挤压边墙对面板堆石坝结构性态的影响分析

为深入了解挤压边墙施工对面板及堆石体应力和变形的影响,以柬埔寨某混凝土面板堆石坝为例,采用三维非线性有限元法建立了坝体三维有限元模型,对比分析了采用传统施工法与挤压边墙施工法时大坝应力和变形的变化规律,研究了挤压边墙对堆石体和面板应力和变形的影响。结果表明,正常蓄水位工况下采用挤压边墙施工对堆石体的应力和变形影响不明显;混凝土面板的顺坡向压应力减少约400kPa,拉应力区明显减小,拉应力值减少约800kPa,面板挠度减少约20mm,可见面板的受力状态和挠度有较大改善。     

基于挤压边墙技术的面板堆石坝应力变形研究

为研究挤压边墙对面板堆石坝应力变形的影响,以某面板堆石坝为例,采用非线性有限元法建立二维、三维几何模型,对比有、无挤压边墙施工方法坝体的应力和变形规律,并分析了挤压边墙混凝土参数 、面板与挤压边墙接触填料参数的敏感性。结果表明,采用挤压边墙技术的该面板堆石坝坝体及面板应力变形均在合理范围内,并获得了挤压边墙混凝土参数取值、面板与挤压边墙接触填料参数取值及坝体与面板应力变形的规律。     

边墙高度与分缝长度对泄洪洞衬砌混凝土温度应力的影响

以溪洛渡水电站无压段泄洪洞为例,采用三维有限元法仿真计算了1 m厚衬砌混凝土的温度应力,分析了不同边墙高度与分缝长度下衬砌温度应力的变化发展规律。边墙高度和分缝长度变化对温度应力的影响明显,尺寸越大,温度应力越大,衬砌混凝土越易产生裂缝,边墙高度对应力的影响略小于分缝长度的影响,边墙高度与分缝长度的比值在1.22~1.25之间时断面较为合理,可为类似工程提供参考。     

碳酸盐岩酸压裂缝内净压力变化规律研究

酸化压裂是开发碳酸盐岩储层最常用的增产技术,而酸压裂缝内净压力是反映裂缝扩展特征、推断裂缝几何形态的重要参数。以水力压裂裂缝延伸机理为基础,基于酸岩反应理论,考虑酸岩反应导致的缝宽变化、CO₂气体膨胀、酸液滤失及岩石力学性质变化,结合PKN模型,建立酸压裂缝内的净压力计算模型并进行验证。研究分析酸压裂缝内净压力的影响因素及其规律,结果表明：距缝口距离越远,水力裂缝与酸压裂缝的缝宽均越小,酸液的溶蚀作用会使裂缝宽度增大。随着液体的滤失,离缝口越远液体越少,水力裂缝与酸压裂缝净压力逐渐减小,越靠近裂缝尖端净压力衰减越快。随着作用时间延长,酸压裂缝缝宽逐渐增大,前期随着大量CO₂生成,净压力迅速增大,随着酸液消耗与滤失增加,之后逐渐减小并趋于稳定。随着排量的增大,滤失增大,酸压裂缝缝宽及净压力均逐渐增大且增量越来越小。在黏度较小的情况下,滤失较大,净压力逐渐减小;在黏度较大的情况下,CO₂膨胀作用大于滤失作用,净压力逐渐增大。随着酸液浓度的增大,酸岩反应速率增大,反应生成CO₂增多,净压力逐渐增大。     

直喷汽油机多孔喷油器喷油过程的数值模拟

针对直喷汽油机多孔喷油器的喷油过程,基于通用计算流体力学三维数值模拟软件Star-CD,建立了一种燃油复合破碎模型.其中,一次雾化采用Huh-Gosman模型与KH模型竞争的方法进行模拟;分裂长度之后的二次破碎采用RT模型与一次雾化机理竞争的方法进行模拟.应用该模型,对定容弹内多孔喷油器在不同喷射压力和背压下的喷油过程进行了研究.结果表明,在喷油初期以及喷口附近,喷口内部产生的湍流对燃油雾化破碎起主导作用,此后喷口湍流的作用逐渐被气动力因素所取代.在喷射压力一定时,背压越大,以破碎液滴数计量的破碎强度越低,由气动力诱发的破碎出现越早、强度越高.在背压一定时,喷射压力越高,以破碎液滴数计量的破碎强度越高,强度的增加程度与喷油时的背压有关,由气动力诱发的破碎也随喷射压力的提高出现得更早、强度更高.     

强度等级对混凝土双K断裂参数的影响

将线弹性断裂理论与虚拟裂缝模型相结合,利用三点弯曲梁试件在试验中测得了最大荷载、裂缝口张开位移等参数,并据此计算了尺寸为1 100mm×300mm×300mm的3组不同强度等级混凝土试件的起裂荷载、临界有效裂缝长度、起裂断裂韧度、失稳断裂韧度(即双K断裂参数)。结果表明,起裂荷载、最大荷载、起裂断裂韧度、失稳断裂韧度均随试件强度等级的增大而增大,且起裂荷载占失稳荷载的比重亦随试件强度等级的增大而增大,试件从起裂到破坏持续时间随强度等级的增大而变短。起裂韧度与失稳韧度的比值小于起裂荷载与最大荷载的比值。试件设计强度等级越大,临界有效裂缝长度值越小,延续越差,脆性越大,由起裂到失稳的时间亦越短。     

围压影响堆石料剪切带的颗粒流模拟

为分析围压对堆石料剪切带的影响,基于颗粒流理论,构造三种不同形态的颗粒簇,建立了堆石料颗粒流模型。通过颗粒流数值模型双轴试验,研究了围压对堆石料剪切带结构的影响。结果表明,试样剪切带呈非对称X形分布,剪切带内颗粒旋转幅度随着围压的增加而增大,剪切带X形轮廓更加清晰。围压对试样颗粒位移影响较大,随着围压增大,颗粒位移不断增大,颗粒位移呈现出的X形剪切带逐渐消退。试样颗粒簇破碎过程与其宏观应力发展同步,剪切带内的颗粒比剪切带外的颗粒更易发生破碎。随着围压的增大,对试样内部颗粒的约束越强,发生局部破坏范围越小,导致试样内部X形剪切带的宽度逐渐变小。研究成果可为工程实践提供指导。     

水布垭堆石坝混凝土面板施工技术创新

针对水布垭堆石坝的混凝土面板具有长度大、长宽比大、厚度较薄的结构特点,在面板施工过程中,通过堆石体施工期沉降变形控制、挤压边墙原材料与结构形式改进、混凝土面板浇筑施工三方面的技术创新与应用,攻克了高面板坝混凝土施工的重大技术难题,有效确保了水布垭堆石坝混凝土面板的各项性能,为坝体的稳定安全运行提供了保障,可供借鏊.     

挤压式混凝土边墙施工及预算简析

挤压式混凝土边墙是混凝土面板堆石坝上游坡面固坡施工的一种新型工艺,本文通 过与传统施工工艺的比较,边墙典型断面及混凝土配合比的应用,新型施工方法的实施并结合 预算,使我们对挤压混凝土边墙有了进一步的了解。     

干湿循环对土体级配分形特性影响分析

为分析粗粒土受水体干湿循环作用时颗粒级配演化规律,采用颗粒筛分试验统计干湿循环作用后土体颗粒粒径分布,引入颗粒质量-粒径分形模型计算粒径分形曲线(GFC)及分形维数(D),揭示了D随围压及干湿循环次数变化的规律,量化了干湿循环作用对粗粒土D的影响,并建立了计算方程。结果表明,等效替代缩尺法对GFC及D影响较小;制样及筛分过程导致D增大0.63%,室内试验方法引起粗粒土颗粒破碎效应不可忽略。低围压条件下(围压小于0.60MPa),D随围压增大及干湿循环次数增多而增大,剪切作用及水体干湿循环作用加剧了粗粒土颗粒破碎效应。所建粗粒土D计算模型为评价干湿循环对涉水工程填筑土体级配劣化效应提供了依据。     

Experimental investigation of hydrogen jet fire mitigation by barrier walls

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. While reducing the extent of unacceptable consequences, the walls may introduce other hazards if not properly configured. This paper describes experiments carried out to characterize the effectiveness of different barrier wall configurations at reducing the hazards created by jet fires. The hazards that are evaluated are the generation of overpressure during ignition, the thermal radiation produced by the jet flame, and the effectiveness of the wall at deflecting the flame.The tests were conducted against a vertical wall (1-wall configuration), and two “3-wall” configurations that consisted of the same vertical wall with two side walls of the same dimensions angled at 135° and 90°. The hydrogen jet impinged on the center of the central wall in all cases. In terms of reducing the radiation heat flux behind the wall, the 1-wall configuration performed best followed by the 3-wall 135° configuration and the 3-wall 90°. The reduced shielding efficiency of the three-wall configurations was probably due to the additional confinement created by the side walls that limited the escape of hot gases to the sides of the wall and forced the hot gases to travel over the top of the wall.The 3-wall barrier with 135° side walls exhibited the best overall performance. Overpressures produced on the release side of the wall were similar to those produced in the 1-wall configuration. The attenuation of overpressure and impulse behind the wall was comparable to that of the three-wall configuration with 90° side walls. The 3-wall 135° configuration’s ability to shield the back side of the wall from the heat flux emitted from the jet flame was comparable to the 1-wall and better than the 3-wall 90° configuration. The ratio of peak overpressure (from in front of the wall and from behind the wall) showed that the 3-wall 135° configuration and the 3-wall 90° configuration had a similar effectiveness. In terms of the pressure mitigation, the 3-wall configurations performed significantly better than the 1-wall configuration.     

泥水盾构中泥浆劈裂地层的影响因素分析

鉴于泥水盾构技术中泥浆压力的合理控制能有效防止泥浆劈裂现象的发生,通过自制的泥浆劈裂装置和常规三轴仪模拟了泥浆劈裂地层的过程,研究了泥浆粘度、泥浆密度和地层围压对泥浆劈裂压力的影响。结果表明,当泥浆粘度在25~35s之间时,劈裂压力随粘度的增大呈近似线性增大,但超过该范围后,劈裂压力随粘度的继续增大而变化较小;当围压由50kPa增大至200kPa时,劈裂压力亦显著提高,但泥浆密度的影响则相对较小;通过与理论计算结果的对比,进一步验证了试验数据的可靠性,为泥浆压力的优化设计提供了参考依据。     

V形阶梯溢洪道水力学特性试验研究

针对V形阶梯溢洪道在大单宽流量下运行存在的问题,研究了坡比为1∶2的V形阶梯溢洪道在不同单宽流量时的流态、时均压强、消能率等水力学特性。试验结果表明,同一阶梯的不同位置,漩涡的强度不同,越靠近中轴线漩涡强度越小;阶梯水平面上的负压区集中于靠近边墙的凹角处,中轴线附近无负压;阶梯竖直面上,凹角处时均压强最大;消能率较高,且适应范围更大。     

含张开单裂隙砂岩破裂过程围压效应的数值模拟

为研究不同倾角裂隙砂岩试样在压缩过程中的围压效应,以室内单轴压缩试验结果标定岩体细观参数,采用改进刚体弹簧元法对不同倾角裂隙试样在不同围压下的破坏过程进行模拟。基于模拟结果,研究了围压对岩样强度、破坏模式及微裂纹发育特征的影响。结果表明,裂隙砂岩试样在压缩过程中具有明显的围压效应,相同裂隙倾角试样,其峰值强度、残余强度、弹性模量和变形模量均表现出随围压增加而增加的规律;不同围压作用下,不同倾角裂隙试样内部微裂纹演化规律相似,且其最终破坏形态均表现出以剪切破坏为主的破裂方式。     

Natural convection in a rectangular cavity with partially active side walls

A numerical study is performed to investigate the effect of aspect ratio on the natural convection of a fluid contained in a rectangular cavity with partially thermally active side walls. The active part of the left side wall is at a higher temperature than that of the right side wall. The top and bottom of the cavity and inactive part of the side walls are thermally insulated. Nine different relative positions of the active zones are considered. The equations are discretized by the control volume method with power law scheme and are solved numerically by iterative method together with a successive over relaxation (SOR) technique. The results are obtained for Grashof numbers between 10³ and 10⁵ and the effects of the aspect ratio on the flow and temperature fields and the rate of heat transfer from the walls of the enclosure are presented. The heat transfer rate is high for the bottom–top thermally active location while the heat transfer rate is poor in the top–bottom thermally active location. The heat transfer rate is found to increase with an increase in the aspect ratio.     

冲角和孔排间距对端壁气膜冷却效率的影响

燃气轮机在变工况运转时透平叶栅和级的特性对燃机总体性能影响极大,而叶栅端壁气膜冷却效率是关键因素。为了提高端壁气膜冷却效率,通过优化气膜孔间距排列的方法,在叶栅端壁20%、50%、90%轴向弦长处和距前缘-10%轴向弦长端壁处布置单排带复合角度的圆柱形气膜冷却孔,运用CFD(计算流体动力学)方法对冲角(10°、0°、-10°)在不同吹风比(1、1.5、2)条件下端壁气膜冷却效率进行对比分析。结果表明:采用气膜孔非等距排列方式能有效缓解因横向压力梯度变化引起的马蹄涡在压力侧的阻隔作用,压力侧冷却效率较高;高吹风比的冷却射流会出现抛射冷却,能有效抑制冷却射流脱离壁面,壁面平均冷却效率提高;主流正冲角有利于提高端壁吸力侧气膜冷却效率,压力侧变化不大。     

Effects of pulsation on separated flow and heat transfer in enlarged channel

Numerical results of three-dimensional separated flow and heat transfer in an enlarged rectangular channel are presented in this paper.The expansion ratio and aspect ratio of the channel are 2.0 and 16.0,respectively.Reynolds number of the flow is 200 and it is over the critical Reynolds number.Over the critical Reynolds number,the flow in the symmetric channel becomes asymmetric and deflects to one side of the walls.Effects of the pulsating fluctuation at the inlet upon the flow in the channel are investigated.It is clarified that the inlet flow with a pulsating fluctuation of Strouhal number 0.05 and 0.10 strongly affects on the flow in the channel,and heat transfer on the walls is enhanced,especially on the wall surface covered with long separation bubble.On the other hand,the pulsation of St=0.0125 oscillates the shear layer more weakly than that of St=0.05,0.10 and the enhancement of heat transfer is smaller,though some vortices are shed from the vicinity of the side wall near the reattachment region.The oscillation of the main flow calms down gradually as the Strouhal number of the pulsation increases over 0.10.The influence of pulsation of St=0.20 on the flow is restricted in the near downstream of the step,and heat transfer on the walls is almost similar to that of the steady flow in the channel.     

添加石蜡的相变水泥墙传热性能分析

利用ANSYS有限元分析软件,模拟添加石蜡的相变水泥墙体和普通水泥墙体的传热性能。通过模拟计算,给出普通水泥墙和相变水泥墙在一侧受到热流时另一侧的表面温度和热流的变化规律,并与实验测试结果进行比较;通过对比研究相变墙体和普通墙体的传热性能,分析相变墙的节能效果和可行性;同时求解相变墙体表面恒温时间随导热系数和相变潜热的变化规律。结果显示:数值模拟结果与实验测试结果较吻合,模拟方法可行;与普通墙体相比,相变墙体的温度变化平缓,热流传递出现滞后,热流量小,节能效果较明显;提高相变材料的导热系数和潜热能提高表面恒温时间,有利于相变材料在墙体中的储能效果。     

卸荷速率对含水砂岩卸荷力学特性的影响

通过三轴卸荷试验,系统分析了卸荷速率对卸荷过程中岩石力学特性的影响,研究了岩体的应力应变特征、卸载变形特征和破环特征,得到卸荷速率与变形模量及峰值围压的关系。结果表明,当卸荷速率小于0.02 MPa/s时,卸荷破坏变形模量随卸荷速率的增大呈非线性增长,破坏时的围压随卸荷速率增加呈非线性递减;当卸荷速率大于0.02 MPa/s时,变形模量呈线性增长,破坏时围压呈线性递减,但当卸荷速率增大到一定值时,变形模量将趋于稳定;不同卸荷速率与峰值围压的二次多项式拟合,相关系数都在0.90左右,说明采用二次多项式进行拟合是可行的。     

Entropy generation due to conjugate natural convection in enclosures bounded by vertical solid walls with different thicknesses

Entropy generation due to conjugate natural convection heat transfer and fluid flow has been studied inside an enclosure with bounded by two solid massive walls from vertical sides at different thicknesses. Enclosure is differentially heated from vertical walls and horizontal walls are adiabatic. Governing equations which are written in streamfunction-vorticity form solved by finite difference technique for the governing parameters as Rayleigh number, 10³ ≤ Ra ≤ 10⁶, length ratio of solid walls as ₁ (for left vertical wall) and ₂ (for right vertical wall) and thermal conductivity ratio of solid to fluid (k), 1 ≤ k ≤ 10. Entropy generation contours due to fluid friction and heat transfer irreversibility, isotherms, streamlines, Nusselt numbers and velocity profiles were obtained. It is found that entropy generation increases with increasing of thermal conductivity ratio and thicknesses of the walls. Entropy generation due to heat transfer is more significant than that of fluid flow irreversibility for all values of thickness of the solid vertical walls.