Arbitrary Lagrangian Eulerian Technique Research Articles

Investigations on a moving target’s penetration into the seabed sediment using the ALE technique

ABSTRACT Accurate prediction about the penetration depth of moving targets is vital for the deep-sea target detection. Moving targets penetrating into the seafloor sediment always produce large deformation, the Arbitrary Lagrangian-Eulerian (ALE) technique has better grid adaptability and it can solve the mesh distortion generated by moving targets penetrating into seafloor sediment. Therefore, in the present work, investigations on the moving targets’ penetration into seafloor sediment are conducted based on the ALE technique. The physical process of moving targets’ penetrating into the seafloor sediment is simulated using the ALE technique. Results by the ALE technique are compared with empirical results and experimental results to verify the ALE method. On the basis of the verification study, the effects of sediment property and target’s mass, impact velocity and penetration angle on penetration depth are also explored.

Finite element analysis and optimization of tube hydroforming process

Tube Hydroforming is one of the most effective manufacturing processes used in modern times since it satisfies the current robust requirements of the manufacturing industry. It finds enormous applications in the automobile and aerospace sectors owing to the inherent advantages over conventional forming processes, like consumption of less material with no compromise on the part strength. Complex geometries can be developed with high accuracy in less number of manufacturing stages, which would, in turn, reduce the overall manufacturing cost. Such an ability of this process to fabricate products with high strength-to-weight ratios at economical costs make it energy-efficient and it does push a step further towards sustainable and modern innovative manufacturing.This paper presents the development of a detailed nonlinear finite element model for the tube hydroforming process that uses Abaqus/Explicit as a computational tool. Elastic-plastic material constitutive behavior is defined using a flow-stress equation, and the Arbitrary Lagrangian-Eulerian technique (ALE) is used to determine the material flow. Input parameters like applied pressure, initial tube thickness, and die-corner radius are considered against output parameters like formed tube thickness, final part dimensions, and stress concentration. The developed model is validated with a previously published literature by Rakesh A. Shinde et al. (2016), and the results are found to agree for the case of percentage of thickness reduction.Following the work done by Rakesh A. Shinde et al., three different numerical cases are created with different die corner radii and tube thicknesses, for 3 different internal pressure values, viz., 41 MPa, 43 MPa, and 45 MPa. The results obtained in the paper are first replicated, and the research is further extended for different loading/unloading rates and peak load holding times (loading paths). Results indicate the sufficiency of only lower loads to produce the required formability. Accordingly, simulations are also performed for cases of lower pressures. Results show that accurate part dimensions at much lower stress concentrations could be obtained at lower values of pressure. The presented work also looks into the optimisation of the process using a well-established DOE technique – Response Surface Methodology. Accordingly, a multi-objective optimisation is performed, considering 20 simulations for the cases of three parameters and three levels. The significant influencing parameter is also identified.

Experimental and numerical study of dynamic soil debris impact load on reinforced concrete debris-resisting barriers

In Hong Kong, design practice adopts the hydrodynamic load model to estimate the dynamic soil debris impact load on reinforced concrete debris-resisting barriers. A dynamic coefficient of 2.5 is empirically adopted, which takes into account the effect of the impact of boulders up to 0.5 m in diameter. With a view to rationalising the design of reinforced concrete debris-resisting barriers, the Geotechnical Engineering Office (GEO), in collaboration with the Hong Kong University of Science and Technology (HKUST), initiated a study to investigate the dynamic impact of soil debris. In particular, a series of large-scale impact tests using 4 m3 realistic debris mix and a 1.8-m-high reinforced concrete model barrier were conducted in the flume facility in the Kadoorie Centre in Hong Kong. The tests were well controlled, and the flow kinematics, including flow depth and flow speed, and the time history of the impact load at the wall stem subject to the debris impact were measured, which provided critical test data on assessment of the hydrodynamic load of soil debris hitting reinforced concrete structures. The scale of these physical impact tests under such a controlled environment was unique as compared with other studies in the literature. To further examine the dynamic impact force, a calibrated numerical model using a three-dimensional finite-element computer package, namely LS-DYNA, was adopted to simulate the impact scenario for a real-scale debris flow event of 400 m3, where an arbitrary Lagrangian-Eulerian technique was adopted to simulate debris materials. Based on both the experiments and numerical analyses, debris run-up along the wall stem was observed when the debris hit the model barriers. Under the experimental setting, the hydrodynamic soil debris pressure coefficients were consistently found close to unity, which are generally in line with that used in overseas technical guidelines or design practice. This study enhances fundamental understanding of the soil debris impact mechanism on reinforced concrete barriers and provides scientific evidence to rationalise the design guidelines used in Hong Kong.

Development of pressure-impulse models and residual capacity assessment of RC columns using high fidelity Arbitrary Lagrangian-Eulerian simulation

Pressure-Impulse (P-I) models as graphical representations are frequently adopted to evaluate damage of structures subjected to extreme loads. The main objectives of this research is to derive analytical formulas to propose pressure (P0) and impulsive (I0) asymptotes of RC columns at different levels of damages, and to develop P-I models and empirical equations of RC columns for prediction and assessment of blast induced damages using an advanced numerical modeling approach. An innovative technique to predict the residual capacity of RC columns when subjected to detonation events is essential to measure the column axial capacity after blast loads. This study can offer a methodology for a reliable, simple and accurate dynamic analysis to study the residual capacity of columns under blast detonation. Available literature mainly focused on the simulation of explosion loads by using simplified pressure time histories to develop P-I curves and rarely simulated the actual explosive. Therefore, there is a gap in the literature concerning general relation between blast damage of columns with different explosive loading conditions for a reliable and quick evaluation of column behavior subjected to blast loading. In this paper, the Arbitrary Lagrangian Eulerian (ALE) technique is implemented to simulate high fidelity blast pressure propagations. The numerical model is calibrated and validated by comparing the results from blast field tests performed by other researchers. To develop the designated P-I curves, damage assessment criteria are used based on the residual capacity of column. Intensive investigations are implemented to assess the effect of column dimension, concrete and steel properties, reinforcement ratio and axial load index on the P-I diagram of RC columns. The produced P-I models can be applied by designers to predict the damage of new columns and to assess existing columns subjected to different blast load conditions.

Protective Mechanism of Helmet Under Far-field Shock Wave

In order to understand the protective mechanism of helmet against shock wave, a head model under far-field blast is investigated experimentally and numerically. The distribution of overpressure on the surface of the head model are obtained and compared. The numerical simulations are carried out using the Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) technique with suitable material models for a Kevlar helmet and soft pads. The differences in the distributions of overpressure on the head models with and without the protection of the helmet are analyzed. The interaction of shock waves around the head and the helmet is investigated. Our experimental observations and numerical results indicate that, if protected by a helmet in the case of a shock wave acting from the front, the peaks of overpressure on the head are reduced at the top area, but increased at the rear area. The numerical simulations also show that the enhancement of the overpressure at the rear is mainly due to the collision of the shock wave. The underwash phenomenon also occurs when the shock wave acts from the side or the rear.

Fluid-structure interaction of a hot flexible thin plate inside an enclosure

This study aims to assess the natural convection heat transfer in a square cavity wherein the buoyancy-induced flow is generated by a thin flexible heater-plate inside the cavity. The vertical walls of the cavity are cold and the horizontal walls are adiabatic. The thin hot plate is assumed to be isothermal and fixed at an alterable point in the middle of the cavity with different inclination angles. To analysis the fluid-structure interaction (FSI), the finite element method along with the Arbitrary Lagrangian-Eulerian (ALE) technique is employed. Isotherms and streamlines, as well as the average Nusselt number, the dimensionless temperature in the cavity, and the maximum applied stress on the flexible plate, are studied. The results are presented as a function of Rayleigh number, Prandtl number, inclination angle, and different positions of the fixed point. The outcomes indicate the importance of the inclination angle and the position of the fixed point of the hot plate. The plate experiences significantly large values of stress when it is mounted horizontally. In the case of a plate fixed at its top, the highest stress occurs with an inclination angle of 40°. In contrast, the lowest stress is associated with the plate when it is positioned vertically.

Effect of multi-pass friction stir processing on thermal distribution and mechanical properties of AZ91

In this paper, the effect of multi-pass friction stir processing on mechanical properties of AZ91 alloy has been studied. For this purpose, the microhardness, tensile, and creep tests were conducted at several temperatures. Optical microscopy and scanning electron micrograph were used to study the microstructure of the processed samples. The experimental results indicated that at room temperature, the microhardness, tensile, and creep strength of the processed samples as compared to the unprocessed ones increased by 23%, 29%, and 38%, respectively. Also, after friction stir processing, the tensile and creep strength of the samples at 210 °C increased by 31% and 47%. In addition, a three-dimensional model was developed to simulate two-pass friction stir processing using ABAQUS/Explicit software. This model involved the Johnson-Cook models for defining material behavior during the process and identifying the fracture criterion. To control the mesh distortion during consecutive passes, the Arbitrary Lagrangian-Eulerian technique was used. Using the developed model, the peak temperature, thermal distribution, and residual stress field during multi-pass friction stir processing on AZ91 have been studied. The empirical results indicated the beneficial influence of the multi-pass friction stir processing on the microstructure and high-temperature mechanical properties of AZ91 alloy.

Effect of Deformable Baffle on the Mixed Convection of Non-Newtonian Fluids in a Channel-Cavity

A simulation of fluid-structure interaction (FSI) and combined convective heat exchange is accomplished in an open trapezoidal cavity-channel. A non-Newtonian (power law fluid) is inspected within the laminar region. The heat source is simulated by an isothermal hot cavity bottom wall, whereas all the rest solid walls are perfectly insulated. A deformable baffle is fixed at the top wall of the channel and its free end extends towards the open cavity. The location of the deformable baffle on the top wall is varied. The baffle position is investigated together with Richardson number (Ri = 0.01-100) and power law index (n = 0.5-1.5). The problem was solved using finite element method with Arbitrary Lagrangian-Eulerian (ALE) technique. The results are compared with the non-baffled channel. The study shows that the proposed baffled channel enhances the heat transfer notably

Numerical Analysis of Structural Soundness by Sloshing Movement in an External Fuel Tank for Rotorcraft

Fuel sloshing during rapid maneuvers of an aircraft causes significant loads on internal components, which in severe circumstances may break components or pipes and cause fuel to leak out of the fuel tank. Moreover, a significant load is applied to the joints of an external fuel tank by such sloshing movements. This may affect the survivability of the crew as well as the safety of the aircraft, when the joints of the external fuel tank are damaged due to a design that does not accommodate the sloshing load. Therefore, to improve the survivability of aircraft and crew members, the design of external fuel tanks should be performed after estimating the structural soundness for the sloshing load through a numerical analysis of the fuel sloshing conditions. In this study, numerical analysis was performed for a sloshing test of an external fuel tank for rotorcraft. The ALE (Arbitrary Lagrangian–Eulerian) technique was used among the methods of FSI (fluid–structure interaction analysis) and the test conditions specified in the US. Military Specifications (MIL-DTL-27422D) were applied as the conditions for the sloshing movement. As a result of the numerical analysis, the structural soundness of the joints was estimated based on the load imposed on the joints of the external fuel tank. The effects of the sloshing movement on structural soundness were assessed using a margin of safety and the failure index. These were based on the stress to the internal components, metal fittings, and the composite container.

Numerical Simulation on Conical Shaped Charge with Copper Liner in Several Typical Shapes

Jet formation and target penetration capabilities from conical shaped charges with liner geometry of five types: (1) cone, (2) round-tipped cone, (3) hemisphere, (4) ellipsoid, and (5) trumpet, have been simulated via LS-DYNA Multi-Materials Arbitrary Lagrangian Eulerian (MMALE) technique. The objective is to observe the influences of liner types on the penetration features in target block while the amount of explosive and liner material are identical in all charge cases. Simulation results show that the hemispherical liner brings out the lowest penetration, while the ellipsoid and trumpet liners are of middle performance, but, the cone and round-tipped cone liners exhibit best penetration. Shaped charges with ellipsoid liner and trumpet liner present no remarkable discrepancy on penetration depth, however, the entrance holes are dramatically different in geometrical shape. Such penetration features are anticipated to be useful in technical design of shaped charges for some specific applications.

Numerical study on the consequences of different ship collision modelling techniques

ABSTRACTShip collisions are marine accidents that may have catastrophic outcome. Commonly, an orthogonal collision with a fully laden oil tanker at its amidships area is considered. Much less attention is given to collisions affecting struck ship fore and aft part, the effect of struck ship speed, collisions with other floating objects etc. In most of these cases the effect of surrounded water becomes pronounced. Present work aims to investigate the consequences of applying two different realistic ship collision modelling techniques involving fluid-structure interaction (FSI) analysis in LS-Dyna: arbitrary Lagrangian–Eulerian (ALE) technique and rigid body MCOL coupling, using LPG ship and a ferry collision scenario as a study case. First, calibration of ALE parameters was made and then ship collision simulation is performed by ALE technique. In parallel, struck ship hydrodynamic parameters were calculated and collision simulation is performed again using MCOL/LS-Dyna coupling. Then, results are compared and discussed.

Underwater explosion of slender explosives: Directional effects of shock waves and structure responses

The shape of a high-explosive is an important factor to consider in the near-field and contact explosion, but this has been rarely studied previously. In this paper, we first conduct experiments to study the directional effects of the underwater explosion shock wave of slender explosives. A numerical model based on the multi-material arbitrary Lagrangian Eulerian (MM–ALE) technique is then developed to study the influence of the explosive slender ratio on the generated shock waves. The numerical model is validated by experiment data. Then, tests are conducted with constant-mass cylindrical explosives with slender ratios ranging from 2.0 to 9.2. By comparing with the center-detonated spherical explosive, the peak pressure, pulse duration, impulse and energy flux of the underwater explosion of slender explosives are analyzed in detail. Furthermore, the effectiveness of the fluid-structure interaction algorithm is verified through the experimental data of a plate subjected to underwater contact explosion. Finally, the response of plates subjected to the underwater explosion of a slender explosive at different azimuths is studied. The interaction between the plate and the directional loads is analyzed. We conclude that the loads and structure responses of the near-field underwater explosion of slender explosives are different from those of spherical explosives. The analyses and results provide a reference for the near-field underwater explosion loads and structural response studies.

Finite element method based sliding wear prediction of steel-on-steel contacts using extrapolation techniques

Wear is a complex phenomenon, which depends on various parameters such as load, velocity, material properties, surface, environmental conditions, etc. Hence, wear prediction is a challenging part of engineering. This paper focuses on numerically predicting the wear of 304 stainless steel pin sliding against AISI 52100 bearing steel disc, using pin-on-disc tribometer setup. The experiments are performed for loads of 10 N, 30 N, and 50 N and a sliding speed of 0.4 m/s. The wear coefficient and coefficient of friction obtained from the experiments are given as input to a 2D elastic finite element method model using a commercially available finite element method-based software ABAQUS. The differential form of the Archard’s wear law is used to obtain the wear depth at the contact nodes. The UMESHMOTION+ Arbitrary Lagrangian–Eulerian technique is used to update the contact geometry after each wear increment. The major drawback of wear simulation is the large computational time requirement. To address this, three extrapolation techniques are used namely, the constant extrapolation, the linear extrapolation, and the constant pressure extrapolation technique. A new criterion for using extrapolation during sliding wear simulation was proposed. The extrapolation techniques take into consideration the evolution of the contact pressure and contact geometry during sliding wear. The effectiveness of these techniques based on the computational time and accuracy are analysed. Based on the accuracy, the linear extrapolation technique was found to be most effective, while the constant pressure extrapolation technique was most useful in reducing the computational time. The numerical results obtained are validated with the experimental results.

Temperature fields in linear stage of friction stir welding: Effect of different material properties

Friction stir welding is one of the procedures for joining the parts in solid state. Thermo-mechanical simulation of the friction stir welding of high-strength aluminium alloys 2024 T3 and 2024 T351 is considered in this work. Numerical models corresponding to the linear welding stage are developed in Abaqus software package. The material behaviour is modelled by Johnson-Cook law (which relates the yield stress with temperature, strain and strain rate), and the Arbitrary Lagrangian-Eulerian technique is applied. The difference in thermo-mechanical behaviour between the two materials has been analysed and commented. The main quantities which are considered are the temperature in the weld area, plastic strain, as well as the rate of heat generation during the welding process.

Distributed Lagrange Multiplier/Fictitious Domain Finite Element Method for a Transient Stokes Interface Problem with Jump Coefficients

The distributed Lagrange multiplier/fictitious domain (DLM/FD)-mixed finite element method is developed and analyzed in this paper for a transient Stokes interface problem with jump coefficients. The semi- and fully discrete DLM/FD-mixed finite element scheme are developed for the first time for this problem with a moving interface, where the arbitrary Lagrangian-Eulerian (ALE) technique is employed to deal with the moving and immersed subdomain. Stability and optimal convergence properties are obtained for both schemes. Numerical experiments are carried out for different scenarios of jump coefficients, and all theoretical results are validated.

The influence of low‐plasticity burnishing process on the fatigue life of friction‐stir‐processed Al 7075‐T6 samples

AbstractThe effects of low‐plasticity burnishing (LPB) on the fatigue life of friction‐stir‐processed (FSP) Al 7075‐T6 plates were examined experimentally and numerically. Aluminum samples were taken from plates to test fatigue response in the presence of heat‐affected zone (HAZ) at different loading magnitudes. Finite element method was employed to numerically evaluate fatigue life of FSPed samples by means of the Smith–Watson–Topper (SWT) model. Through numerical analysis, the FSP and its cooling procedure were modelled on the basis of the arbitrary Lagrangian–Eulerian technique, and then, the effect of the LPB to assess fatigue response of samples was examined. Aluminum samples undergoing friction‐stir process presented lower‐fatigue life as stresses were highly concentrated within FSP regions. Involvement of LPB regained fatigue durability through compressive residual stress induced on the aluminum samples. The higher applied force over the LPB promoted compressive residual stress on the sample surface and improved fatigue life of samples. The predicted life results were found twice more in magnitude than those of experimentally obtained.

Estimation of Jones-Wilkins-Lee parameters of emulsion explosives using cylinder tests and their numerical validation

A microspheres-sensitized emulsion explosive, to be used in rock blasting tests, is characterized by means of the cylinder test. This test measures the expansion of a copper tube upon detonation of an explosive charge inside. Eight cylinder tests have been made with two different diameters (50 mm and 100 mm) and two different densities (1180 kg/m3 and 1030 kg/m3) in a 2 × 2 × 2 test matrix. The expansion energy is affected by the density but not by the test diameter, which suggests that this explosive, at the densities studied, behaves close to ideal already at 50 mm. The explosive velocity of detonation had been also measured within the trials. In addition, velocities of detonation were measured in six production blasts and reported here. The Jones–Wilkins–Lee (JWL) equation of state parameters have been obtained for this emulsion at the densities and diameters tested. The calculation method includes a radial expansion function, with a non-zero initial velocity at the onset of the expansion. The equations reflecting the CJ state conditions and the measured expansion energy were solved for the JWL parameters by a non-linear least squares scheme. These parameters have been validated with three different LS-DYNA models (Lagrangian-Lagrangian, Smooth Particle Hydrodynamic-Lagrangian, Arbitrary Lagrangian Eulerian-Lagrangian). All models show a good correlation with the test results when comparing them against the detonation pressure, the cylinder wall expansion, the Gurney limit velocities and the radial wall velocities. The Smooth Particle Hydrodynamic is the best numerical model for replicating the detonation pressure, the Lagrangian for the cylinder wall expansion radius and velocity history, and Arbitrary Lagrangian Eulerian on the overall performance. Arbitrary Lagrangian Eulerian and Smooth Particle Hydrodynamic techniques are widely used to describe the materials subjected to large deformations, such as explosives, on full-scale simulations for civil and mining applications. The good agreement between numerical and experimental results justifies the use of these methods to model the expansion of detonation products.

On Evaluation and Comparison of Blast Loading Methods Used In Numerical Simulations

It is crucial to assess the dynamic behavior of structures exposed to blast loading in order to improve the integrity and survivability. Numerical simulations are widely used to predict the response of structures under blast loading. A commercial nonlinear finite element code, LS-DYNA provides three blast loading methods: Empirical blast modeling technique CONWEP, Arbitrary Lagrangian Eulerian technique (ALE), and hybrid CONWEP - ALE technique. In this study, an experimental testing of a flat plate subjected to blast loading is modeled using these three blast loading methods in LS-DYNA. Mesh resolution study of ALE formulation is conducted to determine the influence of element mesh size on predicting blast loading effects that is converted through fluid structure interaction algorithm from Eulerian to Lagrangian type of elements. It is drawn a comparison between peak pressures calculated in simulations and maximum dynamic deformation measured in the field test. Finally, the discussion and conclusion are provided.

Blast Damage Assessment of Symmetrical Box-Shaped Underground Tunnel According to Peak Particle Velocity (PPV) and Single Degree of Freedom (SDOF) Criteria

This study aimed to determine the reliability of the damage criteria that was adopted by the peak particle velocity (PPV) method and the single degree of freedom (SDOF) approach to assess the damage level of a box-shaped underground tunnel. An advanced arbitrary Lagrangian Eulerian (ALE) technique available in LS-DYNA software was used to simulate a symmetrical underground tunnel that was subjected to a surface detonation. The validation results of peak pressure into the soil revealed a good consistency with the TM5-855-1 manual within differences that were much less than previous numerical studies. The pressure contours revealed that the blast waves travelled into the soil in a hemispherical shape and the peak reflected the pressure of the tunnel that occurred immediately before the incident pressure reached its highest value. The assessment results proved that the criteria of the above methods could efficiently predict the damage level of a box-shaped tunnel under different circumstances of explosive charge weight and lining thickness at a depth of 4 m within slight differences that were observed during van and small delivery truck (SDT) explosions. However, the efficiency of both the methods was varied with the increase of burial depth. Whereas, using the PPV method significantly underestimated or overestimated the damage level of the tunnel, especially during SDT and container explosions with a lining thickness of 250 mm at burial depths of 6 and 8 m, respectively, the damage level that was obtained by the SDOF method greatly matched with the observed failure modes of the tunnel. Furthermore, new boundary conditions and equations were proposed for the damage criteria of the PVV method.

Large deformation finite element analysis of the installation of suction caisson in clay

ABSTRACTThe suction caisson (or called suction anchor) which is considered as a relatively new type of foundation of offshore structures, has been extensively studied and applied for offshore wind turbines and oil platforms. The installation of the suction caisson is of great importance in the design and construction because it can bring about several issues and further influence the performance of holding capacity in safety service. In this paper, large deformation finite element (FE) analyses are performed to model the installation of suction caisson (SC) by suction and jacking in normally consolidated clay. The penetration of the suction caisson is modeled using an axisymmetric FE approach with the help of the Arbitrary Lagrangian–Eulerian (ALE) formulation which can satisfactorily solve the large deformation problem. The undrained shear strength of the clay and elastic modulus are varied with depth of soil through the subroutine VUFIELD. The numerical results allow quantification of the penetration resistance and its dependence on the installation method. The centrifuge test and theoretical solution are used for the FE model validation. After the validation, the penetration resistance, the soil plug heave, and the caisson wall friction have been examined through the FE model. Based on the numerical results, it is shown that the ALE technique can simulate the entire suction caisson penetration without mesh distortion problem. The installation method can play an important role on the penetration resistance, namely, the suction installation reduces the penetration resistance significantly compared to the purely jacked installation. With a further study on the suction case, it is found that as the final applied suction pressure increases, the soil plug heave increases, while the penetration resistance reduces with increase of the final suction pressure. The effect of the friction of internal caisson walls has been also investigated and a conclusion is drawn that internal wall friction has a significant contribution to the penetration resistance and it can be implicitly represented by varying coefficient of internal wall friction. As for the penetration resistance, both jacked and suction installation have great dependency on the internal wall friction.