Arbitrary Lagrangian Eulerian Approach Research Articles

Performance of a TMD to Mitigate Wind-Induced Interference Effects between Two Industrial Chimneys

The present paper studies the performance of a tuned mass damper (TMD) installed in a 183 m tall chimney located at the edge of the wake shed by another chimney. Numerical and experimental results are available. For the simulations, wind action is considered by solving several 2D flow problems on a selected number of horizontal planes, in the transverse direction to the stacks. On such planes, Navier-Stokes equations are solved to estimate the fluid action at different positions of the chimneys and standard interpolation techniques are applied in the vertical direction. An Arbitrary Lagrangian-Eulerian (ALE) approach is used to consider the moving domain, and a fractional-step scheme is used to solve the fluid field. For the structural modelling, chimneys are meshed using 3D beam finite elements. The time integration procedure used for the structural dynamics is based on the standard second order Bossak method. For each period of time, the fluid problem is solved, the aeroelastic analysis is carried out and the geometry of the fluid mesh of each plane is updated according to the structural movements. With this procedure and model updating techniques, the response of the leeward chimney is evaluated for different scenarios, revealing an interesting dependence of the TMD performance on the wind speed and direction.

Finite-element modeling of vocal fold self-oscillations in interaction with vocal tract: Comparison of incompressible and compressible flow model

Finite-element modeling of self-sustained vocal fold oscillations during voice production has mostly considered the air as incompressible, due to numerical complexity. This study overcomes this limitation and studies the influence of air compressibility on phonatory pressures, flow and vocal fold vibratory characteristics. A two-dimensional finite-element model is used, which incorporates layered vocal fold structure, vocal fold collisions, large deformations of the vocal fold tissue, morphing the fluid mesh according to the vocal fold motion by the arbitrary Lagrangian-Eulerian approach and vocal tract model of Czech vowel [i:] based on data from magnetic resonance images. Unsteady viscous compressible or incompressible airflow is described by the Navier-Stokes equations. An explicit coupling scheme with separated solvers for structure and fluid domain was used for modeling the fluid-structure-acoustic interaction. Results of the simulations show clear differences in the glottal flow and vocal fold vibration waveforms between the incompressible and compressible fluid flow. These results provide the evidence on the existence of the coupling between the vocal tract acoustics and the glottal flow (Level 1 interactions), as well as between the vocal tract acoustics and the vocal fold vibrations (Level 2 interactions).

Fluid-structure interaction simulations with a LES filtering approach in solids4Foam

Abstract The goal of this paper is to test solids4Foam, the fluid-structure interaction (FSI) toolbox developed for foam-extend (a branch of OpenFOAM), and assess its flexibility in handling more complex flows. For this purpose, we consider the interaction of an incompressible fluid described by a Leray model with a hyperelastic structure modeled as a Saint Venant-Kirchho material. We focus on a strongly coupled, partitioned fluid-structure interaction (FSI) solver in a finite volume environment, combined with an arbitrary Lagrangian-Eulerian approach to deal with the motion of the fluid domain. For the implementation of the Leray model, which features a nonlinear differential low-pass filter, we adopt a three-step algorithm called Evolve-Filter-Relax. We validate our approach against numerical data available in the literature for the 3D cross flow past a cantilever beam at Reynolds number 100 and 400.

Lightweight protective configurations against blast and fragments impact: Experimental and numerical studies

Lightweight protective configurations against blast and fragment impacts were studied experimentally and numerically. The configurations comprised different combinations of Kevlar fabrics, laminated GFRP (Glass Fiber Reinforced Polyester), polyurethane (PU) foam, and alumina (Al2O3). The polyurethane (PU)–sand multi-layer composition and a mixture of polyurethane–sand and polyurethane–alumina powder were also studied. The protective configurations were tested under static detonation of a scaled down artillery shell. Protective capabilities were tested against a peak incident overpressure of 57 psi and fragments weighing up to 4.3 g carrying velocities in the range of 961 m/s–1555 m/s. Numerical simulations were performed using ANSYS AUTODYN. The coupled SPH (Smoothed Particle Hydrodynamics)–ALE (Arbitrary Lagrangian–Eulerian) approach was used to simulate the interaction of fragments with protective configurations. A coupled Euler–ALE approach was employed for blast wave loading on protective configurations. The Kevlar fabrics, laminated GFRP, and PU foam compositions provided significant absorption and attenuation to impacting fragments. Configurations employing alumina tile were able to withstand both blast and fragment impacts without significant backface signatures (blunt force trauma). The configurations can be employed as body armor, vehicle armor, and for the safety and security of other critical infrastructures against blast wave and high velocity fragment impact. Numerical simulation results are in fair agreement with experimental results.

Seismic risk assessment of liquid overtopping in a steel storage tank equipped with a single deck floating roof

Major earthquakes have demonstrated that Natech events can be triggered by liquid overtopping in liquid storage tanks equipped with floating roofs. Thus, research on the dynamic behaviour of steel storage tanks with floating roofs is still required. In this paper, the seismic risk against liquid overtopping in a real steel storage tank with a floating roof was analysed using a simplified model that was validated by a refined finite element model based on the arbitrary Lagrangian-Eulerian approach. The simplified model utilizes the Lagrangian of a floating roof-fluid system and is capable of providing a response history of the floating roof. It was demonstrated that it could predict the maximum vertical displacement very accurately, while some differences were observed in the response history of vertical displacement. The computational time for a single response history analysis based on the simplified model amounted to a few minutes, which is significantly less demanding compared to hours required for response history analysis in the case of the refined FE model. The simplified model is thus appropriate for the seismic fragility analysis considering the overtopping limit state. It is shown that the fragility curves are significantly affected by the liquid filling level. The risk for liquid overtopping is quite high in the case of a full tank. However, by considering the variation of filling level during the year, the overtopping risk was observed reduced by approximately 30%. Alternatively, the approximate fragility analysis for the liquid overtopping can be performed by utilizing the Eurocode formula for the vertical displacement of liquid. This approach is straightforward, but the formula does not account for the higher mode effects, which may result in overestimated seismic intensity causing overtopping, as discussed in the paper.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ МЕТОДИК МОДЕЛИРОВАНИЯ ПРОЦЕССА РЕЗАНИЯ С ИСПОЛЬЗОВАНИЕМ ПРОГРАММНЫХ СРЕДСТВ

The paper presents an analytical study for comparing different numerical methods used for the modeling of cutting process using finite element method. The aims of this study is to compare capabilities of FE software package (Deform, AdvantEdge, ANSYS Workbench and ABAQUS). The main stages of modeling are discussed, as well as well-known methods and approaches used for their implementation. Main formulations for description of motion of deformable materials are analyzed to Lagrangian approach, Eulerian approach, Arbitrary Lagrangian Eulerian (ALE) approach. Numerical techniques to model chip separation are grouped as geometrical and physical. In this paper two strategies for time integration, implicit and explicit schemes are reviewed. Various models of friction between the chip and the tool are discussed: Amonton-Coulomb's Law, Prandtl's Law and Zorev. In this work, modeling and simulation of cutting process is carried out by FEM software ABAQUS. As a result of modeling, the stress and strain fields for both the workpiece and the tool are presented, as well as the thermal field of the workpiece and the chip. The numerical results obtained are compared with the results have been carried out previously using software ANSYS Workbench. The numerical values of temperatures, stresses and deformations correspond to traditional concepts of the cutting process, as well as experimental data presented in open sources.

Cork Core Sandwich Plates for Blast Protection

A numerical model is developed and validated to analyse the performance of aluminium skin and agglomerated cork core sandwich plates subjected to blast loads. Two numerical approaches are used and thoroughly compared to generate the blast loading: an Arbitrary-Lagrangian–Eulerian approach and the Load Blast Enhanced method. Both of the models are validated by comparing the numerical results with experimental observations. A detailed analysis of the sandwich behaviour is done for both approaches showing small differences regarding the mechanical response of the sandwich structure. The results obtained from the numerical models uncover the specific energy absorption mechanisms happening within the sandwich plate components. A new core topology is proposed, based on these results, which maximises the energy absorption capacity of the plate, keeping the areal density unchanged. A wavy agglomerated cork core is proposed and the effects of different geometrical parameters on the energy absorption are thoroughly analysed and discussed. The proposed optimised plate configuration shows an increase in the total absorbed energy of close to 40% relative to a reference case with the same areal density. The adopted optimisation methodology can be applied to alternative configurations to increase the performance of sandwich structures under blast events.

Split form ALE discontinuous Galerkin methods with applications to under-resolved turbulent low-Mach number flows

The construction of discontinuous Galerkin (DG) methods for the compressible Euler or Navier-Stokes equations (NSE) includes the approximation of non-linear flux terms in the volume integrals. The terms can lead to aliasing and stability issues in turbulence simulations with moderate Mach numbers (Ma≲0.3), e.g. due to under-resolution of vortical dominated structures typical in large eddy simulations (LES). The kinetic energy or entropy is elevated in smooth, but under-resolved parts of the solution which are affected by aliasing. It is known that the kinetic energy is not a conserved quantity for compressible flows, but for small Mach numbers minor deviations from a conserved evolution can be expected. While it is formally possible to construct kinetic energy preserving (KEP) and entropy conserving (EC) DG methods for the Euler equations, due to the viscous terms in case of the NSE, we aim to construct kinetic energy dissipative (KED) or entropy stable (ES) DG methods on moving curved hexahedral meshes. The Arbitrary Lagrangian-Eulerian (ALE) approach is used to include the effect of mesh motion in the split form DG methods. First, we use the three dimensional Taylor-Green vortex to investigate and analyze our theoretical findings and the behavior of the novel split form ALE DG schemes for a turbulent vortical dominated flow. Second, we apply the framework to a complex aerodynamics application. An implicit LES split form ALE DG approach is used to simulate the transitional flow around a plunging SD7003 airfoil at Reynolds number Re=40,000 and Mach number Ma=0.1. We compare the standard nodal ALE DG scheme, the ALE DG variant with consistent overintegration of the non-linear terms and the novel KED and ES split form ALE DG methods in terms of robustness, accuracy and computational efficiency.

An image-based computational hemodynamics study of the Systolic Anterior Motion of the mitral valve

Systolic Anterior Motion (SAM) of the mitral valve – often associated with Hypertrophic Obstructive Cardiomyopathy (HOCM) – is a cardiac pathology in which a functional subaortic stenosis is induced during systole by the mitral leaflets partially obstructing the outflow tract of the left ventricle. Its assessment by diagnostic tests is often difficult, possibly underestimating its severity and thus increasing the risk of heart failure. In this paper, we propose a new computational pipeline, based on cardiac cine Magnetic Resonance Imaging (cine-MRI) data, for the assessment of SAM. The pipeline encompasses image processing of the left ventricle and the mitral valve, and numerical investigation of cardiac hemodynamics by means of Computational Fluid Dynamics (CFD) in a moving domain with image-based prescribed displacement. Patient-specific geometry and motion of the left ventricle are considered in view of an Arbitrary Lagrangian–Eulerian approach for CFD, while the reconstructed mitral valve is immersed in the computational domain by means of a resistive method. We assess clinically relevant flow and pressure indicators in a parametric study for different degrees of SAM severity, in order to provide a better quantitative evaluation of the pathological condition. Moreover, we provide specific indications for its possible surgical treatment, i.e. septal myectomy.

Analysis of a 3D nonlinear, moving boundary problem describing fluid-mesh-shell interaction

We consider a nonlinear, moving boundary, fluid-structure interaction problem between a time-dependent incompressible, viscous fluid flow, and an elastic structure composed of a cylindrical shell supported by a mesh of elastic rods. The fluid flow is modeled by the time-dependent Navier-Stokes equations in a three-dimensional cylindrical domain, while the lateral wall of the cylinder is modeled by the two-dimensional linearly elastic Koiter shell equations coupled to a one-dimensional system of conservation laws defined on a graph domain, describing a mesh of curved rods. The mesh-supported shell allows displacements in all three spatial directions. Two-way coupling based on kinematic and dynamic coupling conditions is assumed between the fluid and composite structure, and between the mesh of curved rods and Koiter shell. Problems of this type arise in many applications, including blood flow through arteries treated with vascular prostheses called stents. We prove the existence of a weak solution to this nonlinear, moving boundary problem by using the time discretization via a Lie operator splitting method combined with an Arbitrary Lagrangian-Eulerian approach, and a nontrivial extension of the Aubin-Lions-Simon compactness result to problems on moving domains.

CONCEPTION OF A NEW GENERATION OF 3D BIOMIMETIC MICROVALVES FOR MEDICAL APPLICATION

This paper reviews the development of a new microvalve with a cone-shaped tube, inspired by venous valves in the human body. Our microvalves allow fluid flow in one direction while restricting the flow in the opposite direction. When a microvalve is used to control the amount of drug delivery, the efficiency between inlet and outlet flow rate is the key control parameter for regulating and controlling the micro channel (opening/closing). This paper is devoted to the numerical study of flow rate changes in different microvalve geometries (3D) using a Fluid Structure Interaction (FSI) method with an Arbitrary Lagrangian Eulerian (ALE) approach. Numerical simulations were carried out in comsol Multiphysics. In addition, the macrovalve performance was analysed for several pressures where the effect of different geometrical parameters such as the length of the anchor, the diameter at the base and the angle of the cone were studied. An efficiency parameter 𝐸𝑓𝑓 was employed to compare the different structures. For the best design obtained, it was found that the cone angle was the parameter having the most effect on the microvalves’ characteristics, and the forward flow rate was more than doubled compared to the reverse leakage rate.

Capturing the dynamical transitions in the flow-field of a flapping foil using Immersed Boundary Method

The present work investigates the underlying flow physics behind dynamical transitions that take place in the flow-field around a plunging foil as the nondimensional plunge velocity (κh) is increased. The unsteady flow-field is seen to undergo a transition from periodicity to chaos through a quasi-periodic route. Numerical simulations have been performed at different parametric regimes associated with the different dynamical states, using an in-house flow solver developed based on discrete forcing type Immersed Boundary Method (IBM). Results obtained using the IBM methodology are compared both qualitatively and quantitatively with those from a well-validated body-fitted Arbitrary Lagrangian-Eulerian (ALE) approach. This study explores the scope of body non-conformal mesh methods in comparison to body fitted approaches in capturing complex flow topologies, especially, during aperiodic flow regimes. In the discrete direct forcing type IBM solver developed in the present study, application of the momentum forcing and mass/source sink terms at all the grid points inside the solid domain is seen to capture various unsteady flow-mechanisms accurately. These mechanisms are crucial in dictating the dynamics and they play key roles in triggering the aperiodic onsets and sustaining them.

Research on surface residual stresses generated by milling Ti6Al4V alloy under different pre-stresses

Machining-induced residual stress plays a significant role in the corrosion resistance and fatigue life of the manufacturing end product. In the current study, milling experiments were performed to investigate the influence of pre-stress on the surface residual stresses. For this purpose, finite element (FE) simulations of the orthogonal cutting based on arbitrary Lagrangian-Eulerian approach were performed. To validate the simulation results, a device was designed to stretch the workpiece with pre-stresses before the machining process. The residual stresses obtained under different pre-stresses were measured based on the varied bending deflection of the workpiece after each material layer removal. As a result, the general variation trend of residual stress profiles that obtained under different pre-stresses was found well consistent with the finite element simulation results, indicating that the proposed residual stress measuring principle is reliable. Furthermore, the pre-stress loaded on the Ti6Al4V part can significantly affect the distribution of machining-induced residual stresses, implying that surface residual stresses can be adjusted by employing appropriate values of pre-stresses during the machining process.

A 3D Hybrid Model Coupling SPH and QALE-FEM for Simulating Nonlinear Wave-structure Interaction

This paper presents a three-dimensional (3D) hybrid model, which couples the weakly compressible smoothed particle hydrodynamics (SPH) and the Quasi Arbitrary Langangian-Eulerian Finite Element Method (QALE-FEM), for modelling the wave-structure interaction (WSI) in extreme sea states. The former is a fully Lagrangian mesh-free approach, which solves the one-phase incompressible Navier-Stokes model, and has shown a satisfactory performance in simulating the WSI. The latter is an arbitrary Lagrangian Eulerian approach based on the fully nonlinear potential theory and can accurately simulate highly-nonlinear non-breaking water waves in a large scale with a high computational efficiency. These two models are coupled using a one-way zonal approach, in which the SPH uses a small computational domain near the structure, whereas the QALE-FEM covers the rest of the computational domain and provides wave conditions at the inlet of the SPH domain. The present hybrid model is validated against the experimental results and applied to the CCP-WSI blind test on modelling wave energy converters subjected to extreme focusing waves. The accuracy and convergence of the presented model are discussed.

An enhanced model for the capillary rise problem

Starting from the full continuum mechanical description of free surface flows, a model for the rise of a liquid in a capillary is derived. The derivation improves on several aspects: Firstly, the influence of a slip boundary condition on the capillary wall is added to the model. Secondly, the stationary rise height is corrected. Thirdly, a regularization is suggested that uses the mass in interface vicinity. Fourthly, the influence of the velocity field close to the contact line is added. Finally, a convection contribution arises as the analysis considers the capillary without a reservoir. To validate the model, an Arbitrary Lagrangian-Eulerian (ALE) approach is used to solve the full continuum mechanical model that serves as a reference solution. The correction for the stationary height shows excellent agreement with the continuum mechanical results, while the extended model generally improves the classical description. Increasing the viscous term to increase for additional dissipation effects leads to excellent agreement with the fully resolved validation cases. However, in the regime with rise height oscillations, the amplitudes are overestimated by the extended models.

Single-Step Arbitrary Lagrangian–Eulerian Discontinuous Galerkin Method for 1-D Euler Equations

We propose an explicit, single-step discontinuous Galerkin method on moving grids using the arbitrary Lagrangian–Eulerian approach for one-dimensional Euler equations. The grid is moved with the local fluid velocity modified by some smoothing, which is found to considerably reduce the numerical dissipation introduced by Riemann solvers. The scheme preserves constant states for any mesh motion and we also study its positivity preservation property. Local grid refinement and coarsening are performed to maintain the mesh quality and avoid the appearance of very small or large cells. Second, higher order methods are developed and several test cases are provided to demonstrate the accuracy of the proposed scheme.

Vulnerability analysis of bridge superstructures under extreme fluid actions

Vulnerability analyses of bridge structures affected by extreme flood or tsunami wave loads in terms of loading variability and structural and fluid characteristics are conducted. The numerical model is developed by a combined three-dimensional (3D)/two-dimensional analysis based on phase field theory and 3D solid modeling of the fluid and structural systems, respectively. Coupling effects between the fluid and structure are simulated by using a moving mesh method based on an arbitrary Lagrangian–Eulerian approach to take bridge deformability and moving wall conditions into consideration. The proposed model is implemented in a finite element formulation, whose solution is achieved through a substructuring approach by introducing projection map operators defined to connect the structural and fluid systems. Several wave load scenarios related to the initial impact or dam break phenomena depending on inundation and blocking ratios and Froude numbers are considered. The main aim is to quantify the dynamic amplification effects of the kinematic and stress variables produced by the external loads with respect to conventional static analyses. In addition, the influences of bridge deformations on the hydrodynamic loads and vice versa are also discussed in terms of fluid and structural characteristics.

Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.

We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.

Numerical modeling based on moving mesh method to simulate fast crack propagation

An analysis to show the capability of moving mesh strategy to predict dynamic crack growth phenomena in 2D continuum media is proposed. The numerical method is implemented in the framework of the finite element method, which is coupled with moving mesh strategy to simulate the geometry variation produced by the crack tip motion. In particular, a computational procedure based on the combination of Fracture Mechanics concepts and Arbitrary Lagrangian-Eulerian approach (ALE) is developed. This represents a generalization of previous authors’ works in a dynamic framework to propose a unified approach for predicting crack propagation in both static and dynamic frameworks. The crack speed is explicitly evaluated at each time step by using a proper crack tip speed criterion, which can be expressed as a function of energy release rate or stress intensity factor. Experimental and numerical results are proposed to validate the proposed approach. Mesh dependence problem, computational efficiency and numerical complexity are verified by comparative results

Dynamics of a pair of ellipsoidal microparticles under a uniform magnetic field

Under a uniform magnetic field, magnetic particles tend to form chains, clusters or columns due to particle–particle interactions. Non-spherical magnetic particles dispersed in a liquid medium show different rheological properties. However, there is a lack of knowledge about the fundamental mechanism of particle–particle interactions of non-spherical particles under a uniform magnetic field. In this work, we numerically investigate the particle–particle interactions and relative motions of a pair of paramagnetic elliptical particles by using direct numerical simulations to create two-dimensional models that resolve the magnetic and flow fields around the finite-sized particles. The modeling is based on the finite element method and arbitrary Lagrangian–Eulerian approach with full consideration of particle–fluid–magnetic field interaction. The effects of initial position and aspect ratio of the particles are investigated. The results show that the particles spend much more time under global reorientation than local magneto-orientation. Larger initial relative angles and distances, and larger aspect ratios, tend to require more time to form a stable chain. The particle–particle interactions and relative motion of a pair of elliptical particles in this study provide insights into the particle alignment and chaining processes under uniform magnetic fields, which are closely related to the response of magneto-rheological fluids to magnetic fields.