泥石流冲击荷载下拦挡坝的动力响应分析

选取典型的泥石流冲击荷载,把钢筋混凝土拦挡坝简化成悬臂梁,建立其动力偏微分方程,运用数学物理方程中的变量分离法和结构动力学中的振型叠加法求得动力偏微分方程的解析解,最后根据材料力学得到相应的应力以及应变。算例分析表明解析解是可靠的,且在拦挡坝的坝顶处有最大的位移,为实际工程力学计算提供一种思路。       

冲击荷载下钢管混凝土柱模型力学性能试验研究

为研究冲击荷载下钢管混凝土柱（CFT）的力学性能，采用φ57mm轻气炮实验装置和技术，进行了8个钢管混凝土柱模型的冲击试验及模拟分析计算。测得了不同弹体冲击速度下试件表面的应变时程曲线，获取了试件破坏形态及残余变形，比较了不同弹体冲击速度、试件装夹部位、试件外包约束等因素的影响。结果表明，冲击荷载作用下试件残余变形、应变变化直接与弹体冲击速度有关；受弹体碰撞后，试件冲击端的残余变形最大；装夹部位设在试件中部更能真实的模拟试件受力的真实情况．外包碳纤维对试件的抗冲击性能有一定的改善，尤其是在横向变形较大的部位；钢管混凝土柱模型试件的应变量级很大，环境噪声影响较大，可采用大阻值和大量程应变片提高应变准确度。     

泥石流浆体与固体颗粒冲击信号能量分布研究

用小波分析方法对5种浆体黏度、5种固相比与4种颗粒粒径组合的85组泥石流冲击室内模型实验所得冲击信号进行消噪、时频处理,通过对降噪的泥石流冲击信号进行冲击能量计算并分析实验中泥石流冲击能量与频谱间关系。结果表明,随浆体黏度、固相比及颗粒粒径增大,泥石流冲击信号能量呈增长趋势,且相同浆体黏度下固体颗粒粒径大于1.3~1.5 cm时,泥石流冲击能量增幅明显。将冲击信号分解为9个频段(0~1.958 Hz、1.958~3.906 Hz、3.906~7.812 Hz、7.812~15.625 Hz、15.625~31.25 Hz、31.25~62.5 Hz、62.5~125 Hz、125~250 Hz、250~500 Hz),泥石流冲击信号96%以上能量聚集在频率0~1.958 Hz的低频段a8内。该结果对推动泥石流动力特性研究具有积极意义。     

泥石流浆体冲击特性实验研究

进行液相浆体粘度0Pa•s、 0.13 Pa•s、0.37P Pa•s、0.72 Pa•s、0.93 Pa•s的泥石流浆体冲击特性模型实验,采用小波方法揭示泥石流浆体冲击特性,结果体现在三方面：随着泥石流浆体粘度的增大,泥石流冲击力与冲击力标准差呈非线性增大,冲击力概率密度由近似正态分布逐渐偏离;泥石流95%以上的冲击能量分布在小于1.958Hz 的低频部分;泥石流冲击能量百分比总体从低频至高频呈迅速衰减分布趋势,且泥石流粘度越高,低频段至高频段的冲击能量衰减速度越快。本文成果对于推动泥石流动力特性科学研究具有积极意义。     

冲击荷载下石墨矿石破碎能耗特征

为了研究晶质石墨矿石试样在冲击荷载作用下的破碎能耗特征,采用?50 mm的分离式霍普金森压杆(SHPB)试验装置,设置气压间隔为0.1 MPa, 0.2～0.6 MPa共5组冲击气压,进行不同加载速率条件下石墨矿石试样冲击压缩试验,并分析石墨矿石试样破碎能耗规律。试验结果表明：在冲击荷载作用下,石墨矿石试样的动态抗压强度与平均应变率具有较强的三阶多项式关系,且石墨矿石在冲击荷载作用下具有动态硬化作用,其动态抗压强度随着应变率的增大呈非线性增大,呈现明显的应变率效应;石墨矿石试样破碎耗能与入射能具有显著的对数关系,随着入射能增大,试样破碎耗能也随之增大,但其试样破碎耗能所占比例随应变率增大逐渐由0.38下降至0.11;随着平均应变率增大,石墨矿石试样破碎耗能密度呈非线性增长,具有较强的应变率效应;石墨矿石试样的破碎平均粒径与破碎耗能密度具有显著的三阶多项式相关关系,随着石墨矿石试样耗能密度增加,石墨矿石试样破碎程度加剧,可以采用石墨矿石试样破碎块度平均粒径实现对石墨矿石试样破碎程度进行定量描述。     

冲击动荷载系数取值探讨

本文主要介绍了几种计算冲击动荷载系数的方法，指出了经典材料力学计算冲击作用的不足以及瑞利一有限单元法在计算复杂结构时的优点。     

脉动冲击射流的传热特性研究

为了深入理解脉动冲击射流的传热传质特性,研究脉动流的温度相关热物理性质对于靶面局部努塞尔数分布的影响,分别对正弦和方波非稳态脉动冲击射流进行了数值模拟.结果显示单个正弦脉冲的强化传热并不明显,而方波脉冲的强化传热效果却十分明显.对于脉动冲击射流中的流场分析表明,靶面上的瞬态换热效率与非线性热力学和水力学边界层随时间的发展密切相关.     

冲击荷载下花岗岩残积土的滞回曲线特征与损伤定量评价

为评价冲击荷载下花岗岩残积土的损伤发展规律,基于不同振幅(A = 100 ～400 kPa)、频率(f=3 ～15 Hz)和围压(σ'3 =50 ～500 kPa)下室内循环冲击试验得到滞回曲线的形态特征,提出4个反映试样在冲击荷载下的能量消耗、损伤程度、刚度衰减和塑性应变发展特性的定量结构损伤参数:累积耗散能量EN、...     

矩形截面高层建筑扭转向脉动风荷载数学模型

在边界层风洞中完成了一系列矩形截面高层建筑刚性模型的同步测压试验,研究了根方差扭矩系数和基底扭矩功率谱的基本特性。结果表明,层根方差扭矩系数沿高度呈抛物线分布,基底根方差扭矩系数随厚宽比的增大而增大。厚宽比小于1时,基底扭矩功率谱有一个明显的窄带谱峰;厚宽比大于1时,出现两个谱峰,随着厚宽比的增大,两个谱峰逐渐靠近。以厚宽比为自变量,拟合得到了根方差扭矩系数和基底扭矩功率谱的计算公式。     

脉动风荷载作用下声屏障动力响应分析

针对高速铁路脉动风荷载对声屏障影响问题,基于有限元法建立插板式声屏障有限元模型进行动力响应分析。分析比较1跨和8跨声屏障模型自振特性,得出声屏障结构不会发生共振、但相邻声屏障板的振动会相互影响的结论。同时研究车速及立柱间距对结构动力响应的影响,结果表明结构最大位移和最大应力都会随车速、立柱间距的增大呈非线性增大,其中,立柱间距增大会使结构出现多个响应峰值。综合考虑分析结果、结构自重和经济因素,推荐插板式声屏障设计时立柱间距合适范围为1.6 m~2.0 m。     

水石流冲击信号能量分布试验研究

泥石流冲击谱是泥石流固液两相介质运动特性的综合表征,探索泥石流冲击信号的能量大小及其分布特性是合理确定泥石流冲击荷载的关键环节。运用自行研制的试验模型,实施了15种试验工况的泥石流冲击试验,获取了85 000多个测试数据。依据固相比为0.16、粒径组为0.8～1.5 cm水石流冲击测试结果,运用db8小波基变换对试验结果进行8层小波分解,得到频率范围分别为0～0.195Hz,0.195～0.391 Hz,0.391～0.781 Hz,0.781～1.562 5 Hz,1.563～3.125 Hz,3.125～6.25 Hz,6.25～12.5 Hz,12.5～25 Hz和25～50 Hz共九个频率段的冲击信号,据此揭示了不同频段冲击信号能量分布规律。从低频段至中高频段水石流冲击能量非线性衰减,90%以上的冲击能量分布在小于0.195 Hz的低频部分;水石流在中高频段的冲击能量总体呈衰减分布,但在频段三和频段六出现较显著峰值,表明水石流也存在一定阵流现象;水石流中固相粒径越小,低频段至高频段的冲击能量衰减速度越慢。研究成果可为进一步实施泥石流冲击荷载精细实验研究提供一定科学依据。     

Geometrical features of wear debris

Image analysis software was used to analyse the geometry of debris formed during the erosion of low-carbon steel by impinging solid particles. Depending on the two-dimensional aspect ratio (ratio between debris height and debris width), three different debris types could be distinguished. The most frequent type observed was a platelet-type debris as suggested by the Bellman-Levy (1981) model. This wear debris shape type covered about 60% of all acquired debris. Plain micro-machining according to Finnie’s (1959) suggestion played a negligible role only, but other processes, namely ploughing as suggested by Winter and Hutchings (1974), were more important. The statistically estimated mean debris size was about 14 μ m. About 92% of all wear debris had sizes smaller than the target material grain size. This result supports the figure that ‘secondary’ removal modes—lip or platelet, respectively, detachment from crater rims—were responsible for material removal.     

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.     

Characteristics of hypervelocity impact debris clouds

This paper describes an experimental investigation of hypervelocity impact debris clouds produced by impacting metal rods with Kapton flyers in an electric gun facility. Soft copper witness plates placed in the path of the debris were cratered and coated with rod material. From the sizes of the craters on the witness plates we could obtain values for a cratering parameter containing the ,asses and velocities of the debris fragments that formed the craters. By combining the cratering parameter with rough estimates of the fragment masses, we then estimated the fragment velocities. By measuring the thickness and extent of the coating on the witness plates, we obtained a bound on the amount of material vaporized by the impact.     

Spin velocimeters for impact debris fragments

An experimental technique for determining the velocity of individual debris fragments from hypervelocity impacts and correlating these velocity data to fragment size is presented. Design trades and experimental results for fragment spin velocimeters based on this technique are also presented. Validation tests were conducted to verify and optimize the performance of these instruments, and they were subsequently used to collect data for four hypervelocity impact tests. Such data are critical to the development of accurate debris environment models and to support safety hazard analyses of flight tests involving impacts. Comparisons with model predictions are presented.     

Dynamics of submarine debris flow and tsunami

The general two-phase debris flow model proposed by Pudasaini (J. Geophys. Res. 117:F03010, 2012, doi:10.1029/2011JF002186) is employed to simulate subaerial and submarine two-phase debris flows and the mechanics of complex wave generation and interactions between the solid and the fluid phases. This includes the fluid waves or the tsunami generated by the debris impact at reservoirs, lakes, and oceans. The analysis describes the generation, amplification, and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. Accurate and advance knowledge of the arrival of tsunami waves in the coastal regions is very important for the design of early warning strategies. Here, we show that the amount of solid grain in the fluid reservoir plays a significant role in controlling the overall dynamics of the submarine debris flow and the tsunami. For very small solid particle concentrations in the reservoir, the submarine debris flow moves significantly faster than the surface tsunami wave. As the solid volume fraction in the reservoir increases, the submarine debris speed slows down. For relatively large solid volume fractions in the reservoir, the speed of the submarine debris becomes slower than the surface tsunami wave. This information can be useful for early warning strategies in the coastal regions. The fast or slow speed of the submarine wave can be attributed to several dynamical aspects of the model including the generalized drag, basal traction, pressure gradient, virtual mass force, the non-Newtonian viscous stress, and the strong phase interaction between the solid and the fluid as they enhance or diminish the motion of the solid phase. Solid particle concentration in the reservoir dam also substantially influences the interaction between the submarine debris flow and the frontal wall of the dam, and the interaction between the tsunami and the submarine debris wave. The tsunami wave impact generates a largely amplified fluid level at the dam wall. Submarine debris shock waves are observed for small solid volume fractions in the reservoir. Another important aspect of the simulation is to investigate the complex interactions between the internal submarine debris wave and the surface tsunami wave. Three complex waves occur simultaneously: the subaerial debris flow in the upstream region, submarine debris flow in the reservoir basin, and a super tsunami wave on the surface of the reservoir. This helps to develop insight into the basic features of the complex nonlinear solid and fluid waves and their interactions.     

Secondary debris impact damage and environment study

All long-duration spacecraft, such as Space Station Freedom (SSF), are subject to impacts by micrometeoroid and orbital debris (MM/OD) particles in low Earth orbit. The secondary effects of such impacts on SSF was the subject of the Secondary Debris Impact Damage and Environment Study. The primary objective was the assessment of possible damage to SSF hardware in the vicinity of large surface areas impacted by typical MM/OD particles. Several SSF components were evaluated that showed varying degrees of damage due to secondary ejecta. A comparison of the results from 45° and 60° MM/OD impacts revealed that penetration ejecta had greater damage potential at 45° and ricochet ejecta had greater damage potential at 60°. The significant ricochet damage was concentrated within an angle of 15° with respect to the primary target. The impact distribution data was evaluated further using a previous math model. The comparison was inconclusive due to insufficient data within the bounds of the model. Preliminary results of the study showed that secondary debris has the potential to penetrate and induce some damage to SSF hardware. The failure of hardware due to the damage is unknown. Further testing with larger MM/OD particle sizes and varying impact angles is recommended.     

Rotationally symmetric fluctuating flow about a rotating disk

Superposed mean flow due to fluid performing torsional oscillations at large distances from a rotating disk is analysed. For low frequency of oscillations an analytical-numerical solution is obtained for small values of the amplitude parameter, which agrees fairly well with the available numerical results in the limit of zero frequency. Method of multiple scales is employed to derive a solution for high frequency range and for finite values of the amplitude parameter.