Numerical investigation on optimization of thermal analysis due to immersion of hybrid nanostructures in a fluid of shear dependent viscosity using the finite element method

This article considers the dispersion of hybrid and mono nanoparticles in a fluid with viscosity (Williamson) dependent on shear rate, over a heated surface moving with nonuniform velocity and exposed to a magnetic field in the presence of an applied current. Extensive modeling leads to complex coupled mathematical models that are solved numerically via the finite element method (FEM). Convergent simulations are run to investigate the role of parameters on the dynamics of flow fields. The magnetic field intensity plays a role in controlling the magnetohydrodynamic boundary layer thickness (BLT) and thermal radiation controls the thickness of thermal boundary layers (TBL). However, the magnetic field intensity is responsible for an increase in BLT. In contrast to this, thermal radiation plays a role in controlling the thickness of the TBL. The impact of shear rate dependent viscosity on velocity is remarkable for both fluids. The motion of both of the fluids slows down when viscosity varies as a function of shear rate. Viscosity depending on the shear rate has a significant impact on wall shear stress. It is observed from simulations that wall shear increases when the parameters appearing in the model for shear rate dependent viscosity are increased. However, this increase in wall shear stress associated with a hybrid nanofluid is greater than the increase in wall shear stress associated with a mono nanofluid.     

AHRS 的老人跌倒检测算法

独居老人如在室内或室外发生意外摔倒时,没有得到及时医疗救助治疗,将给老年人造成巨大的心理与身体的伤害。 将航姿参考系统(attitude and heading reference system,AHRS)应用在跌倒检测中,将跌倒的过程转变成姿态的变化,从而来判断 跌倒的程度。 AHRS 航姿系统比过去原有实验方案 3 种姿态角度均有所提升,俯仰角( pitch)提升 2. 371%,滚转角( roll)提升 9. 238%,偏航角(yaw)提升 4. 682%,加速度计最大值精确了 0. 171g,AHRS 航姿系统融合扩展卡尔曼滤波器在检测老年人跌倒 姿态中比过去原有实验方案在检测时间计算上提升了 1 s。 综上实验验证 AHRS 航姿融合在检测老年人跌倒上可以数据更精 确,计算时间更少,在研究人体真实跌倒姿态中更贴近了一步。     

Stochastic analysis of strongly non-linear elastic impact system with Coulomb friction excited by white noise

The stochastic response of frictionally damped strongly non-linear elastic impact oscillator subjected to white noise excitation and its stochastic bifurcation are considered. By the stochastic averaging method based on generalized harmonic function, one can obtain the stationary probability density function of this system. The effects of system parameters on the responses are investigated and the analytical results were verified by comparing with numerical results from Monte Carlo simulations. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that the coefficient of friction, damping constant of the elastic impact force respectively, can be treated as bifurcation parameters.     

我国两部制电价制度对天然气发电企业盈利能力的影响

上海、浙江和江苏等地陆续出台了两部制电价制度,以期解决天然气发电(以下简称气电)企业成本高、经营困难等问题。为了研究该电价制度对气电企业盈利能力的影响,在对比分析上述三地电价政策和实施效果的基础上,基于不同类型机组的三大经营指标(项目财务内部收益率、经济净现值、动态投资回收期),采用项目经济性分析模型探究了不同类型燃气电厂的经济性。研究结果表明:①现行两部制电价与单一制电价相比,电价水平小幅度下降,给企业经营带来了一定的冲击,但从长远看,则有利于形成可持续的发展机制;②两部制电价是各地政府经过充分调研和测算后根据该区具体情况制定的,在该政策下多数企业处于盈亏平衡点附近,综合条件优、管理水平高的企业能取得一定的盈利,反之则亏损;③当电量电价一定且大于盈亏平衡点时,企业效益随年利用小时数的增加而提升,反之则随年利用小时数的增加而降低。结论认为:①两部制电价能起到促进企业管理和技术水平提升,引导和鼓励电力投资的作用,符合我国电力体制改革的方向;②政策制定时应针对不同时期建成的项目加以区别对待,实现上网电价、天然气价格和供热蒸气价格的"三个联动";③应建立大数据平台,实行气网、电网联合调度;④发电企业应创新管理,降低电厂建设及维护成本,提升机组效率,降低气耗。     

基于机器学习的用户实体行为分析技术在账号异常检测中的应用

伴随企业业务的不断扩增和电子化发展,企业自身数据和负载数据都开始暴增。然而,作为企业核心资产之一的内部数据,却面临着日益严峻的安全威胁。越来越多以周期长、频率低、隐蔽强为典型特征的非明显攻击绕过传统安全检测方法,对大量数据造成损毁。当前,用户实体行为分析(User and Entity Behavior Analytics,UEBA)系统正作为一种新兴的异常用户检测体系在逐步颠覆传统防御手段,开启网络安全保卫从“被动防御”到“主动出击”的新篇章。因此,将主要介绍UEBA在企业异常用户检测中的应用情况。首先,通过用户、实体、行为三要素的关联,整合可以反映用户行为基线的各类数据;其次,定义4类特征提取维度,有效提取几十种最能反映用户异常的基础特征;再次,将3种异常检测算法通过集成学习方法用于异常用户建模;最后,通过异常打分,定位异常风险最大的一批用户。在实践中,对排名前10的异常用户进行排查,证明安恒信息的UEBA落地方式在异常用户检测中极其高效。     

基于火箭遥测的地面站接收信号情况预估方法

火箭尾焰造成的信号衰减是地面测量点位选择重点考虑的问题,通常采用传统β角确定火箭尾焰对遥测地面站接收信号的影响程度。针对新型固体火箭发射中β角分析法对遥测地面站接收信号情况预测不准确的问题,文中在分析影响遥测地面站信号接收因素的基础上,提出了一种采用信号衰减方向性预估遥测地面站接收信号情况的模型。通过分析火箭遥测实测飞行姿态、位置以及地面遥测设备实际跟踪信号情况确定了模型参数,并通过实例计算证明了该方法优的优越性。     

环氧树脂涂层表面亲水性对微藻黏附性能的影响

在固体材料表面黏附成膜是微藻细胞的一种生理特性。近些年基于微藻生物膜的生物过程，如生物膜贴壁培养和防附着技术受到了很多关注。微藻在固体材料表面的黏附受藻细胞与材料表面之间的相互作用的影响，建立黏附强度与材料表面性质参数间的关系对于通过材料选择来强化或控制微藻生物膜具有非常重要的意义。本工作的目的是揭示和明确材料亲疏水性对微藻黏附的影响，提出了一种双酚A环氧(EP)树脂表面亲疏水改性的方法。通过将亲水性的二乙醇胺(DEA)或疏水性的聚甲基聚硅氧烷(PMHS)加入到EP树脂中反应，EP树脂表面水接触角在36.80?~98.34?范围内可通过加入不同量的DEA或PMHS实现任意可调，材料的表面水接触角与DEA或PMHS加入量之间有线性关系。重要的是这种改性方法获得的材料，其形貌、结构、表面粗糙度等表面性质几乎没有变化，从而在研究和关联微藻黏附量与材料表面亲疏水性(表面水接触角)之间的关系时可以排除亲疏水性之外的其他表面性质的影响；其次，考察了小球藻和栅藻在不同亲疏水性材料表面的黏附行为，结果表明小球藻和栅藻在亲水性和疏水性材料表面均能黏附成膜，但在亲水性材料表面黏附更多更快；建立了微藻最大黏附容量与材料表面接触角之间关联关系，表明微藻最大黏附容量随材料表面水接触角的增大而线性降低，栅藻的表面黏附容量比小球藻大。     

摩擦副表面气膜屏蔽微细电解加工微织构及摩擦性能分析

采用气膜屏蔽微细电解加工方法在金属平面副、圆柱副表面加工不同阵列形貌微织构。通过试验将该方法与微细电解加工的微织构尺寸精度、表面质量、摩擦性能进行对比，研究结果表明，气膜屏蔽微细电解加工的微织构相比微细电解加工方法加工的微织构平面副及圆柱副凹槽深径比分别提高了约45.6%和25.8%，改善了加工的定域性，提高了加工精度。进一步的摩擦磨损试验结果表明，相较于微细电解加工方法，气膜屏蔽微细电解加工出的平面副及圆柱副微凹槽的表面摩擦因数分别减小了13.6%与16.2%，表面摩擦性能得到了提高。     

直接激光沉积Al2O3增强NiCrAlY涂层的微观组织及力学性能

目的改善NiCrAlY涂层微观组织并提高其力学性能。方法采用直接激光沉积方法制备100%NiCrAlY、NiCrAlY+10%Al_2O_3和Ni CrAlY+20%Al_2O_3三种样件,分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)、电子探针X射线显微分析仪(EPMA),对不同成分样件进行相组成分析、微观组织观察以及元素组成检测,使用维式显微硬度测试计和万能摩擦磨损试验机,分别检测各个涂层的显微硬度和摩擦系数。结果在NiCrAlY中添加Al_2O_3后,Al_2O_3以不规则形状或球形分布在晶内或者晶界处,其尺寸小于2μm。三种复合涂层样件均由γ-Ni和β-NiAl相组成,添加Al_2O_3陶瓷颗粒后,涂层一次枝晶臂间距均减小,且Ni-Y相显著减少,Y2O3陶瓷颗粒弥散分布在基体的晶内与晶界处。NiCrAlY、NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3涂层的平均硬度分别为(440.69±30)HV0.2、(482.18±30)HV0.2和(453.09±20)HV0.2,100%NiCrAlY、NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3涂层的摩擦系数分别为0.77、0.55和0.52。结论加入Al_2O_3后,基体晶粒有一定程度的细化。在晶粒细化作用以及陶瓷颗粒弥散作用下,涂层的显微硬度有所提高,其中NiCrAlY+10%Al_2O_3的硬度最高,相比NiCrAlY基体提高了约9.5%。此外,发现添加Al_2O_3后,NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3样件的摩擦系数比NiCrAlY样件下降均超过25%,其中NiCrAlY+10%Al_2O_3样件的磨损量最小,相对于NiCrAlY涂层下降了近13.5%,耐磨性明显改善。     

Strength and deformation properties of frozen sand under a true triaxial stress condition

In recent years, the mechanical properties of frozen soils under complex stress states have attracted significant attention; however, limited by the test apparatus, true triaxial tests on frozen soils have rarely been conducted. To study the strength and deformation properties of frozen sand under a true triaxial stress state, a novel frozen soil testing system, i.e., a true triaxial apparatus, was developed. The apparatus is mainly composed of a temperature control system, a servo host system, a hydraulic servo loading system, and a digital control system. Several true triaxial tests were conducted at a constant minor principal stress (σ₃) and constant intermediate principal stress ratio (b) to study the effect of intermediate principal stress (σ₂) on the mechanical properties of frozen sand. The test results showed that the stress–strain curve can be mainly divided into three stages, with evidence of strain hardening characteristics. The strength, elastic modulus, and friction angle increased with the increase in b from 0 to 0.6, but decreased when increasing b from 0.6 to 1, whereas the cohesion varied little with the variation in b. The deformation in the direction of σ₂ changed from dilative to compressive and that in the direction of σ₃ remained dilative throughout.