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Analysis of the slipstream development around the high-speed trains in tunnels would provide references for assessing the transient gust loads on trackside workers and trackside furniture in tunnels. This paper focuses on the computational analysis of the slipstream caused by high-speed trains passing through double-track tunnels with a cross-sectional area of 100 m2. Three-dimensional unsteady compressible Reynolds-averaged Navier-Stokes equations and a realizable k-ε turbulence model were used to describe the airflow characteristics around a high-speed train in the tunnel. The moving boundary problem was treated using the sliding mesh technology. Three cases were simulated in this paper, including two tunnel lengths and two different configurations of the train. The train speed in these three cases was 250 km/h. The accuracy of the numerical method was validated by the experimental data from full-scale tests, and reasonable consistency was obtained. The results show that the flow field around the high-speed trains can be divided into three distinct regions: the region in front of the train nose, the annular region and the wake region. The slipstream development along the two sides of train is not in balance and offsets to the narrow side in the double-track tunnels. Due to the piston effect, the slipstream has a larger peak value in the tunnel than in open air. The tunnel length, train length and length ratio affect the slipstream velocities; in particular, the velocities increase with longer trains. Moreover, the propagation of pressure waves also induces the slipstream fluctuations: substantial velocity fluctuations mainly occur in front of the train, and weaken with the decrease in amplitude of the pressure wave. [ABSTRACT FROM AUTHOR]

The analysis of a cable with a small bending stiffness is a problem encountered in many engineering applications such as the fatigue assessment of stay cables, the modeling of pipeline laying operation, or the determination of bending stresses in drillpipe assemblies. Because this phenomenon is modeled by a singularly perturbed equation, standard numerical techniques fail to solve these problems efficiently. As an alternative, provided the complexity of the analytical developments does not preclude their application, these problems may be tackled with appealing analytical procedures such as matching asymptotics or multiple scales. Otherwise, advanced numerical simulations combining patching asymptotics within a numerical framework are the only possible approach for problems where the governing equations are too complex. Patching asymptotics also feature a number of merits such as the possibility of using a boundary layer with a finite extent. Aiming at a better understanding of this latter technique, the purpose of this paper was to determine the solution of a cable with a small bending stiffness. Interesting details about patchability conditions and about how to restore higher derivative continuity are included. The accuracy of the patching asymptotics approach is also compared with that of matched asymptotics. [ABSTRACT FROM AUTHOR]

In this paper, we present an accurate, efficient and stable numerical method for the incompressible Navier-Stokes equations (NSEs). The method is based on (1) an equivalent pressure Poisson equation formulation of the NSE with proper pressure boundary conditions, which facilitates the design of high-order and stable numerical methods, and (2) the Krylov deferred correction (KDC) accelerated method of lines transpose (MOLT), which is very stable, efficient, and of arbitrary order in time. Numerical tests with known exact solutions in three dimensions show that the new method is spectrally accurate in time, and a numerical order of convergence 9 was observed. Two-dimensional computational results of flow past a cylinder and flow in a bifurcated tube are also reported. [ABSTRACT FROM AUTHOR]

The context of this paper is the development of a general and efficient numerical haemodynamic tool to help clinicians and researchers in understanding of physiological flow phenomena. We propose an accurate one-dimensional Runge-Kutta discontinuous Galerkin (RK-DG) method coupled with lumped parameter models for the boundary conditions. The suggested model has already been successfully applied to haemodynamics in arteries and is now extended for the flow in collapsible tubes such as veins. The main difference with cardiovascular simulations is that the flow may become supercritical and elastic jumps may appear with the numerical consequence that scheme may not remain monotone if no limiting procedure is introduced. We show that our second-order RK-DG method equipped with an approximate Roe's Riemann solver and a slope-limiting procedure allows us to capture elastic jumps accurately. Moreover, this paper demonstrates that the complex physics associated with such flows is more accurately modelled than with traditional methods such as finite difference methods or finite volumes. We present various benchmark problems that show the flexibility and applicability of the numerical method. Our solutions are compared with analytical solutions when they are available and with solutions obtained using other numerical methods. Finally, to illustrate the clinical interest, we study the emptying process in a calf vein squeezed by contracting skeletal muscle in a normal and pathological subject. We compare our results with experimental simulations and discuss the sensitivity to parameters of our model. [ABSTRACT FROM AUTHOR]

The pre-processing stage of finite element analysis of the Navier–Stokes equations is becoming increasingly important as the desire for more general boundary conditions, as well as applications to parallel computers increases. The set up of general boundary conditions and communication structures for parallel computations should be accomplished during the pre-processing phase of the analysis, if possible, to ensure efficient computations for large scale problems in computational fluid dynamics. This paper introduces a general methodology for geometry based boundary condition application and pre-computing of parallel communication tasks. [ABSTRACT FROM AUTHOR]

This paper reviews the usual open boundary conditions (OBCs) for coastal ocean models and proposes a complete set of open boundaries based on stability criteria, on mass and energy conservation arguments, and on the ability to enforce external information. This set includes a radiation condition for barotropic variables, an equation of wave propagation for baroclinic velocities, and an advection equation for tracers. Considerations on mass and energy conservation properties suggest a suitable numerical treatment of the barotropic scheme, which is different from what is commonly used. Restoring terms, when classically added in the Sommerfeld OBCs, are not consistent with external fields. It is shown that this can be avoided if proper numerical schemes are used or if OBCs are applied on differences between the model and forcing rather than on absolute variables. Finally, this paper shows that simplistic advection-type methods for temperature and salinity should not be used in sigma coordinate models because this introduces errors in the computation of the horizontal pressure gradient. [ABSTRACT FROM AUTHOR]

The effects of surface texture on the lubrication performance of a compression ring-cylinder liner system are studied in this paper. By considering the surface roughness of the compression ring and cylinder liner, a mixed lubrication model is presented to investigate the tribological behaviors of a barrel-shaped compression ring-cylinder liner system with spherical dimples on the liner. In order to determine the rupture and reformulation positions of fluid film accurately, the Jacoboson-Floberg-Olsson (JFO) cavitation boundary condition is applied to the mixed lubrication model for ensuring the mass-conservative law. On this basis, the minimum oil film thickness and average friction forces in the compression ring-cylinder liner system are investigated under the engine-like conditions by changing the dimple area density, radius, and depth. The wear load, average friction forces, and power loss of the compression ring-cylinder liner system with and without dimples are also compared for different compression ring face profiles. The results show that the spherical dimples can produce a larger reduction of friction in mixed lubrication region, and reduce power loss significantly in the middle of the strokes. In addition, higher reduction percentages of average friction forces and wear are obtained for smaller crown height or larger axial width. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we present an immersed boundary method for solving fluid flow problems in the presence of static and moving rigid objects. A FEM is used starting from a base mesh that does not represent exactly rigid objects (non-body-conforming mesh). At each time step, the base mesh is locally modified to provide a new mesh fitting the boundary of the rigid objects. The mesh is also locally improved using edge swapping to enhance the quality of the elements. The Navier-Stokes equations are then solved on this new mesh. The velocity of moving objects is imposed through standard Dirichlet boundary conditions. We consider a number of test problems and compare the numerical solutions with those obtained on classical body-fitted meshes whenever possible. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the fuel spray behavior and variation of the spray characteristics under different injection pressures in internal combustion engines. In diesel engines the fuel spray is affected by the cavitation phenomenon which occurs in the injector orifice. The cavitation is one of the important phenomena which has a significant effect on the fuel spray characteristics. In this paper, for a specified geometry of the nozzle and the combustion chamber, the effect of the cavitation phenomenon on the spray characteristics, i.e. spray penetration length, the Sauter main diameter and evaporation are studied numerically for different values of the injection pressures. High injection pressure causes high velocity of the fuel in the injector orifice which leads to an effective atomization process with small and dispersed fuel droplets. The fluid flow equations are calculated in the combustion chamber to obtain the spray model. Since it is known that, high injection pressure together with low discharge pressure leads to creation of cavitation phenomenon inside the injector orifice, then for having cavitation phenomenon inside the injector orifice and consequently for investigating the cavitation phenomenon effects on the spray characteristics, the injection pressure values of 10–150MPa are considered while the discharge pressure remains constant. The injector and combustion chamber are simulated in separated regions and the results of the outlet of the nozzle are used as the boundary conditions for solving the fuel flow inside the combustion chamber to achieve the spray simulation. The results of this study show that by increasing the injection pressure, the value of the spray penetration length increases and the Sauter main diameter decreases for constant discharge pressure. The Hydraulic Flip phenomenon occurs after the injection pressure of 120MPa on the base of the results of this work. [Copyright &y& Elsevier]

Two-dimensional numerical simulations are carried out to examine the problem of transient electroconvection stability of dielectric liquids subjected to unipolar injection. The entire set of electrohydrodynamics equations associated with the electroconvective phenomena that occur in a layer of a dielectric liquid between two parallel electrodes subjected to a potential difference are solved numerically. We first validate the numerical simulation by comparing our linear stability electroconvection criteria with those obtained by other authors with a stability approach. In this paper, we restrict the study to the strong injection case, which corresponds to values of the non-dimensional injection parameter C greater than or equal to 10. The numerical solution of the electroconvective problem is then presented for rigid lateral boundary conditions. A detailed analysis of the scenario that occurs for different characteristic values of the stability parameter T is provided. The flow structure and its behaviour highlight the existence of different regimes, from laminar to chaotic. The development of charged plumes has been observed in particular. We compute the electrical Nusselt number for different values of the stability parameter and ion mobility. The electrical Nusselt number saturates with increasing T, a fact that it is in agreement with available experimental data. Finally, a spectral analysis is conducted for different aspect ratios of the computational domain. The spectral analysis gives an insight into the physical origin of the velocity and current oscillations. [ABSTRACT FROM AUTHOR]

Abstract: This work concerns the simulation of compressible multi-material fluid flows and follows the method FVCF-NIP described in the former paper (Braeunig et al., 2009 ). This cell-centered finite volume method is totally Eulerian since the mesh is not moving and a sharp interface, separating two materials, evolves through the grid. A sliding boundary condition is enforced at the interface, and mass, momentum and total energy are conserved. Although this former method performs well on 1D test cases, the interface reconstruction suffers of poor accuracy in conserving shapes for instance in linear advection. This situation leads to spurious instabilities of the interface. The Enhanced-NIP method presented in the present paper provides a solution to an inconsistency in the former NIP method. This solution strikingly improves the numerical results. It takes advantage of a more consistent description of the interface in the numerical scheme. Results for linear advection and compressible Euler equations for inviscid fluids are presented to assess the benefits of this new method. [Copyright &y& Elsevier]

Motivated by the reservoir engineering concept of the well productivity index (PI) we study a time dependent functional for general nonlinear Forchheimer equation. The PI of the well characterizes the well capacity with respect to drainage area of the well. Unlike the linear case for which this concept is well developed, there are only a few recent publications dedicated to the PI for nonlinear case. In this paper the PI is comprehensively studied both theoretically and numerically. The impact of the nonlinearity of the flow filtration on the value of the PI is analyzed. Exact formula for the so called 'skin factor' in radial case is derived depending on the rate of the flow, the order of nonlinearity and the geometric parameters. Dynamics of the PI for the class of boundary conditions is studied and its convergence to the specific value of steady state PI was justified. Developed framework is applied to obtain nonlinear analog of Peaceman formula for the well-block pressure in unstructured grid. Numerical simulations sustain theoretical results. [ABSTRACT FROM AUTHOR]

A series of two- and three-dimensional stationary problems of a viscous incompressible fluid flow in a channel caused by a given pressure differential is studied in the paper. It is shown that the solution to this problem is not unique. A numerical method allowing one to obtain the solution without specifying additional conditions for the velocity components on the boundary is considered. [ABSTRACT FROM AUTHOR]

Abstract: We prove existence of weak solutions to the compressible Navier‐Stokes system in barotropic regime (adiabatic coefficient γ > 3 / 2, in three dimensions, γ > 1 in two dimensions) with large velocity prescribed at the boundary and large density prescribed at the inflow boundary of a bounded Lipschitz piecewise regular domain, without any restriction neither on the shape of the inflow/outflow boundaries nor on the shape of the domain. The result applies also to pressure laws that are non‐monotone on a compact portion of the interval [0, ∞). [ABSTRACT FROM AUTHOR]

The contribution of this paper is twofold. Firstly, moving from the very well-known dual-weighted residual (DWR) method, we set up a theoretical framework for a goal-oriented a posteriori analysis of nonlinear partial differential equations accounting for different approximations of the primal and dual problems; nonhomogeneous Dirichlet boundary conditions, even different on passing from the primal to the dual problem; the error due to data approximation; and the effect of a possible stabilization. Secondly, moving from this framework and employing anisotropic interpolation error estimates, a sound anisotropic mesh adaption procedure is devised for the numerical approximation of the Navier-Stokes equations by continuous piecewise linear finite elements. The resulting adaptive procedure is thoroughly addressed and validated on some relevant test cases. [ABSTRACT FROM AUTHOR]

In this paper, we give a global existence theorem of weak solutions to model equations governing interaction fluid structure in a two-dimensional layer, cf. Refs. 8 and 14. To our knowledge this is the first existence theorem of global in time solutions for such model. The interest of our result is double because, first, we change the original initial value problem by deleting one initial condition, second, we construct a solution through the classical Galerkin method for which several computing codes have been constructed. [ABSTRACT FROM AUTHOR]

Metastable behaviour, which refers to an asymptotically exponentially slow time dependent motion to the limiting steady‐state solution, is often associated with certain exponentially ill‐conditioned singularly perturbed problems. As a result of this severe ill‐conditioning, little is known concerning the convergence and stability of the numerical schemes that compute metastable behaviour. In this paper, a rigorous uniform convergence analysis is given for several finite difference schemes applied to a boundary layer resonance problem, which is the simplest linear exponentially ill‐conditioned boundary value problem (BVP). It is found that the numerical computation of this problem does not cause any more difficulties than other standard singular perturbation problems, provided that we can use sufficiently high precision arithmetic. The qualitative results from the detailed study of this specific problem are shown numerically also to be valid for other exponentially ill‐conditioned BVPs and their corresponding time‐dependent equations. [ABSTRACT FROM PUBLISHER]

This paper addresses a general analytical method of superposition for the study of two-dimensional creeping flows in a wedge-shaped cavity a≤r≤b, ∣Θ∣≤Θ0 caused by tangential velocities of its curved walls. The method is illustrated by several numerical examples; the rate of convergence and the accuracy of fulfilling the boundary conditions are investigated. The main objective is to demonstrate the advantages of the method of superposition when analysing streamline patterns and the velocity-field distribution in the whole domain, including the Moffatt eddies near corner points. The equations for the positions of the stagnation and separation points are written analytically. The streamline patterns for uniform velocities at the top and the bottom walls are shown graphically. These patterns represent the transition from the corner eddies into internal eddies. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a ghost fluid (GF) method is utilized to propose a numerical approach to enhance the capability of thermal lattice Boltzmann method (TLBM) in dealing with complex geometries. A ghost fluid approach is imposed on a double-population thermal lattice Boltzmann method. A Cartesian grid handles the flow and the boundaries are imposed by a ghost fluid approach. The essence of this method is to decompose the unknown distribution functions into equilibrium and non-equilibrium parts at each ghost points. The major quantities are extrapolated from the image points to the corresponding ghost points to form the equilibrium parts. The non- equilibrium parts are then determined by using the bounce-back scheme. The method is relatively easy to apply, and second order accurate. There is no need to modify the original governing equations, and both Dirichlet and Neumann boundary conditions can be handled. The method is applied to Couette flow between two concentric circular cylinders, natural convection in a square cavity, natural convection in an annulus, and a forced convection in a lid-driven semi-circular cavity. The results obtained are generally in good agreement with that predicted by other theoretical and numerical efforts. [Copyright &y& Elsevier]

Abstract: The stability of stationary or rotating cylindrical shells interacting with a rotating internal fluid flow is studied. The paper presents the results of the finite element solutions for shells having different linear dimensions and subjected to various boundary conditions. It has been found that the form of stability loss in the stationary and rotating shells under the action of the fluid flow, having both the axial and circumferential components, depends on the type of the boundary conditions specified at their ends. It has been shown that for different variants of boundary conditions and different geometrical dimensions rotation of the fluid in a stationary shell or co-rotation of the shell and the fluid may increase or decrease the critical velocity of the axial fluid flow. [Copyright &y& Elsevier]

Abstract: This paper proposes a coupled fluid layer–foundation–poroelastic half-space vibration model to study how still water affects foundations operating underwater. As an example, we consider the problem of the vertical vibration of a rigid disk on a poroelastic half-space covered by a fluid layer having a finite depth. The solution of the disk vibration problem is obtained using the boundary conditions at the free surface of the fluid layer and the boundary conditions at the fluid layer–poroelastic medium interface. The solution is expressed in terms of dual integral equations that are converted into Fredholm integral equations of the second kind and solved numerically. Selected numerical results for the vertical dynamic impedance coefficient are examined based on different water depths, poroelastic materials, disk permeabilities and frequencies of excitation. Based on the numerical results, it is proposed that the hydrodynamic pressure caused by the foundation vibration is the intrinsic reason that the existence of a fluid layer has such a great effect on the dynamic characteristics of the foundation. In many cases, the hydrodynamic pressure caused by the foundation vibration cannot be ignored when designing dynamic underwater foundations. These results are helpful in understanding the dynamic response of foundations under still water without water waves, such as foundations in pools, lakes and reservoirs. [Copyright &y& Elsevier]

Abstract: This paper demonstrates the effectiveness of a high-resolution numerical scheme in boundary-fitted curvilinear coordinates for simulation of flow at channel bends. Two-dimensional shallow water equations, which are transformed from physical domain to computational domain, are solved by a robust high-resolution scheme particularly developed for boundary-fitted curvilinear coordinates. Finite-volume method is adopted for discretization of governing equations in computational domain. Turbulence shear stresses are included in the model by eddy-viscosity approach. Moreover, the effect of secondary flow, which is significant in channel bends, has been included in the model and the results have been compared with the results achieved by neglecting this phenomenon. Secondary flow intensity is evaluated by an analytical approach; the deviation of bed shear stress from main flow is related to secondary flow intensity and is considered in the model as well. All numerical results are compared with experimental data and they show satisfactory agreement. [Copyright &y& Elsevier]

Abstract: This research is motivated by the recent work which has presented a new loosely-coupled partitioned algorithm for fluid–structure interaction (FSI) [R. Jaiman, P. Geubelle, E. Loth, X. Jiao, Combined interface boundary condition method for unsteady fluid–structure interaction, Comput. Methods Appl. Mech. Engrg. 200 (2011) 27–39]. The loosely-coupled partitioned algorithm is intrinsically exposed to the notorious time lag effect whose remedy promotes the combined interface boundary condition (CIBC) method. In this method, correction terms for velocity and traction are introduced at two sequential time steps with a coupling parameter ω that plays an important part in the stability and accuracy of the coupled system. The structural traction ratio that appears explicitly in the traction correction is estimated based on the solution of the structural subsystem. This handling asks for the structural traction before it is corrected by the CIBC method. In this paper, a new formulation for the CIBC method is developed to repair the aforementioned inconvenience. After simple manipulation, the structural traction ratio is removed in constructing the traction correction. Therefore the structural traction is no more needed in CIBC correction terms. Meantime the ratio ω/Δt is employed to tune the interfacial corrections instead of the coupling parameter ω. An arbitrary Lagrangian–Eulerian finite element method is used to analyze FSI. The characteristic-based split (CBS) scheme is employed to solve incompressible Navier–Stokes equations while the equation for rigid-body dynamics is solved by Newmark-β method. A numerical technique called moving submesh approach is performed for the mesh deformation. For respecting geometric conservation law, a mass source term is implanted into the CBS scheme on the moving mesh. Several numerical examples are tested to validate the proposed methodology for fluid–rigid body interaction. The obtained results are in agreement with the existing data and some famous features of flow phenomena have been detected successfully. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the shape reconstruction of a bounded domain with a viscous incompressible fluid driven by the Oseen equations. For the approximate solution of the ill-posed and nonlinear problem we propose a regularized Gauss–Newton method. A theoretical foundation for the method is given by establishing the differentiability of the boundary value problem with respect to the boundary in the sense of the domain derivative. The results of several numerical experiments show that our theory is useful for practical purpose, and the proposed algorithm is feasible. [Copyright &y& Elsevier]

Abstract: In this paper, firstly, the applicability of the differential quadrature method (DQM) as an efficient and accurate numerical method for solving the problem of variable viscosity and thermally radiative unsteady magneto-hydrodynamic (MHD) flow over a moving vertical plate with suction and heat flux is investigated. The spatial as well as the temporal domains are discretized using the DQM. The fast rate of convergence of the method is demonstrated and for the cases that a solution is available, comparison is done. Then, effects of the temperature dependence of viscosity and different fluid parameters on the velocity and temperature of transient MHD flow subjected to the above mentioned boundary condition are studied. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the numerical solution of the equations governing two-phase gas–solid mixture in the framework of thermodynamically compatible systems theory. The equations constitute a non-homogeneous system of nonlinear hyperbolic conservation laws. A total variation diminishing (TVD) slope limiter centre (SLIC) numerical scheme, based on the splitting approach, is presented and applied for the solution of the initial-boundary value problem for the equations. The model equations and the numerical methods are systematically assessed through a series of numerical test cases. Strong numerical evidence shows that the model and the methods are accurate, robust and conservative. The model correctly describes the formations of shocks and rarefactions in two-phase gas–solid flow. [Copyright &y& Elsevier]

Abstract: In the present paper the natural frequencies of fluid-conveying pipes with pinned–pinned boundary condition are derived explicitly in a systematical and straightforward way with the help of homotopy perturbation method. Numerical results are presented for two cases and the effect of fluid flow velocity on the natural frequencies is discussed. Good agreement with their experimental and FEM counterparts is found numerically over ranges of practical interest. [Copyright &y& Elsevier]

Abstract: This paper reports an analytical and numerical study of natural convection in a shallow rectangular cavity filled with a micropolar fluid. Neumann boundary conditions for temperature are applied to the horizontal walls of the enclosure, while the two vertical ones are assumed insulated. The governing parameters for the problem are the thermal Rayleigh number, Ra, the Prandtl number, Pr, the aspect ratio of the cavity, A and various material parameter of the fluid. For convection in an infinite layer (), analytical solutions for the stream function temperature and angular velocity are obtained using a parallel flow approximation in the core region of the cavity and an integral form of the energy equation. The critical Rayleigh numbers for the onset of supercritical convection are predicted explicitly by the present model. Furthermore, a linear stability analysis is conducted yielding numerically the critical Rayleigh numbers for the onset of motion. Also, results are obtained from the analytical model for finite-amplitude convection for which the flow and heat transfer are presented in terms of the governing parameters of the problem. Numerical solutions of the full governing equations are obtained for a wide range of the governing parameters. A good agreement is observed between the analytical model and the numerical simulations. The influence of the material parameters on the flow and heat transfer is demonstrated to be significant. [Copyright &y& Elsevier]

Abstract: In this paper we consider the numerical solution of the interaction of an incompressible fluid and an elastic structure in a truncated computational domain. As well known, in this case there is the problem of prescribing realistic boundary data on the artificial sections, when only partial data are available. This problem has been investigated extensively for the rigid case. In this work we start considering the compliant case, by focusing on the flow rate conditions for the fluid. We propose three formulations of this problem, different algorithms for its numerical solution and carry out several 2D numerical simulations with the aim of comparing the performances of the different algorithms. [Copyright &y& Elsevier]

Abstract: In this article, the effect of dissipation on local and global stability of fluid conveying pipes is analyzed. The local approach refers to an infinite medium and uses wave propagation analyses without taking boundary conditions into account. The global approach refers to the same medium, but with finite length and associated with a given set of boundary conditions. The finite length system is generally studied by calculating its eigenmodes and eigenfrequencies. Criteria for local instability are derived in the first part of this paper, and dissipation is found to significantly affect local stability. Moreover, dissipation is found to have a stabilizing or destabilizing effect, depending on the other parameters. Next, numerical computations are presented for finite-length systems and results are analyzed and compared with local stability properties of the corresponding media. When the system is sufficiently long, it is found that critical velocity for global instability tends to a local criterion which can be that of local stability of the damped medium or a local transition criterion of the undamped medium, which is not necessarily the local instability criterion. Finally, a reasoning based on lengthscale ratios is developed. It allows to know which criterion is able to predict the global stability for long systems. [Copyright &y& Elsevier]

Abstract: In this paper, a new numerical approach, based on mortar discretization of interface fields, is proposed to solve lubricated contact problems between deformable solid bodies. The Reynolds approximation to the thin film fluid equations is used to describe the fluid behavior on the interface, while the equations of small strain elasticity (to which finite elements are applied) are assumed to govern the solid body behavior. The result of this approach is a monolithic scheme in which the fluid and solid mechanics are solved simultaneously, without the need for iterative or staggered approaches between the fluid and solid phases. Key features of the approach are that the fluid film thickness, directly related to the deformation of the solid phase, is computed from a least squares projection based on dual basis functions (as pioneered by Wohlmuth [B.I. Wohlmuth, Discretization Methods and Iterative Solvers Based on Domain Decomposition, Springer-Verlag, Heidelberg, 2001]). The free boundary problem for the fluid phase, corresponding to the boundary between lubricated and cavitated regions, is regularized with a penalty method and thus resolved as part of the solution. Several numerical examples are given to demonstrate the approach. [Copyright &y& Elsevier]

Abstract: The elastic buckling stresses of channel sections with and without lips and subject to shear forces parallel with the web are determined, where computational modelling of the thin-walled steel sections is implemented by means of a spline finite strip analysis. Both unlipped and lipped channels are studied, where the main variables are flange width, different boundary conditions and shear flow distribution. The channel sections are also analysed at different lengths, to investigate the effect of length/width ratio on the critical shear buckling stresses. Comparisons between cases and with classical solutions are included in this paper. [Copyright &y& Elsevier]

The paper presents a method to increase the computational accuracy by preserving additional constraints on the numerical solution. The new technique can noticeably increase the precision of a standard finite-volume flow solver by a modification to the flux computation procedure without changing its essential features. The efficiency of this method is demonstrated by application to the prediction of sound from high-speed helicopter blades. Several open domain boundary conditions for this application are also developed and compared for a model problem of a two-dimensional transonic aerofoil in an unsteady free stream. [ABSTRACT FROM AUTHOR]

Abstract: The hydrodynamic models that have recently been developed to investigate the nature of flow around coherent, rigid inclusions in simple shear reveal two contrasting patterns with eye-shaped and bow-tie shaped separatrix, even though all the models are based on Navier–Stokes law. In order to find the cause of this variance, this paper reviews the existing models in the light of different boundary conditions imposed on individual models. Scrutiny of the models reveals that inclusion–matrix systems, when considered infinitely extended in space, develop eye-shaped flows. However, those with finite dimensions essentially display bow-tie shaped flows. Using a finite element method (FEM), we advance the study to show the additional effects of model/inclusion dimension ratio (D R) and model aspect ratio (A R) under different boundary conditions. In the flow with bow-tie shaped separatrix, the regions of back flow define a nearly semi-circular geometry when D R is low (<2). These regions assume a semi-elliptical shape with increasing D R. The distance of stagnation points from the inclusion is found to increase non-linearly with D R. Model results suggest that transformation of a flow with eye-shaped separatrix to that with bow-tie shaped separatrix can occur due to increasing A R under a specific boundary condition. Applying FEM results in geological situations thus requires the appropriate choice of dimensional parameters of the model as well as the kinematic conditions imposed at the model boundaries. [Copyright &y& Elsevier]

This paper investigates thermal-fluid transport phenomena in a laminar flow between a rotating bottom disk and a stationary upper disk, from whose center a circular jet is impinged on the heated horizontal bottom disk surface. Emphasis is placed on the effects of the Reynolds number, rotational velocity, and disk spacing on both the formations of velocity and thermal fields and the heat-transfer rate along the heated wall surface. The governing equations are discretized by means of a control volume technique and are numerically solved to determine the distributions of the velocity vector and fluid temperature under the appropriate boundary conditions. It is found from the study that (i) the recirculation zone which appears on the stationary disk moves along the outward direction with an increase in the Reynolds number, (ii) when the Reynolds number is increased, heat transfer performance is intensified over the whole disk surface and the minimum value of the heat-transfer rate moves in the downstream direction, and (iii) the heat-transfer rate is induced due to the disk rotation, whose effect becomes larger in the wider disk spacing. [ABSTRACT FROM AUTHOR]

This paper introduces an augmented Lagrangian method for the imposition of a given flowrate in the numerical simulation of problems where no a priori knowledge of the velocity profile at the inlet of the domain is available. This method can be seen as a convenient way to generate boundary conditions consistent with the Navier-Stokes equations when only the flowrate is known. The theoretical formulation of the problem and a numerical algorithm are presented. The efficiency of the proposed method is verified by numerical simulations. [ABSTRACT FROM AUTHOR]

We consider the generalized Forchheimer flows for slightly compressible fluids. Using Muskat's and Ward's general form of Forchheimer equations, we describe the fluid dynamics by a nonlinear degenerate parabolic equation for the density. We study Galerkin finite elements method for the initial boundary value problem. The existence and uniqueness of the approximation are proved. A prior estimates for the solutions in [ABSTRACT FROM AUTHOR]

Animation techniques for controlling liquid simulation are challenging: they commonly require carefully setting initial and boundary conditions or performing a costly numerical optimization scheme against user-provided keyframes or animation sequences. Either way, the whole process is laborious and computationally expensive. We introduce a novel method to provide intuitive and interactive control of liquid simulation. Our method enables a user to locally edit selected keyframes and automatically propagates the editing in a nearby temporal region using geometric deformation. We formulate our local editing techniques as a small-scale nonlinear optimization problem which can be solved interactively. With this uniformed formulation, we propose three editing metaphors, including (i) sketching local fluid features using a few user strokes, (ii) dragging a local fluid region, and (iii) controlling a local shape with a small mesh patch. Finally, we use the edited liquid animation to guide an offline high-resolution simulation to recover more surface details. We demonstrate the intuitiveness and efficacy of our method in various practical scenarios. [ABSTRACT FROM AUTHOR]

We present a direct raytracing method for implicitly described fluid surfaces that takes into account the effects of capillary solid coupling at the boundaries. The method is independent of the underlying fluid simulation method and solely based on distance fields. We make use of the closed-form solution of the meniscus shape at the fluid interface to achieve the effect of surface tension exerted by the solid object. The shape of the liquid at these boundaries is influenced by various physical properties such as the force of gravity and the affinity between the liquid and the solid material. We generate contact angles at the boundaries without the need for computationally intensive small-scale simulation. At render time, we combine the closed-form solution for a small-scale effect with the numerical solution of a large-scale simulation. Our method is applicable for any implicit representation of the fluid surface and does not require an explicit extraction of the surface geometry. Therefore, it is especially useful for particle-based simulations. Furthermore, the solution is guaranteed to yield the correct contact angle and, for certain scenarios, it delivers the entirely correct solution throughout the interface; even in general scenarios, it yields plausible results. As for an example, we implemented and tested the proposed method in the setting of a smoothed particle hydrodynamics (SPH) fluid simulation. [ABSTRACT FROM AUTHOR]

In this article, we have studied the flow and heat transfer in Sisko fluid with convective boundary condition over a non-isothermal stretching sheet. The flow is influenced by non-linearly stretching sheet in the presence of a uniform transverse magnetic field. The partial differential equations governing the problem have been reduced by similarity transformations into the ordinary differential equations. The transformed coupled ordinary differential equations are then solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting method. Effects of different parameters like power-law index , magnetic parameter , stretching parameter , generalized Prandtl number Pr and generalized Biot number are presented graphically. It is found that temperature profile increases with the increasing value of and whereas it decreases for . Numerical values of the skin-friction coefficient and local Nusselt number are tabulated at various physical situations. In addition, a comparison between the HAM and exact solutions is also made as a special case and excellent agreement between results enhance a confidence in the HAM results. [ABSTRACT FROM AUTHOR]

SUMMARY We present a computational method for solving the coupled problem of chemical transport in a fluid (blood) with binding/unbinding of the chemical to/from cellular (platelet) surfaces in contact with the fluid, and with transport of the chemical on the cellular surfaces. The overall framework is the augmented forcing point method (AFM) ( L. Yao and A.L. Fogelson, Simulations of chemical transport and reaction in a suspension of cells I: An augmented forcing point method for the stationary case, IJNMF (2012) 69, 1736-52.) for solving fluid-phase transport in a region outside of a collection of cells suspended in the fluid. We introduce a novel radial basis function-finite difference (RBF-FD) method to solve reaction-diffusion equations on the surface of each of a collection of 2D stationary platelets suspended in blood. Parametric RBFs are used to represent the geometry of the platelets and give accurate geometric information needed for the RBF-FD method. Symmetric Hermite-RBF interpolants are used for enforcing the boundary conditions on the fluid-phase chemical concentration, and their use removes a significant limitation of the original AFM. The efficacy of the new methods is shown through a series of numerical experiments; in particular, second-order convergence for the coupled problem is demonstrated. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]