Falling water films on a vertical cylinder with a downward step

This study concerns falling water films on a vertical cylinder of 45 mm diameter with a downward step in the region where the film flow is not developed and has very weak waves. Varying the step height H from 1.5 to 5.0 mm and the film Reynolds number Re from 50 to 2000, film flows were observed and film thicknesses were measured by the needle contact method near the step. The effects of the steps on water films were compared with each other and discussed. The streamline shapes of free water films formed under the step were theoretically obtained when the ring-shaped air layer was observed. The results agree well with the experimental curves obtained from the photographs.     

Segregation of cohesive granular materials during discharge from a rectangular hopper

Granular materials may readily segregate due to differences in particle properties such as size, shape, and density. Segregation is common in industrial processes involving granular materials and can occur even after a material has been uniformly blended. The specific objective of this work is to investigate via simulation the effect of particle cohesion due to liquid bridging on particle segregation. Specifically, a bi-disperse granular material flowing from a 3-D hopper is simulated using the discrete element method (DEM) for cohesive particles and the extent of discharge segregation is characterized over time. The cohesion between the particles is described by a pendular liquid bridge force model and the strength of the cohesive bond is characterized by the Bond number determined with respect to the smaller particle species. As the Bond number of the system increases, the extent of discharge segregation in the system decreases. A critical value of Bo = 1 is identified as the condition where the primary mechanism of segregation in the cohesionless hopper system, i.e. gravity-induced percolation, is essentially eliminated due to the liquid bridges between particles.     

铝合金矩形管拉弯成形过程的数值模拟

采用动力显式有限元程序Pam-Stamp2000对铝合金矩形管的一种拉弯成形过程进行了模拟,分析了模具最大作用力、管材截面畸变、成形件回弹的变化规律.模拟结果和文献给出的实验结果相当吻合,即模具最大作用力、管材截面畸变均随预拉力的增加而增加,而成形零件的回弹随预拉的增加而减小;相同预拉状况下,增加壁厚有利于减小截面畸变.此外,数值模拟给出了模具对管材作用力及管材夹持端轴向拉伸作用力随模具行程的变化规律,揭示了本文的拉弯实质上是一种非恒定轴向作用力(呈渐增趋势)的拉弯成形方式,这与本文的解析结果高度一致.     

Relationship between contact stiffness ratio and structural stiffness coefficient of a rectangular granular sample: a numerical analysis

In this study, the relationship between contact stiffness ratio and stiffness coefficient of a rectangular sample of granular material is investigated using the granular element method (GEM). Randomly packed granular samples are studied with different contact force models and particle size distributions in numerical simulation using the GEM. Initial arrangements of particles in the granular samples are generated using different algorithms such as inwards packing method, iterative growth method and compression method. It is demonstrated that the relationship between the stiffness coefficient of the granular sample and the contact stiffness ratio is basically logarithmic (Eq. 6). For granular samples generated by inwards packing method, the deviation for logarithmic relationship is relatively small. For granular samples generated by iterative growth method and compressive method, the deviation for logarithmic relationship is relatively large.     

Stochastic process of fracture in granular materials

By regarding the coefficient of particle friction of granular materials as a random variable distributed on the particle surface, the mechanism of particle sliding is interpreted as a stochastic process. Axial, shearing and volumetric strains are defined with regard to the deformation of a microscopic regular assembly of uniform spheres. For illustration, these strains are calculated for a uniform distribution of the coefficient of particle friction and applied to some triaxial test results reported elsewhere.     

Investigation of process induced warpage for pultrusion of a rectangular hollow profile

A novel thermo-chemical–mechanical analysis of the pultrusion process is presented. A process simulation is performed for an industrially pultruded rectangular hollow profile containing both unidirectional (UD) roving and continuous filament mat (CFM) layers. The reinforcements are impregnated with a commercial polyester resin mixture (Atlac 382). The reactivity of the resin is obtained from gel tests performed by the pultruder. The cure kinetics parameters are estimated from a fitting procedure against the measured temperature. The cure hardening instantaneous linear elastic (CHILE) model is adopted for the evolution of the resin elastic modulus using the temperature-dependent elastic response provided by the resin supplier. The numerical model predictions for the warpage trend at the end of the process are found to agree well with the warpage observed in the real pultruded products. In addition, the calculated warpage magnitude is found to be in the measured range of warpage magnitude for the manufactured part.     

ZnO thin films prepared by a single step sol-gel process

ZnO thin films were prepared on fused silica from a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH ] and isopropanol. Crystallization annealing was performed over the range 500 to 650 °C. X-ray analysis showed that thin films were preferentially orientated along the [002] c-axis direction of the crystal. The films had a transparency of greater than 85% in the visible region for sol-gels with a zinc content of up to 0.7 M and exhibited absorption edges at ∼ 378 nm. The optical band-gap energy was evaluated to be 3.298-3.306 eV. Photoluminescence showed a strong emission centered at ca. 380 nm along with a broad yellow-orange emission centered at ca. 610 nm. Single step sol-gel thin film deposition in the film thickness range from 80 nm to 350 nm was demonstrated. The effect of sol-gel zinc concentration, film thickness and crystallization temperature on film microstructure, morphology and optical transparency is detailed. A process window for single spin coating deposition of c-axis oriented ZnO discussed.     

An expression for the stiffness coefficient of a rectangular sample of granular material with random packing structure

We established a parallel-column model for a rectangular sample of heterogeneous granular material with random packing structure in a biaxial test. Within the framework of the proposed model, an expression for the stiffness coefficient of the rectangular granular sample is derived. The stiffness coefficient can be predicted using the proposed expression without microscopic analysis of the granular sample. To quantify the amount of grain crushing, the concept of relative breakage is adopted. The relative breakage parameter is then introduced into the proposed expression. Numerical results demonstrate the validity of the derived expression and show the effect of grain crushing on the stiffness coefficient of a granular sample.     

Role of flying buttresses in the jamming of granular matter through multiple rectangular outlets

We present a simulation study on the formation of particle arches supported by flying buttresses that arrest the flow of monodisperse spherical particles through two adjacent slots (rectangular outlets) in a three-dimensional (3D) anisometric flat-bottomed silo discharging under gravity. Most previous experimental and simulation studies on the jamming of a silo have focused on a single outlet, and have shown that the mean number of particles exiting the silo before it jams depends on the ratio of outlet size to particle diameter ( $R$ ). In this paper, we look at the nature of jamming if there are two adjacent outlets and discover some new physical insights on how sand arches are mechanically supported and how they interact with each other. For a fixed slot width $D_{o}$ and particle diameter $d$ , the distance separating the two openings $D_{w}$ is varied. The distribution of $N$ particles exiting the silo before both slots are jammed is obtained for each $D_{w}$ . From these distributions, we show that as $D_{w}$ becomes less than approximately $3d$ , the particle arches on adjacent outlets start affecting each other, and mutually stable arches become harder to form. We show that in cases, where for a small orifice ratio $R={D_o}/d$ a single outlet would have easily jammed, two adjacent outlets do not jam. We propose that this is due to the importance of stable particles resting on the base of the silo adjacent to the arches, which redistribute the load much like a flying buttress does in Gothic arches.     

Synthesis of strontium zirconate as nanocrystals through a single step combustion process

Nanocrystals of strontium zirconium oxide (SrZrO₃), a high dielectric constant (ε′ = 60) ceramic, were synthesized using an auto-igniting combustion of a precursor solution containing metal ions, oxidant, and a fuel. Phase-purity and particulate properties of the as-prepared powder were examined using X-ray diffraction, differential thermal and thermogravimetric analyses, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopic techniques. As-prepared powder was single phase, crystalline, and composed of uniform particles with sizes of ∼ 15-25 nm. These nanocrystals were sintered to high density (∼ 98% of the theoretical density) at 1470 °C for 4 h.     

A single step process to design a custom mattress that relieves trunk shear forces

Back pain is a common complaint that may result from the use of an inappropriate mattress. It can be minimized by using a well suited mattress. This paper presents a method for designing a custom foam mattress in an attempt to reduce back pain for the lateral lying position. Body three-dimensional profile and its mass distribution are both estimated by a simple photographic method. Finite element models are established and precalculated to characterize and predict the interaction between the body and the mattress surface. The process is based on two design performance criteria: a spine curvature in the frontal plane similar to a standing one and a given load distribution along the mattress. The process is validated with three mattresses customized to three individuals. Results show a good fit with numerical predictions according to the two performance design criteria.     

Density-driven sinking dynamics of a granular ring in sheared granular flows

This study reports experimental findings on the sinking dynamics of a heavy granular ring caused by the density-driven segregation effect in sheared granular flows. Specifically, this study systematically investigates the influences of the density ratio, shear rate, and solid fraction of the granular material on the sinking behavior of a heavy granular ring. The parameters of the dimensionless sinking depth and sinking rate, respectively, describe the change in the granular ring position and quantify the particle sinking speed. Experimental results show that both the dimensionless sinking depth and the sinking rate increase as the bottom wall velocity (shear rate) and solid fraction increase. The dimensionless sinking depth and the sinking rate also exhibit a linear relation. The dimensionless sinking depth does not increase monotonically as the density ratio increases. The sinking rate increases linearly with the final steady-state sinking depth for the same heavy granular ring structure, regardless of the wall velocity (shear rate), solid fraction, and density ratio.     

Hydrodynamics of a granular medium

The hydrodynamic characteristics of loose granular media are studied experimentally, with due allowance for particular aspects of the pore space structure (the sinuous nature of the paths of penetration and the efficiency with which the intergranular spaces take part in filtration); the results show that Re 80, up to Reynolds numbers of Re_cr 5.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 3, pp. 452–459, September, 1971.     

History-dependent deformation of a rotated granular pile governed by granular friction

We experimentally examined the history dependence of the rotation-induced granular deformation. As an initial state, we prepared a quasi-two-dimensional granular pile whose apex is at the rotational axis and its initial inclination is at the angle of repose. The rotation rate was increased from 0 to 620 (rpm) and then decreased back to 0. During the rotation, deformation of the rotated granular pile was captured by a camera. From the acquired image data, granular friction coefficient $\mu$ was measured as a function of the ratio between centrifugal force and gravity, $\mathrm{\Gamma }$. To systematically evaluate the variation of $\mu$ both in the increasing (spinning up) and decreasing (spinning down) rotation-rate regimes, surface profiles of the deformed granular piles were fitted to a model considering the force balance among gravity, friction, and centrifugal force at the surface. We found that $\mu$ value grows in the increasing $\mathrm{\Gamma }$ regime. However, when $\mathrm{\Gamma }$ was reduced, $\mu$ cannot recover its initial value. A part of the history-dependent behaviors of the rotated granular pile can be understood by the force balance model.     

Systematic electrical characteristics of ideal rectangular cross section Si-Fin channel double-gate MOSFETs fabricated by a wet process

The electrical characteristics of ideal rectangular cross section Si-Fin channel double-gate MOSFETs (FXMOSFETs) fabricated by a wet process have experimentally and systematically been investigated. The almost ideal S-slope of 64 mV/decade was obtained for the fabricated 20 nm Si-Fin and 125 nm gate-length FXMOSFET. This excellent subthreshold characteristic shows that the quality of the rectangular Si-Fin channel with (111)-oriented sidewall is good enough to realize high-performance FXMOSFETs. The current and transconductance multiplication accurately proportional to a number of 30 nm Si-Fin channels was confirmed in the fabricated multi-fin FXMOSFETs. The systematic investigation of the electrical characteristics of the fabricated FXMOSFETs in the 20-110-nm Si-Fin and 2.3-5.2-nm gate oxide regimes reveals that short-channel effects can be effectively suppressed by reducing the Si-Fin thickness to 20 nm or less. The developed processes are quite attractive for fabrication of ultranarrow Si-Fin channel double-gate MOSFETs.     

Analysis of the thermal process in a rectangular parallelepiped and solid cylinder for a time-dependent temperature of the ambient medium

A method is presented for computing the temperature change based on the exact solution of the heat conduction equation under the assumption of the Newton cooling law. The temperature of the ambient medium is here approximated by a piecewise-linear function of the time.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 3, pp. 508–513, September, 1970.