Effect of fibrils on curvature- and rotation-induced hydrodynamic stability

Flow of a suspension of water and nano-fibrillated cellulose (NFC) in a curved and rotating channel is studied experimentally and theoretically. The aim is to investigate how NFC affects the stability of the flow. This flow is subject to a centrifugal instability creating counter-rotating vortices in the flow direction. These rolls can be both stabilised and destabilised by system rotation, depending on direction and velocity of the rotation. Flow visualisation images with pure water and an NFC/water suspension are categorised, and stability maps are constructed. A linear stability analysis is performed, and the effect of fibrils is taken into account assuming straight fibrils and constant orientation distributions, i.e., without time-dependent flow-orientation coupling. The results show that NFC has a less stabilising effect on the primary flow instability than indicated from the increase in viscosity measured by a rotary viscometer, but more than predicted from the linear stability analysis. Several unknown parameters (the most prominent being fibril aspect ratio and the interaction parameter in the rotary diffusion) appear in the analysis.     

复合表面微凹坑对机械端面密封动压性能的影响

针对表面织构可以有效改善相对运动表面的摩擦学性能,建立了均匀分布的微凹坑机械端面密封的理论模型,采用有限差分法对流体动压润滑方程进行求解,获得了密封端面间气膜的无量纲压力分布,并考察了微凹坑形状和复合形式对密封端面的无量纲平均压力pav的影响.结果表明:微凹坑在相同的形状下,大小尺度不同的复合凹坑比单一凹坑具有更强的动压性能,而以矩形凹坑表现得最为明显,其动压性能效率提高率ε3可达6.79％;微凹坑的复合可明显增强密封端面动压性能.     

Effect of hydrogen bonding on the viscosity of alcohols at high pressures

Viscosities of several alcohols and vinyl acetate were measured with a rollingball viscometer. The viscosity measurements were performed at temperatures from 298 to 413 K and pressures up to 195 MPa with an accuracy of ±2%. The viscosities of the alcohols show a stronger dependence on temperature compared with that of substances that do not form hydrogen bonds. In addition, the secondary and tertiary alcohols show a viscosity-temperature dependence not in accordance with an Arrhenius law. An effect of pressure on the association of alcohol molecules resulting from hydrogen bonding was not resolved by means of viscosity data. Separation of the effect of association size upon increasing temperature from the viscosity caused by the change of specific volume was carried out using the Utracki free volume model.     

Effect of void-size distribution on the Hugoniot state at low shock pressures

In most theoretical and experimental investigations into the shock response of underdense solid media, the influence of the medium's mesostructure on the resulting pressure and degree of compaction has not been taken into account. In typical cases examined, shock pressures are well in excess of 1 GPa and this approach is clearly justified. However, at low pressures, calculations show that the distribution of void sizes can affect the final state achieved upon shocking the medium from a given initial porosity. This paper analyzes the response of porous aluminum to low pressure shocking and demonstrates a dependence of the final shocked state on the distribution of void sizes.     

水温分层对热泵热水机性能试验结果的影响

标准水箱作为测试循环加热式热泵热水机性能的重要装置之一,水箱内水温是否出现分层现象,决定着测试结果的准确性。本文对同一台热泵热水机选用2种不同水容量的标准水箱在名义工况下进行对比试验,结果表明水温分层对制热量影响较小,制热消耗功率偏差为2.60%。     

Effect of the elastic factor on the hydrodynamic stability of a structurally viscous medium

The effect of relaxation phenomena on the hydrodynamic stability of the plane gradient flow of a structurally viscous medium is investigated using linear theory.Notation _ij stress tensor deviator - U_i components of the velocity vector - x_i coordinates - t time - P pressure - =₀L/^*V plasticity parameter - _o limiting shear stress - andc dimensionless wave number and the perturbation frequency - Re=VL/* Reynolds number - density - F_ij deformation rate tensor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 868–871, November, 1978.     

Effect of simple stress on the glass transition of polymers at high pressures

Experimental studies, which have been carried out in this laboratory, showed the yield strength in tension, compression, and shear in the rubbery and the glassy states increased with increasing hydrostatic pressure. Moreover, the Young's modulus also increased with pressure and the amount of the increase across the glass transition temperature (T _g) at a given pressure can be as large as three orders of magnitude in the case of elastomers. An extension of the Gibbs-Dimarzio theory is proposed to account for the effect of applied stress on the glass transition temeprature of glass-forming polymers. When a simple stress, such as tensile, compressive or shear stress, is applied to a polymer, the T _g will decrease, compared to a polymer without applied stress. A glass-forming polymer in the vicinity of the transition would behave differently from that predicted by rubber elasticity. The partition function taking into account the effect of stress is suggested to be $$\Gamma = \Sigma W(f, n_0 ){\text{ }}\exp {\text{ }}[ - \beta (PV + U - \sigma V\varepsilon )]$$ where the strain ?=σ (f ? f ₀) in which f and f ₀ are the fraction of flexed bonds with and without stress, respectively. Furthermore, by this model, the Young's modulus across the transition, E _L and E _G, can be evaluated. The Young's modulus increases with increasing pressure at lower and moderate pressure range but the increase is rather small at very high pressure range.     

Effect of increased compacting pressures on the physicomechanical characteristics of metal-filled polyvinyl chloride

Based on the principles of linear thermodynamics, molecular physics, and spatial organization of amorphous polymers, the energy of formation of microdefects and the increments in their volumes as functions of the compacting pressure and the content of the filler of polyvinyl chloride systems are calculated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 807–812, July–August, 2000.     

Effect of dissolved gas on free-convective heat transfer in n-heptane at supercritical pressures

Results are presented from a study of heat transfer for different concentrations of nitrogen dissolved in n-heptane at supercritical pressures in a large volume. The heat transfer takes place in a large volume. It is shown that even small concentrations of the gas may significantly change the heat transfer.     

Effect of water on the triaxial response under monotonic loading of asphalt concrete used in dams

Mechanics of Time-Dependent Materials - Embankment dams with asphalt concrete cores have been constructed on practically all continents with satisfactory results. Nowadays many advantages, such as...     

Effect of the hydrodynamic bearing on rotor/stator contact in a ring-type ultrasonic motor

A hybrid numerical analysis that includes the hydrodynamic bearing effect and elastic contact in a ring-type ultrasonic motor is presented. The two-dimensional time-dependent compressible Reynolds equation is solved numerically by a second-order time accurate, noniterative, factored implicit finite-difference algorithm. The rotor deformation is described by a one-dimensional Green's function. The contact problem is solved by an iteration method so that the contact condition and the hydrodynamic bearing condition are satisfied simultaneously. The results show that the hydrodynamic bearing effect, especially the squeeze effect, is significant for ultrasonic frequency contact of the rotor and stator. Surface roughness, contact area, and normal vibrating speed of the stator are important parameters in the hydrodynamic bearing. A disagreement between the friction coefficient needed in the numerical analysis and the experimentally measured one in a previous study.     

Dependence of hydrodynamic decrement on vibration frequency

Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 7, pp. 99–102, July, 1989.     

Effect of the temperature on the hydrodynamic efficiency and stability of polyethylene oxide and polyacryl amide

The article describes a comparative study of the effect of the temperature on the hydrodynamic efficiency and stability of polyethylene oxide (PEO) and polyacryl amide (PAA).Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 4, pp. 558–565, October, 1984.     

Free vibrations of inflatable dams

Summary Inflatable dams are used for various purposes in a number of countries. They are cylindrical membrane structures which are attached to a rigid foundation along two of their generators and are inflated with water, air, or a combination of water and air. Some studies of their cross-sectional static profiles have been carried out in the past, both for cases when the dam impounds water and when overflow occurs. Experiments on scale models also have been reported. Vibrations have been observed on actual dams and on the physical models, but a theoretical analysis of the dynamic behavior of inflatable dams has not been published previously. In this paper, two-dimensional linear vibrations are considered. The dam is inflated with water and is used to impound water. Its material is assumed to be inextensible. Vibration modes and frequencies are obtained with the use of the finite difference and boundary element methods. The effects of the membrane density, internal head, and upstream head on the frequencies are determined.     

氧压对脉冲激光沉积LaNiO_3薄膜结构和电学性能的影响

通过改变氧分压,利用脉冲激光沉积方法在Si(100)衬底上制备了系列LaNiO3导电氧化物薄膜;经XRD测试研究发现,通过调控氧压,可获得具有高(100)取向薄膜,且氧压对薄膜结晶性有很大影响,在氧分压为7.5Pa时获得结晶性最好的薄膜。经XRF分析表明,La、Ni元素化学成分计量比随氧压增大而减小。经四探针法测试,薄膜电阻率最小为2.03×10-4Ω.cm,表现出了良好的金属导电性。经SEM和AFM分析表明,薄膜晶粒为柱状晶,排列均匀致密,薄膜表面均匀,粗糙度较小,表明LaNiO3薄膜可以用作一种良好的铁电薄膜底电极材料。