Numerical Filling Simulation of Injection Molding Using Three-Dimensional Model

Most injection molded parts are three-dimensional, with complex geometrical configurations and thick/thin wall sections. A 3D simulation model will predict more accurately the filling process than a 2.5D model. This paper gives a mathematical model and numeric method based on 3D model, in which an equal-order velocity-pressure interpolation method is employed successfully. The relation between velocity and pressure is obtained from the discretized momentum equations in order to derive the pressure equation. A 3D control volume scheme is employed to track the flow front. The validity of the model has been tested through the analysis of the flow in cavity.     

Three-dimensional finite element method for the filling simulation of injection molding

With the development of molding techniques, molded parts have more complex and larger geometry with nonuniform thickness. In this case, the velocity and the variation of parameters in the gapwise direction are considerable and cannot be neglected. A three-dimensional (3D) simulation model can predict the filling process more accurately than a 2.5D model based on the Hele–Shaw approximation. This paper gives a mathematical model and numeric method based on 3D model to perform more accurate simulations of a fully flow. The model employs an equal-order velocity–pressure interpolation method. The relation between velocity and pressure is obtained from the discretized momentum equations in order to derive the pressure equation. A 3D control volume scheme is used to track the flow front. During calculating the temperature field, the influence of convection items in three directions is considered. The software based on this 3D model can calculate the pressure field, velocity field and temperature field in filling process. The validity of the model has been tested through the analysis of the flow in cavities.     

Coupling of two- and three-dimensional hydrodynamic numerical models for simulating wind-induced currents in deep basins

The main interest of the present study is the simulation of wind-induced currents in closed water bodies with shallow and deep regions. This paper describes a low time consumption numerical modelling technique for the simulation of free-surface flow over a geometrically complex bed. To achieve this, a technique employing coupled two- and three-dimensional flow solvers is developed for simulation of the flow. The conjunctive model consists of an upper part 2D Shallow Water Flow Solver (2D-SWFS) coupled with a 3D pseudo-compressible flow solver (3D-PCFS) for the deep regions with a proper interface boundary condition. The 2D-SWFS and 3D-PCFS solvers are coupled via an interfacial shear stress gradient and pressure effects. Time stepping is performed for the 2D solver, and an iterative procedure is employed by the 3D solver to satisfy the equilibrium constraints for the interfacial boundary. The model is able to consider 2D wetting and drying shallow regions without any underlying deep water. Both the 2D and 3D models use nodal based Galerkin finite volume method (GFVM) for solving the governing equations on the unstructured meshes. The accuracy of both models in solving the effective phenomena is examined by comparing the results of simulated test cases with readily available analytical solutions and experimental measurements. Finally, the accuracy of the conjunctive model is assessed by comparing its results for test cases with analytical solutions and experimental measurements from the literature. The new simulation method is then used to solve a wind-induced flow problem in a basin with deep water surrounded by shallow water parts.     

VLCC液舱晃荡仿真模型

分别采用3D模型和2D模型对VLCC液舱进行晃荡仿真,通过对两个模型的流体流动情况和对应位置压力的比较,得出短期搜索及长期分析中采用2D模型方案进行VLCC液舱晃荡仿真分析是可行的结论. 讨论两种模型的计算效率,认为2D模型方案可以大大提高仿真效率,具有工程实用性.     

Numerical simulation of Newtonian and non-Newtonian flows in bypass

This paper deals with the numerical solution of Newtonian and non-Newtonian flows with biomedical applications. The flows are supposed to be laminar, viscous, incompressible and steady or unsteady with prescribed pressure variation at the outlet. The model used for non-Newtonian fluids is a variant of power law. Governing equations in this model are incompressible Navier–Stokes equations. For numerical solution we use artificial compressibility method with three stage Runge–Kutta method and finite volume method in cell centered formulation for discretization of space derivatives. The following cases of flows are solved: steady Newtonian and non-Newtonian flow through a bypass connected to main channel in 2D, steady Newtonian flow in angular bypass in 3D and unsteady non-Newtonian flow through bypass in 2D. Some 2D and 3D results that could have application in the area of biomedicine are presented.     

A spring–mass model-based approach for warping cloth patterns on 3D objects

This paper presents a general method for transformations of an object between 2D and 3D which can be used efficiently in computer-aided garment design. A uniform triangular spring–mass-based deformable model is employed. Both 2D-to-3D and 3D-to-2D transformations can be implemented in the same model. An efficient collision detection method is also discussed. © 1998 John Wiley & Sons, Ltd.     

基于改进 L-K 光流的 WebAR 信息可视分析方法

摘 要：信息可视化技术结合移动增强现实(MAR)技术在目标跟踪领域仍然存在设备计算 负载过大的问题。若仍坚持采用同跟踪平面图像特征点的方案来跟踪立体对象各角度的特征点, 则目标跟踪过程所需要获取的多角度特征点数据无疑会加重跟踪过程的计算压力,进而导致移 动设备负载过大,最终影响模型渲染,所渲染的模型常出现剧烈抖动、卡顿或运动滞后于目标 物的现象。针对上述问题,提出了一种基于改进的 L-K (Lucas-Kanade)光流跟踪算法的 WebAR (基于 Web 端的 MAR 技术)解决方案,将特征点的跟踪问题转化为光流估计问题以及一种优化 的三维信息可视化交互策略。实验结果表明,该方法能够提高 MAR 在跟踪目标时的计算效率 和稳定性,丰富信息可视化的呈现效果和交互方式。     

Development of a Variational Multiscale Large-Eddy Simulation Code ‘MISTRAL’ Using Double-Scale Finite Elements

A variational multiscale large-eddy simulation (VMS-LES) code, named MISTRAL, has been developed based upon the finite element method (FEM) for accurate and practical computation of geometrically complicated turbulent flow problems. The numerical strategy of the FEM-based VMS-LES is explained, especially focusing on the double-scale approximation for velocity and pressure in the incompressible Navier-Stokes equations, a pressure stabilization technique and a multiscale turbulence modeling. A unique technique is also employed in the time integration to realize an efficient inversion of the multiscale mass matrix and to form the multiscale pressure Poisson equation used in the approximate projection method for divergence-free constraint of velocity. As a numerical demonstration, a 2D driven cavity flow problem has been solved with the MISTRAL code in a wide range of Reynolds number (Re=1000 to 50000). The results are compared with reference data to quantitatively estimate the accuracy (magnitude of errors in terms of L ² norms) of the proposed VMS-LES method.     

Proper cell dimension and number of particles per cell for DSMC

The Direct Simulation Monte Carlo (DSMC) method models fluid flows using simulation particles which represent a large number of real molecules in a probabilistic simulation to solve the Boltzmann equation. Different opinions still exist on some basic understandings of the controlling factors of DSMC method, such as the proper grid dimension and the proper number of particles in a cell. In this contribution, DSMC simulation of Poiseuille flow was carried out to evaluate the dependence of simulation results on cell dimension and number of particles per cell. In the simulation process a self-adaptive block-structured grid system was employed to guarantee that the number of particles per cell is constant. The simulation covers both 2D and 3D, slip flow regime and transition flow regime, and for each regime, covers both high pressure and low pressure cases. Our simulation results indicate that the number of particles per cell and scaling factor have little influence on simulation result for both slip flow and transition flow when the number of particles per cell is greater than 5, but the dimension of cell influences the accuracy of results significantly. The error caused by cell dimension decreases with the decrease of cell dimension. It is concluded that in the DSMC method it is necessary to ensure that the cell is less than 1/2 of molecular mean free path.     

引入文本检索的混合形状特征的3D模型检索技术

针对三维模型检索性能较低的问题．提出一种快速准确的检索技术。为了提高模型的检索速度．引入于文本与内容相结合的检索方法。为了提高模型检索的准确率,根据基于单一模型特征的三维模型检索存在的不足,提出了结合多种形状特征进行模型的检索方法。模型的面积分布和形状直方图两种特征被应用于模型检索。实验证明该算法在检索准确度和检索效率上都有所提高。     

An approach to modelling high pressure waterjet oil barriers

A numerical model is employed to study flow characteristics of high pressure waterjet barriers. The high pressure waterjet barrier has been developed as a means of containing and deflecting oil spills that float on water. An array of waterjets directed above the contaminated surface will generate an air flow that moves the oil. A two-dimensional model of the turbulent entrained air flow is done using the spectral element method. The moving boundaries of the air flow are modeled analytically and implemented in the computer code. The upper boundary, represented by the high pressure waterjet, is assumed to be moving with the centerline velocity of the jet. The lower boundary is the interface of the air-driven wavy liquid surface for which interfacial shear and pressure drop are directly related to waviness characteristics and mobility of the interface. This boundary is modeled as a solid-like wavy surface. The interfacial speed is neglected at this stage since it is much smaller than the air speed. An algebraic turbulence closure model is used for estimating shear stress at the lower boundary. A case study is presented where the numerical model has been applied to a base case for which experimental data are available. The predicted air flow velocities of the model compare relatively well with experimental values. Results of the model have also shown that the air flow maintains significant momentum over a long distance beyond the range when the waterjet itself has ceased.     

自适应最小误差阈值分割算法

对二维最小误差法进行三维推广, 并结合三维直方图重建和降维思想提出了一种鲁 棒的最小误差阈值分割算法. 但该方法为全局算法, 仅适用于分割均匀光照图像. 为 提高其自适应性, 本文采用Water flow模型对非均匀光照图像进行背景估计, 以此获 得原始图像与背景图像的差值图像, 达到降低非均匀光照对图像分割造成干扰的目的. 为进 一步提高分割性能, 本文对差值图像采用γ 矫正进行增强, 然后采用鲁棒最小误差 法进行全局分割, 从而完成目标提取. 最后本文对均匀光照下以及非均匀光照下图像进行了 实验, 并与一维最小误差法、二维最小误差法、三维直方图重建和降维的Otsu阈值分割 算法、灰度波动变换自适应阈值方法以及一种改进的FCM方法在错误分割率和运行时间上进 行了对比. 实验结果表明, 相对于以上方法, 本算法的分割性能均有明显提升.     

Behavior of microdroplets in diffuser/nozzle structures

This paper investigates the behavior of microdroplets flowing in microchannels with a series of diffuser/nozzle structures. Depending on the imposed flow direction, the serial structures can act either as a series of diffusers or nozzles. Different serial diffuser/nozzle microchannels with opening angles ranging from 15° to 45° were considered. A 2D numerical model was employed to study the dynamics of the microdroplet during its passage through the diffuser/nozzle structures. The deformation of the microdroplet was captured using a level set method. On the experimental front, test devices were fabricated in polydimethylsiloxane using soft lithography. T-junctions for droplet formation, diffuser/nozzle structures and pressure ports were integrated in a single device. Mineral oil with 2% w/w surfactant span 80 and de-ionized water with fluorescent worked as the carrier phase and the dispersed phase, respectively. The deformation of the water droplet and the corresponding pressure drop across the diffuser/nozzle structures were measured in both diffuser and nozzle configurations at a fixed flow rate ratio between oil and water of 30. The results show a linear relationship between the pressure drop and the flow rate. Furthermore, the rectification effect was observed in all tested devices. The pressure drop in the diffuser configuration is higher than that of the nozzle configuration. Finally, the pressure measured results with droplet and without droplet were analyzed and compared.     

Non-rigid 3D shape tracking from multiview video

We present a fast and efficient non-rigid shape tracking method for modeling dynamic 3D objects from multiview video. Starting from an initial mesh representation, the shape of a dynamic object is tracked over time, both in geometry and topology, based on multiview silhouette and 3D scene flow information. The mesh representation of each frame is obtained by deforming the mesh representation of the previous frame towards the optimal surface defined by the time-varying multiview silhouette information with the aid of 3D scene flow vectors. The whole time-varying shape is then represented as a mesh sequence which can efficiently be encoded in terms of restructuring and topological operations, and small-scale vertex displacements along with the initial model. The proposed method has the ability to deal with dynamic objects that may undergo non-rigid transformations and topological changes. The time-varying mesh representations of such non-rigid shapes, which are not necessarily of fixed connectivity, can successfully be tracked thanks to restructuring and topological operations employed in our deformation scheme. We demonstrate the performance of the proposed method both on real and synthetic sequences.     

基于CFD的锥管浮子流量计结构优化

针对量程上限为100m3/h的DN100金属锥管浮子流量计存在的压力损失大、稳定性差、加工难度大、造价高等问题,应用计算流体动力学(CFD)方法,设计并优化浮子流量计的结构参数.利用GAM-BIT的Size Function功能加密网格,提高计算精度,利用"浮子受力平衡度误差分析法"逐步调整入口流速,对浮子流量计的三维...     

Self-adaptive morphable model based collaborative multi-view 3d face reconstruction in visual sensor network

3D face reconstruction is an efficient method for pedestrian recognition in non-cooperative environment because of its outstanding performance in robust face recognition for uncontrolled pose and illumination changes. Visual sensor network is widely used in target surveillance as powerful unattended distributed measurement systems. This paper proposes a collaborative multi-view non-cooperative 3D face reconstruction method in visual sensor network. A peer-to-peer paradigm-based visual sensor network is employed for distributed pedestrian tracking and optimal face image acquisition. Gaussian probability distribution-based multi-view data fusion is used for target localization, and kalman filter is applied for target tracking. A lightweight face image quality evaluation method is presented to search optimal face images. A self-adaptive morphable model is designed for multiview 3D face reconstruction. To adjust the self-adaptive morphable model, the optimal face images and their poses estimation are used. Cooperative chaotic particle swarm optimization is employed for parameters optimization of the self-adaptive morphable model. Experimental results on real data show that the proposed method can acquire optimal face images and achieve non-cooperative 3D reconstruction efficiently.     

A comparison of numerical models for evaporative two-phase flow in a self-heated porous medium

Two different numerical models using the finite difference method (FDM) for one-component time-dependent two-phase flows in a porous medium are investigated: the iterative four-variable model (I4VM) and the direct three-variable model (D3VM). The former includes the pressure gradient and uses the iterative method to solve a system of flow equations, whereas for the latter, the formulation without the pressure gradient is simultaneously solved using the algorithm for tri-tridiagonal equations of three dependent variables. The steady-state solution as well as the unsteady results obtained by two models are compared only for the low heat generation rate below the dryout limit. For the high heat generation rate the effects of two numerical models on the time-dependent flow and dryout behavior up to incipient dryout are discussed in terms of liquid volumetric fraction and liquid superficial velocity distributions. It was found that the I4VM is numerically more stable for the case of strongly nonlinear physical models (e.g. the Ergun constants model of Fand, R. M., Kim, B. Y. K., Lam, A. C. and Phan, R. T., Resistance to the flow of fluids through simple and complex porous media whose matrices are composed of randomly packed spheres. J. Fluids Engng, 1987, 109, 268–274) and enables us to analyze those, whereas the D3VM is advantageous for fast analysis of the weakly nonlinear model (e.g. the Ergun constants model of Macdonald, I. F., El-Sayed, M. S., Mow, K. and Dullien, F. A. L., flow through porous media—the Ergun equation revisited. Ind. Engng Chem. Fundam., 1979, 18, 199–208). Finally, a comparative evaluation of both numerical models is presented.     

Immersed boundary method and lattice Boltzmann method coupled FSI simulation of mitral leaflet flow

Coupling the immersed boundary (IB) method and the lattice Boltzmann (LB) method might be a promising approach to simulate fluid-structure interaction (FSI) problems with flexible structures and moving boundaries. To investigate the possibility for future IB-LB coupled simulations of the heart flow dynamics, an IB-LB coupling scheme suitable for rapid boundary motion and large pressure gradient FSI is proposed, and the mitral valve jet flow considering the interaction of leaflets and fluid is simulated. After analyzing the respective concepts, formulae and advantages of the IB and LB methods, we first explain the coupling strategy and detailed implementation procedures, and then verify the effectiveness and second-order accuracy of the scheme by simulating a benchmark case, the relaxation of a stretched membrane immersed in fluid. After that, the diastolic filling jet flow between mitral leaflets in a simplified 2D left heart model is simulated. The model consists of the simplified transmitral passage of the heart and two curvilinear leaflets. In the simulation, the atrial and ventricular pressure histories of normal human are specified as boundary conditions, and the leaflets are treated as fibers that interact with the fluid to define their deformations and movements. The resulting opening and closing movements of the leaflets and the flow patterns of the filling jet are qualitatively reasonable and compare well with existing numerical and measured data. It is shown that this IB-LB coupling method is feasible for treating flexible boundary FSI problems with rapid boundary motion and large pressure gradient, the results of the mitral leaflet flow are valuable for understanding the transmitral FSI dynamics, and it is possible to simulate the more realistic 3D heart flow by the scheme in the future.     

Fast generation method of 3D scene in Chinese landscape painting

The three-dimensional (3D) modeling of Chinese landscape painting is of great significance for the digital protection of cultural heritage and the production of virtual reality content. A fast modeling method to create 3D landscape scenes for traditional Chinese painting is proposed in this paper, based on integrated terrain modeling and the water flow rendering algorithm. A height map generation algorithm based on auxiliary lines is first proposed to carry out fast modeling from a simple two-dimensional contour to create a 3D mountain model. A realistic flow simulation that fits the topography is then undertaken, based on a flow chart which is calculated using the particle force in the normal grid of topography, and the theory of smoothing particle hydrodynamics. Finally, a stylistic scene that conforms to the artistic concept of traditional Chinese painting is acquired by optimizing the parameters. The interactive modeling platform of the integrated algorithm is tested in this study, and compared with existing research. Results show the method can achieve real-time rendering and realistic rendering to rapidly generate a 3D scene model consistent with a traditional painting scene, and provide support for the follow up development of virtual reality applications.

     

Lattice Boltzmann large eddy simulation of subcritical flows around a sphere on non-uniform grids

In this work, the suitability of the lattice Boltzmann method is evaluated for the simulation of subcritical turbulent flows around a sphere. Special measures are taken to reduce the computational cost without sacrificing the accuracy of the method. A large eddy simulation turbulence model is employed to allow efficient simulation of resolved flow structures on non-uniform computational meshes. In the vicinity of solid walls, where the flow is governed by the presence of a thin boundary layer, local grid-refinement is employed in order to capture the fine structures of the flow. In the test case considered, reference values for the drag force in the Reynolds number range from 2000 to 10 000 and for the surface pressure distribution and the angle of separation at a Reynolds number of 10 000 could be quantitatively reproduced. A parallel efficiency of 80% was obtained on an Opteron cluster.