Generation Of Computational Mesh Research Articles

Деформирование слоистых композитных пластин при низкоскоростном контакте с жестким индентором

The computational finite element model of contact between a steel sphere and a composite plate was developed in the ANSYS software package. The model includes geometric description of the contact, materials management, computational mesh generation using the SOLID186 and SOLID187 finite elements, as well as the surface-to-surface contact model using the CONTA174 and TARGET170 contact elements. The paper identifies influence of the rigid sphere radius on the woven composite structure and shows areas of the local composite destruction. Satisfactory compliance was obtained between the numerical calculation results and full-scale study of a contact between rigid indenter of different radii and the fiberglass laminate. The safety factor values are provided according to four criteria. The developed model of contact between the indenter and the composite plate made it possible to obtain stress fields in the carbon-plastic composite material with the laying layers [45°, –45°]n and [45°, 90°, –45°, 0°]n. Destruction in layers based on the numerical calculation results was analyzed using various stress criteria. Carbon composite had more destroyed layers due to low strength in the transverse direction. Destruction zone in the carbon composite was larger than in the fiberglass composite, and the pattern [45°, –45°]n had a smaller damage area compared to [45°, 90°, –45°, 0°]n.

Fluid Dynamics of Thrust Vectorable Submerged Nozzle

A numerical simulation of the gas-dynamic processes in the thrust vectorable nozzle of the solid rocket motor is considered. Construction of a geometric model and a generation of computational mesh, and reconstruction of model and mesh at each time step are discussed. Calculations of the flowfield of combustion products in the pre-nozzle chamber and nozzle block are carried out for various angles of nozzle rotation. The distributions of the gas dynamic quantities in the pre-nozzle volume corresponding to the outflow of the combustion products from the cylindrical channel and star-shaped channel are compared, as well as the solutions of the problem obtained with quasi-stationary and unsteady formulations. The effects of the channel shape on the distribution of flow quantities and formation of a vortical flow structure in the nozzle block are discussed.

Numerical simulation of sonic boom near-field flow over 69-degree delta wing body

Fast and accurate prediction of sonic boom intensity is important in performing design and optimization studies of a supersonic aircraft. The paper presents the computational mesh generation technique for sonic boom prediction in the near field of complex geometry body. Studies are done on a 69-degree delta wing body model used for testing various prediction techniques in the framework of the AIAA Sonic Boom Prediction Workshops.

GHOST: Geoscientific Hollow Sphere Tessellation

Abstract. I present in this work the GHOST (Geoscientific Hollow Sphere Tessellation) software which allows for the fast generation of computational meshes in hollow sphere geometries counting up to 100 million cells. Each mesh is composed of concentric spherical shells which are built out of quadrilaterals or triangles. I focus here on three commonly used meshes used in geodynamics/geophysics and demonstrate the accuracy of shell surfaces and mesh volume measurements as a function of resolution. I further benchmark the built-in gravity and gravitational potential procedures in the simple case of a constant density geometry and finally show how the produced meshes can be used to visualise the S40RTS mantle tomography model. The code is open source and is available on the GitHub sharing platform.

Spline-Based Parameterization Techniques for Twin-Screw Machine Geometries

The fully automated generation of computational meshes for twin-screw machine geometries constitutes a mandatory aspect for the numerical simulation (and shape-optimization) of these devices but proves to be a challenging task in practice. Therefore, the successful generation of computational meshes requires sophisticated mathematical tools. Commercially available classical mesh generators can produce high quality meshes from no more than a description of the rotor contours. However, since we are particularly interested in numerical simulations using the principles of Isogeometric Analysis, a spline-based geometry description rather than a classical mesh is needed.In this paper, we propose a practical approach for the automated generation of spline-based twin-screw machine geometry parameterizations in two dimensions. For this purpose, we adopt the principles of Elliptic Grid Generation and present a parameterization algorithm that is compatible with an automated simulation pipeline based on the principles of isogeometric analysis.To demonstrate the proposed techniques, we apply them to an example geometry and present the resulting parameterizations. Finally, we give a qualitative explanation of how the discussed techniques can be utilized to generate geometry parameterizations in three dimensions and their applications to shape-optimization on a variable rotor-pitch.

Validation of parametric mesh generation for subject-specific cerebroarterial trees using modified Hausdorff distance metrics

Accurate subject-specific vascular network reconstruction is a critical task for the hemodynamic analysis of cerebroarterial circulation. Vascular skeletonization and computational mesh generation for large sections of cerebrovascular trees from magnetic resonance angiography (MRA) is an error-prone, operator-dependent, and very time-consuming task. Validation of reconstructed computational models is essential to ascertain their accuracy and precision, which directly relates to the confidence of CFD computations performed on these meshes. The aim of this study is to generate an imaging segmentation pipeline to validate and quantify the spatial accuracy of computational models of subject-specific cerebral arterial trees. We used a recently introduced parametric structured mesh (PSM) generation method to automatically reconstruct six subject-specific cerebral arterial trees containing 1364 vessels and 571 bifurcations. By automatically extracting sampling frames for all vascular segments and bifurcations, we quantify the spatial accuracy of PSM against the original MRA images. Our comprehensive study correlates lumen area, pixel-based statistical analysis, area overlap and centerline accuracy measurements. In addition, we propose a new metric, the pointwise offset surface distance metric (PSD), to quantify the spatial alignment between dimensions of reconstructed arteries and bifurcations with in-vivo data with the ability to quantify the over- and under-approximation of the reconstructed models. Accurate reconstruction of vascular trees can a practical process tool for morphological analysis of large patient data banks, such as medical record files in hospitals, or subject-specific hemodynamic simulations of the cerebral arterial circulation.

Automatic recognition of subject-specific cerebrovascular trees.

An image filter designed for reconstructing cerebrovascular trees from MR images is described. Current imaging techniques capture major cerebral vessels reliably, but often fail to detect small vessels, whose contrast is suppressed due to limited resolution, slow blood flow rate, and distortions around bifurcations or nonvascular structures. An incomplete view of angioarchitecture limits the information available to physicians. A novel Hessian-based filter for contrast-enhancement in MR angiography and venography for blood vessel reconstruction without introducing dangling segments is presented. We quantify filter performance with receiver-operating-characteristic and dice-similarity-coefficient analysis. Total extracted vascular length, number-of-segments, volume, surface-to-distance, and positional error are calculated for validation. Reconstruction of cerebrovascular trees from MR images of six volunteers show that the new filter renders more complete representations of subject-specific cerebrovascular networks. Validation with phantom models shows the filter correctly detects blood vessels across all length scales without failing at bifurcations or distorting diameters. The novel filter can potentially improve the diagnosis of cerebrovascular diseases by delivering metrics and anatomy of the vasculature. It also facilitates the automated analysis of large datasets by computing biometrics free of operator subjectivity. The high quality reconstruction enables computational mesh generation for subject-specific hemodynamic simulations. Magn Reson Med 77:398-410, 2017. © 2016 Wiley Periodicals, Inc.

Special Aspects of Wind Wave Simulations for Surge Flood Forecasting and Prevention

The paper is focused on several issues of wind wave simulations with SWAN model for the tasks related to prevention of surge floods in St. Petersburg. It introduces main objectives that are pursued through the use of the model as well as covers problems of computational mesh generation and model parameter calibration. We also examined several assumptions on the necessity to take ice fraction and sea level rise into account in wind wave simulations.

The Role of Mesh Generation, Adaptation, and Refinement on the Computation of Flows Featuring Strong Shocks

Within a continuum framework, flows featuring shock waves can be modelled by means of either shock capturing or shock fitting. Shock-capturing codes are algorithmically simple, but are plagued by a number of numerical troubles, particularly evident when shocks are strong and the grids unstructured. On the other hand, shock-fitting algorithms on structured grids allow to accurately compute solutions on coarse meshes, but tend to be algorithmically complex. We show how recent advances in computational mesh generation allow to relieve some of the difficulties encountered by shock capturing and contribute towards making shock fitting on unstructured meshes a versatile technique.

Wavelet Adaptivity for 3-D Device Simulation

A new technique has been implemented with the aim of providing an adaptive tool for the generation of computational meshes for 3-D semiconductor device simulation. The core of the proposed wavelet-based adaptive method (WAM) is a refinement algorithm based on the wavelet transform, which gives an estimation of solution regularity and progressively adapts the grid by increasing the resolution only in regions where the important physical phenomena take place. WAM is inserted into a validation tool that provides the interfacing filters with both the solver and a meshing engine. Additional features assure the quality of the generated meshes by increasing the selectivity properties of the refinement tool, preventing numerical instabilities or artifacts, such as abrupt variations of I-V curves between successive bias points during quasi-stationary simulations. Simulation results are provided, which show the effectiveness of the proposed approach as a means to guide the automatic refinement of the discretization grid, preserving accuracy with negligible computational overhead and no skilled control from the user.

Hybrid finite element–finite volume discretization of complex geologic structures and a new simulation workflow demonstrated on fractured rocks

AbstractThe generation of computational meshes of complex geological objects is a challenge: their shape needs to be retained, resolution has to adapt to local detail, and variations of material properties in the objects have to be represented. Also mesh refinement and adaptation must be sufficient to resolve variations in the computed variable(s). Here, we present an unstructured hybrid finite element, node‐centred finite‐volume discretization suitable for solving fluid flow, reactive transport, and mechanical partial differential equations on a complex geometry with inhomogeneous material domains. We show that resulting meshes accurately capture free‐form material interfaces as defined by non‐uniform rational B‐spline curves and surfaces. The mesh discretization error is analysed for the elliptic pressure equation and an error metric is introduced to guide mesh refinement. Finite elements and finite volumes are represented in parametric space and integrations are conducted numerically. Subsequently, integral properties are mapped to physical space using Jacobian transformations. This method even retains its validity when the mesh is deformed. The resulting generic formulation is demonstrated for a transport calculation performed on a complex discrete fracture model.

Application of Magnetic Resonance (MR) Imaging for the Development and Validation of Computational Fluid Dynamic (CFD) Models of the Rat Respiratory System

Computational fluid dynamic (CFD) models of the respiratory system provide a quantitative basis for extrapolating the localized dose of inhaled materials and improving human health risk assessments based upon inhalation studies conducted in animals. Nevertheless, model development and validation have historically been tedious and time-consuming tasks. In recognition of this, we previously reported on the use of proton (1H) magnetic resonance (MR) imaging for visualizing nasal-sinus passages in the rat, and for speeding computational mesh generation. Here, the generation and refinement of meshes for rat nasal airways are described in more detail and simulated airflows are presented. To extend the CFD models to the complete respiratory tract, three-dimensional (3D) 1H MR imaging of rat pulmonary casts was also utilized to construct pulmonary airway meshes using procedures developed for the nasal airways. Furthermore, the feasibility of validating CFD predictions with MR was tested by imaging hyperpolarized 3He gas at physiological flow rates in a straight pipe with a diameter comparable to the rat trachea. Results from these diverse studies highlight the potential utility of MR imaging not only for speeding CFD development but also possibly for model validation.

Generation of computational meshes from MRI and CT-scan data

There are fields of engineering where accurate and personalised data are required; biomed- ical applications are one such example. We describe here a general purpose method to create com- putational meshes based on the analysis and segmentation of raw medical imaging data. The various ingredients are not new: a segmentation method based on deformable contours and a surface and vol- ume mesh adaptation method based on discrete metric specifications; but the challenge that motivated this paper is to put them together in an attempt to design an automatic, easy to use and ecient 3D code. For non-engineering (like biomedical) applications, the user interface is often a key point. In this project, we put a great deal of emphasis on the automation of the whole procedure, making then possible to envisage large scale simulations with a minimal amount of user interaction. In particular, the user knowledge is required to help segmenting the image (the user is expected to have the know- how of the body anatomy), all meshing steps rely on fully automatic algorithms depending on a few parameters (for the external surface approximation). One application example is presented and commented, for which the data preparation takes a few hours and results can be obtained overnight on a PC workstation.

Magnitude and Role of Wall Shear Stress on Cerebral Aneurysm. Computational Fluid Dynamic Study of 20 Middle Cerebral Artery Aneurysms

Magnitude and Role of Wall Shear Stress on Cerebral Aneurysm. Computational Fluid Dynamic Study of 20 Middle Cerebral Artery Aneurysms

Geometric reconstruction for computational mesh generation of arterial bifurcations from CT angiography

A methodology for patient-specific model reconstruction and computational mesh generation of arterial bifurcations from angio-CT scans is presented. Three-dimensional models were reconstructed with a level set technique, analyzed with a skeletoning algorithm and automatically decomposed into branches. Cooper scheme was then employed to generate high quality hexahedral mesh. We successfully applied our technique to the carotid bifurcations of two patients affected by severe atherosclerotic plaques. The proposed technique is fast, accurate and reproducible, and can be a useful tool for the evaluation of arterial fluid dynamics within conventional computed tomography investigations.

Requirements for Mesh Resolution in 3D Computational Hemodynamics

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features. Here we examine, for a single arterial geometry, how velocity and wall shear stress patterns depend on mesh characteristics. A well-validated Navier-Stokes solver was used to simulate flow in an anatomically realistic human right coronary artery (RCA) using unstructured high-order tetrahedral finite element meshes. Velocities, wall shear stresses (WSS), and wall shear stress gradients were computed on a conventional "high-resolution" mesh series (60,000 to 160,000 velocity nodes) generated with a commercial meshing package. Similar calculations were then performed in a series of meshes generated through an adaptive mesh refinement (AMR) methodology. Mesh-independent velocity fields were not very difficult to obtain for both the conventional and adaptive mesh series. However, wall shear stress fields, and, in particular, wall shear stress gradient fields, were much more difficult to accurately resolve. The conventional (nonadaptive) mesh series did not show a consistent trend towards mesh-independence of WSS results. For the adaptive series, it required approximately 190,000 velocity nodes to reach an r.m.s. error in normalized WSS of less than 10 percent. Achieving mesh-independence in computed WSS fields requires a surprisingly large number of nodes, and is best approached through a systematic solution-adaptive mesh refinement technique. Calculations of WSS, and particularly WSS gradients, show appreciable errors even on meshes that appear to produce mesh-independent velocity fields.