linearized scheme, we apply a linear implicit Crank–Nicolson scheme in the temporal direction, then unique solvability and momentum conservation are analysed in detail. Numerical experiments are provided for Camassa–Holm equation admitting different types of solutions, which demonstrate the convergence order and accuracy of the proposed methods coincide with theoretical analysis. Moreover, numerical results show that the nonlinear scheme exhibits better accuracy for mass conservation, while the linearized scheme is more time-saving in computation. [ABSTRACT FROM AUTHOR]

The Polymer Electrolyte Membrane Water Electrolyser (PEMWE) has gained significant interest among various electrolysis methods due to its ability to produce highly purified, compressed hydrogen. The spatial configuration of bipolar plates and their flow channel patterns play a critical role in the efficiency and longevity of the PEM water electrolyser. Optimally designed flow channels ensure uniform pressure and velocity distribution across the stack, enabling high-pressure operation and facilitating high current densities. This study uses flow channel geometry inspired by authentic vine leaf patterns found in biomass, based on various plant leaves, including Soybean, Victoria Amazonica, Water Lily, Nelumbo Nucifera, Kiwi, and Acalypha Hispida leaves, as a novel channel pattern to design a PEM bipolar plate with a circular cross-section area of 13.85 c m 2 . The proposed bipolar design is further analysed with COMSOL Multiphysics to integrate the conservation of mass and momentum, molecular diffusion (Maxwell–Stefan), charge transfer equations, and other fabrication factors into a cohesive single-domain model. The simulation results showed that the novel designs have the most uniform velocity profile, lower pressure drop, superior pressure distribution, and heightened mixture homogeneity compared to the traditional serpentine models. [ABSTRACT FROM AUTHOR]

Simple Summary: The environment of caged-laying hen houses is mainly regulated by ventilation, and the performance of the ventilation system directly affects the welfare and production performance of laying hens. In this study, a combined ventilation system was designed and constructed to improve the microclimate of the house in summer. The practicality of the combined ventilation system was verified for the environmental regulation of the laying hen house, comparing with the traditional negative-pressure ventilation system in terms of airflow pattern, airflow velocity uniformity, temperature regulation variability, and relative humidity distribution status. Mechanical ventilation is an important means of environmental control in multitier laying hen cages. The mainstream ventilation mode currently in use, negative-pressure ventilation (NPV), has the drawbacks of a large temperature difference before and after adjustment and uneven air velocity distribution. To solve these problems, this study designed and analyzed a combined positive and negative-pressure ventilation system for laying hen cages. According to the principle of the conservation of mass to increase the inlet flow in the negative-pressure ventilation system on the basis of the addition of the pressure-wind body-built positive-and-negative-pressure-combined ventilation (PNCV) system, further, computational fluid dynamics (CFD) simulation was performed to analyze the distribution of environmental parameters in the chicken cage zone (CZ) with inlet angles of positive-pressure fans set at 45°, 90°, and 30°. Simulation results showed that the PNCV system increased the average air velocity in the CZ from 0.94 m/s to 1.04 m/s, 1.28 m/s, and 0.99 m/s by actively blowing air into the cage. The maximum temperature difference in the CZ with the PNCV system was 2.91 °C, 1.80 °C, and 3.78 °C, which were all lower than 4.46 °C, the maximum temperature difference in the CZ with the NPV system. Moreover, the relative humidity remained below 80% for the PNCV system and between 80% and 85% for the NPV system. Compared with the NPV system, the PNCV system increased the vertical airflow movement, causing significant cooling and dehumidifying effects. Hence, the proposed system provides an effective new ventilation mode for achieving efficient and accurate environmental control in laying hen cages. [ABSTRACT FROM AUTHOR]

The number of pore volumes to breakthrough is one of the most critical indicators of wormhole characterization in the matrix acidizing process. This number is often needed for experimental work that is time-consuming and costly. In this article, an empirical model was used to evaluate the acidizing procedure in the carbonate cores, including limestone and dolomite. This empirical model measures the number of wormholes formed in the carbonate cores after acid injection by using the conservation of mass law. This approach maintained the transport relative reaction rates of core and acid within the wormhole structure during the wormhole formation procedure. In addition, this empirical model accounted for changes in acid concentration as an injected fluid flow. Also, the changes in carbonate porosity, the effect of the Damköhler number, and injection rate were included in the model. Compared to other experimental and semi-empirical works, the established model gave an excellent assessment of 95.45% for the average accuracy and 0.9933 for the average coefficient of determination. Therefore, an empirical technique to approximate this number in the carbonate formations with high accuracy using physical core and acid properties is herein proposed. [ABSTRACT FROM AUTHOR]

The run-up of a vortex hydrodynamic bore onto an inclined beach is the subject of this study. To theoretically analyze this problem, we use the Benny equations, which, within the shallow water model, allow us to take into account the distribution of horizontal fluid velocity along the depth of the fluid layer. We show that the presence of a shear flow behind a bore significantly modifies the different regimes of bore motion toward the shoreline depending on its strength. The subsequent collapse of the bore near the shoreline with the release of a high-speed run-up jet onto the dry shore is also significantly modulated by the degree of vorticity of the fluid flow. The maximum flooding length and run-up height increase significantly with increasing vorticity of the fluid flow. We use a theoretical model based on the characteristic Whitham rule for a bore, supplemented by the laws of conservation of mass and the momentum of a liquid crossing a shock wave. It is assumed that the wave run-up that appears after the "collapse" of the bore is determined by gravity. As a result, the maximum value of the wave run-up, its speed, the influence of flow vorticity, and its structure as a whole are estimated. The acceptable agreement of the simulation results with experimental data can serve as a justification for the applicability of our model to the calculation of the bore run-up onto a sloping beach. [ABSTRACT FROM AUTHOR]

The soil beneath buildings constructed in cold regions is affected by frost heave, causing the walls to crack and even the buildings to incline and collapse. Therefore, predicting the frost heave when subjected to overburden pressure is crucial for engineering buildings in cold areas. Utilizing the conservation equation of mass, Darcy's equation, and the assumption that the pore water pressure at the top of a frozen fringe, denoted as uw, during the quasi-steady state can be approximately estimated using the Clapeyron equation, a quasi-steady frost heave rate model considering the overburden pressure was proposed. This study considered the difference in pore water pressure within the frozen fringe, which causes water to move from the unfrozen zone to the ice lens, where it subsequently accumulates and freezes into ice. The pore water pressure at the bottom of the frozen fringe, denoted as uu, can be estimated using the soil water characteristic curve (SWCC). The thickness of the frozen fringe was determined using the freezing temperature, segregation temperature, and temperature gradient. The segregation temperature was determined using the two-point method. Additionally, the model suggested that, when uw = uu, the movement of water stopped, leading to the end of frost heave. To validate the proposed model, three existing frost-heaving experiments were analyzed. The findings demonstrated that the estimated rates of frost heave of the samples closely matched the experimental data. Additionally, external pressure delayed water migration. This study can offer theoretical support for building engineering in cold regions. [ABSTRACT FROM AUTHOR]

In depositing multiple layers on the surface of failed metal parts, the overlap rate is a critical factor in determining the surface smoothness and uniformity of the coating thickness. Therefore, special attention must be given to the spacing between adjacent melt tracks when planning laser paths on complex metal parts. A strategy for selecting the overlap rate for multi-track cladding is proposed, based on the key parameters of surface curvature, mass conservation, and the profile of single-track coatings. A multi-track overlap model is developed, expressing the relationship between coating morphology and the overlap rate. The optimal spacing value is determined to achieve the goal of high-quality coating remanufacturing. To verify the effectiveness of this method, nickel-based powder was used for laser forming on the surface of metal gears. The results showed that the surface of the cladding layer was smooth and flat, further demonstrating that this model helps improve the repair quality and overall performance of curved metal parts. Thus, it provides valuable guidance for the remanufacturing of failed metal parts. [ABSTRACT FROM AUTHOR]

The lack of data on flood events poses challenges in flood management. In this paper, we propose a novel approach to enhance flood-forecasting models by utilizing the capabilities of Generative Adversarial Networks (GANs) to generate synthetic flood events. We modified a time-series GAN by incorporating constraints related to mass conservation, energy balance, and hydraulic principles into the GAN model through appropriate regularization terms in the loss function and by using mass conservative LSTM in the generator and discriminator models. In this way, we can improve the realism and physical consistency of the generated extreme flood-event data. These constraints ensure that the synthetic flood-event data generated by the GAN adhere to fundamental hydrological principles and characteristics, enhancing the accuracy and reliability of flood-forecasting and risk-assessment applications. PCA and t-SNE are applied to provide valuable insights into the structure and distribution of the synthetic flood data, highlighting patterns, clusters, and relationships within the data. We aimed to use the generated synthetic data to supplement the original data and train probabilistic neural runoff model for forecasting multi-step ahead flood events. t-statistic was performed to compare the means of synthetic data generated by TimeGAN with the original data, and the results showed that the means of the two datasets were statistically significant at 95% level. The integration of time-series GAN-generated synthetic flood events with real data improved the robustness and accuracy of the autoencoder model, enabling more reliable predictions of extreme flood events. In the pilot study, the model trained on the augmented dataset with synthetic data from time-series GAN shows higher NSE and KGE scores of NSE = 0.838 and KGE = 0.908, compared to the NSE = 0.829 and KGE = 0.90 of the sixth hour ahead, indicating improved accuracy of 9.8% NSE in multistep-ahead predictions of extreme flood events compared to the model trained on the original data alone. The integration of synthetic training datasets in the probabilistic forecasting improves the model's ability to achieve a reduced Prediction Interval Normalized Average Width (PINAW) for interval forecasting, yet this enhancement comes with a trade-off in the Prediction Interval Coverage Probability (PICP). [ABSTRACT FROM AUTHOR]

This study investigates the impact of gas product recycling (GPR) on the performance of the steam methane reforming (SMR) process using nickel (Ni) and rhodium (Rh) catalysts. Hydrogen production, a cleaner alternative to fossil fuels, predominantly employs SMR due to its industrial efficacy. The study utilizes numerical simulations with Cantera software to evaluate the effects of recycling up to 30% of gaseous products at temperatures of 800, 1000, and 1200 Kelvin and a steam-to-methane ratio of 3. Key governing equations, including mass and energy conservation, as well as reaction kinetics described by the Arrhenius equation, are applied. The simulations reveal that GPR at 1200 K with a Ni catalyst enhances syngas production and reduces CO2 leakage, making it a viable option within the 20-30% recycling range. However, GPR at lower temperatures (800 K and 1000 K) for both Ni and Rh catalysts, and at 1200 K for Rh catalysts, results in undesirable increases in carbon deposition and CO2 production. Thus, GPR is generally not recommended for Rh catalysts due to significant coke formation. These findings underscore the potential benefits and limitations of GPR in optimizing SMR processes, particularly highlighting the suitability of Ni catalysts at higher temperatures. [ABSTRACT FROM AUTHOR]

Fluid flow in miniature devices is often characterized by a boundary "slip" at the wall, as opposed to the classical paradigm of a "no-slip" boundary condition. While the traditional mathematical description of fluid flow as expressed by the differential forms of mass and momentum conservation equations may still suffice in explaining the resulting flow physics, one inevitable challenge against a correct quantitative depiction of the flow velocities from such considerations remains in ascertaining the correct slip velocity at the wall in accordance with the complex and convoluted interplay of exclusive interfacial phenomena over molecular scales. Here, we report an analytic engine that applies combined physics-based and data-driven modeling to arrive at a quantitative depiction of the interfacial slip via a molecular-dynamics-trained machine learning algorithm premised on fluid structuration at the wall. The resulting mapping of the system parameters to a single signature data that bridges the molecular and continuum descriptions is envisaged to be a preferred computationally inexpensive route as opposed to expensive multi-scale or molecular simulations that may otherwise be inadequate to resolve the flow features over experimentally tractable physical scales. [ABSTRACT FROM AUTHOR]

In this study, we have derived a thermodynamically consistent phase-field model for two-phase flows with thermocapillary effects. This model accommodates variations in physical properties such as density, viscosity, heat capacity, and thermal conductivity between the two components. The model equations encompass a Cahn-Hilliard equation with the volume fraction as the phase variable, a Navier-Stokes equation, and a heat equation, and meanwhile maintains mass conservation, energy conservation, and entropy increase simultaneously. Given the highly coupled and nonlinear nature of the model equations, we developed a semi-decoupled, mass-preserving, and entropy-stable time-discrete numerical method. We conducted several numerical tests to validate both our model and numerical method. Additionally, we have investigated the merging process of two bubbles under non-isothermal conditions and compared the results with those under isothermal conditions. Our findings reveal that temperature gradients influence bubble morphology and lead to earlier merging. Moreover, we have observed that the merging of bubbles slows down with increasing heat Peclect number Pe T when the initial temperature field increases linearly along the channel, while bubbles merge faster with heat Peclect number Pe T when the initial temperature field decreases linearly along the channel. • A thermodynamically consistent phase-field model for two-phase flows with thermocapillary effects. • A semi-decoupled, mass-preserving, and entropy-stable numerical method. • Investigated numerically the merging process of two bubbles under isothermal and non-isothermal conditions. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the classical energy transport equation for pure tidal flows in estuaries by including the effects of residual water level and freshwater discharge. Starting from the one-dimensional mass and momentum conservations, we derive analytical expressions for energy flux and its dissipation, which can be used to explore the interaction between tide and river from an energy perspective. It has been shown that the potential energy flux is dominant over the kinetic energy flux, and the energy contribution made by tide-river interaction is negligible compared with that due to tidal flow and freshwater discharge. A critical position corresponding with zero energy flux can be identified, reflecting a balance between along-channel tidal amplitude and residual water level. Assuming the variation of system energy tends to zero, we derive the long-term equilibrium bed profile with a convex-up shape, where we identify the location of a second estuarine turbidity maximum (ETM) at a position determined by the balance between river- and tide-induced energy flux. The dynamic response of tidal propagation extent and critical position with zero energy flux are shown to adjust to reflect seasonal changes towards the formation of a bed profile that is in dynamic equilibrium. [ABSTRACT FROM AUTHOR]

Mitigation of combustion instability of solid propellant rocket motors is ever being attempted by several researchers as the problem is very complicated in nature. The acoustic admittance of composite solid propellants (AP/HTPB/RDX/Al) is experimentally investigated using Impedance tube technique. It is one of the indirect experimental techniques to determine the combustion response of the solid propellants besides T-burner. The governing equations based on the conservation of mass, momentum and energy (reactive flow is simplified to have only the axial temperature gradient) are linearized and solved to determine the acoustic admittance of the burning propellant. Different methods of analysis were explored to validate/compare the results obtained and are matching well. Some of the unreported details of the analysis are brought out. A novel way of utilizing the outer tube besides the inner tube as against the literature (wherein the inner tube is kept inside the outer tube) to maintain the chamber pressure is explored. A test conducted at fundamental acoustic mode (110 Hz) at 2 MPa at room temperature (303 K) is considered for the analysis. A rotary valve capable of operating up to a mean chamber pressure of 12 MPa is developed in this work to act as an acoustic driver for the experiments. The advantage of the impedance tube technique over T-burner is that the former is capable of measuring both the real and imaginary part of combustion response whereas the latter can only measure the real part. The imaginary part of the combustion response besides the real part is useful to predict the stability characteristics of the solid propellant rocket motor. [ABSTRACT FROM AUTHOR]

Modelling magma transport requires robust numerical schemes for chemical advection. Current numerical schemes vary in their ability to be mass conservative, computationally efficient, and accurate. This study compares four of the most commonly used numerical schemes for advection: an upwind scheme, a weighted essentially non-oscillatory (WENO-5) scheme, a semi-Lagrangian (SL) scheme, and a marker-in-cell (MIC) method. The behaviour of these schemes is assessed using the passive advection of two different magmatic compositions. This is coupled in 2D with the temporal evolution of a melt anomaly that generates porosity waves. All algorithms, except the upwind scheme, are able to predict the melt composition with reasonable accuracy, but none of them is fully mass conservative. However, the WENO-5 scheme shows the best mass conservation. In terms of total running time and when multithreaded, the upwind, SL, and WENO-5 schemes show similar performance, while the MIC scheme is the slowest due to reseeding and removal of markers. The WENO-5 scheme has a reasonable total run time, has the best mass conservation, is easily parallelisable, and is therefore best suited for this problem. [ABSTRACT FROM AUTHOR]

This work focuses on the well-known issue of mass conservation in the context of the finite element technique for computational fluid dynamic simulations. Specifically, non-conventional finite element families for solving Navier–Stokes equations are investigated to address the mathematical constraint of incompressible flows. Raviart–Thomas finite elements are employed for the achievement of a discrete free-divergence velocity. In particular, the proposed algorithm projects the velocity field into the discrete free-divergence space by using the lowest-order Raviart–Thomas element. This decomposition is applied in the context of the projection method, a numerical algorithm employed for solving Navier–Stokes equations. Numerical examples validate the approach's effectiveness, considering different types of computational grids. Additionally, the presented paper considers an interface advection problem using marker approximation in the context of multiphase flow simulations. Numerical tests, equipped with an analytical velocity field for the surface advection, are presented to compare exact and non-exact divergence-free velocity interpolation. [ABSTRACT FROM AUTHOR]

The efficient use of depleted gas reservoirs for hydrogen storage is a promising solution for transitioning to carbon-neutral energy sources. This study proposes an analytical framework for estimating hydrogen storage capacity using a comprehensive material balance approach in depleted gas reservoirs. The methodology integrates basic reservoir engineering principles with thermodynamic considerations to accurately estimate hydrogen storage capacity in both volumetric drive and water drive gas reservoirs through an iterative approach based on mass conservation and the real gas law. This framework is implemented in a Python program, using the CoolProp library for phase behavior modeling with the Soave–Redlich–Kwong (SRK) equation of state. The methodology is validated with numerical simulations of a tank model representing the two reservoir drive mechanisms discussed. Also, a case study of a synthetic complex reservoir demonstrates the applicability of the proposed approach to real-world scenarios. The findings suggest that precise modeling of fluid behavior is crucial for reliable capacity estimations. The proposed analytical framework achieves an impressive accuracy, with deviations of less than 1% compared to estimates obtained through numerical simulations. Insights derived from this study can significantly contribute to the assessment of strategic decisions for utilizing depleted gas reservoirs for hydrogen storage. [ABSTRACT FROM AUTHOR]

This study develops and verifies two advanced wake models based on super-Gaussian distribution: three-dimensional (3D) super-Gaussian (3DSG) and 3D anisotropic super-Gaussian (3DASG) models. They have a smooth Gaussian–top-hat shape (a combination of Gaussian and top-hat shapes) in the near-wake region that gradually transitions to a Gaussian shape in the far-wake region. These models are based on the law of mass conservation and considers wind shear effect; hence, they can accurately describe asymmetric wind distribution in the vertical direction. Because of this Gaussian–top-hat shape, the model is more accurate in simulating the wake in the near-wake region. The anisotropic model also considers different wake expansion rates in various dimensions, rendering the model more realistic. The accuracy and generality of the two models are verified using four wake data sets obtained from wind tunnel tests and wind field measurements. The validation includes the prediction of the wake profile and relative error of the models. The results show that the two models can well predict the wake distribution of various sizes of turbines at any spatial location in the full-wake region. [ABSTRACT FROM AUTHOR]

High salinity gas reservoirs are prone to salt deposition in the middle and late stages of development, resulting in the decrease of porosity and permeability, which seriously affects the development of gas reservoirs. Therefore, it is necessary to understand the changes of reservoir porosity and permeability parameters in time. At present, the relationship between salt deposition, porosity, and permeability parameters is generally determined according to experimental data, which lacks strict theoretical basis. Therefore, based on the phase equilibrium of hydrocarbon-brine and the equation of state of porosity, a model of porosity and permeability variation considering salt deposition is established. The feasibility of the method is verified by matching the experimental data. The reservoir porosity and permeability variation under different salinity were simulated. Combined with the phase distribution, the reasons for the change of salt deposition and pore permeability parameters were analyzed. The results show that the pore permeability parameters are basically unchanged under high pressure, while the pore permeability parameters change obviously under low pressure due to the decrease of liquid water content. According to the downhole pressure and temperature changes, the reservoir porosity and permeability parameters can be monitored in real time, which provides theoretical guidance for the later gas reservoir development. Practical Applications: During the development of high salinity reservoirs, as the temperature increases and the pressure decreases, the water gradually evaporates and the salt precipitates. It causes blockage of the flow channel, greatly affects the porosity and permeability, and causes the reservoir difficulty in maintaining normal development. Based on the theory of phase equilibrium and mass conservation of salt, the mass of precipitated salt is calculated, and the porosity and permeability change models are established. The variation of underground porosity and permeability can be determined according to the produced fluid components, so as to achieve the purpose of real-time monitoring of the properties of underground reservoirs. The change of reservoir property parameters can be controlled by controlling the production pressure. It can avoid the downhole pollution in the production process in time and effectively improve the production efficiency. It is very important to deeply understand the changing characteristics of underground reservoir properties for the subsequent formulation of a reasonable working system. [ABSTRACT FROM AUTHOR]