掺气水流中气泡区域的双层动态阈值分割方法

准确地提取出掺气水流中的气泡，是利用图像测量方法进行水流特性分析的前提。由于掺气水流中的气泡是无色透明的、对比度低，而且由于实验过程的光照不均，从而给图像高精度分割带来困难。由于光照不均，致使掺气水流图像中，气泡信息强弱不均，此时又会因强信息淹没弱信息而导致气泡漏提取或提取气泡缺损，为解决此问题，提出了一种双层动态阈值的分割方法，即首先在第1层完成对气泡所在局部区域的定位，再通过贴标签处理确定出每一个气泡的局部区域；然后在第2层的精分割中，对所有局部区域进行精细分割，以实现气泡区域的精确提取。实验结果证明，该方法可以大大提高气泡提取的精度。     

Automatic Delaunay mesh generation method and physically-based mesh optimization method on two-dimensional regions

Delaunay mesh generation method is a common method for unstructured mesh (or unstructured grid) generation. Delaunay mesh generation method can conveniently add new points to the existing mesh without remeshing the whole domain. However, the quality of the generated mesh is not high enough if compared with some mesh generation methods. To obtain high-quality mesh, this paper developed an automatic Delaunay mesh generation method and a physically-based mesh optimization method on two-dimensional regions. For the Delaunay mesh generation method, boundary-conforming problem was ensured by create nodes at centroid of mesh elements. The definition of node bubbles and element bubbles was provided to control local mesh coarseness and fineness automatically. For the physically-based mesh optimization method, the positions of boundary node bubbles are predefined, the positions of interior node bubbles are adjusted according to interbubble forces. Size of interior node bubbles is further adjusted according to the size of adjacent node bubbles. Several examples show that high-quality meshes are obtained after mesh optimization.

     

Particle‐based simulation of bubbles in water–solid interaction

In this paper, a particle‐based multiphase method for creating realistic animations of bubbles in water–solid interaction is presented. To generate bubbles from gas dissolved in the water on the fly, we propose an approximate model for the creation of bubbles, which takes into account the influence of gas concentration in the water, the solid material, and water–solid velocity difference. As the air particle on the bubble surface is treated as a virtual nucleation site, the bubble absorbs air from surrounding water and grows. The density and pressure forces of air bubbles are computed separately using smoothed particle hydrodynamics; then, the two‐way coupling of bubbles with water and solid is solved by a new drag force, so the generated bubbles’ flow on the surface of solid and the deformation in the rising process can be simulated. Additionally, touching bubbles merge together under the cohesion forces weighted by the smoothing kernel and velocity difference. The experimental results show that this method is capable of simulating bubbles in water–solid interaction under different physical conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

A fast and accurate computational technique for efficient numerical solution of nonlinear singular boundary value problems

This paper is concerned with design and implementation of a computational technique for the efficient solution of a class of singular boundary value problems. The method is based on a modified homotopy analysis method. The method is illustrated by six examples, two of which arise in chemical engineering: the first problem arises in the study of thermal explosions, while the second problem arises in the study of heat and mass transfer within the porous catalyst particles. Numerical results reveal that our method provides better results as compared to some existing methods. Furthermore, it is a powerful tool for dealing with different types of problems with strong nonlinearity.     

Craters produced by underground explosions

Extensive research activities in the field of blast loads have taken place in the last few decades. There are many experimental results related to underground explosions. The mechanism of crater formation is complex and it is related to the dynamic physical properties of air, soil and air/soil interface. Studies concerned with the characteristics of craters caused by explosions usually resort to dimensional analysis and statistics. Some empirical equations proposed for the evaluation of crater dimensions can be found in the literature. Nevertheless, they were obtained for particular type of soils, shapes of explosives, ranges of explosive mass and depth of explosive and they present considerable variability.The main objective of this paper is to prove the accuracy of numerical simulation of craters produced by underground explosions. For this purpose, the numerical analysis of crater formation due to underground explosions is performed with a hydrocode. Several numerical approaches are carried out using different models and processors for the soil. Moreover, different alternatives for the constitutive model of the soil are used.Comparison with experimental results is performed in order to validate the numerical approach and prove its ability to model the crater formation. Many simulations of the same physical model lead to the same crater dimensions and a good agreement between the test results and the predicted crater measures is achieved.     

Simulation of bubble-bubble interaction using a lattice Boltzmann method

This paper presents the results obtained from three-dimensional numerical simulations of multiple bubbles rising under buoyancy in a quiescent viscous incompressible fluid. A lattice Boltzmann method, based on the free-energy model, is developed to simulate the behavior of bubble-bubble interaction while rising in the fluid. A new scheme, which involves eighteen lattice points for the first and second derivative, is proposed to achieve stable computations at high fluid-to-bubble density ratio. The effects of the density ratio and the initial bubble configuration on the flow field induced by rising bubbles and on the evolution of bubble shape during their coalescence are investigated. It is found that for two rising bubbles with the same size, the leading bubble rises like an isolated bubble before coalescence. The trailing bubble is entrained by the leading one, and experiences obvious deformation when it enters the wake region of the leading bubble. The shape evolution of the trailing bubble is different at the high and low density ratios. However, for two rising bubbles with different sizes, the larger bubble always has strong effect on the smaller one in any initial configuration.     

Rate of Return Parity with Robot Asset Traders

Human populated experimental asset markets produce data with two major qualitative consistencies; finite price bubbles and rate of return parity. Robot traders following different behavioural rules are used to create data that is qualitatively similar to that produced by human subjects in a laboratory setting. A trend pricing component of behaviour is required for robots to generate finite price bubbles. A single arbitrageur in combination with trend pricing and simple profit maximization is required to generate rate of return parity.      

掺气水流图象检测中的一种气泡区域提取方法

针对掺气水流图象中气泡的提取问题,提出了一种基于块聚类的二维直方图综合算法.该算法首先采用将图象依次划分为不同大小的子块,并进行二值化处理的方法来解决强气泡信息遮蔽弱气泡信息的问题;然后用块聚类的方法识别出单纯背景子块,并对其进行特殊处理;接着对得到的二值图象进行评价子块划分,并依据所定义的评价函数进行气泡信息的综合处理;最后对原始图象中出现的,无法用图象分割手段分离的叠加气泡区域的面积,用统计特性分析的方法对其进行叠加纠正补偿,同时对所得到的气泡面积分布进行定量估计.大量的实验结果证明该算法是有效的.     

Simulating the Madness of Crowds: Price Bubbles in an Auction-Mediated Robot Market

We simulate a multiagent market with production, consumption, and exchange mediated by a sealed-bid double auction. Marked price bubbles and subsequent crashes occur when value-based (fundamentals-driven) and trend-based traders are both present, and the market equilibrium price is ramped up exogenously. Similarly, negative price bubbles and recoveries occur when the equilibrium price is ramped down. Because the simulated market is auction-mediated, we can observe the operations of traders during these events, and study the interactions that produce and resolve bubbles. Some preliminary circuit-breaker experiments are described, in which bubbles are interrupted during their formation.     

两发武器命中板壳结构的数值仿真分析

爆炸载荷作用下结构的破坏变形是非常复杂的非线性动态响应过程.借助于大型有限元分析软件LS-DYNA中的ALE算法对舰船板壳结构在两发武器攻击下的动态响应进行模拟,分别分析了炸药之间距离不同的三种模型在两发武器同时命中和延时命中下的破坏情况,描述了钢板破口大小、有效应力最大值以及最大位移等动态参数.并对两种攻击方式进行了分析比较,结果表明两种攻击方式下,两发武器之间距离愈大,钢板的破坏越严重.     

Numerical study of seed bubble-triggered evaporation heat transfer in a single microtube

High boiling incipience temperature and flow instabilities in silicon-based microchannels with smooth surface are challenging issues. This work numerically investigates the seed bubble-triggered evaporation heat transfer in a microtube, with a length of 5.0 mm and diameter of 106 μm. Acetone was the working fluid. Seed bubbles were assumed to be generated periodically at the microtube upstream. The fixed grid allocation technique was proposed to successfully perform the parallel computation via a set of computer core solvers. It is found that the seed bubble-guided heat transfer consists of a start-up stage and a steady operation stage. The start-up time equals to the residence time of the first seed bubble growing and traveling in the microtube. The seed bubble frequency is a key parameter to influence the performance. Low-frequency seed bubbles cause alternative flow patterns of liquid flow and elongated bubble flow, corresponding to the apparent spatial-time oscillations of wall and bulk fluid superheats. High-frequency seed bubbles result in quasi-stable elongated bubble flow, corresponding to quasi-uniform and stable wall and fluid superheats. There is a saturation seed bubble frequency beyond which no further performance improvement can be made. There are residual fluid superheats specifying the required minimum superheats to sustain the evaporation heat transfer between the two phases. Elongated bubbles with thin liquid films are responsible for the heat transfer enhancement. Contrary to wall temperatures, the transient local Nusselt numbers are slightly changed due to the fact that heat transfer is more closely related to the dynamic elongated bubble flow evolution within millisecond timescale in the microchannel. The heat transfer coefficients can be 2.0 to 3.5 times of that for the superheated liquid flow before seed bubble injections.     

Chaotic bubbles and phase locking for a shaker system in the vicinity of three coexisting critical points

In this paper, the dynamical model of the shaker system, Poincaré maps, Jacobian matrix and power spectrum are established. Different phase-locking phenomena and chaotic bubbles are investigated in the vicinity of three coexisting critical points including Hopf–Hopf bifurcation point, 1:3 resonance point and 1:4 resonance point. In two strong resonance cases, phase-locking dynamics and associated bifurcations are easily to occur. Coexisting attractors have also been introduced to provide mechanisms for chaotic bubbles with connections between pieces. The occurrence of phase locking on doubling torus to multi-period leads to interruption of torus-doubling bifurcation. Isolated chaotic bubbles are birth via period-doubling bifurcation of such a multi-period. Phase-locking phenomena on T² torus are also observed in such a neighborhood of critical points. The number of periods on torus by phase locking can be identified by power spectrum methods. The system parameters may be optimized by studying of phase-locking dynamics of this system.     

Visualizing Probabilistic Multi‐Phase Fluid Simulation Data using a Sampling Approach

Eulerian Method of Moment (MoM) solvers are gaining popularity for multi‐phase CFD simulation involving bubbles or droplets in process engineering. Because the actual positions of bubbles are uncertain, the spatial distribution of bubbles is described by scalar fields of moments, which can be interpreted as probability density functions. Visualizing these simulation results and comparing them to physical experiments is challenging, because neither the shape nor the distribution of bubbles described by the moments lend themselves to visual interpretation. In this work, we describe a visualization approach that provides explicit instances of the bubble distribution and produces bubble geometry based on local flow properties. To facilitate animation, the instancing of the bubble distribution provides coherence over time by advancing bubbles between time steps and updating the distribution. Our approach provides an intuitive visualization and enables direct visual comparison of simulation results to physical experiments.     

一种用于求解TSP问题的随机最佳插入烟花算法

TSP问题是一个NP难问题,求解时间随问题规模呈几何级数增长,如何在较短时间内求得更精确的解一直是重要的研究问题。因为烟花算法在求解过程中能够快速收敛,而且能跳出局部最优解,所以基于烟花算法改进了爆炸资源分配的方式,创新性地提出了2个算子：抛弃节点重新插入的爆炸算子和抛弃路径重新插入的变异算子。再使用精英与轮盘赌相结合的烟花选择策略,设计了一种随机最佳插入的烟花算法（RBIFWA）。将该算法与基本烟花算法、混沌烟花算法、离散蝙蝠算法和自适应模拟退火蚁群算法进行比较,结果显示,RBIFWA算法在迭代次数上明显优于其他算法,且算法的解更加接近已知最优解,表明RBIFWA算法在求解TSP问题上具有更加优秀的性能和更高的求解质量。     

Seed bubbles trigger boiling heat transfer in silicon microchannels

The smooth channel surface of microsystems delays boiling incipience in heated microchannels. In this paper, we use seed bubbles to trigger boiling heat transfer and control thermal non-equilibrium of liquid and vapor phases in parallel microchannels. The test section consisted of a top glass cover and a silicon substrate. Microheater array was integrated at the top glass cover surface and driven by a pulse voltage signal to generate seed bubbles in time sequence. Each microheater corresponds to a specific microchannel and is located in the microchannel upstream. Five triangular microchannels with a hydraulic diameter of 100 μm and a length of 12.0 mm were etched in the silicon substrate. A thin platinum film was deposited at the back surface of silicon chip with an effective heating area of 4,500 × 1,366 μm, acting as the main heater for the heat transfer system. Acetone liquid was used. With the data range reported here, boiling incipience was not initiated if wall superheats are smaller than 15°C without seed bubbles assisted. Injection seed bubbles triggers boiling incipience and controls thermal non-equilibrium between liquid and vapor phases successfully. Four modes of flow and heat transfer are identified. Modes 1, 2, and 4 are the stable ones without apparent oscillations of pressure drops and heating surface temperatures, and mode 3 displays flow instabilities with apparent amplitudes and long periods of these parameters. The four modes are divided based on the four types of flow patterns observed in microchannels. Seed bubble frequency is a key factor to influence the heat transfer. The higher the seed bubble frequency, the more decreased non-equilibrium between two phases and heating surface temperatures are. The seed bubble frequency can reach a saturation value, at which heat transfer enhancement attains the maximum degree, inferring that a complete thermal equilibrium of two phases is approached. The saturation frequency is about a couple of thousand Hertz in this study.     

Electrodeposition of copper into high aspect ratio PCB micro-via using megasonic agitation

This paper presents the use of micro-particle imaging velocimetry (micro-PIV) to analyse fluid flow and hence ion replenishment in PCB micro-via during the electroplating process. The cross section of a PCB via is fabricated in PMMA to allow optical access to the sample. Fluid flow within two 1:1 aspect ratio blind micro-vias, one with straight side walls and the other with tapered side walls were compared. Flow is also analysed in a 1:1 aspect ratio through via. Flow rates measured using micro-PIV are used to validate simulated flow models. The results show that there are increased flow rates within the blind via with tapered side walls. This goes some way to explaining the improved electroplating results obtained in industry when tapered vias are used. Initial experimental results using megasonic streaming to remove bubbles from blind micro-via and promote ion transportation within high aspect ratio PCB micro-via to enhance electrodeposition are also reported.     

水下爆炸冲击波数据记录仪的设计与实现

本文从水下爆炸冲击波的概念出发,介绍了水下爆炸冲击波的特征,应用爆炸气泡运动理论确定了波形参数。然后根据水下冲击波的特征,分析了水下爆炸冲击波数据记录仪的测试原理,介绍了两种模拟实际水下爆炸冲击波信号的测试方法。再通过简易的水下爆炸试验,得到了冲击波的压力-时间历史曲线及其参数并与理论值作了比较。最后通过直线拟合和误差分析进一步证明了文中提出的水下爆炸冲击波测试方法是一套科学的、有效的冲击波压力测试方法。     

基于改进Fast-SCNN的塑瓶气泡缺陷实时分割算法

在医用塑瓶的瓶身气泡检测时，瓶身气泡位置的任意性、气泡大小的不确定性以及气泡特征与瓶身特征之间的相似性增加了气泡缺陷的检测难度。针对上述气泡缺陷检测难点问题，提出了一种基于改进快速分割卷积神经网络(Fast-SCNN)的实时分割算法。该分割算法的基础框架为Fast-SCNN，而为弥补原有网络分割尺寸的鲁棒性不足，借鉴了SENet的通道间信息的利用与多级跳跃连接的思想，具体为网络进一步下采样提取深层特征，在解码阶段将上采样操作融合SELayer模块，同时增加两次与网络浅层的跳跃连接。设计四组对比实验，在气泡数据集上以平均交并比（MIoU）与算法单张分割时间作为评价指标。实验结果表明，改进Fast-SCNN的综合性能最好，其MIoU为97.08%，其预处理后的医用塑瓶的平均检测时间为24.4 ms，其边界分割准确率较Fast-SCNN提升了2.3%，增强了对微小气泡的分割能力，而且该网络的MIoU相较现有的U-Net提升了0.27%，时间上降低了7.5 ms，综合检测性能远超过全卷积神经网络(FCN-8s)。该算法能够有效地对较小的、边缘不清晰的气泡进行分割，满足对气泡缺陷实时分割检测的工程要求。     

Living in a bubble? Toward a unified bubble theory

We generalise the notion of a bubble beyond the financial domain, by showing how a single social mechanism, based on an information feedback-loop, explains both financial bubbles and other seemingly disparate social phenomena, such as the recognition of academic articles, website popularity, and the spread of rumours.

We discuss examples of phenomena explained by this bubble mechanism, as well as other phenomena that exhibit certain bubble characteristics, yet are not bubbles according to our model. Finally, we present mathematical mechanisms for two phenomena that conform with our model, and show by computer simulation how they exhibit bubble behaviour.     

Controlling shapes of air bubbles in a multi-phase fluid simulation

Controlling shapes is a challenging problem in a multi-phase fluid simulation. Bubble particles enable the details of air bubbles to be represented within a simulation based on an Euler grid. We control the target shapes of bubbles by the gradient vectors of the signed distance field and attraction forces associated with control particles. Our hybrid approach enables to simulate physically plausible movements of bubbles while preserving the details of a target shape. Furthermore, we control the paths of moving bubbles using user-defined curves and the shape of an air bubbles by drag force. An accurate model of the drag force near the fluid surface means that bubbles have realistic ellipsoidal shapes.