Method of triangular mesh modeling in numerical control machining simulation

In the process of numerical control machining simulation,the workpiece surface is usually described with the uniform triangular mesh model.To alleviate the contradiction between the simulation speed and accuracy in this model,two improved methods,i.e.,the local refinement triangular mesh modeling method and the adaptive triangular mesh modeling method were presented.The simulation results show that when the final shape of the workpiece is known and its mathematic representation is simple,the local refinement triangular mesh modeling method is preferred;when the final shape of the workpiece is unknown and its mathematic description is complicated,the adaptive triangular mesh modeling method is more suitable.The experimental results show that both methods are more targeted and practical and can meet the requirements of real-time and precision in simulation.

A Bogus Typhoon Scheme and Its Application to a Movable Nested Mesh Model

A bogus typhoon scheme,designed for the initialization of a typhoon track prediction model,is developed in thispaper.This scheme includes both effects of axisymmetric wind and asymmetric wind.Experimental forecasts using atwo-way interactive movable nested mesh model show that the forecast skill of typhoon tracks has clearly improvedafter introducing the bogus typhoon into the initial fields.

MODELING OF 3-D IMAGES AND SPACE MARKOV CUBIC MESH MODELS

Three-dimensional(3-D)Markov cubic random mesh models are presented andproved in the form of two theorems in details.Its applications to the modeling and description of3-D images are described.The model presented here is a appropriate mathematical tool for thesegmentation,modeling,classification and other processing.Finally,an example is given.

Mesh model building and migration and accumulation simulation of 3D hydrocarbon carrier system

Migration and accumulation simulation of oil and gas in carrier systems has always been a difficult subject in the quantitative study of petroleum geology. In view of the fact that the traditional geological modeling technology can not establish the interrelation of carriers in three dimensional space, we have proposed a hybrid-dimensional mesh modeling technology consisting of body(stratum), surfaces(faults and unconformities), lines and points, which provides an important research method for the description of geometry of sand bodies, faults and unconformities, the 3 D geological modeling of complex tectonic areas, and the simulation of hydrocarbon migration and accumulation. Furthermore, we have advanced a 3 D hydrocarbon migration pathway tracking method based on the hybrid-dimensional mesh of the carrier system. The application of this technology in western Luliang Uplift of Junggar Basin shows that the technology can effectively characterize the transport effect of fault planes, unconformities and sand bodies, indicate the hydrocarbon migration pathways, simulate the process of oil accumulation, reservoir adjustment and secondary reservoir formation, predict the hydrocarbon distribution. It is found through the simulation that the areas around the paleo-oil reservoir and covered by migration pathways are favorable sites for oil and gas distribution.

A TWO-WAY INTERACTIVE MOVABLE NESTED MESH MODEL FOR TYPHOON TRACK PREDICTION

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Nodes2STRNet for structural dense displacement recognition by deformable mesh model and motion representation

Displacement is a critical indicator for mechanical systems and civil structures.Conventional vision-based displacement recognition methods mainly focus on the sparse identification of limited measurement points,and the motion representation of an entire structure is very challenging.This study proposes a novel Nodes2STRNet for structural dense displacement recognition using a handful of structural control nodes based on a deformable structural three-dimensional mesh model,which consists of control node estimation subnetwork(NodesEstimate)and pose parameter recognition subnetwork(Nodes2PoseNet).NodesEstimate calculates the dense optical flow field based on FlowNet 2.0 and generates structural control node coordinates.Nodes2PoseNet uses structural control node coordinates as input and regresses structural pose parameters by a multilayer perceptron.A self-supervised learning strategy is designed with a mean square error loss and L2 regularization to train Nodes2PoseNet.The effectiveness and accuracy of dense displacement recognition and robustness to light condition variations are validated by seismic shaking table tests of a four-story-building model.Comparative studies with image-segmentation-based Structure-PoseNet show that the proposed Nodes2STRNet can achieve higher accuracy and better robustness against light condition variations.In addition,NodesEstimate does not require retraining when faced with new scenarios,and Nodes2PoseNet has high self-supervised training efficiency with only a few control nodes instead of fully supervised pixel-level segmentation.

倾斜摄影Mesh模型与激光点云构建部件级城市三维模型

为构建部件级城市实景三维(3D)模型,本文在倾斜网目(Mesh)模型建模和激光点云建模的技术上,探讨建筑物、部件以及城市场景模型建模的方法,并最终融合构建部件级城市实景3D模型,并应用于国家新型基础测绘北京试点-副中心运河两岸商务区实景3D建模项目中,为北京市新型基础测绘建设提供一份力量。

A blind watermarking algorithm for 3D mesh models based on vertex curvature

We propose a robust blind watermarking algorithm for three-dimensional(3D)mesh models based on vertex curvature to maintain good robustness and improve visual masking in 3D mesh models.In the embedding process,by using the local window of vertex,the root mean square curvature is calculated for every vertex of the 3D mesh model and an ordered set of fluctuation values is obtained.According to the ordered fluctuation values,the vertices are separated into bins.In each bin the fluctuation values are normalized.Finally,the mean of the root mean square curvature fluctuation values of the vertices in each bin is modulated to embed watermark information.In watermark detection,the algorithm uses a blind watermark extraction technique to extract the watermark information.The experimental results show that the algorithm has a very good performance for visual masking of the embedded model and that it can resist a variety of common attacks such as vertex rearrangement,rotation,translating,uniform scaling,noise,smoothing,quantization,and simplification.

Recovery of Sharp Features in Mesh Models

Due to the shortages of current methods for the recovery of sharp features of mesh models with holes,this paper presents two novel algorithms for the recovery of features(especially sharp features)in mesh models.One algorithm defines an energy that is regarded as the difference between the initial features and the ideal features.The optimal solution of the energy optimization problem modifies the initial features.The algorithm has good performance on sharp features.The other method establishes a plane cluster for each initial feature point to obtain a corresponding modified feature point.If necessary,we can obtain the modified feature line by fitting these modified points.Both methods depend little on the result of fillingmodel holes and result in better features,which maintain the sharp geometric characteristic and the smoothness of the model.The experimental results of the two algorithms demonstrate their superiority and rationality compared with the existing methods.

Approximating interior bounded box of 3D character mesh model based on its skeleton and symmetry

Purpose – In the process of robot shell design, it is necessary to match the shape of the input 3D originalcharacter mesh model and robot endoskeleton, in order to make the input model fit for robot and avoidcollision. So, the purpose of this paper is to find an object of reference, which can be used for the process ofshape matching.Design/methodology/approach – In this work, the authors propose an interior bounded box (IBB)approach that derives from oriented bounding box (OBB). This kind of box is inside the closed mesh model.At the same time, it has maximum volume which is aligned with the object axis but is enclosed by all the meshvertices. Based on the IBB of input mesh model and the OBB of robot endoskeleton, the authors can completethe process of shape matching. In this paper, the authors use an evolutionary algorithm, covariance matrixadaptation evolution strategy (CMA-ES), to approximate the IBB based on skeleton and symmetry of inputcharacter mesh model.Findings – Based on the evolutionary algorithm CMA-ES, the optimal position and scale informationof IBB can be found. The authors can obtain satisfactory IBB result after this optimization process.The output IBB has maximum volume and is enveloped by the input character mesh model as well.Originality/value – To the best knowledge of the authors, the IBB is first proposed and used in the field ofrobot shell design. Taking advantage of the IBB, people can quickly obtain a shell model that fit for robot.At the same time, it can avoid collision between shell model and the robot endoskeleton.

Lagrangian Mesh Model with Regridding for Planar Poiseuille Flow

Many biological settings involve complex fluids that have non-Newtonian mechanical responses that arise from suspended microstructures.In contrast,Newtonian fluids are liquids or mixtures of a simple molecular structure that exhibit a linear relationship between the shear stress and the rate of deformation.In modeling complex fluids,the extra stress from the non-Newtonian contribution must be included in the governing equations.In this study we compare Lagrangian mesh and Oldroyd-B formulations of fluidstructure interaction in an immersed boundary framework.The start-up phase of planar Poiseuille flow between two parallel plates is used as a test case for the fluid models.For Newtonian and Oldroyd-B fluids there exist analytical solutions which are used in the comparison of simulation and theoretical results.The Lagrangian mesh results are compared with Oldroyd-B using comparable parameters.A regridding algorithm is introduced for the Lagrangian mesh model.We show that the Lagrangian mesh model simulations with regridding produce results in close agreement with the Oldfoyd-B model.

Mesh Force Modelling and Parametric Studies for Compound Oscillatory Roller Reducer

A compound oscillatory roller reducer(CORR)with a first-stage gear transmission and a second-stage oscillatory roller transmission is presented.The transmission principle of oscillatory roller transmission is introduced,and the tooth profile equation of the inner gear is derived.The analytical model of mesh force considering the installation errors and manufacturing errors is proposed.Then,parametric studies considering different errors on the mesh force are conducted.Results show that the design parameters are significant factors for mesh force.The mesh force is reduced by 17%as the eccentricity of disk cam increases from 2.5 mm to 4 mm.When the radius of the movable roller increases from 7 mm to 20 mm,the mesh force decreases by 8%.As the radius of disk cam increases from 125 mm to 170 mm,the mesh force is decreased by 26.5%.For the impacts of errors,the mesh force has a noticeable fluctuation when these errors exist including the manufacturing error of disk cam,the installation error of disk cam and the manufacturing error of movable roller change.The prototype of the reducer is manufactured and preliminary run-in test proved the feasibility of the transmission principle.

实景三维建模中的建筑物mesh模型立面修整

实景三维模型作为实景三维中国建设中的数据底座,发挥了极其重要的作用。建筑物mesh模型作为实景三维模型中重要的数据,其质量好坏直接影响着实景三维模型的使用效果。本文结合实际工程经验,提出了一种批量化的建筑物mesh模型立面修整方法。首先,以ContextCapture软件生成的实景三维模型为基础,采集建筑物的矢量轮廓线;然后,利用参数化建模软件批量生成平整的建筑物三维矢量面,自动完成建筑物立面到三维矢量面的吸附,使建筑物立面结构平整;最后,以修复好的建筑物mesh模型为参考,在ContextCapture软件中进行建筑物mesh模型纹理映射,批量完成建筑物mesh模型的更新。通过多个试验场景测试,验证了该方法的有效性和高效性。

Model of Random Polygon Particles for Concrete and Mesh Automatic Subdivision

In order to study the constitutive behavior of concrete in mesoscopic level, a new method is proposed in this paper. This method uses random polygon particles to simulate full grading broken aggregates of concrete. Based on computational geometry, we carry out the automatic generation of the triangle finite element mesh for the model of random polygon particles of concrete. The finite element mesh generated in this paper is also applicable to many other numerical methods.

Meshing effects of the 3-D FEM numerical modeling in seismo-electromagnetics:An application in selectivity of seismic electric signal (SES)

We investigated how density and quality of mesh around interest domain affect electromagnetic （EM） responses of 3D Earth layered media using finite element method （FEM）. Effect of different mesh shapes was also investigated using a method of mixing structured and unstructured mesh. As a case study, we estimated the effects of meshing on selectivity phenomenon of seismic electric signal （SES）. Our results suggest that the relative errors resulting from mesh effects may not be negligible, which may lead to some unconvincing explanation of the SES selectivity based on the numerical modeling results.

Surface Modelling and Mesh Generation for Simulating Superplastic Forming

This paper presents an approach which enables surface modelling, mesh generation and the Finite Element (FE) analysis to be integrated together to simulate superplastic forming process for complex shaped components. Techniques have been developed to generate an FE mesh over non-four-sided surface areas, the boundaries of which are Bezier curves of arbitrary degree, using a consistent expression. Theoretical evidence is given to determine the number of Bezier triangular patches required for accurately re-constructing die surfaces within a commercial FE solver. The developed techniques have been successfully used in determining the process parameters for forming a 3D rectangular box.

A Massively Parallel Re-Configurable Mesh Computer Emulator: Design, Modeling and Realization

Emulating massively parallel computer architectures represents a very important tool for the parallel programmers. It allows them to implement and validate their algorithms. Due to the high cost of the massively parallel real machines, they remain unavailable and not popular in the parallel computing community. The goal of this paper is to present an elaborated emulator of a 2-D massively parallel re-configurable mesh computer of size n x n processing elements (PE). Basing on the object modeling method, we develop a hard kernel of a parallel virtual machine in which we translate all the physical properties of its different components. A parallel programming language and its compiler are also devel-oped to edit, compile and run programs. The developed emulator is a multi platform system. It can be installed in any sequential computer whatever may be its operating system and its processing unit technology (CPU). The size n x n of this virtual re-configurable mesh is not limited;it depends just on the performance of the sequential machine supporting the emulator.

交错断层四面体自适应网格分级细化研究

目前四面体自适应网格细化技术多集中于简单层状地质体的三维重构与表达分析,对结构复杂、数据不连续的含交错断层等地质体进行自适应网格细化时,易出现过度细化,导致断层区域的网格结构受到影响。为了提高含复杂断层四面体网格模型的精度,提出一种适用于交错断层的四面体自适应网格分级细化方法。首先,根据断层影响范围公式,自适应确定断层网格附近的细化范围;其次,构建四面体和四面体边的分级细分公式,确定细化范围内的四面体和四面体边的分级;然后,针对四面体网格细分时出现的多种情况,通过对边的升级处理,将细分的8种类型统一为3种类型;最后,在细化范围内,通过新增加顶点和原顶点重新连接四面体,改变网格的单元尺寸,生成高质量的网格模型。以内蒙古自治区某含交错断层露天煤矿的四面体网格模型为例,使用三维网格质量评估算法及FLAC3D模拟软件分析细化前后的网格模型,结果表明:细化后的网格模型失真值从0.3317降低到0.3061,表明网格的质量得到提升;在相同参数下,未细化模型的最大位移为1.16 m,稳定性系数为1.27,分级细化后模型的最大位移为1.29 m,稳定性系数为1.23;细化后模型的位移云图处于断层处,且能够体现断层分布特征和断层对边坡的影响规律,而未细化模型的位移云图的位置偏离断层中心,断层对边坡的影响效果不明显。

多源点云优化的城市三维模型构建

简易模型与传统复杂的单体模型相比,对存储、可视化、传输和后续应用技术要求低,敏感信息承载量少,且能满足大部分应用需求,具有更高的应用价值。考虑应用需求与技术现状,自然资源部将城市三维模型(L0D1.3级)纳入实景三维中国建设任务中。目前相关生产以半自动化采集为主,工程化应用存在技术流程烦琐、效率较低且对数据量限制较大等问题。本文立足山东实际,提出了一种基于多源点云优化的城市三维模型快速构建技术,在充分利用现有数据基础上有效提升了数据处理效率,大幅减少了生产成本,并在实景三维山东建设过程中得到了有效验证,具有较好的社会经济效益与推广价值。

城市实景模型结构化线面特征重构方法

为了改善城市实景模型边缘模糊,提出了一种曲率引导的结构化线面特征重构方法。根据曲率特征将网格分割为平面、可展凹、可展凸以及不可展曲面4类,在平面分割结果内提取平面,在可展凹和可展凸分割结果内提取直线,对过度弯曲的不可展区域进行保留,最终形成包含几何特征的复合网格模型。结果表明,结合曲率信息预先设置几何特征的潜在范围,使得结构化线面特征更可靠,同时保证城市实景中复杂的树结构不被错误地提取为平面。