不同采深煤(岩)体岩爆过程模拟分析

为了研究不同采深条件下诱发的岩体变形、岩爆、凸出和塌落特征,对采深120m~820m,间隔100m的8种工况开采后岩体破坏进行模拟。结合能量守恒理论和ΔU=Ue-U0来确定岩爆后由弹性势能转化为动能的ΔU。使用三维岩体爆破颗粒流模型将ΔU按照一定规则转化为岩爆飞石动能。模拟了各工况下开采后岩体变化情况,结果表明,采深为120m,220m和320m三种工况下不发生岩爆;420m开始发生岩爆;520m和620m在发生岩爆的同时也伴随开采面岩体凸出;720m和820m时具有岩爆、凸出和塌落现象。同时总结了岩爆特点,特别是提出岩爆是岩体系统为了保持自身能量平衡而向系统之外释放能量的过程。     

高轴压和围压共同作用下受频繁冲击时含铜蛇纹岩能量演化规律

探讨高轴压和围压共同作用下频繁冲击扰动试验过程中伴随主要能量的种类,并推演冲击扰动前后弹性能、塑性能等能量的计算公式;采用预加载围压、高轴压、0.5 MPa冲击气压模拟深部岩体承受的水平应力、垂直高应力及爆破开挖扰动的影响开展动力学试验,并基于试验结果分析含铜蛇纹岩的动力学特征及能量演化规律。研究结果表明:含铜蛇纹岩能承受的扰动冲击次数随轴压增大而减小,随围压增大而增大,且动态峰值应力随扰动冲击次数增加而减小;随扰动冲击次数的增加,岩样伴随的弹性能先增大后趋于减小,伴随的塑性能呈增大的趋势发展,反射能和入射能的比值与透射能和入射能比值的变化规律相反,前者呈增大趋势,后者呈减小趋势;单位体积吸(释)能随扰动冲击次数的增加呈下凸曲线趋势变化,其均值随围压增大先减小后增大,随轴压增大而减小。     

弱围压与垂直冲击强扰动下块系岩体超低摩擦效应试验研究

随开采深度增加,深部岩体结构趋于破碎,临近工作面待开采岩体受弱围压作用,遇冲击载荷强扰动时,易诱发超低摩擦型冲击地压。采用自主研制的弱围压块系岩体超低摩擦模拟试验装置,以5个上下叠加花岗岩块体模拟深部临近工作面破碎岩体,通过螺栓加载方式对块系岩体施加弱围压作用、垂直方向施加冲击载荷作用模拟强扰动。以垂直加速度差值变化作为超低摩擦效应强度特征参数,分析得到了冲击载荷强度、围压对块系岩体超低摩擦效应影响规律。研究结果表明:垂直冲击载荷作用下,块系岩体振动分为受迫振动和自由振动两个阶段,随冲击载荷增大,块体垂直加速度差值峰值增大,垂直加速度差值衰减时间延长,此时超低摩擦效应强度和持续时间均显著增加;围压与冲击载荷共同作用下,存在围压临界值使得超低摩擦效应强度达到最大;随围压增加,超低摩擦效应最大强度发生时刻提前,当试验围压达到最大值时,超低摩擦效应最大强度发生时刻趋于一致。     

高瓦斯煤层冲击地压发生条件与影响因素

针对高瓦斯煤层冲击地压问题,用解析方法得到冲击地压发生条件,分析了主要影响因素对满足冲击地压发生条件的临界塑性区半径和临界应力的影响规律.结合五龙矿开采实际情况对影响高瓦斯煤层冲击地压的煤的模量比、煤层瓦斯孔隙压力、支护应力和内摩擦角4个因素做了对比分析.研究发现:高瓦斯煤层在巷道掘进面附近由于存在开挖面空间效应,掘进面前方尚未开挖的煤体对巷道变形起到了限制作用,减少了冲击地压的发生,随着掘进面向前推进,后方一定距离范围内的巷道支护应力增大.随着瓦斯解吸渗流的进行,巷道壁处孔隙压力降低,巷道冲击地压危险性明显提高,此时提高支护应力,冲击危险性有所降低.高瓦斯煤层巷道发生冲击地压的临界塑性区半径和临界应力随模量比、瓦斯孔隙压力的增大而快速减小,随支护应力的增大而增大,临界塑性区半径随内摩擦角的增大而增大,临界应力与内摩擦角不是单调函数关系,存在一个极小值点,当内摩擦角小于此极小值时,临界应力随内摩擦角增大而减小;当内摩擦角大于此极小值时,临界应力随内摩擦角增大而增大.     

冲击速度和轴向静载对红砂岩破碎及能耗的影响

地下岩体工程爆破开挖中,距爆源不同距离处岩体承受的地应力和动载荷大小不同,从动载荷的角度表征岩石动态破坏结果与工程实际更吻合。为研究动载荷和地应力大小对岩体破碎和能量耗散特性的影响,利用动静组合加载试验装置,分别设置7个冲击速度和轴向静应力等级,对红砂岩试件进行冲击试验。根据试件的破碎状况,分析不同静应力工况下冲击速度对岩石破坏模式和机理的影响。计算不同工况下的应力波能量值,研究冲击速度和轴向静应力对岩石能耗特性的影响。对破坏试件进行筛分试验,研究岩石破碎分形维数随冲击速度和轴向静应力的变化关系。结果表明,随着冲击速度的增大,试件的破坏程度逐渐加大。无轴压时岩石试件破坏后整体仍是一个圆柱体,属于张拉破坏;有轴压时岩石试件宏观破坏后呈沙漏状,属于拉剪破坏。岩石耗散能随冲击速度的升高呈二次函数关系递增;轴向静应力越高,递增幅度越小。随着冲击速度的升高,岩石分形维数由零逐渐增加;随着轴向静应力的升高,分形维数由零转为大于零的临界冲击速度先升高后降低。     

金坪引水隧洞围岩变形稳定性评价

金坪引水隧洞埋深较大,部分洞段岩体强度较低,洞室开挖后由于二次应力的作用围岩有可能产生变形,因此合理的评价隧洞围岩变形稳定性问题具有重要的工程意义。鉴于此,文章针对金坪引水隧洞围岩变形稳定性问题,对隧洞在大埋深环境下的围岩应力分布特征进行了数值模拟分析,利用与围岩的应变率和岩体抗压强度相关的两种评价方法,分析了可能发生围岩变形的部位和洞段,对引水隧洞围岩变形稳定性做出了综合评价。     

层状岩体力学特性模拟实验研究

对层状岩体变形特性和强度特性的正确认识,合理选取其变形和强度参数,是水电站等大型岩体工程论证与设计需要解决的关键问题.为此,利用模拟实验对层状岩体的变形特性和强度特性进行了研究,得到了模拟试样的变形模量和强度随试样所含节理数、轴向应力与节理面间的夹角和围压之间的变化关系.结果表明:当最大主应力与节理面间的夹角由0°增加...     

煤层自燃所致上覆露天矿复杂边坡破坏过程模拟与现象研究

为研究煤层自燃过程中,其上覆急倾斜且具有水平裂隙发育岩体组成的边坡稳定性的影响,及其内部破坏与外部形态之间的关系,使用基于颗粒流理论的PFC3D对煤层自燃过程进行了模拟,分析了煤层自燃对边坡稳定性造成的影响及原因,据此提出了模拟煤层自燃的颗粒流方法。对燃空区8种不同的工况进行了模拟研究,其结果表明:煤层自燃过程对边坡的影响可分为三个阶段:燃空深度在距坡脚60m时,坡脚处有岩体开裂现象,边坡外部轮廓变化不明显;120m时,边坡中下部岩体出现鼓凸,标志着边坡大规模变形过程;160m时,边坡坡面岩体鼓凸基本停止,内部岩体变形和运移趋于停止,边坡趋于稳定。据此可表明煤层自燃程度与边坡内部破坏和外部形态有一定的关系。     

层状反倾边坡变形特征及影响因素分析

借助金沙江某水电站左岸边坡岩体参数,利用离散元软件UDEC/3DEC对层状反倾边坡的主控影响因素(边坡高度、边坡坡度、层面倾角、层面力学参数、坡面与层面夹角等)进行多工况数值模拟分析,揭示了不同影响因素下层状反倾边坡倾倒变形的条件及破坏特征。计算结果表明各影响因素均对边坡倾倒变形有显著影响,边坡层面力学参数的影响尤为显著;边坡在坡角β40°,层面倾角γ50°时发生倾倒破坏的特征并不明显,当边坡坡角β40°,层面倾角γ50°时,随着各影响因素的不同组合与变化,边坡倾倒变形趋势显著增加,边坡的破坏模式主要表现为延性弯曲倾倒和脆性折断倾倒破坏;坡面与层面夹角的变化对边坡倾倒变形及边坡潜在破坏模式均有显著影响,当坡面与层面夹角Ψ在0°~90°时,随Ψ值的增大边坡潜在破坏模式由典型的弯折倾倒破坏模式向圆弧形滑动破坏模式转变。     

水电站地下厂房大型岩体洞室的抗爆性能

通过大量的数值模拟试验,以洞室岩体和混凝土衬砌结构的损伤为指标,研究了水电站地下厂房这类大型岩体洞室在强地表爆破荷载作用下,洞室埋深、围岩岩体强度和地应力对洞室抗爆性能的影响。数值计算中,洞室岩体和混凝土衬砌均采用弹塑性损伤本构模型,同时考虑了几何非线性效应。研究结果表明:对于水电站地下厂房这类高边墙洞室,浅埋深洞室的抗爆性能较差,深埋深洞室的抗爆性能较强;岩体强度越高,洞室的抗爆性能越强;当地应力侧压因数λ1时,随地应力侧压因数的增大,洞室的抗爆性能显著下降。 更多还原     

金沙江某水电站上下坝址岩体卸荷差异研究

油水乳化渗流是三元复合驱和热力采油过程中常见的现象,地层介质的微观 孔隙结构特征对乳状液流动有着重要影响. 现有描述乳状液渗流的理论模型都属于确定性方 法,只能反映出介质孔隙结构的体积平均效果. 当介质内部微观非均质性相比其尺寸不能被 忽略时,采用确定性方法描述会与实验结果存在偏差. 基于连续时间随机游走理论建立 了描述乳状液渗流的随机理论模型. 该模型引入反映液滴微观运动特征的跃迁时间和跃迁位 移两个概率分布函数来反映多孔介质微观非均质特征. 研究结果表明该模型能很好地刻画 实验曲线中出现的与介质尺度相关的拖尾现象,可作为更一般的过滤模型.     

Heating characteristics of blunt swept fin-induced shock wave turbulent boundary layer interaction

An experimental study was conducted on shock wave turbulent boundary layer interactions caused by a blunt swept fin-plate configuration at Mach numbers of 5.0, 7.8, 9.9 for a Reynolds number range of (1.0∼4.7)×10⁷/m. Detailed heat transfer and pressure distributions were measured at fin deflection angles of up to 30° for a sweepback angle of 67.6°. Surface oil flow patterns and liquid crystal thermograms as well as schlieren pictures of fin shock shape were taken. The study shows that the flow was separated at deflection of 10° and secondary separation were detected at deflection of ϑ≥20°. The heat transfer and pressure distributions on flat plate showed an extensive plateau region followed by a distinct dip and local peak close to the fin foot. Measurements of the plateau pressure and heat transfer were in good agreement with existing prediction methods, but pressure and heating peak measurements atM≥6 were significantly lower than predicted by the simple prediction techniques at lower Mach numbers. The project supported by China Academy of Launch Vehicle Technology     

Numerical analysis of the effects induced by normal faults and dip angles on rock bursts

The study of mining effects under the influences of a normal fault and its dip angle is significant for the prediction and prevention of rock bursts. Based on the geological conditions of panel 2301N in a coalmine, the evolution laws of the strata behaviors of the working face affected by a fault and the instability of the fault induced by mining operations with the working face of the footwall and hanging wall advancing towards a normal fault are studied using UDEC numerical simulation. The mechanism that induces rock burst is revealed, and the influence characteristics of the fault dip angle are analyzed. The results of the numerical simulation are verified by conducting a case study regarding the microseismic events. The results of this study serve as a reference for the prediction of rock bursts and their classification into hazardous areas under similar conditions.     

基于SPH方法粒子射流破岩数值模拟与实验研究

钻井液中加入体积分数为1%~3%的钢质粒子在钻头喷嘴处高速喷出冲击岩石,实现了粒子射流冲击和钻头机械联合破岩,有效提高了破岩效率。利用瞬态非线性动力学有限元模拟软件,基于光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法,考虑流体对粒子射流冲击的影响,建立了粒子射流冲击破岩的物理模型,获得了粒子射流参数对破岩体积的影响规律,进行了室内实验验证,验证了SPH方法的有效性。结果表明:粒子射流冲击岩石表面形成规则的V型冲击坑;同条件下粒子射流破岩体积是水射流破岩体积的2~4倍;随着粒子射流冲蚀时间的增加,粒子射流破岩体积不断增加,但破岩效率降低;粒子射流压力大于10 MPa后,粒子射流破岩效率迅速增大;喷射角度大于6°后,破岩效率迅速减小。     

Experimental investigation of inclined liquid water jet flow onto vertically located superhydrophobic surfaces

In this study, the behaviour of an inclined water jet, which is impinged onto hydrophobic and superhydrophobic surfaces, has been investigated experimentally. Water jet was impinged with different inclination angles (15°–45°) onto five different hydrophobic surfaces made of rough polymer, which were held vertically. The water contact angles on these surfaces were measured as 102°, 112°, 123°, 145° and 167° showing that the last surface was superhydrophobic. Two different nozzles with 1.75 and 4 mm in diameters were used to create the water jet. Water jet velocity was within the range of 0.5–5 m/s, thus the Weber number varied from 5 to 650 and Reynolds number from 500 to 8,000 during the experiments. Hydrophobic surfaces reflected the liquid jet depending on the surface contact angle, jet inclination angle and the Weber number. The variation of the reflection angle with the Weber number showed a maximum value for a constant jet angle. The maximum value of the reflection angle was nearly equal to half of the jet angle. It was determined that the viscous drag decreases as the contact angle of the hydrophobic surface increases. The drag force on the wall is reduced dramatically with superhydrophobic surfaces. The amount of reduction of the average shear stress on the wall was about 40%, when the contact angle of the surface was increased from 145° to 167°. The area of the spreading water layer decreased as the contact angle of the surface increased and as the jet inclination angle, Weber number and Reynolds number decreased.     

Experimental investigation of mixed convection in a rectangular duct with a heated plate in the middle of cross section

The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 10²–5.78 × 10⁶. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and pressure drops were independent of inclination angles.     

Supersonic leeside flow topology on delta wings revisited

The leeside vortex structures on delta wings with sharp leading edges were studied for supersonic flow at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences in Novosibirsk. The experiments were carried out with three wings with sweep angles of χ=68°, 73°, and 78° and parabolic profiles in the 0.6 × 0.6 m² test section of the blow-down wind tunnel T-313 of the institute. The test conditions were varied from Mach numbers M=2 to 4, unit Reynolds numbers from Re _l=26 × 10⁶ to 56 × 10⁶ m⁻¹, and angles of attack from α=0° to 22°. The results of the investigations revealed that for certain flow conditions shocks are formed above, below, and between the primary vortices. The experimental data were accurate enough to detect the onset of secondary and tertiary separation as well as other boundaries. The various flow regimes discussed in the literature were extended in several cases. The major findings are reported. Received: 6 September 1999/Accepted: 24 January 2000     

Shock tunnel study of spiked aerodynamic bodies flying at hypersonic Mach numbers

A three-component accelerometer balance system is used to study the drag reduction effect of an aerodisc on large angle blunt cones flying at hypersonic Mach numbers. Measurements in a hypersonic shock tunnel at a freestream Mach number of 5.75 indicate more than 50% reduction in the drag coefficient for a 120° apex angle blunt cone with a forward facing aerospike having a flat faced aerodisc at moderate angles of attack. Enhancement of drag has been observed for higher angles of attack due to the impingement of the flow separation shock on the windward side of the cone. The flowfields around the large angle blunt cone with aerospike assembly flying at hypersonic Mach numbers are also simulated numerically using a commercial CFD code. The pressure and density levels on the model surface, which is under the aerodynamic shadow of the flat disc tipped spike, are found very low and a drag reduction of 64.34% has been deduced numerically.