基于八面体理论的岩石循环加-卸载本构模型及修正

探究岩石的受力特点及破坏特性是研究岩石地下工程安全性的关键,诸多学者都期望能在岩石本构模型的研究上取得突破性进展。在此背景下,提出了一种能够描述循环加-卸载条件下岩石的本构模型。首先,假设岩石的微元强度服从八面体剪应力理论并且微元破坏服从Weibull概率公式,将岩石本构中的损伤变量以及岩石微元强度表达式里包含的损伤因子进行本构变换,得到关于应力、应变等其他表现加-卸载下岩石损伤本构模型的参数,表示出岩石微元强度和损伤变量,再将得到的岩石微元强度和损伤变量代入所提出的岩石本构模型中,并进行等式变换得到一个函数表达式。通过将其与实验数据进行拟合对比分析,得出修正后的拟合参数,将其代入函数式中,得到损伤本构模型的修正式。最后将拟合参数进行必要的敏感性分析,得出各拟合参数的实际物理意义。     

爆炸荷载作用下方形夹芯板动力学响应与优化设计数值分析

为研究方形蜂窝铝板在爆炸荷载作用下的动力学响应,基于LS-DYNA非线性有限元软件,建立了TNT炸药-前后面板-蜂窝夹芯-空气的三维有限元模型。采用ALE(任意的拉格朗日欧拉)多物质流固耦合算法分析了蜂窝铝板在冲击荷载作用下的变形机理、塑性变形、能量吸收以及结构的优化。数值模拟结果表明:随着面板厚度、核心高度的增加,蜂窝铝板在冲击荷载作用下的塑性变形明显减小,抵抗变形的能力增强;随着爆轰入射角度的增加,结构的破坏程度有所减小,入射角越大这种效果越发明显。对结构给定边长和受冲击面积以及面板厚度配合比、夹芯量纲为一的高度进行了局部的优化分析,为设计优质铝蜂窝板提供参考。     

纵横载荷作用下功能梯度梁的弯曲和过屈曲

基于一阶非线性梁理论和物理中面概念,导出了纵横向载荷作用下功能梯度材料(FGM)梁非线性弯曲和过屈曲问题的控制方程,并获得了该问题的精确解;据此解研究了梯度材料性质、外载荷、横向剪切变形以及边界条件等因素对功能梯度材料梁非线性力学行为的影响,分析中假设功能梯度材料性质只沿梁厚度方向,并按成分含量的幂指数函数形式变化。结果表明:纵横载荷共同作用下,功能梯度梁的弯曲构形将有无限多个;随着梯度指数的增大,梁的变形减小,临界载荷升高;随着长高比的增大,横向剪切变形的影响减小。     

基于内聚力模型的快速荷载下CFRP-混凝土界面剪切剥离模拟

鉴于纤维增强复合材料(Fiber Reinforced Polymer, FRP)已在混凝土结构加固中普遍应用, 能有效提高结构的承载和变形能力. 为揭示动载作用下FRP-混凝土界面的剥离机理, 本文基于ABAQUS平台, 采用内聚力模型模拟CFRP-混凝土界面层, 实现了快速荷载下CFRP-混凝土界面剥离的高效模拟. 结果表明: CFRP表面应变在加载过程中由加载端向自由端方向传递, 随着加载速率的提高, 界面承载能力也随之提高; 界面峰值剪应力也存在显著的应变率效应; 模拟结果与试验结果基本吻合, 说明了新方法的有效性.     

Hydrodynamic and Thermodynamic Nonequilibrium Effects around Shock Waves: Based on a Discrete Boltzmann Method

A shock wave that is characterized by sharp physical gradients always draws the medium out of equilibrium. In this work, both hydrodynamic and thermodynamic nonequilibrium effects around the shock wave are investigated using a discrete Boltzmann model. Via Chapman–Enskog analysis, the local equilibrium and nonequilibrium velocity distribution functions in one-, two-, and three-dimensional velocity space are recovered across the shock wave. Besides, the absolute and relative deviation degrees are defined in order to describe the departure of the fluid system from the equilibrium state. The local and global nonequilibrium effects, nonorganized energy, and nonorganized energy flux are also investigated. Moreover, the impacts of the relaxation frequency, Mach number, thermal conductivity, viscosity, and the specific heat ratio on the nonequilibrium behaviours around shock waves are studied. This work is helpful for a deeper understanding of the fine structures of shock wave and nonequilibrium statistical mechanics.     

An experimental investigation into non-linear wave loading on horizontal axis tidal turbines

Tidal turbines are subject to large hydrodynamic loads from combinations of currents and waves, which contribute significantly to fatigue, extreme loading and power flow requirements. Physical model testing enables these loads and power fluctuations to be assessed and understood in a controlled and repeatable environment. In this work, a 1:15 scale tidal turbine model is utilised to further the fundamental understanding of the influence of waves on tidal turbines. A wide range of regular waves are generated in both following-current and opposing-current conditions. Wave frequencies range from 0.31 Hz to 0.55 Hz & wave heights from 0.025 m to 0.37 m in a fixed 0.81 m/s current velocity. Waves are selected and programmed specifically to facilitate frequency domain analysis, and techniques are employed to isolate the effect of non-linear waves on turbine power and thrust.Results demonstrate that wave action induces large variations in turbine power and thrust compared to current only conditions. For the range of conditions tested, peak values of thrust and power exceed current-only values by between 7%–65% and 13%–160% respectively. These wave-induced fluctuations are shown to increase with wave amplitude and decrease with wave frequency. Following wave conditions exhibit greater variations than opposing for waves with the same wave height and frequency due to the lower associated wavenumbers.A model is developed and presented to aid the understanding of the high-order harmonic response of the turbine to waves, which is further demonstrated using steady state coefficients under assumptions of pseudo-stationarity. This approach is proven to be effective at estimating wave-induced power and thrust fluctuations for the combinations of waves, currents and turbine state tested. The outcome of which shows promise as a rapid design tool that can evaluate the effect of site-specific wave–current conditions on turbine performance.     

改进的五阶WENO-Z+格式

WENO-ZWENO-Z$+\!$格式的性能提升依赖于新增项的作用,该项的作用是在WENO-Z格式的基础上进一步增大欠光滑子模板上的权重. 系数$\lambda$被设置用来调控该项的作用, 以避免负耗散. 本文指出了WENO-Z$+\!$格式的缺陷,其所采用$\lambda $的取值方式既不能充分发挥格式的潜力, 也未完全消除负耗散;提出$\lambda $的值应随当地流场数据变化,方能充分发挥新增项在降低数值耗散、提高分辨率上的潜力. 基于此,本文重新设计了$\lambda $的计算公式,该公式能自适应地调控新增项的作用: 只在欠光滑子模板上的权重容易过度增大的地方削弱该项的作用,以避免负耗散; 在其他地方则充分发挥新增项的作用,最大限度增大欠光滑子模板上的权重, 提高格式的分辨率.将使用该系数公式的新格式命名为WENO-Z++, 并对其数值性能进行了系统的研究.理论分析表明, 新格式在间断处具有基本无振荡(essentially non-oscillatory,ENO)特性和更低的数值耗散. 对近似色散关系(approximate dispersion relation,ADR)的研究表明,新格式有效地避免了因过度增大欠光滑子模板上的权重而带来的负耗散,其频谱特性也得到了显著提升.本文还推导了使新格式在极值点处也能保持最优阶的精度的参数设置.一系列求解Euler方程的数值试验表明,新格式的激波捕捉能力和对复杂流场结构的分辨率都显著优于原WENO-Z$+\!$格式.}     

泡沫铝防护钢筋混凝土板的抗爆性能

为研究多孔吸能材料泡沫铝板对工程结构的抗爆防护作用,开展室外爆炸破坏实验,分别对设置不同泡沫铝防护层的钢筋混凝土(reinforced concrete,RC)板在爆炸荷载下的动态响应及破坏模式进行了研究,并运用LS-DYNA软件建立了有限元模型。通过与实验对照,验证了模型的可行性,对比分析了有、无泡沫铝防护层钢筋混凝土板的损伤破坏规律,并讨论了泡沫铝密度梯度分布和纵筋配筋率的影响。结果表明:有限元模型能够有效分析含泡沫铝防护层RC板的动态响应及其破坏形态;泡沫铝防护层能够有效减小钢筋混凝土板的挠度变形,降低试件的破坏程度;泡沫铝密度由下到上递增情况对RC板的减爆效果最好;增大配筋率可以提升泡沫铝防护RC板整体抗爆性能。     

不同加载速率下砂岩弯曲破坏的细观机理

岩石细观破裂形貌是岩石破坏机制的重要反映,为研究不同加载速率对砂岩弯曲破坏的影响,通过三点弯曲实验和扫描电镜方法,对某煤矿关键层砂岩弯曲破断裂纹细观形态以及裂纹的自相似性进行了研究。选取6个不同加载速率对岩样进行三点弯曲实验,观察其宏观断裂情况,并利用扫描电镜对弯曲断裂面表面裂纹细观结构进行观察,并拍摄不同倍数下的扫描电镜图片。对图片进行图像处理后得到砂岩弯曲断裂破坏细观裂纹信息,并计算得到微裂纹的分形盒维数值。结果显示:随着加载速率的提高,砂岩穿晶断裂的比例也随之升高,裂纹分形维数亦随着加载速率的增大而增加,同时,分形维数还与弯曲断裂破坏荷载和抗弯强度成正比。可见,加载速率对断裂方式有一定的影响,且加载速率越大断裂所需的破坏能越大,裂纹分布越广,表明开采速度与岩爆等岩体动力灾变有密切关系。     

连续碳纤维增强的聚芳醚酮在Ⅰ型循环载荷下的层间破坏

用双悬臂梁(DCB)试件研究了连续碳纤维增强的聚芳醚酮复合材料(CF/PEK-C),在Ⅰ型循环载荷作用下的层间裂纹扩展行为.循环载荷采用载荷控制模式,最小载荷与最大载荷之比为0.5.在疲劳试验中,仍然发现有“阻力曲线”现象存在.层间裂纹扩展速率用指数定律与相应的应变能释放速率联系起来,并对结果进行了讨论.