Commercial Computational Code Research Articles

A three-dimensional finite strain volumetric cohesive XFEM-based model for ductile fracture

The verification/prediction by numerical simulation of the resistance of large-scale metal structures subjected to extreme loading (e.g. accidental mechanical overload) that can lead to failure constitutes a major issue in the transport, energy, and defense sectors. This work aims to develop a three-dimensional numerical methodology (i) capable of macroscopically accounting for the various dissipative mechanisms of plasticity and damage until failure, (ii) formulated within the framework of large deformation, (iii) implemented in a commercial computation code, and (iv) mesh-objective. The commercial computational code is ABAQUS-std, and the methodology is implemented as a user finite element (UEL). Geometric non-linearities are treated within the framework of an updated Lagrangian formulation (ULF). The more or less diffuse damage phase is described by the Gurson–Tvergaard–Needleman (GTN) microporous plasticity model with standard finite element (FE). The micro-void coalescence phase-induced dilation/shear band is described using an original volumetric cohesive extended finite element method approach (VCZM-XFEM). The progressive loss of cohesion leading to ultimate cracking is treated with extended finite element method (XFEM). Particular attention is paid to transition criteria (damage to localization, localization to cracking), to the orientation of the localization plane (especially in Mode II), to the cohesive zone model and to techniques for overcoming numerical difficulties (volumetric locking, numerical integration). The so-built 3D-FS-GTN-VCZM-XFEM unified methodology is capable of reproducing the degradation mechanisms, and, the failure surface shape and orientation in large elasto-plastic deformation of structures typical of laboratory tests, even for fairly coarse meshes.

A CFD examination of free convective flow of a non-Newtonian viscoplastic fluid using ANSYS Fluent

In this work, a laminar steady-state investigation of free convection in a square cavity with differential heated side walls is examined. The cavity is immersed with a viscoplastic liquid the Bingham prototype. The horizontal walls are assumed as adiabatic and the vertical wall has two spatial differing sinusoidal temperature profiles with diverse phases and amplitudes. The hydro-thermal features are systematically analyzed via a broad choice of Rayleigh numbers Ra (103-106), Bingham numbers Bn, Prandtl numbers Pr (0.1, 1, 10), amplitude ratio ε (0–––1), phase difference ϕ (0-π) and flow index n (0.3–2). The governing equations are treated computationally utilizing a commercial computational simulation code CFD: FLUENT. It has been observed that average Nusselt numbers grow with growing Rayleigh numbers and drop with increasing Bingham quantity Bn, since heat transition occurs primarily due to thermic conductivity. In general, a higher Rayleigh number promotes convection and increases heat transfer efficiency, leading toa higher Nusselt number, whereas a higher Bingham number, indicating a higher degree of viscous or yield-stress behavior, may inhibit convection and decrease heat transfer efficiency, which ended in a lower Nusselt number. These connections frequently appear in heat transport and fluid dynamics simulations. The rise in the phase difference suggests an upsurge in heat transference, as the impact of the phase shift on the Nusselt is perpetually enhanced due to the amount of Rayleigh boosts for all phase differences. Heat transition rate forϕ=πis boosted because of the values. Moreover, when the amplitude ratio goes up, so does heat transfer. The gap between average Nusselt and Rayleigh amounts rose as the Rayleigh rose. The thermal flow rate is bigger in ε=1 than in the other cases. The rise in phase difference suggests a rise in heat transference, as this effect of phase shift on Nusselt continues to be enhanced due to the amount of Rayleigh boosts for all phase differences. Heat transition rate is enhanced forϕ=πbased on the values. Plus, when the amplitude ratio grows, so does heat transmission. The rate of heat transport for ε=1 is larger than in the other cases.

Foreword to the special issue on new developments in structural stability.

Foreword to the special issue on new developments in structural stability.

Impact response prediction of square RC slab of normal strength concrete strengthened with (1) laminates of (i) mild-steel and (ii) C-FRP, and (2) strips of C-FRP under falling-weight load

Reinforced concrete (RC) slab is an indispensable component of all kinds of structures to carry gravity loads in general. Quite often than not, the slabs are subjected to impact loads from accidental mishaps, falling construction equipment, and falling boulders and rocks which are not considered in the structural design. Design codes of practice for RC structures permit the structural design based on the experimental investigation which is not viable because of constraints such as experimental facilities, materials, and time requirements. However, current advancements in the computational techniques available make it possible to obtain the comprehensive response of the slabs subjected to impact loadings. In the present research work, different strength-enhancing techniques such as steel/C-FRP sheet laminates and C-FRP strips are considered for impact resistance enhancement of two-way normal strength concrete slab, 1000 mm × 1000 mm × 75 mm, with 0.88 % conventional tension steel reinforcement subjected to a free-falling concentrated load of 1035 N. For this purpose, a 3-D finite element model of impacting test setup is formed in ABAQUS-v.6.15 explicit commercial computer code. Computational analyses and simulations of free-fall impact are carried out on the validated ABAQUS model by allowing a 105 kg steel weight (impactor) from a height of 2500 mm with an initial impacting velocity of 7 m/ sec on the top surface of the slab at its centroid. The Concrete Damage Plasticity model is implored for nonlinear elastic and inelastic behaviors, degradation of stiffness, and loading rate effect on concrete. The nonlinear behavior of the reinforcing bars is taken into account. Steel is idealized with the Johnson-Cook model but the C-FRP laminate is defined or modeled with ABAQUS Hashin’s criterion. It is found that the used strengthening techniques improve the response of the slab in terms of displacement and damage severity, and alter the mode of failure.

The effects of material properties on solute transport during entrapment of a bubble subject to horizontal solidification

Solute transport in the presence of a pore resulting from an entrapped bubble during horizontal solidification of water containing carbon dioxide is numerically and parametrically investigated. Structural material containing pores degrade microstructure, whereas materials with pores can also be functionally used to enhance efficiencies of engineering, foods and biomedical industries, and control outcome of geophysics and global warming, etc. In this study, transport equations including mass, momentum, energy and concentration transport equations satisfied by their interfacial balances between liquid, gas pore, and solid were solved with the COMSOL commercial computer code. Extending previous work dealing with influence of fluid flow, the present results further find that the effects of metallurgical and thermal properties on solute transport processes during entrapment of a bubble. Decreases in Henry's law constant, partition coefficient and liquid solute diffusivity, and increases in solid thermal conductivity increase solute concentration in solid around an entrapped pore. Predicted contact angle during solidification is in good accordance with computed analytical results confirmed by measured data. The findings of this study can help for better understanding of pore formation in the solid during horizontal solidification.

Effect of design strength parameters of conventional two-way singly reinforced concrete slab under concentric impact loading

Damage evaluation and performance enhancement of the structures due to ever-rising malicious sporadic explosions, accidental detonations, vehicular collisions, aircraft crashing, falling construction equipment, and rock/boulder impact from landslips are of considerable concern and thus generate sufficient interest to structural engineers and researchers. In general, the mode of damage to a structure and its degree depends upon which element(s) of the structure is subjected to such impulsive loadings, damage resistance, and energy transferred to the element(s). For a deeper understanding of the failure mode and impact resistance, analysis of the structural elements under impulsive loadings (blast and impact) with varying design parameters seems necessary. The present work undertakes a numerical study to investigate the dynamic behavior of 1000 mm × 1000 mm × 75 mm two-way square singly reinforced concrete slab subjected to drop-weight impact loading at its centroid using a finite element method based commercial dynamic computer code, ABAQUS/Explicit version 6.15. The impact load is applied via a hard steel cone frustum-headed drop weight with a flat impacting face of mass 105 kg having a free-fall from a height of 2500 mm with an impacting velocity of 7.0 m/sec. Two well-known material models namely; Concrete Damage Plasticity (CDP) and Johnson-Cook (J-C) for concrete and steel, respectively, with strain rate effects have been considered. The numerical model of the slab is validated with the impact test results/observations in the open literature. Analyses have been extended to investigate the influence on the impact resistance of the slab by varying slab thickness and concrete strength without altering cover to the concrete, quantity and yield strength of the flexural steel reinforcement on the impact resistance of the slab. The slab is not provided with shear reinforcement. Three different concrete strengths (30, 40, and 50 MPa) for four slab thicknesses (75, 100, 125, and 150 mm) are considered for the parametric investigation. Results have been compared and discussed with regards to peak displacement and impact resistance of the slab.

Transport processes for a bubble entrapment during horizontal solidification

Transport processes coupling with shape development of a bubble captured by a solidification front advancing in a horizontal direction are numerically studied. Porosity in solid plays important roles on microstructure of materials and functional materials in biology, tissue, MEM, micro- or nano-engineering, foods, and geophysics, etc. In view of significant force torque, pore shape development during horizontal solidification is more significant than that during vertical solidification. In this work, transport equations of fluid flow, energy and concentration with sources governing interfacial balance of momentum, energy and concentration in the presence of a bubble entrapped by the solidification front were solved by the commercial COMSOL computer code. The results find the pore shape development affected by velocity, pressure and concentration fields for different gravity forces and flow boundary conditions. Prediction of contact angle agrees with that from Abel's equation during solidification, previously confirmed by experimental data. Controlling pore formation in solid via selecting different gravitational acceleration or ambient pressure and flow boundary conditions can therefore be achieved.

ГИДРОДИНАМИКА ТУРБУЛЕНТНЫХ ПОТОКОВ В ТВС БЫСТРЫХ РЕАКТОРОВ (ПОЛЕ СКОРОСТИ И МИКРОСТРУКТУРА ТУРБУЛЕНТНОСТИ)

The article describes the factors under the influence of which the formation of thermohydraulic characteristics occurs in the fuel assemblies of the core of fast reactors with liquid metal cooling. It is shown that one of the most important factors is a complex multiply connected geometry of a stochastic nature, subject to deformation during the campaign under the influence of temperature irregularities and radiation effects. The paper presents and analyzes the results of experimental and computational studies of the velocity field and shear stress, the microstructure of turbulence, momentum transfer in the central and peripheral regions of fuel assemblies without and with displacers, as well as in the case of deformation of the lattice of rods. The intensification of turbulent momentum transfer in the channels in the azimuthal direction in the area of the gaps between the rods is demonstrated. The anisotropy coefficient of turbulent momentum transfer reaches 30-40 units. The performed analysis indicated a significant difference in the calculated in the framework of semi-empirical models of turbulent transfer and experimental dependences of the coefficients of turbulent transfer of momentum in the radial and azimuthal directions and the coefficients of anisotropy of turbulent transfer of momentum in rod bundles. The results of an open benchmark on the thermohydraulics of fuel assemblies showed that common commercial computational thermohydraulic codes only approximately describe the experimental data. It is shown that the intensification of turbulent momentum transfer in the channels of rod assemblies is due to the appearance of large-scale turbulent momentum transfer (secondary flows). The contribution of large-scale turbulent momentum transfer to the kinetic energy of turbulent pulsations, azimuthal turbulent shear stresses, and turbulent momentum transfer coefficients in rod assemblies is calculated. An empirical dependence of the coefficient of interchannel turbulent impulse exchange in bundles of smooth rods is obtained, on the basis of a semi-empirical model, data on interchannel turbulent impulse exchange in assemblies of smooth rods are generalized, and the intensification of interchannel turbulent exchange in close lattices of rods is explained. Data on hydraulic resistance in bundles of smooth rods are analyzed. The tasks of further research are discussed.

Residual Ultimate Strength of Steel Plates with Longitudinal Crack and Pitting Corrosion under Axial compression: Nonlinear Finite Element Method Investigations

The main aim of present study was to determine the ultimate strength of cracked and corroded plates under uniform in-plane compression. Corrosion is considered as pitting-type corrosion at one side of the plate with a central longitudinal crack. Nonlinear finite element analysis using commercial computer code, ANSYS, is used to determine the ultimate strength of deteriorated plates. Different geometrical parameters, including the aspect ratio (AR) and thickness of the plate, number of pits, pit depth-to-thickness ratio, and crack length, are considered. It is found that the AR of plates have great influence on the ultimate strength of cracked-pitted plates. Because of the position and orientation of the crack, the length of central longitudinal crack has no influence on ultimate strength reduction of cracked and cracked-pitted plates. The results show that regardless of the number of pits and crack length, in thin plates where buckling controls failure modes at ultimate strength, the number of pits has less influence on reduction of the ultimate strength than thick plates where yielding controls failure mode. Also it is concluded that in rectangular plates, arrangements of pits has more effect on reduction of the ultimate strength of cracked-pitted plates than the number of pits.

Solid strain based finite element implemented in ABAQUS for static and dynamic plate analysis

An existing robust three dimensional finite element based on the strain approach is presented. This element is implemented, for the first time in the commercial computer code ABAQUS, by using the subroutine (UEL), for the static and dynamic analysis of isotropic plates, whatever thin or thick. It is Baptised SBH8 (Strain Based Hexahedral with 8 nodes) and has the advantage to overcome the problems involved in numerical locking, when the thickness of the plate tends towards the smallest values. The implementation is justified by the capacities broader than offers this code, especially, in the free frequencies computation. The results obtained by the present element are better than those given by elements used by ABAQUS code and the other elements found in the literature, having the same number of nodes.

Modeling viscous damping in nonlinear response history analysis of steel moment‐frame buildings: Design‐plus ground motions

AbstractInvestigated in this paper is the question: Can seismic demands on steel moment‐frame buildings due to maximum considered earthquake (MCER) design‐level ground motions (GMs) be estimated satisfactorily using linear viscous damping models or is a nonlinear model, such as capped damping, necessary? This investigation employs an enhanced model with several complex features of a 20‐story steel moment‐frame building. Considered are two linear viscous damping models: Rayleigh damping and constant modal damping; and one nonlinear model where damping forces are not allowed to exceed a predefined bound. Presented are seismic demands on the building due to two sets of GMs: MCER design‐level GMs (2% probability of exceedance [PE] in 50 years) and rarer excitations (1% PE in 50 years). Based on these results, we conclude that linear damping models are adequate for estimating seismic demands on steel moment‐frame buildings—designed to satisfy current story drift and plastic rotation limits due to MCER design‐level GMs. Between the two linear damping models, constant modal damping is preferred; it is available in commercial computer codes for earthquake structural analysis.

Numerical study on mixing flow behavior in gas-liquid ejector

A multiphase mathematic model based on realizable k-e turbulence model for subsonic flow was presented to investigate the mixing flow behaviors between gas and water in the gas-liquid ejector. The simulation was carried out to predict the pumping performance of the ejector by a commercial computational code ANSYS-FLUENT 15.0. General agreements between the predicted results and experimental data validated the present theoretical model. Using the present approach, the pressure, velocity, and turbulence intensity distribution along center-line and contours of gas and liquid volume fraction profiles were predicted. It is found that the mixing process between gas and water in ejector can be divided into three periods, co-axial flow, mixing shock flow, and bubble flow. The prediction results show that the mixing shock is a dominant position in affecting the mixing flow behavior in gas-liquid ejector and the ejector’s performances.

Solute segregation due to a bubble entrapped as a pore in solid during unidirectional solidification

Solute segregation of carbon dioxide in water during entrapment of a bubble by a solidification front is numerically investigated. The bubble can be initiated by supersaturation ahead of the solidification front. Porosity influences not only microstructure of materials, but also formation of functional materials in biology, engineering, foods, and geophysics, and so on. The model was proposed in a previous work accounting for conservation equations with interfacial balances of mass, momentum, energy and concentration. Using commercial COMSOL computer code, this study further finds that different solute distributions in liquid and solid in the presence of an entrapping bubble can be attributed to solute diffusivity of liquid and partition coefficient. A high solute diffusivity of liquid enhances solute diffusion away from the pore along the solidification front, leading to negligible solute transport from liquid to solidification front, whereas a low solute diffusivity of liquid gives rise to significant solute transport from the solidification front to liquid. A decrease in solute diffusivity of liquid or partition coefficient therefore results in high solute accumulation and a high concentration region covering liquid and solid in a triangle shape near the triple-phase line. In contrast to exponential decrease for a high solute diffusivity of liquid, radial variation of solute concentration in solid in the vicinity of pore jumps to high value through the high concentration region and maintains relative constant for a low diffusivity of liquid. Solute concentration in solid significantly decreases as solute diffusivity of liquid or partition coefficient increases. Predicted contact angle agree with solutions of Abel's equation of the first or second kind. This work is critical to understand solute segregation induced by formation of a pore in solid.

CFD modelling of two-phase gas–liquid annular flow in terms of void fraction for vertical down- and up-ward flow

Two-phase flows are present in all the value chain of the oil industry, being of significant interest in pipeline transportation. They are essential for the calculation of production rates or separation process design; therefore, multiphase flows have been studied for several years, and numerous models, data banks and computational software have been developed to design more efficient processes. For this reason, the purpose of this study is to develop a CFD numerical model capable of predicting air–oil and air–water annular flow for up- and down-ward flows in vertical pipes with the objective of present a methodology to develop a reliable numerical model and present CFD tools as an alternative to the empirical models, or other commercial computational codes such as the dynamic multiphase flow simulators, for the study of multiphase flow. To achieve this objective, 36 simulations using CFD were compared against 150 simulations using OLGA and 66 different empirical correlations to predict void fraction and compare the obtained results against experimental data. Different liquid viscosities (0.00089, 0.127, 0.213, 0.408 and 0.586 Pa s) and three different pipelines were used: a 22.72 m long and 0.0508 m ID pipe, a 15.24 m long and 0.0508 m ID pipe, and a 15.24 m long and 0.1016 m ID pipe. The obtained results showed that the CFD model accurately predicts the void fraction for both down- and up-ward cases, while the obtained results using OLGA and the empirical correlations showed a lower accuracy.

Application of Nonlinear Fracture Mechanics Parameter to Predicting Wire-Liftoff Lifetime of Power Module at Elevated Temperatures

Power modules are utilized for electric power control and play a key role in efficient energy conversion. A structural reliability problem of wire bonding, wire-liftoff, in power modules becomes important at high-temperature operation. Wire-liftoff is a thermal fatigue phenomenon caused by thermal stress due to mismatch of coefficients of thermal expansion between a wire and a chip material. According to experimental studies, a saturation phenomenon of wire-liftoff lifetime was observed in power modules above the maximum junction temperature of 200 °C. In this paper, we examine the failure models for predicting wire-liftoff lifetime proposed in the previous studies and also propose a new failure model based on the nonlinear fracture mechanics parameter $T^\ast $ -integral range $\Delta T^\ast $ . Among various failure models, the proposed model is the best to represent a saturation phenomenon of wire-liftoff lifetime. For practical use of the failure model based on $\Delta T^\ast $ -integral range, we propose a simple calculation method of $\Delta T^\ast $ -integral range that can be calculated by using the commercial finite element computer code such as Marc, Ansys, and so on.

Nonlinear flutter and limit-cycle oscillations of damaged highly flexible composite wings

A study on nonlinear flutter of damaged high- wings is presented. Because an undamaged, high- wing is long and slender, it may be properly modeled as a 1D beam, using a geometrically exact beam formulation. However, structural damages in the form of cracks and delaminations are in fact 3D phenomena. Therefore, the area near a crack cannot be accurately modeled as a reduced-dimensional beam. However, finite element analysis of a wing structure modeled entirely as a 3D continuum is computationally expensive. To address this issue, a joined 3D/1D finite element approach has been proposed in which a small area surrounding the crack is regarded as a 3D continuum, and the rest of the wing structure is modeled as a reduced-dimensional 1D beam undergoing large displacements and rotations. The continuity conditions at the intersection between the 3D and 1D models are derived using the variational asymptotic method, by which the two parts are rigorously connected. Hence, the joined 3D/1D method provides a computationally inexpensive, yet accurate, analysis for slender wings. The structural model is then coupled with a reduced-order unsteady aerodynamic model to compute the aerodynamic forces and moments acting on the wing. The resulting nonlinear aeroelastic element is integrated into Abaqus, a commercial finite element computer code as a nonlinear user-defined element. Through nonlinear time-marching, using a generalized $$\alpha $$ method, limit-cycle oscillations associated with the free response of both undamaged and damaged wings undergoing large deformations are studied, and the differences are highlighted.

Fluid-structure coupling of concentric double FGM shells with different lengths

The aim of this study is to develop a semi-analytical method to investigate fluid-structure coupling of concentric double shells with different lengths and elastic behaviours. Co-axial shells constitute a cylindrical circular container and a baffle submerged inside the stored fluid. The container shell is made of functionally graded materials with mechanical properties changing through its thickness continuously. The baffle made of steel is fixed along its top edge and submerged inside fluid such that its lower edge freely moves. The developed approach is verified using a commercial finite element computer code. Although the model is presented for a specific case in the present work, it can be generalized to investigate coupling of shellplate structures via fluid. It is shown that the coupling between concentric shells occurs only when they vibrate in a same circumferential mode number, n. It is also revealed that the normalized vibration amplitude of the inner shell is about the same as that of the outer shell, for narrower radial gaps. Moreover, the natural frequencies of the fluid-coupled system gradually decrease and converge to the certain values as the gradient index increases.

Assessment of the seismic capacity increase of masonry buildings strengthened through the application of GFRM coatings on the walls

The results of a numerical investigation on the seismic performances of masonry buildings strengthened through the application of a glass fibre-reinforced mortar (GFRM) coating are presented. Four different building configurations were modelled (two and three storey, regular and non-regular in plan); solid brick and rubble stone masonry were considered. A simplified modelling method (equivalent frame method) was adopted, with concentration of the non-linear response in shear and bending 'plastic hinges'. Some difficulties needed to be faced for strengthened masonry, so to consider the effect of the reinforcement in available commercial computer codes. The non-linear static analysis provided the capacity curves of the structures. Moreover, by applying the modified capacity spectrum method, it was possible to compare the performances in terms of maximum resisting ground acceleration. The results evidenced for the reinforced buildings increase ranging from 1.8 to 2.6 times that of unreinforced ones, proving the effectiveness of the reinforcement technique.

Juno model rheometry and simulation

The experiment WAVES aboard the Juno spacecraft, which will arrive at its target planet Jupiter in 2016, was devised to study the plasma and radio waves of the Jovian magnetosphere. We analyzed the WAVES antennas, which consist of two non-parallel monopoles operated as a dipole. For this investigation we applied two independent methods: the experimental technique, rheometry, which is based on a down-scaled model of the spacecraft to measure the antenna properties in an electrolytic tank; and numerical simulations, based on commercial computer codes, from which the quantities of interest (antenna impedances and effective length vectors) are calculated. In this article we focus on the results for the low-frequency range up to about 4MHz, where the antenna system is in the quasi-static regime. Our findings show that there is a significant deviation of the effective length vectors from the physical monopole directions, caused by the presence of the conducting spacecraft body. The effective axes of the antenna monopoles are offset from the mechanical axes by more than 30° and effective lengths show a reduction to about 60% of the antenna rod lengths. The antennas' mutual capacitances are small compared to the self-capacitances, and the latter are almost the same for the two monopoles. The overall performance of the antennas in dipole configuration is very stable throughout the frequency range up to about 4–5MHz, and therefore can be regarded as the upper frequency bound below which the presented quasi-static results are applicable.

An elasto-plastic damage constitutive model for jointed rock mass with an application

A forked tunnel, as a special complicated underground structure, is composed of big-arch tunnel, multi-arch tunnel, neighborhood tunnels and separate tunnels according to the different distances between two separate tunnels. Due to the complicated process of design and construction, surrounding jointed rock mass stability of the big-arch tunnel which belongs to the forked tunnel during excavation is a hot issue that needs special attentions. In this paper, an elasto-plastic damage constitutive model for jointed rock mass is proposed based on the coupling method considering elasto-plastic and damage theories, and the irreversible thermodynamics theory. Based on this elasto-plastic damage constitutive model, a three dimensional elasto-plastic damage finite element code (D-FEM) is implemented using Visual Fortran language, which can numerically simulate the whole excavation process of underground project and perform the structural stability of the surrounding rock mass. Comparing with a popular commercial computer code, three dimensional fast Lagrangian analysis of continua (FLAC3D), this D-FEM has advantages in terms of rapid computing process, element grouping function and providing more material models. After that, FLAC3D and D-FEM are simultaneously used to perform the structural stability analysis of the surrounding rock mass in the forked tunnel considering three different computing schemes. The final numerical results behave almost consistent using both FLAC3D and D-FEM. But from the point of numerically obtained damage softening areas, the numerical results obtained by D-FEM more closely approach the practical behaviors of in-situ surrounding rock mass.