Mechanical behaviours of bedded sandstone under hydromechanical coupling

The combination of the dipping effect and hydromechanical(H-M)coupling effect can easily lead to water inrush disasters in water-rich roadways with different dip angles in coal mines.Therefore,H-M coupling tests of bedded sandstones under identical osmotic pressure and various confining pressures were conducted.Then,the evolution curves of stress-strain,permeability and damage,macro-and mesoscopic failure characteristics were obtained.Subsequently,the mechanical behaviour was characterized,and finally the failure mechanism was revealed.The results showed that:(1)The failure of the sandstone with the bedding angle of 45°or 60°was the structure-dominant type,while that with the bedding angle of 0°,30°or 90°was the force-dominant type.(2)When the bedding angle was in the range of(0°,30°)or(45°,90°),the confining pressure played a dominant role in influencing the peak strength.However,withinβ∈(30°,45°),the bedding effect played a dominant role in the peak strength.(3)With the increase in bedding angle,the cohesion increased first,then decreased and finally increased,while the internal friction angle was the opposite.(4)When the bedding angle was 0°or 30°,the“water wedging”effect and the“bedding buckling”effect would lead to the forking or converging shear failure.When the bedding angle was 45°or 60°,the sliding friction effect would lead to the shear slipping failure.When the bedding angle was 90°,the combination of the“bedding buckling”effect and shear effect would lead to the mixed tension-shear failure.The above conclusions obtained are helpful for the prevention of water inrush disasters in water-rich roadways with different dips in coal mines.

Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling

This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.

分数阶转子-轴承耦合系统非线性动力学分析

为深入挖掘水轮发电机组转子-轴承系统的非线性耦合振动特性,将该系统的阻尼力从传统的固定整数阶扩展到灵活多变的分数阶范围。建立了含分数阶阻尼的转子与含分数阶的轴承在耦合作用下的动力学模型,分析了不同分数阶阶次对系统的影响,探讨了含分数阶阻尼转子与轴承的耦合模型在阶次对称系统和阶次非对称系统中的不同运动形态,给出了系统不同条件下的运动状态分布图,对比了碰摩故障在整数阶和分数阶条件下不同形态的动力特征,验证了所提出分数阶阻尼的优越性。结果表明,分数阶阻尼相比于整数阶阻尼具有非局部性、记忆性和适应非线性等新的动力学特征。

基于统计相关分析的雅砻江周家滑坡主控因素和变形机理研究

周家滑坡位于卡拉水电站上游,具有变形大、方量大、破坏迹象明显的特征,若出现滑坡失稳,可能将造成涌浪、堵江和水库淤积等灾害,威胁大坝施工期及运行期工程安全及环境安全.本文基于lasso-Random Forest(lasso-RF)、Spearman双变量相关性分析方法,依据滑坡现场原位监测数据,对周家滑坡进行了诱发因素相关性及变形破坏机理分析.结果表明:周家滑坡变形与降雨的相关性大于地震因素,变形的主要影响因素为降雨,且降雨对滑坡变形的影响具滞后性;滑坡B1区的表观位移与深部位移相关性较强,滑坡具有整体滑移特征,应当加强对B1区各指标的监测.

多级水力压裂应力阴影效应的数值分析

多级水力压裂作为储层改造的主要技术手段,广泛用于提高致密油气藏的气体产量。裂缝在扩展过程中的应力阴影效应对于有效连通储层的天然裂缝并形成有利于油、气体流动的复杂裂缝网络至关重要。本研究采用了自适应的有限元-离散元方法,通过改进网格自动细化和识别多个裂缝扩展模拟含天然裂缝储层的多级水力压裂。数值模型中考虑了水力裂缝、天然裂缝和微观孔隙结构的相互作用,整合了非线性的Carter滤失模型来描述多级压裂过程中压裂液的滤失效应。引入了理想平行板流的支撑剂运输方程,并采用了达西定律来分析裂缝网络中的流体渗透效应。通过比较无裂缝均质模型和天然裂缝模型的裂缝网络和流体流动,评估了天然裂缝对多级压裂裂缝行为和气体产量的影响。研究为确定和优化致密气藏中压裂簇间距提供了一种新的方法。

Experimental study and modeling of hydromechanical behavior of concrete fracture

In this study, the hydromechanical behavior of a concrete fracture under coupled compressive and shear stresses was investigated. A special experimental device was designed to create a planar fracture in a cylindrical sample and to carry out different kinds of hydromechanical tests on the fracture. Four series of laboratory tests were performed on an ordinary concrete sample. Hydrostatic compression tests were first conducted to characterize the normal compressibility of the fracture. In the second series, direct shear tests were conducted on the fracture under different normal stresses. The maximal shear stress of the fracture was determined as a function of the normal stress. In the third series, fluid flow tests were carried out in view of characterizing the overall hydraulic conductivity of the fracture as a function of its opening and closure. Shear tests with a constant fluid pressure were finally performed to investigate the influence of fluid pressure on the deformation behavior of concrete fractures. Based on the experimental investigation, an elastoplastic model is proposed. This model takes into account the nonlinear elastic behavior of a fracture under normal compression and the plastic deformation and failure due to shear stress. The model was coupled with the classical Darcy's law to describe the fluid flow along the fracture by considering the variation of permeability with fracture aperture. Numerical results agree with experimental data from various laboratory tests.

Formulations of a hydromechanical interface element

A hydromechanical interface element is proposed for the consideration of the hydraulic-mechanical coupling effect along the interface.The fully coupled governing equations and the relevant finite element formulations are derived in detail for the interface element.All the involved matrices are of the same form as those of a solid element,which makes the incorporation of the model into a finite element program straightforward.Three examples are then numerically simulated using the interface element.Reasonable results confirm the correctness of the proposed model and motivate its application in hydromechanical contact problems in the future.

Hydromechanical behavior of unsaturated expansive clay under repetitive loading

Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading(RLU)conditions.Two series of onedimensional(1D)oedometer tests were conducted under controlled matric suction up to 1500 kPa using the axis translation technique(Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading(NRLU)cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strainε_(a)(s),axial swell pressure ss(s),compression index C_(c)(s),and swell index C_(s)(s)with suction reduction.The estimated loadecollapse(LC)curves obtained from NRLU series(LCN)and RLU series(LCR)indicated increasing yield stress sy(s)with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_(c)(s)at the same level of suction,whereas swell index C_(s)(s)seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LCR curve).

Hydromechanical behaviors of andesite under different stress states during fluid injection

Water reinjection into the formation is an indispensable operation in many energy engineering practices.This operation involves a complex hydromechanical(HM)coupling process and sometimes even causes unpredictable disasters,such as induced seismicity.It is acknowledged that the relative magnitude and direction of the principal stresses significantly influence the HM behaviors of rocks during injection.However,due to the limitations of current testing techniques,it is still difficult to comprehensively conduct laboratory injection tests under various stress conditions,such as in triaxial extension stress states.To this end,a numerical study of HM changes in rocks during injection under different stress states is conducted.In this model,the saturated rock is first loaded to the target stress state under drainage conditions,and then the stress state is maintained and water is injected from the top to simulate the formation injection operation.Particular attention is given to the difference in HM changes under triaxial compression and extension stresses.This includes the differences in the pore pressure propagation,mean effective stress,volumetric strain,and stress-induced permeability.The numerical results demonstrate that the differential stress will significantly affect the HM behaviors of rocks,but the degree of influence is different under the two triaxial stress states.The HM changes caused by the triaxial compression stress states are generally greater than those of extension,but the differences decrease with increasing differential stress,indicating that the increase in the differential stress will weaken the impact of the stress state on the HM response.In addition,the shear failure potential of fracture planes with various inclination angles is analyzed and summarized under different stress states.It is recommended that engineers could design suitable injection schemes according to different tectonic stress fields versus fault occurrence to reduce the risk of injection-induced seismicity.

钛/铁复合板平底球形薄壁件充液拉深工艺研究

目的选用充液拉深先进成形技术制备钛/铁复合板平底球形薄壁件,并研究其充液拉深变形行为,以解决传统拉深工艺制备平底球形薄壁件极易产生褶皱的问题。方法对钛/铁复合板平底球形薄壁件在不同液压力、压边间隙及凸模与板料间摩擦因数等工艺参数下的充液拉深过程进行数值模拟。对数值模拟结果进行分析,讨论工艺参数对零件成形性能的影响以及抑制起皱的机理。最后在不同拉深工艺下进行成形试验,制备钛/铁复合板平底球形薄壁件并与数值模拟结果进行对比。结果数值模拟和成形试验结果表明,传统拉深工艺制备的钛/铁复合板平底球形薄壁件出现了明显的褶皱,采用充液拉深工艺可以有效解决零件侧壁起皱的问题。增大液压力、减小压边间隙或增大凸模与板料间摩擦因数会导致零件减薄率的提高并降低零件侧壁起皱的风险。在压边间隙1.5 mm、液压力25 MPa的条件下,采用充液拉深工艺可以制备出侧壁无褶皱的平底球形薄壁件。结论通过充液拉深工艺可以有效解决钛/铁复合板平底球形薄壁件成形过程中起皱的问题。

流体力学视角下竞技游泳动力学研究进展

竞技游泳的动力学研究对游泳动作技术优化和运动表现提升具有重要意义,但一直以来受制于流体运动量化技术发展的限制。本研究旨在对流体力学视角下的竞技游泳动力学相关进展及发展历程进行系统梳理,深入探讨流体力学研究方法和技术进步对游泳动力学量化研究的贡献。该综述通过检索Web of Science、PubMed、Scopus、Google Scholar、中国知网(CNKI)等数据库,根据所检文献标题筛选相关文献,并对文献的出版信息、研究目的、方法、结果和结论进行提取、归纳、分析和总结。长久以来,游泳的流体力学分析受到流体运动量化技术和研究手段的制约,目前依然存在大量难以测量和预测的物理量。近年来,随着流体力学研究技术和设备的更新与发展,游泳推进的动力学机制已有多种假说被提出,包括升力和阻力机制假说、涡旋能量机制假说和轴向流(射流)机制假说。同时,泳者在游泳时所受到的各种作用力及作用力之间的相互作用也得到了更精确的量化。目前而言,游泳流体力学研究进展和人体运动生物力学研究前沿相比,仍有较大差距,两者结合深度依然不足。未来研究应聚焦流场可视化技术应用下的游泳流体力学量化分析,将流体力学研究前沿与人体运动生物力学实践相结合,科技助力泳者优化技术,提升运动表现。

新型椭圆固定阀塔板的流体力学性能

在现有固定阀塔板的基础上进行结构改进,开发一种新型抗堵塞塔板——椭圆固定阀塔板。采用空气-水为试验体系,在直径1200 mm的冷模塔内对椭圆固定阀塔板的流体力学性能进行试验研究,通过改变结构参数和操作参数测定了塔板压降、雾沫夹带及漏液率。结果表明:椭圆固定阀塔板的雾沫夹带率和漏液率较低,压降较高。从整体上相较筛孔塔板有明显改观,气相负荷性能表现更好,综合性能更优异。同时为了优化塔板结构设计,对椭圆固定阀塔板两相流场进行了计算流体力学(CFD)分析,进一步提升了塔板性能,拓宽椭圆固定阀塔板在石化领域的应用前景。

新型聚光玻璃幕墙动力学分析

为了利用照射到玻璃幕墙上的太阳能,采用聚甲基丙烯酸甲酯设计了一种新型聚光器,用聚甲基丙烯酸甲酯代替玻璃幕墙中的玻璃成分。为验证其可行性,建立了有限元模型,并通过仿真和现场实测验证了仿真数据的可信度。考虑玻璃幕墙的工作环境,对其进行流体力学分析,风速设置为18 m/s,施加风荷载后光效率损失变为0.2%。同时,对聚光引起的热变形也进行了分析,发现玻璃幕墙在长时间工作时,热变形会导致光学效率损失变为0.1%。最后,对外部激励振动引起的结构变化进行了谐响应分析,为结构优化提供了建议。

Assessments of the effects of various fracture surface morphology on single fracture flow: A review

Natural rock joint permeability deviates from the classic fluid flow governing equations due to the inher-ent fracture surface roughness(i.e.,contact points,spatial correlation,matching,varying aperture,iso-lated voids,infilling material,tortuosity and channellings)and engineering disturbance such as excavations.To improve the accuracy of fracture permeability evaluation,many efforts have been made in analytical,experimental,and numerical methods.This study reviews the modified mathematical gov-erning equations of fluid flow and classifies them based on different influencing factors,such as friction factor,aperture,tortuosity,inertia,and various in situ stress effects.Various experimental and simulation techniques for the coupled normal-and shear-stress flow problems were assessed,and their advantages and disadvantages were also analysed.Furthermore,different surface roughness descriptions and their impacts on mechanical and hydraulic behaviours were discussed,followed by the potential research directions for fracture flow problems.

Groundwater flow through fractured rocks and seepage control in geotechnical engineering: Theories and practices

Groundwater flow through fractured rocks has been recognized as an important issue in many geotechnical engineering practices.Several key aspects of fundamental mechanisms,numerical modeling and engineering applications of flow in fractured rocks are discussed.First,the microscopic mechanisms of fluid flow in fractured rocks,especially under the complex conditions of non-Darcian flow,multiphase flow,rock dissolution,and particle transport,have been revealed through a com-bined effort of visualized experiments and theoretical analysis.Then,laboratory and field methods of characterizing hydraulic properties(e.g.intrinsic permeability,inertial permeability,and unsaturated flow parameters)of fractured rocks in different flow regimes have been proposed.Subsequently,high-performance numerical simulation approaches for large-scale modeling of groundwater flow in frac-tured rocks and aquifers have been developed.Numerical procedures for optimization design of seepage control systems in various settings have also been proposed.Mechanisms of coupled hydro-mechanical processes and control of flow-induced deformation have been discussed.Finally,three case studies are presented to illustrate the applications of the improved theoretical understanding,characterization methods,modeling approaches,and seepage and deformation control strategies to geotechnical engi-neering projects.

一种可预测非饱和土壤中入渗和汇水的水力耦合模型

非饱和土壤在自然和工程实践中广泛存在,进一步了解非饱和多孔介质渗透过程中的水力耦合效应,对岩土工程和水文学界有着重要意义。本文提出一个非线性的完全水力耦合模型,用于控制可变形多孔介质中非饱和水的流动。该模型依赖于有限元(FE)求解器来计算受瞬态流作用下土壤中的水力耦合响应。使用已有的水力耦合解析解和积水入渗试验数据作为参考,对模型模拟结果的准确性进行验证。模拟结果表明,该模型在非稳定降雨条件和地表积水条件下能够准确模拟出降雨过程中的土壤入渗量和地表汇水量。此外,分别考虑吸力弹性模量、渗透模型的控制参数、饱和渗透系数以及边坡角度四个因素的变化而进行入渗和汇水过程的模拟结果进一步表明,土壤的膨胀性延迟了孔隙水压力的增长,而土壤的湿陷性则促进了孔隙水压力的增长;土壤孔径分布越粗糙,水力耦合效应越明显;土壤饱和渗透系数增大会导致更大的降雨入渗量和土体变形,并延缓地表开始积水的时间。边坡坡度对入渗过程的影响则存在争议,在本研究中,边坡坡度增大,土壤中的降雨入渗量减少,地表流失水增加,有待进一步探索。长远来看,在水力耦合系统中进一步考虑弹塑性耦合法则是更全面了解多孔介质中降雨入渗和地表汇水过程有用的方法。

煤矿大吨位防爆胶轮车液力传动系统匹配与参数优化

分析了10 t级大吨位防爆胶轮车液力机械传动防爆发动机和液力变矩器的工作特性,介绍了防爆发动机与液力变矩器的匹配计算方法与过程,提出了动力匹配的评价指标,在此基础上推导出了整车的牵引特性曲线与结果。最后以最大功率利用率为目标,对10 t级大吨位防爆车辆传动系统进行了参数优化,经优化,整车加速时间、最大爬坡度,百公里油耗等指标都得到了明显的改善。

长背鳍波动推进游动研究

以依靠长背鳍推进的“尼罗河魔鬼”为研究对象,对弓鳍目模式推进进行了研究。在“尼罗河魔鬼”巡航游动试验的基础上,通过对鱼体几何形态和柔性长背鳍波动的运动学分析,建立了“尼罗河魔鬼”长背鳍波动推进的简化运动学模型,并利用大摆幅伸长体理论分析了长背鳍波动推进的水动力学特性。计算表明:“尼罗河魔鬼”在0．728～0．985身长／s的速度范围内,长背鳍波动推进的水动力学效率介于81．664％-86．420％之间,表明长背鳍波动推进游动是一种适应水中环境的高效游动模式。

输电线路悬式复合绝缘子雨凇与轻雾凇覆冰形态和覆冰过程对比研究

覆冰形态是影响输电线路绝缘子闪络的重要因素之一。目前未见各类型覆冰形态差异及其原因的相关研究,绝缘子覆冰形态形成的微观物理过程研究较少。覆冰过程包括水滴撞击,捕获和冻结三个过程。对比研究了南方电网电线路灾害(覆冰)预警系统监测的悬式复合绝缘子雨凇、轻雾凇覆冰形态,通过Fluent仿真研究了两类覆冰形态的水滴与绝缘子撞击过程,计算了绝缘子伞裙上表面、伞裙边缘和杆径的水滴撞击数和撞击密度,通过微气象数据分析研究水滴冻结过程,从水滴撞击和冻结两个过程理论解释了雨凇和轻雾凇两类覆冰形态差异的原因。

新型催化精馏塔流体力学特性研究

提出了一种新型的催化剂散装式催化精馏塔结构，并开发了两种新型的塔板。实验表明，这种新型催化精馏塔结构，催化剂装卸方便，不易泄漏。两种与其相适应的新型塔板效率高，压降小，特别适用于板间距较大的场合，具有较高的推广应用价值。