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Fluid-driven subsurface fractures interact with a variety of heterogeneous elements in the surrounding environment, including fluid-filled pores, material discontinuities, and other cracks and fissures. Their complex propagation is governed by fluid-solid interactions, characterized by nonlinear and coupled dynamics between the flow and the fracture. This thesis focuses on addressing a variety of such problems related to fluid-driven fractures or hydraulic fractures within increasingly realistic situations. Initially, we examine the post-shut-in behavior of a hydraulic fracture in the viscous regime, where viscous dissipation is the dominant form of energy dissipation. Subsequently, we investigate the propagation of a hydraulic fracture driven by displacement flows of two immiscible fluids and the propagation of a hydraulic fracture across a material discontinuity.When pressurized fluid is injected in a homogeneous infinite solid medium, a simple penny-shaped fracture forms and grows in the direction of the minimum confining stress. This type of fracture offers a representative focus for experimental investigations in a laboratory environment, serving as a powerful tool to understand the various physical mechanisms governing the growth of the fracture. Throughout the thesis, we vary different material properties of the solid media and fracturing fluids, including the Young's modulus of the solids, the viscosity of the fluids and, the flow rate of the injection. Gelatin serves as the clear brittle elastic solid medium, that allows us to observe and record the fracture growth because of its transparent nature. In the first study, we examine the post-shut-in behavior of a penny-shaped hydraulic fracture in the viscous regime. We measure both the fracture aperture and radius, noting that the fracture radius continues to grow slowly over time even after injection stops, until it reaches a saturation point.Next, we investigate the injection of an immiscible fluid at the center of a liquid-filled fracture. We study the displacement of the interface between the two fluids and its effect on fracture propagation. We conduct experiments and derive scales to predict the growth dynamics of the fracture. Finally, we present an experimental investigation into the propagation of hydraulic fractures in layered brittle media in the toughness regime, where the creation of new fracture surfaces is the dominant means of energy dissipation. We report that the relative stiffness of the initiating layer significantly influences fracture propagation: A fracture that forms in a soft layer remains trapped, whereas a fracture that originates in a stiffer layer experiences a rapid fluid transfer into the neighboring softer layer upon reaching the interface. Additionally, we present a quantitative model that captures the competing effects of elastic deformation and fracture propagation and report good agreement with experiments.

In this paper, the elasto-hydrodynamic (EHD) performance of partial journal bearings has been studied. A numerical analysis has been conducted using the ANSYS Workbench (17.2) platform to investigate the performance of partial journal bearings. The lubricant used is considered Newtonian and incompressible fluid that flows steadily under laminar conditions, while the bearing material is assumed to be elastic, isotropic with smooth surface conditions. In the current FSI analysis, the lubricant flow has been predicted according to the finite_ volume method, while the finite element method has been adopted to compute the deformation and stress in the bearing surface. A wide range of operating and design conditions have been considered including the eccentricity ratio (0.1≤ε≤0.82), and arc bearing angle bearing (90ᵒ≤θ≤180ᵒ), while the values of bearing length to diameter ratio (L /D) and rotation speed (N) have been fixed at=0.77 and 1500r.p.m, respectively. The hydrodynamic pressure, performance characteristic of journal bearing, stress, and deformation have all been computed. It was found that the arc bearing angle and eccentricity ratio has a clear effect on the elasto-hydrodynamic properties of the partial bearings especially at high values of them.

In order to study the variation of vortices and heat transfer enhancement characteristics of piezoelectric vibrating cantilever in liquid-cooled channels, the effects of fluid density and viscosity, mainstream velocity, and excitation voltage on vortices were analyzed. The theoretical and numerical simulation of piezoelectric vortices was carried out by using fluid-solid coupling method. On the basis of hydrodynamic function considering the additional effect of liquid viscosity and density on piezoelectric vibrator, the vortex structure of piezoelectric vibrator was analyzed by panel method free-wake model. It is found that the larger the density of the liquid, the smaller the vortex shedding strength and the radius of the core. The larger the viscosity of the liquid, the easier to fully develop the vortex generated by the excitation. The increase of the mainstream flow velocity is beneficial to the development of the vortex structure and the increase of the vorticity intensity. Compared with the increase of the mainstream flow velocity, the excitation voltage is more conducive to the enhancement of the vorticity structure, then make it easier to mix hot and cold fluids, thus enhancing heat transfer.

Energy is released during explosions, and this creates shock waves. The dynamic pressure generated from an explosion is transmitted through soil in the form of compression waves. In military engineering and industrial safety protection, soil, a blast-resistant material, is used to achieve blast resistance. This study used the blast pressure and ground acceleration measured in an experimental explosion to verify the results of finite element numerical analysis. A fluid–solid interaction numerical analysis method was employed to simulate a trinitrotoluene explosion on the ground. Through analysis of the dynamic characteristics of soil after an explosion, the relationship between the dynamic stress wave formed by the explosion and the plastic deformation of the soil was studied. The results may provide a reference for the design of blast-resistant protective soil layers.

We present a numerical model of a contactless test commonly used to assess the biomechanics of the human cornea. The test, consisting in a rapid air jet applied to the anterior surface of the cornea, is controversial. Although the numerous studies documented in the literature have not been able yet to clarify its relevance as a diagnostic tool, the test has the potential to be combined with inverse analysis procedures to characterize the parameters of numerical models of the cornea. With the final goal of employing the air puff test in advanced material identification algorithms, here we propose to model the cornea with standard finite elements and the fluids filling the anterior chamber of the eye with a meshfree discretization. The interaction between moving fluids and deforming cornea is accounted for by modifying the interface boundary conditions of both fluid and solid. The proposed model represents the first fully 3D example of an aqueous-cornea fluid-solid interaction analysis which uses a robust meshfree approach for the fluid. Although we restrict our scope to isotropic nonlinear materials, numerical results confirm the undeniable importance of including internal fluids in the simulation of the air puff test. Thus the proposed approach stands as a procedural paradigm for the identification of the mechanical parameters of the human cornea.

In this study, the active vibration control of a rectangular plate submerged in water was investigated. Mass dampers were attached to the plate, and the system was modeled via assumed mode. Water is modeled as an inviscid fluid with moving boundaries at fluid&ndash, solid interaction surfaces and applied forces on the plate being calculated by Bernoulli equation. The natural frequencies of the plate in vacuum and in water (for partial and fully submerged cases) found from numerical calculations are compared with experimental results to prove the accuracy of the model. Subsequently, for frequency computations, particular frequencies were chosen and active damping was applied for them. To actively control the plate&rsquo, s vibration by a moving mass with static stable methods, the displacement data of some points were used as input. First, to increase the damping of target mode at low-frequency, the negative acceleration feedback control algorithm in modal-space was applied. Then, the decentralized method was examined. Both methods were successful in suppressing vibration of the submerged rectangular plate.

We developed a computational framework for simulating thin fluid flow in narrow interfaces between contacting solids, which is relevant for a range of engineering, biological and geophysical applications. The treatment of this problem requires coupling between fluid and solid mechanics equations, further complicated by contact constraints and potentially complex geometrical features of contacting surfaces. We developed a monolithic finite-element framework for handling mechanical contact, thin incompressible viscous flow and fluid-induced tractions on the surface of the solid, suitable for both one- and two-way coupling approaches. Additionally, we consider the possibility of fluid entrapment in "pools" delimited by contact patches and its pressurisation following a non-linear compressibility constitutive law. Furthermore, image analysis algorithms were adapted to identify the local status of each interface element within the Newton-Raphson loop. First, an application of the proposed framework for a problem with a model geometry is given, and the robustness is demonstrated by the residual-wise and status-wise convergence. The full capability of the developed two-way coupling framework is demonstrated on a problem of a fluid flow in contact interface between a solid with representative rough surface and a rigid flat. The evolution of the contact pressure, fluid flow pattern and the morphology of trapped fluid zones until the complete sealing of the interface is displayed. Additionally, we demonstrated an almost mesh-independent result of a refined post-processing approach to the real contact-area computation. The developed framework permits not only to study the evolution of effective properties of contact interfaces, but also to highlight the difference between one- and two-way coupling approaches and to quantify the effect of multiple trapped fluid "pools" on the coupled problem., 38 pages, 15 figures

Seismic surface wave mitigation using metamaterials is a growing research field propelled by intrinsic theoretical value and possible application prospects. Up to date, the complexity of site conditions found in engineering practice, which can include layered stratigraphy and variable water table level, has been discarded in the development of analytical frameworks to favor the derivation of simple, yet effective, closed-form dispersion laws. This work provides a further step towards the analytical study of “seismic metasurfaces” in real site conditions considering the propagation of Rayleigh waves through a layered porous substrate equipped with local resonators. To this aim, we combine classical elasticity theory, Biot’s poroelasticity and an effective medium approach to describe the metasurface dynamics and its coupling with the poroelastic substrate. The developed framework naturally includes simpler configurations like seismic metasurfaces atop homogeneous dry or saturated soils. Apart from known phenomena like wave-resonance hybridization and surface wave band gaps, we predict the existence of an extended frequency range where surface waves are attenuated due to energy leakage in the form of slow pressure waves, as a result of the fluid-solid interaction. Besides, we demonstrate that the surface wave band gap and the related surface-to-shear wave conversion is robust to variations in the water table level. Conversely, when the dry and saturated layers have different material parameters, for example, due to different porosity ratios, the surface-to-shear wave conversion can be accompanied by the excitation of higher-order surface modes, which remain channeled below the metasurface. These analytical findings, augmented and confirmed by numerical simulations, evidence the importance of accounting for fluid-solid interaction in the dynamics of seismic metasurfaces.

The interfacial condition between the human brain and the skull is complex and has been difficult to emulate in a surrogate system. Surrogate head models have typically been built using a homogenous viscoelastic material to represent the brain, but the effect of different interfacial conditions between the brain and the skull on pressure transduction into the brain during blast has not been studied. In the present work, three interfacial conditions were generated in physical surrogate human head models. The first surrogate consisted of a gel brain separated from the skull by a layer of saline solution similar in thickness to the cerebrospinal fluid (CSF) layer in the human head: the fluid interface head model. The second surrogate head had the entire cranial cavity filled with the gel: the fixed interface head model. The third surrogate head contained a space-filling gel brain wrapped in a thin plastic film: the stick-slip interface head model. The human head surrogates were evaluated in a series of frontal blast tests to characterize the effect of the skull-brain interfacial conditions on overpressure propagation into the gel brains. The fixed and the stick-slip interface head models showed nearly equal peak brain overpressures. In contrast, the fluid interface head model had much higher in-brain peak overpressures than the other two models, thus representing the largest transmission of forces into the gel brain. Given that the elevated peak overpressures occurred only in the fluid interface head model, the presence of the saline layer is likely responsible for this increase. This phenomenon is hypothesized to be attributed to the incompressibility of the saline and/or the impedance differences between the materials. The fixed interface head model showed pronounced high frequency energy content relative to the other two models, implying that the fluid and the stick-slip conditions provided better dampening. The cumulative impulse energy entering the three brain models were similar, suggesting that the interface conditions do not affect the total energy transmission over the positive phase duration of a blast event. This study shows that the fidelity of the surrogate human head models would improve with a CSF-emulating liquid layer.

Micromixers are significant segments inside miniaturized scale biomedical frameworks. Numerical investigation of the effects of galloping cylinder characteristics inside a microchannel Newtonian, incompressible fluid in nonstationary condition is performed. Governing equations of the system include the continuity equation, and Navier–Stokes equations are solved within a moving mesh domain. The symmetry of laminar entering the channel is broken by the self-sustained motion of the cylinder. A parameter study on the amplitude and frequency of passive moving cylinder on the mixing of tiny particles in the fluid is performed. The results show a significant increase to the index of mixing uses of the galloping body in biomedical frameworks in the course of micro-electromechanical systems (MEMS) devices.

Cavitation bubble collapse close to a submerged sphere on a microscale is investigated numerically using a finite volume method in order to determine the likelihood of previously suspected mechanical effects to cause bacterial cell damage, such as impact of a high speed water jet, propagation of bubble emitted shock waves, shear loads, and thermal loads. A grid convergence study and validation of the employed axisymmetric numerical model against the Gilmore’s equation is performed for a case of a single microbubble collapse due to a sudden ambient pressure increase. Numerical simulations of bubble-sphere interaction corresponding to different values of nondimensional bubble-sphere standoff distance δ and their size ratio e are carried out. The obtained results show vastly different bubble collapse dynamics across the considered parameter space, from the development of a fast thin annular jet towards the sphere to an almost spherical bubble collapse. Although some similarities in bubble shape progression to previous studies on larger bubbles exist, it can be noticed that bubble jetting is much less likely to occur on the considered scale due to the cushioning effects of surface tension on the intensity of the collapse. Overall, the results show that the mechanical loads on a spherical particle tend to increase with a sphere-bubble size ratio e , and decrease with their distance δ . Additionally, the results are discussed with respect to bacteria eradication by hydrodynamic cavitation. Potentially harmful mechanical effects of bubble-sphere interaction on a micro scale are identified, namely the collapse-induced shear loads with peaks of a few megapascals and propagation of bubble emitted shock waves, which could cause spatially highly variable compressive loads with peaks of a few hundred megapascals and gradients of 100 MPa/ μ m.

Tubing string is one of the most important tools in flowing production. In the state of lateral vibration instability of the tubing string, severe collisions between the string and casing may lead to tubing string failure and borehole wall sloughing. Stability of the tubing string is a potential safety hazard in the process of oil and gas production and discussed in this paper. Considering interaction among the gravity, internal fluid hydrodynamic force, reservoir pressure and liquid cushion in the annular, a mechanical model of lateral vibration of the tubing string, which is simplified as a uniform pipe conveying fluid upwards in vertical well, is developed, and the stability of the system is analyzed by the finite element method. The influences of the flow velocity, the bottom hole pressure and the height and density of liquid cushion on the stabilities of tubing string are discussed. It is found that the increase of either the flow velocity or the bottom hole pressure can cause the buckling of tubing string, however, increasing the height or density of liquid cushion is helpful to improve the stability of tubing string.

Scour of rock is a challenging and interesting problem that combines rock mechanics and hydraulics of turbulent flow. On a practical level, rock erosion is a critical issue facing many of the world’s dams at which excessive scour of the dam foundation or spillway can compromise the stability of the dam resulting in significant remediation costs, if not direct personal property damage or even loss of life. This interaction between the blocky rock mass and water is analyzed by directly modeling the solid and fluid phases—the individual polyhedral blocks are modeled using the discrete element method (DEM) while water is modeled using the lattice Boltzmann method (LBM). The LBM mesh is entirely independent of the DEM discretization, making it possible to refine the LBM mesh such that transient and varied fluid pressures acting on the rock surfaces are directly modeled. This provides the capability to investigate the effect of water pressure inside the fractured rock mass, along potential sliding planes, and can be extended to rock falls and slides into standing bodies of water such as lakes and reservoirs. Results show that the coupled DEM–LBM implementation is able to accurately capture the interaction between polyhedral rock blocks and fluid by analytically solving for the solid volume fraction in the coupling computations using convex optimization and simplex integration; however, further performance improvements are necessary to simulate realistic, field-scale problems. Particularly, adaptive mesh refinement and multigrid methods implemented in a parallel computing environment will be essential for capturing the highly computationally intensive and multiscale nature of rock–fluid interaction.

The lattice Boltzmann method (LBM) is implemented in the Particle Flow Code (PFC) as a pore-scale CFD module and coupled with the particulate discrete element assemblage in PFC using an immersed boundary scheme. The implementation of LBM and LBM-PFC coupling is validated with the analytical solutions in a couple of hydrodynamics and fluid-particle interaction problems, i.e., the accuracy of LBM as a CFD solver is verified by solving channel flow driven by a pressure gradient for which the closed-form solution is also derived; the accuracy of LBM-PFC coupling is validated by solving flow across a cylinder, Taylor-Couette flow, Karman vortex street, and fluid flow through a cylinder array. To demonstrate potential applications of this coupling code, a perforation cavity subjected to axial fluid flush is then tested, showing that the collapse and reconstruction of sand arch in the perforation cavity can be reproduced in this coupling system. The developed system is ready for exploring more complicated physical issues involved in sand production.

Physical-based simulation technique has been widely used in creating astounding fluid appearances for film industries and computer games. However, stable and realistic fluid simulation based on Smoothed Particle Hydrodynamics (SPH) method is still challenging, as unstable solid boundary handling and numerical dissipation always plague current SPH fluid solvers. To solve these issues, we present a new method for improving SPH fluid simulation using position-based dynamics (PBD). For the stable fluid-solid interaction, by combining the position constraint solved by PBD and the relative contribution of solid boundary particles, we significantly alleviate the penetration issues at fluid-solid interfaces. And in order to stably simulate turbulence diffusion of SPH fluids, we enforce a novel nonlinear vorticity constraint on each fluid particle, and then solve it using PBD to smooth the vorticity field. The implementation results demonstrate that our method significantly improves SPH method for simulating realistic and stable animations of fluid phenomena.

Coupled fluid-structure is significant in many aspects of engineering applications such as aerospace fuel tanks, the seismic safety of storage tanks and tuned liquid dampers. Numerical investigation of the effects of thin plate cover over a cylindrical rigid fuel tank filled by an inviscid, irrotational, and incompressible fluid is investigated. Governing equations of fluid motion coupled by plate vibration are solved analytically. A parameter study on the natural frequency of coupled fluid-structure interaction is performed. The results show the non-dimensional natural frequency of coupled fluid-structure is a function of mass ratio, plate elasticity number and aspect ratio. This function is derived numerically for high aspect ratios which in companion with a semi-analytical could be used in the engineering design of liquid tanks with a cover plate.

Sand production is a complex phenomenon caused by the erosion of borehole walls during the extraction of hydrocarbons. In this paper, the sanding process in a typical Thick-Walled Hollow Cylinder (TWHC) test is numerically simulated. The main objective of the study is to model the particulate mechanism of sand production in granular assemblies with different bonding conditions and examine the effects of parameters such as stress level and cavity size on the sanding model. Due to the discrete nature of sand particles, the Discrete Element Method (DEM) is chosen to model solid particles, and the Lattice-Boltzmann Method (LBM) is implemented to simulate fluid flow through the solid particulate medium. A computer program is developed using the Immersed Moving Boundary (IMB) approach to couple the two methods and model fluid–solid interactions. After the program is validated, the simulations were conducted on 2D models representing cross-sections of TWHC samples under radial fluid flow. The results show that the developed program is able to capture complicated stages of sand production already observed in experiments. The program also proves to be a promising tool in the parametric study of sand production. It successfully simulates different aspects of the sanding phenomenon, including the scale effect, the extension of failure zones in samples under incremental stress, and the stress relaxation during rapid particle erosion.

The sloshing behavior of systems is influenced by different factors related to the liquid level and tank specifications. Different approaches are applicable for the assessment of sloshing behavior in a tank. In this paper, a new numerical model based on the differential quadrature method and boundary element approaches is adopted to investigate the sloshing behavior of a tank with an elastic thin-walled beam. The model is developed based on small slope considerations of the free surface. The main assumption of fluid modeling is homogeneity, isotropy, inviscid, and only limited compressibility of the liquid. Indeed, the formulation is represented based on the reduced-order method and then is employed for simulating the coupling between structure and fluid in symmetric test cases. The results are verified with the ANSYS and literature for symmetric rigid structural walls and then the code is employed to study the behavior of fluid-structure interaction in a symmetric tank with new and efficient immersed structure.

Due to micro-nanopores in tight formation, fluid-solid interaction effects on fluid flow in porous media cannot be ignored. In this paper, a novel model which can characterize micro-fluid flow in micro scales is proposed. This novel model has a more definite physical meaning compared with other empirical models. And it is validated by micro tube experiments. In addition, the application range of the model is rigorously analyzed from a mathematical view, which indicates a wider application scope. Based on the novel model, the velocity profile, the average flow velocity and flow resistance in consideration of fluid-solid interaction are obtained. Furthermore, the novel model is incorporated into a representative pore scale network model to study fluid-solid interactions on fluid flow in porous media. Results show that due to fluid-solid interaction in micro scales, the change rules of the velocity profile, the average flow velocity and flow resistance generate obvious deviations from traditional Hagen-Poiseuille’s law. The smaller the radius and the lower the displacement pressure gradient (∇P), the more obvious the deviations will be. Moreover, the apparent permeability in consideration of fluid-solid interaction is no longer a constant, it increases with the increase of ∇P and non-linear flow appears at low ∇P. This study lays a good foundation for studying fluid flow in tight formation.

The air puff test is an in-vivo investigative procedure commonly utilized in ophthalmology to estimate the intraocular pressure. Potentially the test, quick and painless, could be combined with inverse analysis methods to characterize the patient-specific mechanical properties of the human cornea. A rapid localized air jet applied on the anterior surface induces the inward motion of the cornea, that interacts with aqueous humor-the fluid filling the narrow space between cornea and iris-with a strong influence on the dynamics of the cornea. While models of human cornea reproduce accurately patient-specific geometries and have reached a considerable level of complexity in the description of the material, yet scant attention has been paid to the aqueous humor, and no eye models accounting for the physically correct fluid-solid interaction are currently available. The present study addresses this gap by proposing a fluid-structure interaction approach based on a simplified two-dimensional axis-symmetric geometry to simulate the anterior chamber of the eye undergoing the air puff test. We regard the cornea as a membrane described through an analytical model and discretize the fluid with a mesh-free particle approach. The membrane is assumed to be nonlinear elastic and isotropic, and the fluid weakly compressible Newtonian. Numerical analyses reveal a marked influence of the fluid on the dynamics of the cornea. We perform a parametric analysis to assess the quantitative influence of geometrical and material parameters on the mechanical response of the model. Additionally, we investigate the possibility to use the dynamics of the test to estimate the intraocular pressure.

The wind-induced motion of the foliage in a tree is an important phenomenon both for biological issues (photosynthesis, pathogens development or herbivory) and for more subtle effects such as on wi-fi transmission or animal communication. Such foliage motion results from a combination of the motion of the branches that support the leaves, and of the motion of the leaves relative to the branches. Individual leaf dynamics relative to the branch, and branch dynamics have usually been studied separately. Here, in an experimental study on a whole tree in a large-scale wind tunnel, we present the first empirical evidence that foliage motion is actually dominated by individual leaf flutter at low wind velocities, and by branch turbulence buffeting responses at higher velocities. The transition between the two regimes is related to a weak dependence of leaf flutter on wind velocity, while branch turbulent buffeting is strongly dependent on it. Quantitative comparisons with existing engineering-based models of leaf and branch motion confirm the prevalence of these two mechanisms. Simultaneous measurements of the wind-induced drag on the tree and of the light interception by the foliage show the role of an additional mechanism, reconfiguration, whereby leaves bend and overlap, limiting individual leaf flutter. We then discuss the consequences of these findings on the role of wind-mediated phenomena.

Multi-stage fracturing is the current preferred method of completion of horizontal wells in unconventional hydrocarbon reservoirs. Its core component consists in simultaneously initiating and propagating an array of hydraulic fractures. We develop a numerical model for the initiation and growth of an array of parallel radial hydraulic fractures. The solution accounts for fracture growth, coupling between elastic deformation and fluid flow in the fractures, elastic stress interactions between fractures and fluid flow in the wellbore. We also take into account the presence of a local pressure drop (function of the entering flow rate) at the connection between the well and the fracture, i.e., a choke-like effect due to current well completion practices, also referred to as entry friction. The partitioning of the fluid into the different fractures at any given time is part of the solution and is a critical indicator of simultaneous (balanced fluid partitioning) versus preferential growth. We validate our numerical model against reference solutions and a laboratory experiment for the initiation and growth of a single radial hydraulic fracture. We then investigate the impact of stress interaction on preferential growth of a subset of fractures in the array. Our results show that a sufficiently large local entry friction provides a strong feedback in the system and thus can counteract elastic stress interaction between fractures, thereby ensuring simultaneous growth. We propose a dimensionless number capturing the competition between stress interaction and local entry friction. This dimensionless number is a function of rock properties, fracture spacing and injection parameters. We verify that it captures the transition from the case of simultaneous growth (entry friction larger than interaction stress) to the case of preferential growth of some fractures (interaction stress larger than entry friction). We also discuss the implication of these results for multi-stage fracturing engineering practices. (C) 2015 Elsevier Ltd. All rights reserved.

The efficiency of two coupling formulations, the boundary element method (BEM)-meshless local Petrov–Galerkin (MLPG) versus the BEM-finite element method (FEM), used to simulate the elastic wave propagation in fluid-filled boreholes generated by a blast load, is compared. The longitudinal geometry is assumed to be invariant in the axial direction (2.5D formulation). The material properties in the vicinity of the borehole are assumed to be nonhomogeneous as a result of the construction process and the ageing of the material. In both models, the BEM is used to tackle the propagation within the fluid domain inside the borehole and the unbounded homogeneous domain. The MLPG and the FEM are used to simulate the confined, damaged, nonhomogeneous, surrounding borehole, thus utilizing the advantages of these methods in modeling nonhomogeneous bounded media. In both numerical techniques the coupling is accomplished directly at the nodal points located at the common interfaces. Continuity of stresses and displacements is imposed at the solid–solid interface, while continuity of normal stresses and displacements and null shear stress are prescribed at the fluid–solid interface. The performance of each coupled BEM-MLPG and BEM-FEM approach is determined using referenced results provided by an analytical solution developed for a circular multi-layered subdomain. The comparison of the coupled techniques is evaluated for different excitation frequencies, axial wavenumbers and degrees of freedom (nodal points). Ministerio de Economía y Competitividad BIA2013-43085-P Centro Informático Científico de Andalucía (CICA)

In the present work, the energy conservation properties of the Smoothed Particle Hydrodynamics (SPH) are investigated in the presence of fluid–solid interactions. Similarly to the fluid phase, the solid bodies are modeled through solid particles so that the whole solid–fluid domain can be described as a unique particle system. The pressure and velocity fields are, then, extended over the solid particles in different ways, taking into account consistency issues related to the SPH differential operators and using the projection of the Navier–Stokes equations on the solid boundary. It is shown that, when solid particles are considered, the energy equation of the particle system contains some extra terms that depend on the pressure–velocity field extensions. The presence of these extra terms does not affect the consistency of the SPH model, since they tend to vanish when the spatial resolution is increased. Three prototypical numerical test cases are considered in order to provide a quantitative perspective of the matter and confirm the theoretical developments of the paper. These test cases show that the nature of these terms is globally dissipative, being thus in accordance with the Second Law of Thermodynamics. In particular, the viscous extra term displays a remarkably slow rate of convergence, this being a relevant outcome for those SPH practitioners that deal with these types of flows.

This work outlines a unified multi-threaded, multi-scale High Performance Computing (HPC) approach for the direct numerical simulation of Fluid-Solid Interaction (FSI) problems. The simulation algorithm relies on the extended Smoothed Particle Hydrodynamics (XSPH) method, which approaches the fluid flow in a La-grangian framework consistent with the Lagrangian tracking of the solid phase. A general 3D rigid body dynamics and an Absolute Nodal Coordinate Formulation (ANCF) are implemented to model rigid and flexible multibody dynamics. The two-way coupling of the fluid and solid phases is supported through use of Boundary Condition Enforcing (BCE) markers that capture the fluid-solid coupling forces by enforcing a no-slip boundary condition. The solid-solid short range interaction, which has a crucial impact on the small-scale behavior of fluid-solid mixtures, is resolved via a lubrication force model. The collective system states are integrated in time using an explicit, multi-rate scheme. To alleviate the heavy computational load, the overall algorithm leverages parallel computing on Graphics Processing Unit (GPU) cards. Performance and scaling analysis are provided for simulations scenarios involving one or multiple phases with up to tens of thousands of solid objects. The software implementation of the approach, called Chrono:Fluid, is part of the Chrono project and available as an open-source software.

We formulate a unified equation for fluid flow and elastic solid deformation.The formulation allows a monolithic resolution of fluid-structure interaction.Mechanical and heat equations are both formulated with velocity and flux variables.The formulation can model either acoustic or long time scale thermo-mechanics.Elastic wave propagation is modeled in fluid and elastic solid system. A novel non-conservative formulation for equations governing thermo-mechanical phenomena is developed to address multi-material and multi-physics issues. The first key point is that this formulation achieves a unifying equation for compressible viscous fluid flow and elastic solid deformation. The second is that the thermo-mechanical equations are both written with velocity and thermal flux variables to solve them simultaneously. With that formulation, interaction conditions at the fluid-structure interface become implicit and state equation is no longer necessary. Multi-time scale problems are solved, from the time scale of acoustic and thermoacoustic wave propagation, to longer time scale of fluid flow and thermal diffusion.

International audience; This paper deals with the numerical simulation of the quicksand phenomenon using a coupled Discrete Elements – Lattice Boltzmann hydromechanical model. After the presentation of the developed numerical model, simulations of ascending fluid flow through granular deposits are performed. The simulations show that the quicksand actually triggers for a hydraulic gradient very close to the critical hydraulic gradient calculated from the global analysis of classical soil mechanics, that is, when the resultant of the applied external pressure balances submerged weight of the deposit. Moreover, they point out that the quicksand phenomenon does not occur only for hydraulic gradients above the critical hydraulic gradient, but also in some cases with slightly lower gradients. In such cases, a more permeable zone is first gradually built at the bottom of the deposit through a grain rearrangement, which increases the hydraulic gradient in the upper zones and triggers the phenomenon.

This paper presents applications of a recently proposed immersed boundary method to the solution of fluid–solid interaction. Solid objects immersed into the fluid are considered rigid and their movement is determined from the interaction forces with the fluid. The use of body-conformal meshes to solve such problems may involve extensive mesh adaptation work that has to be repeated each time a change in the shape of the domain or in the position of immersed solids is needed. Mesh generation and solution interpolation between successive grids may be costly and introduce errors if the geometry changes significantly during the course of the computation. These drawbacks are avoided when the solution algorithm can tackle grids that do not fit the shape of immersed objects. We present here an extension of our recently developed immersed boundary (IB) finite element method to the computation of interaction forces between the fluid and immersed solid bodies. A fixed mesh is used covering both the fluid and solid regions, and the boundary of immersed objects is defined using a time dependent level-set function. Boundary conditions on the immersed solid surfaces are imposed accurately by using a Body Conformal Enrichment (BCE) method. In this approach, the finite element discretization of interface elements is enriched by including additional degrees of freedom which are latter eliminated at element level. The forces acting on the solid surfaces are computed from the enriched finite element solution and the solid movement is determined from the rigid solid momentum equations. Solutions are shown for various fluid–solid interaction problems and the accuracy of the present approach is measured with respect to solutions on body-conformal meshes.

International audience; We consider the gravity-driven motion of a heavy two-dimensional rigid body freely falling in a viscous fluid.We introduce a quasi-static linear model of the forces and torques induced by the possible changes in the body velocity,or by the occurrence of a nonzero incidence angle or a spanwise rotation of the body. The coefficients involved in this model are accurately computed over a full range of Reynolds number by numerically resolving the Navier 13Stokes equations, considering three elementary situations where the motion of the body is prescribed. The falling body is found to exhibit three distinct eigenmodes which are always damped in the case of a thin plate with uniform mass loading or a circular cylinder,but may be amplified for other geometries,such as in the case of a square cylinder.

Parametric studies on the optimization of baffles on vibration suppression of partially filled tanks coupled by structure have been widely conducted in literature. However, few studies focus on the effect of the position of the baffles on fluid flow stratification and dampening the motion. In the present study, a numerical investigation, an engineering analysis, and optimal design study were performed to determine the effect of external flow on circular obstacle baffles performance on suppressing the vibrations of coupled structure in a closed basin. The single degree of freedom model (mass&ndash, spring&ndash, damper) is used to model the structure that holds the tank. The coupled system is released from an initial displacement without a velocity. The governing mass, turbulent Navier&ndash, Stokes momentum, volume of fluid, and one degree of freedom structure equations are solved by the Pressure-Implicit with Splitting of Operators algorithm in fluids and Newmark method in structure. Based on a detailed study of transient structure motion coupled with sloshing dynamics, the optimal baffle location was achieved. Optimal position of the baffle and its width are systematically obtained with reference to the quiescent free surface.

A reduced-order model for the two-dimensional interaction of a sharp-edged solid body and a high-Reynolds number flow is presented, based on the inviscid representation of the solid’s wake as point vortices with unsteady intensity. This model is applied to the fall of a rigid card in a fluid and to the flapping instability of a flexible membrane forced by a parallel flow.

A method is proposed for the study of the two-dimensional coupled motion of a general sharp-edged solid body and a surrounding inviscid flow. The formation of vorticity at the body’s edges is accounted for by the shedding at each corner of point vortices whose intensity is adjusted at each time step to satisfy the regularity condition on the flow at the generating corner. The irreversible nature of vortex shedding is included in the model by requiring the vortices’ intensity to vary monotonically in time. A conservation of linear momentum argument is provided for the equation of motion of these point vortices (Brown–Michael equation). The forces and torques applied on the solid body are computed as explicit functions of the solid body velocity and the vortices’ position and intensity, thereby providing an explicit formulation of the vortex–solid coupled problem as a set of non-linear ordinary differential equations. The example of a falling card in a fluid initially at rest is then studied using this method. The stability of broadside-on fall is analysed and the shedding of vorticity from both plate edges is shown to destabilize this position, consistent with experimental studies and numerical simulations of this problem. The reduced-order representation of the fluid motion in terms of point vortices is used to understand the physical origin of this destabilization.

International audience; Stokes, Darcy and solid mechanics coupling is a matter of interest in many domains of engineering such as soil mechanics, bio-mechanics, and composites. The aim of this paper is to present a robust iterative method to deal with this coupling for low permeability media within the framework of industrial simulation, and especially for composite manufacturing processes. Stokes and Darcy problems are solved using a mixed velocity-pressure finite element using a mini-element formulation, and coupled together by the so-called Beavers-Joseph-Saffman conditions through their interface. This fluid formulation is then coupled to a non-linear solid mechanics formulation in finite deformations using Terzaghi's law at the pore level, and an explicit dependence of permeability with respect to porosity that is exactly computed from the solid mechanics kinematics. Then, those formulations are validated with test-cases and by the Method of the Manufactured Exact Solution (MMES) (Knupp and Salari, 2003[1]). Finally, a 3D curved transient example of application is presented.

In 2007 Fernandes et al. reported a surprising delay of the onset of instabilities for freely rising cylinders of aspect ratio (χ=diameter/thickness of the cylinder) 10 and more. At Reynolds numbers at which instabilities develop in the wake of the same body kept fixed, the path was still found to be vertical and the wake axisymmetric. In this paper, we explain this delay by investigating numerically the transition scenario of the solid–fluid system represented by the freely moving body interacting with the ambient fluid by hydrodynamic forces. We show that the free body degrees of freedom can have a stabilizing effect on the onset of the primary bifurcation. This effect explains, however, only partly the experimental observation. We show that the primary bifurcation is followed by a sequence of weakly oscillating, virtually unobservable, bifurcating states before the observable path oscillations set in. For aspect ratio smaller than 8, the free body degrees of freedom destabilize the system in agreement with expectations. The primary bifurcation is, however, a Hopf bifurcation instead of regular one in the wake of a fixed body. In our study we focus to the intermediate interval of aspect ratio between 8 and 10. We show that, for χ > 8 , the primary Hopf bifurcation is replaced by a new one with much lower frequency and leading to weakly oscillating periodic oscillations, later (for χ > 9 ) the Hopf bifurcation is replaced by a regular one disappearing again for very thin cylinders ( χ > 10 ).

The membrane tension of some kinds of ciliates has been suggested to regulate upward and downward swimming velocities under gravity. Despite its biological importance, deformation and membrane tension of a ciliate have not been clarified fully. In this study, we numerically investigated the deformation of a ciliate swimming freely in a fluid otherwise at rest. The cell body was modelled as a capsule with a hyperelastic membrane enclosing a Newtonian fluid. Thrust forces due to the ciliary beat were modelled as torques distributed above the cell body. The effects of membrane elasticity, the aspect ratio of the cell's reference shape, and the density difference between the cell and the surrounding fluid were investigated. The results showed that the cell deformed like a heart shape, when the capillary number was sufficiently large. Under the influence of gravity, the membrane tension at the anterior end decreased in the upward swimming while it increased in the downward swimming. Moreover, gravity-induced deformation caused the cells to move gravitationally downwards or upwards, which resulted in a positive or negative geotaxis-like behaviour with a physical origin. These results are important in understanding the physiology of a ciliate's biological responses to mechanical stimuli.

International audience; A two-dimensional turbulent wall jet over a shallow cavity is studied numerically. The present paper investigates the wall jet outer layer effect on a shallow cavity flow structure. This layer is an important turbulence source which is added to that of the inner shear layer. It was found that the reattachment process seems to be accelerated in the turbulent wall jet incoming flow compared to that of the cavity in duct flow. The present study shows that the flow structure is very sensitive to the cavity depth to nozzle height ratio; the increasing of this ratio induces a reattachment length decrease.

Bu çalışma, 07-08 Haziran 2012 tarihleri arasında Montreal[Kanada]’da düzenlenen 5. Automotive Technology Conference (OTEKON)’da bildiri olarak sunulmuştur. This paper presents a numerical investigation on the momentum and thermal characteristics of an intercooler connection hose that is in use in the 1.3 SDE 75 CV type FIAT engine. Computational analyses are carried out with ANSYS FLUENT v.12.0.1, where both stationary and vibrating scenarios are handled. The work is structured in accordance with the "Subsystem Functional Description for Charge Air Hoses Fiat 225 Euro 5" FIAT standard, where the air mass flow rate, temperature, and gage pressure at the hose inlet are identified as = 0.085 kg/s, (in) = 90A degrees C, and (in) = 130 kPa, respectively. In the stationary case, it is determined that the pressure loss value in the air domain of the hose is Delta (K) = 1.50 kPa; moreover, the corresponding data for the temperature drop is Delta = 0.80A degrees C. Vibration is characterized by employing simple harmonic motion at the engine side of the hose. The fluid-solid interaction methodology showed that pressure loss values grow due to vibration; moreover, the impact of vibration came out to generate diverse fluctuation schemes at different sections of the hose.

International audience; The dynamics of falling leaves is studied by means of numerical simulations. The two-dimensional incompressible Navier-Stokes equations, coupled with the equations governing solid body dynamics, are solved using a Fourier pseudo-spectral method with volume penalization to impose no-slip boundary conditions. Comparison with other numerical methods is made. Simulations performed for different values of the Reynolds number show that its decrease stabilizes the free fall motion.

We analyse the influence of pre-stress on the propagation of interfacial waves along the boundary of an incompressible hyperelastic half-space that is in contact with a viscous fluid extending to infinity in the adjoining half-space. One aim is to derive rigorously the incremental boundary conditions at the interface; this derivation is delicate because of the interplay between the Lagrangian and the Eulerian descriptions but is crucial for numerous problems concerned with the interaction between a compliant wall and a viscous fluid. A second aim of this work is to model the ultrasonic waves used in the assessment of aortic aneurysms, and here we find that for this purpose the half-space idealization is justified at high frequencies. A third goal is to shed some light on the stability behaviour in compression of the solid half-space, as compared with the situation in the absence of fluid; we find that the usual technique of seeking standing waves solutions is not appropriate when the half-space is in contact with a fluid; in fact, a correct analysis reveals that the presence of a viscous fluid makes a compressed neo-Hookean half-space slightly more stable. For a wave travelling in a direction of principal strain, we obtain results for the case of a general (incompressible isotropic) strain-energy function. For a wave travelling parallel to the interface and in an arbitrary direction in a plane of principal strain, we specialize the analysis to the neo-Hookean strain-energy function., 11 pages

A new pseudo-continuous model, describing the fluid flow through packed bed reactors, is developed by formulating the Navier–Stokes equations for a statistically described domain geometry. A coupling term, occurring in the momentum equation, represents the fluid–solid interaction and is modelled by comparison with the exact Navier–Stokes equations. Static and dynamic, inviscid and viscous contributions are separated, and stringent requirements for the dependence on the local voidage are found which are met by a simple model. Good agreement with correlations and experiments is found for the predictions of the pressure drop and the radial distribution of the axial velocity.

A two-dimensional two-phase flow framework for fluid- sediment flow simulation in the surf and swash zones was described. Propagation, breaking, uprush and backwash of waves on sloping beaches were studied numerically with an emphasis on fluid hydrodynamics and sediment transport characteristics. The model includes interactive fluid- solid forces and intergranular stresses in the moving sediment layer. In the Euler-Euler approach, two phases were defined using the Navier-Stokes equations with interphase coupling for momentum conservation. The k-e closure model and Volume- Of-Fluid approach were used to describe the turbulence and tracking of the free surface, respectively. Numerical simulations explored incident wave conditions, specifically spilling and plunging breakers, on both dissipative and intermediate beaches. It was found that the spatial variation of sediment concentration in the swash zone is asymmetric, while the temporal behavior is characterized by maximum sediment concentrations at the start and end of the swash cycle. The numerical results also indicated that the maximum turbulent kinetic energy and sediment flux occurs near the wave breaking point. These predictions are in general agreement with previous observations, while the model describes the fluid and sediment phase characteristics in much more detail than existing measurements. With direct quantifications of velocity, turbulent kinetic energy, sediment concentration and flux, the model provides a useful approach to improve mechanistic understanding of hydrodynamic and sediment transport in the nearshore zone.