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The Zeno line is the locus of points on the temperature–density plane where the compressibility factor of the fluid is equal to one. It has been observed to be straight for a broad variety of real fluids, although the underlying reasons for this are still unclear. In this work, a detailed study of the Zeno line and its relation to the vapor–liquid coexistence curve is performed for two simple model pair-potential fluids: attractive square-well fluids with varying well-widths λ and Mie n-6 fluids with different repulsive exponents n. Interestingly, the Zeno lines of these fluids are curved, regardless of the value of λ or n. We find that for square-well fluids, λ ≈ 1.8 presents a Zeno line, which is the most linear over the largest temperature range. For Mie n-6 fluids, we find that the straightest Zeno line occurs for n between 8 and 10. Additionally, the square-well and Mie fluids with the straightest Zeno line showed the closest quantitative agreement with the vapor–liquid coexistence curve for experimental fluids that follow the principle of corresponding states (e.g., argon, xenon, krypton, methane, nitrogen, and oxygen). These results suggest that the Zeno line can provide a useful additional feature, in complement to other properties, such as the phase envelope, to evaluate molecular models. [ABSTRACT FROM AUTHOR]

This work presents a monolithic finite element strategy for the accurate solution of strongly‐coupled fluid‐structure‐electrostatics interaction problems involving a compressible fluid. The complete set of equations for a compressible fluid is employed within the framework of the arbitrary Lagrangian–Eulerian (ALE) fluid formulation on the reference configuration. The proposed numerical approach incorporates geometric nonlinearities of both the structural and fluid domains, and can thus be used for investigating dynamic pull‐in phenomena and squeeze film damping in high aspect‐ratio micro‐electro‐mechanical systems (MEMS) structures immersed in a compressible fluid. Through various illustrative examples, we demonstrate the significant influence of fluid compressibility on the dynamics of MEMS devices subjected to constrained geometry and/or high‐frequency electrostatic actuation. Moreover, we compare the proposed formulation with the nonlinear compressible Reynolds equation and highlight that, particularly at low pressures and high fluid viscosity, the Reynolds equation fails to provide a reliable approximation to the complete set of equations utilized in our proposed formulation. [ABSTRACT FROM AUTHOR]

Pneumatic control mechanisms have long been integral to microfluidic systems, primarily using solenoid valves, pressurized gases, and vacuums to direct liquid flow. Despite advancements in liquid-driven self-regulated microfluidic circuits, gas-driven systems leveraging fluid compressibility remain underexplored. This study presents a mathematical and experimental investigation of gas-driven microfluidic circuits, focusing on forced-air oscillators. We derive and validate a first-principles model of microfluidic circuit elements operated under positive pressurization, using a 'molecular packets' analogy to elucidate compressibility effects. Our findings reveal that gas compressibility impacts circuit behavior, by acting similar to a large capacitor in the system, which inherently results in longer oscillation periods. As the syringe evacuates, the capacitance decreases, which in turn reduces the oscillation period. Experimental validation of our system demonstrates persistent behavior when using forced air to drive the microfluidic oscillators, this includes assessing devices with various PDMS membrane thicknesses, as well as evaluating device performance under different flow rates and syringe sizes. The forced air oscillators exhibited decreasing periods and capacitance over time, aligning with our theoretical predictions. [ABSTRACT FROM AUTHOR]

In this work, poroelastic properties of Sierra White granite namely elastic moduli, Biot's effective stress coefficient, α, and Skempton's pore pressure coefficient, B, are determined. The Biot's coefficient of this rock was determined using two different approaches. It is found that overall, the Biot's coefficient decreases from 0.77 at low effective stress (3–4 MPa) to 0.45–0.55 at high effective stress levels (30–40 MPa). Unlike the Biot's effective stress coefficient, which is related only to the solid rock, Skempton's B is a property related to both solid rock and the pore fluid. Although a single undrained hydrostatic compression test can theoretically be used to measure B, two types of laboratory tests were performed to fully reveal this parameter's behavior. In the first test, back pressure and confining pressure are increased stepwise to maintain a constant effective stress (usually very low), and Skempton's B is measured at different back pressure levels. This test reveals the Skempton's B behavior related to pore fluid compressibility, and consequently, this test can be used to evaluate if the pore fluid is free of air. In the second test, the back pressure is maintained at a constant level, and the confining pressure is increased stepwise, and then Skempton's B is determined at different confining pressure levels. This test correlates Skempton's B with effective stress. Details of the laboratory test protocol for combining these two types of tests are described and the results for Sierra White granite are provided. It is also found that the dead volume of the drainage system during the undrained compression test for the measurement of Skempton's B has an obvious impact on the measurement accuracy, with smaller dead volume yielding more accurate results. Highlights: The development of laboratory test protocol for Skempton's B measurement with consideration of both fluid and solid properties by two types of tests under two different boundary conditions. A comparison of using two different approaches to measure the Biot's effective stress coefficient. Determination of Biot's effective stress coefficient, α, and Skempton's pore pressure coefficient, B, for Sierra White granite. [ABSTRACT FROM AUTHOR]

The Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable detection methods for these applicable to magnetohydrodynamics (MHD) are currently lacking. A novel method is derived based on the well-established A-family of hydrodynamic vortex identification techniques, which define a vortex as a local minimum in an adapted pressure field. The J x B Lorentz force is incorporated into this method by using an effective total pressure in MHD, including both magnetic pressure and a pressure-like part of the magnetic tension derived from a Helmholtz decomposition. The AMHD method is shown to comprise of four physical effects: vortical momentum, density gradients, fluid compressibility, and the rotational part of the magnetic tension. A local three-dimensional MHD simulation representative of near-flank magnetopause conditions (plasma 's 0.5-5 and convective Mach numbers Mf ~ 0.4) under northward interplanetary magnetic field (IMF) is used to validate AMHD. Analysis shows it correlates well with hydrodynamic vortex definitions, though the level of correlation decreases with vortex evolution. Overall, vortical momentum dominates AMHD at all times. During the linear growth phase, density gradients act to oppose vortex formation. By the highly nonlinear stage, the formation of small-scale structures leads to a rising importance of the magnetic tension. Compressibility was found to be insignificant throughout. Finally, a demonstration of this method adapted to tetrahedral spacecraft observations is performed. [ABSTRACT FROM AUTHOR]

The purpose of this article is the mathematical analysis of a new class of models to describe the flow in shallow aquifers, as alternatives to the 3d-Richards model. This type of models was introduced in a previous work and consists of the coupling of an almost 1d vertical flow in the upper part of the aquifer with a 2d horizontal flow in the lower part. These two regions being separated by a time-dependent interface, an unknown of the problem. A result of existence of weak solutions is proved for a very general form of the hydraulic conductivity (anisotropic case). The strategy is based on the classical framework of parabolic equations in non-cylindrical domains. It also exploits the compressibility of the fluid to overcome the difficulty associated with the degeneracy in the time derivative term of Richards equation. [ABSTRACT FROM AUTHOR]

The natural circulation loop is crucial for the safe and stable operation of nuclear reactors and other applications. Traditional numerical algorithms, based on the Boussinesq approximation, have limitations when dealing with large temperature differences and density disparity, and they do not fully address fluid compressibility. This paper adopts the decoupled and stabilized lattice Boltzmann method (DSLBM) with a non-Boussinesq algorithm to study the natural circulation loop. The DSLBM provides a detailed flow description under large temperature and density differences, incorporating the pseudopotential multiphase model, temperature equation, and state equation, without relying on assumptions. The study examines the loop's performance under various temperature differences, central height differences, and heating source lengths, focusing on mass flow rate, driving head, and heating power. It reveals the energy performance, flow characteristics, and heat transfer properties of the loop, highlighting the physical mechanisms involved. Comparison with the empirical formulation of the incompressible equation from the theoretical aspect shows that when the temperature difference coefficient is lower than 0.15, the two methods are not much different from each other. When the temperature difference coefficient reaches 0.2, 0.3, and 0.4, the difference between the two methods is 9.47%, 19.11%, and 42.64%, respectively. Consequently, the Boussinesq approximation can be compensated by DSLBM, which proves the value of the application of the algorithm in exploiting the compressibility of fluids. The dimensionless fitting correlation with greater universality is obtained, which helps to predict the properties of the natural circulation loop with varying temperature differences, friction coefficients, and geometric structures. The research in this paper will lay the foundation for optimizing the system design of the natural circulation loop and improving energy utilization efficiency. [ABSTRACT FROM AUTHOR]

The flow control mechanism and skin friction drag reduction characteristics of micro-blowing on a Ma2.25 supersonic turbulent boundary layers are investigated through direct numerical simulations, and the effects of blowing intensity and micro-hole arrangement on turbulent structure and skin friction drag in the local control region and downstream region are considered. The results show that the skin friction drag decreases remarkably in the control region under the influence of micro-blowing, and a certain drag reduction can still be maintained in the downstream region. The drag reduction performance in the control region is jointly determined by blowing intensity and micro-hole arrangement. The drag reduction performance of the staggered arrangement is 5.7% and 11.1% higher than that of the inline arrangement at blowing intensities of 0.2% and 0.5%, respectively. However, it is found that the drag reduction in the downstream region is only determined by the blowing intensity and almost independent of the micro-hole arrangement. The effect of micro-blowing on turbulent structures is quantitatively characterized by energy spectrum analysis, and it shows that the streamwise scales of the near-wall streaks are significantly reduced under the influence of micro-blowing. In addition, the compressibility of fluids and the local reverse transfer in the strong expansion region are significantly improved under the influence of micro-blowing. These effects should be considered when performing Large Eddy Simulation modeling of supersonic turbulent boundary layers with micro-blowing. [ABSTRACT FROM AUTHOR]

To study the effects of fluid compressibility on the dynamics of a cavitating vortex street flow in a regime where the vortex shedding frequency increases as a result of the cavitation increase, the cavitating wake behind a wedge was simulated employing both incompressible and compressible solvers. To do this, a compressible cavitation model was implemented, modifying the Zwart-Gerber-Belamri (ZGB) incompressible solver and including a pressure limit and absorbing boundary conditions to prevent a non-physical pressure field. To validate the performance of the compressible model, preliminary simulations were carried out on a 1D Sod cavitating tube and the cavitating vortex shedding behind a circular body at laminar flow conditions. The results of the cavitating wake behind the wedge with the incompressible and the compressible solvers showed similar predictions in terms of pressure, vortex shedding frequency, and instantaneous and average vapor volume fraction profiles. In spite of this, differences were obtained in the energy content of the fluid force fluctuations on the body at higher frequencies, which appear to be better resolved and amplified when the compressibility model is considered. Overall, both solvers provided comparable results in terms of cavitation phenomena that are well aligned with experimental observations. [ABSTRACT FROM AUTHOR]

The resistance to liquefaction of soils can be significantly increased by slightly reducing the degree of saturation. Many experimental studies demonstrated that the augmented compressibility of the pore fluid mixture composed by entrapped bubbles within a continuous fluid phase reduces the amount of seismically induced excess pore water pressure. On the contrary, interpretation through constitutive models of the cyclic response of nearly saturated soils, often referred to as gassy soils, is by far less explored in the literature. This paper addresses this topic by considering the gas–water mixture as a homogeneous equivalent fluid whose compressibility has been used along with the elastoplastic constitutive model formulated by Dafalias and Manzari (2004). The model has been calibrated on the experimental data obtained from monotonic triaxial tests on saturated sandy soils and then validated with the results of cyclic triaxial tests on saturated and non-saturated liquefiable sandy soils. The selected calibration has been used to perform parametric analyses by varying the initial conditions of the soil (i.e., the relative density and degree of saturation), thus further emphasizing the beneficial effect of quasi-saturated fluid to delay the onset of liquefaction instabilities. [ABSTRACT FROM AUTHOR]

AbstractAsymptotic analysis based on the fluids governing equations with the exponential model of thermophysical properties is introduced to quantify the influence of each property on the heat and mass transfer behavior of the near-critical fluid. The one-dimensional asymptotic model finds the different behavior in boundary layers and bulk regions controlled by the diffusion and wave mode, respectively. From the asymptotic model, three characteristic parameters are found: nondimensional wave velocity for wave mode, nondimensional diffusion coefficient for diffusion mode, and nondimensional mass transport coefficient for the coupling in between. Larger thermal conductivity, fluid compressibility, and lower specific heat are found to enhance the thermal wave. However, the efficiency of heat transfer by thermal waves is irrelevant to the thermal diffusivity but related to the fluid compressibility. From the calculation of the asymptotic model for supercritical carbon dioxide (sCO2), such efficiency is 0.150, which indicates that most of the thermal energy is accumulated in the boundary layers. [ABSTRACT FROM AUTHOR]

This study investigates the buckling and free vibration behavior of functionally graded saturated porous (FGSP) using a refined quasi-3D theory that ensures zero transverse shear stress at the top and bottom surfaces of the plate. The material properties depend on the porosity coefficient according to three patterns. Hamilton's principle and Biot's poroelasticity theory are employed to derive the equations of motion, which are then solved using Navier's technique. After examining the accuracy of the suggested approach, the effect of fluid compressibility on natural frequency and critical buckling load is investigated in the undrained condition. Also, the effect of porosity, geometrical parameters, and elastic foundation on the vibration and buckling response of FGSP plates are examined. The study reveals that saturating the pores with fluid leads to increased plate stiffness. This translates to higher critical buckling loads and fundamental frequencies. [ABSTRACT FROM AUTHOR]

Earthquake-induced soil liquefaction is a catastrophic phenomenon that can damage existing building foundations and other structures, resulting in significant economic losses. Traditional mitigation techniques against liquefaction present critical aspects, such as high construction costs, impact on surrounding infrastructure and effects on the surrounding environment. Therefore, research is ongoing in order to develop new approaches and technologies suitable to mitigate liquefaction risk. Among the innovative countermeasures against liquefaction, Induced Partial Saturation (IPS) is considered one of the most promising technologies. It consists of introducing gas/air bubbles into the pore water of sandy soils in order to increase the compressibility of the fluid phase and then enhance liquefaction resistance. IPS is economical, eco-friendly and suitable for urbanised areas, where the need to reduce the risk of liquefaction must be addressed, taking into account the integrity of existing buildings. However, IPS is still far from being a routine technology since more aspects should be better understood. The main aim of this review is to raise some important questions and encourage further research and discussions on this topic. The review first analyses and discusses the effects of air/gas bubbles on the cyclic behaviour of sandy soils, focusing on the soil volume element scale and then extending the considerations to the real scale. The use of useful design charts is also described. Moreover, a section will be devoted to the effect of IPS under shallow foundations. The readers will fully understand the research trend of IPS liquefaction mitigation and will be encouraged to further explore new practical aspects to overcome the application difficulties and contribute to spreading the use of this technology. [ABSTRACT FROM AUTHOR]

The jet dynamics during cavitation bubble collapsing between unequal-sized dual particles are investigated utilizing a numerical model that combines the finite volume approach alongside the volume of fluid approach. The model incorporates the compressibility of the two-phase fluid and accounts for mass and heat transfer between two phases. The computational model utilizes an axisymmetric model, where the axis of symmetry is defined as the line that connects the centers of the particles and the bubble. A comprehensive analysis is presented on the influence of the particle radius and bubble–particle distance on the jet behavior. Furthermore, the variations of surface pressure on the particles induced by jet impingement are quantitatively analyzed. Four distinct jet behaviors are categorized, depending on the formation mechanism, as well as the number and the direction of the jets. For case 1, the bubble produces a single jet directed toward a small particle; for case 2, the bubble fragments produces double jets receding from each other; for case 3, the bubble produces double jets approaching each other; and for case 4, the bubble produces a single jet directed toward a large particle. The pressure perturbations induced by jet impingement upon the particles exceed those caused by shock wave impacts. The larger the bubble volume at the moment of jet formation, the longer the duration of the pressure variation caused by the jet impinging on the particles. [ABSTRACT FROM AUTHOR]

The pressures produced by underwater explosions present serious threats to ships, submarines, and other marine structures. A significant part of underwater explosion pressure comes from the explosion bubble. Most computational studies on bubble pressure have considered the case of an incompressible fluid or have confined calculations to the time before the formation of a toroidal bubble, because of the complexity and strong nonlinearity of a compressible flow field with a doubly connected geometry. The few compressible models that are capable of calculating the pressure after jet impact suffer from computational difficulties. In this paper, we calculate the bubble pressure by constructing a new form for solving an auxiliary function based on a boundary integral method that takes account of the compressibility of the flow field. We verify out numerical algorithm by comparison with a classical theoretical model and a set of experimental results. We then compare the bubble pressure in a compressible flow field in both the first and second oscillation periods with that in an incompressible flow field. The results of this comparison confirm that it is necessary to consider the compressibility of the fluid and the multiperiod pulsations of a bubble in pressure calculations. We present a comprehensive discussion of the pressure characteristics in the central axial and circumferential directions induced by a nonspherical bubble in a free field. Finally, we obtain a critical bubble–wall distance r w > 1.8 for which the bubble is prevented from splitting after the first jet impact, and we investigate the pressure characteristics of a bubble near a rigid wall for both cases of r w < 1.8 and r w > 1.8. [ABSTRACT FROM AUTHOR]

The greatest challenge when performing large deformation simulations using the CFD‐DEM coupling method lies in the dynamical update of the fluid meshes. To address this problem, a novel CFD‐DEM coupling method integrated with the dynamic unstructured grid is proposed in this work. The mesh initialization and reconstruction are performed by the Constrained Delaunay triangulation (CDT) implemented by the tetgen algorithm. Moreover, the equation of state (EOS) is introduced to consider the impact of fluid compressibility. The reliability of this coupling method is preliminarily verified by the particle sedimentation test. Additionally, undrained triaxial shear and one‐dimensional consolidation tests are conducted to examine the applicability of the proposed method in simulating geotechnical cases. From our analysis, it is found that the shear responses in the undrained triaxial shear test obtained from the proposed method with dynamic mesh are in direct accordance with those led by the constant volume (CV) method. However, difficulties arise in accurately describing the moving boundary by the fixed mesh, leading to unreliable results. Moreover, in the one‐dimensional consolidation test, both the dynamic and fixed grids can capture the Mandel—Cryer effect, which is more pronounced under the dynamic grid, mainly due to the dual impact of the loading device and particle skeleton on the fluid. A greater compressibility specified under the dynamic grid led to a weakening of this effect, whereas its duration is increased. Our work provides valuable insights for effectively dealing with dynamic fluid boundaries. [ABSTRACT FROM AUTHOR]

This study reports the development and characterization of a multiple-supersonic-jet wind tunnel designed to investigate the decay of nearly homogeneous and isotropic turbulence whose generation process is strongly influenced by fluid compressibility. The interaction of 36 supersonic jets generates turbulence that decays in the streamwise direction. The velocity field is measured with particle image velocimetry by seeding tracer particles with ethanol condensation. Various velocity statistics are evaluated to diagnose decaying turbulence generated by the supersonic jet interaction. The flow is initially inhomogeneous and anisotropic and possesses intermittent large-scale velocity fluctuations. The flow evolves into a statistically homogeneous and isotropic state as the mean velocity profile becomes uniform. In the nearly homogeneous and isotropic region, the ratio of root-mean-squared velocity fluctuations in the streamwise and vertical directions is about 1.08, the longitudinal integral scales are also similar in these directions, and the large-scale intermittency becomes insignificant. The turbulent kinetic energy per unit mass decays according to a power law with an exponent of about 2, larger than those reported for incompressible grid turbulence. The energy spectra in the inertial subrange agree well with other turbulent flows when normalized by the turbulent kinetic energy dissipation rate and kinematic viscosity. The non-dimensional dissipation rate C ε is within a range of 0.56–0.87, which is also consistent with incompressible grid turbulence. The dependence of C ε on the turbulent Reynolds number aligns with the scaling of non-equilibrium turbulence, leading to the large decay exponent. [ABSTRACT FROM AUTHOR]

The importance of high-speed water entry is acknowledged within the defense industry. This study numerically investigates the water entry of a high-speed rectangle projectile, focusing on cavity dynamics and shock wave generation. A computational model is employed to accurately simulate the intricate fluid dynamics of compressible multiphase flows. This model integrates a dual-phase flow algorithm with a thermally sensitive Tait equation of state for the liquid phase. The primary focus lies in understanding the effects of fluid compressibility on cavity evolution and shock wave propagation across different Froude numbers. The findings reveal that compressibility induces changes in cavity formation size, leading to significant variations in phase composition within the cavity. Furthermore, compressibility enhances the air cushion effect upon surface impact, resulting in delayed water entry and concurrent reduction in projectile drag. Moreover, a prognostic model is proposed, correlating shock pressure with propagation distance, thereby validating theoretical hypotheses advanced by Lee et al. [J. Fluid Struct., 11, 819–844 (1997)]. [ABSTRACT FROM AUTHOR]

Tsunamis are a significant coastal hazard that pressurise sediment pore water, which can potentially induce liquefaction, enhance erosion and scour, and undermine the stability of beach sediments supporting natural and built infrastructure in the coastal nearshore environment. Tsunami-induced pressurisation of pore water is attributed to (a) mechanical pressurisation associated with the soil skeleton's tendency to contract or expand around the soil's pore fluid under the changing overlying water weight and (b) seepage of tsunami water into and out of the sand bed. The pore fluid compressibility, which is influenced by air entrainment due to water table fluctuations caused by the tides, can significantly influence development of stabilising and destabilising hydraulic gradients during tsunami runup and drawdown, respectively. Previous work has effectively assumed a constant air content in sand beds and neglected (a) the compression and dissolution of entrained air that influences the pore fluid compressibility and (b) the interaction between saturated sediment underlying sediment with entrained air. By considering the gas kinetics influencing the pore fluid compressibility in a seepage–deformation model, the effect of different pore fluid compressibility assumptions, thickness of sediment with entrained air, initial degree of saturation and tsunami wave properties (height and duration) were studied. The thickness of sediment containing entrained air, the assumed pore fluid compressibility assumption and subtle differences in the initial degree of saturation can significantly influence the predicted maximum depth and duration of tsunami-induced liquefaction. [ABSTRACT FROM AUTHOR]

A hierarchy of asymptotic models governing long-wave low-frequency in-plane motion of a fluid-loaded elastic layer is established. In contrast to a layer with traction-free faces, modelled by Neumann boundary conditions, a fluid-loaded one assumes more involved conditions along the interfaces, dictating a special asymptotic scaling. The latter corresponds to a fluid-borne bending wave, controlled by elastic stiffness of the layer and fluid inertia. In this case, the transverse inertia of the layer and fluid compressibility do not appear at zero-order approximation. The first-order approximation is associated with a Kirchhoff plate, immersed into incompressible fluid. In the studied free vibration setup, the fluid compressibility has to be taken into account only at third order, along with elastic rotary inertia. Transverse shear deformation enters the second-order approximation along with a few other corrections. The conventional impenetrability condition has to be also refined at second order. Dispersion relations corresponding to the developed asymptotic models are compared with the polynomial expansions of the full dispersion relation, obtained from the plane-strain problem of linear elasticity. [ABSTRACT FROM AUTHOR]

This paper presents a coupled model that considers the nonlinear compressibility effect in fluid–structure interaction (FSI) during air-blast loading on flexible structures. In this coupled model, structural behaviour is idealized as a linear single-degree-of-freedom mass-spring-damper system whereas nonlinear fluid compressibility is considered by applying Rankine–Hugoniot jump conditions across a moving plate. The surrounding fluid medium is modelled with an ideal gas equation and hence, this model can be applied for FSI analysis with relatively strong shocks (reflection coefficient of up to 8). The nonlinear compressibility of the fluid medium at the backside of the plate is also considered in this coupled formulation and its effects on the structural responses are examined. Moreover, the negative/underpressure phase of the reflected wave profile, which is typically neglected in a decoupled model, is also considered in the proposed model and its influence on the structural response is also investigated. The study reveals that the nonlinear compressibility of fluid medium significantly influences the coupled FSI phenomena, especially in flexible lightweight structures. Numerical examples are presented to highlight the implications of the nonlinear compressibility effect in FSI on the reflected pressure profile and the response of flexible structures. Parametric dependencies of response on structural mass and natural frequency are examined thoroughly and a response spectrum is obtained. It is envisaged that the lightweight protective structure design under higher blast intensity may benefit from this study. [ABSTRACT FROM AUTHOR]

The ventilation design of mines is based on fluid dynamics. Air is the main fluid in mining ventilation. This fluid is analyzed by two models: incompressibility and compressibility. The air-fluid in the compressibility model is examined in two models of dry and wet air along with thermal analysis. This paper argues that a number of presented parameters in the common thermodynamic analysis of mine ventilation should be modified. Accordingly, issues of the Earth's true gravity acceleration, potential energy difference, the specific heat capacity of air at constant pressure and volume, enthalpy difference of air, the average volumetric mass of dry air, and the amount of output moisture are rechecked. Therefore, a new method is presented in this paper for correcting thermodynamic equations in mine ventilation design. The name of this method is the Complete Model of Wet Air Analysis (CMWAA method). The results of this paper show that the CMWAA method can accurately perform thermodynamic analysis of air-fluid in mine ventilation without requiring a specified evaporation rate in mine networks, with minimal iteration of calculations. [ABSTRACT FROM AUTHOR]

The paper presents a comparative analysis of three systems of dynamic equations for fluid‐saturated solids: the exact equations and two simplified versions known as the u‐p approximations obtained by neglecting certain acceleration terms in the exact equations. The constitutive relations for the solid skeleton are written in the general anisotropic incrementally linear form without considering any specific constitutive model or a particular type of anisotropy. The dynamic equations are compared in relation to the existence of solutions in the form of plane harmonic waves. Emphasis is placed on finding conditions for the non‐existence or existence of growing waves whose amplitude increases in time or space as the wave propagates. The conditions are formulated in terms of the acoustic tensor of the skeleton and the compressibility of the pore fluid. In particular, it is shown that for a hyperelastic skeleton, the exact equations and one of the u‐p approximations do not have growing wave solutions, whereas the other u‐p approximation may have such solutions even if the skeleton is hyperelastic. [ABSTRACT FROM AUTHOR]

Ethylene‐alpha olefin elastomers have versatile applications. Solution copolymerization makes them, using ethylene and alpha olefin‐rich comonomer feed and metallocene and postmetallocene precatalysts, at laboratory and industry conditions. Hence, this study models ethylene solubility in toluene‐1‐hexene and n‐hexane‐1‐hexene mixtures using VLE criterion, Peng–Robinson EoS, vdW1f mixing rule, and Shulgin's activity coefficient‐Henry's constant formalism. Levenberg–Marquardt algorithm, with initial conditions comprising quasi‐ideal K factor correlation and Tait liquid phase EoS, solved the model equations. This eliminates present cumbersome literature approach. The predicted solubilities well match the experimental values at all temperature and pressure. Ethylene solubility correlates the liquid phase fluid compressibility to the corresponding catalyst active center residential environment. This offers a new approach to investigate catalyst and copolymerization phenomena and develop ethylene‐1‐hexene elastomer process. Evaluating copolymerization and microstructural property, using ethylene solubility ignoring that in 1‐hexene, introduces significant errors. The present work corrects them and solves a long‐standing polymer reaction engineering problem. [ABSTRACT FROM AUTHOR]

Simulations of flow fields around microscopic objects typically require methods that both solve the Navier–Stokes equations and also include thermal fluctuations. One such method popular in the field of soft-matter physics is the particle-based simulation method of multi-particle collision dynamics (MPCD). However, in contrast to the typically incompressible real fluid, the fluid of the traditional MPCD methods obeys the ideal-gas equation of state. This can be problematic because most fluid properties strongly depend on the fluid density. In a recent article, we proposed an extended MPCD algorithm and derived its non-ideal equation of state and an expression for the viscosity. In the present work, we demonstrate its accuracy and efficiency for the simulations of the flow fields of single squirmers and of the collective dynamics of squirmer rods. We use two exemplary squirmer-rod systems for which we compare the outcome of the extended MPCD method to the well-established MPCD version with an Andersen thermostat. First, we explicitly demonstrate the reduced compressibility of the MPCD fluid in a cluster of squirmer rods. Second, for shorter rods, we show the interesting result that in simulations with the extended MPCD method, dynamic swarms are more pronounced and have a higher polar order. Finally, we present a thorough study of the state diagram of squirmer rods moving in the center plane of a Hele-Shaw geometry. From a small to large aspect ratio and density, we observe a disordered state, dynamic swarms, a single swarm, and a jammed cluster, which we characterize accordingly. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to investigate the performance of C-D (converging-diverging) nozzles with slanted perforated tabs through numerical simulations. Specifically, the paper focuses on the simulation of supersonic jets controlled by these slanted perforated tabs to evaluate their effectiveness in enhancing mixing efficiency. The simulation methodology involves developing a computational model of the jet and the tabs, utilizing mathematical equations and numerical techniques to solve for fluid flow, pressure, and other relevant variables. This computational approach enables the prediction of jet behaviour and the assessment of how different types of control tabs impact the system. This helps for the design of improved jet engines and other fluid systems that require effective mixing capabilities. The introduction of tabs introduces changes to the potential core and velocity profiles, primarily due to enhanced mixing effects facilitated by the tabs. In a supersonic flow, the potential core is typically shorter than in subsonic flows due to the compressibility effects of the fluid. Even though in literature many studies have been done on sonic jets with perforated tabs and some on supersonic jets with perforated tabs, the uniqueness in this paper is on the blockage area. Blockage area has been kept at a minimum of around one percent for solid tab and for 30° perforated tab it's as low as 0.5%. By incorporating perforated tabs into a supersonic jet, the size of the potential core can be further reduced through enhanced mixing between the jet and the surrounding fluid. Thus, with minimal thrust loss this paper explores maximum benefit of potential core reduction and thereby better mixing efficiency and lesser noise production. Solid tab has better potential core reduction but with lesser blockage area, 30º perforated tab is better in ratio of potential core reduction to blockage area. [ABSTRACT FROM AUTHOR]

The analysis of ocean wave-induced dynamic response of a porous seabed is particularly important for coastal and geotechnical engineers when designing and constructing maritime structures. In this study, an analytical solution is presented to analyze the dynamic response and liquefaction potential of a poro-elastic seabed induced by partial standing waves with arbitrary reflectivity. The porous seabed is modeled using Biot's theory describing the propagation of elastic waves, and coupled deformation and water flow of porous media, whereas the ocean waves are described using linear ocean wave theory. Based on the mixed boundary-value conditions, explicit expressions of displacements, effective stresses and excess pore water pressure of seabed are derived with consideration of the effects of inertial forces, compressibility of solid and fluid, and arbitrary reflectivity of standing waves. The results of degenerated analytical solutions are compared with the existing ones to verify the correctness of the proposed method. The effects of several pertinent parameters of ocean wave-seabed system, including reflection coefficient, phase lag and period of standing waves, depth of water, permeability, degree of saturation, and shear modulus of seabed deposits, etc., on the dynamic response of seabed and liquefaction potential, are examined and discussed. It is found that the reflection of standing wave has a significant effect on the dynamic response and liquefaction potential of porous elastic seabed. Compared with that of no wave reflection, the liquefaction depth of seabed induced by fully-reflected standing waves increases 82.49% under certain conditions of wave-seabed system. In addition, phase lag, wave period, water depth and mechanical and physical properties of seabed soil such as saturation, permeability and shear modulus have different effects on the dynamic response and liquefaction potential of porous elastic seabed. The investigation of the dynamic response and liquefaction of the porous elastic seabed under partial standing ocean waves will help to better predict the influence of standing waves on breakwaters and seabed soil, and can provide some guidance for the design of offshore structures. [ABSTRACT FROM AUTHOR]

Measurements of compressed liquid density and speed of sound have been performed in cis -1-chloro-2,3,3,3-tetrafluoro-1-propene, also known as R-1224yd(Z). Density has been measured in the temperature range from 273.15 K to 353.15 K and for pressure up to 35 MPa. The relative expanded uncertainty (k = 2) for the obtained results has been estimated to be better than 0.05%. Speed of sound has been measured in the temperature range from 263 K to 353 K and for pressure up to 35 MPa. The expanded relative uncertainty (k = 2) for these measurements has been estimated to be better than 0.06%. Using the properties measured in this work and including measurements of vapor pressure and ideal gas specific heat capacity published in scientific literature, a Patel-Teja equation of state has been implemented for describing the properties of the refrigerant both in liquid and in vapor phase. An independent model for predicting the speed of sound has been proposed to allow to calculate the adiabatic compressibility of the fluid with an accuracy higher than that accessible from Patel-Teja formulation. • Density measurements of cis-1-chloro-2,3,3,3-tetrafluoro-1-propene (R-1224yd(Z)). • Speed of sound measurements of cis-1-chloro-2,3,3,3-tetrafluoro-1-propene (R-1224yd(Z)). • Implementation of the Patel-Teja equation of state for describing the properties of R-1224yd(Z) both in liquid and in vapor phase. • Comparison between experimental values and model predictions. [ABSTRACT FROM AUTHOR]

In high-speed rotating channels, significant compressive effects are observed, resulting in distinct flow characteristics compared to incompressible flows. This study employs a finite volume method, based on the implicit formulation, to solve for low-speed compressible laminar flow in rotating channels using an orthogonal uniform grid. The governing equations include the full Navier–Stokes equations and the energy equation. The alterations in flow within rotating channel are primarily influenced by the compressive effects of centrifugal force and the compressibility of fluid within the flow's normal section. The first effect involves a reduction in the velocity due to centrifugal force, leading to an increasing influence of the Coriolis force compared to inertial forces. This trend change aligns closely with the increase in rotation speed. The second effect arises from the increase in the rotating Mach number and the Coriolis compression, resulting in slight density differences within the cross section. Strong centrifugal forces generate significant centrifugal additional force (buoyancy force). Consequently, under the same local rotation number, the velocity profiles of the mainstream experience considerable changes. Additionally, a higher rotating Mach number significantly impacts wall shear stress, with the leading side being notably affected. For instance, at cross-sectional Ro = 0.6 and MaΩ = 2.1, the dimensionless shear stress on the leading side decreased by 13%. Furthermore, while an increase in the rotating Mach number has minimal impact on the cross-sectional secondary flow structure, changes in mainstream velocity profiles influence secondary flow intensity, resulting in an enhanced velocity peak and a shift toward the trailing side. [ABSTRACT FROM AUTHOR]

A compressible cavitation model is developed in this paper, in which the bubble wall velocity is obtained by solving the compressible Rayleigh–Plesset (R–P) equation. Additionally, vapor compressibility is also included during evaporation/condensation to correct the phase change rate. The predicted results around a National Advisory Committee for Aeronautics (NACA) 66 (mod) hydrofoil are compared with the available experimental data, and a satisfied agreement is obtained. By (mod), we mean the NACA 66 hydrofoil modified by Brockett ["Minimum pressure envelopes for modified NACA-66 sections with NACA a = 0.8 camber and BuShips type I and type II sections," Technical Report No. 1780 (David Taylor Model Basin Washington DC Hydromechanics Lab, 1966)] and Valentine ["The effect of nose radius on the cavitation-inception characteristics of two-dimensional hydrofoils," Technical Report No. 3813 (Naval Ship Research and Development Center, 1974)]. Several crucial flow properties, e.g., fluid compressibility, cavitation evolution features, and pressure statistical characteristics, are studied in detail. The results suggest that the developed compressible cavitation model is better suited for predicting the collapse behavior of cavitation. Moreover, our work captures the liquid re-entrant jet and bubbly shock waves well and reveals that these two mechanisms jointly dominate the cavity shedding dynamics. Shock-induced pressure pulses play a more important role in flow features, with a maximum amplitude exceeding 200 kPa, significantly larger than the pressure pulse caused by liquid re-entrant jets. Finally, the statistical analysis indicates that the pulsating pressure presents non-Gaussian nature with positive skewness, and shock waves exhibit high-frequency and high-energy characteristics. [ABSTRACT FROM AUTHOR]

Context. Solving hydrodynamic problems is associated with high computational complexity and therefore requires considerable computing resources and time. The proposed approach makes it possible to significantly reduce the time for solving such problems by applying a combination of two improved modeling methods. Objective. The goal is to create a comprehensive hydrodynamic modeling method that requires significantly less time to determine the dynamics of the velocity field by using the modified lattice Boltzmann method and the pressure distribution by using a convolutional neural network. Method. A method of hydrodynamic modeling is proposed, which realizes the synergistic effect arising from the combination of the improved lattice Boltzmann method and a convolutional neural network with a specially adapted structure. The essence of the method consists of implementing a sequence of iterations, each of which simulates the process of changing parameters when moving to the next time layer. Each iteration includes a predictor step and a corrector step. At the predictor step, the lattice Boltzmann method works, which allows us to obtain the field of fluid velocities in the working area at the next time layer using the field of velocities at the previous layer. At the corrector step, we apply an improved convolutional neural network trained on a previously created data set. Using a neural network allows us to determine the pressure distribution on a new time layer with a predetermined accuracy. After adding the fluid compressibility correction on the new time layer, we get a refined value of the velocity field, which can be used as initial data for applying the lattice Boltzmann method at the next iteration. Calculations stop when the specified number of iterations is reached. Results. The operation of the proposed method was studied on the example of modeling fluid movement in a fragment of the human gastrointestinal tract. The simulation results showed that the time spent implementing the simulation process was reduced by 6-7 times while maintaining acceptable accuracy for practical tasks. Conclusions. The proposed hydrodynamic modeling method with a convolutional neural network and the lattice Boltzmann method significantly reduces the time and computing resources required to implement the modeling process in areas with complex geometry. Further development of this method will make it possible to implement real-time hydrodynamic modeling in three-dimensional domains [ABSTRACT FROM AUTHOR]

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In this study, the response of the steel water storage tank considering the water-structure interaction under the effects of the transitional and rotational components of the earthquake as well as the soil-structure interaction was evaluated using the Eulerian-Lagrangian method. Seismic loading consisted of rotational and transitional components of the earthquake. Rotational components of the earthquake were first obtained using the transitional components. Then, the seismic analysis of the tanks considering four different tank models with empty and 90% full reservoirs and five different foundation models with and without considering the rotational components was done. Foundation flexibility and its effect on the structure performance were addressed by changing the foundation stiffness from the rigid to the very soft one. Water-structure interaction was considered in the analysis taking into account the fluid compressibility and the energy absorption boundaries. Results showed that in most cases by applying the rotational components, the maximum displacements and shear stress decreased. Maximum displacement reduction values for tanks with height to radius ratios of 0.4, 1, 2, and 3 for empty tanks are 51.62, 32.32, 24.0, and 23.79, respectively, and tanks with 90% full are 49.42, 42.86, 28.88, 26.74, respectively. Also, principle stress decreased in most cases, and in few cases, an increase was observed. This decrease in shear stress was far higher for empty reservoirs than full reservoirs. By increasing the tank height, reducing effects of the rotational components in the seismic response of the tanks reduced, and the structural responses with and without applying the rotational components got close to each other. Results also showed that the rotational components have a significant effect on the structural response in terms of changing the location of the maximum responses in whole cases as well as increasing the maximum response in a few cases. [ABSTRACT FROM AUTHOR]

Productivity prediction of perforation completion is key for well optimizing completion methods and reservoir engineering research. Productivity prediction models using an additional pressure drop to represent skin factor are limited. In this study, a steady-state productivity prediction model coupled with reservoir seepage and fluid flow in the wellbore was developed. The impact of different perforation parameters on well production was studied. Considering perforation depth, perforation density, perforation diameter, phase angle, depth of contaminated zone, and pollution degree of the contaminated zone, a semi-analytical skin calculation model under different reservoir conditions and completion methods with the least-squares method combining the consideration of perforation depth, perforation density, perforation diameter, phase angle, depth of contaminated zone, and pollution degree of the contaminated zone was developed. Perforation parameters were optimized. A 3D directional well unsteady productivity prediction model was established using the finite-volume method considering the influence of conventional perforation completion parameters, gravel packing perforation completion parameters, natural fractures, reservoir heterogeneity, reservoir scale, skin factor, fluid gravity, fluid compressibility, and rock compressibility. A new method for optimizing perforation parameters and characterizing skin factors was developed, providing a theoretical basis and simulation means for deeper understanding of the development law of directional wells. [ABSTRACT FROM AUTHOR]

In this work, we carry out direct numerical simulations of particle suspensions in the compressible turbulent vertical channel (TVC) flows with Mach number Ma = 1.5 and particle Stokes number St = 1–100. The compressibility effect is considered in the particle dynamic model for the first time in the study of compressible particle-laden wall turbulence. We find that in both incompressible and compressible flow, gravity weakens the wall-normal and spanwise fluctuations of particle velocities as the Stokes number increases. However, compared to the incompressible flow case, the compressible effect amplifies the mean velocity, fluctuations of velocity, and slip velocity of particle in the streamwise direction. The wall-normal and spanwise fluctuations of particle velocities are augmented by the compressible effect in the channel core region. Moreover, in the core region, the effect of fluid compressibility on the wall-normal and spanwise fluctuations of particle velocities attenuates as the Stokes number increases, indicating a competition between the compressible effect and the particle inertia effect. We, furthermore, conduct the quadrant analysis of the local fluctuation velocities of fluid at particle positions and observe preferential distributions in the second and the fourth quadrants at y+ = 12.5–13.5. For compressible TVC flows, the pattern of probability distributions is more elongated, and the percentage is slightly higher in the second and fourth quadrants than that of incompressible flows. This observation implies that more particles locate in the ejection and sweep events in compressible flows than that in incompressible flows, which is anticipated to influence the particle wall-normal transport. [ABSTRACT FROM AUTHOR]

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when p i n / P in reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x / d ≈ 2–3. The pressure fluctuations concentrate in the range of x / d ≈ 2 – 5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59 – 0.66 under the effect of cavitation. [ABSTRACT FROM AUTHOR]

A novel porous tilting pad gas bearing (PTPGB) with hermetic squeeze film dampers based on multilayer diaphragm structure (MLD-HSFD) is proposed for oil-free turbomachinery. A dynamic model of MLD-HSFDs including the frequency dependence effect is presented by considering the compressibility of the damper fluid. An experimental test rig was assembled to measure the performance of MLD-HSFDs. The model predicts well the test data, including the frequency dependence of force coefficients. A comprehensive theoretical model of PTPGBs with MLD-HSFDs is proposed based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support and porous models. The effects of thickness of diaphragms thickness, bearing clearance, and supply pressure on bearing performance are discussed. [ABSTRACT FROM AUTHOR]

A new quasi-3D higher-order shear deformation theory is introduced to investigate the static behaviour of functionally graded saturated porous (FGSP) plate resting on Pasternak's elastic foundation for the first time. The governing equations are derived from eleven-unknowns higher-order shear deformation theory and using Biot's poroelasticity theory taking into account transverse shear stress-free boundary conditions on the top and bottom surface of the plate. Three porosity distribution patterns of FGSP materials namely uniform, non-uniform symmetric and non-uniform asymmetric are considered. Navier's technique is employed to obtain an analytical solution. The present results are compared with 3D and higher-order solutions available in the existing literature to validate the proposed model. Parametric studies show efficiency of proposed quasi-3D plate theory in analyzing FGSP thick plates, and exploring the effects of material, geometrical and elastic foundation parameters, as well as fluid compressibility, stretching effect on transverse displacement and stress field. [ABSTRACT FROM AUTHOR]

Perfectly incompressible materials do not exist in nature but are a useful approximation of several media which can be deformed in non-isothermal processes but undergo very small volume variations. In this paper, the linear analysis of the Darcy-Bénard problem is performed in the class of extended-quasi-thermal-incompressible fluids, introducing a factor β which describes the compressibility of the fluid and plays an essential role in the instability results. In particular, in the Oberbeck-Boussinesq approximation, a more realistic constitutive equation for the fluid density is employed in order to obtain more thermodynamically consistent instability results. The critical Rayleigh-Darcy number for the onset of convection is determined, via linear instability analysis of the conduction solution, as a function of a dimensionless parameter β ^ proportional to the compressibility factor β , proving that β ^ enhances the onset of convective motions. Article Highlights: The onset of convection in fluid-saturated porous media is analyzed, taking into account fluid compressibility effect. The critical Rayleigh-Darcy number is determined in a closed algebraic form via linear instability analysis. The critical Rayleigh-Darcy number is shown to be a decreasing function of the dimensionless compressibility factor. [ABSTRACT FROM AUTHOR]

Mechanical vibrations can alter static and dynamic distributions of fluids in porous matrices. A popular theory that explains non-destructive changes in fluids percolation induced by vibrations involves elasticity of a solid matrix and compressibility of fluids. Owing to strong damping, elastic and acoustic deformations always remain bounded to narrow zones (a few centimetres) near the source of vibrations. However, field trials prove the existence of the effects that are induced by vibrations in geological reservoirs on a longer scale (100 m). In this study, we develop a non-elastic theory, assessing the time-averaged effects induced by small-amplitude high-frequency vibrations. We examine the immiscible liquid/liquid displacement flows in a capillary (which is a building element of a porous matrix) subjected to translational vibrations. We find that strong-enough vibrations alter the shapes of menisci and change the rates of displacement flows. We find that vibrations slow down or even stop the displacement flows (which is contrary to a common expectation that vibrations help to release fluids from a porous matrix). This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'. [ABSTRACT FROM AUTHOR]

At present, extended reach wells (ERWs) are widely applied on oil and gas exploitation in numerous reservoirs around the globe, and this is attributed to their superiority in the development of marginal oil and gas fields and cost-effectiveness. Identifying the effects of reservoir properties on production is significant to the operation of ERWs for oil and gas extraction. This work utilizes numerical modeling techniques to simulate the application of ERWs in low-permeability formations. The impacts of low permeability on the oil production and the pressure distribution of the reservoirs with different formation properties are analyzed, and the simulation results of the oil exploitation by ERWs are compared with the oil production and pressure distribution of that by horizontal wells (HWs). A test scheme is designed to analyze the effect of reservoir properties on oil extraction through ERWs and quantify the sensitivity of oil production to reservoir properties. The reservoir properties of formation rock compressibility, formation fluid compressibility, initial reservoir pressure, reservoir saturation pressure, formation porosity, and absolute permeability are studied through 66 ERW cases. The results illustrate that low permeability leads to a fast decrease of oil production rates and significantly uneven pressure distribution. The pressure is lower at the center of the ERW but is higher at both ends of the ERW, while the pressure is evenly distributed along the horizontal well in the HW cases. In addition, the oil production is in direct proportion with the initial reservoir pressure, formation rock compressibility, formation porosity, and formation fluid compressibility but is in an inverse ratio with the reservoir saturation pressure. Furthermore, the initial reservoir pressure has the largest impact on both the total cumulative oil production driven out by natural energy and the cumulative oil production after the development of ten years by natural energy; on the contrary, the absolute permeability has no effect on the total cumulative oil production driven out by natural energy. [ABSTRACT FROM AUTHOR]

We revisit the competition between attractive and repulsive interparticle forces in simple fluids and how this governs and connects the macroscopic phase behavior and structural properties, as manifested in pair correlation functions. We focus on the asymptotic decay of the total correlation function h(r) which is, in turn, controlled by the form of the pair direct correlation function c(r). The decay of rh(r) to zero can be exponential (monotonic) if attraction dominates repulsion and exponentially damped oscillatory otherwise. The Fisher-Widom (FW) line separates the phase diagram into two regions characterized by the two different types of asymptotic decays. We show that there is a new and physically intuitive thermodynamic criterion which approximates well the actual FW line. This new criterion defines a line where the isothermal compressibility takes its ideal gas value χ T = χ T id . We test our hypothesis by considering four commonly used models for simple fluids. In all cases, the new criterion yields a line in the phase diagram that is close to the actual FW line for the thermodynamic state points that are most relevant. We also investigate (Widom) lines of maximal correlation length, emphasizing the importance of distinguishing between the true and Ornstein-Zernike correlation lengths. [ABSTRACT FROM AUTHOR]

Due to their computational efficiency, coarse-grained (CG) models are widely adopted for modeling soft materials. As a consequence of averaging over atomistic details, the effective potentials that govern the CG degrees of freedom vary with temperature and density. This state-point dependence not only limits their range of validity but also presents difficulties when modeling thermodynamic properties. In this work, we systematically examine the temperature- and density-dependence of effective potentials for 1-site CG models of liquid ethane and liquid methanol. We employ force-matching and self-consistent pressure-matching to determine pair potentials and volume potentials, respectively, that accurately approximate the many-body potential of mean force (PMF) at a range of temperatures and densities. The resulting CG models quite accurately reproduce the pair structure, pressure, and compressibility of the corresponding all-atom models at each state point for which they have been parameterized. The calculated pair potentials vary quite linearly with temperature and density over the range of liquid state points near atmospheric pressure. These pair potentials become increasingly repulsive both with increasing temperature at constant density and also with increasing density at constant temperature. Interestingly, the density-dependence appears to dominate, as the pair potentials become increasingly attractive with increasing temperature at constant pressure. The calculated volume potentials determine an average pressure correction that also varies linearly with temperature, although the associated compressibility correction does not. The observed linearity allows for predictions of pair and volume potentials that quite accurately model these liquids in both the constant NVT and constant NPT ensembles across a fairly wide range of temperatures and densities. More generally, for a given CG configuration and density, the PMF will vary linearly with temperature over the temperature range for which the entropy associated with the conditioned distribution of atomic configurations remains constant. [ABSTRACT FROM AUTHOR]

In this work, we established a novel theory for the dynamics of oscillating bubbles such as cavitation bubbles, underwater explosion bubbles, and air bubbles. For the first time, we proposed bubble dynamics equations that can simultaneously take into consideration the effects of boundaries, bubble interaction, ambient flow field, gravity, bubble migration, fluid compressibility, viscosity, and surface tension while maintaining a unified and elegant mathematical form. The present theory unifies different classical bubble equations such as the Rayleigh–Plesset equation, the Gilmore equation, and the Keller–Miksis equation. Furthermore, we validated the theory with experimental data of bubbles with a variety in scales, sources, boundaries, and ambient conditions and showed the advantages of our theory over the classical theoretical models, followed by a discussion on the applicability of the present theory based on a comparison to simulation results with different numerical methods. Finally, as a demonstration of the potential of our theory, we modeled the complex multi-cycle bubble interaction with wide ranges of energy and phase differences and gained new physical insight into inter-bubble energy transfer and coupling of bubble-induced pressure waves. [ABSTRACT FROM AUTHOR]

As a kind of partially saturated soil often containing dissolved gas with a high degree of saturation (S > 85%), gassy sand sediment widely exists in the marine environment all over the world. Due to the effect of gas dissolution and exsolution on the pore fluid compressibility, its stress–strain and pore pressure responses are quite different from those of common saturated and unsaturated soils when subjected to undrained loading. Since almost all the gas bubbles are occluded in the pore water of offshore gassy sand, the matric suction may be neglected, and an undrained constitutive model for gassy sand is developed based on the existing hypoplastic bounding surface model for saturated sand. Both Boyle's and Henry's laws are employed in the model to characterize the equilibrium behavior of the gas compressibility and solubility, and then the equivalent compressibility coefficient of the pore fluid is obtained. To avoid unrealistic volumetric expansion, the concepts of the critical state and state-dependent dilatancy stress ratio are incorporated to describe its ultimate shear strength and dilatancy characteristics, respectively. Finally, the triaxial undrained test results on gas-charged sand from Hangzhou Bay are analyzed at three initial saturation degrees of 85%, 90%, and 100%, and two effective confining pressures of 50 kPa and 200 kPa. Moreover, carbon dioxide (CO2) was selected in the test, and the samples were loose with a relative density of 30%. It is noted that a good agreement is achieved between the simulation results and the experimental data, including the influence of gas content and confining pressure on the shear dilatancy and the mean effective stress increase at the beginning of the effective stress path, among others. [ABSTRACT FROM AUTHOR]

Multi-branch junctions are commonly used in highly integrated supercharged internal combustion engines. Accurate prediction of flow performance is critical to engine cycle simulation. However, the few studies on this type of junction boundary model focus on incompressible fluid, which leads to insufficient accuracy in predicting compressible flow. In this study, based on a constant-pressure model commonly used to calculate multi-branch junctions, by considering fluid compressibility, we developed a momentum conservation model and a pressure loss coefficient model, respectively, that are tailored to multibranch junctions. The momentum conservation model accounts for structural parameters such as branch angle and the influence of Mach number, and hence it improved the prediction accuracy. For a certain type of high-power-density internal combustion engine, the maximum simulation error is reduced from 7.58% to 2.47% in the engine performance prediction at the rated speed after using the momentum conservation model. The proposed pressure loss coefficient model was mainly used to compensate for the shortcomings of the momentum conservation model in the multi-branch calculation efficiency reduction, which is more dependent on the pressure loss coefficient database provided by the experiment. The influence of fluid compressibility was also considered. This investigation can provide tailored tools for multi-branch junction performance prediction in different functional simulation scenes. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the coupled dynamics of a collapsing bubble and the motion of a nearby elastic plate at different initial distances. This was achieved using a combination of experimental and computational models. In the experiments, high-speed photography was used to record the temporal and spatial evolution of the collapse of a single bubble near an elastic boundary under normalized standoff distances γ ranging from 1.0 to 3.3. Digital image correlation was used to synchronously record the motion of the elastic plate. For the numerical simulations, taking the fluid compressibility and boundary motion into account, the immersed-boundary method was introduced to simulate the interaction between the elastic plate and bubble collapse. The results show that, with different initial distances, the dynamic behaviors of the bubble, including oscillation time, impact mode, and energy conversion, are different, and this is caused by the elastic rebound of the plate. In addition, the direction and amplitude of the deformation of the elastic plate are also influenced by the impact effects during bubble oscillation and rebound. The combined form of these impact behaviors changes with initial distance, and there are three typical impact patterns: the shock-wave effect, jet-effect, and hybrid shock-wave and jet-effect modes. In particular, when γ < 1.5, the jet effect and hybrid impact forms, which are dominated by the high-speed jet, can result in asymmetric deformation and cause greater local damage to the elastic plate. Finally, we summarize the combined mechanisms that govern the impact of a collapsing bubble on an elastic plate. [ABSTRACT FROM AUTHOR]

An electrical hydraulic control system (electro-hydraulic system) is thought to be a key component in excavator operation systems. Control methods with fixed parameters may not yield optimal system performances because a hydraulic system has various nonlinear uncertainties due to the leakage and compressibility of the fluid medium. Hence, a novel PID controller based on improved differential evolution (IDE) is introduced to excavator electro-hydraulic systems for interconnected hydraulic systems. The proposed algorithm not only adjusts the PID parameters of the different working conditions but also adjusts the scaling factor and crossover probability. Then, the proposed PID controller based on IDE and the excavator bucket control system are modeled and simulated on the MATLAB simulation platform. The simulation results demonstrate that the proposed controller has better performance in settling time, rise time, and convergence speed compared to the PID controller based on standard differential evolution and the Ziegler–Nichols (ZN) PID controller with a novel object function. Eventually, the IDE-PID controller is assessed on a 23-ton excavator, and good transient behavior and trajectory accuracy are obtained in comparison to the SDE-PID controller. [ABSTRACT FROM AUTHOR]

Fractures are ubiquitous in Earth's upper crust and strongly affect its physical properties. Their visibility for elastic waves hinges on their stiffness, a measure of the relation between changes in fracture aperture and applied stress, which itself significantly increases with increasing stress according to laboratory data. We constrained normal stiffness (and its stress dependence) of two fractures intersecting a borehole in the research mine 'Reiche Zeche' in Freiberg, Saxony, Germany, from pressure-recovery behaviour observed when the pressure in a double-packer interval enclosing them was briefly released during shut-in sequences. For the evaluation of the pressure recovery, we developed a generic model that accounts for the inherent convolution of mechanical closing of the fracture, fluid flow in the fracture, fluid exchange between fracture and the surrounding rock, here addressed as fracture leakage, and effects associated with finite borehole storage. We address the hydraulic system by considering three different 'storage containers', described by non-dimensionless storage parameters: the wellbore with a fixed storage capacity, the fracture with storage capacities related to fluid compressibility and fracture stiffness, and the surrounding rock constituting a container with unlimited storage capacity. To examine the model's characteristics, we investigated pressure transients predicted for specific cases, such as negligible fracture leakage, and subsequently numerically determined the sensitivity of the model predictions to the involved model parameters. The model's application to the field data yield estimates of properties of the fractures (length, aperture and stiffness) and of the surrounding rock mass (product of permeability and specific storage capacity). The parameters derived from the modelling compare well with independent constraints. An analysis of currently available fracture-stiffness data shows that the lack of knowledge of the stress dependence of stiffness severely hampers firm conclusions on scale dependence and the bias between methods. [ABSTRACT FROM AUTHOR]