Mesh-based Model Research Articles

Photogrammetry-based computational fluid dynamics

Computational fluid dynamics (CFD) is the cornerstone of the design and analysis process in many engineering applications. Not only has it been applied in the design phase, but it has also been employed for analyzing the fluid flow phenomena during the operation phase for many in-use structures, such as vehicles, buildings, and landscapes. However, creating a 3D mesh-based model of in-use structures that can be used by conventional boundary-fitted CFD methods is labor-intensive, time-consuming, and sometimes impossible. Due to the challenges introduced by geometry complexity and lack of design information, it is often difficult to perform an accurate and efficient CFD analysis of these objects. This paper aims to overcome such challenges by proposing a novel photogrammetry-based CFD framework for simulating in-use structures whose design models and analysis meshes are hard to obtain. The proposed framework integrates machine learning-based 3D point cloud reconstruction of structures from 2D images obtained from portable devices (e.g., cell phones and drones) and an immersogeometric approach that can carry out flow analysis directly on reconstructed point clouds. We first present the technical details of point cloud reconstruction techniques and the immersogeometric analysis method. We then simulate the flow past a standard 12 oz soda can reconstructed using photogrammetry and compare the results with reference solutions to assess the accuracy of the approach. Finally, the proposed photogrammetry-based CFD is applied to simulations of a bell tower and the Kavita and Lalit Bahl Smart Bridge on the University of Illinois Urbana-Champaign (UIUC) campus to demonstrate the robustness of the framework and its applicability to real-world in-use civil structures.

A Feature-Extraction-Based Adaptive Refinement Method for Solving the Reynolds Equation in Piston–Cylinder System

A fast local refinement algorithm based on feature extraction is developed. In the mesh-based Reynolds equation solutions, two refinement features based on the physical parameters of fluid lubrication are firstly defined, namely, pressure value feature and pressure gradient feature. Then, a fast adaptive strategy different from the traditional methods based on residuals or recovery errors is constructed according to the features, which are expected to determine the element needed to be refined. Considering the update requirement of the feature parameters, an adaptive update strategy for feature parameters is also developed. Finally, the feasibility of the scheme is verified on a single-cylinder gasoline engine. Results show that the current algorithm can effectively reduce the computational scale while ensuring the computational accuracy of the mesh-based model, compared with the traditional global and local refinement strategy.

Yarn level simulation of warp-knitted clothing elements – first results and challenges

To simulate a warp-knitted product with a specific shape, a mesh-based model for modeling and simulation is proposed. The three-dimensional geometry of the final fabric is represented as a set of polygons, each of them containing information about the 3D orientation of the yarns in the warp knitted structure. Using spatial mapping, stitch coordinates are transformed from the flat mesh model to the three-dimensional mesh model and the final rendering is accomplished. The method provides yarn level data for the complete structure and can be used for speeding up the design process of clothing with warp-knitted products. Several challenges with the larger data amount and possible ways for their solutions are discussed.

A mesh-based model of liver vasculature: implications for improved radiation dosimetry to liver parenchyma for radiopharmaceuticals

PurposeTo develop a model of the internal vasculature of the adult liver and demonstrate its application to the differentiation of radiopharmaceutical decay sites within liver parenchyma from those within organ blood.MethodComputer-generated models of hepatic arterial (HA), hepatic venous (HV), and hepatic portal venous (HPV) vascular trees were algorithmically created within individual lobes of the ICRP adult female and male livers (AFL/AML). For each iteration of the algorithm, pressure, blood flow, and vessel radii within each tree were updated as each new vessel was created and connected to a viable bifurcation site. The vascular networks created inside the AFL/AML were then tetrahedralized for coupling to the PHITS radiation transport code. Specific absorbed fractions (SAF) were computed for monoenergetic alpha particles, electrons, positrons, and photons. Dual-region liver models of the AFL/AML were proposed, and particle-specific SAF values were computed assuming radionuclide decays in blood within two locations: (1) sites within explicitly modeled hepatic vessels, and (2) sites within the hepatic blood pool residing outside these vessels to include the capillaries and blood sinuses. S values for 22 and 10 radionuclides commonly used in radiopharmaceutical therapy and imaging, respectively, were computed using the dual-region liver models and compared to those obtained in the existing single-region liver model.ResultsLiver models with virtual vasculatures of ~ 6000 non-intersecting straight cylinders representing the HA, HPV, and HV circulations were created for the ICRP reference. For alpha emitters and for beta and auger-electron emitters, S values using the single-region models were approximately 11% (AML) to 14% (AFL) and 11% (AML) to 13% (AFL) higher than the S values obtained using the dual-region models, respectively.ConclusionsThe methodology employed in this study has shown improvements in organ parenchymal dosimetry through explicit consideration of blood self-dose for alpha particles (all energies) and for electrons at energies below ~ 100 keV.

Trefftz co-chain calculus

We are concerned with a special class of discretizations of general linear transmission problems stated in the calculus of differential forms and posed on {mathbb {R}}^n. In the spirit of domain decomposition, we partition {mathbb {R}}^n=Omega cup Gamma cup Omega _{+}, Omega a bounded Lipschitz polyhedron, Gamma :=partial Omega , and Omega _{+} unbounded. In Omega , we employ a mesh-based discrete co-chain model for differential forms, which includes schemes like finite element exterior calculus and discrete exterior calculus. In Omega _{+}, we rely on a meshless Trefftz–Galerkin approach, i.e., we use special solutions of the homogeneous PDE as trial and test functions. Our key contribution is a unified way to couple the different discretizations across Gamma . Based on the theory of discrete Hodge operators, we derive the resulting linear system of equations. As a concrete application, we discuss an eddy-current problem in frequency domain, for which we also give numerical results.

Equidistant and Uniform Data Augmentation for 3D Objects

Data augmentation is commonly used to increase the size and diversity of the datasets in machine learning. It is of particular importance to evaluate the robustness of the existing machine learning methods. With progress in geometrical and 3D machine learning, many methods exist to augment a 3D object, from the generation of random orientations to exploring different perspectives of an object. In high-precision applications, the machine learning model must be robust with respect to the small perturbations of the input object. Therefore, there is a need for 3D data augmentation tools that consider the distribution of distance metrics between the original and augmented objects. Here we present Eurecon, the first 3D data augmentation approach with spatial control over the augmented samples. It generates objects uniformly distributed over a sphere with a user-defined radius, which is a distance with respect to the original object. Eurecon is applicable to both point cloud and polygon mesh representations of the 3D objects, as demonstrated on the ModelNet dataset. The method is particularly useful in assessing and improving the machine learning models’ robustness with respect to the transformations of a small magnitude. We demonstrated the superior performance of a point cloud-based model (PointNet++) and a mesh-based model (MeshNet) when trained on datasets augmented with Eurecon, compared to non-augmented and randomly augmented models. Eurecon is computationally efficient, taking ~ 0.1 seconds to generate 1, 000 samples of an object of 1, 000 3D points. Eurecon works with the most common 3D file formats including point cloud and polygon mesh formats.

Simultaneous Video Stabilization and Rolling Shutter Removal.

Due to the delay in the row-wise exposure and the lack of stable support when a photographer holds a CMOS camera, video jitter and rolling shutter distortion are closely coupled degradations in the captured videos. However, previous methods have rarely considered both phenomena and usually treat them separately, with stabilization approaches that are unable to handle the rolling shutter effect and rolling shutter removal algorithms that are incapable of addressing motion shake. To tackle this problem, we propose a novel method that simultaneously stabilizes and rectifies a rolling shutter shaky video. The key issue is to estimate both inter-frame motion and intra-frame motion. Specifically, for each pair of adjacent frames, we first estimate a set of spatially variant inter-frame motions using a neighbor-motion-aware local motion model, where the classical mesh-based model is improved by introducing a new constraint to enhance the neighbor motion consistency. Then, different from other 2D rolling shutter removal methods that assume the pixels in the same row have a single intra-frame motion, we build a novel mesh-based intra-frame motion calculation model to cope with the depth variation in a mesh row and obtain more faithful estimation results. Finally, temporal and spatial motion constraints and an adaptive weight assignment strategy are considered together to generate the optimal warping transformations for different motion situations. Experimental results demonstrate the effectiveness and superiority of the proposed method when compared with other state-of-the-art methods.

Decentralized Mesh-Based Model Predictive Control for Swarms of UAVs.

This paper deals with the design of a decentralized guidance and control strategy for a swarm of unmanned aerial vehicles (UAVs), with the objective of maintaining a given connection topology with assigned mutual distances while flying to a target area. In the absence of obstacles, the assigned topology, based on an extended Delaunay triangulation concept, implements regular and connected formation shapes. In the presence of obstacles, this technique is combined with a model predictive control (MPC) that allows forming independent sub-swarms optimizing the formation spreading to avoid obstacles and collisions between neighboring vehicles. A custom numerical simulator was developed in a Matlab/Simulink environment to prove the effectiveness of the proposed guidance and control scheme in several 2D operational scenarios with obstacles of different sizes and increasing number of aircraft.

Influence of Convex and Concave Curvatures in a Coastal Dike Line on Wave Run-up

Due to climatic change and the increased usage of coastal areas, there is an increasing risk of dike failures along the coasts worldwide. Wave run-up plays a key role in the planning and design of a coastal structure. Coastal engineers use empirical equations for the determination of wave run-up. These formulae generally include the influence of various hydraulic, geometrical and structural parameters, but neglect the effect of the curvature of coastal dikes on wave run-up and overtopping. The scope of this research is to find the effects of the dike curvature on wave run-up for regular wave attack by employing numerical model studies for various dike-opening angles and comparing it with physical model test results. A numerical simulation is carried out using DualSPHysics, a mesh-less model and OpenFOAM, a mesh-based model. A new influence factor is introduced to determine the influence of curvature along a dike line. For convexly curved dikes (αd = 210° to 270°) under perpendicular wave attack, a higher wave run-up was observed for larger opening angles at the center of curvature whereas for concavely curved dikes (αd = 90° to 150°) under perpendicular wave attack, wave run-up increases at the center of curvature as the opening angle decreases. This research aims to contribute a more precise analysis and understanding the influence of the curvature in a dike line and thus ensuring a higher level of protection in the future development of coastal structures.

Mixed-Mesh Finite-Volume Model for Shallow Water Flow with Drying and Wetting

The Godunov-type finite-volume model is able to accurately simulate complex fluid flows without numerical oscillation. In particular, the mesh-based finite-volume model can capture the feature geometry with precision at the nodes of the grid, and thus has a benefit in flood modeling. However, the mesh-based model may cause partial drying and wetting, which are challenges to solve in the 2D numerical model. Begnudelli and Sanders (2006) proposed a triangular mesh-based volume/free surface relationship (VFR) for resolving partial drying and wetting, and Kim et al. (2014) extended the method to mixed mesh. In this study the accuracy and applicability of VFRs extended by Kim et al. (2014) were examined by applying three mesh types, namely triangular, quadrilateral and mixed mesh, with various resolutions. Model errors and run times were acceptable and VFRs applied in this study performed well regardless of mesh type and resolution. Keywords: Mixed Mesh, VFRs, Drying and Wetting, Dam-break, Mesh Type

A Coupled Model for Wave Run-up Simulation

AbstractSimplified models like the shallow water equations (SWE) are commonly adopted for describing a wide range of free surface flow problems, like flows in rivers, lakes, estuaries, or coastal areas. In the literature, numerical methods for the SWE are mostly mesh-based. However, this macroscopic approach is unable to accurately represent the complexity of flows near coastlines, where waves nearly break. This fact prompted the idea of coupling the mesh-based SWE model with a meshless particle method for solving the Euler equations. In a previous paper, a method to couple the staggered scheme SWE and the smoothed particle hydrodynamics (SPH) Euler equations was developed and discussed. In this article, this coupled model is used for simulating solitary wave run-up on a sloping beach. The results show strong agreement with the experimental data of Synolakis. Simulations of wave overtopping over a seawall were also performed.

Direct Mesh-Based Model Order Reduction of PEEC Model for Quasi-Static Circuit Problems

In this paper, a new concept of matrix-inversion-less derived physically expressive circuit method of model order reduction for large-scale high-speed/microwave circuit problems is proposed. It is the first model that is derived based on the mesh information of partial element equivalent circuit modeling. This new proposed method absorbs insignificant nodes and parallel branches while retaining the physical meaning of all the inductive and capacitive elements. This method does not involve any matrix inversions or decompositions and its computational overhead is dominated by outer products that can be simply accelerated by the massive GPU acceleration technique. The resultant order-reduced circuit is very useful for not only speeding up the analysis of a large-scale high-speed/microwave circuit but also interpreting the physical insight of the circuit layout from the circuit domain point of view. Three numerical examples are given, demonstrating the versatility, scalability, accuracy, and simplicity of the method.

Numerical modeling of free surface flow in hydraulic structures using Smoothed Particle Hydrodynamics

A meshless particle numerical model based on the Smoothed Particle Hydrodynamics (SPH) is developed and evaluated for two-dimensional simulation of free-surface flows passing through an orifice and over a sharp crested weir. A practical technique is introduced making the model capable of handling the inlet and outlet boundaries. This technique is able to impose known-inflow flux (as in sub-critical open channel flow) at the inlet boundary, while the inlet pressure/depth is automatically adjusted (without imposing any unwanted boundary reflection and pressure fluctuation). Solution stabilizer techniques, such as XSPH and artificial viscosity, are also employed to increase the accuracy and stability of the model, and their effects on the results are evaluated. The developed model proves to be able to reproduce the free surface complexity with good accuracy. A 3-D finite volume mesh-based model is also employed to verify the result of the present SPH model, showing quite compatible pressure and velocity fields.

An efficient hybrid push-pull methodology for peer-to-peer video live streaming system on mobile broadcasting social media

With the rapid growth of wireless communication technology, the availability of highly flexible and video-friendly mobile terminal platforms (such as smartphones and tablets), the emergence of major video content providers (like YouTube, Ustream, and PPTV, which provide a large catalog of attractive contents), Peer-to-Peer (P2P) live video streaming over the wireless and Internet is becoming more and more attractive to users. One of the main challenges is to provide a good quality of service though the dynamic behavior of the network. Traditionally, tree-based model uses a push method, that broadcaster transfers data to other users. This model has low start-up delay. However, there are two main problems in this method: if the bandwidth of an internal node is low, children nodes may lose data and when an internal node failure, other nodes can't receive data until completing the recovery of the tree. On the other hand, mesh-based model uses a pull method, has low bandwidth of a neighbor node by pulling necessary data from a number of neighbor nodes. However, mesh-based model requires large buffers to support pull data from neighbor peers and there is an adjustment between minimum delay by sending pull request and overhead of whole system. So, both models have their own strengths and weaknesses. This paper proposes a new hybrid push-pull live P2P video streaming protocol called MobileCast that combines the benefits of pull and push mechanisms for live video delivery. We present new topology for P2P network with more stable and provide better video streaming quality. Our main goal is to minimize the network end-to-end delay, startup time, overhead, packet loss compared to the pure mesh networks, pure tree networks and provide a good quality of service though the dynamic behavior of the network.

Finite element electro‐thermal modelling of nanocrystalline phase change elements using mesh‐based crystallinity approach

Phase change memory cells composed of nanocrystalline Ge2Sb2Te5 with a heater diameter of 10 nm and Ge2Sb2Te5 thickness of 100 nm are studied by using two-dimensional finite element simulations with COMSOL Multiphysics. The nanocrystalline Ge2Sb2Te5 is emulated by using a mesh-based model incorporating crystalline grains of random size and location embedded in the amorphous media. The material parameters are modelled with temperature dependency from 300 to 1000 K, including electrical resistivity, thermal conductivity, electric field breakdown and Seebeck coefficient. This model is shown to capture the cycle-to-cycle and device-to-device variability in phase change memory cells.

A non-conforming multi-element DGTD method for the simulation of human exposure to electromagnetic waves

The great majority of numerical calculations of electric energy deposition in human tissues exposed to microwaves are performed using the finite-difference time-domain FDTD method and voxel-based geometrical models of the tissues. The straightforward implementation of the method and its computational efficiency are among the main reasons for FDTD being currently the leading method for numerical assessment of human exposure to electromagnetic waves. However, the rather difficult departure from the commonly used Cartesian grid and cell size limitations regarding the discretization of very detailed structures of human tissues are often recognized as the main weaknesses of the FDTD method in this application context. In particular, interfaces between tissues where sharp gradients of the electromagnetic field may occur are hardly modeled rigorously in these studies this is generally referred as the staircasing effect. We present here an alternative numerical dosimetry methodology that is based on a DGTD method designed to work with non-conforming cubic-tetrahedral meshes for more flexibility in the discretization process of complex propagation scenes. For example, in the context of head tissues exposure to mobile phone radiation, the computation domain is divided in two regions: an unstructured tetrahedral mesh-based heterogeneous model of head tissues and an orthogonal cartesian mesh of the vacuum part of the propagation domain. We present numerical results comparing this approach with strategies based on fully Cartesian and fully tetrahedral meshes of the whole computational domain. Copyright © 2013 John Wiley & Sons, Ltd.

Junction-Level Thermal Analysis of 3-D Integrated Circuits Using High Definition Power Blurring

The degraded thermal path of 3-D integrated circuits (3DICs) makes thermal analysis at the chip-scale an essential part of the design process. Performing an appropriate thermal analysis on such circuits requires a model with junction-level fidelity; however, the computational burden imposed by such a model is tremendous. In this paper, we present enhancements to two thermal modeling techniques for integrated circuits to make them applicable to 3DICs. First, we present a resistive mesh-based approach that improves on the fidelity of prior approaches by constructing a thermal model of the full structure of 3DICs, including the interconnect. Second, we introduce a method for dividing the thermal response caused by a heat load into a high fidelity “near response” and a lower fidelity “far response” in order to implement Power Blurring high definition (HD), a hierarchical thermal simulation approach based on Power Blurring that incorporates the resistive mesh-based models and allows for junction-level accuracy at the full-chip scale. The Power Blurring HD technique yields approximately three orders of magnitude of improvement in memory usage and up to six orders of magnitude of improvement in runtime for a three-tier synthetic aperture radar circuit, as compared to using a full-chip junction-scale resistive mesh-based model. Finally, measurement results are presented showing that Power Blurring high definition (HD) accurately determines the shape of the thermal profile of the 3DIC surface after a correction factor is added to adjust for a discrepancy in the absolute temperature values.

MPS mesh-free particle method for multiphase flows

By treating the multiphase system as a multi-density multi-viscosity fluid, a straightforward model has been proposed in this paper based on the Moving Particle Semi-implicit (MPS) mesh-free particle method for incompressible multiphase flow. The weakly-compressible MPS (WC-MPS) formulation (developed by the authors) is used to solve a single set of equations for all of the phases. In the model, the multiphase forces are introduced in a straightforward way. Dealing with multi-viscosity systems, different methods for defining the viscosity, by which particles of different phases interact, is examined. To evaluate the accuracy of each of these methods, a stratified multi-viscosity Poiseuille flow test case is used and model results are compared with the analytical solution. The results show that selection of this interaction viscosity has an important role in the accuracy of the results. The model is then validated and applied to two basic hydrodynamic instability cases (Rayleigh–Taylor and Kelvin–Helmholtz instabilities). The results are then compared to a mesh-based model (with volume of fluid interface tracing method) to examine the ability of the model to deal with the multi-density systems. Comparisons show the model has reasonable accuracy. The results of this work offer the potential of modeling of multiphase incompressible immiscible systems in an extensive range of conditions using MPS.

A Comparison of Nodal- and Mesh-Based Magnetic Equivalent Circuit Models

The magnetic equivalent circuit (MEC) technique is a powerful analysis and design tool that combines relative accuracy with moderate computational effort. In this paper, a nodal-based MEC formulation and a mesh-based MEC formulation of a magnetic system are compared. The Newton-Raphson algorithm is used to solve the algebraic system, and to draw conclusions about the computational efficiency of the two formulations under linear and nonlinear operation. Although the two formulations exhibit similar performance under linear operating conditions, the performance of the mesh-based model is significantly better than that of the nodal-based model under nonlinear operation.

A VLSI architecture for video object motion estimation using a novel 2-D hierarchical mesh

Abstract This paper proposes a novel hierarchical mesh-based video object model and a motion estimation architecture that generates a content-based video object representation. The 2-D mesh-based video object is represented using two layers: an alpha plane and a texture. The alpha plane consists of two layers: (1) a mesh layer and (2) a binary layer that defines the object boundary. The texture defines the object’s colors. A new hierarchical adaptive structured mesh represents the mesh layer. The proposed mesh is a coarse-to-fine hierarchical 2-D mesh that is formed by recursive triangulation of the initial coarse mesh geometry. The proposed technique reduces the mesh code size and captures the mesh dynamics. The proposed motion estimation architecture generates a progressive mesh code and the motion vectors of the mesh nodes. The performance analysis for the proposed video object representation and the proposed motion estimation architecture shows that they are suitable for very low bit rate online mobile applications and the motion estimation architecture can be used as a building block for MPEG-4 codec.