A laboratory acoustic emission experiment and numerical simulation of rock fracture driven by a high-pressure fluid source

In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with fluid injection in the laboratory. Furthermore, we tested a number of numerical models using the FLAC;modeling software to find the best model to represent the experimental results. The high-speed multichannel acoustic emission（AE） waveform recording system used in this study made it possible to examine the total fracture process through detailed monitoring of AE hypocenters and seismic velocity.The experimental results show that injecting high-pressure oil into the rock sample can induce AE activity at very low stress levels and can dramatically reduce the strength of the rock. The results of the numerical simulations show that major experimental results, including the strength, the temporal and spatial patterns of the AE events, and the role of the fluid can be represented fairly well by a model involving（1） randomly distributed defect elements to model pre-existing cracks,（2） random modification of rock properties to represent inhomogeneity introduced by different mineral grains, and（3）macroscopic inhomogeneity. Our study, which incorporates laboratory experiments and numerical simulations, indicates that such an approach is helpful in finding a better model not only for simulating experimental results but also for upscaling purposes.

CFD Simulation and Experimental Study of a New Elastic Blade Wave Energy Converter

Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).

Comparison of numerical simulations and experiments in conical gas–solid spouted bed

Flow behavior of gas and particles in conical spouted beds is experimentally studied and simulated using the twofluid gas-solid model with the kinetic theory of granular flow.The bed pressure drop and fountain height are measured in a conical spouted bed of 100 mm I.D.at different gas velocities.The simulation results are compared with measurements of bed pressure drop and fountain height.The comparison shows that the drag coefficient model used in cylindrical beds under-predicted bed pressure drop and fountain height in conical spouted beds due to the partial weight of particles supported by the inclined side walls.It is found that the numerical results using the drag coefficient model proposed based on the conical spouted bed in this study are in good agreement with experimental data.The present study provides a useful basis for further works on the CFD simulation of conical spouted bed.

Experimental study on interaction between simulated sandstone and acidic fluid

In order to investigate the controlling mechanism of temperature, fluid and other factors on water-rock interaction in the diagenetic process, we performed a series of simulated experiments on the interaction between two kinds of fluids with different salinity and a composite mineral system （simulated sandstone）, which contains albite, K-feldspar and other minerals. The experimental results showed that acidity was the most important factor that affected the dissolution of minerals in the composite mineral system. The lower the pH value, the more easily the minerals dissolved. At the same pH value, the dissolution abilities of different acids for various mineral components were also different. Compared to hydrochloric acid （inorganic acid）, oxalic acid （organic acid） was more able to dissolve aluminosilicate minerals. However, the dissolution ability of oxalic acid for carbonate minerals was lower than that of hydrochloric acid. In the process of fluid-rock interaction, dissolution of feldspar was relatively complicated. Increase of temperature would accelerate the dissolution of feldspar. Under acidic conditions, albite had a higher dissolution rate than K-feldspar. K-feldspar could dissolve and convert into montmorillonite and kaolinite, while albite could dissolve and convert into kaolinite both at 40℃ and 80℃. Presence of organic acid, and decrease of pH value and water salinity were all favorable for the dissolution of feldspar, but weakened the ability to form clay minerals.

Study on the origin and rock-forming simulation experiments of aquamarine-bearing pegmatites of Ailaoshan,Yunnan,China

The Ailaoshan aquamarine-bearing pegmatites are associated with Proterozoic metamorphic rocks in the southern portion of the Ailaoshan fault-folded complex.The gem-bearing pegmatite mineralization zones of the region occur in areas generally consistent with the regional tectonic trend.The pegmatites are found in metamorphic rocks,migmatites and in the inner/outer contact zones of gneissoid granites. The Rb-Sr isochron drawn for the pegmatites is 26～31 Ma,(i.e.in Himalayan).The homogenization temperatures of melt and liquid inclusions in minerals vary from 185 to 920℃,which are comparable to the inclusions observed in banded migmatites and ptygmatic quartz veins in the surrounding metamorphic rocks. The mineralization fluids of the pegmatite were rich in HCO_3 and CO_2,and their compositional assemblages are comparable to metamorphic fluids.Results of H,O,C,Si etc.isotopic analyses and REE,and Be analyses indicates that the sources of mineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphic rocks. A pegmatite structure simulation experiment was conducted at high temperature and pressure(840℃and 1,500×105Pa.),with various metamorphic rock samples in a water-rich and volatile-rich environment.When the liquidus was reached,the temperature was gradually decreased at the rate of 5～10℃/day over a time period of three months.SEM energy-dispersive spectrum analyses were performed on the experimental products.A series of pegmatoid textures were observed including zonal texture,megacryst texture,drusy cavities,crystal druses,and vesicular texture along with more than ten types of minerals including plagioclase,microcline,quartz and biotite.Different metamorphic rock melts generated different mineral assemblages.Experiment results revealed that the partial melting of metamorphic rocks could form melts similar to pegmatite magmas. Based upon the geological characteristics,geochemistry,and pegmatite texture simulation experimental results,it is concluded that the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks.The petrogenetic model for the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis.

基于CFD的YJ17卷烟机风室流场分析与优化设计

目的针对ZJ17卷接机YJ17供丝系统中烟丝堵塞、竹节烟和烟支标偏大的现象进行改进。方法采用流体仿真分析软件Solidworks Simulation模拟分析、正交实验及试验验证的方法,设计优化YJ17供丝系统的风室装置,通过模拟仿真不同正压风入口形状、数量、位置对设备运行效率、产品质量的影响,找到三者最优的参数组合。模拟分析发现,在正压风入口形状为圆形,正压风入口数量为3个,正压风入口距离气室边缘的距离为15mm时,风室气流分布更均匀,同时烟丝在离开抛丝辊后受到的下吹风力最大,可使烟丝快速到达吸丝带。结果气室经改进后烟丝堵塞次数降低了39.3%,SD值(20支烟支质量标偏)降低了25%,有效提升了设备的运行效率和卷烟产品的质量。结论基于仿真及正交实验结果,优化了风速出风口位置和直径,气室的流场分析结果可为烟丝吸丝成型及风室结构优化提供一定技术支持。

井底流固耦合环境下PDC钻头切削齿冷却仿真实验

PDC钻头已成为开发深部资源的主体钻头,但在钻井过程中产生的热损伤是影响钻进效率及钻头寿命的重要因素之一。该文针对PDC钻头切削齿热损伤问题,开展基于不同影响因素的井底流固耦合环境下切削齿冷却仿真实验。建立了PDC钻头井底冷却流固耦合模型,结合实际钻井工况制定了数值仿真方案,根据仿真实验结果分析了井底流固耦合环境中不同影响因素下钻头切削齿的温度变化规律,并通过正交试验对钻头冷却效果与各影响因素间的敏感性进行了评价。切削齿冷却敏感因素从大到小依次为:钻井液排量>钻井机械参数、钻井液温度>地层温度。研究成果为探索井底工况下钻头破岩过程中切削齿热损伤问题和优化PDC钻头设计提供了理论依据。

盾构克泥效浆液成分与渗透扩散研究

盾构隧道近接既有结构施工中常采用克泥效工法辅助控制地层位移。克泥效浆液的流变和渗透扩散性能对盾壳外环向间隙的填充效果具有重要影响。基于克泥效浆液X射线衍射试验(X-ray diffraction, XRD)和黏度试验,研究浆液微观成分及流变性能。基于多孔介质多相流控制方程,建立砂土中克泥效浆液扩散数值模型,分析浆液配比、地层渗透系数和注浆压力对扩散性能的影响。结合宾汉姆流体砂土渗流公式,验证数值模型的可靠性。结果表明:克泥效浆液成分主要为石英、斜长石、伊利石、正长石,且随A液水粉比增加,斜长石含量增加,伊利石含量减小。克泥效浆液的塑性黏度与屈服强度随A液水粉比的减小而增大,宾汉姆模型对浆液流变曲线的拟合优度大于0.95。克泥效浆液在环向间隙中的填充扩散阶段约为25s,而后再向地层中发生渗透扩散,渗透扩散速度远小于填充扩散。随A液水粉比、地层渗透系数、注浆压力增加,克泥效在地层渗透距离均会增加。

FluidSIM在液压与气动控制仿真实验中的应用

采用基于FluidSIM软件的系统仿真技术,简化了液压与气动控制系统的设计和分析。介绍了最新版FluidSIM软件的功能特点,并分别通过电液比例控制系统的建模及仿真、气动步进顺控系统的建模及仿真两个实例,说明FluidSIM在现代液压与气动控制新技术中的应用方法和实现过程。仿真过程及结果表明,FluidSIM的运用有助于液压与气动控制系统的分析、设计和工程应用研究。

基于CFD的具有首翼的新型飞翔形式AUV升力和阻力估计:对阻力极曲线和推力估计的见解

To achieve hydrodynamic design excellence in Autonomous Underwater Vehicles(AUVs)largely depends on the accurate prediction of lift and drag forces.The study presents Computational Fluid Dynamics(CFD)-based lift and drag estimations of a novel torpedo-shaped flight-style AUV with bow-wings.The horizontal bow-wings are provided to accommodate the electromagnetic arrays used to perform the cable detection and tracking operations near the seabed.The hydrodynamic performance of the AUV due to addition of these horizontal bow-wings is required to be investigated,particularly at the initial design stage.Hence,CFD techniques are employed to compute the lift and drag forces observed by the flight-style AUV,maneuvering underwater at different angles of attack and varying speeds.The Reynolds-Averaged Navier-Stokes Equations(RANSE)closure is achieved by employing the modified k-ϵ model and Two-Scale Wall Function(2-SWF)approach is used for boundary layer treatment.Further,the study also highlights the unique mesh refinement and solution-adaptive meshing techniques to perform the CFD simulations in Solidworks Flow Simulation(SWFS)environment.The drag polar curve for flight-style AUV with and without bow-wings is generated using the computed lift and drag coefficients.The curve provided essential insights for achieving hydrodynamically efficient and optimized AUV design.From the drag polar curve,it is revealed that due to horizontal bow-wings,the flight-style AUV is capable to generate higher lift with less drag and thus,it gives better lift-to-drag ratio compared to the AUV without bow-wings.Moreover,simulated results of axial drag observed by the AUV have also been compared with free-running experimental results and are found in good agreement.

Experimental and Numerical Investigation of Local Scour Around Submarine Piggyback Pipeline Under Steady Current

As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.

Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.

TWO BIFURCATION TRANSITION PROCESSES IN FLOATING HALF ZONE CONVECTION OF LARGER PRANDTL NUMBER FLUID

Processes of the onset oscillation in the thermocapillary convection under the Earth's gravity are investigated by the numerical simulation and exper- iments in a floating half zone of large Prandtl number with different volume ratio. Both computational and experimental results show that the steady and axisymmetric convection turns to the oscillatory convection of m=l for the slender liquid bridge, and to the oscillatory convection before a steady and 3D asymmetric state for the case of a fat liquid bridge.It implies that,there are two critical Marangoni numbers related,respectively,to these two bifurcation transitions for the fat liquid bridge.The computational results agree with the results of ground-based experiments.

Numerical simulation of vortex-induced drag of elastic swimmer models

We present numerical simulations of simplified models for swimming organisms or robots, using chordwise flexible elastic plates. We focus on the tip vortices originating from three-dimensional effects due to the finite span of the plate. These effects play an important role when predicting the swimmer＇s cruising velocity, since they contribute significantly to the drag force. First we simulate swimmers with rectangular plates of different aspect ratios and compare the results with a recent experimental study. Then we consider plates with expanding and contracting shapes. We find the cruising velocity of the contracting swimmer to be higher than the rectangular one, which in turn is higher than the expanding one. We provide some evidence that this result is due to the tip vortices interacting differently with the swimmer.

核磁共振双等待时间测井储层流体识别仿真实验设计

针对核磁共振(NMR)测井教学理论性强、原理抽象复杂等特点,设计了基于MATLABGUI的NMR双等待时间(TW)测井储层流体识别仿真实验,设计的MATLAB GUI交互界面包含地层T2谱模型构建、流体极化及双TW回波数据正演和回波数据处理等模块。通过在仿真实验中输入不同参数,模拟得到的地层T2谱模型、长短TW回波数据和处理结果将实时显示在图形界面,并对实际NMR测井资料进行了处理。该仿真实验操作简单,能将NMR双TW测井储层流体识别过程及结果直观地展示给学生,增强学生对该流体识别方法的理解,提高NMR测井教学效果。

工程流体力学课程虚拟仿真实验

为使学生在工程流体力学课程实体实验前能熟悉实验操作流程,搭建了虚拟仿真实验平台。使用HTML5网页语言制作界面,学生通过点击相应控件完成虚拟仿真实验。为避免学生逃避或者应付,设置Apache Tomcat容器,通过Ajax技术将学生登录信息和操作过程作为发送请求发送到Java后台,实现后端监督记录功能,以此作为实体实验的准入依据。针对雷诺实验,介绍虚拟仿真实验平台的操作过程和效果,以提高学生进行实体实验的熟练程度,改善实验教学质量。

气吸双滚筒式棉花精量排种器的设计与试验

【目的】为提高气吸滚筒式排种器充种性能,降低负压风机能耗,设计了一种气吸双滚筒式排种器。【方法】理论分析排种过程中棉花种子的受力状态,利用Solidworks对排种器进行三维建模,运用流体仿真软件对3.8 mm孔径的滚筒进行内流场模拟,掌握内流场速度及压力变化的规律,对比有无内置滚筒结构对型孔处气体流速的影响。利用Design-expert 13.0软件设计了两因素五水平二次旋转正交组合试验方案,以负压和前进速度为试验因素,建立了漏播率、合格率和重播率等评价指标的响应曲面,进而对工作性能进行评价。【结果】通过优化回归方程得到最佳参数组合,并经台架试验验证。在负压为2.39 kPa、前进速度为4.55 km/h的条件下,排种器播种棉花种子的合格率为91.8%,漏播率为3.3%,重播率为4.9%。【结论】自行设计的排种器可满足棉花种子精量播种的农艺要求,显著降低风机能耗,为机械化播种提供技术性参考。

水下储气装置的水动力学特性分析

在复杂的海洋环境中,由于受到海流的影响,水下储气装置会发生疲劳破坏。针对这一问题,采用模型实验与数值模拟相结合的方法对水下储气装置的水动力学特性进行了研究。首先,选取气球状储气装置作为研究对象,依据相似原理设计了储气装置的缩尺模型,并对其进行了水动力学实验;然后,采用大涡模拟(LES)方法对储气装置进行了数值模拟,分析了其流场结构及受力特性;最后,通过对比数值模拟结果与实验结果,对数值模拟结果的可靠性进行了验证。研究结果表明:气球状储气装置的涡结构复杂、旋涡尺度丰富,并且装置后方存在明显的卡门涡街,0.4 m/s流速下平均阻力系数和升力系数分别稳定在0.09和0.04。该结果描述了气球状水下储气装置在复杂海洋环境中的水动力学特性,可以为储气装置的优化设计提供一定的理论依据。

涵道推进器近水面垂推工况推力损失机理研究

针对水空跨域航行器在水面垂直起飞时出现的推力损失问题,开展实验测试航行器150 mm直径涵道推进器在距离水面0.1~0.5 m高度垂直推进状态下的推力特性。为分析涵道推进器的近水面推力损失机理,采用多相流计算流体动力学(CFD)仿真对涵道推进器近水面垂直推进工况下的流场进行模拟。仿真发现,推进器尾流冲击水面形成的气水混合物被推进器吸入,使推进器周围空气流动进入不稳定的涡环状态。推进器近水面运转时与空气中同转速下相比产生了推力损失,随着近水面高度的增大,反弹气流的影响减弱,推力损失逐渐减小。

克拉苏构造带博孜段古隆起及盐层对盐下冲断带的控制

克拉苏构造带是库车坳陷油气勘探的主要区带。以克拉苏构造带博孜段三维地震资料为基础,进行一体化建模,明确盐下冲断带构造变形差异及古隆起、盐层分布特征;基于物理模拟实验,分析古隆起、盐层对盐下冲断带的控制作用。结果表明:研究区薄盐层分层作用差,断裂数少,规模大,易传递至盐上层;厚盐层易形成盐背斜和盐焊接等构造,盐下层多排逆冲断裂向盆地内部传递;古隆起发育区北翼断裂表现为倾角小、水平断距大和沿斜坡滑脱等特征,古隆起不发育区断裂表现为倾角陡、断距大且断裂数多的特征。古隆起发育区易形成滑脱冲断和盐背斜构造,古隆起不发育区易形成阶梯冲断和盐焊接构造;古隆起与盐层的双重叠加是影响盐下冲断带复杂变形的主要因素,古隆起限制冲断体系变形空间,盐层缓冲应力传递,起调节作用。该结果对研究区下一步天然气勘探开发具有指导意义。