Capillary Pressures by Fluid Saturation Profile Measurements During Centrifuge Rotation

A novel centrifuge technique to obtain the capillary pressure curve by measuring the local fluid distribution in a spinning core is presented. The Nuclear Tracer Imaging Centrifuge (NTIC) method measures the fluid saturation profile along the length of the core to directly obtain the capillary pressure curve. The proposed method is superior to conventional centrifuge techniques because (1) the capillary pressure curve is obtained at one rotational speed, (2) core plugs are not removed from the spinning centrifuge for imaging, and (3) no mathematical solution is needed to calculate the capillary pressure curve. The literature states that the various mathematical solutions used in conventional centrifuge tests are the greatest source of error, not the uncertainty in the experimental data. By eliminating the dependence of such solutions, the NTIC represents an alternative to conventional centrifuge tests, and may be used to validate the various mathematical procedures applied in conventional centrifuge capillary pressure tests. NTIC may also confirm the applicability of other imaging techniques that rely on core plug removal for saturation imaging, by verifying if there is no fluid re-distribution at static conditions.     

Nonlinear azimuthal waves in a centrifuge

Azimuthal wave motions in a liquid which partially fills a cylinder (centrifuge) rapidly rotating about a horizontal axis are discussed in this paper. Under the action of centrifugal force the liquid is pressed to the wall of the cylinder and moves together with it about the central air core. The vibrations of the free surface which arise are called centrifugal waves [1]. The difficulties of their theoretical investigation are related to the nonlinearity both of the basic equations and also of the boundary condition for the pressure on the free surface; therefore they have previously been studied only by linear methods [1, 2]. Nonlinear azimuthal waves in a centrifuge with an infinite radius of the rotating cylinder are analytically described below. The waves found are an analog of Gerstner trochoidal waves on a cylindrical surface. An approximate solution for a centrifuge with a finite outer radius is constructed by matching the waves obtained to the known linear ones.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 86–89, May–June, 1984.In conclusion the author expresses his gratitude to E. I. Yakubovich for useful discussion.     

烟幕初始云团半径变化规律理论模型及实验研究

为了评估烟幕的遮蔽效能,需要对烟幕云团初始参数进行计算,即烟幕云团在爆炸能量下形成的最大半径。本文中基于一种简单烟幕发生装置,把云团的膨胀过程分为2个阶段,分别为等熵膨胀阶段和自由膨胀阶段,建立了烟幕云团膨胀的理论模型,对模型进行分析建立了烟幕云团膨胀过程微分方程组。采用四阶龙格-库塔方法求解得到烟幕云团的半径变化规律。通过实验结果分析可知,该理论模型能够描述给定装置烟幕云团膨胀的基本规律。通过缩比效应,可将其用于爆炸发烟装置初始云团参数的计算。     

我国土工离心模型试验技术发展综述

小尺寸物理模型试验是岩土力学与岩土工程研究的重要手段。常规小比尺模型由于其自重产生的应力远低于原型,以及原型材料明显的非线性,因而不能再现原型的特性。解决这一问题的唯一途径是提高模型的自重,使之与原型等效。提高模型的自重应力水平、增大材料自重的最简便的方法就是用离心机。本文在总结回顾大量文献资料的基础上,根据离心模型试验技术的研究深度和应用范围,将我国土工离心模型试验技术的发展历史分为3个阶段,并分别阐述了各阶段土工离心模型试验技术在我国的应用类型及研究状况,介绍了试验设备、试验技术、数据采集等几个方面的发展历程。最后,总结指出了目前离心模型试验技术研究存在的问题,并对今后的研究和工作做了展望。     

改进的容重增加法原理及离心模型试验数值模拟

容重增加法作为一种边坡稳定分析方法本身具有一定的缺陷,计算结果常常偏差较大,甚至可能无法得出结果。针对容重增加法的缺陷,定量分析了容重增加法的误差来源,并通过公式推导对改进容重增加法的原理进行了分析。针对改进的容重增加法,设计了不同参数的边坡模型,将容重增加法、强度折减法与改进的容重增加法进行对比分析,研究改进方法的改进效果。然后,利用ACADS边坡稳定分析例题,验证了改进方法在非均质边坡中的应用效果。最后,将改进前后的容重增加法运用到土工离心模型试验的结果分析中,并将试验结果与模拟结果进行对比分析,验证了用改进的容重增加法分析离心模型试验结果的可行性。本文的研究为容重增加法改进方法的应用提供了理论依据,并为土工离心模型试验的相关分析提供了参考。     

Compression of solid and annular circular discs bonded to rigid surfaces

Although it is noted in the literature that the presence of a central hole in an elastic layer bonded to rigid surfaces can cause significant drop in its compression modulus, not much attention is given for investigating thoroughly and in detail the influence of the hole on the layer behavior. This paper presents analytical solutions to the problem of the uniform compression of bonded hollow circular elastic layers, which includes solid circular layers as a special case as the radius of hollow section vanishes. The closed-form expressions derived in this study are advanced in the sense that three of the commonly used assumptions in the analysis of bonded elastic layers are eliminated: (i) the incompressibility assumption, (ii) the “pressure” assumption and (iii) the assumption that plane sections remain plane after deformation. Through the use of the analytical solutions derived in the study, the compressive behavior of bonded circular discs is studied. Particular emphasis is given to the investigation of the effects of the existence of a central hole on the compression modulus, stress distributions and maximum stresses/strains in view of three key parameters: radius ratio of the hole, aspect ratio of the disc and Poisson’s ratio of the disc material.     

复合型裂纹断裂的新准则

以Ⅰ-Ⅱ复合型裂纹为研究对象,对裂纹尖端的塑性区分布规律进行了理论分析。引入两组评价裂纹尖端应力场对裂纹扩展影响的参数,考虑裂纹尖端存在的局部塑性变形,并采纳如下两个假设,(1)裂纹沿最短路径穿过塑性区向弹性区扩展,(2)当在扩展方向上的弹塑性边界极半径r大于其临界极半径rC时,裂纹开始扩展。在此基础上,导出了新的复合型裂纹断裂准则,并与现有部分断裂准则及实验结果进行了对比。结果表明：新建立的复合裂纹断裂准则与实验结果吻合程度非常高。最后,阐明了以单一KIC或KIIC建立的复合裂纹扩展准则的局限性以及考虑裂纹尖端当前应力场的必要性。     

Source below the free surface of a heavy liquid

The problem of the motion of a source under the free surface of an infinitely deep heavy liquid has been studied by Keldysh [1] under the assumptions used in the theory of small amplitude waves. However, these assumptions are no longer valid [2] for large Froude numbers F.A method using only one of the four assumptions of small amplitude wave theory (the assumption that the absolute value of the velocity at the free surface is nearly constant) was described in [2], In the following, this method is used to construct a solution of the problem which becomes exact as F . When F is not large our results are close to those of Keldysh if the source intensity is low. For F=0, both methods lead to exact results.     

移动简谐荷载作用下桥梁响应的高效计算

在计算移动荷载过桥问题中广泛使用的Newmark方法必须在每一时间步内限制荷载的大小和作用位置都不能改变。精细积分法虽然允许荷载的大小在每一时间步长内发生变化,但是仍假定其作用位置是不变的,未能采取措施以描述荷载沿着桥面的连续移动性。本文提出三种精细积分格式,在每一时间步内不但允许移动荷载的大小按简谐规律连续变化,而且模拟了简谐荷载在空间域的连续移动。通过与Newmark方法和简单问题的解析解进行数值比较,表明用本文提出的方法可以用较粗的结构单元和较大的时间步长而获得很高的计算精度。在精度相同的前提下,计算效率比Newmark方法可提高1~2个数量级。     

INVESTIGATION ON COMPLIANCE ROTATION CORRECTION FOR COMPACT TENSILE SPECIMEN IN UNLOADING COMPLIANCE METHOD

The rotation correction method of unloading compliance for a compact tensile (CT) specimen in the current Jintegral resistance curves or critical Jintegral test standards was under suspicion by tracing to its source, and a new rotation correction method was proposed. The rotation center of the specimen is close to the crack tip, and the material constitutive relationship has little effect on the rotational radius R. If the formula for rotation correction recommended in current standards is used to measure the crack length of CT specimen, it will lead to larger error. A new formula with better accuracy for the crack length measurement of the CT specimen was presented.     

基于气压鼓泡法研究石墨烯力学性能

通常假设二维材料为连续介质薄膜,然后采用连续介质薄膜的研究方法进行二维材料力学性能研究,其中气压鼓泡法是一种主要测试方法．但实验观测发现,悬空石墨烯并非处于气压鼓泡测试分析模型中假设的固支边界条件,而是处于一种粘附边界条件：靠近孔壁边界处,有小部分材料通过范德华吸引粘附在基底柱形孔的侧壁上,而且粘附部分可以在极小载荷作用下剥离．这导致石墨烯悬空部分的实际半径大于基底孔半径,即鼓泡实验中的石墨烯是一种松弛薄膜,而非通常认为的预拉伸薄膜．通过有限元数值模拟研究发现,可基于含有名义松弛应变的鼓泡分析模型获得处于粘附边界条件下的石墨烯弹性模量．     

Permeability of Porous Media from Simulated NMR Response

Nuclear Magnetic Resonance (NMR) is an increasingly popular well-logging tool in petroleum industry because it is the only tool that attempts to estimate formation permeability. In this paper, spatially correlated porous media are generated. Permeabilities of these media are computed by the lattice Boltzmann method. NMR relaxation responses are simulated by a random walk technique and formation factors are computed by solving a Laplacian equation. The testing of commonly used NMR permeability correlations shows that three conditions should be met for the validity of these correlations. The surface relaxivity should not vary significantly. The formation factor should depend only on porosity. And the characteristic pore body radius should be proportional to the characteristic throat radius. The correlations are improved by including surface relaxivity and formation factor.     

Revisiting the Drainage Relative Permeability Measurement by Centrifuge Method Using a Forward–backward Modeling Scheme

Measurement of drainage relative permeability by the centrifuge method was first introduced by Hagoort (SPE J. 29(3):139–150, 1980). It has been shown that capillary end effects can cause error in the measurement of relative permeability if a minimum rotational speed is not honoured. To determine the minimum rotational speed that makes the capillary end effect negligible, ω _min, we propose that the value of capillary-gravity number, N _cg, should be of the order of 10⁻² or smaller. This conclusion is based on the use a Forward–backward scheme consisting of a forward numerical simulator developed for centrifuge experiments and applying Hagoort’s method as a backward model. The article presents the use of this Forward–backward scheme as a powerful tool for error analysis such as determining the impact of capillary end effects. By using this loop, we first determine ω _min for specific core and fluid properties. Later, we generalize the ω _min calculations by using the definition of N _cg as a “rule of thumb” for designing relative permeability experiments by centrifuge method. We also demonstrate another use of this loop for controlling the quality of the experimental data.     

离心机水下爆炸缩比实验原理及数值研究

对离心机水下爆炸缩比实验方法进行探究,对离心机水下爆炸缩比实验的相似理论进行了推导,通过数值计算分析,探究了原模型、离心机缩比实验及常规缩比实验的冲击波载荷、气泡载荷以及气泡动力学行为。结果表明:常规缩比实验不能对气泡行为及垂直方向的近场载荷进行准确的预报,若要保证远场气泡脉冲峰值误差小于10%,则爆距需大于9.5倍气泡最大半径。而离心机缩比实验能够对原模型进行准确的预报,以小当量装药模拟大当量装药水下爆炸整个物理过程,且冲击波和气泡两个阶段完全相似。同时,水深也可以进行几何缩比,克服了常规缩比方法的缺陷。     

Evaluation of the High-Speed Drilling Technique for the Incremental Hole-Drilling Method

The incremental hole-drilling method is frequently used for residual stress depth distribution analyses, due to its fast and economical experimental execution. Depending on the planned use of the component, the drilled hole that is made to measure the residual stress can often be repaired or ignored if it does not affect the intended use of the part. Nevertheless an important experimental issue and assumption is the introduction of an ideal cylindrical hole into the component without additional plastic deformation. Although high-speed drilling is well established the consequences of the resulting hole geometries compared to ideal assumptions are not well known. Therefore, a detailed comparison between different bits and drilling techniques was carried out and is discussed in this paper in order to detect the best experimental conditions and to find out reasons especially for the lack of accuracy of the hole-drilling method for the first increments close to the specimens surface. It comes out that the orbital drilling with common used six-blade bits results in the best compromise of an ideal cylindrical hole and centricity to the center of the strain gage rosette. In the case of conventional drilling the hole geometry differs from the ideal one if six-blade bits were used due to the influence of chamfers at the cutting edges and a non 180° plane end face and also in the case of a two-blade bit due to a non 180° plane end face and the tendency to more eccentric holes. Diamond bits cannot be recommended under all tested conditions due to their geometrical undefined shape.     

An improved proximal-based decomposition method for structured monotone variational inequalities

The proximal-based decomposition method was originally proposed by Chen and TebouUe(Math.Programming,1994,64:81-101 for solving convex minimization problems.This paper extends it to solving monotone variational inequalities associated with separable structures with the improvements that the restrictive assumptions on the involved parameters are much relaxed,and thus makes it practical to solve the subprob- lems easily.Without additional assumptions,global convergence of the new method is proved under the same mild assumptions on the problem's data as the original method.     

有限厚度砂床对波浪载荷的响应

本文采用水-土两相介质混合物的连续介质力学理论分析了有限厚度砂床对波浪载荷的响应。土床看作饱和孔隙弹性介质,用Biot理论来描述流动和变形的耦合效应,波浪用线性水波描述。在上述假设下得到了描述土床对波浪载荷响应的基本方程。用解沂-数值方法给出了土床中位移、应力和孔隙水压力的分布并将理沦计算结果与波浪-砂床模型试验的实验资料进行了比较。文章还对影响土床对波浪响应的参量特性进行了分析和讨论。根据参量研究、理论计算与实验资料比较的结果,可以得出结论:本文所提供的理论模型和计算方法能用来估算海床对波浪载荷的影响。     

Modeling the interaction of solitary waves and semi-circular breakwaters by using unsteady reynolds equations

A vertical 2 -D numerical wave model was developed based on unsteady Reynolds equations. In this model, the k-epsilon models were used to close the Reynolds equations, and volume of fluid( VOF) method was used to reconstruct the free surface. The model was verified by experimental data. Then the model was used to simulate solitary wave interaction with submerged, alternative submerged and emerged semi-circular breakwaters. The process of velocity field, pressure field and the wave surface near the breakwaters was obtained. It is found that when the semi-circular breakwater is submerged, a large vortex will be generated at the bottom of the lee side wall of the breakwater ; when the still water depth is equal to the radius of the semi-circular breakwater, a pair of large vortices will be generated near the shoreward wall of the semi-circular breakwater due to wave impacting, but the velocity near the bottom of the lee side wall of the breakwater is always relatively small. When the semi-circular breakwater is emerged, and solitary wave cannot overtop it, the solitary wave surface will run up and down secondarily during reflecting from the breakwater. It can be further used to estate the diffusing and transportation of the contamination and transportation of suspended sediment.     

圆形月池流激振荡实验研究

采用基于经验模态分解(EMD)的本征模态函数(IMF)分析方法和对比研究的实验方 法,实验研究了圆形月池在均匀流条件下的流激振荡特性. 通过实验研究发现,尽管腔内的 流体在不同来流的条件下运动趋势有所不同,但归纳起来对于月池结构,其内部存在两类振 荡源,一类是腔内流体的固有振荡,该频率与腔体结构形式、尺寸、腔内流体深度有关,与 来流无关;另一类则是流体流经腔口时产生的流体动力振荡,该频率与来流特性、速度有关. 当二者频率相近时将会激起腔内流体的共振,即会有``活塞(piston)'现象产生. 实验中,还在腔体侧壁上布置了压力传感器,用来分析腔体侧壁受到的流体压力特性及 其变化趋势.