靠背式测速探头感受特性的数值模拟研究

本文针对在流场中速度、方向的测量问题,提出一种新型的靠背式测速探头的设计方案,并通过数值的手段模拟了靠背式测速探头的不同切向角对气流流向的感受特性。研究发现,当气流方向与靠背式测速探头的迎流面之夹角为15°时,靠背式测速探头比例系数值会出现极值点。这一现象的发现为在流动测量中对方向进行识别提供了依据。     

塑料发泡中复杂流场流体动能气泡成核理论

气泡成核、长大与固化定型是泡沫塑料成型的三个基本过程,而气泡成核是最关键的一步。本文分析指出了经典成核理论对于动态聚合物熔体中气泡成核分析的局限性,对静态熔体和复杂流场熔体的气泡成核过程分别进行了能量描述,在此基础上建立了塑料发泡中复杂流场流体动能气泡成核理论,以期对塑料发泡中气泡成核过程进行更加全面的描述并更好地指导发泡过程。最后指出了气泡成核研究的发展方向。     

五孔探针在气流速度测量中的应用

气速是工程和实验研究所关注的重要参数之一,在化工领域内对流体速度进行准确测量对实验结果至关重要.本文对五孔探针在气速测量相关方法中的应用进行说明,尤其是对在高速测量中五孔探针的使用进行详细的研究.对五孔探针在Ma＞0.3的高速气流速度测量中的应用进行了研究,探讨了五孔探针在高速气流中的标定和测量方法,设计加工了锥形五孔...     

小型直流标定风洞的研制

标定风洞是开展风速传感器标定的重要设备,研制了一套专门用于风速传感器标定的低风速直流风洞。对小型风洞的技术参数确定、洞体气动轮廓设计、洞体整体结构设计与制作等内容进行了介绍,并对风洞的流场进行了全面的校测。流场校验结果表明,该小型直流标定风洞的变频器输出频率与风速有良好的线性关系,出口气流的动压稳定性、均匀性较为理想,湍流度较小,表明小型直流风洞的研制是成功的,可用于风速传感器的标定。     

扫描探针显微镜培训与开放管理

从实验室扫描探针显微镜的平台管理模式、仪器介绍与运行情况分析出发,针对扫描探针显微镜培训人员的选拔、培训的时间安排、培训的基本内容、培训的方式方法、其他功能的培训方法等多个角度对扫描探针显微镜的培训与开放管理进行了全面的分析,提出了扫描探针显微镜培训的新方法与管理新理念,加深学生对扫描探针显微镜的理论认识,加强同学们的动手能力,提高仪器的使用效率。     

扫描探针显微镜培训与开放管理北大核心

从实验室扫描探针显微镜的平台管理模式、仪器介绍与运行情况分析出发,针对扫描探针显微镜培训人员的选拔、培训的时间安排、培训的基本内容、培训的方式方法、其他功能的培训方法等多个角度对扫描探针显微镜的培训与开放管理进行了全面的分析,提出了扫描探针显微镜培训的新方法与管理新理念,加深学生对扫描探针显微镜的理论认识,加强同学们的动手能力,提高仪器的使用效率。     

卡门涡街效应与“不起眼的瓶子”

以流体力学卡门涡街原理为理论基础,对2020年度国际青年物理学家竞赛设计题“不起眼的瓶子”针对性地开展了相关力学设计分析。基于自主搭建的高速纹影测试系统并结合CFD高保真数值仿真计算方法解释了该实验现象背后隐藏的流体力学机理。研究结果表明：在不同工况条件下,高速纹影系统很好地捕捉了蜡烛附近流场变化特征,揭示了圆柱瓶子后方气流流动最大速度大于瓶子前方气流流动初始速度,气流流经瓶子进行绕流产生卡门涡街导致蜡烛熄灭;结合仿真计算结果揭示了该实验在不放置瓶子时气流可以吹灭蜡烛,相同条件下放置瓶子时依然可以吹灭蜡烛原因。     

利用纹影法测量气体的喷流速度

通过自主设计搭建纹影系统和气流发生器,获取了非接触观测不同流量的气体喷流时的流场演化图像,实时展现了流场演化过程中的诸多细节,结合Tracker软件图像分析和COMSOL有限元模拟,定量测量了气体的喷流速度,研究了气体喷流时的动态演化规律.研究结果发现,空气阻力对气体的喷流速度有较大的影响,在空气阻力的作用下喷流速度初...     

软件工程(冶金方向)专业人才培养模式的探讨

根据培养适应冶金行业需求的软件工程人才要求,在分析冶金行业软件人才应具备的基本能力的基础上,确定了软件工程(冶金方向)专业人才的培养目标,从课程体系建设、教材建设、师资队伍建设、教学模式改革、实训基地建设五个方面,探索软件工程(冶金方向)专业人才培养模式。     

新型引射式逆流控制矢量喷管的气动性能

为提高逆流控制矢量喷管的气动性能,提出一种逆流控制矢量喷管的引射设计方案,在喷管外套管尾部沿切线方向引入一股射流,通过改变外套管内部流场及高速气流的卷吸作用,提高整个喷管的推力矢量角。运用数值模拟的方法,对原型喷管与引射式喷管(称为改进型喷管)在相同设计工况下进行计算,先后得到了流场的压力系数、马赫数、流线等分布情况并进行分析。研究表明：引射会对推力矢量角及推力系数产生影响,与同等工况下的原型喷管相比较,改进型喷管的矢量角提高2.89°,推力系数提高0.72%;引射会增大主流两侧压差,同时对主流卷吸使其向上偏转;当引射压强增大时,改进型喷管主流两侧的压差也会随之增大,从而提高推力矢量角。     

Analysis of 1D consolidation with non-Darcian flow described by exponent and threshold gradient

Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom （PTPB） or for pervious top and impervious bottom （PTIB）. For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper.     

沿江出海口平坦城镇雨水管道设计方法探讨

结合沿江出海口平坦地区的水文地理特点 ,提出雨水管道水力计算须按压力流考虑 ,管道水力计算的设计坡度采用水力坡降 ,管道连接采用管底平接的设计思想与计算方法     

动水条件下单裂隙注浆模型试验系统设计

结合工程实践中大多数注浆工程都是在动水条件下进行注浆堵水,研制了动水条件下单裂隙注浆模型试验系统,并进行了验证性试验。模型试验系统主要包括动水水源、注浆系统、模拟裂隙和数据采集系统设备。研制的模型试验系统解决了动水水源进入裂隙时为裂隙流、水头稳定、水头高度可调,注浆系统设备的注浆量可调,注浆压力和注浆速度可控,模拟裂隙设备的裂隙开度可调,裂隙粗糙度可变,扩散规律易于观察和数据易于采集,监测系统中浆液扩散、渗流压力和流出液体重量实时记录等关键问题。验证试验结果表明,模型试验系统可以在动水条件下进行单裂隙注浆试验并能获得浆液扩散规律、流出液体重量和渗流压力变化规律。     

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result. Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097)     

Low frequency oscillatory flow in a rotating curved pipe

INTRODUCTIONThemotionoftheflowinarotatingcurvedpipeisafundamentalproblem ,whosesolutionhaspotentialapplicationsingasturbines ,elec tricgenerators ,electricmotorsandsomeequip mentsusedinseparationprocesses.Itisimpor tanttoknowtheflowstructurecharacteristic…     

论破产管理人民事责任的归责原则

民事责任的归责原则关系到民事纠纷的正确解决和当事人权利的保护．体现了法律对相互冲突的民事利益的平衡和选择。无论从实际情况来分析,还是从过错责任原则的制度价值以及国外破产立法来看,破产管理人民事责任的归责原则只能是过错责任原则。无过错责任说不仅无益于侵权行为的预防与遏制．反而只能打击和挫伤破产管理人的工作积极性。     

Low frequency oscillatory flow in a rotating curved pipe

The low frequency oscillatory flow in a rotating curved pipe was studied by using the method of biparameter perturbation. Perturbation solutions up to the second order were obtained and the effects of rotation on the low frequency oscillatory flow were examined in detail. The results indicated that there exists evident difference between the low frequency oscillatory flow in a rotating curved pipe and in a curved pipe without rotation. During a period, four secondary vortexes may exist on the circular cross-section and the distribution of axial velocity and wall shear stress are related to the ratio of the Coriolis force to centrifugal force and the axial pressure gradient. Project (No: 10272096) supported by the National Natural Science Fundation of China     

诊断彩色显像管的一种巧妙方法

从阴极引脚接点互换和偏转线圈引线互换两个方面对“引脚线互换法”及其用法进行了阐述。该法可巧妙地诊断彩电或彩显偏(缺)色故障和非对称性异常光栅故障。     

浅析如何提高每股收益信息的使用价值

从公司利润对每股收益的决策作用这个角度，分析了公司利润在确认、计量、报告中存在的质量问题，从而揭示了每股收益信息存在的问题，进而提出解决问题的几点措施。