Arbitrary Lagrangian Eulerian Research Articles

Vulnerability Analysis of Structural Systems under Extreme Flood Events

Vulnerability analyses of coastal or inland bridges in terms of flood actions and structural and fluid flow characteristics are carried out. In particular, a numerical model based on a two-phase fluid flow is implemented for the multiphase fluid system, whereas a three-dimensional formulation based on shell/volume finite elements is adopted for the structure. The governing equations can simulate the interaction between fluids and the structures, by using the Arbitrary Lagrangian–Eulerian (ALE) strategy. The results of the hydrodynamic forces, bridge displacements and dynamic amplification factors (DAFs) show that the existing formulas, available in the literature or in structural design codes, do not accurately predict the maximum design effects. For the investigated cases, the DAFs may vary from 1 to 4.5. The worst scenarios are observed for the upload vertical direction. Finally, the performance of the protection fairing system is investigated. The results show that such devices are able to efficiently reduce the effects of the wave load in terms of the applied hydraulic forces on the structure and bridge deformability, in particular, with 40% more accuracy than the unprotected configuration.

Effect of Geo-Material on Dynamic Response of Tunnel Subjected to Surface Explosion

Prime materials involved in a problem such as underground structures are concrete, reinforcement steel, and geo-material surrounding the tunnel. Among these three materials, concrete and steel are manufactured materials and their properties can be controlled up to a certain extent. However, geo-material is a naturally occurring material whose constitutive properties vary from region to region, making it highly unpredictable. Findings from one study cannot be applied to other geotechnical problems directly, especially in the case of tunnels subjected to surface explosions. The blast wave generated has to travel through the geo-material before it interacts with the tunnel. As the shock wave propagates radially, its characteristics are likely to be altered by the geo-material. Limited study has been carried out considering this problem. In the present study, the effect of various types of geo-material on the blast response of tunnels subjected to surface explosions is investigated. Finite element analysis has been carried out using LS-DYNA®, wherein the problem has been modeled using the multi-material arbitrary Lagrangian–Eulerian (MM-ALE) method. Materials with fluid behavior such as air, explosives, and soil are modeled using ALE formulation. Other materials including tunnel lining, reinforcement steel, and rock are modeled using Lagrangian formulation. Blast loading is simulated using the Jones–Wilkins–Lee (JWL) equation of state. Geo-materials considered for the comparative study are sandy loam, saturated clayey soil, sandstone, and granite. Vertical displacement measured at the crown of the tunnel is used to determine the response of the tunnel. Sandy loam soil, being a highly compressible soil, exhibits non-linear and fluid-like behavior under high-strain loading such as explosions. Tunnels undergo extreme deformation in the case of sandy loam soil and clayey soil compared to rock cases. Further, the effect of saturation in sandy loam on tunnel stability is studied. It is observed that with the increase in saturation of soil, more blast energy is transmitted to the structure, which results in higher deformation. Lastly, the effect of the weathering of rock on the tunnel’s response is investigated in the case of sandstone and granite. It was observed that weathering in rock led to more displacement of tunnel crown when compared to intact rock.

Microstructural damage and response of stiffened composite submersible pressure hull subjected to underwater explosion

ABSTRACT Submerged structures in naval applications are susceptible to underwater explosion and predicting the transient response and damage is a prime concern for the designer. Coupled Arbitrary Lagrangian-Eulerian (ALE) based numerical investigation using LS-DYNA for the inelastic dynamic response and microstructure failures of composite hull subjected to UNDEX is presented. As a prelude to the study, shock pressure in fluid domain and strain values obtained on the composite pressure hull is compared with that available in literature. The numerical study is extended to predict the large deformation, puncture and microstructural behaviours of the hull by varying the charge weight of the explosive. The results of the predicted large deformation, puncture of the hull and the microstructural failures such as fibre tension, fibre compression, matrix shear, matrix tension, and matrix compression based on the Chang- Chang composite failure model, Tsai-Wu failure theory and maximum stress theory are presented.

Numerical studys on passive paramerters of a fluid-solid interaction problem derived by natural convection in a circular enclosure

The natural convection through a partitioned circular enclosure by a deformable middle wall was analyzed. To solve the FSI problem, a forceful connection between the fluid and flexible wall was established. In order to solve the problem under consideration, the Arbitrary Lagrangian-Eulerian (ALE) perspective was utilized. The finite element method (FEM), was also unilized in solving a set of model equations. Effect of wall Angle (30 ≤ η ≤ 90), flexibility (0.71 ≤ Eτ ≤ 200), Position of heat source and sink (-60 ≤ α ≤ +60) has been studied within a circular enclosure. The results indicate that a reduction in flexibility reduces the force (stress) applied to the wall as well as the average Nusselt number to some extent. Also, Increased angle of the wall leads to an enhancement in the Nu. The maximum applied stress and also wall distortion occur at specific positions of hot and cold sector, the buoyancy force and, therefore, the strength of the fluid flow are also higher, causing the heat transfer rate to increase. For The average Nusselt number, A decrease of 8.5 % for η = 90° has been reported compared to η = 30°. Also, the average Nusselt number for α = −60° is up to 124.5 % higher than for α = 60°.

Cooling of hot cylinder placed in a flexible backward-facing step channel

This paper copes with the mixed convection heat transfer and fluid–structure interaction (FSI) of a hot cylinder placed in a backward-step channel. The step is set to be flexible and deforms according to the force imparted by fluid. To attain the best cooling, different configurations of the flexible step were assessed. Equations governing the problem are solved using the finite element technique with the Arbitrary Lagrangian–Eulerian (ALE) approach to go along the moving domain. The influential parameters of such a problem are the Reynolds number Re, Richardson number Ri and the configuration of the flexible back step. Results demonstrated an improvement in the Nusselt number where at Ri = 100, a step of horizontal flexible wall augments the Nusselt number by 7.3% and 1.4% when Re = 100 and 500, respectively. Including the pressure drop in a performance criterion, it is shown that making the vertical wall of the step flexible (VFW) improves the aspects of heat transfer and the hydrodynamic of low Reynolds number, while at high Reynolds number, all suggested configurations of flexible step do not improve the performance criterion. It is found also that Reynolds number greatly improves the performance criterion while Richardson number does not.

A Revision of the Formation Conditions of the Vredefort Crater

AbstractThe Vredefort impact structure, located in South Africa and formed 2.02 Ga, is the largest confirmed remnant impact crater on Earth. The widely accepted impactor diameter and velocity to form this crater are 15 km and 15 km/s, respectively, which produce a crater diameter of 172 km. This is much smaller than the most commonly cited estimates (250–280 km), and while previous results were able to match the geologic evidence known at that time, these impact parameters are not consistent with more recent geological constraints. Here, we conduct impact simulations to model the Vredefort crater formation with the shock physics code impact Simplified Arbitrary Lagrangian Eulerian (iSALE). Our numerical simulations show that combinations of the impactor diameter and impact velocity of 25 km and 15 km/s or 20 km and 25 km/s are able to recreate the larger crater size of ∼250 km. Moreover, these configurations can reproduce shock‐metamorphic features present in the impact structure today, including the distributions of breccia, shatter cones, planar deformation features in quartz and zircon, and melt. Our model also predicts that Vredefort and Karelia, Russia, where an ejecta layer from the impact was found, were approximately 2,000–2,500 km apart based on the layer thickness. Additionally, we use this model to predict the potential global effects of such a large impact by estimating the amount of climatically important gases released to the atmosphere at the time. Our work demonstrates the need to revisit previously estimated impactor parameters for large terrestrial craters in order to better characterize impact events on Earth and elsewhere.

Performance-based probabilistic deflection capacity models and fragility estimation for reinforced concrete column and beam subjected to blast loading

Due to the mounting of ongoing anti-social activities of explosions and inaccuracy of codes (UFC 3-340-02, Eurocode 1, IS 4991) current study has developed performance-based capacity models for Reinforced Concrete (RC) column/beam subjected to near field blast. The chosen three performance levels are deflection based and allied with four damage states of target (elastic limit with minimal damage, elasto-plastic with moderate damage, ultimate limit with total collapse). To estimate deflection levels, a numerical method LS-DYNA is used to acquire data using Arbitrary Lagrangian-Eulerian (ALE) method. Four models are accurately validated with experimental results and chosen parameters are deflection, damage pattern and pressure achieved. The deflection of the RC beam/column subjected to blast is reproduced with combination of mechanical model (UFC 3-340-02 code) and dimensionless explanatory functions. These functions are used to develop six probabilistic models for RC beam/column subjected to blast loading grounded on Bayesian inference and posterior statistics. These models account for all aleatoric and epistemic uncertainties in dynamic blast events. The estimated capacity models are compared with experimentation, and acquired results show the reliability of the probabilistic equations. This study also assessed fragility for three levels of normalized deflection demand and obtained plots are well authenticated.

Influence of Coulomb’s Friction Coefficient in Finite Element Modeling of Orthogonal Cutting of Ti6Al4V

The reliability of the pertinent parameters set of Johnson-Cook constitutive model is highly linked with the friction condition at the tool-chip-workpiece interface. In the present work, a study on the influence of Coulomb’s friction coefficient on the observables such as forces, chip thickness and chip curvature by FE simulation of orthogonal cutting of Ti6Al4V alloy has been carried out. A FE model with an Arbitrary Lagrangian-Eulerian (ALE) approach is employed to simulate the cutting process for different cutting conditions. The simulated results, for a wide range of friction conditions, are analyzed and compared with experimental results. The analysis show that the Coulomb’s friction coefficient has a direct link with the observables. The paper reveals that for accurate prediction of observables an optimized value of the coefficient of friction in correlation with the parameters values of the constitutive model is imperative.

Numerical and Experimental Investigations in Orthogonal Milling of 15-5PH Stainless Steel

The present work presents the development of a numerical model to assess the machining performance in milling of a 15-5PH stainless steel. At first an experimental campaign was conducted using PVD coated TPUN inserts under three levels of cutting speed and feed: 100-170-240 m/min & 0.25-0.35-0.45 mm/rev. Forces were recorded using a Kistler 9257A dynamometer. For each experimental test, chips were mounted and polished to evaluate the chip thicknesses and contact lengths measured on inserts’ rake face. Regarding the numerical simulation, a 2D Arbitrary-Lagrangian-Eulerian (ALE) was then developed in the study. A tool motion was implemented to mimic the chip thickness evolution occurring during the milling process. These simulations allowed to numerically predict the chip thicknesses, contact lengths and cutting forces which were further compared to the experimental data.

Study on the Formation Mechanism of Cutting Dead Metal Zone for Turning AISI4340 with Different Chamfering Tools.

Tools with chamfered edges are often used in high speed machining of hard materials because they provide compelling cutting toughness and reduced tool wear. Chamfered tools are also responsible for the dead metal zone (DMZ). Through numerical simulation of orthogonal cutting with AISI 4340 steel, this paper examines the mechanism of the DMZ, the cutting speed, the impacts of the chamfer angle, and the coefficient of friction on the generation of the DMZ. The analysis is based upon the Arbitrary Lagrangian-Eulerian (ALE) finite element method (FEM) for the continuous process of chip formation. The different chamfered angles, cutting speeds, and friction coefficient conditions are utilized in the simulation. The research demonstrates that a zone of trapped material called DMZ has been formed beneath the chamfer and serves as an effective cutting edge of the tool. Additionally, the dead metal zone DMZ becomes smaller while the cutting speed increases or the friction coefficient decreases. The machining forces rise with increasing chamfer angles, rise with increasing friction coefficients, and fall with increasing cutting speed in both the cutting and thrust directions. In this paper, the effect of different chamfering tools on AISI 4340 steel using carbide tools in the simulation environment is studied. It has certain reference significance for studying the formation mechanism of the dead zone of difficult-to-machine materials such as AISI4340 and improving the processing efficiency and workpiece surface quality.

Understanding the heating characteristics in microwave heating moving and deforming foods by a hybrid double-layer ALE/implicit algorithm

Multiphysics modeling is an essential tool to understand the heating characteristics of microwave processing food products. However, when the heated sample is moving and deforming during the heating process (e.g. the long-term microwave drying process), the huge mesh distortions caused by the sample's motion and deformation will make the simulation impossible. To solve this problem, a hybrid double-layer Arbitrary-Lagrange-Eulerian (ALE)/implicit algorithm is proposed in this paper, where the sample's motion and deformation is tracked by a double-layer ALE framework and convert to time-varying implicit variables. By doing so, the influence of the sample motion and deformation on the electromagnetic field distribution will be characterized by the evolution of time-varying implicit variables, rather than by explicit modeling, which reduces the mesh distortion and makes the calculation possible. A two-dimensional and a three-dimensional model of microwave cavities containing a rotating and deforming food are given to describe the algorithm in detail. Experiments for the three-dimensional model are also conducted to validate the proposed method. Results show that the shrinkage of the food may have a negative impact on the heating performance (especially energy efficiency) and corresponding remedies need to be performed for long-term microwave heating processes.

Improved Volume-Of-Solid Formulations for Micro-Continuum Simulation of Mineral Dissolution at the Pore-Scale

We present two novel Volume-of-Solid (VoS) formulations for micro-continuum simulation of mineral dissolution at the pore-scale. The traditional VoS formulation (VoS-ψ) uses a diffuse interface localization function ψ to ensure stability and limit diffusion of the reactive surface. The main limitation of this formulation is that accuracy is strongly dependent on the choice of the localization function. Our first novel improved formulation (iVoS) uses the divergence of a reactive flux to localize the reaction at the fluid-solid interface, so no localization function is required. Our second novel formulation (VoS-ψ′) uses a localization function with a parameter that is fitted to ensure that the reactive surface area is conserved globally. Both novel methods are validated by comparison with experiments, numerical simulations using an interface tracking method based on the Arbitrary Eulerian Lagrangian (ALE) framework, and numerical simulations using the VoS-ψ. All numerical methods are implemented in GeoChemFoam, our reactive transport toolbox and three benchmark test cases in both synthetic and real pore geometries are considered: 1) dissolution of a calcite post by acid injection in a microchannel and experimental comparison, 2) dissolution in a 2D polydisperse disc micromodel at different dissolution regimes and 3) dissolution in a Ketton carbonate rock sample and comparison to in-situ micro-CT experiments. We find that the iVoS results match accurately experimental results and simulation results obtained with the ALE method, while the VoS-ψ method leads to inaccuracies that are mostly corrected by the VoS-ψ’ formulation. In addition, the VoS methods are significantly faster than the ALE method, with a speed-up factor of between 2 and 12.

Progressive collapse of Murrah Federal Building: Revisited

As a typical incident of progressive collapse of RC structures caused by the terroristic vehicular bomb attack, the large-scale collapse of Murrah Federal Building (MFB) in 1995 has been attracting extensive attentions. The alternate path method and the direct simulation method are commonly adopted to evaluate the progressive collapse resistance of buildings. However, the simultaneous damage of the structural members adjacent to the removed column and the instantaneous interactions between the blast wave and the structures are neglected. This paper aims to revisit the progressive collapse of MFB through the high-fidelity numerical simulations. Firstly, the hybrid finite element model of MFB was established including both the near-range refined model and far-range simplified model. Secondly, based on the explicit dynamic finite element program LS-DYNA, the Arbitrary Lagrangian-Eulerian (ALE) method and Fluid-Structure Interaction (FSI) algorithms were adopted to simulate the ignition of explosive, propagation of air blast wave and its interactions with the building structures, which was validated based on an external explosion test on RC frame structure. Furthermore, the collapse of MFB was predicted and compared with the on-site photographs in terms of the collapse scopes of entire building and the damage of local structural members. Finally, three seismic resistant design schemes of MFB were proposed, and the corresponding progressive collapse resistance of which was further evaluated. It derives that, (i) the numerical simulation combining the hybrid modelling and ALE approaches can well reproduce the collapse process of MFB; (ii) the progressive collapse of MFB is mainly caused by the insufficiency of flexural bearing capacity of the transfer girder due to the failure of three supporting ground columns, rather than the rotation of the transfer girder; (iii) the three improved schemes can partially prevent the shear failure of the ground columns and mitigate the collapse scopes of MFB by 25%–50%, while the progressive collapse still occurs due to the shear failure of transfer girder; (iv) transfer girder is not recommended for blast-resistant buildings due to its low redundancy.

Study of the Influence of Cutting Edge on Micro Cutting of Hardened Steel Using FE and SPH Modeling.

Micromachining allows the production of micro-components with complex geometries in various materials. However, it presents several scientific issues due to scale reduction compared to conventional machining. These issues are called size effects. At this level, micromachining experiments raise technical difficulties and significant costs. In this context, numerical modeling is widely used in order to study these different size effects. This article presents four different numerical models of micro-cutting of hardened steel, a Smooth Particle Hydrodynamics (SPH) model and three finite element (FE) models using three different formulations: Lagrangian, Arbitrary Eulerian–Lagrangian (ALE) and Coupled Eulerian–Lagrangian (CEL). The objective is to study the effect of tool edge radius on the micro-cutting process through the evolution of cutting forces, chip morphology and stress distribution in different areas and to compare the relevance of the different models. First, results obtained from two models using FE (Lagrangian) and SPH method were compared with experimental data obtained in previous work. It shows that the different numerical methods are relevant for studying geometrical size effects because cutting force and stress distribution correlate with experimental data. However, they present limits due to the calculation approaches. For a second time, this paper presents a comparison between the four different numerical models cited previously in order to choose which method of modeling can present the micro-cutting process.

Fluid structure computational model of simulating mitral valve motion in a contracting left ventricle

Background:Fluid structure interaction simulations h hold promise in studying normal and abnormal cardiac function, including the effect of fluid dynamics on mitral valve (MV) leaflet motion. The goal of this study was to develop a 3D fluid structure interaction computational model to simulate bileaflet MV when interacting with blood motion in left ventricle (LV). Methods:The model consists of ideal geometric-shaped MV leaflets and the LV, with MV dimensions based on human anatomical measurements. An experimentally-based hyperelastic isotropic material was used to model the mechanical behaviour of the MV leaflets, with chordae tendineae and papillary muscle tips also incorporated. LV myocardial tissue was prescribed using a transverse isotropic hyperelastic formulation. Incompressible Navier–Stokes fluid formulations were used to govern the blood motion, and the Arbitrary Lagrangian Eulerian (ALE) method was employed to determine the mesh deformation of the fluid and solid domains due to trans-valvular pressure on MV boundaries and the resulting leaflet movement. Results:The LV–MV generic model was able to reproduce physiological MV leaflet opening and closing profiles resulting from the time-varying atrial and ventricular pressures, as well as simulating normal and prolapsed MV states. Additionally, the model was able to simulate blood flow patterns after insertion of a prosthetic MV with and without left ventricular outflow tract flow obstruction. In the MV–LV normal model, the regurgitant blood flow fraction was 10.1 %, with no abnormality in cardiac function according to the mitral regurgitation severity grades reported by the American Society of Echocardiography. Conclusion:Our simulation approach provides insights into intraventricular fluid dynamics in a contracting LV with normal and prolapsed MV function, as well as aiding in the understanding of possible complications after transcatheter MV implantation prior to clinical trials.

Testing and multiscale modeling of a foam-based lung surrogate subjected to underwater shock loading

A combined experimental and computational study was conducted to investigate the structural response of a foam-based lung simulant subjected to underwater pressure wave. In the physical experiments, a lung surrogate made from porous medium was exposed to underwater pressure wave in an impact force - driven testing tube. The pressures in the water and surrogate deformation profile were recorded throughout the event. A numerical model of the underwater shock tube was developed using finite element (FE) method and validated against experimental data. An arbitrary Lagrangian-Eulerian (ALE) fluid–structure coupling algorithm was then utilized to simulate the interaction between the underwater pressure wave and the lung surrogate. Based on the numerical model, a multiscale modeling strategy was used to link the surrogate responses in macro and micro scales. The modeling process consists of two steps, namely (1) macro scale FE modeling to predict the overall surrogate reponse; and (2) micro scale Representative Volume Element (RVE) modeling for the detailed microstructure response. The strain tensors computed in Step (1) were applied to the RVE as the boundary condtions in Step (2) to calculate its response in the micro scale. With this multiscale modeling approach, a parametric study was carried out to study the influence of waveform on the RVE strain response. The results indicate that for current input pressure levels, the strain response within the foam surrogate model is more sensitive to the overpressure than the duration of pulse. The modeling approach developed in this work can potentially serve as a basis for further numerical models to gain a deeper insight into the mechanism of underwater blast-induced lung injury.

An Arbitrary Lagrangian Eulerian formulation for tire production simulation

Tire production is a complex process due to large deformations, highly non-linear uncured rubber material and large temperature. It can be observed, that the production conditions have a strong influence on the cured tire behaviour and should be studied to minimize possible defects in the final product. In this contribution, an Arbitrary Lagrangian Eulerian (ALE) formulation is presented to overcome convergence issues stemming from large distortion of elements in a pure Lagrangian description. In an ALE formulation, the computational mesh is not fixed in space and can move relatively to the material motion, which allows to control the distortion of the mesh by a smoothing algorithm. Coupling the material motion with the newly obtained mesh is done by an advection algorithm to project the internal variables of a thermo-mechanically consistent material model. Based on the assumption that the internal variables are projected directly from the integration points, an additional mesh is generated with the integration points of the old mesh as grid. To show the capabilities of the presented algorithm, several numerical examples are shown ranging from a simple forging example to a complex tire production process. • A new algorithm for the projection of history variables in an Arbitrary Lagrangian Eulerian framework. • A finite strain thermo-mechanically consistent material model for rubber curing. • Applied ALE framework to the tire production process.

Experimental and numerical study on rapid inflation process of air-launched balloon

The rapid inflation process is the most important stage in the whole working process of rapid deployment of aerostat. However, it is difficult to reveal its mechanical mechanism by existing experimental and numerical methods and reasonably explain the damage and helium leakage during the inflation process. An air-launched balloon for rapid deployment was designed and manufactured, and the related ground steady inflation experiment was carried out in this work. Then, the rapid inflation process of the folded balloon was studied by using the Simplified Arbitrary Lagrangian- Eulerian (SALE) method. Here, the folded balloon model was obtained by the reverse folding method. The structure and flow field were described by Lagrangian elements, and the coupling between them was obtained by a contact algorithm. The numerical results were in good agreement with the experimental results. The numerical method in this work could obtain abundant information on the structure and flow field which couldn’t be obtained by the experimental method. The change law of structure and flow field was obtained and the failure mechanism in the destructive experiment was explained. The numerical method proposed in this work could provide a reference for the material selection, gas source selection and structure optimization of the rapid deployment aerostat system.

Mesh Moving Methods in Flow Computations with the Space–Time and Arbitrary Lagrangian–Eulerian Methods

A good mesh moving method is an important part of flow computations with moving-mesh methods like the space–time (ST) and Arbitrary Lagrangian–Eulerian (ALE) methods. With a good mesh moving method, we can decrease the remeshing frequency even when the fluid–solid and fluid–fluid interfaces undergo large displacements, decrease the element distortion in parts of the flow domain where we care about the solution accuracy more, and maintain the quality of the boundary layer meshes near the fluid–solid interfaces as the mesh moves to follow those interfaces. Since 1990, quite a few good mesh moving methods have been developed for use with the ST computational methods, from the mesh Jacobian-based stiffening to a mesh moving method based on fiber-reinforced hyperelasticity to a linear-elasticity mesh moving method with no cycle-to-cycle accumulated distortion. These methods have been used in computation of many complex flow problems in the categories of fluid–particle interaction, fluid–structure interaction, and more generally, moving boundaries and interfaces. The computations were with both the ST and ALE methods. We provide an overview of these methods and present examples of the computations performed.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Numerical Study of the Elasto-Hydrodynamic Behavior of a Metallic Structure Subjected to a Nanofluid Flow

In this paper, the behavior of an elastic barrier subjected to isothermal laminar flow of Al2O3-water nanofluid in a channel has been studied numerically by the finite element method. A CFD based on the arbitrary Lagrange-Euler (ALE) formulation, has been developed in an attempt to solve the Navier-Stokes and stress-strain equations of the structure. The objective is to study the effects of inertia (Re) and nanoparticle volume fraction (φ) on the overall hydrodynamic behavior, as well as on the nanofluid-structure interface. The results showed that the deformation of the structure was mainly caused by the pressure loading of the nanofluid and the viscous drag imposed on the structure walls. In addition, the structure was strongly affected by the increase in Reynolds number and volume fraction of the nanoparticles. Finally, a numerical correlation was established to determine the maximum displacement caused by the bending of the structure.