Explicit Finite Element Method Research Articles

Beirut explosion 2020: A case study for a large-scale urban blast simulation

In the face of continued global urbanization, cities are challenged to satisfy increasing standards in terms of quality of life, environmental conditions, safety, security, health, economic growth and mobility. The concept of “smart cities” aims at utilising advanced technologies, artificial intelligence and high computational capacity to increase their resilience and improve the services provided to the citizens. Computation-based numerical simulations have been essentially used to estimate the effects of explosion events in urban environments in terms of both structural damage and human casualties. These provide urban planners and decision makers with valuable information for vulnerability assessment and aid developing prevention or mitigation solutions. In this article, we present a framework to generate a 3D large-scale urbanistic finite element model, where the desired geospatial data are extracted from the open-source world map OpenStreetMap. The model is used to simulate blast wave propagation effects in a wide urban area taking into account the reflections at building surfaces via a sophisticated Fluid-Structure interaction technique integrated in the EUROPLEXUS explicit finite element method software. The explosion in the Port of Beirut in Lebanon, which took place on the 4th of August 2020, was remarkable for the large amount of explosive material causing considerable damage to surrounding structures and a high number of deaths and injured. Such characteristics make the event suitable for assessing the performance of the proposed computational approach in a widely exposed (by the blast wave) urban zone.

Fully coupled model for simulating highly nonlinear dynamic behaviors of a bubble near an elastic-plastic thin-walled plate

On the basis of the boundary element method and explicit finite element method, a three-dimensional fully coupled model is developed to investigate the interaction between a bubble and an elastic-plastic thin-walled plate. The model can accurately calculate the bubble loading acting on the plate surface and describe the structural motion coupling with the flow field on two sides of the plate. As a result of the elastic-plastic effects of the thin-walled plate, the bubble displays attractive motion, repulsive motion, or splitting.

An improved material point method for coining simulation

Extremely small time step caused by large deformation in coining process significantly increases computational time in dynamic explicit finite element method (FEM). Furthermore, negative volumes of distortion elements in the rim of coin lead to abnormal termination of simulation. In order to overcome these problems, dynamic explicit material point method (MPM) is employed for coining process. However, most of the point-to-point contact algorithms in MPM cause fake contacting detection. In addition, abundant tiny patterns on die surfaces put forward high requirement for the contact algorithm to calculate the normal vectors. A point-to-segment based contact algorithm is proposed to obtain accurate normal vectors at real physical contact point and embedded into the framework of modified update stress last (MUSL) for simulating coining. Amount of data storage and computations are reduced since the background domain only contains the deformable workpiece and one velocity field is required. The improved MPM is applied to predict insufficient filling during minting, and its performance is validated by experimental results.

Development of an MTF in ADINA and its application to the study of the Yuxi Basin effect

A three-dimensional multitransmitting formula is developed in ADINA to simulate the input of seismic waves and the scattering of infinite domains at the same time, consistent with the progress of the explicit finite element method of lumped mass. A three-dimensional cube model is built, and a delta pulse wave is input to compare the simulation results with the analytical solutions. The simulation results show that the peak error is 0.2% of the input wave, which meets the requirements of the usual numerical simulation. This method has a certain efficiency advantage in site effect analyses of fine models for localized fields. A velocity structure model of the Yuxi Basin is built, and the associated basin effect is studied by numerical simulation. The distribution of the focusing effect is related to the structure of the narrow east-west and wide north-south features in the Yuxi Basin, and the edge effect is related to the slope of the basin base. A distribution map is given of the amplification effect of ground motion in the basin.

Numerical studies of the low velocity impact behaviour on hybrid fiber metal laminates

Abstract The Fiber metal laminates (FML) are the advanced composites that comprise the property of metal and FRP layers. FMLs are used for the manufacturing of fuselage skins, Cargo floors and the leading edge of aircraft etc. In this paper, Explicit Finite element method used for the simulation of low velocity impact behaviour on the fiber metal laminates. The FML with glass fiber (GFML) and FML with hybrid (Carbon + Glass) fiber (HFML) have been considered for the simulation. The Johnson-Cook material model is used to model the plasticity and damage of the Aluminium layer. Hashin Damage criteria were used for the FRP layers. Comparison of Force-Time and Force- Displacement histories are carried out. From the studies it is found that Carbon and Glass fiber based HFML are superior compared to the GFML.

Explicit finite element analysis of slope stability by strength reduction

The construction of stable slopes and vertical cuts is an important step in many geotechnical projects. Limit equilibrium methods (LEMs) are well-accepted procedures to compute factors of safety (FoS); however, they fail to provide any information about the distribution of the field variables within the soil mass because they do not include any stress-strain relationship in their formulation. On the other hand, the iterative finite element method (FEM/I) can estimate the field variables, but in the current study, we show that, for steep slopes and vertical cuts, it underestimates the FoS compared to the LEM. To overcome the obstacles that exist in this method, this study proposes a new approach to define the initiation of instability based on an abrupt change in the kinetic energy of the system. We also suggest a procedure to calculate the minimum FoS based on the explicit finite element method (FEM/E). Comparison of the results obtained from the proposed method, LEM, and FEM/I revealed that the FoS computed by the proposed method is in good agreement with the results of the LEM for a wide range of material parameters, geometries and external loading conditions, while no assumption regarding the critical slip surface needs to be made.

High-fidelity damage modelling of CFRP laminates for impact and crashworthiness applications – dynamic tube crushing simulations

Drop weight impact experiments were conducted on angle-ply carbon fibre reinforced polymer (CFRP) composite crush tubes. The dynamic response was modelled using explicit finite element methods and continuum damage mechanics and cohesive zone modelling in both Abaqus/Explicit and LS-DYNA. User-defined constitutive models for the intra-ply behaviour were used and a fibre-aligned meshing technique was implemented. The results of the experiments and simulations are compared to evaluate accuracy of the different modelling techniques, highlighting the advantages and drawbacks of each approach. Among these, the choice of meshing strategy is shown to be especially important in capturing the physical propagation of cracks and damage mechanisms in CFRP laminates.

Fluid Independent Flow Determination by Surface Acoustic Wave Driven Ultrasonic Techniques

A fluid-independent ultrasonic approach for flow determination in microchannels in the harsh environment of an ultra high pressure liquid chromatography (UHPLC) system is presented. Ultrasonic waves in the fluid are excited by separate media surface acoustic waves (SAW) of Rayleigh-Wave type. The LiNbO3 SAW chip being equipped with interdigitated transducers for SAW excitation also marks the bottom of the fluid channel and thus allows for very effective SAW coupling to the fluid. The channel ceiling acts as an acoustical mirror for longitudinal ultrasonic waves propagating through the fluid. To deduce the fluid flow from the ultrasonic transmission after reflection, we employ a combination of time differential phase and time of flight measurements with a two port vector network analyzer. To verify and assign our experimental results, we use an adapted time explicit finite element method. In the simulation, both the piezoelectric single crystal and the fluid are included and we solve the linear Navier-Stokes equation to evaluate the background flow. By changing the ultrasonic propagation direction, we are able to deduce the fluid volume flow over time with very high accuracy, independent of the actual liquid in the channel.

Cutting dynamics sample generator for artificial neural networks based on design space exploration and explicit simulation synergy

The cutting operations represent the main methods in surface generation for mass production. The dynamic control of these processes is directly linked to various phenomena like chatter, adhesion and wear. Left undetected or/and uncontrolled, these phenomena can have a great impact on cost and productivity.Novel numerical solutions development that can accurately predict nonlinear behaviors of such mechanical processes are possible with increasing computation efficiency. As such, artificial neuronal networks (ANN) have become increasingly used in all industries, including manufacturing.In order to train an ANN, the requirement is to have a large, varied, and representative number of samples. Prediction performance will be given by the number of samples and their distribution over physical ranges. Also, the complexity level of the dynamic system modeled with ANN depends on the number of samples required for training, further strengthening the demand for a solution to generate them synthetically.This paper presents an innovative method for synthetic generation of cutting data which takes advantage of design space exploration (DSE) solutions and is based on 2D explicit finite element method (CAE) simulations. The synergy created between the DSE and CAE solutions can create guided simulation loops that are very powerful due to the overall control of the optimization parameters. This well-suited environment for supervised data generation represents a very important part of ANN training and it has a great impact on training efficiency.The present paper offers a possible solution for implementing this method, focusing on simulating the cutting dynamics for turning and on the parameter interdependencies definition such that all quantities (input and output) can be used to train an ANN. The paper concludes with an analysis of the obtained samples, data structure, and the applicability of the data for the intended purpose.

Nonlinear Blast Responses of Thin Shell Roof Over Long Span Structures

This paper adopts both explicit and implicit finite element methods in a specialist package LS-DYNA to investigate the nonlinear, dynamic response of a long span shell roof structure when subjected to blast loading. Parametric studies have been carried out on blast loaded laminated glass plates with reference to experimental results obtained by European researchers. A case study that has been chosen is a light rail station in The Netherlands called The Erasmusline. Following the detonation of 15[Formula: see text]kg TNT charge, explicit analysis showed breakage surrounding the rigid supports along the edge beam where modal vibrations are restrained. An implicit analysis has confirmed the resonances in global eigen-frequencies where most blast damage is localized around the roof canopy hence producing cracking and potential glass detachment from the panels without full structural demolition. This insight from this study will inform structural engineers about the potential modes of failure and preventative strategies to minimize further secondary losses of life or assets from a terrorist attack.

Optimization and Numerical Analysis of the Ricochet of Conical Nose Projectile in the Collision with Ceramic-Aluminum Armor

The anti-armored bullets have more kinetic energy due to additional mass than ordinary bullets which increases their likelihood function of penetration for a different target. It is necessary to seek solutions to reduce the possibility of penetration of this type of bullets. One of the most important parameters influencing penetration is projectile impact velocity. The mechanism of penetration varies in different velocity ranges. In this paper, the phenomenon of buckling steel cone with a nose cone in a collision with ceramic targets was investigated by the explicit finite element method using LS-Dayna software. The numerical simulation shows acceptable accuracy after comparing the results with previous research. In this study, the critical angle of ricochet at a different velocity ranging from 700 m/s to 1000 m/s and optimization of the optimal thickness ratio of ceramic/metal targets has been considered. According to the simulation outputs and analytical relations, it is clear that the critical ricocheting angle has increased with increasing velocity and the probability of projectile penetration is higher. The results also show that in the case of an oblique collision at a certain angle, the projectile velocity decreases with increasing target thickness with no drastic changes in the directional angle. As the angle of oblique increases, the amount of penetration in the target decreases. For long rod projectiles, the reduction in kinetic energy at the same collision velocities is not much different for both vertical and oblique collision modes. The erosion of the projectile mass in oblique collisions is less than in vertical collisions at the same time.

Finite element method based computational time reversal in elastodynamics: Refocusing, reconstruction and its numerical sensitivity

In this paper, we study the accuracy and robustness of the computational time reversal approach based on the explicit finite element method for application in nondestructive testing in solids. The main goal of this paper is to find a methodology for correct and accurate reconstruction of the original source time history. For numerical modeling of frontal (forward) and reverse (backward) problems of elastic wave propagation, we use the finite element method and explicit time integration with the lumped mass matrix. The suggested methodology is applicable in each finite element open source or commercial software. A special attention is paid to prescription of boundary conditions/loading for the reverse problem for accurate reconstruction of time history of the original source. For evaluation of the reconstruction quality, we suggest certain cost functions. Based on several numerical tests, we show effects of prescription of boundary conditions/loading in time reversal, effect of mesh size and time step size, an unknown obstacle, a number of sources, and environmental disturbance (noise) on the correctness of reconstruction of the original source.

Tool Wear Evaluation Based on Design Space Exploration Coupled with Explicit Cutting Simulations and Cutting Forces Excitation Signature

Cutting operations are still one of the main methods used in the industry for surface generation in mass production. The dynamics of these processes are complex and having a good insight into the interdependencies of the nonlinear physical phenomena can be translated into better cutting performance. One of the main cutting tool geometrical parameter, usually associated with wear, is the cutting edge radius. Continuous direct evaluation of this parameter exhibits some important limitations offline, if this evaluation needs to be online the whole process becomes very complicated due to the measurement limitations that might appear. For online cases, the best approach is to determine the amplitude of this parameter indirectly using various side effects that can be correlated. One possible option is to monitor the vibrations generated by the resulting cutting forces. In the latest years, the usage of explicit finite element methods (FEM) to simulate the cutting processes has grown exponentially with the continuous increase of computation efficiency. With the help of Computer-Aided Engineering (CAE in short) solutions and using the latest advances in design space exploration (DSE) solutions, it is possible to create models able to parametrically explore a design space (DS), having precise targets, and also get the important correlations for all the important, quantifiable, cutting parameters. This paper presents an innovative method to create tool wear evaluation models focused mainly on the cutting edge radius indirect evaluation. The proposed method uses guided simulation loops able to generate a variety of dynamic signatures which are further post-processed to get a complex correlative model. The model can be applied in real cutting cases using the reciprocity property and can determine online the state of the cutting edge radius for further tool wear evaluation. The paper concludes with an analysis of the obtained model and the applicability of the data for the intended purpose.

A Fully Coupled Thermomechanical Damage Analysis of Hot Closed Die Forging Using Finite Element Modeling

Advanced simulations are needed in the industry nowadays for reliable design of various machine parts. A complex computation is presented here to describe the whole manufacturing process, apart from the machining, of forged spur gear for a reverse transmission from a car gearbox. A coupled thermomechanical analysis was realized through the explicit finite element method, while the stress–strain analysis was conducted in all phases of the production with time- and temperature-dependent constitutive law. The influence of process parameters was assessed, and the magnitudes of forging load were compared for selected dimensions of intermediate product (blank) and its initial temperature (preheating). The numerical simulation was finished with the flash trimming along the circumference, so the temperature-dependent ductile failure criterion proposed by Johnson and Cook was accounted for as well.

Optimization and Numerical Analysis of the Ricochet of Conical Nose Projectile in the Collision with Ceramic-Aluminum Armor

The anti-armored bullets have more kinetic energy due to additional mass than ordinary bullets which increases their likelihood function of penetration for a different target. It is necessary to seek solutions to reduce the possibility of penetration of this type of bullets. One of the most important parameters influencing penetration is projectile impact velocity. The mechanism of penetration varies in different velocity ranges. In this paper, the phenomenon of buckling steel cone with a nose cone in a collision with ceramic targets was investigated by the explicit finite element method using LS-Dayna software. The numerical simulation shows acceptable accuracy after comparing the results with previous research. In this study, the critical angle of ricochet at a different velocity ranging from 700 m/s to 1000 m/s and optimization of the optimal thickness ratio of ceramic/metal targets has been considered. According to the simulation outputs and analytical relations, it is clear that the critical ricocheting angle has increased with increasing velocity and the probability of projectile penetration is higher. The results also show that in the case of an oblique collision at a certain angle, the projectile velocity decreases with increasing target thickness with no drastic changes in the directional angle. As the angle of oblique increases, the amount of penetration in the target decreases. For long rod projectiles, the reduction in kinetic energy at the same collision velocities is not much different for both vertical and oblique collision modes. The erosion of the projectile mass in oblique collisions is less than in vertical collisions at the same time.

An empirical approach for penetration of tandem warheads into concrete targets

We develop a semi-empirical or semi-analytical model based on the spherical cavity expansion theory in order to simulate the normal penetration of tandem warheads into concrete targets, which consist of two stages: penetration into a cavity region (or damaged region), and subsequent penetration into an undamaged region. To formulate the semi-empirical model, we consider the first impact of rigid projectiles on the damaged region with a pre-drilled cavity and the second on the undamaged region. For the penetration into the undamaged region corresponding to the second stage, an empirical constant used in the semi-empirical model is determined based on the penetration depth obtained by experiments in the literature. The semi-empirical model is then verified by comparing its results to experimental data and numerical results of the explicit finite element method (FEM) in terms of kinematic quantities of projectiles. For the penetration into damaged concrete targets in which a cavity is considered as a pre-drilled hole, which provides a basis of the formulation for the first stage, the results of the semi-empirical model are compared to experimental data, and an empirical constant is also estimated based on the numerical results of the explicit FEM. Finally, the concrete targets with a finite-length cavity, into which a tandem warhead penetrates, can be regarded as a combination of the damaged region with a finite-length cavity and the undamaged region. In the semi-empirical model for the penetration of tandem warheads, the empirical constants for the first and second stages are employed as those estimated for the damaged region with a cavity of finite length and for the undamaged region, respectively. The results from the semi-empirical model are compared with those from the explicit FEM due to the lack of experimental data. The good agreement of the results of the semi-empirical model and the explicit FEM demonstrates that the proposed semi-empirical model can predict the dynamic behavior of the tandem warheads in a simple and accurate manner.

Experimental and Numerical Crashworthiness Study of a Full-Scale Composite Fuselage Section

This work deals with the development of an improved numerical model, based on the explicit finite element method, aimed at investigating the energy absorption capabilities of a full-scale composite fuselage section of a regional aircraft and the related biomechanical injuries affecting the passengers. The experiment, conducted within the Italian national research project named “Innovative and Advanced Verification and Certification methods,” consisted in a drop test of a fully equipped barrel performed at the Italian Aerospace Research Centre, according to the special conditions of the Federal Aviation Regulation Certification Specification 25. From a free-fall height of about 4 m, a ground contact impact velocity of was measured. The numerical model has been developed faithfully to the experiment. Numerical analysis results, in terms of global deformations, failures, local accelerations, and biomechanical injuries, have been compared with the experimental ones to assess the prediction capability of the proposed numerical modeling procedure with a focus on improved crashworthy components for certification by analysis future purpose.

A GPU-accelerated fluid–structure-interaction solver developed by coupling finite element and lattice Boltzmann methods

This study focuses on finding high-performance numerical solutions to fluid–structure coupling problems encountered in biomechanical engineering. A numerical framework for simulating fluid–structure interaction (FSI) is proposed by strongly coupling the finite element and lattice Boltzmann methods. The lattice Boltzmann method is efficient for solving weakly compressible fluid flows. The explicit finite element method (FEM) is used to solve solid structure deformation. A partitioned iterative solution is adopted to couple these two methods together. A fixed point iteration method is used with the Aitken dynamic relaxation algorithm to improve numerical stability. A multi-direct forcing immersed boundary method with a sub-iteration scheme is adopted to represent the interaction between fluid and structure. Validation of the proposed coupling method was conducted on a vortex induced vibration problem. The numerical results are in good agreement with the reference results (Li and Favier, 2017). The proposed method does not have to solve large systems of linear equations, so it is suited to parallel computation. Therefore, we then present a parallel implementation of our method on a graphics processing unit, which increases the computation speed more than 18-fold. Our developed FSI solver is very efficient, which makes it possible to provide more accurate results with finer meshes. Finally, our method is applied to the simulation of complicated motions of a bileaflet heart valve caused by blood flow.

Seismic slope stability and failure process analysis using explicit finite element method

Earthquake is one of the primary factors that triggers the failure of slopes and the landslides in the mountainous area. In this study, an efficient method for the seismic slope stability analysis and seismic failure process simulation is proposed. The seismic slope stability and the failure process of a two-dimensional slope model are analyzed via the explicit finite element method with the influence of the dynamic mechanical behavior of soil and the frictional resistance characteristic of the slope rupture surface. A dynamic visco-elasto-plastic constituted model for soil is established and written in FORTRAN as a user subroutine of the finite element method code of ABAQUS. The validation of the visco-elasto-plastic constituted model and the explicit finite element method are compared with the experimental results and the implicit method. The seismic factor of safety and the sliding distance of the soil slopes under the natural earthquake conditions are calculated via the dynamic visco-elasto-plastic constituted model and the explicit finite element method. The influence of the ground motion characteristics on the seismic slope stability is analyzed in this study via the specified elastic response acceleration spectrum. The analysis results of this paper suggest that the seismic slope stability analysis and the progressive failure process of the slope under the seismic condition can be analyzed by the explicit finite element method efficiently. The results show that the dynamic mechanical behavior of soil and the ground motion characteristics are both critical influence factors for the seismic slope stability. The frictional resistance characteristic of the slope rupture surface is the principal influence factor for the sliding distance of the slope, and it also has more influence on the sliding distance of a high slope than that of the small slope.

Mathematical model for degradation and drug release from an intravitreal biodegradable implant

In this paper we study from a mathematical point of view the drug release and the degradation process in the context of biodegradable intravitreal implants. In particular, two different clinical situations are considered: non-vitrectomized and vitrectomized eyes. In the former case we assume that the vitreous humor is replaced by a saline solution or a silicone oil. In intravitreal space, the intravitreal liquid enters the implant by non-Fickian diffusion causing the degradation of the poly(lactic-co-glycolic acid) based implant. Then, drug in the implant dissolves and diffuses out of the polymeric matrix. The transport of drug in the vitreous chamber and retina is modeled by Fickian diffusion and convection generated by the flow of the vitreous humor. In order to numerically solve the system of partial differential equations that define the model, we propose an Implicit–Explicit finite element method that allows for the decoupling of the solution reducing the computational cost of the simulations. Several numerical experiments showing the effectiveness of the proposed numerical schemes are also included. The proposed mathematical model may be useful to optimize patient specific treatments in clinical practice.