Mesh Matching Research Articles

Bc-hexmatching: an improved hexahedral mesh matching approach based on base-complex structure

Bc-hexmatching: an improved hexahedral mesh matching approach based on base-complex structure

Rigorous Modal Characterization of First- and Second-Order Symmetric Waveguides Using Specular Periodic Boundary Conditions in 2D-FEM

Symmetries are widely exploited in the electromagnetic characterization of millimeter-wave devices and antennas, as they usually bring an improvement in resource usage and accuracy in full-wave simulations. Given the rising relevance of higher order symmetric devices, a challenge of integrating many different symmetries into compact formulations appears, with the objective of finding synergies and combining the strengths each one separately brings. In this work, we present a 2-D finite element method (FEM) formulation that fulfills this task for arbitrary waveguide cross sections presenting at the same time specular first-order and rotational second-order symmetries. It is based on newly introduced specular periodic boundary conditions (SPBCs), which effectively exploit the best case simulation domain for this problem. Furthermore, they avoid the need of using a mesh matching or projection procedure for periodic boundaries, while also bringing an improvement to mode classification.

Automatic matching of multi-scale road network under the constraint of small-scale road mesh

Aiming at the problem of road network multi-scale matching, a multi-scale road matching method under the constraint of road mesh of small-scale data has been proposed. First, two road meshes with different scale data are constructed; Secondly, under the constraint of the small-scale road mesh, the composite mesh composed of several road meshes in the large-scale road is extracted, and the mesh matching with the small-scale road mesh is completed; Then, many-to-many matching of road meshes with different scales is realized; finally, the matching relationship between composite mesh and small-scale road mesh is transformed into the matching between multi-scale road mesh boundary roads and internal roads, and the matching of the whole road network is completed. The experimental results show that this method can better realize the matching of multi-scale road network.

Investigation on artificial boundary problem in the combined finite-discrete element method (FDEM)

The combined finite-discrete element method (FDEM) is an advanced finite and discrete element coupling method, which can commendably simulate the large deformation and fracture process of materials. The explicit solution method in FDEM is naturally suitable for solving dynamic problems, and the key to dynamic analysis is to establish artificial boundary conditions that can be prepared to simulate infinite domain motion. At present, there is only the viscous boundary condition in the original FDEM, but this is only applicable for solving the internal source wave problems (e.g., blasting, mechanical vibration), and there are no artificial boundary conditions for solving the external source wave problems (e.g., earthquake). Therefore, three artificial boundary conditions have been developed in the present study to enhance the ability of FDEM to conduct dynamic response analysis. Firstly, the basic principle of FDEM and the existing viscous boundary condition are briefly introduced. Then, three newly added boundary conditions are introduced in sequence: (1) viscous-spring boundary condition, which can absorb stress wave energy at the boundary and restore the residual displacement to meet the actual engineering; (2) free-field boundary condition, which is coupled with free-field motion to absorb scattered waves at the lateral boundaries of the model, and the algorithms of mesh matching retrieval and coupling calculation are also introduced; (3) static-dynamic unified boundary condition, which can accurately transform the fixed boundary under the quasi-static analysis into the non-reflective boundary condition under the dynamic analysis. Finally, several classic models are built to verify the feasibility of the newly added boundary conditions. The comparison with the shaking table test also shows that the improved FDEM can be used for seismic response analysis under actual earthquakes.

Stable generalized finite element method (SGFEM) for parabolic interface problems

We study a stable generalized finite element method (SGFEM) for parabolic interface problems with smooth interfaces. The standard finite element (FE) space based on a simple mesh is enriched by a one-side distance function to simulate gradient jumps of exact solutions on the interfaces. The mesh is (quasi)uniform and independent of the interfaces so that mesh matching or refinement along the interfaces is not needed. The main idea to derive the SGFEM is to modify the one-side distance function by subtracting its FE interpolant. The SGFEM approximates the parabolic interface problem with an optimal convergence rate and is stable in that its scaled condition number is of the same order as the FEM (O(h−2), h is a mesh-size parameter) and does not depend on the relative positions of the mesh and interfaces. The proposed SGFEM is a conforming method and is free from any penalty parameters or stability schemes. Moreover, the components of the approximation functions of the SGFEM are independent when extended to vector-valued interface problems. The optimal convergence rates of SGFEM for curved interfaces are proven theoretically for the backward Euler and Crank–Nicolson formulations. The convergence and conditioning are tested by numerical experiments.

Numerical simulation of unsteady dense granular flows with rotating geometries

In chemical engineering applications, it is not uncommon to encounter reactors featuring rotating parts. As these rotating parts are present in order to enhance processes such as chemical reactions and/or ensure homogeneity, it is essential to take them into account to perform predictive numerical simulations. This aspect can be particularly challenging, even more so when complex industrial geometries are to be treated.In this paper a numerical methodology for simulating unsteady granular flow in rotating geometries is presented. The method is based on splitting the domain into static and rotating parts. The information between rotating and static parts is passed by a non-conformal mesh matching technique. The presented methodology is validated numerically by comparing its results with other conventional methods. The method is then applied to an industrial scale problem. The applicability of the method and the way it may be used to investigate complex flow is demonstrated.Therefore this approach enables to consider the full geometry of complex reactors. It opens the door to further investigation, optimization and design of industrial scale chemical processes.

Adaptive hexahedral mesh generation and regeneration using an improved grid-based method

An improved grid-based algorithm for the adaptive generation and regeneration of hexahedral element mesh is presented in this paper. The method for the mesh density generation and control is introduced. The refinement field is generated based on the surface curvatures, geometry features, density windows and field variables distribution. To give good description of the geometry features, eight different types of free element facet configurations are given for the mesh matching to the surface of the solid model. Scaled Jacobian and the Condition Number of the Jacobian matrix are used to evaluate the hexahedral element mesh quality. A curvature-based Laplacian smoothing approach is employed to improve the quality of boundary elements and preserve the boundary characters of mesh. To improve the quality of the surface meshes and the interior elements, an optimization approach is proposed by using mesh quality metric as the objective function. By combining the Laplacian smoothing method with the optimization approach, the mesh quality is improved significantly. For the surface meshes, the Condition Number of a set of Jacobian metric associated with the quadrilateral elements is taken as the optimization objective function. For the interior elements, the Condition Number metric associated with the hexahedral elements is employed as the optimization objective function. The effectiveness and robustness of the approaches are demonstrated through two complex three-dimensional models.

An approach to achieving optimized complex sheet inflation under constraints

Sheet inflation is an enhanced and more general version of the classic pillowing procedure [1] used to modify hexahedral meshes. The flexibility of sheet inflation makes it a valuable tool for hex mesh generation, modification and topology optimization. However, it is still difficult to generate self-intersecting sheet within a local region while assuring the mesh quality. This paper proposes an approach to achieving optimized complex sheet inflation under various constraints. The approach can generate complex sheets that intersect themselves more than once and maximize the quality of the resultant mesh. We successfully apply this approach to mesh matching and mesh boundary optimizing.

Development of the R2SUNED Code System for Shutdown Dose Rate Calculations

R2SUNED is a code system implementing the mesh-based Rigorous-two-step method for shutdown dose rates calculations, making use of MCNP and ACAB codes. In addition to the most relevant features of state-of-the-art R2S systems, novel and unique features have been implemented in R2SUNED to overcome limitations common to the current mesh-based R2S implementations. One of particular interest is the cell-under-voxel approach intended to address most of the issues associated with the conventional averaging technique used in the neutron flux determination. The underlying idea is to identify the cells enclosed in each voxel and calculate the average value of the neutron flux within each cell fraction. Subsequently, the activation of each material, filling the cell delimited by the voxel, is calculated using the neutron flux evaluated in the corresponding cell. This capability enables to properly resolve the strong spatial gradients of the neutron flux independently of geometrical considerations. Another relevant feature is that a flexible decay gamma source sampling has been incorporated to assure an efficient decay gamma transport in a vast diversity of problems. A verification of R2SUNED has been addressed on the ITER computational shutdown dose rate benchmark. It is highlighted both the limitations of voxel averaged neutron flux standard approach, and the ability of R2SUNED to overcome this issue. The excellent agreement of the results with those obtained using a mesh matching perfectly the geometry tells that R2SUNED performs correctly. Finally, a description of the most representative applications carried out with R2SUNED is provided for fusion relevant facilities.

An improved hexahedral mesh matching algorithm

Mesh matching is an effective way to convert the non-conforming interfaces between two hexahedral meshes into conforming ones, which is very important for achieving high-quality finite element analysis. However, the existing mesh matching algorithm is neither efficient nor effective enough to handle complex interfaces and self-intersecting sheets. In this paper, the algorithm is improved in three aspects: (1) by introducing a more precise criteria for chord matching and the concept of partition chord set, complex interfaces with internal loops can be handled more effectively; (2) by proposing a new solution, self-intersecting sheet can be inflated and extracted locally; and (3) by putting forward a mesh quality evaluation method, the sheet extraction operation during mesh matching can be done more efficiently. Our improved mesh matching algorithm is fully automatic, and its effectiveness is demonstrated by several examples in different matching situations.

3D and 4D Face Recognition: A Comprehensive Review

Facial Recognition has gained interested of many researchers due to its various purposes and practical applications. Recent developments in 3D imaging technology have made it possible to use a true 3D mesh of the face for recognition. Moreover, it is now also possible to use 4D data (3D meshes changing over time) from publicly-available databases. Since the use of 3D and 4D data promises to bypass many of the issues that plague 2D images and video, such as pose and facial expression variations, the challenge is to perform expression analysis on 3D and 4D domains to achieve high face recognition rate. The key contribution of this article is two fold, firstly, we present various 3D Face Recognition techniques and secondly, we present a systematic pipeline for 4D Face Recognition (dynamic 3D sequences) which consist of Mesh Matching, RANdomSAmple Consensus (RANSAC), consecutive Annotated Face Model (AFM) Fitting and Feature Description. We evaluated both latest state of the art 3D and 4D Facial Recognition pipelines on two publicly available facial expression databases BU-3DFE and BU-4DFE and made the following observations. Among various 3D face recognition algorithms analysed Matching Tensors for Pose Invariant Automatic 3D Face Recognition gives the best recognition rate of 96.4% on BU-3DFE. Among various 4D face recognition algorithms, a dynamic geometry-based approach for 4D facial expressions recognition gives the best recognition rate of 96.71% on BU-4DFE. We have also considered several patents, such as ‘Face recognition apparatus, face recognition method, Gabor filter application apparatus, and computer program’ ‘Gabor filtering and joint sparsity model-based face recognition method’ ‘Principal component analysisbased (PCA-based) three-dimensional (3D) face recognition system’ ‘3d face recognition method based on intermediate frequency information in geometric image’ ‘Three-dimensional human face recognition method based on intermediate frequency information in geometry image’.

Hierarchical segmentation and identification of thoracic vertebra using learning-based edge detection and coarse-to-fine deformable model

Precise segmentation and identification of thoracic vertebrae is important for many medical imaging applications though it remains challenging due to the vertebra’s complex shape and varied neighboring structures. In this paper, a new method based on learned bone-structure edge detectors and a coarse-to-fine deformable surface model is proposed to segment and identify vertebrae in 3D CT thoracic images. In the training stage, a discriminative classifier for object-specific edge detection is trained using steerable features and statistical shape models for 12 thoracic vertebrae are also learned. For the run-time testing, we design a new coarse-to-fine, two-stage segmentation strategy: subregions of a vertebra first deform together as a group; then vertebra mesh vertices in a smaller neighborhood move group-wise to progressively drive the deformable model towards edge response maps by optimizing a probability cost function. In this manner, the smoothness and topology of vertebrae shapes are guaranteed. This algorithm performs successfully with reliable mean point-to-surface errors 0.95±0.91mm on 40 volumes. Consequently a vertebra identification scheme is also proposed via mean surface mesh matching. We achieve a success rate of 73.1% using a single vertebra, and over 95% for 8 or more vertebra which is comparable or slightly better than state-of-the-art [5].

A 3D Facial Expression Tracking Method Using Piecewise Deformations

We present a new fast method for 3D facial expression tracking based on piecewise non-rigid deformations. Our method takes as input a video-rate sequence of face meshes that record the shape and time- varying expressions of a human face, and deforms a source mesh to match each input mesh to output a new mesh sequence with the same connectivity that reflects the facial shape and expressional variations. In mesh matching, we automatically segment the source mesh and estimate a non-rigid transformation for each segment to approximate the input mesh closely. Piecewise non-rigid transformation significantly reduces computational complexity and improves tracking speed because it greatly decreases the unknowns to be estimated. Our method can also achieve desired tracking accuracy because segmentation can be adjusted automatically and flexibly to approximate arbitrary deformations on the input mesh. Experiments demonstrate the efficiency of our method.

Scale-Invariant Features for 3-D Mesh Models

In this paper, we present a framework for detecting interest points in 3-D meshes and computing their corresponding descriptors. For that, we propose an intrinsic scale detection scheme per interest point and utilize it to derive two scale-invariant local features for mesh models. First, we present the scale-invariant spin image local descriptor that is a scale-invariant formulation of the spin image descriptor. Second, we adapt the scale-invariant feature transform feature to mesh data by representing the vicinity of each interest point as a depth map and estimating its dominant angle using the principal component analysis to achieve rotation invariance. The proposed features were experimentally shown to be robust to scale changes and partial mesh matching, and they were compared favorably with other local mesh features on the SHREC'10 and SHREC'11 testbeds. We applied the proposed local features to mesh retrieval using the bag-of-features approach and achieved state-of-the-art retrieval accuracy. Last, we applied the proposed local features to register models to scanned depth scenes and achieved high registration accuracy.

Hexahedral Mesh Matching: Converting non‐conforming hexahedral‐to‐hexahedral interfaces into conforming interfaces

AbstractThis paper presents a new method, called Mesh Matching, for handling non‐conforming hexahedral‐to‐hexahedral interfaces for finite element analysis. Mesh Matching modifies the hexahedral element topology on one or both sides of the interface until there is a one‐to‐one pairing of finite element nodes, edges and quadrilaterals on the interface surfaces, allowing mesh entities to be merged into a single conforming mesh. Element topology is modified using hexahedral dual operations, including pillowing, sheet extraction, dicing and column collapsing. The primary motivation for this research is to simplify the generation of unstructured all‐hexahedral finite element meshes. Mesh Matching relaxes global constraint propagation which currently hinders hexahedral meshing of large assemblies, and limits its extension to parallel processing. As a secondary benefit, by providing conforming mesh interfaces, Mesh Matching provides an alternative to artificial constraints such as tied contacts and multi‐point constraints. The quality of the resultant conforming hexahedral mesh is high and the increase in number of elements is moderate. Copyright © 2009 John Wiley & Sons, Ltd.

Application of Topology, Size and Shape Optimization Methods in Polymer Metal Hybrid Structural Lightweight Engineering

Application of the engineering design optimization methods and tools to the design of automotive body‐in‐white (BIW) structural components made of polymer metal hybrid (PMH) materials is considered. Specifically, the use of topology optimization in identifying the optimal initial designs and the use of size and shape optimization techniques in defining the final designs is discussed. The optimization analyses employed were required to account for the fact that the BIW structural PMH component in question may be subjected to different in‐service loads be designed for stiffness, strength or buckling resistance and that it must be manufacturable using conventional injection over‐molding. The paper demonstrates the use of various engineering tools, i.e. a CAD program to create the solid model of the PMH component, a meshing program to ensure mesh matching across the polymer/metal interfaces, a linear‐static analysis based topology optimization tool to generate an initial design, a nonlinear statics‐based size and shape optimization program to obtained the final design and a mold‐filling simulation tool to validate manufacturability of the PMH component.

Quantitative evaluation of flow-induced structural vibration and noise in turbomachinery by full-scale weakly coupled simulation

Abstract This article reports on a full-scale structural simulation of flow-induced mechanical vibrations and noise in a 5-stage centrifugal pump. An interior flow field is simulated by an LES-based CFD program, which can be found elsewhere. We developed a data-interface tool to enable mesh matching and data transfer between the fluid and structure meshes. The vibration of the pump's structure was simulated using a parallel explicit dynamic FEM code. This provided a time series of pressure fluctuations on the internal surface as force-boundary conditions. The calculated vibration of the outer surface of the structure agrees reasonably well with measured data. Using Fourier transformation, the vibration modes at blade passing frequencies (BPFs) were extracted and presented as a visual image. The simulation clarified the mechanisms of resonant noise generation and propagation, which can then be used for noise reduction. This study shows that it is feasible to use fluid–structure weakly coupled simulations to estimate the flow-induced noise generated in turbomachinery.

Mesh matching and contact patch test

Mesh matching discussed in this paper refers to a situation when two adjacent lines or surfaces with different meshes on them joint together. A mesh matching formulation is given by enforcing sticking conditions on the jointed lines and surfaces. The preservation of uniform displacements (stress distributions) across the matched meshes is investigated. This, in the contact context, is usually called patch test. The conditions to ensure the formulation pass the patch test are derived, that include partition of unity and compatible conditions of shape functions, as well as the inf-sup condition of the augmented equilibrium equations. The proposed formulation is a general one from which some special cases, such as one-pass and two-pass node-to-surface contact procedures, can be recovered. Various examples are given to show the patch test performances of lower and higher-order mesh matching (contact) formulations for both straight and curved inter faces in 1-D. For a general 2-D problem, an example demonstrates that, unlike its behaviours in 1-D, two-pass node-to-surface contact procedure using linear elements could not pass the patch test.

Generating Realistic Facial Expressions with Wrinkles for Model-Based Coding

Due to the limitations of current computer graphics technology mimicing realistic facial textures, such as wrinkles, is very difficult. Facial texture updating and compression are crucial to achieving realistic facial animation for low bit rate model-based coding. In this paper, we present a partial texture updating method for realistic facial expression synthesis with facial wrinkles. First, fiducial points on a face are estimated using a color-based deformable template matching method. Second, an extended dynamic mesh matching algorithm is developed for face tracking. Next, textures of interest (TOI) in the potential expressive wrinkles and mouth–eye texture areas are captured by the detected fiducial points. Among the TOI, the so-called active textures or expressive textures are extracted by exploring temporal correlation information. Finally, the entire facial texture is synthesized using the active texture. Compared to the entire texture updating scheme, partially updating and compressing facial textures significantly reduce the computational complexity and bit rates while still producing an acceptable visual quality. Experiments on the video sequences demonstrate the advantage of the proposed algorithm.

The mesh-matching algorithm: an automatic 3D mesh generator for finite element structures

Several authors have employed finite element analysis for stress and strain analysis in orthopaedic biomechanics. Unfortunately, the definition of three-dimensional models is time consuming (mainly because of the manual 3D meshing process) and consequently the number of analyses to be performed is limited. The authors have investigated a new patient-specific method allowing automatically 3D mesh generation for structures as complex as bone for example. This method, called the mesh-matching (M-M) algorithm, generated automatically customized 3D meshes of anatomical structures from an already existing model. The M-M algorithm has been used to generate FE models of 10 proximal human femora from an initial one which had been experimentally validated. The automatically generated meshes seemed to demonstrate satisfying results.