Role of grain boundary networks in vortex motion in superconducting films

We study the vortex dynamics of the polycrystalline superconductors in the presence of both random point defects and the generated grain boundary(GB) networks with Voronoi diagram. The synergistic effect of adjacent GBs on restricting the vortex motion in intragranular region is proposed and the corresponding intensity factor of the synergistic effect which characterizes the strength of the synergistic restriction of adjacent grain boundaries is also determined in the present work.The interconnected GBs offer easy-flow channels for vortices in addition to pinning effects on the vortices. The combined channels and the vortex flow patterns in the superconducting film are analyzed in detail from molecular dynamics simulations. Furthermore, it is discovered that the critical current increases with the decrease of magnetic field intensity,temperature, and the average grain size. The large number of vortices results in the enhanced repulsive interaction forcing the vortices to move out from the GBs. The thermal depinning from GBs leads to the lower Lorentz force range. The increase of the grain size causes the number of GBs to decrease. In summary, these effects leads the critical current to become a decreasing function of magnetic field, temperature, and grain size.

A NUMERICAL STUDY OF THE VORTEX MOTION IN OSCILLATING FLOW AROUND A CIRCULAR CYLINDER AT LOW AND MIDDLE Kc NUMBERS

A new hybrid model, which is based on domain decomposition and proposed by the authors is used for calculating the flow around a circular cylinder at low and middle Keulegan-Carpenter numbers (Kc=2～18)respectively.The vortex motion patterns in asymmetric regime,single pair(or transverse)regime and double pair(or diagonal)regime are successfully simulated.The calculated drag and inertial force coefficients are in better agreement with experimental data than other recent computational results.

Numerical analysis on the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model

This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of incompressible fluid are directly related to on the vortex motion.The results of the Q criterion-based iso-vortex surface could well reflect the tendency of the vortex structure,in which the iso-vortex surface exhibited a distorted distribution rather than around the center axis.At the turning point of velocity vector,vortices were formed and developed,and the point was the center of the local vortex core.In addition,the vortex formed an irregular annular region around the wall at the bottom of vortex finder.The vortex structure near the dust hopper presented a strong distortion.Moreover,there were two rotating flow in the opposite direction within the dust hopper.These phenomena would affect the separation performance,which was significance to cyclone separator.

Barrier or easy-flow channel: The role of grain boundary acting on vortex motion in type-Ⅱ superconductors

Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical current density.Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion,while an easy-flow channel just under some certain conditions.In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works,in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱsuperconductors.The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel,and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions.Such the competition effect essentially depends on the attributes of both the GB(described by the GB strength and angleθ)and no-GB pining regions(by the relative disorder strengthα_(p)/α_(v)).Specifically,for a YBa_(2)Cu_(3)O_(7-x)(YBCO)sample,to obtain a clear knowledge of vortex motion in GB region,we visualized the three typical trajectories of vortices during the three vortex movement stages.Further,in order to understand how GB results in the macro current-carrying property,corresponding to the current-voltage relation of the YBCO conductor,we obtained the average velocity v_(y) of vortices varying with their driving force,which is nearly identical with the previous observations.

Calculation of the Centrally Symmetric and Vortex Forces Acting on Momentum in Distortion Tensor Field: Explanation of High-Temperature Plasma and Vortex Motions

The paper deals with calculation of the centrally symmetric and vortex forces for the momentum of a particle in the distortion tensor field from the action minimum, by analogy with the calculation of forces for a charge in an electromagnetic field. It is demonstrated that: 1) The compensating interaction tensor corresponds to the distortion tensor in a solid. 2) The centrally symmetric force of the distortion tensor acts on the momentum as a charge, and is analogous to the Coulomb force. In a gas, it results in change in the momentum value of the molecules exponentially to some extent. The action of this force explains the high-temperature plasma in the gas. 3) The vortex force of the distortion tensor is equivalent to the Peach-Koehler force in a solid. It acts on the momentum flow, similar to the Lorentz magnetic force, and explains the vortex motions in space, in the form of “black holes”, and in the atmosphere, in the form of cyclones and anticyclones.

Analysis of Vortex Motion in Porous Media

In vortex motion fluid moves in curve path and the stream lines are curved. When the fluid flows between curved stream line, the centrifugal forces are setup which is counter balanced by pressure forces acting in the radial direction. The vortex motion has two types of curved motion. The first type called free vortex type, the fluid moves due to its own natural effect but energy is not added to fluid when moving in curved path. The second type called forced vortex, in which energy is added to fluid. A two dimensional steady laminar free convective flow of viscous incompressible flow in porous media voids is considered. In this paper the motion of fluid is studied while moving in the porous media. It is studied that the motion of the fluid in the porous media is vortex motion at the low Reynolds’s number, where the motion is laminar motion and the fluid obeys the laws of vortex motion.

基于Vortex的客滚船拉锚仿真分析

针对拉锚试验仿真提出一种分析方法。以某客滚船为研究对象,基于变质量运动学理论,利用SolidWorks和Vortex软件开发、创建一种实时有效的锚系动态仿真方法,并与现场拉锚场景进行比对,以验证该方法的可行性和可靠性,为锚系仿真提供有效参考,并为取代木模试验提供条件。

Modelling of the Vortex-Induced Motion of A Single-Column Platform with Non-Linear Mooring Stiffness Using the Coupled Wake Oscillators

A phenomenological model for predicting the vortex-induced motion (VIM) of a single-column platform with non- linear stiffness has been proposed. The VIM model is based on the couple of the Duffing-van der Pol oscillators and the motion equations with non-linear terms. The model with liner stiffness is presented for comparison and their results are compared with the experiments in order to calibrate the model. The computed results show that the predicted VIM amplitudes and periods of oscillation are in qualitative agreements with the experimental data. Compared with the results with linear stiffness, it is found that the application of non-linear stiffness causes the significant reductions in the in-line and transverse motion amplitudes. Under the non-linear stiffness constraint, the lock-in behavior is still identified at 8<Ur<15, and the trajectories of the VIM on the xy plane with eight-figure patterns are maintained. The results with different non-linear geometrically parameters show that both in-line and transverse non-linear characteristics can significantly affect the predict in-line and transverse motion amplitudes. Furthermore, the computed results for different aspect ratios indicate that the in-line and transverse motion amplitudes increase with the growth of aspect ratio, and the range of lock-in region is enlarged for the large aspect ratio.

Study on Vortex-Induced Motions of A New Type of Deep Draft Multi-Columns FDPSO

A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform’s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V;≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform’s motion trajectories.

naoe-FOAM-SJTU Solver for Numerical Study of Vortex-Induced Motions of a Buoyancy Can in Currents

这份报纸论述 3D (三维) CFD (计算液体动态) 特别分析 FIR (导致流动的反应) 的模拟快活的 yaw 运动能。数字盒子在利用我们的内部代码 naoe-FOAM-SJTU 的不同减少的速度下面与一个快活罐头被进行，一个解答者基于开放源代码工具箱 OpenFOAM。SST-DDES (砍压力推迟运输的分开旋涡的模拟) 模型被使用处理 flowseparation 并且搅乱格子方法被利用解决大振幅 6-DOF (自由的 6 度) 运动。免费腐烂测试和活力(导致旋涡的运动) 测试数字地被造。在活力情况中，轨道的回答，振幅，频率在一系列减少的速度被计算。随减少的速度的增加，偏航频率被增加，它是类似的澎湃并且摇晃频率。并且偏航频率等于摇摆频率，它与试验性的结果一致。而且，比较二个盒子，依次修理的盒子和另一个依次释放，在旋转罐头减少的度释放摇摆振幅，但是没在巨浪振幅有差别，这能被结束。

Experimental Research on Salt-out Particle Motion and Concentration Distribution in a Vortex Pump Volute

The vortex pump is suitable for salt solution transportation. But the salt-out flow mechanism in the pump has not been understood fully. Salt-out layer formation and growth rate are closely related to crystal particle motion and concentration distribution. Study on the particle hydrodynamic characteristics in the pump volute becomes a key problem, because the crystal particles are mainly distributing in this zone after they enter the pump. Phase Doppler particle analyzer（PDPA） is used to measure the two-phase flow field in a model pump volute to get more understanding about the salt-out phenomenon. The crystal particle velocities are obtained in all three peripheral, radial and axial directions. Particle size and particle number density（PND） measurements are also performed in the experiment. Results are presented and discussed along the radial direction under different pump operating conditions, as well as various axial measurement positions. It is found that particle velocity gradient of peripheral component varies with the pump discharge. There is a turning point of relation between peripheral velocity component and discharge. Radial flow velocity curves look like a saddle shape and velocity magnitudes are changing greatly with the discharge. The non-equilibrium velocity feature between liquid and solid phase on this direction is also remarkable. Particles flow into the impeller at radial position R〈I, and the axial velocity component increases in this region. The particle size curve shows an open-up parabola distribution. The largest particles are distributing near the casing peripheral wall. As flow rate increases, accordingly PND increases. It also grows up in the axial-outward direction towards the suction cover. Crystal particle aggregation phenomenon can be revealed from the analysis of particle size and PND distribution, and the aggregation region is determined as well. Research results are helpful for optimal design of this kind of pump preventing salt-out.

Research on the Effects of in-Line Oscillatory Flow on the Vortex-Induced Motions of A Deep Draft Semi-Submersible in Currents

A Deep Draft Semi-submersible （DDS） under certain flow conditions could be subjected to Vortex-Induced Motions （VIM）, which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics （CFD） method was conducted. The issues of the VIM of multi-column floaters can be con＇,＇eniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal time- dependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.

Simulation on motion of particles in vortex merging process

In a two-phase flow, the vortex merging influences both the flow evolution and the particle motion. With the blobs-splitting-and-merging scheme, the vortex merging is calculated by a corrected core spreading vortex method （CCSVM）. The particle motion in the vortex merging process is calculated according to the particle kinetic model. The results indicate that the particle traces are spiral lines with the same rotation direction as the spinning vortex. The center of the particle group is in agreement with that of the merged vortex. The merging time is determined by the circulation and the initial ratio of the vortex radius and the vortex center distance. Under a certain initial condition, a stretched particle trail is generated, which is determined by the viscosity, the relative position between the particles and the vortex, and the asymmetrical circulation of the two merging vortices.

深吃水圆筒型浮式核能平台涡激运动数值模拟

深吃水圆筒型浮式核能平台是一种新型多功能高效平台,可有效解决南海岛礁开发过程中的能源供给问题。在一定来流速度下,尾流区交替泄涡进而诱导平台发生涡激运动(vortex induced motions,VIM),这将严重加速系泊和立管系统疲劳损害,同时对平台内部核反应堆运行产生不利影响。基于改进的延迟分离涡方法(improved delayed detached eddy simulation,IDDES)对平台在不同折合速度下的横荡、纵荡、艏摇运动响应进行数值模拟,并从水平面内质心运动轨迹、运动频率、三维流场特性等角度分析涡激运动关键特征。研究结果表明:当折合速度5.45<Ur<9.08时,平台横荡、艏摇振幅均逐渐增加且运动轨迹类似“香蕉”形,横荡与艏摇运动频率基本一致且横荡未出现明显的“锁定”区间变化;当7.26<Ur<9.08时,艏摇振幅近似线性递增且运动频率中主频附近出现多个峰值,运动轨迹在顺流方向上逐渐变宽;三维流场中发现尾流区三维漩涡结构相当复杂且平台底部柱靴结构对表面流动分离造成干扰,柱靴结构具有一定的减涡效果。

电磁涡旋波斜平面旋转目标运动参数估计方法

相较于传统平面电磁波,电磁涡旋波具有螺旋分布的波前相位、特殊的环形天线方向图、独特的涡旋方位维信息等特点。近几年来,得益于其特殊的物理特性,电磁涡旋波在目标运动参数估计领域受到了广泛的关注,其目标多普勒效应具有线性多普勒与旋转多普勒两维多普勒信息。现有参数估计方法实现了运动平面与涡旋天线口面平行时的目标旋转参数测量。然而,目标斜平面旋转下,现有方法将不再适用。基于电磁涡旋波所提供的目标旋转多普勒信息,提出一种斜平面旋转目标运动参数估计方法。该方法推导了一般形式下旋转目标的多普勒信号模型,通过分析斜平面下的多普勒信息特征,建立了目标运动参数表征式,给出了斜平面目标旋转参数的计算方法。最后通过仿真分析,验证了模型及参数计算方法的正确性及有效性。

组合三棱柱振子流致振动运动特性分析

以流致振动能量转换系统(flow induced motion energy conversion system,FIMECS)为基础,以截面形式和刚度为变量针对组合三棱柱振子进行试验,评估振幅、频率等指标。试验选取了组合三棱柱振子进行了模型试验,通过改变截面排布形式以及系统刚度来研究截面布局、刚度对组合三棱柱振子的影响。该研究旨在探究组合振子流致振动的最佳振动条件,为后续多振子流致振动研究扩展思路。试验结果表明:三种不同排布形式的组合振子,在不同刚度工况下都有较好的振动效果,Ⅰ型和Ⅲ型振子振动随流速变化表现为典型的涡激振动,Ⅰ型排布振子具有最好的振动表现。

基于Vortex的6自由度平台洗出运动仿真

为了研究并联6自由度平台在车辆驾驶过程中的洗出运动,实现车辆动力学模型和6自由度运动平台模型的联合仿真,提出一种利用Vortex多体动力学软件对6自由度平台进行建模,复现车辆模型运动过程的仿真方法.平台液压油缸初始位姿采用解析法进行确定,在Matlab/Simulink中实现运动平台的洗出滤波算法和运动学反解算法,利用转弯和直线2种典型运动进行仿真验证.在给定路面上进行虚拟驾驶,Vortex车辆动力学模型解算结果使车辆产生相应的连续运动状态,相关动力学参数经过洗出滤波算法、平台运动学反解运算得到各油缸伸长量,驱动Vortex软件中建立的6自由度运动平台模型.结果表明,利用Vortex软件可以将车辆动力学模型和并联6自由度平台模型进行联合仿真,实现平台洗出运动的可视化.

MOTION ANALYSIS OF A SPINNING SATELLITE SYSTEM WITH OFF-CENTRE TANKS PARTIALLY FILLED WITH LIQUID

The sloshing problem for a spherical tank partially filled with liquid is analysed in this paper The study is based on the goveming equations of fluid dynamics and the Euler's equations of systems with the influences of tank off centering,fluid vortices and the Coriolis'acceleration on the motion states of the systems taken into consideration.In the study,we adopt the concept of uniform vortex motion of fluid gen- eralized by Pfeiffer and apply the boundary element method(BEM)to the calculation of the natural frequence and the velocity field of the liquid sloshing.The motion charateristics of the flow-solid spinning system is then analysed.

“Click”运动高升力机制

研究了具有“Click”运动的模型翼在三维流场中的气动特性.采用计算流体力学方法求解三维非定常不可压缩Navier-Stokes方程,对比了简谐和“Click”运动所产生的升力与阻力,研究了升力最大时的前缘涡特性和展向流动.结果表明,在下拍过程的升力最大处,“Click”和简谐运动的前缘涡能够分别维持至翼展的80%和60%处.两种运动都会在翼展方向存在维持展向流动的压力梯度,而“Click”运动具有更显著的展向压力梯度,对展向涡度的能量输运效率更高,因此其前缘涡能够保持更完整的形态.在上拍过程中,两种运动的前缘涡形态差异不明显,“Click”运动快速上拍的运动特点使其能够快速地摆脱尾涡的干扰,从而维持升力.

气体轴承-高速永磁电机转子系统亚同步涡动效应研究

气体箔片轴承(gas foil bearings-GFBs)在高速永磁电机中应用广泛,为了进行合理的轴系设计,预测GFBs-高速电机转子系统的动力学行为,基于刚性气膜假设,建立GFBs-非对称刚性转子动力学模型,研究了转子不平衡量和箔片结构刚度对转子动力学行为的影响规律。结果表明:对于一根特定的刚性转子,存在一个与之匹配的最佳的结构刚度,使得转子的振幅和亚同步涡动效应最弱。计算结果表明,气体轴承支承的高速永磁电机轴系的综合设计,需要考虑转子与箔片结构刚度的合理匹配,以抑制亚同步涡动对轴系振动的影响。