Three-Dimensional Convection in an Inclined Porous Layer Subjected to a Vertical Temperature Gradient

In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a liquid.The layer is subjected to a gravitational field and a strictly vertical temperature gradient.Typically,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)states.The boundary conditions considered in the present work allow a conductive state and are representative of typical geological applications.In an earlier work,we carried out a linear stability analysis of the conductive state.It was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal rolls.Moreover,a non-zero velocity component exists in z-direction.In the present work,threedimensional non-linear convection regimes are studied.The original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear theory.The number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity geometry.Calculations carried out at low supercriticalities show that a direct bifurcation takes place.With increasing supercriticality,no transitions to other convective regimes are detected.The situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.

A hybrid ventilation scheme applied to bidirectional excavation tunnel construction with a long inclined shaft

The breakage and bending of ducts result in a difficulty to cope with ventilation issues in bidirectional excavation tunnels with a long inclined shaft using a single ventilation method based on ducts.To discuss the hybrid ventilation system applied in bidirectional excavation tunnels with a long inclined shaft,this study has established a full-scale computational fluid dynamics model based on field tests,the Poly-Hexcore method,and the sliding mesh technique.The distribution of wind speed,temperature field,and CO in the tunnel are taken as indices to compare the ventilation efficiency of three ventilation systems(duct,duct-ventilation shaft,duct–ventilated shaft-axial fan).The results show that the hybrid ventilation scheme based on duct-ventilation shaft–axial fan performs the best among the three ventilation systems.Compared to the duct,the wind speed and cooling rate in the tunnel are enhanced by 7.5%–30.6%and 14.1%–17.7%,respectively,for the duct-vent shaft-axial fan condition,and the volume fractions of CO are reduced by 26.9%–73.9%.This contributes to the effective design of combined ventilation for bidirectional excavation tunnels with an inclined shaft,ultimately improving the air quality within the tunnel.

Preparation of Semisolid A356 Alloy Feedstock Cast via a Pipe Consisting of Partial Inclined and Partial Vertical Sections

In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock with ideal microstructures can be obtained at higher temperatures 645℃ and above by the proposed process, and the solid shell inside the pipe can be avoided at the optimum pouring temperature. Thus the process is attractive for industrial applications. The slanted angle of inclined section has an influence on the optimum pouring temperature. That is, the bigger the slanted angle, the higher the optimum pouring temperature, but accordingly, the greater the possibility of solid shell occurring inside the pipe. Therefore, small slanted angle should be considered first on the premise of ensuring a certain nucleation. The formation of semisolid feedstock is owed to the coactions of wall nucleation and stirring resulting from fluid flow. The inclined section greatly affects nucleation, and the vertical section has an important effect on both nucleation and generating stirring.

Two-phase slug flow in vertical and inclined tubes

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Cavitating Propeller Performance in Inclined Shaft Conditions with OpenFOAM:PPTC 2015 Test Case

In this paper,we present our analysis of the non-cavitating and cavitating unsteady performances of the Potsdam Propeller Test Case(PPTC)in oblique flow.For our calculations,we used the Reynolds-averaged Navier-Stokes equation(RANSE)solver from the open-source OpenFOAM libraries.We selected the homogeneous mixture approach to solve for multiphase flow with phase change,using the volume of fluid(VoF)approach to solve the multiphase flow and modeling the mass transfer between vapor and water with the Schnerr-Sauer model.Comparing the model results with the experimental measurements collected during the SecondWorkshop on Cavitation and Propeller Performance– SMP’15 enabled our assessment of the reliability of the open-source calculations.Comparisons with the numerical data collected during the workshop enabled further analysis of the reliability of different flow solvers from which we produced an overview of recommended guidelines(mesh arrangements and solver setups)for accurate numerical prediction even in off-design conditions.Lastly,we propose a number of calculations using the boundary element method developed at the University of Genoa for assessing the reliability of this dated but still widely adopted approach for design and optimization in the preliminary stages of very demanding test cases.

Theoretical Investigation on Vertical Additional Force on Shaft Lining in Special Stratum

The model of skaft lining under force is developed on the basis of the special stratum condition led to sbart cracking- The model is broken into 3 sub-questions to solve separately. According to the principle of superposition and strain compatibility, a second kind Fredholm integral equation is generated.A theoretical solution to vertical additional force on shaft lining is obtained by numerical method to the integral equation.

Prediction and safety analysis of additional vertical stress within a shaft wall in an extra-thick alluvium

An alluvium with a sandy aquifer at the bottom,but lacking an effective impermeable layer between the sandy aquifer and bedrock is referred to as a special alluvial stratum.Impacted by the drainage of the aquifer due to mining activities,a shaft wall in this special alluvial stratum will be subject to a downward load by an additional vertical force which must be taken into consideration in the design of the shaft wall.The complexity of interaction between shaft wall and the surrounding walls makes it extremely difficult to determine this additional vertical force.For a particular shaft wall in an extra-thick alluvium and assuming that the friction coefficient between shaft wall and stratum does not change with depth,an analysis of a numerical simulation of the stress within the shaft wall has been carried out.Growth and size of the additional vertical stress have been obtained,based on specific values of the friction coefficient,the modulus of elasticity of the drainage layer and the thickness of the drainage layer.Subsequently, the safety of shaft walls with different structural types was studied and a more suitable structural design,providing an important basis for the design of shaft walls,is promoted.

THE MINED NONLIEAR STUDY OF MEASURING METHOD AND CALCULATION ABOUT STRESS AND STRAIN IN THE VERTICAL SHAFT AND SURROUNDING ROCK

The damage of the overburden is a complex nonliear mechanical problem. To immediately master the stress state of the vertical shaft in process of the damage of overburden, and protect the shaft, in this paper, a series of new type of rock mass stress and strain compatible sensors are used. The vertical shaft wall mechanical parameter and surrounding mechanical parameter are calculated by the result of the measurement. A set of the calculation method of the vertical shaft and surrounding rock parameter are defined.

THE MEASUREMENT AND STUDY OF BLASTING VIBRATION AFFECTING IN SITU CAST CONCRETE LINING OF VERTICAL SHAFT

Vertical shaft is main form of drivage in deep mineral depoist. They also serve as the entrance into and the exit from the underground mine. The main problems in shaft and tunnel engineering is to solve the contradiction between drivage and lining. The measurement of blasting vibration affecting concrete lining strength of vertical shaft is carried out in experiment and theory in this paper.

Study on optimal design of vertical-shaft mechanical mixer based on numerical simulation of flow field

In the paper the three-dimensional flow fields are numerically simulated in the vertical-shaft mechanical mix tank of a water treatment plant by means of FLUENT software based on the method of Computational Fluid Dynamics (CFD). The influences of design parameters on flow fields and the mixing effect are analyzed. Firstly,the prediction capability of the turbulence model adopted in simulations is evaluated. And then,the mesh independence is checked up. Finally,the flow fields in various dimensionless blade diameters and dimensionless shaft spans are numerically simulated respectively. The results have shown that the numerical simulation method based on CFD is a feasible assistance for the optimal designs of mixers. Moreover,the optimal design of the blade diameter should take into account both the flow field and the power consumption. The optimization of the shaft span is to achieve a relatively even distribution of the flow field without any rupture. With the consideration of an optimal design,the dimensionless blade diameter and dimensionless shaft span should be 0.45 and 0.57 respectively in the case.

导、隔板倾斜对竖缝式鱼道水力特性的影响

为了明晰鱼道在建造以及组装时产生的误差对其内部水力特性的影响,针对导、隔板倾斜类误差展开研究.当前国内外竖缝式鱼道应用广泛,但在前期的鱼道工程现场勘测中,施工误差普遍存在于鱼道中,针对导、隔板倾斜类型的误差并依据现场对该误差情况的统计,采用三维数值模拟的方法,并通过物理模型试验对数学模型计算参数进行修正,在倾斜角度±15°的范围内每隔5°共测试了7种计算工况.结果表明:导、隔板倾斜(倾斜角度±15°内)后,鱼道池室内水流结构的二维特性所受影响有限且不足以造成不同规律;主流轨迹线范围增大,主流流速的衰减效果更加明显;目标导、隔板竖缝处的紊动能整体高于鱼类偏好紊动能上限,高总水力应变的分布范围明显增大,且有随着导、隔板倾斜幅度增大而增大的趋势;目标导、隔板下游竖缝平均流速有所升高.

前置宽体竖井进水流道水泵装置特性

为解决水泵机组设备布置与泵装置性能优化之间的矛盾,提出宽体竖井设计方法.基于三维湍流数值计算方法和熵产理论,比较了宽体竖井进水流道与2个常见的尖锥形竖井进水流道的水力特性.设计制作宽体竖井进水流道水泵装置模型,并试验测试5个叶片角下泵装置的能量特性、空化特性和飞逸特性.结果表明:宽体竖井方案与其他2个方案的内流场相似,在设计流量工况下流速均匀度均为95%左右,加权平均角度均大于89°;不同流量工况下,3种方案水力损失均接近,竖井前段熵产仅占后段的7.470%,竖井前段宽体型线对流道能量耗散无影响;当叶片角为0°时,水泵装置效率最高达79.19%;5个叶片角的泵装置临界空化余量均小于6.0 m;当叶片角为-6°时,扬程为2.36 m的最大飞逸转速为278.6 r/min;宽体竖井的水力特性与常规竖井相近,具有可同时满足设备布置与泵装置性能需求的特点.

袁大滩煤矿主斜井带式输送机提能改造设计

以袁大滩煤矿主斜井带式输送机为例,介绍了主斜井带式输送机提能改造的设计特点:采用低噪声节能托辊和低滚阻节能型输送带来降低运行阻力,采用工期最短的改造方案来减少矿井停产造成的经济损失。改造的思路和方案,可供相关煤矿和设计人员参考借鉴。

受限空间新型竖井提升机的布置

缙云抽蓄尾水调压井采用ME20+4.5T-12 m门式起重机作为提升系统,较传统使用矿用绞车作为提升系统来说,门式起重机具有安全可靠、施工效率高、操作简便、现场安全文明施工整体较好等优势,打开了竖井施工的局限性,文章重点介绍了新型门式竖井提升机在受限空间的布置方案,解决地下洞室门式起重机在空间上的制约。

双模式多支护深竖井敞开式TBM施工工法

由于传统的竖井施工方法存在井下作业人员多、工序复杂、施工环境极其恶劣等难以解决的问题,因此亟需在实际工程中探索以机械破岩为主的竖井非爆开挖方法,提高竖井施工的机械化、自动化水平,简化竖井的施工工序,改善井下施工人员的施工环境。文章从全断面竖井掘进机的设备组成和性能参数、分体始发和整体始发阶段的详细吊装及施工流程以及对现有出渣模式及换步技术的改进创新等方面,对全断面竖井掘进机在火山隧道竖井工程施工中的应用进行了全面的介绍,形成全断面竖井掘进机始发及掘进关键技术,为后续采用全断面竖井掘进机进行竖井施工提供参考。

抽水蓄能电站竖井下排渣掘进技术研究

介绍竖井下排渣掘进技术及其在竖井施工中的应用,该技术通过优化排渣环节,提高掘进效率,缩短工期。文章详细阐述了掘进原理、操作要点、井壁支护工艺以及特殊条件下的安全对策。实践案例显示,采用该技术可显著提升施工效率,同时,还强调团队协作和关注特殊条件下的安全问题,确保井筒质量与安全。

高铁长大隧道斜井进正洞挑顶施工技术

隧道斜井进正洞处相比正常掘进具有开挖断面渐变、跨度大、结构复杂等特点,且过程中初支结构需要多次的应力转化,施工难度大、安全风险高,易出现冒顶、掉块等问题。西渝高铁樊哙隧道斜井进正洞挑顶施工,对过渡段进行小导管注浆和异形钢拱架加强,先纵向、横向开挖导洞再纵向分三台阶开挖正洞,拱顶变形和围岩水平收敛符合控制要求。挑顶方案有效的控制了交叉段的变形,总体效益良好,施工方案科学合理。

斜井提升钢丝绳合理选型分析和应用

为提高矿山斜井提升钢丝绳使用寿命及系统的安全稳定性,需要合理选择钢丝绳。针对提升钢丝绳种类进行了研究,分析了钢丝绳在斜井提升系统中的受力情况,将丝径比纳入钢丝绳选型体系中,研究了一种结合安全系数、绳径比及丝径比的全新钢丝绳合理选型体系,表明了丝径比中钢丝绳最粗钢丝直径的计算方法。利用矿山实例进行验证,结果表明:在同等工况下,全新钢丝绳选型体系较原有选型体系选出的钢丝绳使用寿命高出约50%,安全系数高出约6%。全新钢丝绳选型体系更为合理可靠,对后续矿山斜井提升钢丝绳选型具有较好的指导意义。

Properties of New Mullite-SiC Bricks for CDQ Shafts

Currently the service life of CDQ shafts in China is mainly restricted by the properties of the inclined flue bricks.In this work,based on the systematic analysis of the damage mechanism of inclined flue refractories,high performance mullite-SiC bricks were developed.The bricks were produced by corundum,andalusite,SiC and other high purity raw materials.Metal silicon and alumina ultra micropowder were added to form dispersion multi-phase structure,fortifying the matrix and improving the microstructure.The products have excellent properties such as low porosity,high density,good wear resistance,high refractoriness under load,and good thermal shock resistance.The products can replace the ordinary mullite-SiC bricks and obtain a good service life.

Numerical Simulation and Reinforcing Technology Research on Collapse of Weak Interlayer Shaft

The three-level shaft of the mixed pit shaft of Yixin Mine,built in 1983,failed continuously due to the influence of geological structure and the effect of water,which formed a collapsed space with a length of 18m,a depth of 12m,and a height of 12m at the level of-255m and to the southwest end.The 54m pit shaft below the-258m elevation of the pit shaft was filled with collapsed rocks forming a large loose body.The comprehensive processing plan for falling grouting and anchoring was proposed according to the geological conditions of the vertical shaft of the mixed pit shaft,adopting three-dimensional numerical simulation software as well as calculating the mechanical state of the vertical pit shaft surrounding rocks and using 3 to 5 parameters of Williams-Warnke failure criterion.