ASYMPTOTIC RAREFACTION WAVES FOR BALANCE LAWS WITH STIFF SOURCES

We study the long time formation of rarefaction waves appearing in balance laws by means of singular perturbation methods. The balance laws are non standard because they contain a variable u that appears only in the flux terms. We present a concrete example occurring in flow of steam, nitrogen and water in porous media and an abstract example for a class of systems of three equations. In the concrete example the zero-order equations resulting from the expansion yield a type of conservation law system called compositional model in Petroleum Engineering. In this work we show how compositional models originate from physically more fundamental systems of balance laws. Under appropriate conditions, we prove that certain solutions of the system of balance laws decay with time to rarefaction wave solutions in the compositional model originating from the system of balance laws.

基于复合材料性能退化规律的疲劳剩余刚度预测模型构建

针对现有复合材料剩余刚度预测模型考虑因素不全的问题,提出了一种考虑到最大应力、初始刚度、临界剩余刚度、循环周次及恒幅疲劳寿命共同作用的复合材料疲劳剩余刚度预测模型。结果表明:所提模型符合三阶段性能退化规律,可用于描述复合材料的剩余刚度退化,吻合精度高;模型在高应力区表现出比在低应力区更高的预测精度,这与高应力下数据点较为集中有关;与已有模型进行对比,本文所提模型对复合材料疲劳剩余刚度具有较高的预测精度和普适性。

三明治结构复合材料对甲烷-空气混合气体爆炸传播规律的影响

为探究非金属芯层三明治结构复合材料对甲烷-空气混合气体爆炸传播规律的影响,利用自主搭建的爆炸管网实验平台,开展不同芯层材料(聚偏二氟乙烯(Polyvinylidene Fluoride,PVDF)泡沫板、三角帆蚌贝壳和高吸水性树脂(Super Absorbent Polymer,SAP)胶体)的爆炸实验,分析非金属芯层复合材料对爆炸超压、火焰传播速度、火焰温度以及熄爆参数影响规律。研究结果表明:三明治结构复合材料对甲烷-空气混合气体爆炸传播具有良好的抑制效果;当芯层为PVDF泡沫板时,对火焰温度的抑制效果最好;当芯层材料为SAP胶体时,对爆炸超压和火焰传播速度的抑制效果最好,且后端熄爆参数为9.20 MPa·℃,表现出优异的抑爆效果。

A Novel Technique for Preparation of Electrically Conductive ABS/Cu Polymeric Gradient Composites

A novel technique for preparing functionally gradient electrically conductive polymeric composites was developed by using of solution casting technique on the principle of Stokes＇ law. Acrylonitrile- butadiene-styrene/Cu （ABS/Cu） gradient polymeric composites were prepared successfully using this technique. The gradient structures, electrically conductive performance and mechanical properties of the ABS/Cu composites were investigated. Optical microscope observation shows that the gradient distribution of Cu particles in ABS matrix was formed along their thickness-direction. The electrically conductive testing results indicate that the order of magnitude of surface resistivity was kept in 10^15 Ω at ABS rich side, while that declined to 10^5 Ω at Cu particles rich side, and the percolation threshold was in the range of 2.82 vo1%- 4.74 vol% Cu content at Cu particles rich side. Mechanical test shows that the tensile strength reduced insignificantly as the content of Cu increases owing to the gradient distribution.

Elevated temperature compressive deformation behavior of 2024Al matrix composite reinforced by sub-micro Al_2O_3 particles

The compressive behavior of sub-micro Al2O 3P （40%, volume fraction）/2024Al composite was investigated within the temperature range from 270℃ to 620℃ under various strain rates from 0.00042s -1 to 0.14s -1. Results show that the critical compression reduction of the composite presents a saddle law under the combined influence of temperature and strain rate. That means the composites exhibit better deformation ability at higher temperature with higher strain rate （445℃, 0.14s -1） or at lower temperature with lower strain rate （320℃, 0.0042s -1）.

Oxidation of Al_2O_3-30%TiCN-0.2%Y_2O_3 Composite

The oxidation behavior of Al2O3-30%TiCN-0.2%Y2O3 composite and its effect on high temperature bending strength was studied. The result indicates that the mass gain during static oxidation of the material under normal atmosphere follows the parabolic law. Oxide increases with increasing temperature and prolonging time. It has good oxidation resistance. The product of oxidation of the material is TiO2. Therefore, the volume of the material expands. The oxide film is destroyed because residual stress inside the oxide film is released. Proper oxidation is beneficial to the improvement of bending strength of Al2O3-30%TiCN-0.2%Y2O3 composite. The strength increase is up to 4.5%.

Properties of frictional bridging in fiber pull-out for fiber-reinforced composites

Stress equilibrium equations, boundary- and continuity-conditions were used to establish a theoretical model of progressive debonding with friction at the debonded interface. On a basis of the minimum complementary energy principle, an expression for the energy release rate G was derived to explore the interfacial fracture properties. An interfacial debonding crite- rion G≥Γi was introduced to determine the critical debond length and the bridging law. Numerical calculation results for fi- ber-reinforced composite SCS-6/Ti-6Al-4V were compared with those obtained by using the shear-lag models.

Effects of Strain Rate and Fiber Content on the Dynamic Mechanical Properties of Sisal Fiber Cement-Based Composites

In this paper,a split Hopkinson pressure bar(SHPB)was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites(SFRCCs),and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy(SEM)and energy-dispersive X-ray spectrome-try(EDS).The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials.Compared with ordinary cement-based composites(OCCs),the SFRCCs demonstrate higher post-peak strength,ductility,and energy absorption capacity with higher fiber content.Moreover,the SFRCCs are strain rate sensitive materials,and their peak stress,ultimate strain,and energy integrals all increase with increasing strain rate.From the perspective of fracture failure characteristics,the failure of OCCs is dominated by the brittle failure of crystal cleavage.In contrast,the failure mode of the SFRCCs changes to microscale matrix cracks,multi-scale pull-out interface debonding of fibers(fine filaments and bundles),and mechanical interlock.This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.

Using MATLAB to Design and Analyse Composite Lami-nates

This work deals with the generation of MATLAB script files that assists the user in the design of a composite laminate to operate within safe conditions. The inputs of the program are the material properties, material limits and loading conditions. Equations based on Hooke’s Law for two-dimensional composites were used to determine the global and local stresses and strains on each layer. Failure analysis of the structure was performed via the Tsai-Wu failure theory. The output of the program is the optimal number of fibre layers required for the composite laminate, as well as the orientation of each layer.

The spatial-temporal evolution of coherent structures in log law region of turbulent boundary layer

The spatial-temporal evolution of coherent structures （CS） is significant for turbulence control and drag re- duction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component （3D-3C） velocity fields of the flat plate turbulent boundary layer （TBL） measured by a Tomographic and Time-resolved PIV （Tomo TRPIV） system. Using multi-resolution wavelet transform and conditional sampling method, we extracted the intrinsic topologies and found that the streak structures appear in bar-like patterns. Furthermore, we seized locations and velocity information of transient CS, and then calculated the propagation velocity of CS based on spatial-temporal cross-correlation scanning. This laid a foundation for further studies on relevant dynamics properties.

Variation law of microscopic pore of loess-like soil after several freeze-thaw cycles in seasonal frozen soil region

In seasonal frozen soil region,the engineering geological properties of loess-like soil will be deteriorated after freeze-thaw cycles.Through the freeze-thaw cycle experiment of remolded loess-like soil,under different freezing temperatures,the authors carried out freeze-thaw cycle tests for 3 times and 20 times,respectively.With mercury intrusion porosimetry and granulometric analysis,from the micro-structure,the authors studied the law that freeze-thaw cycle times and frozen temperature effect on the variation of microscopic pore of loesslike soil.This result can provide theoretical basis for comprehensive treatment of problems in the construction of the project in seasonal frozen loess-like soil region.

磷石膏基复合充填胶凝材料强度性能的分析研究

为了提高磷石膏的综合资源利用率,结合镍矿充填需要,以磷石膏为基本材料,生石灰和矿渣微粉等固体废弃物为辅助材料开展替代水泥的新型复合充填胶凝材料的试验研究。通过正交试验研究分析磷石膏添加量对充填胶凝材料强度的作用。利用遗传规划获得磷石膏基复合充填胶凝材料强度规律的函数关系,使用遗传算法对回归函数进行有约束优化。结果显示:当生石灰为4.48%,磷石膏为32.42%,芒硝为2.35%,氢氧化钠为2.5%和渣粉为58.3%时,磷石膏基复合充填胶凝材料强度能够满足矿山充填需要。采用SEM和XRD分析了磷石膏复合充填胶凝材料的水化机理,水化产物主要是C-S-H凝胶和钙矾石,相比水泥对比试验,磷石膏基新型充填胶凝材料水化产生的钙矾石数量更多。氢氧化钠的加入能够加速水化反应的速度,增强充填体龄期抗压强度。随着养护时间的增加,水化产物不断增长,孔隙不断被填满,结构变的更加致密,使得充填体具有了较好的力学性能。

纤维水泥基复合材料的力学性能影响因素分析

为改善传统混凝土抗拉韧性差、变形能力弱的不足,制备了9种纤维水泥基复合材料(ECC)哑铃型与棱状体试件,通过单抽拉伸、抗折抗压试验分析了纤维体积掺量、水胶比、砂胶比、粉煤灰掺量对ECC力学性能影响。利用有限元软件对基体1、5进行了应力分析。结果表明:随粉煤灰掺量增大,ECC极限抗拉应变提高,应变数值最高为5.21%,抗拉应力则随之降低。水胶比低于0.33则会显著降低拉伸应变,但拉应力较高为2.8 MPa,砂胶比大于或小于0.36时,会降低ECC拉伸性能,减少裂缝开展数目,9种基体纤维体积的最佳掺量为2.0%。9种ECC均产生应变硬化与多缝开裂现象,基体1和基体5裂缝开展状况较为优异,且有限元应力分析结果与试验结果基本一致。粉煤灰掺量过大会降低ECC抗压强度,但由于纤维桥接阻裂效应,抗折强度提升较高。在水泥基体中掺加纤维起到的桥接阻裂效应可提升水泥复合基体的抗变形能力与延性,且粉煤灰所起到的“滚珠效应”可润滑纤维-基体界面,减少摩擦力,并有利于ECC应变-硬化现象的形成。

论洗钱罪的犯罪构成

正确理解洗钱罪的犯罪构成对于正确定罪具有重要的基础性作用。对现行刑法规定的研究表明,该罪的犯罪客体要件既包括国家的金融管理秩序,又包括司法活动秩序;客观要件是刑法明文规定的五类洗钱行为;犯罪主体包括具有刑事责任能力的自然人与有关单位,值得注意的是,《刑法修正案(十一)》把上游犯罪主体纳入了洗钱罪的主体范围;关于主观要件,其认识因素即行为人明知其掩饰、隐瞒毒品犯罪、黑社会性质的组织犯罪、恐怖活动犯罪等上游犯罪的违法所得及其产生的收益的行为具有社会危害性,意志因素即希望或者放任其洗钱行为实施的心理态度。

基于数值模拟的桩网复合地基加固效果对比分析

利用有限元分析软件ABAQUS建立了二维桩网复合地基模型,分析了预应力高强度混凝土(prestressed high-strength concrete,简称PHC)桩网复合地基、桩承式复合地基、PHC桩砂桩复合地基这3种复合地基加固方式,在路堤荷载下的变形、受力特性。数值计算结果表明:桩承式复合地基的路面沉降最小,PHC桩网复合地基其次,PHC桩砂桩复合地基最大;桩承式复合地基的桩土应力比、桩体荷载分担比最大,土拱效应最明显。计算分析数据说明,针对复杂的、软土较深厚的高速公路、铁路的路基,可采用桩承式复合地基加固,加固效果更好。

阻燃输送带火灾早期温度变化与烟气成分研究

为实现带式输送机火灾早期预警,改进滚筒摩擦实验平台并监测阻燃输送带温度。利用质谱(MS)技术,分析钢丝绳芯阻燃输送带在摩擦事故早期的升温规律与烟气成分。研究表明,随着摩擦持续进行,阻燃输送带表面温度分布呈现出较强的对称性,最高温度区域逐渐向输送带中心集聚,烟气成分随温度变化而改变。根据实验中烟气产物主要成分以及对应的反应过程,将钢丝绳芯阻燃输送带升温过程分为氧化反应阶段(环境温度至100℃)、取代反应阶段(100~160.2℃)和热解反应阶段(160.2℃以后)。当阻燃输送带处于氧化反应阶段时,输送带热容量较小、升温快,产物多为烷基和酯类化合物;取代反应阶段热容量逐渐增加,升温放缓,产物多为硝基、醚类、羧酸类化合物;热解反应阶段输送带内部热容量基本稳定,升温速率最小,在160.2℃时在烟气成分中首次检测到含氯化合物。

基于PSO的飞行器姿态智能控制技术研究

以气动舵/推力矢量/直接力复合控制飞行器为对象,研究了多维异构复合姿态控制系统的控制律及分配律一体化智能设计问题。首先提出了基于PSO(Particle Swarm Optimization)算法的“智能控制律+智能分配律”飞行器姿态多维异构智能复合控制算法框架,并建立了控制系统数学模型,然后重点研究了控制律及分配律参数的智能优化算法实现方法,最后通过数学仿真验证了提出方法的有效性。仿真结果表明,所设计智能优化复合控制系统在标称模型以及模型摄动情况下均能够实现对姿态角指令的准确快速跟踪。

杉木人工林林分空间结构分析及综合指数评价

基于广东省羊角山林场、连山林场和金鸡林场9个杉木人工林样地的实测数据,对杉木人工林林分空间结构参数进行评价和分析,为优化和调整杉木人工林的林分空间结构奠定基础。采用角尺度、混交度、大小比数、开敞度和竞争指数5个林分空间结构参数,分析不同龄组(幼龄林、中龄林、近成熟林)以及不同密度(1 700、2 000、2 300株/hm^(2))杉木林林分空间结构特征,通过熵权法构建林分空间结构综合指数。结果表明,9个样地的杉木林各龄组的角尺度处于均匀分布和随机分布状态之间;林分混交度普遍较低;杉木各龄组的大小比数都接近中庸状态,林木分化水平较低;开敞度在不同龄组间差异显著;竞争指数在3个龄级之间呈极小幅度的波动;不同龄组的林分空间结构理想程度为:中龄林>近成熟林>幼龄林;不同密度的林分空间结构理想程度为:低密度>中密度>高密度。以样地林分空间结构分析与评价为依据,采取合理的营林措施,可以使杉木人工林的林分水平分布格局逐渐趋向随机分布,混交状态逐渐趋向最高混交,林分竞争状态逐渐趋向优势态竞争,从而促进其可持续经营。

荷载作用下UHPC+AC复合试件裂缝发展的分形分析

基于道路及相关材料发展现状,提出UHPC+AC复合式路面,制作UHPC+AC复合小梁试件并开展梯度荷载加载试验,记录得到复合试件表面裂缝的生长过程,利用分形分析方法分别对复合试件AC层、UHPC层裂缝进行量化分析。研究分析发现复合试件AC层裂缝分形维数随荷载增加呈线性关系增加,复合试件UHPC层裂缝分形维数随荷载增加呈指数关系增加,裂缝最终损伤形态分别为网状和线状。研究结论为UHPC+AC复合式路面的设计和维护提供理论依据。

基于XFEM的再生复合路面反射裂缝扩展研究

为了探究裂缝扩展路径及在不同条件下的扩展规律,该文基于ABAQUS软件中扩展有限元方法(extended finite element method,XFEM)模拟分析沥青混凝土半圆弯曲断裂试验中的裂缝扩展规律。通过对比他人试验及数值模型数据,验证了基于XFEM的有限元模型分析裂缝扩展的有效性。此外,该文建立干法油石分离再生复合路面二维模型,研究模型中施工缝宽度、预埋裂缝长度、偏转角及预设位置对裂缝尖端应力影响,结果表明尖端应力随着裂缝长度、偏转角增加而增大,而随着施工缝宽度增大呈现先减小后增大趋势,随着偏移距离变大则先增大后减小。该文研究结果有助于复合路面反射裂缝定量分析与表征,为复合路面设计及后期养护提供了参考与依据。