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An effective multiscale treatment of turbulent reacting flows is presented with the use of a stabilized finite element formulation. The method proposed is developed based on the streamline-upwind/Petrov–Galerkin (SUPG) formulation, and includes discontinuity capturing in the form of a new generation “DRD” method, namely the “DRDJ” technique. The stabilized formulation is applied to finite-rate chemistry modelling based on mixture-fraction approaches with the so-called presumed-PDF technique. The turbulent combustion process is simulated for an aero-engine combustor configuration of RQL concept in non-premixed flame regime. The comparative analysis of the temperature and velocity fields demonstrate that the proposed SUPG+DRDJ formulation outperforms the stand-alone SUPG method. The improved accuracy is demonstrated in terms of the combustor overall performance, and the mechanisms involved in the distribution of the numerical diffusivity are also discussed. [ABSTRACT FROM AUTHOR]

The manuscript presents the results of the application of a numerical method to solve one-dimensional hyperbolic equations. These equations simulate the dynamics of liquid in a pipe with varying cross-sections. The equations are written in terms of pressure-head and discharge. Radial-basis functions and least-squares optimization are used for the numerical simulation. This numerical method is specialized for working with arbitrary nodal distribution in the problem domain. The basics of the application of the numerical method were introduced in our previous work. In the current work, we updated previously applied methods by means of (1) getting rid of the time-marching approach and (2) applying a new adaptive refinement. Three cases of the simulations of the reservoir-pipe-valve system are described, indicating that the sharp time-gradient phenomenon is reproduced by the model. [ABSTRACT FROM AUTHOR]

Advanced mesh generation and update methods for parallel 3D computation of complex flow problems are presented. The complexities of the class of problems targeted include complex geometries, unsteady behavior, and moving boundaries and interfaces, such as those encountered in fluid-object interactions. Parallel 3D simulation of 1000 spheres falling in a liquid-filled tube, and other computations, are presented in this paper to demonstrate the challenges involved in this class of flow problems and the methods developed to address these challenges. [ABSTRACT FROM AUTHOR]

Elucidating the flow features around piles in local scouring processes is crucial for studies of local scouring mechanisms and scour depth estimates. This study details the flow turbulence characteristics of two submerged piles that are determined by solving the Navier-Stokes equations with the improved delayed detached eddy simulation model. This model is verified by comparing experimental and numerical results for hydrodynamic parameters with the literature for both square-crossing piles (SCPs) and circular-crossing piles (CCPs). Original topographies of flat and scoured beds (i.e., the initial and equilibrium scouring stages) are based on experimental results obtained by the authors in the present paper. SCP and CCP flow features in the scouring process are discussed. The results indicate that during the scouring process, the time-averaged drag coefficient and root mean square (rms) of the lift coefficient increase linearly in the CCP test, while the rms of the lift coefficient in the SCP test decreases linearly. Moreover, the minimum pressure coefficient is always located in the upstream corners in the SCP case but moves from 72.5° to 79.5° when the scour hole is completely developed in the CCP case. Downward flow behind the pile, which is generated by separated boundary layers above the top face of the pile, can reach the sand bed and turn the separated shear layers into patches of small vortices in the near-wake regions. Thus, the high shear stress zones are mainly at the scour edges under scoured-bed conditions. [ABSTRACT FROM AUTHOR]

Coronary artery disease is the leading global cause of mortality and Fractional Flow Reserve (FFR) is widely regarded as the gold standard for assessing coronary artery stenosis severity. However, due to the limitations of invasive FFR measurements, there is a pressing need for a highly accurate virtual FFR calculation framework. Additionally, it’s essential to consider local haemodynamic factors such as time-averaged wall shear stress (TAWSS), which play a critical role in advancement of atherosclerosis. This study introduces an innovative FFR computation method that involves creating five patient-specific geometries from two-dimensional coronary angiography images and conducting numerical simulations using computational fluid dynamics with a three-element Windkessel model boundary condition at the outlet to predict haemodynamic distribution. Furthermore, four distinct boundary condition methodologies are applied to each geometry for comprehensive analysis. Several haemodynamic features, including velocity, pressure, TAWSS, and oscillatory shear index are investigated and compared for each case. Results show that models with average boundary conditions can predict FFR values accurately and observed errors between invasive FFR and virtual FFR are found to be less than 5%. [ABSTRACT FROM AUTHOR]

The article presents a study of a two-fluid turbulence model in the Comsol Multiphysics software package for the problem of a subsonic flow around the DSMA661 and NACA 4412 airfoils with angles of attack of 0 and 13.87 degrees, respectively. In this paper, the finite element method is used for the numerical implementation of the turbulence equations. To stabilize the discretized equations, stabilization by the Galerkin least squares method was used. The results obtained are compared with the results of other RANS, LES, DES models and experimental data. It is shown that in the case of continuous flow around the DSMA661 airfoil, the results of the two-fluid model are very close to the SST results and are in good agreement with the experimental data. When flowing around the NACA 4412 airfoil, flow separation occurs and a recirculation zone appears. It is shown that in such cases the two-fluid model gives more accurate results than other turbulence models. Implementation of the Comsol Multiphysics software package showed good convergence, stability, and high accuracy of the two-fluid turbulence model. [ABSTRACT FROM AUTHOR]

Stroke remains a global health concern, necessitating early prediction for effective management. Atherosclerosis-induced internal carotid and intra cranial stenosis contributes significantly to stroke risk. This study explores the relationship between blood pressure and stroke prediction, focusing on internal carotid artery (ICA) branches: middle cerebral artery (MCA), anterior cerebral artery (ACA), and their role in hemodynamics. Computational fluid dynamics (CFD) informed by the Windkessel model were employed to simulate patient-specific ICA models with introduced stenosis. Central to our investigation is the impact of stenosis on blood pressure, flow velocity, and flow rate across these branches, incorporating Fractional Flow Reserve (FFR) analysis. Results highlight differential sensitivities to blood pressure variations, with M1 branch showing high sensitivity, ACA moderate, and M2 minimal. Comparing blood pressure fluctuations between ICA and MCA revealed heightened sensitivity to potential reverse flow compared to ICA and ACA comparisons, emphasizing MCA's role. Blood flow adjustments due to stenosis demonstrated intricate compensatory mechanisms. FFR emerged as a robust predictor of stenosis severity, particularly in the M2 branch. In conclusion, this study provides comprehensive insights into hemodynamic complexities within major intracranial arteries, elucidating the significance of blood pressure variations, flow attributes, and FFR in stenosis contexts. Subject-specific data integration enhances model reliability, aiding stroke risk assessment and advancing cerebrovascular disease understanding. [ABSTRACT FROM AUTHOR]

In this work, a new global-in-time solution strategy for incompressible flow problems is presented, which highly exploits the pressure Schur complement (PSC) approach for the construction of a space–time multigrid algorithm. For linear problems like the incompressible Stokes equations discretized in space using an inf-sup-stable finite element pair, the fundamental idea is to block the linear systems of equations associated with individual time steps into a single all-at-once saddle point problem for all velocity and pressure unknowns. Then the pressure Schur complement can be used to eliminate the velocity fields and set up an implicitly defined linear system for all pressure variables only. This algebraic manipulation allows the construction of parallel-in-time preconditioners for the corresponding all-at-once Picard iteration by extending frequently used sequential PSC preconditioners in a straightforward manner. For the construction of efficient solution strategies, the so defined preconditioners are employed in a GMRES method and then embedded as a smoother into a space–time multigrid algorithm, where the computational complexity of the coarse grid problem highly depends on the coarsening strategy in space and/or time. While commonly used finite element intergrid transfer operators are used in space, tailor-made prolongation and restriction matrices in time are required due to a special treatment of the pressure variable in the underlying time discretization. The so defined all-at-once multigrid solver is extended to the solution of the nonlinear Navier–Stokes equations by using Newton's method for linearization of the global-in-time problem. In summary, the presented multigrid solution strategy only requires the efficient solution of time-dependent linear convection–diffusion–reaction equations and several independent Poisson-like problems. In order to demonstrate the potential of the proposed solution strategy for viscous fluid simulations with large time intervals, the convergence behavior is examined for various linear and nonlinear test cases. [ABSTRACT FROM AUTHOR]

With the advantages of biosafety and efficiency, increasing attention has been paid to the devices for gene and macromolecular drug delivery based on mechanoporation. The transient pore formation on the cell membrane allows cargo transportation when the membrane areal strain is beyond the critical pore value and below the lysis tension threshold. Based on this principle, we propose a method to apply the proper fluid stress on cells moving in a microchannel under the action of zero-net-mass-flux (ZNMF) jets. In this study, an immersed finite element method (IFEM) is adopted to simulate the interaction between the cells and the fluid fields so as to investigate the cell movement and deformation in this mechanoporation system. To evaluate the efficiency of the cargo delivery, a pore integral is defined as the mean pore rate when the cell passes through the jet region. By analyzing the effects of the parameters, including the pressure gradient along the microchannel, the jet amplitude, and the jet frequency, on the pore integrals, a group of optimized parameters for cargo delivery efficiency are obtained. Additionally, the stability and safety of this system are analyzed in detail. These results are helpful in designing the mechanoporation devices and improving their efficiency of drug delivery. [ABSTRACT FROM AUTHOR]

In this work, we propose and validate a new stabilized compressible flow finite element framework for the simulation of aerospace applications. The framework is comprised of the streamline upwind/Petrov–Galerkin (SUPG)-based Navier–Stokes equations for compressible flows, the weakly enforced essential boundary conditions that act as a wall function, and the entropy-based discontinuity-capturing equation that acts as a shock-capturing operator. The accuracy and robustness of the framework is tested for various Mach numbers ranging from low-subsonic to transonic flow regimes. The aerodynamic simulations are carried out for 2D and 3D validation cases of flow around the NACA 0012 airfoil, RAE 2822 airfoil, ONERA M6 wing, and NASA Common Research Model (CRM) aircraft. The pressure coefficients obtained from the simulations of all cases are compared with experimental data. The computational results show good agreement with the experimental findings and demonstrate the accuracy and effectiveness of the finite element framework presented in this work for the simulation of aircraft aerodynamics. [ABSTRACT FROM AUTHOR]

A numerical simulation method for parachute Fluid-Structure Interaction (FSI) problem using Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm is proposed. This method could be used in both coupling computation of parachute FSI and flow field analysis. Both flat circular parachute and conical parachute are modeled and simulated by this new method. Flow field characteristics at various angles of attack are further simulated for the conical parachute model. Comparison with the space-time FSI technique shows that this method also provides similar and reasonable results. [ABSTRACT FROM AUTHOR]

We consider the finite element (FE) approximation of the two dimensional shallow water equations (SWE) by considering discretizations in which both space and time are established using a stable FE method. Particularly, we consider the automatic variationally stable FE (AVS-FE) method, a type of discontinuous Petrov-Galerkin (DPG) method. The philosophy of the DPG method allows us to establish stable FE approximations as well as accurate a posteriori error estimators upon solution of a saddle point system of equations. The resulting error indicators allow us to employ mesh adaptive strategies and perform space-time mesh refinements, i.e., local time stepping. We establish a priori error estimates for the AVS-FE method and linearized SWE and perform numerical verifications to confirm corresponding asymptotic convergence behavior. In an effort to keep the computational cost low, we consider an alternative space-time approach in which the space-time domain is partitioned into finite sized space-time slices. Hence, we can perform adaptive mesh refinements on each individual slice to preset error tolerances as needed for a particular application. Numerical verifications comparing the two alternatives indicate the space-time slices are superior for simulations over long times, whereas the solutions are indistinguishable for short times. Multiple numerical verifications show the adaptive mesh refinement capabilities of the AVS-FE method, as well the application of the method to some commonly applied benchmarks for the SWE. [ABSTRACT FROM AUTHOR]

Flow simulation is a computational tool for exploring science and technology involving flow applications. It can provide cost-effective alternatives or complements to laboratory experiments, field tests and prototyping. Flow simulation relies heavily on high performance computing (HPC). We view HPC as having two major components. One is advanced algorithms capable of accurately simulating complex, real-world problems. The other is advanced computer hardware and networking with sufficient power, memory and bandwidth to execute those simulations. While HPC enables flow simulation, flow simulation motivates development of novel HPC techniques. This paper focuses on demonstrating that flow simulation has come a long way and is being applied to many complex, real-world problems in different fields of engineering and applied sciences, particularly in aerospace engineering and applied fluid mechanics. Flow simulation has come a long way because HPC has come a long way. This paper also provides a brief review of some of the recently-developed HPC methods and tools that has played a major role in bringing flow simulation where it is today. A number of 3D flow simulations are presented in this paper as examples of the level of computational capability reached with recent HPC methods and hardware. These examples are, flow around a fighter aircraft, flow around two trains passing in a tunnel, large ram-air parachutes, flow over hydraulic structures, contaminant dispersion in a model subway station, airflow past an automobile, multiple spheres falling in a liquid-filled tube, and dynamics of a paratrooper jumping from a cargo aircraft. [ABSTRACT FROM AUTHOR]

In this article, we present our investigation and comparison of the SUPG-stabilized finite element formulations for computation of viscous compressible flows based on the conservation and entropy variables. This article is a sequel to the one on inviscid compressible flows by Le Beau et al. (1992). For the conservation variables formulation, we use the SUPG stabilization technique introduced in Aliabadi and Tezduyar (1992), which is a modified version of the one described in Le Beau et al. (1992). The formulation based on the entropy variables is same as the one introduced in Hughes et al. (1986). The two formulations are tested on three different problems: adiabatic flat plate at Mach 2.5, Reynolds number 20,000; Mach 3 compression corner at Reynolds number 16,800; and Mach 6 NACA 0012 airfoil at Reynolds number 10,000. In all cases, we show that the results obtained with the two formulations are very close. This observation is the same as the one we had in Le Beau et al. (1992) for inviscid flows. [ABSTRACT FROM AUTHOR]

A finite difference simulation method for the time dependent viscous incompressible flow around a transversely and longitudinally oscillating circular cylinder at Reynolds numbers of Re=4×10 and 4×10 is presented. The Navier-Stokes equations in finite difference form are solved on a moving grid system, based on a time dependent coordinate transformation. Solution of the vortex street development behind the cylinder is obtained when the cylinder remains stationary and also when it is oscillating. Time eholution of the flow configuration is studied by means of stream lines, pressure contours and vorticity contours. The computer results predict the lock-in phenomenon which occurs when the oscillation frequency is close to the vortex shedding frequency in the transverse mode or around double the vortex shedding frequency in the longitudinal mode. The time dependent lift and drag coefficients are obtained by the integration of the pressure and shear forces around the body. The drag, lift and the displacement relations are also discussed. [ABSTRACT FROM AUTHOR]

Prediction of aerodynamic force is a crucial issue for parafoil canopy as the strong nonlinear fluid–structure interaction (FSI) between the flexible canopy material and flow field. Flight tests and wind tunnel experiments are difficult to analyze the aerodynamics of parafoil because of the limitation and difficulty of data measurement in an unknown environment. The objective of this study was to computationally derive the aerodynamic characteristics of parafoil, as an alternative to expensive and unrepeatable test regimes. Different from previous works that assume canopy structure as a rigid body and serve for the design of parafoil, this study focused on the precise dynamic modeling of parafoil based on FSI simulations. To investigate the aerodynamic performance of the full-scale canopy with stabilizers for better control, the strong coupling FSI simulations were performed using the incompressible computational fluid dynamics techniques. The highlight of this paper is to explore the effects of canopy inflation and trailing edge deflections on aerodynamic performance. Then the aerodynamic coefficients are identified by a linear regression method using the obtained database of high fidelity lift and drag forces. Furthermore, an accurate six-degree-of-freedom dynamic model of the parafoil system is implemented based on the estimated coefficients. Simulations are conducted to prove the dynamic stability of the model and the feasibility of trajectory tracking. At last, simulation results of basic motions are compared with airdrop testing data, which demonstrates that the established model is capable of accurately predicting the flight behaviors of the parafoil system. [ABSTRACT FROM AUTHOR]

Soil-based water filtering devices can be described by models of viscous flow in porous media coupled with an advection–diffusion–reaction system modelling the transport of distinct contaminant species within water, and being susceptible to adsorption in the medium that represents soil. Such models are analysed mathematically, and suitable numerical methods for their approximate solution are designed. The governing equations are the Navier–Stokes–Brinkman equations for the flow of the fluid through a porous medium coupled with a convection-diffusion equation for the transport of the contaminants plus a system of ordinary differential equations accounting for the degradation of the adsorption properties of each contaminant. These equations are written in meridional axisymmetric form and the corresponding weak formulation adopts a mixed-primal structure. A second-order, (axisymmetric) divergence-conforming discretisation of this problem is introduced and the solvability, stability, and spatio-temporal convergence of the numerical method are analysed. Some numerical examples illustrate the main features of the problem and the properties of the numerical scheme. [ABSTRACT FROM AUTHOR]

In this work, we set up a new, general, and computationally efficient way to tackle parametrized fluid flows modeled through unsteady Navier-Stokes equations defined on domains with variable shape, when relying on the reduced basis method. We easily describe a domain by flexible boundary parametrizations, and generate domain (and mesh) deformations by means of a solid extension, obtained by solving a harmonic extension or a linear elasticity problem. The proposed procedure is built over a two-stage reduction: (i) first, we construct a reduced basis approximation for the mesh motion problem, irrespective of the fluid flow problem we focus on; (ii) then, we generate a reduced basis approximation of the unsteady Navier-Stokes problem, relying on finite element snapshots evaluated over a set of reduced deformed configuration, and approximating both velocity and pressure fields simultaneously. To deal with unavoidable nonaffine parametric dependencies arising in both the mesh motion and the state problem, we apply a matrix version of the discrete empirical interpolation method, allowing treating a wide range of geometrical deformations in an efficient and purely algebraic way. The same strategy is used to perform hyper-reduction of nonlinear terms. To assess the numerical performances of the proposed technique, we address the solution of parametrized fluid flows where the parameters describe both the shape of the domain and relevant physical features. Complex flow patterns such as the ones appearing in a patient-specific carotid bifurcation are accurately approximated, as well as derived quantities of potential clinical interest. [ABSTRACT FROM AUTHOR]

The space–time (ST) computational method "ST-SI-TC-IGA" has recently enabled computational analysis of tire aerodynamics with actual tire geometry, road contact and tire deformation. The core component of the ST-SI-TC-IGA is the ST Variational Multiscale (ST-VMS) method, and the other key components are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and the ST Isogeometric Analysis (ST-IGA). These ST methods played their parts in overcoming the computational challenges, including (i) the complexity of an actual tire geometry with longitudinal and transverse grooves, (ii) the spin of the tire, (iii) maintaining accurate representation of the boundary layers near the tire while being able to deal with the flow-domain topology change created by the road contact, and (iv) the turbulent nature of the flow. The combination of the ST-VMS, ST-SI and the ST-IGA has also recently enabled solution of fluid film problems with a computational cost comparable to that of the Reynolds-equation model for the comparable solution quality. This was accomplished with the computational flexibility to go beyond the limitations of the Reynolds-equation model. Here we include and address the computational challenges associated with the road roughness and the fluid film between the tire and the road. The new methods we add to accomplish that include a remedy for the trapped fluid, a method for reducing the number of control points as a space occupied by the fluid shrinks down to a narrow gap, and a method for representing the road roughness. We present computations for a 2D test problem with a straight channel, a simple 2D model of the tire, and a 3D model with actual tire geometry and road roughness. The computations show the effectiveness of our integrated set of ST methods targeting tire aerodynamics. [ABSTRACT FROM AUTHOR]

The numerical results of studying the impact of an axisymmetric liquid jet upon a flat rigid wall covered by a layer of similar liquid are presented. Primary attention is paid to the effect the layer thickness on the wall has on loading in the range of impact velocities 150–350 m/s. The loading character is studied, and the estimations of wall pressure are obtained in the case of a small layer thickness, which are topical for the applications associated with the droplet and cavitation erosion. It is shown that under the conditions considered the known results of two-dimensional modeling overestimate the maximum of the average pressure on the wall by 1.8 times. [ABSTRACT FROM AUTHOR]

We discuss methods to compute the flow of non-Brownian, non-cohesive, and non-spherical rigid bodies immersed in a single homogeneous fluid. We address both the case of negligible effect of the surrounding fluid corresponding to dry granular flows in which the dynamics of rigid bodies is controlled by gravity and collisions only, and the case of non-negligible effect of the surrounding fluid in which rigid bodies not only exchange momentum by collisions but also by two-way coupling with the surrounding fluid flow. We review the common computational methods to compute rigid body collisions and the two-way interaction of rigid bodies with the surrounding fluid flow. We specifically discuss the extension or applicability of these methods to non-spherical rigid bodies. [ABSTRACT FROM AUTHOR]

This paper aims to discuss the boundary conditions techniques employed in the solution of physical and engineering problems using the Lagrangian particle approach in continuum mechanics. Simulations using different boundary treatment techniques have been performed, and in addition, a review of the literature on the techniques commonly employed in SPH simulations was also performed. The fictitious (virtual/ghost), the dynamic particles and the artificial repulsive forces are widely employed in problem-solving, mixing concepts of molecular and continuum scales, being inadequate for the use in continuum scale (considering the disrespect of the classical physics laws). On the other hand, the reflective boundary conditions, based on fundamentals of Physics (Newton's restitution law) and analytic geometry, are in accordance with the continuum hypothesis and their use is recommended in continuum mechanics problems, out of the molecular scale. In many boundary conditions employed in particle methods, models of repulsive molecular forces in conjunction with virtual particles are being used without theoretical foundation in continuum mechanics and classical Physics. Purely computational solutions employing fictitious particles and artificial molecular forces should be avoided, and methods that respect the continuum theory, such as the reflective boundary conditions, should be employed on the macroscopic scale. Both hydrostatic and hydrodynamics analysis have been performed. An excellent agreement with the analytical solution or experimental results have been achieved. From the results found, the applicability of the reflexive boundary technique in the continuum domain, discretized by particles, was verified. [ABSTRACT FROM AUTHOR]

Superhydrophobic surfaces (SHSs) are widely reported and applied to modify flow features. In this work, the two-dimensional flows past a rotating circular cylinder with SHSs are studied to explore its effect. The present numerical simulations take SHSs into account by alternating shear-free and no-slip boundary conditions with different gas fraction (GF) for non-dimensional rotation rates of 0≤α≤6 at Re=100. Numerical results indicate that SHSs can obviously modify the critical rotation rates of vortex shedding, frequency of vortex shedding, force acting on the cylinder as well as the instantaneous and mean velocities near the cylinder. Moreover, such variation exhibits diverse behaviors in different flow regimes. For instance, both drag enhancement and drag reduction are found in the presence of SHSs. For the rotation rate corresponding to a vortex shedding regime, the drag of cylinder is reduced by SHSs. On the contrary, SHSs enhance the drag of cylinder in the steady regime. SHSs play different roles in different flow regimes so that the first critical rotation rate decreases monotonically with the increase of GF, while the second and the third critical rotation rates increase monotonically with increasing GF. The effect of SHSs in such flow could have some potential application. [ABSTRACT FROM AUTHOR]

Abstract: Matrix-free conjugate gradient algorithms are described as applied to large systems of algebraic equations arising in the implementation of implicit schemes intended for problems in continuum mechanics. The algorithms are shown to reduce the computer memory requirements and provide a higher computer performance. Additional advantages include the robustness of the algorithms and the simplicity of their implementation and debugging. [ABSTRACT FROM AUTHOR]

In this study, the propagation of a pressure wave inside a tunnel due to explosion near the blast proof door is investigated. In addition, the peak pressures and its arrival time are measured experimentally. Trinitrotoluene of 12 kg was detonated in front of a 20 mm thick steel blast proof door. Based on the experimental data, a finite element analysis was performed to analyze the pressure wave propagation phenomena inside the tunnel. The experimental measurements with four peak pressures match up well with the finite element analysis results. Additionally, the finite element analysis clearly showed pressure wave propagation sequence inside the tunnel. As it is difficult to explain the pressure wave propagation phenomena through experimental results, the finite element analysis can be useful for supporting the complex analysis. [ABSTRACT FROM AUTHOR]

In this paper, we develop an energy dissipative numerical scheme for gradient flows of planar curves, such as the curvature flow and the elastic flow. Our study presents a general framework for solving such equations. To discretize the time variable, we use a similar approach to the discrete partial derivative method, which is a structure-preserving method for gradient flows of graphs. For the approximation of curves, we use B-spline curves. Owing to the smoothness of B-spline functions, we can directly address higher order derivatives. Moreover, since B-spline curves require few degrees of freedom, we can reduce the computational cost. In the last part of the paper, we present some numerical examples of the elastic flow, which exhibit topology-changing solutions and more complicated evolution. Videos illustrating our method are available on YouTube. [ABSTRACT FROM AUTHOR]

It has been almost automatically assumed for a quarter century that the numerical solution of hyperbolic conservation laws is best accomplished by making a reconstruction of the initial data that is only piecewise continuous. The effect of the discontinuities is taken into account by means of Riemann solvers. This strategy has enjoyed great practical success but introduces only one-dimensional physics as a guide to the discretization of multidimensional problems. This article points out some of the resulting defects and proposes an alternative viewpoint. The chief novelty of the new 'Active Flux' method, apart from the elimination of discontinuities, is the division into advective and acoustic disturbances, with acoustics being handled by exploiting classical solutions to the scalar wave equation. Results for a standard test problem for the compressible Euler equations indicate that an order of magnitude increase in cost effectiveness may be possible by following this approach, compared to the traditional one. [ABSTRACT FROM AUTHOR]

A new family of locking-free finite elements for shear deformable Reissner-Mindlin plates is presented. The elements are based on the 'tangential-displacement normal-normal-stress' formulation of elasticity. In this formulation, the bending moments are treated as separate unknowns. The degrees of freedom for the plate element are the nodal values of the deflection, tangential components of the rotations and normal-normal components of the bending strain. Contrary to other plate bending elements, no special treatment for the shear term such as reduced integration is necessary. The elements attain an optimal order of convergence. [ABSTRACT FROM AUTHOR]

A novel finite element discretization for nonlinear potential flow water waves is presented. Starting from Luke's Lagrangian formulation we prove that an appropriate finite element discretization preserves the Hamiltonian structure of the potential flow water wave equations, even on general time-dependent, deforming and unstructured meshes. For the time-integration we use a modified Störmer-Verlet method, since the Hamiltonian system is non-autonomous due to boundary surfaces with a prescribed motion, such as a wave maker. This results in a stable and accurate numerical discretization, even for large amplitude nonlinear water waves. The numerical algorithm is tested on various wave problems, including a comparison with experiments containing wave interactions resulting in a large amplitude splash. [ABSTRACT FROM AUTHOR]

We study a nonlinear fluid-structure interaction (FSI) problem between an incompressible, viscous fluid and a composite elastic structure consisting of two layers: a thin layer (membrane) in direct contact with the fluid, and a thick layer (3D linearly elastic structure) sitting on top of the thin layer. The coupling between the fluid and structure, and the coupling between the two structures is achieved via the kinematic and dynamic coupling conditions modeling no-slip and balance of forces, respectively. The coupling is evaluated at the moving fluid-structure interface with mass, i.e., the thin structure. To solve this nonlinear moving-boundary problem in 3D, a monolithic, fully implicit method was developed, and combined with an arbitrary Lagrangian-Eulerian approach to deal with the motion of the fluid domain. This class of problems and its generalizations are important in e.g., modeling FSI between blood flow and arterial walls, which are known to be composed of several different layers, each with different mechanical characteristics and thickness. By using this model we show how multi-layered structure of arterial walls influences the pressure wave propagation in arterial walls, and how the presence of atheroma and the presence of a vascular device called stent, influence intramural strain distribution throughout different layers of the arterial wall. The detailed intramural strain distribution provided by this model can be used in conjunction with ultrasound B-mode scans as a predictive tool for an early detection of atherosclerosis (Zahnd et al. in IEEE international on ultrasonics symposium (IUS), pp 1770-1773, 2011). [ABSTRACT FROM AUTHOR]

Impulse action of a cavitation bubble on a rigid wall is studied depending on the distance between them. We determine the distances at which the periphery pressure maximums on a wall are preserved as well as the distances at which these maximums exceed the water hammer pressure. [ABSTRACT FROM AUTHOR]

Flow in a convergent-divergent nozzle is studied for pressure ratios (NPR) of 1-11 and exit-to-throat area ratios of 1.2 to 2.0. The unsteady compressible Navier-Stokes equations along with the Spalart-Allmaras turbulence model are solved using a stabilized finite element method in two dimensions. Asymmetric flow is observed at moderate NPR. The side loads due to the flow asymmetry increase with increases in NPR and area ratio. Various flow regimes that are possible in the entire parameter space are identified. The introduction of boundary layer bleed results in steady and symmetric flow conditions at all NPR. Consequently, the nozzle does not experience a lateral force for any NPR. Application of bleed leads to a significant downstream shift in the shock location at low to moderate NPR. Compared to no-bleed, the nozzle experiences a loss of thrust in this regime. The thrust performance for $$\text {NPR} > 6$$ is, however, unaffected by bleed. The effect of nozzle geometry on the flow at various NPR is studied. Four different geometries with the same area ratio and nozzle length are considered. These geometries differ from each other in terms of the nozzle surface profile, including the discontinuity in slope of the surface. Barring some minor differences at low to moderate NPR, the flow is similar for all the geometries considered. [ABSTRACT FROM AUTHOR]

A reconstructed edge-based smoothed triangular element, which is incorporated with the discrete shear gap (DSG) method, is formulated based on the global coordinate for analysis of Reissner-Mindlin plates. A symbolic integration combined with the smoothing technique is implemented to calculate the smoothed finite element matrices, which is integrated along the boundaries of each smoothing cell. Numerical results show that the proposed element is free from shear locking, and its results are in good agreement with the exact solutions, even for very thin plates with extremely distorted elements. The proposed element gives more accurate results than the original DSG element without smoothing, and it can be taken as an alternative element for analysis of Reissner-Mindlin plates. The prominent feature of the present element is that the integration scheme is unified in the smoothed form for all of the finite element matrices. [ABSTRACT FROM AUTHOR]

The use of replacement heart valves continues to grow due to the increased prevalence of valvular heart disease resulting from an ageing population. Since bioprosthetic heart valves (BHVs) continue to be the preferred replacement valve, there continues to be a strong need to develop better and more reliable BHVs through and improved the general understanding of BHV failure mechanisms. The major technological hurdle for the lifespan of the BHV implant continues to be the durability of the constituent leaflet biomaterials, which if improved can lead to substantial clinical impact. In order to develop improved solutions for BHV biomaterials, it is critical to have a better understanding of the inherent biomechanical behaviors of the leaflet biomaterials, including chemical treatment technologies, the impact of repetitive mechanical loading, and the inherent failure modes. This review seeks to provide a comprehensive overview of these issues, with a focus on developing insight on the mechanisms of BHV function and failure. Additionally, this review provides a detailed summary of the computational biomechanical simulations that have been used to inform and develop a higher level of understanding of BHV tissues and their failure modes. Collectively, this information should serve as a tool not only to infer reliable and dependable prosthesis function, but also to instigate and facilitate the design of future bioprosthetic valves and clinically impact cardiology. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) is becoming more and more popular in various fields of engineering due to improvement of turbulence model and availability of high performance computing system. In bluff body and bridge aerodynamics fields CFD is applied to predict the aerodynamic response for reconfirming experimental results and revealing the flow mechanism. Accurate prediction of response largely depends on the accurate generation of grid system having converged solution. However, conventional grid convergence test takes much time to obtain the desired grid system. It becomes even worse for a beginner or user having lack of experience. In this paper, a strategy was proposed and demonstrated for faster generation of accurate and converged grid system for two-dimensional bluff bodies. First, the strategy was proposed and demonstrated by conducting simulation for a square rectangular cylinder at Reynolds number ( R ) of 1.22 × 10. An equation was derived to initialize the first grid height ( y) and a Growth Factor (GF) was recommended to expand the grid away from the target body to obtain a grid system having converged solution. The strategy was checked and examined by conducting standard grid convergence test and by comparing solution of various aerodynamic parameters with past experimental works. Finally, the strategy was applied for an elongated rectangular cylinder and for a streamlined bridge deck for further checking the performance of the strategy and found to be efficient enough for faster and quick generation of accurate and converged grid system. [ABSTRACT FROM AUTHOR]

This paper considers the numerical solution of time-dependent linear convection-diffusion-reaction equations. We shall employ combinations of streamline-upwind Petrov-Galerkin and local projection stabilization methods in space with the higher order variational time discretization schemes. In particular, we consider time discretizations by discontinuous Galerkin methods and continuous Galerkin-Petrov methods. Several numerical tests have been performed to assess the accuracy of combinations of spatial and temporal discretization schemes. Furthermore, the dependence of the results on the stabilization parameters of the spatial discretizations are discussed. In addition, the long-time behavior of overshoots and undershoots is studied. The efficient solution of the obtained systems of linear equations by GMRES methods with multigrid preconditioners will be investigated. [ABSTRACT FROM AUTHOR]

The natural permeability of geothermal reservoirs is low and needs to be enhanced to ensure an efficient use and economic viability. Next to chemical enhancement, the main technique used for that purpose is hydraulic fracturing. Here, hydraulic fracturing is introduced in a thermo-poroelastic framework. The main addition to this framework is a fracturing model, phrased in terms of Terzaghi's effective stress that governs the evolution of size and aperture of the fractures in all directions of space. At any geometrical point, a fracture-induced anisotropic permeability tensor is calculated: Next to the injection pressure and thermal shrinking, the directional properties of this tensor are strongly influenced by geological stresses. The fully integrated framework is henceforth used in simulating thermal recovery from enhanced geothermal reservoirs. Evidently, the credibility of the numerical simulations cannot be sufficiently trusted with large spurious wiggles in the temperature field and consequently in those of the effective stresses. This paper provides several approaches to stabilize convection of heat due to extreme injection conditions at early stages, sudden increase in permeability due to hydraulic fracturing, and near the production wells at late injection stages. Emphasis is paid to the subgrid scale/gradient subgrid scale method where the transient problem is placed into a stabilized advection-diffusion-reaction problem. [ABSTRACT FROM AUTHOR]

A stabilized finite element algorithm potential for wind-structure interaction (WSI) problem is presented in this paper. Streamline upwind Petrov-Galerkin (SUPG) scheme of the large eddy simulation (LES) of dynamic sub-grid scale (DSGS) is developed under the framework of arbitrary Lagrangian-Eulerian (ALE) description to solve the governing equations. High stabilization is achieved by a three-step technique in the temporal discretization. On the other hand, the partitioned procedure is employed for the consideration of the coupled WSI problem. Newmark integral method is introduced for the computation of structure domain, while spring analogy method is used for the grid update of the mesh domain. The developed computational codes are applied to the analysis of wind-induced effect of a spatial latticed structure. The numerical predictions of the three-dimensional wind flow features, the wind pressures and the wind-induced effect of spatial structures are given. Comparisons are made between the effects of rigid structure in view of the WSI. [ABSTRACT FROM AUTHOR]

Although drug-eluting stents (DES) have greatly reduced arterial restenosis, there are persistent concerns about stent thrombosis. DES thrombosis is attributable to retarded vascular re-endothelialization due to both stent-induced flow disturbance and the inhibition by the eluted drug of endothelial cell proliferation and migration. The present computational study aims to determine the effect of DES design on both stent-induced flow disturbance and the concentration of eluted drug at the arterial luminal surface. To this end, we consider three closed-cell stent designs that resemble certain commercial stents as well as three 'idealized' stents that provide insight into the impact of specific characteristics of stent design. To objectively compare the different stents, we introduce the Stent Penalty Index (SPI), a dimensionless quantity whose value increases with both the extent of flow disturbance and luminal drug concentration. Our results show that among the three closed-cell designs studied, wide cell designs lead to lower SPI and are thus expected to have a less adverse effect on vascular re-endothelialization. For the idealized stent designs, a spiral stent provides favorable SPI values, whereas an intertwined ring stent leads to an elevated SPI. The present findings shed light onto the effect of stent design on the concentration of the eluted drug at the arterial luminal surface, an important consideration in the assessment of DES performance. [ABSTRACT FROM AUTHOR]

Region partition (RP) is the key technique to the finite element parallel computing (FEPC), and its performance has a decisive influence on the entire process of analysis and computation. The performance evaluation index of RP method for the three-dimensional finite element model (FEM) has been given. By taking the electric field of aluminum reduction cell (ARC) as the research object, the performance of two classical RP methods, which are Al-NASRA and NGUYEN partition (ANP) algorithm and the multi-level partition (MLP) method, has been analyzed and compared. The comparison results indicate a sound performance of ANP algorithm, but to large-scale models, the computing time of ANP algorithm increases notably. This is because the ANP algorithm determines only one node based on the minimum weight and just adds the elements connected to the node into the sub-region during each iteration. To obtain the satisfied speed and the precision, an improved dynamic self-adaptive ANP (DSA-ANP) algorithm has been proposed. With consideration of model scale, complexity and sub-RP stage, the improved algorithm adaptively determines the number of nodes and selects those nodes with small enough weight, and then dynamically adds these connected elements. The proposed algorithm has been applied to the finite element analysis (FEA) of the electric field simulation of ARC. Compared with the traditional ANP algorithm, the computational efficiency of the proposed algorithm has been shortened approximately from 260 s to 13 s. This proves the superiority of the improved algorithm on computing time performance. [ABSTRACT FROM AUTHOR]