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Landslide-generated impulse waves (LGIWs) often cause enormous damage. This study proposes a two-way coupled discrete element method (DEM) and smoothed particle hydrodynamics (SPH) method to study the whole hazard chain of LGIWs in mountain reservoirs. In this method, a two-way coupling code is developed to connect the DEM program Particle Flow Code 3D (PFC3D) and the SPH code DualSPHysics for simulating landslide sliding and fluid motion. A series of discretization operations are conducted to transform the DEM balls into discrete balls composed of SPH particles, and the dynamic boundary condition method is used to calculate the interaction forces between fluid and solid phases. This work is validated through a comparative analysis with published physical model experiments. Using the proposed method, the LGIWs induced by the RS deposit in the RM reservoir is simulated. The processes of landslide motion, impulse waves generation, propagation, and running up on the dam are studied. The results show that the proposed method possesses the capability to simulate and predict the hazards of LGIWs. This article represents the first implementation of PFC3D within a coupled DEM-SPH framework to study LGIWs, and provides a valuable way for assessing the associated risks. [ABSTRACT FROM AUTHOR]

With brain white matter can be considered as a periodic fibrous porous medium mainly consisting of axons and interstitial fluid (ISF), the corresponding hydraulic permeability reflects the resistance of ISF flow in the extracellular space (ECS), thus playing a key role in molecular transport and drug delivery. As the ECS exhibits a typical width of 10–80 nm, the ISF flow poses a microscale flow problem with the wettability effect, which may induce a flow with a slip boundary and hence remains elusive. In this study, we idealized brain white matter as a periodic fibrous porous medium to quantify the effect of wettability on its hydraulic permeability, with fluid viscosity and slip boundary duly accounted for. We found that wettability led to enlarged hydraulic permeability by diminishing the effective viscosity and enlarging the slip length. We also found that, for the square arrangement of axons, wettability had a greater effect on perpendicular permeability relative to the parallel one, while for hexagonally arranged axons, the opposite held. Results presented in this study may provide theoretical guidance for cerebral edema treatment regimens and drug delivery. [ABSTRACT FROM AUTHOR]

Purpose: The free vibration problem of a thin nanoplate with surface energy immersed in a viscous fluid medium is investigated in this article to assess the influence of different fluids on the vibration behavior of small-scale plates. Methods: Fluid–solid interaction is modeled based on Navier-Stokes equations, and surface energy is considered to apply small-scale effects. Finally, the solution of the equation of motion of nanoplate coupled with fluid is realized using the Galerkin weighted residual method. Results and Conclusion: According to the findings of this study, fluid density has a considerable impact on the reduction of the natural frequencies of plates at small scales, whereas viscosity has a negligible effect on the system's vibrational response. Moreover, the thickness of a nanoplate is inversely proportional to the influence of surface parameters on the nanoplate vibration as well as the effect of fluid on natural frequencies. [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]

The work concerns dynamic similarity criteria of various phenomena occurring in aerodynamics of buildings and structures, hydraulics and fluid dynamics derived from ratios of forces and forces moments affecting these phenomena. It consists of three parts. Part I concerns the bases of dynamic similarity criteria formulated in such a way in relations to the problems of fluid–solid interaction at different fluid–solid relative motions. At the end of this part, authorial method and procedure for determination of dynamic similarity criteria in fluid–solid interaction issues have been presented. [ABSTRACT FROM AUTHOR]

As a typical fluid-solid interaction problem, vortex-induced vibration (VIV) is common in engineering, so it is vital to study its control mechanism. Numerical simulations of the active control of VIV of a cylinder are carried out in this study. The splitter plate with harmonic oscillation is used as the control device for the dynamic response of the cylinder. The displacement response, lift and drag coefficient, vibration frequency of the cylinder, energy efficiency of control strategy, and characteristics of the flow field are widely analyzed to reveal the physical mechanism of the control system. The results show that the displacement response of the cylinder can be limited in a small range by the control without feedback in most cases except for high reduced velocity. In addition, the control strategy can be changed through feedback control to keep much superior control effects at the high reduced velocity. The oscillatory splitter plate delays the vortex shedding of shear layers generated on the cylinder, the wake vortices with opposite sense of rotation are paralleled with the streamwise direction, and crosswise distances of them are reduced. Thus, the lift on the cylinder is greatly decreased due to the modification of the flow pattern induced by the oscillatory splitter plate. [ABSTRACT FROM AUTHOR]

Target signatures are discrete quantities computed from measured scattering data that could potentially be used to classify scatterers or give information about possible defects in the scatterer compared to an ideal object. Here, we study a class of modified interior transmission eigenvalues that are intended to provide target signatures for an inverse fluid–solid interaction problem. The modification is based on an auxiliary problem parametrized by an artificial diffusivity constant. This constant may be chosen strictly positive, or strictly negative. For both choices, we characterize the modified interior transmission eigenvalues by means of a suitable operator so that we can determine their location in the complex plane. Moreover, for the negative sign choice, we also show the existence and discreteness of these eigenvalues. Finally, no matter the choice of the sign, we analyze the approximation of the eigenvalues from far field measurements of the scattered fluid pressure and provide numerical results which show that, even with noisy data, some of the eigenvalues can be determined from far field data. [ABSTRACT FROM AUTHOR]

pH-sensitive hydrogels are classified as soft materials that can be employed for future imaginative applications due to their interesting characteristics. Smart hydrogels undergo large deformation under exterior stimuli. However, the swelling behaviors of hydrogels that can be harnessed for microfluidic applications are not well perceived. In this paper, the functionality of an assortment of micro-valves which are composed of pH-sensitive cylindrical hydrogel jackets coated on rigid pillars is inspected considering fully coupled fluid–solid interaction analysis. Therefore, in order to introduce the theory of transient swelling of a pH-sensitive micro-check valve, a transient constitutive model capturing electrical, chemical, and mechanical fields for the hydrogel domain is utilized with fluid fields passing around the micro-valve. In this regard, the Nernst–Planck equation is employed to describe the ions' diffusion, and Gent hyperelastic model is used to account for the large deformation of the hydrogel. Implementing this nonlinear finite element framework, we examine the performance of one cylindrical jacket and also three patterns of multiple cylindrical valves considering transient 3D FSI behavior of the hydrogel micro-valve. The foremost emphasized novelty of this paper is considering three-dimensional geometry, new designs of micro-valves, and time-dependent swelling of hydrogels by coupling ions diffusion and their large deformation. Article Highlights: Three-dimensional single and multiple pH-sensitive hydrogel micro-valves Electro-chemo-mechanical theory for pH-sensitive hydrogels to predict their transient swelling Fluid–solid interaction of Newtonian fluid and hydrogel which can undergo large reversible deformation [ABSTRACT FROM AUTHOR]

Target signatures are discrete quantities computed from measured scattering data that could potentially be used to classify scatterers or give information about possible defects in the scatterer compared to an ideal object. Here, we study a class of modified interior transmission eigenvalues that are intended to provide target signatures for an inverse fluid–solid interaction problem. The modification is based on an auxiliary problem parametrized by an artificial diffusivity constant. This constant may be chosen strictly positive, or strictly negative. For both choices, we characterize the modified interior transmission eigenvalues by means of a suitable operator so that we can determine their location in the complex plane. Moreover, for the negative sign choice, we also show the existence and discreteness of these eigenvalues. Finally, no matter the choice of the sign, we analyze the approximation of the eigenvalues from far field measurements of the scattered fluid pressure and provide numerical results which show that, even with noisy data, some of the eigenvalues can be determined from far field data. [ABSTRACT FROM AUTHOR]

The aim of this study is to analyse the behaviour of a thin plate with air flow velocities of 0.3–0.9 Ma. Data from the experiment and numerical tools were used for the analysis. For fluid–solid interaction calculations, the arbitrary Lagrange–Euler approach was used. The results of the measurements are twofold. The first one is the measurement of the flow before and after vibrating plate, i.e. pure flow plate, and the second consists in measuring the characteristics of vibration of the plate. The character of the vibration was measured with an oscilloscope, and then the results were subjected to FFT analysis to determine the natural and flow induced vibrations. For numerical calculations example, the velocity of 0.7 Ma was selected. The deflections of the platelet under the influence of airflow were obtained. The trace of the friction layer that forms the boundary between the flow from the platelet and the separation formed behind the platelet. [ABSTRACT FROM AUTHOR]

A multibody dynamics-based solution to the fluid dynamics problem is compared herein to two established Lagrangian-based techniques used by the computational fluid dynamics (CFD) community. The multibody dynamics-based solution has two salient attributes: it enforces the incompressibility condition through bilateral kinematic constraints, and it treats the coupling with the solid phase via unilateral kinematic constraints. The multibody dynamics-based solution, called herein the Kinematically Constrained Smoothed Particle Hydrodynamics (KCSPH) method, is a Lagrangian approach to solving the CFD problem. It relies on the Smoothed Particle Hydrodynamics (SPH) method to discretize the spatial differential operators in the Navier–Stokes equations, and on the Newton–Euler equations of multibody dynamics to convect the SPH particles forward in time. We show that the multibody dynamics-based approach is efficient and accurate by comparing its performance with the two most commonly used SPH algorithms in the CFD community: the weakly compressible SPH (WCSPH), and the implicit SPH (ISPH) methods. The comparison is carried out in conjunction with four tests: an incompressibility benchmark test, dam break, floating cylinder, and sloshing tank. We conclude that KCSPH is a robust alternative to conventional CFD approaches for fluid–solid interaction (FSI) problems with complex/moving boundaries. The solvers and models used herein are publicly available in an open-source software called Chrono; the implementations use GPU (for WCSPH and ISPH), and multicore CPU (for KCSPH) parallel computing. [ABSTRACT FROM AUTHOR]

Interactions between an incompressible fluid passing through a flexible tube and the elastic wall is one of the strongly coupled fluid–solid interaction (FSI) problems frequently studied in the literature due to its research importance and wide range of applications. Although incompressible fluid is a prevalent model in many simulation studies, the assumption of incompressibility may not be appropriate in strongly coupled FSI problems. This paper narrowly aims to study the effect of the fluid compressibility on the wave propagation and fluid–solid interactions in a flexible tube. A partitioned FSI solver is used which employs a finite volume-based fluid solver. For the sake of comparison, both traditional incompressible (ico) and weakly compressible (wco) fluid models are used in an Arbitrary Lagrangian–Eulerian (ALE) formulation and a PISO-like algorithm is used to solve the unsteady flow equations on a collocated mesh. The solid part is modeled as a simple hyperelastic material obeying the St-Venant constitutive relation. Computational results show that not only use of the weakly compressible fluid model makes the FSI solver in this case more efficient, but also the incompressible fluid model may produce largely unrealistic computational results. Therefore, the use of the weakly compressible fluid model is suggested for strongly coupled FSI problems involving seemingly incompressible fluids such as water especially in cases where wave propagation in the solid plays an important role. Article highlights: Flow in a flexible tube is a strongly coupled FSI problem. The weakly compressible fluid model has computational merits in FSI problems. The incompressibility assumption for liquids leads to unrealistic results in some FSI cases. [ABSTRACT FROM AUTHOR]

Resin infusion is a pressure-gradient-driven composite manufacturing process in which the liquid resin is driven to flow through and fill in the void space of a porous composite preform prior to the heat treatment for resin solidification. It usually is a great challenge to design both the infusion system and the infusion process meeting the manufacturing requirements, especially for large-scale components of aircraft and wind turbine blades. Aiming at addressing the key concerns about flow fronts and air bubble entrapment, the present study proposes a modelling framework of the multiphase flow of resin and air in a dual scale porous medium, i.e. a composite preform. A finite strain formulation is discussed for the fluid–solid interaction during an infusion process. The present study bridges the gap between the microscopic observation and the macroscopic modelling by using the averaging method and first principle method, which sheds new light on the high-fidelity finite element modelling. [ABSTRACT FROM AUTHOR]

The fluid-solid interaction force has a decisive influence on the flow characteristics of micro-nano scale. Based on the dissipative particle dynamics (DPD) method, static and flow simulations of fluid in typical shale slits were carried out. The Lennard-Jones (LJ) potential function of 96X was applied to characterize the fluid-solid interaction force. The slit width ranged 3–10nm, the wall material was quartz, the fluid was n-hexane, and the driving force of the flow simulation ranged 1–20kcal/(mol·Å). The results show that due to the attraction of solid wall, the aggregation of fluid molecules near the wall was enhanced, fluid density there increased, and the diffusion coefficient there was significantly lower than that in the middle of the slit. The fluidity of the fluid near the wall is significantly reduced. In the flow model, when the fluid-solid interaction force was ignored, the flow profile was piston-like, and the velocity gradient at the edge of the slit was extremely large, showing the characteristics of slip flow. When the fluid-solid interaction force was taken into account, the velocity was reduced significantly, and the profile was parabolic. When the LJ96X was replaced by LJ126X potential function to characterize the fluid-solid interaction force, the attractive force from the wall on the fluid near the wall decreased, the fluidity was enhanced, and the velocity profile increased. When the conservative force parameter of fluid was changed, enhancing the wettability of oil phase, the affinity between fluid and solid was increased, and the velocity profile was reduced. [ABSTRACT FROM AUTHOR]

Explosions release energy and generate shock waves. Analysis of how shock waves damage transmission media is crucial in protection engineering. Soil liquefaction due to explosions occurs in a highly nonlinear manner. The time point at which soil receives stress waves has yet to be determined. Therefore, this study analyzed the dynamic reaction and liquefaction phenomenon that protects soil after it has received a shock wave. A numerical analysis model was developed and verified through on-site explosion experiments for measuring ground acceleration and excess water pressure. Finite element analysis was employed to establish a numerical analysis model based on experimental site conditions. The LS-DYNA finite element program was used for numerical simulations. The analysis model had a three-dimensional structure with fluid–solid coupling and consisted of eight-node elements. To analyze the dynamic reaction and liquefaction phenomenon that occurs after soil has received a shock wave, a multimaterial arbitrary Lagrangian–Eulerian calculation model was combined with an element erosion algorithm. Meshes were overlapped to achieve fluid–solid coupling for subsequent analysis. The nonlinear dynamic reaction in soil triggered by shock wave transmission and the liquefaction of the material due to excess water pressure were analyzed. The research results showed that the relative errors between numerical analysis and experimental results were within 10%, verifying that the fluid–solid coupling numerical model developed in this study can effectively be used to analyze the dynamic reactions of materials receiving shock waves. Shock waves from both multisite time-delayed explosions and from continual explosions at a single nearby site lead to soil liquefaction. Compared with single-site explosions, multisite time-delayed explosions more easily trigger liquefaction in saturated sandy soil. Analysis of shock wave transmission characteristics and ground shock effects revealed that at a distance of 600 cm from the explosion center, the shock wave was substantially attenuated. The results of shear strain failure analysis indicated that soil liquefaction had an approximate area of scale distance Z = 30.81–64.89 cm/g1/3 and approximate depth of Z = 17.62 cm/g1/3. The results verify the validity of the numerical model and algorithm developed in this study, which can describe the liquefaction process of saturated soil under explosion loading. [ABSTRACT FROM AUTHOR]

In the emerging field of deformable microfluidics, we propose a new geometry in which the height and angle of a channel are controlled, thanks to the deformability of the microfluidic elastomer down to thicknesses of a few microns. The particularity of our set-up is that the height of the channel under study is fully closed at rest, which reveals especially well suited to address micro-nanoconfinement problems such as clogging, transport selectivity and flow rectification. Using fluorescence microscopy and light absorption, we probe the channel shape from the measurement of the PDMS-displacement field. We demonstrate that the maximal PDMS displacement can be inferred from finite elements numerical simulations and predicted reliably with simple analytical relations from elasticity continuum mechanics. [ABSTRACT FROM AUTHOR]

Most landslides induced by reservoir impoundment and rainfall in the Three Gorges Reservoir area of China are usually characterized by bedding-plane shear zones. This paper presents an experimental study of the interaction between water and shear-zone materials. A series of tests, including wetting-drying cycles and soaking tests, were carried out. The results show that the fluid-solid interaction not only reduces the shear strength of shear-zone soil but also accelerates the disintegration process of clastic rock from shear zone. After the fluid-solid interaction at different pH values, the clastic rock samples produce the most clay minerals in acidic solution. Similarly, the clay minerals of shear-zone soil samples increase dramatically after 45 days of soaking in acidic environment. According to the tests, it is found that the shear-zone soil in eluvium may originate from the weathered clastic rock near the shear zones under long-term fluid-solid interaction. [ABSTRACT FROM AUTHOR]

This paper is concerned with the inverse scattering of time-harmonic acoustic plane waves by a multi-layered fluid–solid medium in the three dimensional space. We establish the global uniqueness in identifying the embedded penetrable solid obstacle, the surrounding fluid medium and its wave number from the acoustic far-field pattern for all incident plane waves at a fixed frequency. The proof depends on constructing different kinds of interior transmission problems in appropriate small domains and the a priori estimates derived for both the elastic wave fields in the embedded solid obstacle and the acoustic wave fields in the surrounding fluid medium. [ABSTRACT FROM AUTHOR]

This paper is concerned with the mathematical analysis of a time-dependent fluid-solid interaction problem associated with a bounded elastic body immersed in a homogeneous air or fluid above a local rough surface. We reformulate the unbounded scattering problem into an equivalent initial-boundary value problem defined in a bounded domain by proposing a transparent boundary condition (TBC) on a hemisphere. Analyzing the reduced problem with the Lax-Milgram lemma and the abstract inversion theorem of the Laplace transform, we prove the well-posedness and stability for the reduced problem. Moreover, an a priori estimate is established directly in the time domain for the acoustic wave and elastic displacement by using the energy method. [ABSTRACT FROM AUTHOR]

Bicuspid aortic valve (BAV) anatomy has routinely been considered an exclusion in the setting of transcatheter aortic valve implantation (TAVI) because of the large dimension of the aortic annulus having a more calcified, bulky, and irregular shape. The study aims to develop a patient-specific computational framework to virtually simulate TAVI in stenotic BAV patients using the Edwards SAPIEN 3 valve (S3) and its improved version SAPIEN 3 Ultra and quantify stent frame deformity as well as the severity of paravalvular leakage (PVL). Specifically, the aortic root anatomy of n.9 BAV patients who underwent TAVI was reconstructed from pre-operative CT imaging. Crimping and deployment of S3 frame were performed and then followed by fluid-solid interaction analysis to simulate valve leaflet dynamics throughout the entire cardiac cycle. Modeling revealed that the S3 stent frame expanded well on BAV anatomy with an elliptical shape at the aortic annulus. Comparison of predicted S3 deformity as assessed by eccentricity and expansion indices demonstrated a good agreement with the measurement obtained from CT imaging. Blood particle flow analysis demonstrated a backward blood jet during diastole, whereas the predicted PVL flows corresponded well with those determined by transesophageal echocardiography. This study represents a further step towards the use of personalized simulations to virtually plan TAVI, aiming at improving not only the efficacy of the implantation but also the exploration of "off-label" applications as the TAVI in the setting of BAV patients. Graphical abstract Computational frameworks of TAVI in patients with stenotic bicuspid aortic valve. [ABSTRACT FROM AUTHOR]

Consider the inverse problem of recovering a multi-layered fluid-solid medium from many acoustic measurements corresponding to time-harmonic acoustic plane waves. We prove that both the supports of the embedded solid obstacle and the surrounding layered fluid medium can be uniquely identified by means of acoustic far-field pattern for all incident wave fields at a fixed frequency. Our proof is based on the constructions of some well-posed partial differential equation systems in sufficiently small domains combined with the a priori estimates for the solutions of the forward scattering problem. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A numerical model was established to simulate the activation of the fault zone with a soft infill during a water inrush event. Distribution of the failed areas at different times was acquired. Then, a parametric sweep analysis was conducted to see the influence of permeability. By analyzing the results, a new parameter called the "activation coefficient" was proposed to characterize the fault zone activation process. A functional relationship was established between the activation coefficient and permeability. A series of numerical cases with different conditions were calculated to determine the parameters in the function. A method to evaluate the risk of water inrush is proposed, based on these results. By comparing the acceptable and actual values of the activation coefficient, the activation speed of the fault zone, and time for excavation and support can be determined; thus, the risk of water inrush can be evaluated. The research results were used during construction of line 1 of the Qingdao subway tunnel engineering project in China, which provided valuable data for assessing the risk of water inrush in a mine. [ABSTRACT FROM AUTHOR]

As a typical disaster-causing geological structure, karst collapse pillar (KCP) is widely distributed in coalfields of northern China. The interior of KCP is filled with loose and weakly cemented rock masses. Fine particles can be eroded under the hydraulic pressure and the disturbance of the coal mining operation. Then, water inrush pathway can be formed easily, resulting in water inrush hazard. The release of untreated coal mine water can pollute the environment and waste the limited water resource in China. To investigate the particle erosion effect on the water inrush mechanism of KCP, FLAC3D numerical investigations were conducted to simulate the water flow process of KCP in the mining floor during the coal seam excavation, according to the stress-seepage coupling model with the consideration of the particle erosion. Besides, the evolution of shear stress field, seepage field, and plastic zone along was obtained as working plane advances. Meanwhile, the influence of the thickness of a waterproof rock floor and the hydraulic pressure of aquifer on the formation of water inrush pathway was analyzed. Numerical results indicated that: (1) Shear failure of the KCP near the side of the working plane occurs under the effect of mining excavation; then, the KCP connects with the damage area around the working plane; finally, the water inrush pathway is formed. (2) Water inrush disaster will not occur immediately when the KCP is connected with the damaged area around the working plane; it only occurs when the KCP is completely exposed in the mining. (3) With the mining advances, the thinner the waterproof rock floor and the greater the hydraulic pressure of the aquifer, the easier the groundwater can lead up, and the KCP tends to be damaged with the formation of water inrush pathway. [ABSTRACT FROM AUTHOR]

In this paper, a novel 3D numerical method has been developed to simulate red blood cells (RBCs) based on the interaction between a shell-like solid structure and a fluid. RBC is assumed to be a thin shell encapsulating an internal fluid (cytoplasm) which is submerged in an external fluid (blood plasma). The approach is entirely based on the smoothed particle hydrodynamics (SPH) method for both fluid and the shell structure. Both cytoplasm and plasma are taken to be incompressible Newtonian fluid. As the kinematic assumptions for the shell, Reissner-Mindlin theory has been introduced into the formulation. Adopting a total Lagrangian (TL) formulation for the shell in the realm of small strains and finite deflection, the presented computational tool is capable of handling large displacements and rotations. As an application, the deformation of a single RBC while passing a stenosed capillary has been modeled. If the rheological behavior of the RBC changes, for example, due to some infection, it is reflected in its deformability when it passes through the microvessels. It can severely affect its proper function which is providing the oxygen and nutrient to the living cells. Hence, such numerical tools are useful in understanding and predicting the mechanical behavior of RBCs. Furthermore, the numerical simulation of stretching an RBC in the optical tweezers system is presented and the results are verified. To the best of authors' knowledge, a computational tool purely based on the SPH method in the framework of shell-fluid interaction for RBCs simulation is not available in the literature. [ABSTRACT FROM AUTHOR]

In this paper, a fully adaptive multiresolution (MR) finite difference scheme with a time-varying tolerance is developed to study compressible fluid flows containing shock waves in interaction with solid obstacles. To ensure adequate resolution near rigid bodies, the MR algorithm is combined with an immersed boundary method based on a direct-forcing approach in which the solid object is represented by a continuous solid-volume fraction. The resulting algorithm forms an efficient tool capable of solving linear and nonlinear waves on arbitrary geometries. Through a one-dimensional scalar wave equation, the accuracy of the MR computation is, as expected, seen to decrease in time when using a constant MR tolerance considering the accumulation of error. To overcome this problem, a variable tolerance formulation is proposed, which is assessed through a new quality criterion, to ensure a time-convergence solution for a suitable quality resolution. The newly developed algorithm coupled with high-resolution spatial and temporal approximations is successfully applied to shock-bluff body and shock-diffraction problems solving Euler and Navier-Stokes equations. Results show excellent agreement with the available numerical and experimental data, thereby demonstrating the efficiency and the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Fluid-solid interaction has been a challenging subject due to their strong nonlinearity and multidisciplinary nature. Many of the numerical methods for solving FSI problems have struggled with non-convergence and numerical instability. In spite of comprehensive studies, it has still been a challenge to develop a method that guarantees both convergence and stability. Our discussion in this work is restricted to the interaction of viscous incompressible fluid flow and a rigid body. We take the monolithic approach by Gibou and Min (J Comput Phys 231:3245-3263, 2012) that results in an augmented Hodge projection. The projection updates not only the fluid vector field but also the solid velocities. We derive the equivalence between the augmented Hodge projection and the Poisson equation with non-local Robin boundary condition. We prove the existence, uniqueness, and regularity for the weak solution of the Poisson equation, through which the Hodge projection is shown to be unique and orthogonal. We also show the stability of the projection in the sense that the projection does not increase the total kinetic energy of the fluid or the solid. Finally, we discuss a numerical method as a discrete analogue to the Hodge projection, then we show that the unique decomposition and orthogonality also hold in the discrete setting. As one of our main results, we prove that the numerical solution is convergent with at least first-order accuracy. We carry out numerical experiments in two and three dimensions, which validate our analysis and arguments. [ABSTRACT FROM AUTHOR]

In order to improve structure performance of the dish solar concentrator, a three-dimensional model of dish solar concentrator was established based on the high-precision numerical algorithms. And a virtual wind tunnel experiment with constant wind is adopted to investigate the pressure distribution of the reflective surface, velocity distribution of the fluid domain for the dish solar concentrator in different poses and wind speeds distribution. Some results about wind pressure distribution before and after dish solar concentrator surface and wind load velocity distribution in the entire fluid domain had been obtained. In particular, it is necessary to point out that the stiffness at the center of the dish solar concentrator should be relatively raised. The results can provide a theoretical basis for the improvement of solar concentrator dish structure as well as the failure analysis of dish solar concentrator in engineering practice. [ABSTRACT FROM AUTHOR]

We propose an implicit Newmark method for the time integration of the pressure-stress formulation of a fluid-structure interaction problem. The space Galerkin discretization is based on the Arnold-Falk-Winther mixed finite element method with weak symmetry in the solid and the usual Lagrange finite element method in the acoustic medium. We prove that the resulting fully discrete scheme is well-posed and uniformly stable with respect to the discretization parameters and Poisson ratio, and we provide asymptotic error estimates. Finally, we present numerical tests to confirm the asymptotic error estimates predicted by the theory. [ABSTRACT FROM AUTHOR]

This paper presents the simulation of tsunamis due to rigid and deformable landslides with consideration of submerged conditions by using particle methods. The smoothed particle hydrodynamics (SPH), as a particle based method, is for solving problems of fast moving boundaries in the field of continuum mechanics. Other particle based methods, like the discrete element method (DEM), are suitable for modeling the displacement and the collision related to the rigid landslides. In the present work, we use the SPH and the DEM to simulate tsunamis generated by rigid and deformable landslides with consideration of submerged conditions. The viscous free-surface flows are solved by a weakly compressible SPH and the displacement and the rotation of the rigid body slides are calculated using a multi-sphere DEM allowing for modeling solids of arbitrarily complex shapes. The fluid-solid interactions are simulated by coupling the SPH and the DEM. A rheology model combining the Papanastasiou and the Herschel-Bulkley models is applied to represent the viscoplastic behavior of the non-Newtonian flow in the submarine deformable landslide cases. Submarine landslide tsunamis due to rigid and deformable landslides are both simulated as typical landslide cases in this investigation. Our simulated results and the previous experimental results in the literatures are in good agreement, which shows that the proposed particle based methods are capable of modeling the submarine landslide tsunamis. [ABSTRACT FROM AUTHOR]

Background: Mineral precipitates (scaling) from deep saline thermal waters often constitute a major problem during geothermal energy production. The occurrence of scale-fragments accumulating and clogging pipes, filters, and heat exchangers is of particular concern regarding an efficient energy extraction. Methods: Carbonate scale-fragments from different sections of two geothermal power plants were collected and studied in a high-resolution scaling forensic approach comprising of microstructural characterization, elemental mapping, and stable carbon and oxygen isotope transects. The solid-phase analyses were evaluated in the context of natural environmental and technical (man-made) production conditions. Results and discussion: Our results indicate an interaction of metal sulfide mineral layers mainly from HS corrosion of the steel pipes and CaCO nucleation and crystal growth. A conceptual model of scale-fragment development addresses the relevance of two key interfaces: 1) the corrosion layer between the steel substrate and calcite scale and 2) the scale surface versus thermal fluid flow. The corrosion products constitute an attractive crystallization substrate of brittle and mechanically weak consistency. A rough carbonate scale surface tends to induce (micro) turbulences and increased flow resistance (frictional forces). These factors promote partial exfoliation, scale-fragment mobilization, and rapid clogging. This investigation highlights the potential of detailed petrographic and geochemical analyses of mineral precipitates for evaluating favorable versus unfavorable processes in geotechnical environmental settings. [ABSTRACT FROM AUTHOR]

Atherosclerosis develops due to different hemodynamic factors, among which time-averaged Wall shear stress (mean WSS) and Oscillatory shear index (OSI) are two of the most important. These two factors not only depend on flow geometry, but are also influenced by rheological characteristics of blood. Since analytical solutions are limited to simple problems and since experimental tests are costly and time consuming, CFD solutions been prominently and effectively used to solve such problems. We conducted a numerical study via ADINA 8.8 software on the non-Newtonian pulsatile flow of blood through an elastic blood artery with single and consecutive stenosis. The studied stenosis cross sectional area was 70 % that of the unstenosed artery. The single stenosis results were compared with the consecutive stenosis results. The five non-Newtonian flow models, the Carreau model, the Carreau-Yasuda model, the modified Casson model, the power-law model, and the generalized power-law model, were used to model the non-Newtonian blood flow. The obtained results showed that increasing the number of stenoses would lead to reduced length of the oscillatory area after the first stenosis, thus forming another oscillatory area with a larger length after the second stenosis. Thus, a consecutive stenosis would develop a larger disease prone area. Upon examining the mean WSS and OSI, we found that, as compared with the other models, the modified Casson model and the power-law model produced predictions for the most extent of damage to endothelial cells and the most disease prone areas, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a 3D computational model has been developed to investigate biofilms in a multi-physics framework using smoothed particle hydrodynamics (SPH) based on a continuum approach. Biofilm formation is a complex process in the sense that several physical phenomena are coupled and consequently different time-scales are involved. On one hand, biofilm growth is driven by biological reaction and nutrient diffusion and on the other hand, it is influenced by fluid flow causing biofilm deformation and interface erosion in the context of fluid and deformable solid interaction. The geometrical and numerical complexity arising from these phenomena poses serious complications and challenges in grid-based techniques such as finite element. Here the solution is based on SPH as one of the powerful meshless methods. SPH based computational modeling is quite new in the biological community and the method is uniquely robust in capturing the interface-related processes of biofilm formation such as erosion. The obtained results show a good agreement with experimental and published data which demonstrates that the model is capable of simulating and predicting overall spatial and temporal evolution of biofilm. [ABSTRACT FROM AUTHOR]

In this article, the transonic inviscid flow over a deformable airfoil with plunging motion is studied numerically. A finite volume method based on the Roe scheme developed in a generalized coordinate is used along with an arbitrary Lagrangian-Eulerian method and a dynamic mesh algorithm to track the instantaneous position of the airfoil. The effects of different governing parameters such as the phase angle, the deformation amplitude, the initial angle of attack, the flapping frequency, and the Mach number on the unsteady flow field and aerodynamic coefficients are investigated in detail. The results show that maneuverability of the airfoil under various flow conditions is improved by the deformation. In addition, as the oscillation frequency of the airfoil increases, its aerodynamic performance is significantly improved. [ABSTRACT FROM AUTHOR]

The classical Couette-Taylor problem is to describe the motion of a viscous incompressible fluid in the region between two rigid coaxial cylinders, which rotate at constant angular velocities. This paper treats a generalization of this problem in which the rigid outer cylinder is replaced by a deformable (nonlinearly elastic) cylinder. The inner cylinder is rigid and rotates at a prescribed angular velocity. We study steady rotationally symmetric motions of the fluid coupled with steady axisymmetric motions of the deformable outer cylinder in which it rotates at a prescribed constant angular velocity, typically different from that of the inner cylinder. The motion of the outer cylinder is governed by a geometrically exact theory of shells and the motion of the liquid by the Navier-Stokes equations, with the domain occupied by the liquid depending on the deformation of the outer cylinder. The nonlinear fluid-solid system admits a (trivial) steady solution, termed the Couette solution, which can be found explicitly. This paper treats the global (multiparameter) bifurcation of steady-state solutions from the Couette solution. This problem exhibits technical mathematical difficulties directly due to the fluid-solid interaction: The smoothness of the shell's configuration restricts the smoothness of the fluid variables, and their boundary values on the shell determine the smoothness of the shell's configuration. It is essential to ensure that this cycle of implications is consistent. [ABSTRACT FROM AUTHOR]

This article investigates the pulsatile and turbulent blood flows in flexible artery with single and double stenoses. The changes in pressure drop, mean wall shear stress (WSS), radial displacement of the artery, and oscillating shear index are investigated. Similar to experimental data, the results of the present study show that a laminar flow occurs for stenosis of up to 70%, and for 80% stenosis the flow is turbulent. The mean WSS analysis shows that assuming the flow is laminar causes more errors than assuming the walls are solid. The comparison of the results for single stenosis with those for double stenosis reveals that the dilation in the arterial walls in double stenoses is much more common than in single stenosis. Therefore, the maximum mean WSS in double stenoses is less than that in single stenosis. The results also indicate that the axial pressure drop in double stenoses is higher than that in single stenosis. [ABSTRACT FROM AUTHOR]

A fully coupled mathematical model of land subsidence caused by groundwater pumping was established based on the mechanics of porous seepage and the theory of fluid-solid interaction. The mathematical model employing the Galerkin finite element method was proposed to simulate the deformation dependencies of hydraulic properties due to the water pressure decrease in aquifers. This model has been verified by comparing with the known analytical solutions in the confined aquifer. Results show that the simulated drawdown and displacements match well with those of analytical solutions. To evaluate the nonlinear effects of hydraulic properties in the seepage and consolidation coupling phenomena, the numerical model is applied to an ideal three layers numerical experiment. The results show that the subsidence rate is faster than conventional groundwater theory when the nonlinear hydraulic properties (NHP) are considered in the coupled model. The reason is that the water level decline due to groundwater withdrawal induces the soil compression and the porosity and permeability decrease. Decrease of permeability in regions adjacent to the pumping well produces hydraulic gradient and seepage forces that may result in accelerated subsidence. Therefore, the effect of the NHP is an interaction process of pore water pressure and soil consolidation deformation and should not be ignored. Further studies of various hydrogeology problems are recommended to consider the heterogeneity concerning different stratigraphic condition in the field. [ABSTRACT FROM AUTHOR]

Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration (VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation (LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters. [ABSTRACT FROM AUTHOR]

This paper deals with investigation of fluid flow on static and dynamic behaviors of carbon nanotubes under electrostatic actuation. The effects of various fluid parameters including fluid viscosity, velocity, pressure and mass ratio on the deflection and pull-in behaviors of the cantilever and doubly clamped carbon nanotubes are studied. Furthermore, the effects of temperature variation on the static and dynamic pull-in voltages of the doubly clamped carbon nanotubes are reported. The results reveal that altering the fluid parameters significantly changes the mechanical and pull-in behaviors. Hence, the proposed system can be applied properly as a nano fluidic sensor to sense the various parameters of the fluid. [ABSTRACT FROM AUTHOR]

In the present study, we reconstructed upper airway and soft palate models of 3 obstructive sleep apnea-hypopnea syndrome (OSAHS) patients with nasal obstruction. The airflow distribution and movement of the soft palate before and after surgery were described by a numerical simulation method. The curative effect of nasal surgery was evaluated for the three patients with OSAHS. The degree of nasal obstruction in the 3 patients was improved after surgery. For 2 patients with mild OSAHS, the upper airway resistance and soft palate displacement were reduced after surgery. These changes contributed to the mitigation of respiratory airflow limitation. For the patient with severe OSAHS, the upper airway resistance and soft palate displacement increased after surgery, which aggravated the airway obstruction. The efficacy of nasal surgery for patients with OSAHS is determined by the degree of improvement in nasal obstruction and whether the effects on the pharynx are beneficial. Numerical simulation results are consistent with the polysomnogram (PSG) test results, chief complaints, and clinical findings, and can indirectly reflect the degree of nasal patency and improvement of snoring symptoms, and further, provide a theoretical basis to solve relevant clinical problems. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new boundary element (BEM) formulation is proposed for wave load analysis of submerged or floating bodies. The presented formulation, through establishing an impedance relation, permits the evaluation of the hydrodynamic coefficients (added mass and damping coefficients) and the coefficients of wave exciting forces systematically in terms of system matrices of BEM without solving any special problem, such as, unit velocity or unit excitation problem. It also eliminates the need for scattering analysis in the evaluation of wave exciting forces. The imaginary and real parts of impedance matrix give, respectively, added mass and damping matrices whose elements describe the fluid resistance against the motion of the body. The formulation is explained through the use of a simple fluid-solid system under wave excitations, which involves a uniform fluid layer containing a solid cylindrical body. In the formulation, the solid body is taken first as deformable, then, it is specialized when it is rigid. The validity of the proposed method is verified by comparing its result with those available in literature for rigid submerged or floating bodies. [ABSTRACT FROM AUTHOR]

Doppler ultrasound is a usual non-invasive method to estimate the stenosis percentage in large arteries such as carotid by measuring maximum velocity of blood flow. Based on clinical investigations, because of vessel wall motions, Doppler positioning and angle correction, some errors can arise in Doppler results which lead to incorrect diagnosis. The aim of this study was to compare the results of Doppler test and the numerical simulation of blood flow in the same case. For this evaluation, two patients including an 87-year-old man and a 72-year-old woman suffering from stenosis in the internal carotid artery were selected. First, clinical information of each patient such as CT-Angio scan images and Doppler ultrasound results on different locations of the stenosed artery were obtained. Then, the geometries were reconstructed and numerical simulations were carried out using ANSYS software. Results showed that the velocity profile of Doppler test and numerical simulation were in good agreement at the regions of pre-and post-stenosis. However, the value of maximum velocity at the stenotic region had significant differences. [ABSTRACT FROM AUTHOR]

The resistance loss of transportation was studied and the influences of buoyancy layout, mineral content and elastic modulus of flexible hose were investigated based on three-dimensional finite element model of fluid-solid interaction by MSC.MARC/MENTAT software. The numerical results show that the resistance losses increase with the increase of mineral content C and velocity of internal fluid v and decrease with the increase of elastic modulus E of flexible hose. The buoyancy layout and the velocity of internal fluid have greater impacts on the resistance losses than the elastic modulus of flexible hose. In order to reduce the resistance losses and improve the efficiency of the deep-ocean mining, C and v must be restricted in a suitable range (e.g. 10%-25% and 2.5-4 m/s). Effective buoyancy layout (such as Scheme C and D) should be adopted and the suitable material of moderate E should be used for the flexible hose in deep-ocean mining. [ABSTRACT FROM AUTHOR]

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 $$ {\mathop m\limits^ \cdot }$$ = 0.085 kg/s, T = 90°C, and P = 130 kPa, respectively. In the stationary case, it is determined that the pressure loss value in the air domain of the hose is Δ P = 1.50 kPa; moreover, the corresponding data for the temperature drop is Δ T = 0.80°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. [ABSTRACT FROM AUTHOR]

An integrated fluid-thermal-structural analysis approach is presented. In this approach, the heat conduction in a solid is coupled with the heat convection in the viscous flow of the fluid resulting in the thermal stress in the solid. The fractional four-step finite element method and the streamline upwind Petrov-Galerkin (SUPG) method are used to analyze the viscous thermal flow in the fluid. Analyses of the heat transfer and the thermal stress in the solid are performed by the Galerkin method. The second-order semiimplicit Crank-Nicolson scheme is used for the time integration. The resulting nonlinear equations are linearized to improve the computational efficiency. The integrated analysis method uses a three-node triangular element with equal-order interpolation functions for the fluid velocity components, the pressure, the temperature, and the solid displacements to simplify the overall finite element formulation. The main advantage of the present method is to consistently couple the heat transfer along the fluid-solid interface. Results of several tested problems show effectiveness of the present finite element method, which provides insight into the integrated fluid-thermal-structural interaction phenomena. [ABSTRACT FROM AUTHOR]

At a time when sequential computing is limited to marginal year-to-year gains in speed, multi- and many-core architectures provide teraflop-grade performance to cost-conscious users. The ongoing shift to parallel computing spurs new research into solution methods that emphasize algorithmic concurrency. It also provides an opportunity to revisit complex real-life applications whose solutions have been until recently infeasible due to prohibitively heavy computational burdens. This paper concentrates on the use of commodity parallel computing in the field of multibody dynamics by illustrating how many-body frictional-contact dynamics, fluid-solid interaction analysis, and proximity computation have benefited from parallel computing. Preliminary results are encouraging and show one to two orders of magnitude reductions in simulation times. A set of open questions and final remarks round up the contribution. [ABSTRACT FROM AUTHOR]

The studies on the mechanisms and performances of the mechanical seals in reactor coolant pumps are very important for the safe operations of the pressurized water reactor power plants. Based on the hydrostatic mechanical seal in reactor coolant pumps, an analytical fluid-solid strong-interaction model is proposed in this paper. According to the design features and operational principles of the seal, an analytical method to calculate the mechanical deformation of the seal assembly is developed based on the ring deformation theory. A strong-interaction algorithm combining the analysis of the mechanical deformation of the seal assembly and flow field between the seal faceplates is utilized, in which the three kinds of equations including the fluid domain, solid domain and coupling action are constituted in the same equations set and all the variables are solved simultaneously. So the analytical fluid-solid strong-interaction model used for the seal is built. Moreover, the model is verified by the experimental results. Based on the model, the design parameters of the seal are studied. Two different conditions of the general case and fixed seal leakage rate are discussed respectively, and the regularities that the seal behaviors are affected by the parameters of the holding screws on the clamp rings and seal faceplates are obtained. The research results can provide a theoretical basis for performance analysis, design and assemblage of the seal. Compared to the numerical methods, the proposed model has the unique advantages of high efficiency, convenience and easy application of constraints. [ABSTRACT FROM AUTHOR]

The purpose of this article is to validate numerical simulations of flow and pressure incorporating deformable walls using in vitro flow phantoms under physiological flow and pressure conditions. We constructed two deformable flow phantoms mimicking a normal and a restricted thoracic aorta, and used a Windkessel model at the outlet boundary. We acquired flow and pressure data in the phantom while it operated under physiological conditions. Next, in silico numerical simulations were performed, and velocities, flows, and pressures in the in silico simulations were compared to those measured in the in vitro phantoms. The experimental measurements and simulated results of pressure and flow waveform shapes and magnitudes compared favorably at all of the different measurement locations in the two deformable phantoms. The average difference between measured and simulated flow and pressure was approximately 3.5 cc/s (13% of mean) and 1.5 mmHg (1.8% of mean), respectively. Velocity patterns also showed good qualitative agreement between experiment and simulation especially in regions with less complex flow patterns. We demonstrated the capabilities of numerical simulations incorporating deformable walls to capture both the vessel wall motion and wave propagation by accurately predicting the changes in the flow and pressure waveforms at various locations down the length of the deformable flow phantoms. [ABSTRACT FROM AUTHOR]

The main physiological function of coughing is to remove from the airways the mucus and foreign particles that enter the lungs with respirable air. However, in patients with endotracheal tubes, further surgery has to be performed to improve cough effectiveness. Thus, it is necessary to analyze how this process is carried out in healthy tracheas to suggest ways to improve its efficacy in operated patients. A finite element model of a human trachea is developed and used to analyze the deformability of the tracheal walls under coughing. The geometry of the trachea is obtained from CT of a 70-year-old male patient. A fluid structure interaction approach is used to analyze the deformation of the wall when the fluid (in this case, air) flows inside the trachea. A structured hexahedral-based grid for the tracheal walls and an unstructured tetrahedral-based mesh with coincident nodes for the fluid are used to perform the simulations with the finite element-based commercial software code (ADINA R&D Inc.). Tracheal wall is modeled as an anisotropic fiber reinforced hyperelastic solid material in which the different orientation of the fibers is introduced. The implantation of an endotracheal prosthesis is simulated. Boundary conditions for breathing and coughing are applied at the inlet and at the outlet surfaces of the fluid mesh. The collapsibility of a human trachea under breathing and coughing is shown in terms of flow patterns and wall stresses. The ability of the model to reproduce the normal breathing and coughing is proved by comparing the deformed shape of the trachea with experimental results. Moreover the implantation of an endotracheal prosthesis would be related with a decrease of coughing efficiency, as clinically seen. [ABSTRACT FROM AUTHOR]