节理岩体边坡采动损伤与可靠性分析

为定量分析节理岩体边坡的采动损伤对边坡可靠性的影响,通过对大孤山铁矿下盘混合岩边坡进行现场勘测与模糊C均值聚类优化分析,确定了岩体2组优势节理的倾向、倾角、迹长和密度的随机分布参数。利用Hoek-Brown强度准则参数m和s与岩体质量分类指标GSI和扰动系数的关系,采用Monte-Carlo模拟抽样技术获得了节理岩体强度的随机分布参数。建立了节理岩体损伤与扰动系数D的联系,应用Kawarnoto损伤张量对采动损伤进行了数值分析,并根据Rosenblueth原理获得了扰动系数D以及反映时空效应和各向异性的岩体强度随机分布参数。基于此,定量分析了大孤山铁矿下盘混合岩节理岩体边坡采动损伤的时空变化特征及其对边坡稳定性的影响。结果表明,采场底标高从-87 m降至最终-450 m时,坡顶至-87 m水平同一高度滑弧可靠性指标相对下降7.7%,原因为采场下移导致节理岩体损伤加剧、强度降低所致,并且危险滑面逐渐向坡面偏移,与坡面近处岩体的损伤较大相关。     

低渗储层注水伤害研究

低渗透的宝浪油田是中偏强水敏储层,在进行了各种防膨措施后,注水压力仍不断上升,从25MPa上升至32MPa,依然欠注,即使频繁进行酸化、洗井等增注作业,效果也不理想。文章通过注入水水质分析和控含铁、含氧量进行的模拟地层水岩心流动驱替实验,认为注水造成储层堵塞的真正原因是注入水含铁含氧量偏高。注入水中含铁含氧,形成了Fe(OH)_2、Fe(OH)_3胶体,这类铁氧化合物,或包裹注入水中的固有颗粒,使颗粒粒径增大,形成"软颗粒",或产生新的颗粒,同注入水中的刚性颗粒相互作用,造成储层严重堵塞。即使少量的铁氧化合物,因低渗储层孔喉细小,其造成的堵塞也非常明显,在避免水敏的情况下,驱替120PV时伤害率达37.0%,而常规刚性颗粒堵塞,驱替180PV仅3.4%。所以,该低渗油藏注水开发,不但要防膨和控制注入水的颗粒粒径和颗粒浓度,尤为重要的是控制注入水的含铁、含氧量。     

纤维网络加砂压裂工艺技术先导性试验

纤维技术是近年国外发展的一项新技术,目前国内外水力压裂施工中主要通过在施工末端尾追一定量的纤维,起到防止支撑剂回流、加快压后返排的作用.而纤维在水力压裂中的作用更在于纤维的携砂作用,通过纤维的携砂可以降低聚合物浓度、降低裂缝的伤害,获得更好的裂缝铺置剖面和有效裂缝长度,同时可以降低管柱摩阻.目前该技术在国内还没有现场实施的相关介绍.川西某气藏DS101井储层为一口评价井,射孔敞井天然气仅0.34×104m3/d,针对该井区域构造上孔渗性差、水敏伤害大、地层压力低等特征,在DS101井开展了全程纤维网络加砂压裂工艺技术的先导性试验研究.现场顺利完成了60m3陶粒的压裂施工,配合660kg纤维、18m3液氮的全程加入以及压后的大油嘴快速返排,使得该井开井16h返排率达到79.8%,在油压17.25MPa、套压17.5MPa下获得3.9283×104m3/d的天然气测试产量,显示了纤维加砂压裂技术的良好应用前景.     

盐岩单轴压缩损伤演化及声发射特征研究

盐岩具有低渗透性、良好的蠕变特性和损伤恢复功能等,是油气储存的重要介质,但是盐穴储气库注采运行中,盐岩变形存在大变形的力学行为,影响储气库的安全性。利用MTS815岩石力学测试系统对不同类型盐岩进行单轴压缩实验,配合声发射监测系统对实验全过程进行声发射监测,展开了盐岩变形破坏过程的力学特性及声发射特征研究,并对其损伤演化特征进行探索。结果表明：(1)在盐岩样品中存在夹层可以明显提高其抗压强度,通过3组实验岩心平均抗压强度对比发现盐岩中存在夹层强度可提高20%,3类岩心实验过程中声发射事件在抗压强度的40%以下较为平静,超过40%时声发射事件激增;(2)通过对声发射事件空间位置研究可以得到其对应岩心的破坏演化过程：含泥盐岩最初在样品各处均发生微小裂隙,随着应力的增加微小裂隙扩展连通主要发生在泥质含量较高区域,并在该区域形成宏观裂隙;含夹层盐岩破坏首先发生在硬夹层,然后向盐岩层扩展,最终穿透盐岩层丧失承载能力;纯盐岩首先在样品中部发生损伤,然后向两端传递,但是破坏主要在样品中部聚集,最终形成宏观断裂面;(3)利用能量累计值建立损伤变量,将损伤变量的演化曲线分为四部分,并提出工程的安全预警阈...     

水中聚能战斗部毁伤双层圆柱壳的数值模拟与试验研究

为研究聚能战斗部的水下作用特性,基于光滑粒子流体动力学-有限元方法耦合算法,模拟了聚能战斗部对双层圆柱壳结构的毁伤过程。分析金属射流的形成和射流速度衰减规律,研究高速金属射流、强冲击波与气泡载荷联合作用下对双层圆柱壳结构的毁伤模式和毁伤特性,并进行了海上模型试验验证。数值模拟与试验结果吻合良好。研究表明：水中聚能战斗部对双层圆柱壳结构的破坏载荷主要有金属射流、冲击波载荷及气泡载荷3种,金属射流穿透力强,造成结构的局部小尺寸破口;冲击波载荷及气泡载荷作用面积大,引起结构的大面积破口及塑性凹陷。     

聚能战斗部在防空反导中的毁伤效能研究

为研究聚能战斗部在防空反导中的毁伤效能,介绍等效靶板论证与装药结构设计,给出数值计算方案,并通过AUTODYN软件对3种典型聚能侵彻体以不同角度侵彻等效运动靶板进行数值模拟.结果表明:聚能侵彻体和等效靶板的相对运动影响毁伤效能,存在开坑体积逆向叠加效应,同时聚能射流较易受等效靶板扰动,杆式射流毁伤效果更优,爆炸成型弹丸开口直径更大但穿深不足.     

多次冲击下泡沫铝动态压缩力学性能试验与本构模型研究

基于分离式霍普金森压杆装置对泡沫铝试样进行多次冲击加载试验,研究泡沫铝在中低应变率下的动态压缩力学性能。通过分析泡沫铝破坏形貌、透波率、应力-应变曲线以及能量吸收效率随冲击加载次数的变化规律,研究了损伤累积对材料动态力学性能以及吸能特性的影响机理。试验结果表明：随着冲击次数的增加,泡沫铝内部胞孔结构逐步崩溃压实,对应力波的衰减作用减弱,弹性极限应力及对应应变均有增强效应,且多次冲击下的损伤累积效应有助于提高理想吸能效率。基于试验所得应力-应变曲线,将损伤累积变量引入Sherwood-Frost方程,建立泡沫铝材料多次冲击下损伤累积本构模型,分析了形状函数参考曲线对应损伤累积能量与多次冲击试验损伤累积能量差值对本构模型准确性的影响,并进行了试验验证。     

Research on seasonal correlation of wavelet packet energy spectrum and temperature of Runyang Suspension Bridge

In order to establish an environmental-condition-normalized structural damage alarming method, the seasonal correlation analysis of wavelet packet energy spectrum (WPES) and temperature of Runyang Suspension Bridge is performed by means of the 236-day health monitoring data. The analysis results reveal that the measured WPES has remarkable seasonal correlation with the environmental temperature. The seasonal change of environmental temperature accounts for the variation of the damage alarming parameter I _p of the dominant frequency bands with an averaged variance of 200%. The statistical modeling technique using a 6th-order polynomial is adopted to formulate the correlation between the WPES and temperature, on the basis of which the abnormal changes of measured damage alarming parameter I _p are detected using the mean value control chart. It is found that the proposed method can effectively eliminate temperature complications from the time series of WPES and exhibit good capability for detecting the damage-induced 10% variances of the damage alarming parameter I _p . And the proposed WPES-based method is superior the modal frequency and hence is more suitable for online real-time damage alarming for long-span bridges. Supported by the National Natural Science Foundation of China (Grant Nos. 50725828, 50808041) and the Natural Science Foundation of Jiangsu Province (Grant No. BK2008312)     

Prevention of Internal Cracks in Forward Extrusion by Means of Counter Pressure: A Numerical Treatise

In the context of forward bulk extrusion, where product defects are frequently observed, the effect of counter pressure on damage accumulation materializing a Continuum Damage Mechanics (CDM) approach is presented. A Lemaitre variant damage model accounting for unilateral damage evolution coupled with a multiplicative finite plasticity is utilized for this purpose. After a presentation of the crack governing mechanism, it is demonstrated that application of counter pressure introduces a marked decrease in the central damage accumulation, which in turn increases the formability of the material through keeping the tensile triaxiality in tolerable limits. It is also shown that, for a crack involving process, through systematic increase of the counter pressure, the crack sizes diminish; and at a certain level of counter pressure chevron cracks can be completely avoided.     

3D-FE-Analysis of CT-specimens including viscoplastic material behavior and nonlocal damage

In order to describe the time-dependent inelastic behavior of steel structures up to failure, a material model is developed within the framework of thermodynamics considering viscoplastic material behavior, isotropic hardening, softening, and isotropic ductile damage. Since softening and damage lead to localization of deformations, the model is extended by a non-local implicit gradient formulation. An additional gradient equation is formulated for the local damage variable in order to achieve results independent of the finite-element discretization. The approach is verified by 3D-structural analysis of CT-specimens.