颗粒在斜槽中流动的实验研究

用示踪颗粒法对细玻璃球在斜槽中的低速流动进行了实验研究。结果发现 ,颗粒的流动行为与斜槽表面特征密切相关 ,对光滑表面存在明显的壁面滑移 ,而对粗糙壁面 ,在低速流情况下不存在滑移。实验测量了不同条件下的速度分布和流层厚度 ,并分析了斜槽倾角、流率及壁面状况对流动的影响     

粉粒体斜面慢速流的三维颗粒流程序仿真

为了研究粉粒体斜面慢速流的机理,在分析粉体流动性影响因素的基础上,应用颗粒离散元法三维颗粒流程序建立斜槽仿真模型并进行三维流动过程模拟,观察颗粒在斜槽内的流动情况及单个颗粒在流动过程中的受力、位移和速度,测量颗粒内部力场和颗粒速度场变化。结果表明,随着斜槽倾角的增大,粉粒流的速度呈连续、不均匀增大,堆积颗粒之间的接触力与不平衡力显著增大,并对流速产生一定的影响。     

斜槽式超声变幅杆纵扭特性研究

利用斜槽式结构进行模式转换能有效实现纵扭复合,其局限在于设计不合理会导致纵扭转换效率低下。通过分析纵波斜入射固-气界面的反射和折射特性,仿真不同斜槽结构下的变幅杆在其谐振状态下的纵扭转换效率,探究了斜槽的角度、宽度、个数、深度、长度等因素对纵扭模式转换效率的影响。仿真结果表明:存在最佳的斜槽角度和斜槽宽度,使得纵扭转换效率最大;斜槽个数的增加能明显提升纵扭转换效率,且最佳斜槽宽度随斜槽个数增大而减小;斜槽深度和斜槽长度越大,纵扭转换效率越大,但达到一定长度值时趋于稳定。进而,通过对优化设计后的斜槽式变幅杆进行试验测试,验证了该研究的有效性,试验条件下获得的纵振和扭转幅值分别为9.5μm和29μm。     

活塞斜槽测量直径的计算

介绍了活塞斜槽测量量针直径的选取方法,并推导了斜槽测量直径公式。     

空气输送斜槽在钢渣微粉生产线上的应用

引言 空气输送斜槽主要用来输送粉状干燥物料,空气斜槽在输送物料中没有传动的零件,与它同功用的胶带输送机、螺旋输送机、埋刮输送机相比较具有构造简单、磨损少、易维护、耗电少、操作安全可靠,同时易于改变输送方向和多点喂、卸料等优点。     

刮板细度计非接触测量数据处理研究

对基于光谱共焦技术搭建的刮板细度计斜槽面深度测量装置的非接触测量数据进行处理算法研究。引入高斯滤波对整段测量数据进行滤波分析,再分左上平面、右上平面、斜槽底面三段进行高斯滤波,分离三个测量面的表面粗糙度信号及波纹度信号,解算出粗糙度值。对于高斯滤波中线,利用最小二乘法进行拟合,结果表明左右上平面的直线倾斜度一致,可拟合为一条直线。以再次拟合的直线为基准线,求得斜槽面扫描点至基准线的深度值,得到斜槽面深度标称值为90μm的示值误差为0.27~1.97μm。与电感测微仪接触测量所得数据进行比对,结果表明本文提出的刮板细度计非接触测量数据处理方法准确可靠。     

坐标测量机测量活塞斜槽角度及测量不确定度分析

本文介绍了坐标测量机测量活塞斜槽角度值的测量方法 ,并进行测量不确定度分析     

空间斜槽三坐标检测技术

机匣类零件具有空间斜槽结构，该结构与发动机轴线偏置一定距离，以斜槽侧壁某一点为回转中心进行位置度评价，位置度要求0．1，该回转中心同样是与该结构进行装配的叶片积叠轴位置。因其结构的特殊性，该位置度的检测无法用常规手段进行。以往该结构的检测都是采用检测预钻孔位置度，靠机床位置度来间接保证的方法进行，无法得到直接检测数据，更好地对零件质量进行检测和控制。基于PC—DMIS测量系统的三坐标测量机能够提供特定的算法，编程实现该结构的直接检测，实现空间斜槽的自动化检测技术，更好的监控和保证零件质量。     

处理机匣径向斜槽高效铣削加工技术研究

不锈钢处理机匣加工径向斜槽传统工艺方法为分层加工,刀具种类较多,加工难度大,加工时间长,加工效率低。本位以不锈钢处理机匣铣槽工艺为载体,开展径向斜槽特征高效加工的技术研究,围绕处理机匣铣槽工艺,综合应用螺旋铣、插铣、快进给铣削等加工方式的优势,经过多轮试验迭代实现处理机匣铣槽工序的高效加工,达到缩短加工时间的目的。     

刮板细度计检定装置的研制及刮板斜槽底平面平面度的检定方法探讨

刮板细度计是用来测量清（色）漆、油墨和食物等产品内颜料、杂质及填充料的颗粒细度的常用的计量器具,为保证刮板细度计计量性能的准确可靠,研制刮板细度计检定装置对刮板细度计的主要计量性能进行测量。文章重点介绍了该检定装置的结构和对刮板细度计斜槽底平面的平面度的检定方法。     

Position dependent velocity profiles in granular avalanches

We present velocity profile measurements in granular avalanches flowing down a flat chute with wide rectangular cross section. The flow is recorded through a transparent side-wall by a high-speed camera, which is able to capture 1,825 pictures in a second. Due to the high frame rate of the camera, several flow features can be observed. Quantitative statements can be made by analysing the images with a pattern matching algorithm. This provides us with flow-normal velocity profiles with a very high temporal and spatial resolution. We find that even on flat surfaces, velocity profiles are strongly changing through the flow and for the range of investigated chute angles (from 26° to 36°) clear trends can be recognised. In the head of the avalanche the velocity is highest, decreasing continuously over the length of the avalanche. Thus, the investigated granular avalanches stretch through the flow. The experimental method allows us to study the evolution of characteristic flow properties such as depth averaged velocity, slip velocity, surface velocity, shear rates or flow depth. Side-wall friction effects are estimated.     

散状物料转载系统设计DEM仿真方法的研究

颗粒仿真技术可以对散状物料的运动进行观察、机理分析、受力分析、磨损(寿命)估计和系统优化.比较了散状物料转载计算方法,给出了采用DEM方法的建模与模型检验的基本步骤.针对DEM计算方法存在所需计算时间过长的问题,实验比较了降低剪切模量和增大颗粒粒度等方法对DEM计算时间和实验结果的影响,结果表明,在不影响计算结果的前提下可通过降低剪切模量和增大颗粒粒度来缩短DEM仿真计算时间.利用EDEM软件实现了散料转载过程的可视化,比较分析了直线型溜槽、折线型溜槽和曲线型溜槽中物料转载效果.仿真表明：采用变曲率半径效果更好;U型溜槽截面能够减少物料不对中情况的发生.     

Wireless sensors as a tool to explore avalanche internal dynamics: Experiments at the Weissflühjoch Snow Chute

Specially designed wireless accelerometers units were used in a series of experiments at the snow chute operated by the SLF at Weissflühjoch (Switzerland) during 2008-2009 winter. The purpose of the experiment was to evaluate the best design and the performance of these innovative instruments to provide information on the internal dynamics of flowing snow. The wireless accelerometers were placed in the snow chute starting zone prior to the experiments and traveled within the flow when the avalanche was released. The characteristics of the units (size and density) allow them to evolve like active particle tracers. Acceleration measurements obtained at 85 Hz in the different experiments were analyzed. The analysis methods used include Empirical Mode Decomposition and Kalman filtering techniques. The developed methodologies were used to obtain reliable speed and position values from the single 2D acceleration measurements. The obtained results were compared to independent speed and position measurements. The results show to be in agreement with that obtained from independent speed measurements from optoelectronic sensor arrays and video images and open a new perspective for future avalanche research. The extracted information could provide valuable data related to internal dynamics of the avalanche. Small-scale chutes are the ideal scenario to test these new technologies. Moreover, we consider these sites essential to develop and test new instrumentation (to be deployed), in the future, in full-scale experiments. In addition, the experiments performed show for the first time the potential of the wireless technologies and wireless sensors to study snow avalanches.     

EFFECT OF MASS FLOWRATE ON POWDER FLOW VELOCITIES

The effect of mass flowrate on powder velocities during flow down a chute and in free fall from a hopper was studied using a microwave Doppler technique. The velocities on an inclined chute, which was either smooth or had its surface roughened by coating with a layer of the sample, increased as the mass flowrate increased; this effect was most significant at large angles of inclination. Free fall from a hopper also led to higher velocities being monitored as the mass flowrate increased.

The distribution of particle velocities was also estimated; during flow on a chute at high angles of inclination the distribution of velocities was greater for low flowrates while at low angles, where the powder only just managed to flow, the trend was reversed. There was no difference in the distribution of velocities measured for the free fall of particles as the mass flowrate varied.     

Flow–obstacle interaction in rapid granular avalanches: DEM simulation and comparison with experiment

This paper investigates the interaction between rapid granular flow and an obstacle. The distinct element method (DEM) is used to simulate the flow regimes observed in laboratory experiments. The relationship between the particle properties and the overall flow behaviour is obtained by using the DEM with a simple linear contact model. The flow regime is primarily controlled by the particle friction, viscous normal damping and particle rotation rather than the contact stiffness. Rolling constriction is introduced to account for dispersive flow. The velocity depth-profiles around the obstacles are not uniform but varying over the depth. The numerical results are compared with laboratory experiments of chute flow with dry granular material. Some important model parameters are obtained, which can be used to optimize defense structures in alpine regions.     

Transient behavior of granular materials as result of tumbler shape and orientation effects

Granular flows are most often investigated at steady-state conditions. This allows time-averaged analysis to display results such as velocity profiles and convective accelerations within the thin flowing layer. Typically in rotating tumblers, constant rotation rates and circular shapes are used as they jointly produce a steady, uniform flowing layer at the free surface. Conversely, unsteady flowing layers can be generated through any combination of varying the rotation rate of a tumbler or using a non-circular cross-sectional shape to change the length of the flowing layer. The unsteady conditions, however, require the additional complexity of ensemble-averaged analysis of images in a sequence of multiple trials. The experiments of this paper examine the properties of unsteady flow produced by triangular-shaped rotating tumblers at constant rotation rates. The geometric shape naturally causes periodic changes in the flowing layer as a function of the instantaneous orientation of the triangle. Multiple experiments were conducted in which the parameters of tumbler dimension, particle size, fill level and rotation rate were varied in all combinations. The free surface properties of angle of repose and flowing layer length, position, and curvature are reported. Results show that the arithmetic difference between the angle of repose and the tumbler orientation has a functional relationship with the instantaneous flowing layer length in the form of a catenary indicating a minimization of energy in the granular flow. Furthermore, the oscillation of the flowing layer position appears to affect the free surface curvature in the upstream regions. This is likely due to the rapidly increasing and decreasing length of the free surface limiting the space where particles can enter or exit the flowing layer. Ultimately, the unsteady macroscopic properties of the free surface flowing layer in the triangular tumblers provide some indication of the complexities of granular velocity and acceleration that contribute to the mixing and segregation in this unique tumbler shape.     

Cross-sectional and axial flow characteristics of dry granular material in rotating drums

Cross-sectional and axial flow behaviors of dry granular material in rotating drums are closely related to the dynamic characteristics and velocity distributions between the surface layer and bed material. In this study, both 2D and 3D dry granular flow patterns in horizontal rotating drums are experimentally investigated with flow imaging analysis. A dimensionless flow parameter combining the effects of Froude number, relative particle size and volume filling is proposed in this study, which controls the flow characteristics in a rational drum such as dynamic angle of repose, thickness of the flowing layer, relative free surface velocity, and the shear rates in the flowing layer. The dimensionless granular temperature exhibits linear distribution in the flowing layer, being maximum at the free surface and being negligible at the interface in the rolling regime. The measured shear rate of the plug flow departs from drum angular velocity under the wall slip conditions when the drum surface is smooth. Due to the existence of axial convection and lateral surface profile, the mass flux in the flowing layer is always less than that of the plug flow in the 3D granular flows based on sidewall particle images. One the other hand, the mass flux in the flowing layer is always equal or greater than that of the plug flow in the 2D granular flows. 2D granular flows exhibit higher angles of repose and surface velocities than those of the 3D granular flows at the same volume fillings.     

Near-infrared spectroscopic method for real-time monitoring of pharmaceutical powders during voiding

A near-infrared (NIR) spectroscopic method has been developed to monitor flowing pharmaceutical powders during their voiding and detect post-blending segregation. The method is capable of providing both chemical and physical information (particle size differences) on the flowing pharmaceutical powders. Particle size differences are widely recognized as the predominant driver for segregation. Pharmaceutical powders may segregate following blending as they are voided down pipes to compressing machines, increasing the variability of the drug content and dissolution of the final product tablets because of segregation. NIR diffuse reflectance spectra of pharmaceutical powders were obtained following voiding through a six-foot pipe. Spectral subtraction was used to eliminate baseline differences but maintain particle size differences. The NIR spectra indicated differences in the particle size of the flowing powder. Particle size differences were also tracked throughout the voiding of pharmaceutical powders by plotting the absorbance at 1536 nm. The method was also applied to the voiding of two layers of lactose particles with different particle sizes. The system described in this report provides an approach to study post-blending segregation in pharmaceutical powders and other relevant materials.     

敷设粘弹性材料的溜槽的试验模态分析

针对传统溜槽振动和噪声非常大的情况,设计了内部自由敷设粘弹性阻尼层的溜槽。文中应用了锤击激励法和LMS test. Lab振动测试系统对内部敷设粘弹性阻尼层的溜槽进行了模态试验,得到了前6阶固有频率、阻尼和振型,经过模态置信准则检验,所测试验模态参数真实有效。通过对试验结果的分析发现溜槽出口处的振动为扭转振动和弯曲振动的叠加,加工时应该加强出口处的强度以减小局部振动。研究结果为敷设粘弹性阻尼层的溜槽的优化设计提供了参考。     

Falling process of a rectangular granular step

This study experimentally investigates the falling process of a dry granular step in a transparent plexiglass chute by particle image analysis. Three types of uniform spherical beads and one type of quartz sand were piled up with various bed slopes and widths to elucidate their flow characteristics. The surface angles during the early slipping phase are close to the failure angles that are associated with the active earth pressure, based on the Mohr-Coulomb friction law. For a given size of particles (d) and slope (θ), the retreating upper granular surface follows a theoretical curve, and dimensionless mobile length decreases as the dimensionless time parameter t* increases. Velocity profiles measured at the side wall exhibit an exponential-like tail close to the static region at the bottom of the chute. As determined by the conservation of mass and momentum, the relationship between the characteristic velocity and the characteristic depth is linear in the transient flow.