多层桨搅拌槽内的液相流场研究

针对多层桨搅拌槽的结构配制问题,对多层Rushton桨搅拌槽内的液相湍流流场采用计算流体动力学方法进行了数值模拟研究。首先分析了一个高径比为H/T=1.4的双层Rushton桨搅拌槽内的流型,通过与实验结果的对比,验证了模拟方法的可靠性;随后分析了底层搅拌桨的离底高度、桨间距、桨径比、以及搅拌桨数目对一个高径比为1.6的Rushton桨椭圆底搅拌槽内流型、湍动能和搅拌功耗的影响。研究结果表明,对于所研究的搅拌槽,采用桨径比D/T=0.48、底层桨离底高度C1=0.4T的双层Rushton桨配置为最佳选择,相同雷诺数的条件下,具有湍动均匀度高、搅拌功耗低的优势。     

搅拌槽内固液悬浮特性的试验研究

在直径为300mm的平底圆筒搅拌槽内,对固相体积分数为1%～40%的固液两相体系的悬浮特性进行试验研究.利用固体激光器和数码相机,采用可视化方法详细分析固相体积分数、搅拌转速、颗粒性质和叶轮离底间隙对悬浮特性的影响.结果表明,悬浮高度主要受固相体积分数、颗粒直径和叶轮离底间隙影响;壁面颗粒堆积高度主要受叶轮离底间隙影响;槽底面中心区域和边缘角落区域是颗粒不易悬浮区,叶轮离底间隙和固相体积分数对槽底面何处颗粒最后悬浮有影响;较低的叶轮离底间隙有利于颗粒的悬浮,能获得较高的悬浮高度,但过低的叶轮离底间隙造成搅拌功率增大;壁面颗粒堆积高度降为零时的搅拌转速和悬浮高度达到液面高度85%时的搅拌转速均可视为固液悬浮操作的完全离底临界悬浮转速.     

椭圆底封头十字形挡板搅拌釜内流场研究

以底部椭圆形封头十字形挡板搅拌反应釜为研究对象,采用Fluent软件分析搅拌桨流型、离底高度、直径、底部加装挡板及其高度和长度对该搅拌釜内流场的影响,利用标准k-ε湍流模型对其在单相流体水中产生的流场进行模拟。开展搅拌轴转矩的试验研究,并与模拟值进行对比。研究表明,径向流搅拌桨更适合于底部加装挡板搅拌釜流场的研究。与六直叶圆盘涡轮搅拌桨相比,六直叶开启涡轮搅拌桨更有利于反应釜内物料的悬浮及混合。搅拌桨离底高度取0.7倍液面高比0.6倍更合适。搅拌桨直径越大,轴向速度越大,反应釜中心部位形成的螺旋向上轴向流越明显。在十字形挡板高度或长度固定时,搅拌桨下部区域中心部位的轴向速度比其他部位大,搅拌釜内上桨、下桨叶区将形成一个循环。同等条件下,随着搅拌转速不断增大,搅拌轴转矩随之增大。搅拌轴转矩的模拟值与试验值的相对误差在10%左右,两者具有很好的一致性。     

基于Fluent的陶瓷浆料搅拌槽的结构优化

采用Fluent软件对陶瓷浆料搅拌槽的内部流场经行了模拟.选用非结构化四面体网格,利用MRF模型和标准k-ε湍流模型,在稳态条件下模拟了不同桨型、不同桨叶离底高度及不同搅拌桨直径下的流场.模拟结果表明:24°三折叶桨所产生的轴向流流型比较适合固液搅拌操作;桨叶直径d=0.5D=250mm,离底高度C=0.25D=125mm时槽内流场分布比较均匀.     

桨式搅拌器安装高度对搅拌效果的数值模拟

搅拌器安装高度对搅拌效果的影响一般采用实验研究方法,运用数值模拟技术系统的研究较少.通过FLUENT软件系统地研究了桨式搅拌器在不同安装高度下搅拌槽内流场的湍流强度分布、流速分布以及在不同安装高度下搅拌功率的大小.结果表明,搅拌器在合适的安装高度下,搅拌功率随着安装高度的增加有细微的减小;在不合适的安装高度下,搅拌效果会受到影响,功率会增加.     

搅拌槽内部固-液悬浮流场的数值模拟及实验研究

随着计算机技术的迅速发展和计算流体力学理论的不断进步,国内外许多研究者利用CFD软件对搅拌器内部流场进行了大量的模拟。同时,也有不少学者针对搅拌设备内部流场利用LDV和PIV等测量技术进行了实验研究,结果表明,CFD模拟的结果与实验数据吻合较好。利用滑移网格法计算了六折叶圆盘涡轮搅拌器内部固-液悬浮流场。采用标准湍流模型及欧拉法来建立流体力学模型,研究了搅拌器在不同转速及不同安装高度下,流场的分布情况,分析了数值模拟和实验研究之间的功率消耗差异。通过数值模拟,为搅拌器的优化和放大提供参考。     

基于Fluent的搅拌反应罐流场的优化研究

基于计算流体动力学对搅拌反应罐流场的各影响因素(如桨间距、罐桨径比等)进行分析和研究，最后根据分析和研究的结果提出了搅拌反应罐内部结构的改进方向和措施。     

基于FLUENT的7022铝合金搅拌摩擦焊接过程数值模拟与分析

铝合金搅拌摩擦焊接焊缝区域金属流是单相流。针对这种单相流搅拌摩擦焊接过程应用大型计算流体动力学(CFD)软件FLUENT进行了数值模拟与分析,得到其三维流场。根据流场得到的相关结果可以观察焊缝区塑性金属流动形态与轨迹,为探究与揭示搅拌摩擦焊接过程中焊缝区塑性金属流变机理提供参考。     

双层直斜叶及其组合桨搅拌槽三维流场数值模拟

采用计算流体力学的方法,对双层六直叶涡轮桨、双层六斜叶涡轮桨以及双层六直斜叶交替涡轮桨搅拌槽流场进行研究。利用Laminar层流模型对其在甘油与水的混合物中产生的流场进行数值计算,得到三种不同结构形式的双层桨以恒转速200 r/min在搅拌槽内转动时所产生的流场结构,对比分析轴向、径向和周向的速度矢量图、速度云图以及速度分布曲线,为层流搅拌槽的设计和实际应用提供了理论依据。     

基于PIV的四斜叶桨搅拌反应器中非牛顿流体流场研究

针对机械搅拌反应器内非牛顿流体混合效率问题,对机械搅拌反应器内非牛顿流体流场特性进行了研究。采用非接触式流场测试PIV技术,对试验规模四斜叶桨搅拌反应器内非牛顿流体流场进行了测量,讨论和分析了不同溶液浓度和不同搅拌速度对机械搅拌反应器内流场分布的影响。研究结果表明:搅拌速度不仅可以影响流体间对流强度,而且会改变流体流场结构;溶液浓度对流场结构影响不大,但影响桨叶下部高流速区域大小和流体的最大速度。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

Fifth International Summer School on Screw-Theory Based Methods in Robotics

正3-11 September,2014University of Bologna,Bologna,Italy www.summerscrews.org summerscrews2014.ing.unibo.it SUMMER 20SCREWS 14In 2014,our screw-theory school comes to the world's oldest university.In early September,Summer Screws'14 will gather six experts in the application of screw theory in robotics and up to 40 participants at the University of Bologna,Bologna,Italy.The school will teach attendees how to apply existing methods and empower them to develop new ones in their own research.The basic theoretical notions will be introduced in a rigorous manner,emphasizing examples,applications,and exercises.Scholarships are available.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.