Distribution pattern of acoustic and streaming field during multi-source ultrasonic melt treatment process

The ultrasonic melt treatment(UMT)is widely used in the fields of casting and metallurgy.However,there are certain drawbacks associated with the conventional process of single-source ultrasonic(SSU)treatment,such as the fast attenuation of energy and limited range of effectiveness.In this study,the propagation models of SSU and four-source ultrasonic(FSU)in Al melt were respectively established,and the distribution patterns of acoustic and streaming field during the ultrasonic treatment process were investigated by numerical simulation and physical experiments.The simulated results show that the effective cavitation zone is mainly located in a small spherical region surrounding the end of ultrasonic horn during the SSU treatment process.When the FSU is applied,the effective cavitation zone is obviously expanded in the melt.It increases at first and then decreases with increasing the vibration-source spacing(Lv)from 30 mm to 100 mm.Especially,when the Lv is 80 mm,the area of effective cavitation zone reaches the largest,indicating the best effect of cavitation.Moreover,the acoustic streaming level and flow pattern in the melt also change with the increase of Lv.When the Lv is 80 mm,both the average flow rate and maximum flow rate of the melt reach the highest,and the flow structure is more stable and uniform,with the typical morphological characteristics of angular vortex,thus significantly expanding the range of acoustic streaming.The accuracy of the simulation results was verified by physical experiments of glycerol aqueous solution and tracer particles.

Method of calculation of a methane concentration field in gob areas with a known velocity field based on the model of stream tubes

在有已知的速度域的嘴区域的煤气的集中地的控制方程是有可变系数的部分微分方程，谁的传统的数学计算方法是很复杂的。一个数字模拟方法能被用来计算煤气的集中地，但是它也需要计算机资源的可观的数量，在嘴区域的不同的点的煤气的集中的关系是未定义的。基于流试管的模型，在流试管以内的集体、煤气的部件的保存方程被用来与已知的速度域在一个嘴区域推出煤气的集中域的方程。一块煤气的集中地的计算的这个方法在一个嘴区域被使用， U 类型通风工作面对，它建议这个新方法有准确计算的优点简单操作并且有清楚的物理解释。

Simulation and Analysis on the Two-Phase Flow Fields in a Rotating-Stream-Tray Absorber by Using Computational Fluid Dynamics

The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The simulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, mad a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall;the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.

双组分层撞击流反应器流场时空演化数值模拟

为了研究双组分层撞击流反应器流场时空演化规律,利用大涡模拟方法进行数值模拟。结合第三代涡识别方法在空间尺度上,对轴向面、周向环面和径向面的速度场、涡量场进行分析;在时间尺度上,揭示速度场、涡量场和涡当地旋转轴的演化规律。结果表明:轴向面和径向面的涡强度呈多峰分布,周向环面涡强度的变化分为增强-稳定-增强3阶段。以XOY面作为研究参考,在两层喷嘴间依据涡发生位置的变化和多尺度涡的碰撞、破碎情况,涡发生期分为6个阶段,涡演化周期分为12个阶段,可据此预测反应器内部流型变化和流场所处阶段。

图书直播营销场域研究

直播作为一种新型媒介平台逐渐演化成为社会建设的基础设施,在这种背景下,图书的营销也在探索与直播的结合,从而形成了图书直播营销的新场域。在此场域中,内容、渠道、受众、情绪、关系都有了新的变化,赋予了此场域独有的特征。本文借助科学哲学领域的概念对此场域的未来发展进行了解释,认为在内容层面要提高“信息熵”、渠道层面要进行时空维度的转化、受众层面要遵循注意力守恒原则、情绪层面要情绪代入传播、关系层面要寻找“量子关联”。

龙腾Stream流处理器验证

芯片设计复杂度的提高迫切地需要先进的方法学以应对巨大的验证工作量。通过开发基于System Verilog的覆盖率驱动的自动化验证平台,对龙腾Stream流处理器的指令集进行了功能验证。实验结果表明,该验证平台提高了验证效率和功能覆盖率,具有良好的重用性和可移植性。搭建FPGA原型验证系统对流处理器的功能和系统性能进行了评测,并提出了优化流处理器加速性能的方法。

MHD flow and heat transfer from continuous surface in uniform free stream of non-Newtonian fluid

An analysis is carried out to study the steady flow and heat transfer characteristics from a continuous flat surface moving in a parallel free stream of an electrically conducting non-Newtonian viscoelastic fluid. The flow is subjected to a transverse uniform magnetic field. The constitutive equation of the fluid is modeled by that for a second grade fluid. Numerical results are obtained for the distribution of velocity and temperature profiles. The effects of various physical parameters like viscoelastic parameter, magnetic parameter and Prandtl number on various momentum and heat transfer characteristics are discussed in detail and shown graphically.

直播电商沉浸式教学模式的现实必要与实现路径

从沉浸式教学角度,研究直播电商沉浸式教学的实现,对接行业、市场和区域产业需求,制定沉浸式的人才培养计划;面向直播电商专业知识与基础技能需要,制定沉浸式课程体系;针对学生实战能力训练与核心技能提升,构建沉浸式实践场域;针对沉浸式教学效果,构建评估标准与方法。

正弦交流介质阻挡放电等离子体激励器诱导流场研究的进展与展望

正弦交流介质阻挡放电等离子体流动控制技术是基于等离子体激励的主动流动控制技术,具有响应时间短、结构简单、能耗低、不需要额外气源装置等优点,在飞行器增升减阻、抑振降噪、助燃防冰等方面具有广阔的应用前景.针对“激励器消耗的大部分能量尚未被挖掘利用、诱导流场的完整演化过程尚未完全掌握、诱导流场的演化机制尚不明确”这三方面问题,本文首先从激励器诱导流场的空间结构、时空演化过程、演化机制三个方面回顾总结了激励器诱导流场的研究进展.在诱导流场空间结构方面,发现了高电压激励下诱导射流的湍流特性,辨析了壁面拟序结构与无量纲激励参数之间的关联机制;从激励器诱导声能方面挖掘出了激励器潜在的能量,发现了“等离子体诱导超声波与诱导声流”的新现象,提出了声激励机制;在时空演化过程方面,阐明了激励器诱导流场从薄型壁射流发展为“拱形”射流、再演变为启动涡,最终形成准定常射流的完整演化过程;在演化机制方面,结合声学特性提出了以“升推”为主的诱导流场演化机制.其次,围绕激励器诱导流场,进一步凝练出下一步研究重点,为突破等离子体流动控制技术瓶颈,打通“概念创新—技术突破—演示验证”的创新链路,实现工程应用提供支撑.

The Classical Hall Effect in Multiply-Connected Plane Regions Part I: Topologies with Stream Function

Typical Hall plates for practical magnetic field sensing purposes are plane, simply-connected regions with peripheral contacts. Their output voltage is the sum of even and odd functions of the applied magnetic field. They are commonly called offset and Hall voltage. Contemporary smart Hall sensor circuits extract the Hall voltage via spinning current Hall probe schemes, thereby cancelling out the offset very efficiently. The magnetic field response of such Hall plates can be computed via the electric potential or via the stream function. Conversely, Hall plates with holes show new phenomena: 1) the stream function exists only for a limited class of multiply-connected domains, and 2) a sub-class of 1) behaves like a Hall/Anti-Hall bar configuration, i.e., no Hall voltage appears between any two points on the hole boundary if current contacts are on their outer boundary. The paper studies the requirements under which these effects occur. Canonical cases of simply and doubly connected domains are computed analytically. The focus is on 2D multiply-connected Hall plates where all boundaries are insulating and where all current contacts are point sized.

不同动量比撞击流反应器流场特性数值模拟

目前撞击流技术在化学工程及多种过程工业中具有广泛应用.为了对撞击流混合器内的流动特征进行更深入地研究,利用数值模拟对撞击流混合器内流场特性进行分析.通过模拟得到不同动量比及不同喷嘴间距下撞击流反应器内流体速度、湍动能及压力分布,探究不同入口动量比对撞击流混合器流场特性的影响.结果表明:在xOy截面上两喷嘴的动量比越大,流体压力值越大,压力梯度分布越大;湍动能分布沿径向逐渐减小.对撞击面径向流体速度和压力进行分析,研究发现:当喷嘴间距L=2 D时,径向流体速度呈双峰分布,流体压力呈单峰分布;随着动量比的增加,流体的速度和压力整体增大.当L=4 D时,非等动量撞击下径向流体速度呈单峰分布;等动量撞击(K=1.0)下,撞击面径向上流体速度呈双峰分布;非等动量撞击的压力水平均低于等动量撞击.

Single-particle 3D reconstruction on specialized stream architecture and comparison with GPGPUs

The wide acceptance and data deluge in medical imaging processing require faster and more efficient systems to be built.Due to the advances in heterogeneous architectures recently,there has been a resurgence in the first research aimed at FPGA-based as well as GPGPU-based accelerator design.This paper quantitatively analyzes the workload,computational intensity and memory performance of a single-particle 3D reconstruction application,called EMAN,and parallelizes it on CUDA GPGPU architectures and decouples the memory operations from the computing flow and orchestrates the thread-data mapping to reduce the overhead of off-chip memory operations.Then it exploits the trend towards FPGA-based accelerator design,which is achieved by offloading computingintensive kernels to dedicated hardware modules.Furthermore,a customized memory subsystem is also designed to facilitate the decoupling and optimization of computing dominated data access patterns.This paper evaluates the proposed accelerator design strategies by comparing it with a parallelized program on a 4-cores CPU.The CUDA version on a GTX480 shows a speedup of about 6 times.The performance of the stream architecture implemented on a Xilinx Virtex LX330 FPGA is justified by the reported speedup of 2.54 times.Meanwhile,measured in terms of power efficiency,the FPGA-based accelerator outperforms a 4-cores CPU and a GTX480 by 7.3 times and 3.4 times,respectively.

The Classical Hall Effect in Multiply-Connected Plane Regions Part II: Spiral Current Streamlines

Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be defined, with special reference to Hall/Anti-Hall bar configurations. In part II, we focus on topologies where no conventional stream function can be defined, like Corbino disks. If current is injected and extracted at different boundaries of a multiply-connected conductive region, the current density shows spiral streamlines at strong magnetic field. Spiral streamlines also appear in simply-connected Hall plates when current contacts are located in their interior instead of their boundary, particularly if the contacts are very small. Spiral streamlines and circulating current are studied for two complementary planar device geometries: either all boundaries are conducting or all boundaries are insulating. The latter case means point current contacts and it can be treated similarly to singly connected Hall plates with peripheral contacts through the definition of a so-called loop stream function. This function also establishes a relation between Hall plates with complementary boundary conditions. The theory is explained by examples.

南浦溪流域水稻田氮磷流失空间变化特征分析

以福建省南平市水稻主要生产地南浦溪流域为研究区,通过构建SWAT模型,模拟南浦溪流域2017~2019年水稻田氮磷流失情况,以分析该流域氮磷流失空间变化特征,确定南浦溪流域水稻田氮磷流失重点区域。结果表明:南浦溪流域水稻田年均总氮流失量为23.60kg·ha^(-1),其中流域西北部的永兴镇、莲塘镇、临江镇以及西南部的水吉镇、小湖镇等地总氮流失最为严重;同时,该流域年均总磷流失量为3.07kg·ha^(-1),流域南部的漳墩镇、水吉镇以及小湖镇等地总磷流失较为严重。因此,将上述总氮、总磷流失严重区域确定为南浦溪流域水稻田氮磷流失重点区域。

明槽支流交汇区水动力特性PIV试验研究

针对低流量比条件下明槽干支流交汇支流汇入区水流结构十分复杂的问题,基于物理模型试验的方法,采用PIV粒子图像测速技术观测不同交汇条件下明槽支流时均流速及三维流速空间分布,分析支流流场的变化特征。结果表明,汇流比较小时,由于干流水体的顶托作用,支流表层水体会出现不同程度上的回流现象,底层水体顺流汇入干流,且有较为明显的斜向混合界面;随着汇流比的增大,干流对支流左岸水流结构影响逐渐减小。在交汇角为30°、90°时,靠近支流右岸的水流结构受干流水体顶托作用影响最大;在交汇角为150°时,支流基本处于回流状态,交汇口处形成最大回流流速区。研究结果可为库区支流营养盐富集导致水华频发等研究提供理论支撑。

撞击流反应器内流场特性的激光多普勒测速实验与模拟

采用激光多普勒测速仪(LDV)与Fluent数值模拟相结合的方法研究了撞击流反应器内流场特性。通过对比两种方法得到的径向位置r/R=1,Z=±9两点处竖直方向速度大小,验证了本文采用的Fluent数值模拟方法研究撞击流流场的可靠性,并分析了误差存在的原因。同时,数值模拟结果显示,重力的存在造成撞击流流场的不对称分布,转速为200 rpm、400 rpm、600 rpm、800 rpm相对应的撞击面向上偏移的距离分别为1.21 mm、1.61 mm、1.685 mm和1.766 mm。随着桨叶转速的增大,反应器内湍动强度明显呈增强趋势,最大湍动强度依次为1.49%、3.00%、4.53%、6.04%。观察湍流强度场分布云图可得出撞击流明显加强了反应器内湍流强度。

液体媒质超声波电机运行特性的实验研究与分析

该文介绍了一种基于液体媒质的非接触型超声波电机,其转子浸于液体之中,不与定子直接接触,有效地克服了接触型超声波电机的易磨损、不能长时间连续工作等缺点,是超声波电机领域的一个新的研究方向。结合液体媒质超声波电机的基本结构及运行机理,文中阐述了电机运行过程中将超声振动所产生的能量通过液体传递给转子,从而驱动转子旋转这一能量传递的基本过程,揭示了液体中的雷诺剪切应力是电机声流场的驱动力。然后,用实验测定了电机转速与驱动频率、驱动电压、液体粘性、液位高度和转子半径之间的关系。并对实验结果进行了比较分析,且在此基础上结合本电机的运行机理以及驱动控制系统、液体环境和转子半径等因素对电机转速的影响,对液体媒质超声波电机的运行条件进行了优化分析。

我国和东亚地区硫化物的大气输送研究——流场分型统计输送模式

提出了一种流场分型欧拉酸沉降输送模式，计算了１９９３年４月东亚地区硫氧化物平均浓度的时空分布以及我国各省区和东亚主要国家的硫沉降量。通过与实测资料对比，模式有较好的可信度，是一个计算硫氧化物长期平均浓度和硫沉降的简便、实用的酸沉降输送模式。

近50年我国冰雹年代际变化及北方冰雹趋势的成因分析

利用1958—2007年中国755个站的逐日冰雹资料和同期NCEP/NCAR再分析资料及环流特征量,研究了中国近50年冰雹时空变化特征。研究表明,20世纪70年代末、80年代初我国冰雹呈下降趋势,尤其是80年代末以来降雹次数基本低于近50年的平均值,其中我国北方冰雹下降趋势比南方显著,除黄淮、江淮、长江中下游和华南地区外,全国大部分地区冰雹下降趋势都通过了0.05的显著性水平检验,尤其是东北、华北、西北和青藏高原中东部地区。分析表明,20世纪70年代末大尺度环流系统的一系列调整是我国北方冰雹减少的主要原因,200 hPa高空西风急流南移,导致我国北方纬向风场减弱,风速垂直切变减小,对流减弱;850 hPa高度场升高不利于极地冷空气南下和对流系统的建立;同时副高增强,极涡减弱使大气层结稳定,冷空气活动减弱。伴随着大尺度环流的调整,局地垂直温度场结构的变化是影响降雹次数的一个重要原因,局地0℃线和-20℃线之间过冷却水滴累积区距离缩短,不利于雹粒充分地碰并增长,这对东北、华北和西北西部降雹出现显著减少具有十分重要的作用。