发动机机油滤清器虑层强度分析及优化

针对机油滤清器工作工况下进出口压差、机油滤层强度及导流桩高度等问题, 通过试验测试与仿真相结合, 对滤清器初步设计进行了评估及优化, 以确保滤清器在工作工况下进出口压降及滤层强度能满足要求. 首先进行滤层性能试验, 得到滤层的惯性阻力系数和黏性阻力系数; 再通过滤层多孔介质CFD分析, 对滤清器进出口压降进行分析计算. 结果表明: 在-18℃、25℃和70℃的工况下, 进出口压降都小于10kPa, 满足相关要求. 针对滤层的最大主应力超过其抗拉强度的问题, 通过CAE仿真分析, 优化滤层与导流桩间隙, 将滤层最大主应力由110.1MPa降至36.99MPa, 小于其抗拉强度42.8MPa.     

Controlling thermomechanical behavior of semicrystalline hydrogenated polynorbornene through the cis- to trans-cyclopentylene ratio

Though polynorbornene synthesized by ring-opening metathesis polymerization has an intrinsically all-cis configuration of the cyclopentylene backbone rings, a fraction of these rings can be epimerized to the trans configuration during hydrogenation over suitable catalysts. By varying the method of hydrogenation, semicrystalline hydrogenated polynorbornenes (hPNs) with trans levels between 0 and 36% were obtained. With increasing trans content, the glass transition temperature, melting point, and enthalpy of melting decrease modestly. By contrast, the temperature at which the hPN crystal transitions into a rotationally disordered polymorph varies strongly with trans content, ranging from 126 °C (all-cis) to 71 °C at 27% trans; at trans contents of 34% and above, no rotationally-ordered phase is observed at any temperature. The room-temperature Young's modulus shows no dependence on trans content, while the yield stress drops by 20% at 1% trans content and slowly decreases further with additional epimerization. The temperature dependence of the Young's modulus differs for trans-containing versus all-cis polymers, while the temperature dependence of the yield stress is set by the polymorph type (rotationally ordered vs. disordered).     

Nonlinear elastic constitutive relations of residually stressed composites with stiff curved fibres

Applied Mathematics and Mechanics - Mechanical models of residually stressed fibre-reinforced solids, which do not resist bending, have been developed in the literature. However, in some residually...     

Agave fructans and oligofructose decrease oxidative stress in brain regions involved in learning and memory of overweight mice

Obesity is currently a public health problem worldwide. Recently, non-reducing carbohydrates, that include β(2→1) and β(2→6) linkages in their structure, have been of particular interest in the field of obesity because they are involved in lipid metabolism. Some of these are agave fructans (AF) and oligofructose (OF). In this study, we evaluated both AF and OF on oxidative stress (OS) markers in the brain of overweight mice (OM). AF and OF decreased TBARS levels and carbonyls at different levels in hippocampus (HP), frontal cortex (FC) and cerebellum (CB) of OM. The results indicated that fructans may have anti-oxidative potential and can be used as an alternative treatment for the prevention of the consequences of this pathology.     

Enhancing hydrogen evolution of MoS2 basal planes by combining single-boron catalyst and compressive strain

MoS₂ is a promising candidate for hydrogen evolution reaction (HER), while its active sites are mainly distributed on the edge sites rather than the basal plane sites. Herein, a strategy to overcome the inertness of the MoS₂ basal surface and achieve high HER activity by combining single-boron catalyst and compressive strain was reported through density functional theory (DFT) computations. The ab initio molecular dynamics (AIMD) simulation on B@MoS₂ suggests high thermodynamic and kinetic stability. We found that the rather strong adsorption of hydrogen by B@MoS₂ can be alleviated by stress engineering. The optimal stress of −7% can achieve a nearly zero value of ΔG_H (~ −0.084 eV), which is close to that of the ideal Pt–SACs for HER. The novel HER activity is attributed to (i) the B– doping brings the active site to the basal plane of MoS₂ and reduces the band-gap, thereby increasing the conductivity; (ii) the compressive stress regulates the number of charge transfer between (H)–(B)–(MoS₂), weakening the adsorption energy of hydrogen on B@MoS₂. Moreover, we constructed a SiN/B@MoS₂ heterojunction, which introduces an 8.6% compressive stress for B@MoS₂ and yields an ideal ΔGH. This work provides an effective means to achieve high intrinsic HER activity for MoS₂.     

HgCdTe薄膜的输运特性及其应力调控

窄禁带直接带隙半导体材料碲镉汞(Hg1–xCdxTe)是一种在红外探测与自旋轨道耦合效应基础研究方面都具有重要应用意义的材料.本文对单晶生长的体材料Hg0.851Cd0.149Te进行阳极氧化以形成表面反型层,将样品粘贴在压电陶瓷上减薄后进行磁输运测试,在压电陶瓷未加电压时观察到了明显的SdH振荡效应.对填充因子与磁场倒数进行线性拟合,获得样品反型层二维电子气的载流子浓度为ns=1.25×10^16m^-2.在不同磁场下,利用压电陶瓷对样品进行应力调控,观测到具有不同特征的现象,分析应是样品中存在二维电子气与体材料两个导电通道.零磁场下体材料主导的电阻的变化应来源于应力导致的带隙的改变;而高场下产生类振荡现象的原因应为应力导致的二维电子气能级的分裂.     

超声速流动中非线性EASM湍流模式应用研究

针对超声速复杂流动区域精确模拟的需要，发展了基于k-ω可压缩修正形式的非线性显式代数雷诺应力模式（EASM），提高了该模式对超声速复杂流动的数值模拟精度。通过对二维超声速凹槽和三维双椭球的数值计算表明，与SA和SST常规线性涡黏性湍流模式比较，非线性的EASM模式对大分离以及剪切层流动结构的刻画能力更精细，对剪切层再附区的压力及摩擦系数分布模拟更加精确；EASM模式能够准确地模拟二次激波引起的压强和热流分布情况。     

Information Network Modeling for U.S. Banking Systemic Risk

In this work we investigate whether information theory measures like mutual information and transfer entropy, extracted from a bank network, Granger cause financial stress indexes like LIBOR-OIS (London Interbank Offered Rate-Overnight Index Swap) spread, STLFSI (St. Louis Fed Financial Stress Index) and USD/CHF (USA Dollar/Swiss Franc) exchange rate. The information theory measures are extracted from a Gaussian Graphical Model constructed from daily stock time series of the top 74 listed US banks. The graphical model is calculated with a recently developed algorithm (LoGo) which provides very fast inference model that allows us to update the graphical model each market day. We therefore can generate daily time series of mutual information and transfer entropy for each bank of the network. The Granger causality between the bank related measures and the financial stress indexes is investigated with both standard Granger-causality and Partial Granger-causality conditioned on control measures representative of the general economy conditions.     

热对流作用下筒壁涂层的边裂行为

边裂(边缘开裂)是涂层热致损伤的主要模式之一. 边缘裂纹穿透涂层后,常导致界面脱粘从而驱使涂层与基体剥离,最终丧失对基体的保护作用. 本文以热应力强度因子表征边缘裂纹的扩展驱动力,研究筒壁涂层在热对流作用下的边裂行为. 首先,利用拉普拉斯变换法,得到了瞬态温度场及热应力场的封闭解. 其次,运用Fett等的三参数法确定了筒壁涂层边缘裂纹的权函数. 最后,基于叠加原理和权函数方法计算了边缘裂纹的热应力强度因子. 探讨了无量纲时间、边缘裂纹深度、基体/涂层厚度比、热对流强度等参数对热应力强度因子的影响规律. 结果表明:热应力强度因子的峰值既非发生在热载荷初始时刻,也非发生在热稳态时刻,而出现在时间历程的中间时刻;增大热对流强度不仅可提高热应力强度因子的峰值,而且使峰值提前出现;其他条件相同时,热应力强度因子随着边缘裂纹长度的增大而降低;增大涂层厚度或减小基体厚度可增强涂层抵抗瞬态热载荷的能力.      

DISCRETE GRADIENT METHOD FOR IMAGE-BASED BIOMECHANICAL STRESS ANALYSIS 1)

介绍一种可用于计算生物力学的离散梯度方法,此方法可利用离散的点云模型直接进行数值模拟分析而不需要传统的几何模型。将离散梯度法应用于点云模型需要首先确定模型中点之间的相邻关系和每个点所分配的材料体积,然后通过用广义的有限差分的形式定义了梯度插值向量,并以此向量来近似函数在每个离散点上的梯度。从弱形式出发,推导建立了适用于弹性固体大变形问题的求解器,并具有和有限元法中双线性四边形单元一致的准确性和收敛性。着重描述了一种可以从医学图像中快速提取材料点并建立点云模型的方法,以及利用三角划分和重心划分确定材料点之间的相邻关系和每个材料点体积的具体过程。通过腹主动脉瘤膨胀的静力学模拟分析,展示了离散梯度法的实用性和准确性。该算法实现了基于医学图像进行生物力学分析的过程自动化,为病体特异性的研究和治疗提供便利和实用的工具。