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Based on Biot's theory of two-phase media, the screening effectiveness of a multi-row pile barrier system on incident Rayleigh waves in a fluid-saturated poroelastic half-space is investigated using a high-precision three-dimensional indirect boundary element method for multi-domain scattering. A companion paper has described the theoretical derivation of the model. In this paper, numerical results indicate that the scattering of waves by piles in fluid-saturated poroelastic media is different from that in single-phase elastic media. The group piles effectively reduce the vibration amplitude in the poroelastic half-space, and the dynamic response strongly depends on the incident frequency, porosity, pile length and spacing, number of pile rows, and row spacing of multi-row piles. Higher values of the frequency and porosity (i.e., softer soil) produce a better vibration isolation effect by the group piles. Special attention should be paid to piles embedded in poroelastic media, as the existence of fluid produces a negative effect on the vibration isolation compared with the case of a single-phase medium. [ABSTRACT FROM AUTHOR]

Based on Biot's theory of two-phase media, the screening effectiveness of a multi-row pile barrier system on incident Rayleigh waves in a fluid-saturated poroelastic half-space is investigated using a high-precision threedimensional indirect boundary element method for multi-domain scattering. According to the single-layer potential theory, the scattered wavefield in a poroelastic half-space can be constructed using the distributed loads in three orthogonal directions and the fluid source, which are virtually applied on the surface of all the scatterers. This paper describes the theoretical derivation of the model. A companion paper presents the numerical results. [ABSTRACT FROM AUTHOR]

In the poroelasticity theory of de la Cruz and Spanos, fluid shearing within the viscous boundary layer, i.e. fluid vorticity, manifests as an independent process, namely the diffusive slow shear wave. Quantifying its impact on elastic wave propagation remains a research challenge. We analyse the transmissivity of a horizontally polarized shear wave travelling across a stack of porous fluid-saturated layers. The fluid shearing developed at each contact is captured, in a macroscopic sense, through conversion scattering into this diffusive slow shear wave. Generalizing the reflectivity method for elastic waves to the poroelastic case, we develop semi-analytical results for an arbitrary number of layers. We find that the conversion scattering into this diffusion wave reduces the shear wave amplitude, and this reduction accumulates with the number of layers. In the limit when the layer thickness corresponds to the pore diameter, the resulting wave quality factor is close to the predictions of previously reported attempts to capture the fluid vorticity. However, our approach is distinctively different since it is purely based on a wave-theoretic analysis of interacting waves, acknowledging vorticity diffusion as an independent process, thereby avoiding the problems arising when incorporating a pore-scale phenomenon in a macroscopic wave propagation theory. [ABSTRACT FROM AUTHOR]

The well‐known 'Biot–Gassmann' formula for the undrained compressibility of porous rock is in error. The error was introduced by Gassmann (implicitly revising earlier work by Biot) and results in an expression which is simpler than Biot's corresponding expression, containing only one material parameter (KS) in place of Biot's two (H and R). The error occurred when Gassmann applied a hydraulically open theorem to a hydraulically closed system, thus violating the assumptions of the undrained compressibility. Similar errors have marred the many subsequent derivations of Gassmann's result. Biot's (prior) correct formulation was subsequently rederived exactly (in different notation) by Brown and Korringa, and separately by Rice and Cleary. The inconsistency between Gassmann and these three analyses is caused by Gassmann's logical error, rather than by the issue of solid micro‐homogeneity. The additional parameter may be experimentally determined via the 'Skempton B‐coefficient' (the ratio of fluid pressure to external pressure in an undrained quasi‐static compression test). This correction resolves a long‐established inconsistency between Gassmann's result and effective‐medium theory. A new generation of experimentation is required to determine the systematics of the magnitude of the correction to the Gassmann result. [ABSTRACT FROM AUTHOR]

The sediments underneath Mexico City have unique mechanical properties that give rise to strong site effects. We investigated temporal changes in the seismic velocity at strong-motion and broadband seismic stations throughout Mexico City, including sites with different geologic characteristics ranging from city center locations situated on lacustrine clay to hillside locations on volcanic bedrock. We used autocorrelations of urban seismic noise, enhanced by waveform clustering, to extract subtle seismic velocity changes by coda wave interferometry. We observed and modeled seasonal, co- and post-seismic changes, as well as a long-term linear trend in seismic velocity. Seasonal variations can be explained by self-consistent models of thermoelastic and poroelastic changes in the subsurface shear wave velocity. Overall, sites on lacustrine clay-rich sediments appear to be more sensitive to seasonal surface temperature changes, whereas sites on alluvial and volcaniclastic sediments and on bedrock are sensitive to precipitation. The 2017 Mw 7.1 Puebla and 2020 Mw 7.4 Oaxaca earthquakes both caused a clear drop in seismic velocity, followed by a time-logarithmic recovery that may still be ongoing for the 2017 event at several sites or that may remain incomplete. The slope of the linear trend in seismic velocity is correlated with the downward vertical displacement of the ground measured by interferometric synthetic aperture radar, suggesting a causative relationship and supporting earlier studies on changes in the resonance frequency of sites in the Mexico City basin due to groundwater extraction. Our findings show how sensitively shallow seismic velocity and, in consequence, site effects react to environmental, tectonic and anthropogenic processes. They also demonstrate that urban strong-motion stations provide useful data for coda wave monitoring given sufficiently high-amplitude urban seismic noise. [ABSTRACT FROM AUTHOR]

We present a new stress/total-pressure formulation for poroelasticity that incorporates the coupling with steady nonlinear diffusion modified by stress. This nonlinear problem is written in mixed-primal form, which combines a perturbed twofold saddle-point system with an elliptic problem. We analyze the continuous formulation within the framework of abstract fixed-point theory and Fredholm alternative for compact operators. A mixed finite element method is proposed, and its stability and convergence are rigorously analyzed. We also provide a few representative numerical examples to illustrate the effectiveness of the proposed formulation. The resulting model can be used to study the steady case of waste removal in the brain, providing insight into the transport of solutes in poroelastic structures under the influence of stress. [ABSTRACT FROM AUTHOR]

In this paper, radial vibrations of a fluid‐filled poroelastic cylindrical bore saturated with two immiscible fluids of infinite extent are investigated. By considering the stress‐free boundaries, the frequency equation is obtained. Particular case, namely, fluid‐filled poroelastic cylinder saturated with single fluid is discussed. In both cases, phase velocity is computed as a function of wavenumber for different porosity values. The parameter values of Columbia fine sandy loam saturated with air‐water mixture are used for the numerical evaluation. The numerical results are presented graphically and then discussed. Wave propagation in a fluid‐filled borehole embedded in an infinite poroelastic medium is of great importance due to its various applications. Bore hole studies are of great help in exploration of oils, gases, and hydro‐carbons. This interest is strongly linked to the oil industry and the need to estimate the fluid mobility in reservoirs. Beyond the scope of geophysical applications, the understanding of wave propagation in cylindrical poroelastic structures is of great importance in the areas of non‐destructive testing, Mechanical Engineering and Civil Engineering. [ABSTRACT FROM AUTHOR]

The large size embedded foundation is widely used in the engineering, but the finite thickness of soil layer underlying this foundation is usually neglected in design, which leads to the non‐negligible error of calculation. By virtue of Biot's elastodynamic theory, this paper proposes a simple method to discuss the horizontal dynamic response of the cylindrical rigid foundation partially embedded in a poroelastic soil layer. First, based on the Novak plane strain model, the shaft resistance from the surrounding soil is simulated and solved. Second, the foundation end soil is assumed as a continuous medium of finite thickness, whose initial mechanism is derived from the dynamic interaction between the rigid disk and soil. Finally, the horizontal dynamic response factor is calculated by adopting newton's second law. Several cases are set to verify the rationality of the presented solution and to develop the analysis of key parameters. The numerical results suggest that the soil layer thickness has a significant influence on the dynamic vibration of the embedded foundation, and its effect is consistent with that of poroelastic half‐space when the thickness exceeds certain value. [ABSTRACT FROM AUTHOR]

We propose and analyze an H(div) conforming discontinuous galerkin (CDG) method for the three-field Biot's consolidation model with the displacement reconstruction technique. The displacement is discretized by the k th-order Brezzi-Douglas-Marini (BDM) element, and the fluid flux and pore pressure are approximated by the k-1 th-order Raviart-Thomas-Nedelec element pairs. The H(div) CDG method is derived from the H(div) conforming formulation by replacing the classical gradient operator with a weak gradient operator, where the weak one is locally computed by the k th-order Raviart-Thomas (RT) element. We prove optimal a-priori error estimates for both semi-discrete scheme and fully-discrete scheme with the backward Euler discretization in time. The implicit constants in the error estimates are robust for the arbitrarily large Lamé coefficient and the arbitrarily small constrained specific storage coefficient. Our method has no stabilizers, which simplifies the finite element formulations. Meanwhile, it can also overcome the poroelasticity locking mathematically and preserve the pointwise mass conservation on the discrete level. The validity and accuracy of the proposed method are verified by numerical experiments. [ABSTRACT FROM AUTHOR]

We introduce a novel heterogeneous multi‐scale method for the frequency response analysis of waves propagating in porous domains with a complex micro‐structure. In this, the domain is decomposed onto polygonal coarse elements each clustering its local micro‐structure. The micro‐structure is resolved using the virtual element method hence providing ample flexibility into capturing fine scale heterogeneities of arbitrary polygonal shapes. The upscaling is performed through a set of numerically evaluated multi‐scale basis functions. Rather than evaluating the basis for a broad band set of frequencies, a reduced order modeling approach is opted for. In this, the basis is evaluated for a select subset of frequencies, that is used as a basis for the evaluation of the remaining set through a proper orthogonal decomposition procedure. The solution of the coupled governing equations is then performed at the coarse‐scale at a reduced computational cost. The performance of the method in terms of accuracy and computational efficiency is evaluated through a set of numerical examples for poro‐elastic materials with heterogeneities of various shapes. [ABSTRACT FROM AUTHOR]

This contribution introduces and discusses a formulation of poro-hyperelasticity at finite strains. The prediction of the time-dependent response of such media requires consideration of their characteristic multi-scale and multi-physics parameters. In the present work this is achieved by formulating a non-dimensionalised fluid–solid interaction problem (FSI) at the pore level using an arbitrary Lagrange–Euler description (ALE). The resulting coupled systems of PDEs on the reference configuration are expanded and analysed using the asymptotic homogenisation technique. This approach yields three partially novel systems of PDEs: the macroscopic/effective problem and two supplementary microscale problems (fluid and solid). The latter two provide the microscopic response fields whose average value is required in real-time/online form to determine the macroscale response (a concurrent multi-scale approach). In order to overcome the computational challenges related to the above multi-scale closure, this work introduces a surrogate approach for replacing the direct numerical simulation with an artificial neural network. This methodology allows for solving finite strain (multi-scale) porohyperelastic problems accurately using direct automated differentiation through the strain energy. Optimal and reliable training data sets are produced from direct numerical simulations of the fully-resolved problem by including a simple real-time output density check for adaptive sampling step refinement. The data-driven approach is complemented by a sensitivity analysis of the RVE response. The significance of the presented approach for finite strain poro-elasticity/poro-hyperelasticity is shown in the numerical benchmark of a multi-scale confined consolidation problem. Finally, to show the robustness of the method, the system response is dimensionalised using characteristic values of soil and brain mechanics scenarios. [ABSTRACT FROM AUTHOR]

Stress and pore pressure changes due to depletion of or injection into a reservoir are key elements in stability analysis of overburden shales. However, the undrained pore pressure response in shales is often neglected but needs to be considered because of their low permeability. Due to the anisotropic nature of shales, the orientation of both rock and stresses should be considered. To account for misalignment of the medium and the stress tensor, we used anisotropic poroelasticity theory to derive an angle-dependent expression for the pore pressure changes in transversely isotropic media under true-triaxial stress conditions. We experimentally estimated poroelastic pore pressure parameters of a shale from the Lista formation at the Valhall field. We combined the experimental results with finite element modelling to estimate the pore pressure development in the Valhall overburden over a period of nearly 40 years. The results indicate non-negligible pore pressure changes several hundred meters above the reservoir, as well as significant differences between pore pressure and effective stress estimates obtained using isotropic and anisotropic pore pressure parameters. We formulate a simple model approximating the undrained pore pressure response in low permeable overburden. Our results suggest that in the proximity of the reservoir the amplitude of the undrained pore pressure changes may be comparable to effective stresses. Combined with the findings of joint analysis of locations of casing deformation and total and effective stresses, the results suggest that pore pressure modelling may become an important element of casing collapse and caprock failure risk analysis and mitigation. Highlights: We propose a workflow for pore pressure change modelling in shales based on the anisotropic poroelasticity theory, Modeling of Valhall oil field overburden indicates significant pore pressure changes a few hundred meters above the producing reservoir, Pore pressure changes predicted using anisotropic and isotropic poroelastic parameters differ significantly in magnitude and spatial distribution, Pore pressure changes in anisotropic shales can be approximated with the use of a single poroelastic parameter and vertical stress changes, Results suggest that the undrained pore response modelling could become a useful tool for casing collapse risk analysis and mitigation. [ABSTRACT FROM AUTHOR]

In this work, static bending responses and natural frequency characteristics of functionally graded porous plates on elastic foundations are investigated. To serve this purpose, we present a hyperbolic quasi-3D shear deformation theory that takes into account both shear strain and normal deformation but requires only four variables to approximate the displacement field regardless of the shear correction factor. The virtual work principle is utilized to derive the equations of motion. The analytical solution in closed form is obtained by using Navier's technique. Numerical comparisons are conducted to validate the accuracy and efficiency of the present approach. Using this numerical model, the influences of gradient index, porosity fraction, geometric parameters, and foundation stiffness parameters on the deflection and fundamental frequency of FGP sandwich plates are comprehensively studied. [ABSTRACT FROM AUTHOR]

A new class of unilaterally constrained problems for fully coupled poroelastic models stemming from hydraulic fracturing is introduced and studied with respect to its well-posedness. The poroelastic medium contains a fluid-driven crack, which is subjected to non-penetration conditions and cohesion forces between the crack faces. Existence of solution for the governing elliptic–parabolic variational inequality under the unilateral constraint with a small cohesion is established using the incremental approximation based on Rothe’s semi-discretization in time.

Detecting inclusions in materials at small scales is of high importance to ensure the quality, structural integrity and performance efficiency of microelectromechanical machines and products. Ultrasound waves are commonly used as a non-destructive method to find inclusions or structural flaws in a material. Mathematical continuum models can be used to enable ultrasound techniques to provide quantitative information about the change in the mechanical properties due to the presence of inclusions. In this paper, a nonlocal size-dependent poroelasticity model integrated with machine learning is developed for the description of the mechanical behaviour of spherical inclusions under uniform radial compression. The scale effects on fluid pressure and radial displacement are captured using Eringen’s theory of nonlocality. The conservation of mass law is utilised for both the solid matrix and fluid content of the poroelastic material to derive the storage equation. The governing differential equations are derived by decoupling the equilibrium equation and effective stress–strain relations in the spherical coordinate system. An accurate numerical solution is obtained using the Galerkin discretisation technique and a precise integration method. A Dormand–Prince solution is also developed for comparison purposes. A light gradient boosting machine learning model in conjunction with the nonlocal model is used to extract the pattern of changes in the mechanical response of the poroelastic inclusion. The optimised hyperparameters are calculated by a grid search cross validation. The modelling estimation power is enhanced by considering nonlocal effects and applying machine learning processes, facilitating the detection of ultrasmall inclusions within a poroelastic medium at micro/nanoscales.

Induced seismicity linked to geothermal resource exploitation, hydraulic fracturing, and wastewater disposal is evolving into a global issue because of the increasing energy demand. Moderate to large induced earthquakes, causing widespread hazards, are often related to fluid injection into deep permeable formations that are hydraulically connected to the underlying crystalline basement. Using injection data combined with a physics-based linear poroelastic model and rate-and-state friction law, we compute the changes in crustal stress and seismicity rate in Oklahoma. This model can be used to assess earthquake potential on specific fault segments. The regional magnitude-time distribution of the observed magnitude (M) 3+ earthquakes during 2008-2017 is reproducible and is the same for the 2 optimal, conjugate fault orientations suggested for Oklahoma. At the regional scale, the timing of predicted seismicity rate, as opposed to its pattern and amplitude, is insensitive to hydrogeological and nucleation parameters in Oklahoma. Poroelastic stress changes alone have a small effect on the seismic hazard. However, their addition to pore-pressure changes can increase the seismicity rate by 6-fold and 2-fold for central and western Oklahoma, respectively. The injection-rate reduction in 2016 mitigates the exceedance probability of M5.0 by 22% in western Oklahoma, while that of central Oklahoma remains unchanged. A hypothetical injection shut-in in April 2017 causes the earthquake probability to approach its background level by ∼2025. We conclude that stress perturbation on prestressed faults due to pore-pressure diffusion, enhanced by poroelastic effects, is the primary driver of the induced earthquakes in Oklahoma.

The results of laboratory studies to determine the effect of effective stress on the permeability of sandstone are presented. During the test, the samples were subjected to a stepwise increase or decrease of the effective stress (at a constant pore pressure) in a specified step. The values of rock permeability at different values of effective stress were determined, and the influence of the grain size of the reservoir rock matrix on the character of the change in the sandstone permeability coefficient was also established. During the test, a decrease in permeability was observed with an increase in effective stress. It was found that as a result of gradual loading/unloading of the sandstone sample, the original permeability values were not restored, which indicates the beginning of the formation of residual strains in the rock. This effect should be taken into account when modeling field development because in the process of reserves extraction the effective stress acting on the reservoir rock skeleton changes, which results in a significant chang in rock permeability. The results of laboratory studies showed that the deviation of permeability in medium-grained sandstones relative to the initial value was greater than in medium- and fine-grained sandstones. The pressure sensitivity coefficient and constant of material, which are used in empirical relationships between permeability and effective stress, were numerically estimated. At the same time, the constant of material showed no such convergence, which indicates that the values of this parameter are individual for each rock.

The open-source finite element code FEniCS is considered as an alternative to commercial finite element codes for evaluating complex constitutive models of multiphysics phenomena. FEniCS deserves this consideration because it is well-suited for encoding weak forms corresponding to partial differential equations arising from the fundamental balance laws and constitutive equations. It is shown how FEniCS can be adopted for solving boundary-value problems describing viscoelastic flows, poroelasticity, and tumor growth. Those problems span a wide range of models of continuum mechanics, and involve Eulerian, Lagrangian, and combined Eulerian-Lagrangian descriptions. Thus it is demonstrated that FEniCS is a viable computational tool capable of transcending traditional barriers between computational fluid and solid mechanics. Furthermore, it is shown that FEniCS implementations are straightforward, and do not require advanced knowledge of finite element methods and/or coding skills.

When a rigid object approaches a soft material in a viscous fluid, hydrodynamic stresses arise in the lubricated contact region and deform the soft material. The elastic deformation modifies in turn the flow, hence generating a soft-lubrication coupling. Moreover, soft elastomers and gels are often porous. These materials may be filled with solvent or uncrosslinked polymer chains, and might be permeable to the surrounding fluid, which further complexifies the description. Here, we derive the point-force response of a semi-infinite and permeable poroelastic substrate. Then, we use this fundamental solution in order to address the specific poroelastic lubrication coupling associated with contactless colloidal-probe methods. In particular, we derive the conservative and dissipative components of the force associated with the oscillating vertical motion of a sphere close to the poroelastic substrate. Our results may be relevant for dynamic surface force apparatus and contactless colloidal-probe atomic force microscopy experiments on soft, living and/or fragile materials, such as swollen hydrogels and biological membranes. [ABSTRACT FROM AUTHOR]

When a suspension of spherical or near-spherical particles passes through a constriction the particle volume fraction either remains the same or decreases. In contrast to these particulate suspensions, here we observe that an entangled fiber suspension increases its volume fraction up to 14-fold after passing through a constriction. We attribute this response to the entanglements among the fibers that allows the network to move faster than the liquid. By changing the fiber geometry, we find that the entanglements originate from interlocking shapes or high fiber flexibility. A quantitative poroelastic model is used to explain the increase in velocity and extrudate volume fraction. These results provide a new strategy to use fiber volume fraction, flexibility, and shape to tune soft material properties, e.g., suspension concentration and porosity, during delivery, as occurs in healthcare, three-dimensional printing, and material repair. When a suspension of particles passes through a constriction the particle volume fraction either decreases or remains the same. Pan et al. report that an entangled fiber suspension increases its volume fraction greater than a factor of 10 after passing through a constriction. [ABSTRACT FROM AUTHOR]

In this work, a numerical 3D finite element method is developed to investigate the natural frequencies and static responses of saturated FG porous annular elliptical sector plate. 3D elasticity theory is utilized to model the problem. Three various porosity patterns are assumed along the thickness direction such as porosity nonlinear symmetric distribution (PNSD), porosity nonlinear nonsymmetric distribution (PNND), and porosity uniform distribution (PUD). Biot theory of poroelasticity instead of the simple Hooke's law is applied to describe the relation between stress and strain. To derive the governing equations, finite element approach according to Rayleigh-Ritz energy formulation is applied. A thorough investigation studies the sensitivity of the static behavior and natural frequencies of the plate to different parameters, including the Skempton and porosity coefficients, geometric parameters, and various patterns of porosity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a fully discrete multiphysics finite element method to solve a nonlinear poroelasticity model with finite strain. To reveal the multi-physical processes of deformation and diffusion and propose a stable numerical method, we reformulate the original model into a fluid–fluid coupled problem—a generalized nonlinear Stokes problem of displacement vector field and pseudo pressure field and a diffusion problem of other pseudo pressure field by a new technique. Then, we propose a multiphysics finite element method to approximate the spatial variables and use Newton method to solve the nonlinear problem, prove that the proposed numerical method is stable and has the optimal convergence orders, and give some numerical tests to show that the proposed numerical method is stable and has no oscillation for displacement and pressure. Finally, we draw conclusions to summary the main results of this work. [ABSTRACT FROM AUTHOR]

The combined effects of oil and gas production and saltwater disposal in stacked reservoirs can result in poroelastic-stress changes that affect fault stability and induced seismicity but that are not captured by models that consider disposal only. While the significance of these combined effects has been demonstrated in site-generic geomechanical simulations, their significance is yet to be quantified for specific sites of observed induced seismicity. We conducted 3D monolithically coupled poroelastic finite-element simulations for a site-specific geomechanical analysis to assess the potential for reactivation of basement-rooted faults in response to saltwater injection and hydrocarbon production near Venus, Johnson County, Texas. Earthquake activity with magnitudes as high as Mw 4.0 primarily occurred in the basement section of a listric normal fault extending from basement across the Ellenburger disposal reservoir and into the overlying gas-producing Barnett Shale. We find that using the best estimates of in-situ stress and fault orientation, and fault frictional coefficient of 0.6, do not hindcast fault reactivation. Increasing the maximum horizontal stress azimuth by 10° and the basement fault dip by 5°, both within the uncertainty space of the input parameters, and lowering the friction coefficient of the fault in basement to 0.35, leads to fault reactivation in basement. Using the same model geometry but a friction coefficient of 0.6 leads to fault reactivation within the Ellenburger disposal reservoir, which is inconsistent with observed hypocenter depths. Including the effects of production from Barnett reduces the potential for fault reactivation compared to simulations of disposal only. Comparing simulations with only five disposal wells to results of simulating 35 wells, we demonstrate the sensitivity of fault reactivation to selected number of wells. In addition to showing the sensitivity of simulation outcomes on the availability of high-quality field parameters, these results demonstrate the need for coupled poroelastic simulations unlike common hydrogeological and reservoir engineering simulations that may significantly over- or under-estimate the potential for fault reactivation and thus for induced-seismicity hazard. Highlights: We developed fully coupled poroelastic models for the Barnett-Shale and Ellenburger reservoirs to assess causative mechanisms for MW 4.0 earthquake sequence near Venus, TX. Models using a most favorable stress state require a fault friction coefficient of 0.35 for slip in the basement consistent with observed hypocenter depths. Models using the best estimates of stress azimuths, fault dip, and a 0.6 friction coefficient fail to hindcast fault slip. Model domains should be at least four times the distance between the closest injections and the earthquake epicenter to minimize boundary effects and include more disposal wells. [ABSTRACT FROM AUTHOR]

This article derives the effective poroelastic properties of N-layered composite assemblage. The derivation is based on the Hashin composite sphere assemblage (CSA) model and the linear elastic solution of n-layer coated inclusion-reinforced materials proposed by Hervé and Zaoui. The contribution of this study consists in the consideration of the poromechanical coupling to derive not only the bulk and shear drained moduli but also the Biot coefficient and the solid Biot modulus. The theoretical solutions are used for studying the oolitic limestone from Bourgogne (France), in which the microstructure exhibits generally an assemblage of oolite grains surrounded by a matrix. They are linked via interphase where most of the macropores locate. A two-step homogenisation scheme is proposed. The first step consists in upscaling the mesoscopic poroelastic properties of each porous phase by using the differential self-consistent scheme. In the second step, the three different porous constituents (oolite, ITZ and matrix) are homogenised using the CSA model. Results are validated against the data collected from the open literature. [ABSTRACT FROM AUTHOR]

Full-waveform inversion (FWI) is considered as a high-resolution imaging technique to recover the geophysical parameters of the elastic subsurface from the entire content of the seismic signals. However, the subsurface material properties are less well estimated with elastic constraints, especially for the near-surface structure, which usually contains fluid contents. Since Biot theory has provided a framework to describe seismic wave propagations in the poroelastic media, in this work, we propose an algorithm for the 2-D time-domain (TD) poroelastic FWI (PFWI) when the fluid-saturated poroelastic equations are applied to carve the physical mechanism in the shallow subsurface. To detect the contribution of the poroelastic parameters to shallow seismic wavefields, the scattered P - SV & SH wavefields corresponding to a single model parameter are derived explicitly by Born approximation and shown numerically afterward. The Fréchet kernels are also derived and exhibited in P - SV & SH schemes to analyse the sensitivities of the objective function to different poroelastic parameters. Furthermore, we verify the accuracy of the derivations through model parameter reconstructions. We perform a series of numerical tests on gradients with respect to different model parameters to further evaluate inter-parameter trade-offs. PFWI holds potential possibilities to directly invert fluid-related physical parameters of the shallow subsurface. [ABSTRACT FROM AUTHOR]

• The pattern formation of morphogens is studied in geometrically-confined microtissues during early embryogenesis. • The microtissue consisted of human stem cells is modeled as a piece of biphasic poroelastic material. • The active contractility is fully-coupled with the reaction-diffusion of the morphogens through the poroelasticity. • Linear stability analysis is performed to determine ranges of parameters that leads to diffusion-induced instability. • A comprehensive parameter study, including the sizes and geometries of the tissues, is carried out in the paper. The reaction-diffusion models have been extensively applied to explain the mechanism of pattern formations in early embryogenesis based on geometrically confined microtissues consisting of human pluripotent stem cells. Mechanical cues, such as the cellular stresses and strains, have been found to dictate the pattern formation in human stem cell differentiation. As a result, the traditional reaction-diffusion models are modified by adding mechanically related terms to consider the role played by the mechanical cues during the very early stage of embryogenesis. However, these models either do not consider the activeness of the cellular tissues or neglect their poroelastic nature that biological tissues are made by both cells and interstitial fluid. Here we propose a modified reaction-diffusion model that couples with the active contraction of cellular tissues. The cellular tissue is modelled as a piece of biphasic poroelastic material, where mechanical forces naturally regulate the transport of chemical cues. Such chemical cues direct cell fate and hence yield certain types of pattern formations observed in previous experiments. [ABSTRACT FROM AUTHOR]

There is a mathematical analogy between the poroelastic and thermoelastic behavior of the compressional P wave, whose dissipation is due to the coupling between the elastic deformation and the phenomenon of pressure and heat diffusion, represented by Darcy's law and heat conduction, respectively. This attenuation effect is more pronounced in heterogeneous media, where conversion of the fast P wave to the slow (Biot) and thermal diffusive modes occurs at material interfaces. Specifically, the problem is to obtain the P-wave properties of a porous medium due to temperature gradients between the solid and fluid phases. Then, we consider a simplified one-dimensional porous medium and obtain the quality factor, Q, and phase velocity as a a function of frequency, based on an isostress condition and using Gassmann equation and the Kramers Kronig relations.The model allows for the incorporation of a relaxation time to simulate a proper wave-like behavior at high frequencies, avoiding in this way infinite velocities. Moreover, we perform a complete analysis varying the different parameters, namely, the heat conduction, the specific heat, the thermal expansion, the types of solid and fluid and the pore size. [ABSTRACT FROM AUTHOR]

The paper presents a framework for analysis of beams interacting with nonlinear‐poroelastic, layered continuums (e.g., clayey soils) when subjected to time‐dependent loads. The poroelastic layered continuum is characterized by a nonlinear‐elastic constitutive relationship that relates the secant shear modulus to the induced shear strain. The Biot's theory of consolidation is combined with a dynamic beam‐continuum interaction model to develop the analysis. The vertical consolidation settlement of the beam and the excess pore pressure in the porous continuum are assumed to be products of separable functions, and the extended Hamilton's principle of least action is applied to obtain the differential equations governing the inertial consolidation motion of the beam‐continuum system and the dissipation of excess pore pressure. An iterative numerical algorithm is used to solve these coupled differential equations following one‐dimensional finite element analysis in which the implicit Wilson‐Θ time integration scheme is used to obtain the time history of beam and continuum responses. The novelty of the framework is that it rigorously takes into account the nonlinear poroelastic soil‐structure interaction within a dynamic time‐integration framework with minimal computational resources. The characteristics of this newly developed model are illustrated through examples. [ABSTRACT FROM AUTHOR]

This work presents a double-permeability poroelasticity model for fluid flows in both the microvascular and interstitial networks in a biological tissue. In the newly developed model, both networks are modeled as porous structures with distinct permeabilities and porosities. The microvascular and the interstitial fluid pressures are hydraulically as well as mechanically coupled together. The numerical results for the steady-state flow in a one-dimensional capillary bed using some preliminary material parameters show that the vascular pressure decreases almost linearly from the arteriole-side to the venule-side. The interstitial fluid pressure (IFP) is elevated by an increase in the venule-side vascular pressure as well as by a decrease in the lymphatic drainage capability. Under a transient flow condition induced by a sudden drop in the venule-side vascular pressure, the IFP may pop up during a very short period of time before decreasing to the reduced steady-state value at long times due to the mechanical coupling between the vascular pressure and IFP which acts much faster than the hydraulic coupling between the two pressures through the vascular walls. Oscillatory mechanical load may produce comparable IFP and promote fluid exchange between the microvessels and interstitium. Finally, a perturbation analysis reveals that a boundary layer for the IFP develops near the tissue boundary. For the first-order approximation, the vascular pressure is decoupled from the IFP and the IFP may be obtained with the first-order vascular pressure as a source. [ABSTRACT FROM AUTHOR]

Hydrogels can exhibit a remarkably complex response to external stimuli and show rich mechanical behavior. Previous studies of the mechanics of hydrogel particles have generally focused on their static, rather than dynamic, response, as traditional methods for measuring single particle response at the microscopic scale cannot readily measure time-dependent mechanics. Here, we study both the static and the time-dependent response of a single batch of polyacrylamide (PAAm) particles by combining direct contact forces, applied by using Capillary Micromechanics, a method where particles are deformed in a tapered capillary, and osmotic forces are applied by a high molecular weight dextran solution. We found higher values of the static compressive and shear elastic moduli for particles exposed to dextran, as compared to water ( K Dex ≈ 63 kPa vs. K water ≈ 36 kPa, and G Dex ≈ 16 kPa vs. G water ≈ 7 kPa), which we accounted for, theoretically, as being the result of the increased internal polymer concentration. For the dynamic response, we observed surprising behavior, not readily explained by poroelastic theories. The particles exposed to dextran solutions deformed more slowly under applied external forces than did those suspended in water ( τ Dex ≈ 90 s vs. τ water ≈ 15 s). The theoretical expectation was the opposite. However, we could account for this behaviour by considering the diffusion of dextran molecules in the surrounding solution, which we found to dominate the compression dynamics of our hydrogel particles suspended in dextran solutions. [ABSTRACT FROM AUTHOR]

The location of the instantaneous centre of rotation (ICR) of a lumbar unit has a considerable clinical importance as a spinal health estimator. Consequently, many studies have been conducted to measure or estimate the ICR during rotations in the three anatomical planes; however the results reported are widely scattered. Even if some inter-subjects variability is to be expected, such inconsistencies are likely explained by the differences in methods and experiments. Therefore, in this paper we seek to model three behaviours of the ICR during lateral bending and axial rotation based on results published in the literature. In order to assess the metabolic and mechanical sensibility to the assumption made on the ICR kinematics, we used a previously validated three dimensional non-linear poroelastic model of a porcine intervertebral disc to simulate physiological lateral and axial rotations. The impact of the geometry was also briefly investigated by considering a 11 ∘ wedge angle. From our simulations, it appears that the hypothesis made on the ICR location does not significantly affect the critical nutrients concentrations but gives disparate predictions of the intradiscal pressure at the centre of the disc (variation up to 0.7 MPa) and of the displacement fields (variation up to 0.4 mm). On the contrary, the wedge angle does not influence the estimated intradiscal pressure but leads to minimal oxygen concentration decreased up to 33% and increased maximal lactate concentration up to 13%. While we can not settle on which definition of the ICR is more accurate, this work suggests that patient-specific modeling of the ICR is required and brings new insights that can be useful for the development of new tools or the design of surgical material such as total lumbar disc prostheses. [ABSTRACT FROM AUTHOR]

This research was conducted to determine how the incorporation of different poroelastic equations would affect the measured rock matrix bulk modulus in the laboratory. To do this, three experimental methods were used to measure the matrix bulk modulus, K s , of seven sandstone specimens taken from the Świętokrzyskie mine in Poland. Those experimental methods were based on the different governing equations in poroelasticty theory. The matrix bulk modulus has a substantial impact on the rock strength against external stresses. Moreover, the rock bulk modulus depends directly on two components: the pore fluid bulk modulus and matrix bulk modulus. The second one is more important as it is much higher than the first one. In this study, the accuracy of those three methods in the measurement of the matrix bulk modulus was evaluated. For this purpose, an acoustic wave propagation apparatus was used to perform the required tests. For each method, an empirical correlation was extracted between the matrix bulk modulus and the applied hydrostatic stress. In all the experiments, an exponential correlation was observed between the matrix bulk modulus and the hydrostatic stress applied on the rock. Furthermore, it was found that the incorporation of the dry bulk modulus in the calculations led to an underestimation of the matrix bulk modulus. In addition, as the hydrostatic stress was raised, the matrix bulk modulus also increased. The applied methodology can be deployed to determine the matrix bulk modulus in coupled rock-fluid problems such as reservoir depletion, hydraulic fracturing, oil recovery enhancement, underground gas storage and land subsidence. [ABSTRACT FROM AUTHOR]

The current work investigates axisymmetric vibration of saturated porous circular micro-plates subjected to uniform in-plane force and coupled with piezoelectric sensor and actuator layers. Including the material length scale parameter, the modified coupled stress theory is chosen to capture the size-dependent behavior of the model. The micro-structure is embedded on an elastic substrate medium modeled by Winkler–Pasternak foundation. In addition, the fluid pressure in the pores is partitioned in the formulation via the linear poroelasticity theory of Biot. Based on first-order shear deformation theory, governing equations of motion and corresponding boundary conditions are obtained by employing Hamilton's principle and solved by a semi-analytical approach called the differential transform method. To ensure the accuracy and reliability of the developed model, natural frequencies of the presented micro-plate are compared with available data in the literature. Finally, numerical examples are presented for studying the effect of some parameters including material length scale parameter, in-plane force, porosity, fluid pressure, electro-mechanical interaction, and the ratio of the elastic core thickness to piezoelectric layers thickness on vibrational responses of the proposed model for two cases of clamped and simply supported edges. The obtained results show that the proposed method is a reliable way of studying the free vibration response of the micro-structures. On the other hand, it is observed that porosity, fluid pressure, tensile in-plane force, size-effect, and open-circuit electrical condition increase the natural frequency of the system. [ABSTRACT FROM AUTHOR]

This article presents the development process of designing and testing poroelastic pavement based on highly polymer-modified bitumen. Poroelastic wearing course was composed of mineral and rubber aggregate mixed with highly polymer-modified bitumen, in contrast to previous trials, during which polyurethane resins were mainly used as binder, which led to several serious technological problems concerning difficult production, insufficient bonding to the base layer, and unsatisfactory durability. The laboratory testing phase was aimed at finding the proper composition of the poroelastic mixture that would ensure required internal shear strength and proper bonding of the poroelastic layer with the base layer. After selecting several promising poroelastic mixture compositions, field test sections were constructed and tested in terms of noise reduction, rolling resistance and interlayer bonding. Despite the very good acoustic properties of the constructed poroelastic wearing course, it was not possible to solve the problem of its insufficient durability. Still, the second major issue of poroelastic pavements that concerns premature debonding of the poroelastic layer from the base layer was completely solved. Experience gained during the implementation of the described research will be the basis for further attempts to develop a successive poroelastic mixture in the future. [ABSTRACT FROM AUTHOR]

A new class of constrained variational problems, which describe fluid-driven cracks (that are pressurized fractures created by pumping fracturing fluids), is considered within the nonlinear theory of coupled poroelastic models stated in the incremental form. The two-phase medium is constituted by solid particles and fluid-saturated pores; it contains a crack subjected to non-penetration condition between the opposite crack faces. The inequality-constrained optimization is expressed as a saddle-point problem with respect to the unknown solid phase displacement, pore pressure, and contact force. Applying the Lagrange multiplier approach and the Delfour–Zolésio theorem, the shape derivative for the corresponding Lagrangian function is derived using rigorous asymptotic methods. The resulting formula describes the energy release rate under irreversible crack perturbations, which is useful for application of the Griffith criterion of quasi-static fracture. [ABSTRACT FROM AUTHOR]

Abnormal seismic activities near reservoirs usually show a strong spatiotemporal correlation with the water filling history. Reservoir-induced seismicity is thought to be related to crustal pore pressure and stress changes caused by water impounded behind the dams. Though the Coulomb-type stress analysis helps illuminate areas that would be under risk following reservoir impoundment, it lacks the ability to explain the temporal characteristics of reservoir-induced seismicity. We present a numerical investigation of the seismicity rate evolution of reservoir-induced earthquakes. Our modelling employs a fully coupled 2-D poroelastic model to calculate the pore pressure and stress changes caused by water impoundment and incorporates the rate- and state-dependent friction law to investigate the seismicity rate. We demonstrate that shallow earthquakes are mainly caused by pore pressure increase, while poroelastic stress transfer takes the dominant role at depth. Whether a fault would be brought close to failure depends on its geometrical properties and its relative location to the reservoir. The temporal evolution of reservoir-induced earthquakes is primarily controlled by tectonic environment instead of the diffusion of pore pressure. [ABSTRACT FROM AUTHOR]

• Novel mathematical model for deriving semi-analytical Green's function solutions. • First time on the coupled horizontal and rocking vibrations in poroelasticity. • Anisotropic and layered poroelastic half-space via Biot's poroelastodynamic theory. • Handling layering via the powerful and stable dual variable and position method. • Soil-structure interaction (SSI) via a novel integral least-square approach. The coupled horizontal and rocking vibrations of a rigid circular disc resting on a transversely isotropic (TI) and layered poroelastic half-space is solved by a newly developed semi-analytical method for the first time. The poroelastic medium is modelled via Biot's poroelastodynamic theory. The Green's function corresponding to the horizontal uniform and vertical linearly changing patch loads on the surface of the layered half-space are first derived by virtue of the cylindrical system of vector functions and dual variable and position method. To solve the dynamic interaction, the influence function by the ring load is then introduced and calculated via the method of superposition. Together with the mixed boundary-value conditions, the dynamic horizontal, rocking, and coupling compliances are finally solved by a novel discretization scheme and an integral least-square approach. The developed fundamental solutions are verified by comparing with existing solutions in the purely elastic and poroelastic media. Numerical examples are presented to investigate the influence of poroelastic properties on the coupled vibration characteristics, which could be useful to the dynamic design of foundation on the saturated soil. It should be emphasized that the effect of the coupling compliance must be considered since its contribution can be as large as 26%, compared to the diagonal compliances. [ABSTRACT FROM AUTHOR]

We study the response of an endothelial cell monolayer lining the bottom surface of a cartesian Couette geometry in variations of critical shearing parameters that affect the fluid environment, such as the gap distance between the upper moving and the bottom stationary plates and the velocity of the moving plate. Specifically, we propose an in silico rheometric emulation based on startup shear experiments in a representative two-dimensional domain of the monolayer that accounts for the interaction of the blood plasma and the deformable multilayer poroelastic endothelial cells. We present quantitative predictions for the shear and normal stresses on each cell compartment (membrane, cytoplasm, and nucleus) and their structural changes. We show that the variation of the Wall Shear Stress (WSS) along the cell membrane is considered significant and strongly dependent on the shape of the cell, while membrane thinning is more prominent at the locus of high WSS in the range of physiological velocities. However, under extreme velocities, wall thinning prevails at the locus of flow stagnation. [ABSTRACT FROM AUTHOR]

The theory of vertical pile vibration is the essential basis for pile integrity determination and dynamic analysis. The pile vibration characteristics are inevitably affected when the surrounding soil is frozen due to the low environmental temperature. Therefore, the investigation of pile vibration considering the surrounding soil as a saturated frozen porous medium is of great importance. In this paper, an analytical model for vertical pile vibration was established by employing the theory of composite saturated porous media, that is, by simplifying the upper frozen soil layer as a homogeneous isotropic saturated frozen porous medium and the foundation soil beneath the pile as an elastic half-space subjected to the motion of a rigid disk. By employing the integral transform and variable separation method, analytical solutions for the proposed model were derived under the three-dimensional axisymmetric condition. The analytical model and its solutions were verified by comparing them with the existing solutions for an end-bearing pile embedded in a homogeneously frozen soil layer as well as for a saturated half-space. A parametric study was conducted by utilizing the proposed solutions, and the results indicated that the pile bottom stiffness, the freezing temperature, the shear modulus of the unfrozen soil, etc., had a significant influence on the dynamic responses of the vertical pile vibration in both the frequency and the time domains. [ABSTRACT FROM AUTHOR]

This research presents the geometrically nonlinear investigation of functionally graded saturated porous material (FGSPM) plate under undrained conditions. In conjunction with von Karman's nonlinearity, the refined shear deformation plate theory (RSDPT) is implemented to model the FGSPM plate. The effective material characteristics of the saturated porous plate change constantly in the thickness direction. The pores of the saturated porous plate are examined in fluid-filled conditions. Thus, the constitutive equations are established using Biot's linear poroelasticity theory. The governing equations are developed by combining a nonlinear finite element technique with Hamilton's principle. Then, the direct iterative approach is utilized to extract the geometrically nonlinear numerical results. The emphasis is placed on exploring the effects of numerous parameters such as Skempton coefficient, volume fraction grading index, porosity volume index, porosity distributions, and boundary conditions during the extensive numerical analyses on the linear frequency, large amplitude frequencies, and nonlinear central deflections of the FGSPM plate. It is evident from the investigation that saturated fluid in the pores substantially impacts the nonlinear deflection and vibration behavior of the FGSPM plate. [ABSTRACT FROM AUTHOR]

The storage of fluids in the subsurface is critical for a broad spectrum of applications including managed aquifer recharge, storage of liquefied carbon dioxide and hydrogen, geothermal heat extraction and exploitation of hydrocarbon. It is surprising then, that there has been relatively little measurement of the vertical distribution of poroelastic storage in geologic formations as compared with permeability. We present experiments in which fluid was injected into an important regional aquifer and the depth‐dependent strain response measured using fiber optic distributed acoustic sensing. The formation expansion and contraction in response to fluid injection were several 100 nanostrain. Strain, and the implied storage distribution, was highly localized in specific strata and demonstrated complex, hydromechanical behavior. This new window into fluid‐geomechanical coupling undermines some typically use models and observations currently in practice, but provides potential for complete representation and prediction of fluid storage in the subsurface. Plain Language Summary: A fiber optic cable was used to measure strain in response to water injection and withdrawal in a sandstone aquifer. The strain was found to be focused in limited strata within the aquifer. In some strata, the formation expanded with injection, and in others the formation contracted with injection. This complex behavior is attributed to the interaction between fluid flow and mechanical strain in the porous rock and is contrary to common models of water storage which predict a proportionate expansion of pore space with injection. These results provide important insight into understanding transient flow response to impulse and oscillatory pressure loading of the well. Key Points: Strain and flow direction was correlated or anti‐correlated with injection head, depending on injection intervalInjection and strain behavior was not simply correlated to geophysical or lithologic logsDynamic injection/withdrawal tests are of limited predictive value to managed aquifer recharge [ABSTRACT FROM AUTHOR]

The intensity and damage potential of earthquakes are linked to the speed at which rupture propagates along sliding crustal faults. Most earthquakes are sub-Rayleigh, with ruptures that are slower than the surface Rayleigh waves. In supershear earthquakes, ruptures are faster than the shear waves, leading to sharp pressure concentrations and larger intensities compared with the more common sub-Rayleigh ones. Despite significant theoretical and experimental advances over the past two decades, the geological and geomechanical controls on rupture speed transitions remain poorly understood. Here we propose that pore fluids play an important role in explaining earthquake rupture speed: the pore pressure may increase sharply at the compressional front during rupture propagation, promoting shear failure ahead of the rupture front and accelerating its propagation into the supershear range. We characterize the transition from sub-Rayleigh to supershear rupture in fluid-saturated rock, and show that the proposed poroelastic weakening mechanism may be a controlling factor for intersonic earthquake ruptures. [ABSTRACT FROM AUTHOR]

The scattered seismic waves of fractured porous rock are strongly affected by the wave-induced fluid pressure diffusion effects between the compliant fractures and the stiffer embedding background. To include these poroelastic effects in seismic modeling, we develop a numerical scheme for discrete distributed large-scale fractures embedded in fluid-saturated porous rock. Using Coates and Schoenberg's local effective medium theory and Barbosa's dynamic linear slip model characterized by complex-valued and frequency-dependent fracture compliances, we derive the effective viscoelastic compliances in each spatial discretized cell by superimposing the compliances of the background and the fractures. The effective governing equations of the fractured porous rock are then characterized by the derived anisotropic, complex-valued, and frequency-dependent effective compliances. We numerically solved the effective governing equations by mixed-grid stencil frequency-domain finite-difference method. The good consistency between the scattered waves off a single horizontal fracture calculated using our proposed scheme and those calculated using the poroelastic linear slip model shows that our modeling scheme can properly include the FPD effects. We also find that for a P-point source, the amplitudes of the scattered waves from a single horizontal fracture are strongly affected by the fluid stiffening effects due to fluid pressure diffusion, while for an S-point source, the scattered waves are less sensitive to fluid pressure diffusion. In the case of the conjugate fracture system, the scattered waves from the bottom of the fractured reservoir and the reflected waves from the underlying formation are attenuated and dispersed by the FPD effects for both P- and S-point sources. The proposed numerical modeling scheme can also be used to improve migration quality and the estimation of fracture mechanical characteristics in inversion. [ABSTRACT FROM AUTHOR]

Viable Enhanced Geothermal Systems (EGS) require (1) access to large reservoir volumes at high temperatures and (2) sufficient permeability for large production flow rates. However, working fluid injection might quickly decrease the recoverable heat energy. Thermal destressing increases fracture transmissivity and reduces the production temperature. Large fracture openings cause the injection fluid to localize in a single fracture, or a few dominant fractures, and leads to thermal short-circuiting within the EGS hydraulic network. This work provides novel numerical simulations of a multi-fracture EGS that models the fracture aperture from initially closed to mechanically open. Fractures are modeled as discontinuities within a three dimensional thermo-poroelastic rock mass. We derived weak-form equations of mass balance, energy balance, and mechanical contact for fractures and wells and coupled those equations to the Comsol Multiphysics base package. The simulations investigate the full reservoir behavior through coupling of fluid flow through wellbores and fractures with the surrounding rock. Results show that large in-situ stresses contribute to a uniform fluid flow distribution in the fracture network because high compressive contact stresses decrease fracture compressibility and prevent large fracture openings. Initial or late large fracture openings cause thermal short-circuiting and are more likely to arise in locations with low initial stress and compliant fractures. Geometrical and operational properties of the EGS hydraulic network can minimize the severity of thermal short-circuiting including wellbore diameter, fracture spacing, injector/producer lateral spacing, EGS doublet orientation, and number of transmissive fractures. Thermo-mechanical interference between fracture stages causes (1) larger fracture opening displacements and (2) thermal short-circuiting earlier in time. Distinct initial fracture geometries and compliance causes the EGS hydraulic network to flow a non-uniform distribution of the injection fluid from the beginning and tends to decrease heat recovery. [Display omitted] • Initially large hydraulic apertures or late re-opening decreases heat recovery. • Fractures with high compliance tend to short-circuit. • EGS hydraulic network design can minimize the severity of short-circuiting. • Thermo-mechanical fracture interaction greatly decreases heat recovery. • Heat recovery benefits from homogeneous fracture aperture and high initial stress. [ABSTRACT FROM AUTHOR]

In this paper, the combined effects of the characteristic size and concentration of inorganic fullerene-like tungsten disulphide nanoparticles (IF-WS2 NPs) or molybdenum disulphide nanoparticles (IF-MoS2 NPs) on the nonlinear dynamic behaviour of a gasoline engine crankshaft bearing subject to an arbitrary force torsor (effective applied force and moment vector) are theoretically and numerically investigated using the V. K. Stokes micro-continuum theory. These NPs are the most common additives for lubrication purposes due to their excellent tribological characteristics along with their effect on reducing friction and wear. It is assumed that the journal (crankshaft) currently made of a forged steel is rigid and the main bearing consists of a thin poroelastic liner made of low elastic modulus materials like Babbitt metals fixed in a stiff housing as defined by ASTM B23-00. The Krieger-Dougherty law is included in the proposed EHD model to account for the viscosity variation with respect to the volume fraction of nanoparticles dispersed in the base lubricant. On the other hand, the characteristic size of nanomaterials is introduced by a new material entity, denoted l, which is responsible for a couple-stress property. The Reynolds equation is derived in transient conditions and modified to account for the size of nanoparticles and the bearing-liner permeability property. For an arbitrary force torsor, the hydrodynamic pressure distribution, the squeeze film velocities, and the misalignment angular velocities are determined simultaneously by solving the discretized Reynolds equation and the equilibrium equations with the damped Newton-Raphson iterative method at each crank angle step. The crankshaft center trajectories in three sections of the main journal axis as well as the misalignment angles are deduced from the squeeze film velocities and the misalignment angular velocities by means of a Runge-Kutta scheme. According to the obtained results, the combined effects of the size and concentration of fullerene-like nanoparticles on the dynamic behavior of a compliant dynamically loaded crankshaft bearing operating with dynamic misalignment are significant and cannot be overlooked. [ABSTRACT FROM AUTHOR]

The earthquake sequence, with a maximum earthquake magnitude of MW 3.8, that occurred during January–February 2022 at the northern Dead Sea fault, is shown to be induced by extensive groundwater abstraction in Wadi Al‐Arab basin. Wadi Al‐Arab basin, which is bordered in the west by the Dead Sea fault, has been overexploited by extensive groundwater abstraction causing significant drawdowns. Relative earthquake relocation indicates an elongated S‐N sequence subparallel to the Dead Sea fault. We simulate the three‐dimensional hydraulic head changes in the past 40 years at Wadi al Arab basin. Results show that the drawdowns at the Dead Sea fault wells reached a value greater than 180 m. We use these results to further model the poroelastic effects of the drawdown on the stability of the Dead Sea fault using a typical fault architecture including fault core surrounded by damage zone. Upward groundwater drainage through the permeable damage zone leads to compaction and strengthening. Failure on the Dead Sea fault is expected to occur on the impermeable fault core or at the protholith where weakening is expected. Groundwater abstraction in Wadi Al‐Arab basin cause changes of a few MPa in the Coulmb Failure Stress (ΔCFS) and trigger seismicity in these sections. This is the second location along the Dead Sea fault where groundwater abstraction was shown to recently induce earthquakes. With growing demand for water and long lasting droughts in the Middle East, seismicity induced by groundwater abstraction might reoccur in the near future. Plain Language Summary: Earthquakes are shown in many cases to be induced by water injection but they can also be induced by groundwater pumping. We analyze an earthquake sequence that occurred along the Dead Sea fault during January–February 2022 and show that it was induced by groundwater pumping. The location of the earthquakes form an elongated cluster subparallel to the trace of the main plate boundary. Groundwater levels in the area have dropped by more than 100 m in the last 40 years due to extensive pumping. We model the effects of pumping on groundwater levels in the basin and use these results to simulate the triggered seismicity on the active Dead Sea fault. This is the second place along the Dead Sea fault where groundwater overexploitation has triggered seismicity. With growing demand for water and long lasting droughts in the Middle East, seismicity induced by groundwater abstraction might reoccur in the near future. Key Points: Earthquake sequence that occurred at the northern Dead Sea fault is shown to be induced by extensive groundwater abstractionAn elongated earthquake sequence, subparallel to the Dead Sea fault occurred in two main clusters separated by 1 km and 18 days apartFailure on the Dead Sea fault is predicted to occur on the impermeable fault core or at the protholith but not in the damage zone [ABSTRACT FROM AUTHOR]

We study the existence of a weak solution to a regularized, moving boundary, fluid-structure interaction problem with multi-layered poroelastic media consisting of a reticular plate located at the interface between the free flow of an incompressible, viscous fluid modeled by the 2D Navier--Stokes equations, and a poroelastic medium modeled by the 2D Biot equations. The existence result holds for both the elastic and viscoelastic Biot model. The free fluid flow and the poroelastic medium are coupled via the moving interface (the reticular plate) through the kinematic and dynamic coupling conditions. The reticular plate is "transparent" to fluid flow. The nonlinear coupling over the moving interface presents a major difficulty since both the fluid domain and the poroelastic medium domain are functions of time, and the finite energy spaces do not provide sufficient regularity for the corresponding weak formulation to be well-defined. This is why in this manuscript we consider a regularized problem by employing convolution with a smooth kernel only where needed. The resulting problem is still very challenging due to the nonlinear coupling and the motion of the fluid and Biot domains. We provide a constructive existence proof for this regularized fluid-poroelastic structure interaction problem. This regularized problem is consistent with the original, nonregularized problem in the sense that the weak solutions constructed here, converge, as the regularization parameter tends to zero, to a classical solution of the original, nonregularized problem when such a classical solution exists, assuming viscoelasticity in the Biot poroelastic matrix [1]. Furthermore, the existence result presented in this manuscript, is a crucial stepping stone for the singular limit problem in which the thickness of the reticular plate tends to zero. Namely, in [1] we will show that, in the case of a Biot poroviscoelastic matrix, the moving boundary problem obtained in the singular limit as the thickness of the plate tends to zero, has a weak solution. [ABSTRACT FROM AUTHOR]

Solving poroelastic problems on a single grid is of paramount importance in the applications, especially in geosciences. However, these applications sometimes require to work with meshes made of distorted cells. With such grids, dedicated numerical schemes should be chosen to obtain consistent approximations for the stresses and for the fluxes. In J. Coulet et al. (2020), a coupled scheme based on the joint use of linear virtual elements and a two-point finite volume approximation on the same grid was proposed for Biot's poroelastic problem. This work has also provided an analytic and numerical convergence study of the discrete coupled system. As a continuation, we here propose an extension of this study to more general polyhedral meshes and to heterogeneous anisotropic mobility tensors for the flow equations. At this occasion, a general finite-volume framework, which includes non-linear or sushi finite volume methods for instance, is introduced to extend this analysis. [ABSTRACT FROM AUTHOR]

In this article, we propose a multiphysics mixed finite element method with Nitsche's technique for Stokes‐poroelasticity problem. Firstly, we reformulate the poroelasticity part of the original problem by introducing two pseudo‐pressures to into a "fluid–fluid" coupled problem so that we can use the classical stable finite element pairs to deal with this problem conveniently. Then, we prove the existence and uniqueness of weak solution of the reformulated problem. And we use Nitsche's technique to approximate the coupling condition at the interface to propose a loosely‐coupled time‐stepping method to solve three subproblems at each time step–a Stokes problem, a generalized Stokes problem and a mixed diffusion problem. And the proposed method does not require any restriction on the choice of the discrete approximation spaces on each side of the interface provided that appropriate quadrature methods are adopted. Also, we give the stability analysis and error estimates of the loosely‐coupled time‐stepping method. Finally, we give the numerical tests to show that the proposed numerical method has a good stability and no "locking" phenomenon. [ABSTRACT FROM AUTHOR]