Explicit Finite Element Method Research Articles

Nonlinear Computational Welding Mechanics for Large Structures

In the construction of thin plate steel structures, including ships, welding is widely used to join parts. Welding inevitably causes deformation in thin plate structures, which may cause various problems. In the present study, an analysis method is developed to realize the prediction of deformation during the construction of large-scale structures based on the thermal elastic plastic analysis method. The developed method uses the idealized explicit finite element method (IEFEM), which is a high-speed thermal elastic plastic analysis method, and an algebraic multigrid method (AMG) is also introduced to the IEFEM in order to realize an efficient analysis of large-scale thin plate structures. In order to investigate the analysis accuracy and the performance of the developed method, the developed method is applied to the analysis of deformation on the welding of a simple stiffened structure. The developed method is then applied to the prediction of welding deformation in the construction of a ship block. The obtained results indicate that the developed method has approximately the same analysis accuracy as the conventional method, and the computational speed of the developed method is dramatically faster than that of the conventional method. The developed method can analyze the welding deformation in the construction of the ship block structure which consists of more than 10 million degrees-of-freedom and is difficult to solve by the conventional method.

Finite element evaluation of the effects of curvature in Lamb waves for composites structural health monitoring

Abstract This work presents the effect of the high curvature to thickness ratio on the characteristics of Lamb Waves propagating over the skins of composite structures. It is accessed how the curvature on composite skins affects the group velocity of the symmetrical (S0) and asymmetrical (A0) wave modes. It is also accessed the gradient of curvature effect, when the wave propagates from a flat to a curved part on the skin. The results are intended to be used for the improvement of structural health monitoring of wings and wind turbine blades. This is accomplished through dynamic explicit linear finite element method simulations of plates with flat and curved parts made of Eglass-epoxy bidirectional laminate. As the skin structures are often designed to withstand torsional loads, the fibers are aligned with 45 degrees from the leading edge (curved region) throughout the analysis. Several skins with different curvature to thickness ratios are generated and simulated. Results and trends are presented and can be used to improve the algorithms for damage detection on those structures. It is shown that the group velocity of the incoming waves change considerably with the presence of curvature, for both main modes of vibration.

Numerical modeling of dynamic frictional rolling contact with an explicit finite element method

The modeling of dynamic frictional rolling contact is crucial for accurately predicting behavior and deterioration of structures under dynamic interactions such as wheel/rail, tire/road, bearings and gears. However, reliable modeling of dynamic frictional rolling contact is challenging, because it requires a careful treatment of friction and a proper consideration of the dynamic effects of the structures on the contact. This study takes the wheel-rail dynamic interaction as an example to systematically explore the core algorithms for the modeling of dynamic frictional rolling contact by way of explicit finite element analyses. The study also theoretically demonstrates that the explicit finite element method handles nonlinearities in friction, material properties, arbitrary contact geometries and boundary conditions, and fully couples the calculation of frictional rolling contact with the calculation of high-frequency structural dynamics. An indirect validation method for dynamic contact solutions is proposed. To promote the broad use of the method, this paper proposes a detailed procedure for establishing robust wheel-rail dynamic interact tion models and obtaining dynamic contact responses. The proposed procedure can also be applied to the modeling of dynamic interactions occurring to tire-road, bearings and gears.

Nonlinear dynamics of a planar beam\u2013spring system: analytical and numerical approaches

The multiple timescales method is applied to the exact partial differential equations of the planar motion of a hinged–simply supported beam with a linear axial spring of arbitrary stiffness. The forced-damped and free oscillations of the system around frequencies corresponding to nth natural bending mode are examined thoroughly and compared with numerical simulations as well as with already published results obtained by Lindstedt–Poincaré method. A special numerical technique using explicit finite element method to draw the frequency–response curves is appositely developed. The well-known jump phenomena between resonant and non-resonant branches, as well as superharmonic resonances, have been detected numerically.

Experimental and numerical research on damage localization in plate-like concrete structures using hybrid approach

This paper presents an experimental–numerical analysis of damage localization of concrete plate-like elements on the basis of hybrid approach. The proposed hybrid approach uses the fast discrete wavelet transform, energy approach, and time of flight criterion for the purpose of localization of single and multidamage problems inside or on the periphery of concrete elements. Verification of the proposed damage localization approach has been performed under laboratory conditions using a laser scanning-based system with piezoelectric excitation of the wave propagation. Numerical simulation of the wave propagation is performed using the explicit finite element method using 3D models with linear-elastic material model of concrete with Rayleigh damping. The Rayleigh damping coefficients are determined on the basis of experimental data and implemented in numerical models. Validation of the numerical model is conducted, based on the comparison with sensor output signals obtained through experimental measuring and a very good agreement of results is obtained. The proposed hybrid approach to damage localization is verified using 15 different models/specimens, varying the number, shape (circular or notched), and position of damage, as well as the number and placement of actuators/sensors. For all the analyzed scenarios, the hybrid approach successfully localized the damage even for the least number of used sensor positions. In the models with the circular damage, the damage image created on the basis of the hybrid approach is almost identical to the actual shape of the damage, indicating a good potential of the method for damage localization.

A Wireless Sensor Telemeter for in situ Cage Vibration Measurement and Corroboration with Analytical Results

ABSTRACTThis article presents both experimental and analytical investigations on the dynamic behavior of the cage in a ball bearing. For the experimental investigation, a wireless sensor telemeter system was designed and developed to monitor the cage motions. The sensor, which was integrated on the bearing cage, is composed of a commercially available capacitor–inductor (LC) circuit. The LC circuit on the rotating cage was coupled to a transceiver that was stationary and positioned in close proximity to the cage. In order to achieve the objective of the analytical investigation, the explicit finite element method (EFEM) was used to simulate the bearing cage. The EFEM cage model was then combined with the dynamic bearing model to simulate the cage motion during operation. The results from the experimental measurement using the telemeter were then compared with the analytical modeling. The developed telemeter demonstrated the capability of the cage telemeter in detecting various bearing frequencies. These include the cage frequency, shaft frequency, and ball pass frequency on the outer race (BPFO), which was introduced by creating a spall on the bearing outer race. Compared to standard accelerometers that are commonly used to measure vibrations on the bearing housing, the cage telemeter has shown advantages in sensing cage motions and detecting bearing defects regardless of the location of the damage. Analytical simulation using the EFEM cage model correlated well with the experimental results and provided more insight into the bearing cage dynamics.

3D explicit finite element analysis of tensile failure behavior in adhesive-bonded composite single-lap joints

The tensile failure behavior in adhesive-bonded composite single-lap joints with different overlap lengths is investigated through experiments and various three-dimensional (3D) explicit finite element methods (FEMs). Different failure modes are observed in different overlap lengths. Three parameterized finite element models are developed to discuss the accuracy and applicability of the 3D explicit FEMs based on different modeling strategies and improved failure criteria. All criteria are programmed with the explicit user subroutines employing element deletion to avoid convergence problems caused by element distortion. The load-displacement curves predicted by these models are consistent with the experimental results, while the prediction of failure morphology depends on model types. The models neglecting interface elements cannot simulate the delamination when cohesive zone models (CZMs) are adopted to predict adhesive failure. The influence of CZMs on delamination is analyzed comprehensively to address this problem. Analysis of stress distribution in an overlap of a length of 10 mm indicates that the peak stress of the adhesive layer occurs on the overlap ends along the axial direction, coinciding with implicit results.

Reliability analysis of H-section steel columns under blast loading

In order to prevent structural collapse by terrorist attacks, the column behavior is highlighted since when a column is damaged consequently losing its load bearing capacity, failure will spread to the rest of the structure resulting in the collapse of the entire structure. In this paper, using the reliability theory and taking into account the uncertainties associated with blast loading and material properties, a methodology is improved for determining the damage probability of a steel column under various blast scenarios. Damage is determined according to damage index based on axial load-bearing capacity. The Monte Carlo simulation method is utilized using an explicit finite element method to obtain the failure probability. The results are described in terms of damage probability, effects of boundary conditions, effect of type of probability density function and sensitivity analyses. The results show the importance of considering the uncertainties in assessing the damage index of the columns against explosion. Also, it is found that in the flexural mode the probability of damage decreases as the support condition changes from pinned to fixed ends. Furthermore, the safe protective distances are estimated based on the concept of damage probability. Likewise, results for log-normal random variables are relatively identical with truncated normal random variables. The results of the sensitivity analyses show that damage index has the highest sensitivity to peak reflected pressure.

Effect of inclination and anteversion angles on kinematics and contact mechanics of dual mobility hip implants

BackgroundSteep inclination and excessive anteversion angles of acetabular cups could result in adverse edge-loading. This, in turn, increases contact pressure and impingement risk for traditional artificial hip joints. However, the influence of high inclination and anteversion angles on both the kinematics and contact mechanics of dual mobility hip implants has rarely been examined. MethodsThis study focuses on investigating both the kinematics and contact mechanics of a dual mobility hip implant under different inclination and anteversion angles using a dynamic explicit finite element method developed in a previous study. FindingsThe results showed that an inclination angle of both the back shell and liner ranging from 30° to 70° had little influence on the maximum contact pressure and the accumulated sliding distance of inner and outer surfaces of the liner under normal walking gait. The same results were obtained for an anteversion angle of the liner varying between −20° and +20°. However, when the anteversion angle of the liner was beyond this range, the contact between the femoral neck and the inner rim of the liner occurred. Consequently, this caused a relative rotation at the outer articulation. InterpretationsThis suggests that both inclination and modest anteversion angles have little influence on the kinematics and contact mechanics of dual mobility hip implants. However, too excessive anteversion angle could result in a rotation for this kind of hip implant at both articulations.

Investigation of conjugation nodes of a structure's loadbearing elements in the nonlinear formulation

When designing beam grids and frameworks for industrial and public buildings, contemporary engineering makes use of finite-element complexes. Loadbearing structures are usually modeled with beam-type finite elements. The joints between elements are typically modeled as perfect hinges or entirely rigid. Nodes are designed separately depending on the previously obtained loads aided by different tools, ad-hoc software among others. The actual behavior of nodes is different from that of a perfect model. This necessitates a research on the effect the assumptions and simplifications make on the stress (strained) condition of loadbearing structures and nodes. The paper scrutinizes the behavior of hinged nodes. The research is centered around a welded steel I-beam hinged on both sides. The beam was modeled in two ways: using rod finite elements supported with perfect hinges on both sides and via dimensional finite elements, where modeling in its own right was performed for the hinged nodes located on the welds. The structure was stressed evenly with a distributed one-parameter load increasing from zero to a certain finite value at which the beam collapses. The beam is considered to fail as soon as fiber yielding behavior arises in the flanges of the welded I-beam. The calculation was run in the multipurpose software complex LS-DYNA employing explicit and implicit finite element methods as well as nonlinear static techniques. The research has revealed that the actual hinged node is not a perfect hinge and has a certain finite rigidity. Thus, the actual beam, as opposed to a perfect beam, will exhibit a bending moment, while the moment will have a smaller value across the span. Since the node was designed for a transverse force only, the real behavior of the weld exhibits plastic deformations driven by the bending moment. Moreover, deformations arise in the gusset plates and in the web of the welded I-beam where the maximum strain caused by bending moments manifests itself. Research has discovered that failure does not happen due to the minuteness of such deformations. Thus, the conclusion can be made that a hinged beam can be designed as a beam with perfect hinges, but it will at the same time modeled with a surplus. The results obtained are backed up by the data given in various sources.

Numerical study on the water entry of curved wedges

ABSTRACTThe water entry problem of wedges has attracted a great deal of research, as the V-shaped cross-section is a typical section form of the bottom of high-speed crafts. While most investigations focus on flat wedges, the effect of geometric curvature on the water entry of rigid sections is yet to fully be analysed. In this paper, the water entry of curved wedges is numerically investigated using the explicit finite element method. A convergence study is conducted for two typical curved wedges. The numerical method is validated by comparing the impact velocity and the penetration depth with the experimental data. Moreover, the water entry of different curved wedges is simulated with different impact velocities and motion states. And the influences of the curvature and the impact velocity on the impact force, the slamming pressure distribution and the wetted width are investigated and discussed.

Simulation of 2D linear crack growth under constant load using GFVM and two-point displacement extrapolation method

• A novel GFVM formulation is introduced for modeling 2D irregular crack propagation . • Unstructured GFVM is useful to solve crack propagation in geometrically complex structures. • Matrix free GFVM reduces computation time of iterative or time-dependent solutions. • Linear GFVM produces accurate results near the crack, where small elements are needed. A new approach to model two-dimensional linear crack propagation, based on the Galerkin Finite Volume Method (GFVM), is proposed. The displacement field is calculated using the GFVM method by solving two-dimensional equilibrium equations on an unstructured triangular mesh. An essential feature of this method is that it does not require matrix operations; hence, it obviously reduces computation time. The Two-Point Displacement Extrapolation (TPDE) technique is employed to calculate Stress Intensity Factors (SIFs). The accuracy of the structural solver that has been developed is evaluated using five test cases. In the first example, a Timoshenko cantilever beam, carrying an end point load, is analyzed. In the second and third examples, stress intensity factors are computed for edge and inner crack development in plates under transient loading. The GFVM results are then compared with their counterparts that resulted from the Explicit Finite Element Method (E-FEM). The comparison indicates that the FVM has an accuracy close to E-FEM, whereas the FVM drastically reduces the computational time. A case study is conducted to simulate the gradual propagation of crack. The results computed by the numerical simulation presented are in excellent agreement with the corresponding results from the analytical solution as well as experimental measurements.

Critical helical buckling load assessment of coiled tubing under axial force by use of the explicit finite-element method

Previous theoretical formulations for helical buckling of drill strings vary significantly and are mostly proposed for the linear questions. But there are a little no-linear questions in the mechanical behaviour of tubulars. Explicit finite element analysis (FEA)method has the ability to consider geometric details and nonlinearities. This paper builds an explicit FEA model to describe the behaviors of comprehensive buckling and transmission of axial force for coiled tubing (CT) with residual bending in a horizontal well. The calculational results show that the CT with residual bending is easier to buckle than a straight CT. For the CT with an initial sinusoidal shape, the parameters of initial amplitude and initial pitch are inversely proportional to the helical buckling force, and the outer diameter (OD) is proportional to the helical buckling force. In the process of axial force transmission, the parameters of initial amplitude and frictional coefficient are inversely proportional to the axial force, the OD and initial pitch are proportional to axial force. Residual curvature in coiled tubing appears to have only a small effect on its downhole performance, based on FEA modeling of CT with sinusoidal curvature.

A multi-field analysis of hydrodynamic lubrication in high speed rolling of metal strips

This paper presents a multi-field analysis of full hydrodynamic lubrication in high speed cold rolling of metal strips. A robust method was developed to solve the fluid field (the lubricant flow at the roll-strip interface) and solid field (the elastoplastic deformation of a metal strip) in a simple step. The elastoplastic deformation of the strip was solved by a dynamic explicit finite element method while the hydrodynamic pressure was calculated by the Reynolds equation. A cavitation boundary was introduced to determine the hydrodynamic pressure when the lubricant film breaks down. In addition, the coupled interaction between the lubricant flow and the elastoplastic deformation of the strip, which was caused by the hydrodynamic pressure and lubricant shear stress at the solid-liquid interface, were successfully treated by an additional penalty term. Both the pressure-driven term and lubricant shearing term were used to calculate the lubricant shear stress. The introduced penalty method enables a stable numerical calculation of Reynolds equation at a high hydrodynamic pressure. The method has overcome the traditional difficulties in solving the interface contact pressure within separated zones and has led to new understanding of the effects of rolling speed and pressure coefficient of the lubricant on the hydrodynamic pressure and lubricant film thickness.

Experimental and numerical studies on flow behavior of surface defects in the heavy rail rolling

PurposeSurface defects are often present on the surface of continuous casting slabs and rolled products. A lot of surface defects of hot rolled products are inherited from initial defects on continuous casting slabs. This work aims to trace the original surface defect during the whole heavy rail rolling and avoid black line surface defect that appears on the surface of heavy rail finial product.Design/methodology/approachArtificial round hole-shaped surface defects on the surface of continuous casting slab during the hot rolling of 60 kg/m heavy rail are analyzed experimentally and by means of explicit dynamic finite element method (FEM) and modified model rebuilding method.FindingsThe calculated results of surface defect locations of heavy rail finial product are in good agreement with the experimental ones. It is shown that the explicit dynamic FEM and modified model rebuilding method can be used effectively to predict the flow behavior of surface defects in the hot rolling of 60 kg/m heavy rail.Originality/valueThe three-dimensional finite element model for whole heavy rail rolling is built using explicit dynamic code and modified model rebuilding method. Flow behavior of black lines is studied in the 60-kg/m heavy rail rolling. The simulation results of six typical points are in good agreement with the experimental results.

Suppression mechanism study of attached apex drogue on undesirable inflation phenomena

At present, the studies of suppression effect of attached apex drogue on undesirable inflation were seriously dependent on experiments. The experiments were difficult to reveal the suppression mechanism due to the difficulty of data collection. In this paper, a FSI (Fluid Structure Interaction) model based on explicit finite element method was proposed to study the suppression mechanism. The graphical deformation method was used to realize the movement of computational domain. At the same time, the velocity conditions were applied on the boundaries of computational domain, which was used to simulate the external wind field. The coupling between the fluid and structure described by Lagrangian meshes was realized by contact algorithm. Finally, an extra-large parachute was taken as the research object, and the suppression mechanism of attached apex drogue was analyzed according to the numerical results. The effect of different attached apex drogues with different resistance characteristics also was analyzed by the above FSI model. The analysis model and method proposed in this paper could provide the design basis of extra-large parachute.

Numerically stable explicit time-domain finite element method for room acoustics simulation using an equivalent impedance model

This article presents a numerically stable explicit time-domain finite element method (TD-FEM) for room acoustic simulation using an equivalent impedance model. Performance over a conventional explicit TD-FEM is demonstrated using numerical experiments. Both explicit TD-FEMs were based on simultaneous first-order ordinary differential equations. The conventional method has a stability problem derived from backward difference approximation of time derivative of sound pressure related to a dissipation term for treating absorption at a boundary. The numerically stable explicit TD-FEM avoids the stability problem through the combined use of first-order forward and backward difference approximation. A completely explicit algorithm is obtainable using a lumped dissipation matrix. Numerical results demonstrate that the proposed explicit TD-FEM is stable for changing impedance values at boundary surfaces. In addition, numerical dissipation and dispersion error analyses revealed that both explicit TD-FEMs have small dissipation error. Moreover, the proposed method has slightly lower accuracy than the conventional explicit TDFEM. However, the proposed method is computationally more efficient than the conventional method for acoustics simulation of rooms with smaller impedance values at boundaries.

Bearing failure of single-/double-shear composite bolted joints: An explicit finite element modeling

A three-dimensional explicit finite element method was presented to investigate the bearing failure of single- and double-shear composite bolted joints. To predict the various failure modes of composite laminates, three-dimensional solid elements accompanied by mixed-mode failure criteria considering nonlinear shear behavior were employed in the model. A linear damage propagation law based on the fracture energy and the characteristic length was adopted to alleviate the mesh dependency. In addition, reduced integration elements were used in the models of single- and double-shear joints to avoid the overstiffness. The simulated models were implemented in the Abaqus/Explicit solver with a user-defined material subroutine. The numerical analysis run successfully without any convergence issues. The predictions of mechanical behavior agreed well with the experimental results, with typical damages in the laminates including matrix crack and fiber failure. The effect of secondary bending in the single-shear bolted joint was also analyzed in the explicit modeling.

Dispersion Properties of Explicit Finite Element Methods for Wave Propagation Modelling on Tetrahedral Meshes

We analyse the dispersion properties of two types of explicit finite element methods for modelling acoustic and elastic wave propagation on tetrahedral meshes, namely mass-lumped finite element methods and symmetric interior penalty discontinuous Galerkin methods, both combined with a suitable Lax–Wendroff time integration scheme. The dispersion properties are obtained semi-analytically using standard Fourier analysis. Based on the dispersion analysis, we give an indication of which method is the most efficient for a given accuracy, how many elements per wavelength are required for a given accuracy, and how sensitive the accuracy of the method is to poorly shaped elements.

Dynamic analysis of lunar lander during soft landing using explicit finite element method

In this paper, the soft-landing analysis of a lunar lander spacecraft under three loading case was carried out in ABAQUS, using the Explicit Finite Element method. To ensure the simulation result's accuracy and reliability, the energy and mass balance criteria of the model was presented along with the theory and calculation method, and the results were benchmarked with other software (LS-DYNA) to get a validated model. The results from three loading case showed that the energy and mass of the models were conserved during soft landing, which satisfies the energy and mass balance criteria. The overloading response, structure steady state, and the crushing stroke of this lunar lander all met the design requirements of the lunar lander. The buffer energy-absorbing properties in this model have a good energy-absorbing capability, in which up to 84% of the initial energy could be dissipated. The design parameters of the model could guide the design of future manned landers or larger lunar landers.