Percolation of meltwater through a snowpack

The hydraulics of meltwater percolation through a snowpack is analyzed in some detail. An implicit numerical model is used for determining the meltwater movement. The effect of freezing fronts of the free liquid water in the snowpack is evaluated. It is shown that even after a moderately cold night, it takes several hours of snowmelt before the snowpack again reaches its irreducible liquid content. The meltwater flux front moves very slowly down through the depth, where the liquid water has been refrozen during a preceding night. The time delay between the initiation of snowmelt at the surface and the start of run-off at the base of the snowpack is shown to be determined from a simple continuity reasoning. Finally, a comparison between theory and field measurements is made.     

Spectral albedos of an alpine snowpack

Spectral albedos (α_λ) from 380 to 2500 nm are reported for a snowpack in the Cascade Mountains of Washington. Data were obtained from just after an 0.4 m snowfall on 13 March 1980 until the pack had metamorphosed to melting coarse grains about 1 mm in diameter mixed with dust. Measurements were made under cloudy conditions to obtain a diffuse incident radiation field. Structural parameters of the snow were measured concurrently for all cases, and on three occasions, estimates of absorbing impurity content were obtained. The dependence of the spectral albedos of the snowpack on grain size and impurity content is illustrated. Comparison of wavelength-integrated albedos (α_obs) obtained using Kipp and Zonen radiometers with corresponding albedos derived from α_λ data show good agreement, and suggests a correlation between α_obs and the amount of incident radiation transmitted by the cloud layer. Comparison with theoretical models confirms that impurities in the snow depress α_λ at visible wavelengths but have little effect beyond 900 nm in the infrared; however, quantitative agreement with theory is uncertain at present.     

Experimental determination of preferential mechanisms of stress relaxation during deformation of HCP metals

Stages of the process of plastic deformation in twinning materials have been experimentally studied for VT1-0 titanium alloy. Mechanisms of hardening and stress relaxation are established based on analysis of the signals of acoustic emission recorded during microindentation.     

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.     

Influence of snowpack layering on human-triggered snow slab avalanche release

Dry-snow slab avalanches involve the release of a cohesive slab over an extended plane of weakness. In most fatal avalanches, the triggering of the initial failure occurred by localized rapid near-surface loading by people — followed by fracture propagation. Whereas a limit-equilibrium (LE) approach to snow slope failure only takes into account slab depth, slab density and weak layer strength, it omits properties such as the stiffness of adjacent layers and the fracture propagation process. Nevertheless, LE has been applied with some success to the frequency of skier triggering, suggesting that it is relevant to failure initiation. Since field studies have shown that, for a given slab thickness, stiffer slabs are less likely to be triggered, slab properties influence failure initiation, fracture propagation or both. A highly simplified finite element (FE) model of static skier loading was used to assess the effect of slab and substratum properties on skier-induced stresses in the weak layer. Compared to a uniform slab, the skier-induced stress at the depth of the weak layer varied by a factor of 2 due to layering. In particular, the simplified FE model suggests that while stiffer layers in the slab will reduce the skier-induced stress in the weak layer, stiff layers just below the weak layer can increase the shear stress. These results were incorporated into a modified stability index and compared to stability test results. However, by taking into account snowpack layering the correlation between the modified stability index and stability test results did not improve. While our simulations suggest that less stress penetrates through stiffer slabs and thus fracture initiation is less likely, other studies show that, once initiated, fractures under stiffer slabs have high propagation propensity.     

自然对流深冷结霜工况下湿空气流动状态实验分析

利用设计的竖直平板实验台,对自然对流深冷竖直平板结霜工况下湿空气流动状态进行了动态描述,并分析了竖直平板附近温度分布。实验结果表明:湿空气在竖直平板附近自上而下进行主流动,其余方向的湿空气汇入主流动中,且湿空气中的温度分布沿竖直平板切线方向自上而下,沿竖直平板法线方向自远处到竖直平板表面依次降低。     

Flexibly driving micro flow in a Lab-on-Chip system via dry porous structure

This paper is dedicated to present a low cost way for flexibly driving micro flow in a Lab-on-Chip system through utilizing the wetting mechanism. The unique merit of the method lies in its intentional employment of the wettability between liquid and the dry porous structure. The device thus fabricated only constitutes with a piece of dry porous material and a micro tube filled with liquid. When starting driving, connecting the objective liquid to the micro tube with pre-filled liquid at the entrance; then attaching the dry material to the exit end of the micro tube. Due to wettability between the pre-filled liquid and the dry material, the volume of the pre-filled liquid would decrease which subsequently induce a pressure reduction in the micro tube. As a result, the objective liquid will be jammed into the micro tube by the atmospheric pressure. With this working principle, the driving device is provided with several advantages such as being simple, cheap, safe, and clean; it also owns a wide range of applications in micro fluidics analysis. Theoretical interpretation and demonstration experiments were performed to evaluate the working performances of the driving device. Several factors liable to affect the running state of the driving device have been proposed and evaluated. It has been proved that this driving device is highly feasible and can be adopted as a micro pump for disposable Lab-on-Chip.     

Experimental and numerical determination of mechanical properties of polygonal wood particles and their flow analysis in silos

Responding to a lack in the literature, mechanical properties of polygonal wood particles are determined for use in a discrete element model (DEM) for flow analysis in silos, and some methods are proposed for determining such parameters. The parameters arrived at here have also formed part of the input to the SPOLY software, developed in-house to compute the DEM model with spheropolyhedron elements. The model is validated using a 2D physical model, where “prismatic” particles with polygonal cross sections are placed inside a silo with variable aperture and hopper angle. Validation includes comparison of flow-rates computed by SPOLY, displacement profiles, and clogging thresholds with experimental results. The good agreement that emerges will encourage future use of miniature triaxial tests, grain-surface profilometry, inclined slope tests, and numerical analysis of the intragranular stresses—toward a direct construction of the contact-deformation relations required in realistic DEM modelling of particle flow with angular-shaped particles.     

Experimental investigation of a cooled thick fin in dry and humid air flows

The results of a study are reported in which a cooled, thick vertical fin was tested in a closed loop tunnel with and without condensation from the air flowing over it. In particular, the temperature distributions for the dry and wet fin cases, together with the condensate film thickness in the wet fin case, were investigated. From a flow visualization investigation, it was found that the boundary layer separates at the leading edge, resulting in a higher air heat transfer coefficient. The wet fin test results also indicated that the mode of condensation was dependent on fin surface characteristics and that the wet fin performance was governed by the air flow parameter. Within the laminar air flow range, the condensate film flowed downward under the action of gravity. However, at higher air velocities, both gravity and shear forces affected the condensate flow, a variation in the condensate film in the direction of air flow being noticed.     

振动管外流动与传热实验研究及场协同分析

采用实验与数值模拟相结合的方法研究了振动管外的流动及传热特性,利用正交设计方法分析了振幅、频率等参数对换热性能的影响,得到了低频区内换热效果与振动参数间的拟合关联式,并基于场协同理论得到了管外近壁区的协同角余弦值随频率、振幅的变化规律。通过分析发现：振动强化传热的效果随着频率和振幅的升高而显著增强,共振工况下换热最强。对比不同管型的换热性能,沿椭圆管短轴方向振动的传热效果最好,圆管次之,长轴最差,证明管型也为影响振动工况下对流换热性能的重要参数。     

Experimental analysis of magneto rheological abrasive flow finishing process on AISI stainless steel 316L

In this experimental study, the surface quality of AISI stainless steel 316L was improved to a nano-level surface finish by means of magneto rheological abrasive flow finishing process. In order to determine the effect of input process parameters toward the responses such as final surface roughness (SR) and material removal rate (MRR), response surface model was built up and optimal parameters were found using the desirability analysis. Based on the experimental design, 20 experiments were conducted and the minimum SR and maximum MRR obtained are 53.46?nm and 1.757?mg/s, respectively, and their optimized values are 53.10?nm and 1.817?mg/s. By using the regression equations obtained for SR and MRR as input, an evolutionary optimization algorithm called as firefly algorithm has been utilized where the required surface finish was constrained as ≤60?nm and the optimized results were confirmed by means of validation experiments. The obtained results depict that the voltage to the electromagnet plays a most significant role to produce minimum SR and maximum MRR. Moderate and least significant contributions are given by the hydraulic pressure and number of cycles, respectively, toward the responses.     

Experimental study of dry stone masonry walls using digital reflection photoelasticity

Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five-step phase-shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non-uniformity of block geometry even in very regular dry stack masonry.     

Experimental study of turbulent flow in a rotating channel

Results are shown of measurements pertaining to the turbulence of flow in a short channel rotating about its axis.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 6, pp. 1103–1108, June, 1973.     

活性焦在溜管内流动的实验研究

为了降低物料在流动过程中的损耗和对设备的磨损,提高活性焦烟气净化装置的安全性和经济性,通过活性焦在溜管内的流动实验,探究活性焦在不同溜管倾角和底面粗糙度条件下的流动特性。结果表明,在溜管底部设置挡板能够有效地减小活性焦的流动速度和流量,流动速度可减小至无挡板时的70%左右;在溜管底部设置挡板时,应综合考虑活性焦因冲击和磨损产生的损耗;底部设置挡板的溜管的最小使用倾角在45°左右。     

Experimental study of nonstationary liquid flow in capillary-porous bodies

This paper describes the method and results of an experimental study of liquid flow in models of capillary-porous bodies and in capillary-porous bodies under isothermal conditions.     

Experimental and theoretical progress in pipe flow transition

There have been many investigations of the stability of Hagen-Poiseuille flow in the 125 years since Osborne Reynolds' famous experiments on the transition to turbulence in a pipe, and yet the pipe problem remains the focus of attention of much research. Here, we discuss recent results from experimental and numerical investigations obtained in this new century. Progress has been made on three fundamental issues: the threshold amplitude of disturbances required to trigger a transition to turbulence from the laminar state; the threshold Reynolds number flow below which a disturbance decays from turbulence to the laminar state, with quantitative agreement between experimental and numerical results; and understanding the relevance of recently discovered families of unstable travelling wave solutions to transitional and turbulent pipe flow.     

Experimental and computational failure analysis of TR upset-bending equipment for heavy crankshaft with continuous grain flow

The objective is to analyze the fracture of TR upset-bending equipment for the heavy crankshaft with continuous grain flow, in which the die base was broken in the first service when the crankshaft’s formation was changed as the closed-die forging. The chemical composition, mechanical properties and the hardness of the die base’s material were examined in comparison with the design requirement. The metallurgical properties inspection and SEM observation were conducted to seek the failure reason of the die base. At the same time, the computational failure analysis was also carried out. The heavy crankshaft forging process was simulated by software DEFORM-3D, through which the forming load was obtained. The forging simulation result was introduced to software I-dears as the boundary condition of the structural strength analysis for upset-bending equipment. The field of stress and deformation in the die base was calculated and the maximum load capacity was estimated. Structural optimization was performed in the high risk region of the die base, by which the stress magnitude was decreased and the load capacity was improved. This research achievement will be helpful to the design of heavy crankshaft’s forging process and die structure optimization.     

Surface derivative method for inverse thermal analysis in dry grinding

Starting from Jaeger’s classical formula for the field of temperature rise during dry surface grinding, an analytical expression for the profile of the heat flux going to the workpiece is derived. This analytical approach, termed the surface derivative method, can be applied very easily to inverse thermal analysis in surface grinding, and is compared herein with other inverse analysis methods reported in literature, viz. the temperature matching method and the Gauss–Newton method. In contrast to these methods, the surface derivative method is much less computationally expensive and does not collapse for high Péclet number.     

Experimental modelling of free-surface dry granular flows under a centrifugal acceleration field

We investigate the dynamics of granular flows under the action of a centrifugal acceleration field. The granular flows consist of a monodisperse set of glass beads flowing down an inclined plane. The experiments are performed at variable slope angles \(\zeta \) and equivalent centrifugal accelerations \(a_\text {cf}\equiv Ng\). We study the effect of this parameters on the superficial flow velocity u and flow height h. Two trends are observed, by increasing \(\zeta \) and \(a_\text {cf}\), u increases proportionally, and h decreases asymptotically until a constant height. This relation is analysed in terms of the system potential and kinetic energy, leading to the estimation of equivalent impact forces one order of magnitude larger than those observed in small scale 1g laboratory experiments, with the possibility to reach higher forces by increasing N. Finally, considering the trend of u and h, our results suggest a scaling principle of inertial velocity proportional to \(\sqrt{N}\).     

多级爪型干式真空泵原理分析

多级爪型干式真空泵的结构对于其材料消耗、体积、能耗等性能有着非常重要的作用。本文介绍了北京朗禾科技的最新型结构——螺旋反爪结构,就其原理和国际上最经典的两种结构:螺旋型(德国)和反爪型(英国)做了介绍和对比,说明螺旋反爪结构可以大幅度缩短泵的长度、节约大量的材料、提高抽气效率、降低加工精度、提高抽气性能,对爪型干式真空泵的发展和普及有很好的推动作用。