Mesh Scheme Research Articles

Flow analysis of airfoil having different cavities on its suction surface

The paper presents the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges. The leading edge cavity shapes were distorted using Bezier polynomial so that vortex trapping pattern in the cavities can be captured. Structured meshing scheme via a multi-block strategy was employed. Unsteady simulations were performed by a Reynolds averaged Navier-Stokes (RANS) solver. Lift, drag, pressure and skin friction coefficients were monitored at Reynolds number (Re) = 15 × 104 and 6 × 105 and different angles of attack. Cavity placed at the trailing edge produced better lift to drag ratio as compared to that of the other cavities. The distorted cavities performed badly in terms of lift and drag coefficients. The elliptical cavity shape showed better results at the angles of attack up to 10°.

EFFICIENT MESHING SCHEME FOR BODIES OF REVOLUTION-APPLICATION TO PHYSICAL OPTICS PREDICTION OF ELECTROMAGNETIC SCATTERING

EFFICIENT MESHING SCHEME FOR BODIES OF REVOLUTION-APPLICATION TO PHYSICAL OPTICS PREDICTION OF ELECTROMAGNETIC SCATTERING

A cohesive finite element model based ALE formulation for z-pins reinforced multilayered composite beams

A computational formulation able to simulate fast crack growth in multilayered composite reinforced with z-pins is proposed. In particular, in order to identify the initiation and the growth of the crack, a moving mesh strategy, based on ALE approach, is combined with a cohesive methodology, in which weak based moving connections with the boundary adjoining layers are implemented by using a finite element formulation. Contrarily, z-pin reinforced area was simulated with a deformation of a set of discrete nonlinear springs fixed to material domain. Despite existing methodologies available from the literature, the present paper proposes a computational procedure able to study the dynamic crack growth in composite structures with a relatively low computational efforts. The analysis is proposed also in a non-stationary framework, in which the influence of time dependence and the inertial forces is taken into account. In order to investigate the accuracy and to validate the proposed methodology, comparisons with experimental data and numerical results are compared. Finally, the parametric study in terms of z-pins characteristics is also developed.

Numerical simulation of circular cylinders in free-fall

In this work, we combined the use of (i) overset meshes, (ii) a 6degree-of-freedom (6-DOF) motion solver, and (iii) an eddy-resolving flow simulation approach to resolve the drag and secondary movement of large-sized cylinders settling in a quiescent fluid at moderate terminal Reynolds numbers (1500<Re<28,000). These three strategies were implemented in a series of computational fluid dynamics (CFD) solutions to describe the fluid-structure interactions and the resulting effects on the cylinder motion. Using the drag coefficient, oscillation period, and maximum angular displacement as baselines, the findings show good agreement between the present CFD results and corresponding data of published laboratory experiments. We discussed the computational expense incurred in using the present modeling approach. We also conducted a preceding simulation of flow past a fixed cylinder at Re=3900, which tested the influence of the turbulence approach (time-averaging vs. eddy-resolving) and the meshing strategy (continuous vs. overset) on the numerical results. The outputs indicated a strong effect of the former and an insignificant influence of the latter. The long-term motivation for the present study is the need to understand the motion of an autonomous sensor of cylindrical shape used to measure responses to the hydraulic conditions occurring in operating hydropower turbines.

Vortex development on the AVT-183 diamond wing configuration – numerical and experimental findings

Within the NATO Science and Technology Organization (STO), the task group AVT-183 focuses on the “Reliable Prediction of Flow Separation Onset and Progression for Air and Sea Vehicles”. In this context, a 53° leading-edge sweep diamond wing configuration with blunt leading-edge contour is considered. At low speed wind tunnel (W/T) conditions, the separation onset of the emerging leading-edge vortex is studied in detail. In numerous experimental investigations, an extensive data base has been set up, which is to be used for general CFD validation of this kind of flow separation problem. In the combined numerical and experimental study of the present publication, three different CFD analyses are compared to each other and are opposed to the available experimental results. Both the surface flow and the flow field characteristics are regarded. From the W/T investigations, global force and moment data are available as well as surface pressure data and flow field measurements (Stereo Particle Image Velocimetry PIV) in defined chord-wise sections. The CFD analyses are based on Unsteady Reynolds-Averaged Navier–Stokes ((U)RANS) equations and differ in mesh strategy, turbulence model and the CFD solver applied. In the numerical results shown in this paper, differences in the flow separation onset are noticed. Based on the underlying flow physics, these differences are discussed in detail. In addition, the downstream progression of the vortex separation is considered. Based on the location of the onset, the bursting behavior of the leading-edge vortex in the rear sections of the wing is considerably influenced. With the analysis and comparison of different flow field characteristics in several chord-wise sections, the discussion is furthermore deepened. The flow separation onset and progression of the AVT-183 diamond wing configuration are discussed in detail.

Numerical investigation of interfacial mass transfer in two phase flows using the VOF method

ABSTRACTA mass transfer model is developed using the volume-of-fluid (VOF) method with a piecewise linear interface calculation (PLIC) scheme in ANSYS FLUENT for a free-rising bubble. The mass flow rate is defined via the interface by Fick's law and added into the species equation as a source term in the liquid phase using the user-defined functions (UDFs) in ANSYS FLUENT. The interfacial concentration field for the mass flow rate is discretized by two numerical methods. One of them is based on the calculation of the discretization length between the centroid of the liquid volume and the interface using the liquid void fraction and interface normal vectors at the interface cells, while in the second method the discretization length is approximated using only the liquid void fraction at the interface cells. The influence of mesh size, schemes, and different Schmidt numbers on the mass transfer mechanism is numerically investigated for a free-rising bubble. Comparison of the developed mass transfer model with the theoretical results shows reasonable and consistent results with a smaller time-step size and with cell size.

Nodal scheme for the radiation transport equation on an unstructured tetrahedral mesh

A nodal scheme of the discrete ordinate method for the radiation transport equation on an unstructured tetrahedral mesh is presented. The scheme is based on the solution of the transport equation in a tetrahedron and on its facets by linear functions, whose coefficients are found from the condition of the best approximation to the analytical solution. The features of the mesh scheme are discussed and the results of the test calculations are given.

A Hybrid Meshing Technique for Ferromagnetic Structure Based on PEEC Method

This paper presents a hybrid meshing scheme for improving the solution accuracy for modeling 3-D ferromagnetic plates. Combining with the assumption of double exponential distribution across plate thickness, another analytical expression of the 2-D bilinear basis functions is proposed for the distribution of electromagnetic components on the planar of the plate. Then, the mesh refinement is assigned to the edge region of the plate. The numerical testing validates this hybrid meshing technique, and proves that it can reduce the number of unknowns and improve the accuracy of solution.

Positivity-preserving moving mesh scheme for two-step reaction model in two dimensions

In this paper, we have proposed a moving mesh scheme for the two-step chemical reaction model in two dimensions. This moving mesh scheme consists of two independent parts: governing equations evolution and mesh-redistribution. The second-order finite volume scheme is used in the governing equations evolution part. In the mesh-redistribution part, the mesh points are first redistributed, and then the cell averages of the conservative variables are remapped onto the new mesh in a conservative way. In addition, the positivity-preserving improvements are shown for the two parts. The positivity-preserving thresholds guarantee the average value positive, and then an improved implementation is given to make each cell value positive. Several numerical experiments are carried out to demonstrate the accuracy and effectiveness of the proposed method.

Numerical simulation of phase images and depth reconstruction in pulsed phase thermography

In this work we apply the finite element (FE) method to simulate the results of pulsed phase thermography experiments on laminated composite plates. Specifically, the goal is to simulate the phase component of reflected thermal waves and therefore verify the calculation of defect depth through the identification of the defect blind frequency. The calculation of phase components requires a higher spatial and temporal resolution than that of the calculation of the reflected temperature. An FE modeling strategy is presented, including the estimation of the defect thermal properties, which in this case is represented as a foam insert impregnated with epoxy resin. A comparison of meshing strategies using tetrahedral and hexahedral elements reveals that temperature errors in the tetrahedral results are amplified in the calculation of phase images and blind frequencies. Finally, we investigate the linearity of the measured diffusion length (based on the blind frequency) as a function of defect depth. The simulations demonstrate a nonlinear relationship between the defect depth and diffusion length, calculated from the blind frequency, consistent with previous experimental observations.

A mesh differential refinement scheme for solving elastic fields of half-space inclusion problems

This work quantitatively explores the dependence of the truncation errors on computational mesh settings for image-inclusion approaches and proposes a corresponding amendment. The new method is based on FFT algorithms and involves four individual portions. A mesh differential refinement scheme, consisting of independent and flexible selections-combinations of the surface, source, and target domains, is conceived to assist the proposed method. Comparisons of the results produced by the new and conventional mesh schemes demonstrate the significant improvements in computational performances. The new method can facilitate the numerical evaluation of local elastic characteristics caused by distributed inclusions or defects in contacting components.

Development of a varying mesh scheme for finite element crack closure analysis

Large amount of computation time is inevitable for finite element crack closure analysis when the crack propagates a long distance. This is because numerous elements are needed along the crack path. A method using a varying mesh technique is proposed to reduce the number of elements. In the method, a new finite element model is constructed before crack tip release, thus, compared to the conventional scheme, two additional tasks are required for the new approach: remeshing and state variable mapping. The proposed technique using a simple variable mapping produces unacceptable results for the plane strain condition. Investigations show that the residual nodal forces resulted from the mapped stresses cause the difficulty. A new remeshing method is proposed to overcome the difficulty. Also, significant computation time saving by the new technique is confirmed.

Method for Calculating Normal Pressure Distribution of High Resolution and Large Contact Area

The exact calculation of contact stresses below the surface is the basis for optimizing load capacity of heavily loaded rolling–sliding contacts. The level of stress is significantly influenced by the normal pressure distribution within the contact area, which occurs as a result of the transferred normal force and the contact geometry. In this paper, a new method for high resolution pressure calculation of large contact areas is presented. By this, measured surface topography can be taken into account. The basis of the calculation method is the half-space theory according to Boussinesq/Love. Instead of regular grids, optimized meshing strategies are applied to influence the calculation efforts for large contact areas. Two objectives are pursued with the targeted meshing strategy: on the one hand, the necessary resolution for measured surface structures can be realized; while on the other hand, the total number of elements is reduced by a coarse grid in the surrounding areas. In this way, rolling–sliding contacts with large contact areas become computable with conventional simulation computers. Using the newly developed “method of combined solutions,” the overall result is finally composed by the combination of section of separate solutions, which are calculated by consecutively shifting the finely meshed segment over the entire contact area. The vital advancement in this procedure is the introduction of irregular grids, through which the cross influences are not neglected and fully regarded for every separate calculation. The presented methodology is verified stepwise in comparison to the Hertzian theory. The influence of irregular grids on the calculation quality is examined in particular. Finally, the calculation approach is applied to a real disk-on-disk rolling contact based on measured surface topography.

A force evaluation free method to N-body problems: Binary interaction approximation

We recently proposed the binary interaction approximation (BIA) to N-body problems, which, in principle, excludes the interparticle force evaluation if the exact solutions are known for the corresponding two-body problems such as the Coulombic and gravitational interactions. In this article, a detailed introduction to the BIA is given, including the error analysis to give the expressions for the approximation error in the total angular momentum and the total energy of the entire system. It is shown that, although the energy conservation of the BIA scheme is worse than the 4th order Hermite integrator (HMT4) for similar elapsed, or the wall-clock times, the individual errors in position and in velocity are much better than HMT4. The energy error correction scheme to the BIA is also introduced that does not deteriorate the individual errors in position and in velocity. It is suggested that the BIA scheme is applicable to the tree method, the particle–mesh (PM), and the particle–particle-particle–mesh (PPPM) schemes simply by replacing the force evaluation and the conventional time integrator with the BIA scheme.

Comparative analysis of turbulence models for the aerodynamic simulation of H-Darrieus rotors

The importance of wind energy has increased at a rapid pace in the last years. As a result, increasing efforts are taken to improve the efficiency and extend the applicability of wind turbines to all suitable locations. Although HAWTs (horizontal axis wind turbines) are clearly the most well-spread, VAWTs (vertical axis wind turbines) show several advantages. In this category, the H-Darrieus configuration is particularly popular.For evaluating the performance of an H-Darrieus wind turbine, two-dimensional simulations relying on CFD (computational fluid dynamics) have been widely employed, since detailed full three-dimensional simulations for an optimization remain beyond reach with current computer power. Unfortunately, there is up to now no agreement in the scientific literature concerning the best possible model and model parameters for such conditions. At the same time, different models, different solvers and different meshing strategies may yield very different results.The aim of the current study is to perform a systematic numerical analysis in order 1) to identify the necessary mesh resolution for the different turbulence models, 2) to choose a model suitable for optimization and 3) to compare the characteristic curves obtained with the different models for four different configurations.

An enhanced grain-boundary framework for computational homogenization and micro-cracking simulations of polycrystalline materials

An enhanced three-dimensional (3D) framework for computational homogenization and intergranular cracking of polycrystalline materials is presented. The framework is aimed at reducing the computational cost of polycrystalline micro simulations, with an aim towards effective multiscale modelling. The scheme is based on a recently developed Voronoi cohesive-frictional grain-boundary formulation. A regularization scheme is used to avoid excessive mesh refinements often induced by the presence of small edges and surfaces in mathematically exact 3D Voronoi morphologies. For homogenization purposes, periodic boundary conditions are enforced on non-prismatic periodic micro representative volume elements ($$\mu $$μRVEs), eliminating pathological grains generally induced by the procedures used to generate prismatic periodic $$\mu $$μRVEs. An original meshing strategy is adopted to retain mesh effectiveness without inducing numerical complexities at grain edges and vertices. The proposed methodology offers remarkable computational savings and high robustness, both highly desirable in a multiscale perspective. The determination of the effective properties of several polycrystalline materials demonstrate the accuracy of the technique. Several microcracking simulations complete the study and confirm the performance of the method.

A polygonal finite element method for modeling crack propagation with minimum remeshing

In this paper, a polygonal finite element method is presented for crack growth simulation with minimum remeshing. A local polygonal mesh strategy is performed employing polygonal finite element method to model the crack propagation. In order to model the singular crack tip fields, the convex and concave polygonal elements are modified based on the singular quarter point isoparametric concept that improves the accuracy of the stress intensity factors. Numerical simulations are performed to demonstrate the efficiency of various polygonal shape functions, including the Wachspress, metric, Laplace and mean value shape functions, in modeling the crack tip fields. Eventually, analogy of the results with the existing numerical and experimental data is carried out depicting accuracy of the propounded technique.

A multiscale model for the numerical simulation of the anchor bolt pull-out test in lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) has been increasingly used as a construction material in civil and building engineering, especially in earthquake hazard zones, due to its higher strength-to-weight ratio and efficient handling with respect to ordinary concrete. The aim of the present work is to perform complete failure analyses in LWAC taking into account the effects of the underlying microstructure on its overall structural behavior. To this end, a concurrent multiscale method is adopted, in conjunction with an innovative crack modeling framework. Continuous crack propagation along a non-prescribed path is modeled in the LEFM setting, taking advantage of a shape optimization method coupling a moving mesh strategy and a gradient-free optimization solver. The crack penetration through a material interface is also taken into account, by means of a novel re-initiation criterion at interface, based on a material characteristic length. Numerical computations have been carried out with reference to the complete failure analysis of a LWAC specimen subjected to the anchor bolt pull-out test; the related results have shown that the peak and post-peak response is strongly affected by volume fraction and Young’s modulus of lightweight aggregates. Their validation has been performed by means of comparisons with a fully homogenized model uniquely based on LEFM approach.

Hybrid Compliant Mechanism Design Using a Mixed Mesh of Flexure Hinge Elements and Beam Elements Through Topology Optimization

This paper proposes a topology optimization framework to design compliant mechanisms with a mixed mesh of both beams and flexure hinges for the design domain. Further, a new type of finite element, i.e., super flexure hinge element, was developed to model flexure hinges. Then, an investigation into the effects of the location and size of a flexure hinge in a compliant lever explains why the point-flexure problem often occurs in the resulting design via topology optimization. Two design examples were presented to verify the proposed technique. The effects of link widths and hinge radii were also investigated. The results demonstrated that the proposed meshing scheme and topology optimization technique facilitate the rational decision on the locations and sizes of beams and flexure hinges in compliant mechanisms.

Numerical Simulation of In-Line Response of a Vertical Cylinder in Regular Waves

ABSTRACT Han, Y.; Zhan, J-M.; Su, W.; Li, Y.S., and Zhou, Q. 2015. Numerical simulation of in-line response of a vertical cylinder in regular waves. In-line response of a flexibly mounted, vertical cylinder in a series of regular waves was studied with numerical simulation. A dynamic mesh scheme and a laminar flow model were adopted. The experimental and simulated time histories of five wave gages and the response of the cylinder were compared. At low-incident wave frequencies, although the ratios of the diameters of the cylinders to the wavelength were small, the oscillating cylinder had little influence on the flow field. The numerical responses of the cylinder were in very good agreement with the experimental data. As the frequency of the incoming wave increased, the diffraction effect caused by the cylinder became significant, and the simulated responses of the cylinder were slightly weaker than those of experiment. When the incident wave frequency approached the natural frequency of the cylinder, the...