设计参数对涡流二极管泵性能影响的试验研究

为了得到涡流二极管流体泵输送系统主要系统参数的设计依据,建立了系统参数可调的性能试验装置,试验测试了气源压力、供液槽液位及气液换能筒内液位变化行程等系统参数变化条件下系统的水力性能变化特证,分析了系统参数对系统水力性能的影响。试验结果表明,在保证系统稳定的前提下,适当增大气源压力,提高供液槽液位,增大换能筒液位变化行程可以提高涡流二极管泵系统的时均排液量和容积效率,获得较为理想的周期特性。     

Decentralized controllers design for open-channel hydraulic systems via eigenstructure assignment

In this paper, we propose the design of both a proportional (P) and a proportional integral (PI) decentralized controller for open-channel hydraulic systems by assigning the closed-loop eigenstructure. The system dynamic is described by a linear, time-invariant model deduced from the Saint-Venant equations. A constant-volume control law is designed, satisfying the requirement of decentralization, typical of large-scale systems like the hydraulic one herein examined. The synthesis procedure followed in this paper allows us to derive a parametric expression for the set of feedback gains of decentralized controllers which achieve the desired eigenvalue assignment. The free parameters in this parametric expression can be used to assign eigenvectors as close to the desired ones as possible, while achieving the required eigenvalue assignment.     

船舶交流轴带发电机液压耦合研究

针对现有的轴带发电机的耦合方式不同程度地存在着当柴油机在变速运行时会产生供电频率不稳问题,提出船舶交流轴带发电机液压耦合方式,该耦合系统采用油马达转速作为控制信号控制变量泵的流量,从而使得主机在变速运行时轴带发电机供电频率稳定.     

Flow underneath a pair of structures with intermediate filters on a drained stratum

This paper presents a solution, using a conformal mapping technique, for the problem of seepage beneath two structures with intermediate filter built on two pervious strata. The lower stratum has a higher permeability than the upper one. Formulae are derived for calculating the dimensionless heads acting on both the upstream and downstream structures. Also, equations are derived for determining the values of the exit gradients along both the intermediate filter and the downstream bed, and the seepage discharges. For given boundary conditions, the seepage characteristics are calculated using the derived formulae; a sample from the results of such calculations is presented.     

Problem of propagation of a gas fracture in a porous medium

The problem of gas fracture formation in a porous medium is investigated. An inertialess viscous polytropic gas flow along the fracture is considered. The assumption of small fracture width with respect to the height and length makes it possible to adopt the vertical plane cross-section hypothesis on the basis of which the dependence of the gas pressure inside the fracture on its width can be reduced to a linear law. Initially, the soil surrounding the fracture is soaked with oil-bearing fluid. During fracturing the reservoir gas penetrates into the soil mass and displaces the fluid. A closed system of equations, which describes the evolution of the fracture opening, the depth of gas penetration into the reservoir, and the gas velocities inside the fracture, is constructed. The limiting regimes of gas seepage into the surrounding reservoir are considered and a one-parameter family of self-similar solutions of the system is given for each. The asymptotics of the solution in the neighborhood of the fracture nose is investigated and analytic expressions for the fracture length are obtained. The solution of the problem of gas fracture is compared with the hydraulic fracturing problem in an analogous formulation within the framework of the plane cross-section hypothesis.     

Connectivity and Effective Hydraulic Conductivity

The effect of the connectivity of high-conductivity elements on the value the effective hydraulic conductivity of a saturated porous medium is investigated. The increase in effective conductivity due to the connectivity is estimated on the basis of a simple combinatorial model.     

Modelling of a Switching Control Hydraulic System

Modelling of a hydraulic system featuring a specific type of switching control is presented. Despite conventional hydraulic drive technology where rather smooth changes of pressure and flow rate are intended and where oscillations constitute undesired phenomena, switching control provokes oscillations as an indispensable element to achieve high energetic efficiency with valve control. The system under study is one which comprises a novel switching valve, a long line with considerable wave propagation dynamics, a hydraulic cylinder, and the valve's dynamics.     

Role of pH in Electro-Osmosis: Experimental Study on NaCl–Water Saturated Kaolinite

Electro-osmosis experiments were conducted on rigid cylindrical samples containing 0.01 M NaCl–water saturated Speswhite kaolinite. It is experimentally found that the electro-osmotic permeability is pH-dependent. It is also experimentally found that time and spatial variations of the sample pH and of the pore water pressure correlate. This is qualitatively confirmed by a simple analysis that couples the electro-osmotic and hydraulic flows through the pH-dependent electro-osmotic permeability. However quantitative agreement between the experimental and numerical values of the pore water pressure is not obtained throughout the whole sample. This suggests that the hydraulic permeability may also depend on the pH.     

小型轴流式管路液力涡轮的试验研究

为获得小型管路液力涡轮的水力模型和工作特性,对不同参数下液力涡轮的水力性能进行了试验研究,分析了涡轮输出转速及扭矩的变化特性及影响因素,主要探讨了通过涡轮的流体流量、压力以及叶片安装角对涡轮水力性能的影响.多种工况的试验结果表明,液体流量是影响涡轮输出性能的主要动力参数,可以通过流量的变化调节涡轮的输出转速和输出扭矩;叶片安装角对涡轮工作效率的影响较大,不同安装角度涡轮的设计转速要与其最高效率点相对应.     

Percolation Cluster Statistics and Conductivity Semi-Variograms

Cluster statistics of percolation theory have been shown to generate expressions for the distribution of hydraulic conductivity values in accord with field studies. Percolation theory yields directly the smallest possible generalized resistance value, R _c, for which a continuous path through an infinite heterogeneous system can avoid all larger resistances. R _c, defines an infinite system hydraulic conductivity. Cluster statistics generate the number of clusters of resistors of a given size with a given R, for which a continuous path through the cluster can avoid resistances larger than R. The probability that a volume of size x ³ falls on a particular cluster gives the probability that volume has a characteristic resistance, R. Determining the semi-variogram of the hydraulic conductivity is now elementary; it is necessary only to determine whether translation h of the center of the volume x ³ removes it from the cluster in question. If the cluster is larger than (x+h)³, then, on the average, the same cluster resistance R will control K. Otherwise, the value of K at x+h will be uncorrelated with its value at x. The condition is then expressed as an integral related to the one, which gives the distribution of K. Then an integral over the derived distribution of K gives the variogram. Results obtained are that the variogram should be similar to either the exponential or Gaussian forms typically in use, if K is a power law function of random variables (as in Poiseuilles Law), or more closely related to the spherical approximation if K is an exponential function of random variables.