微波诱导光学核极化进展

微波诱导光学核极化（Microwave-Induced Optical Nuclear Polarization,MIONP）技术利用光激发三重态样品来极化电子,再用微波将处于非热平衡态的电子极化转移到待检测原子核,将原子核的检测灵敏度提高几个量级甚至更多．这种灵敏度极化增强方法可以用来进行蛋白质结构和动力学检测、光化学和光物理进程的基础研究、量子计算和低场核磁共振（Low-field Nuclear Magnetic Resonance,Low-field NMR）与磁共振成像（Magnetic Resonance Imaging,MRI）应用研究．该文简要分析了MIONP的物理原理及其在核极化增强中的优势,结合实验条件综述了一些重要的成果．最后,对微波诱导光学核极化的前景作了展望．     

巡天光谱中拼接异常光谱的自动检测和异常分级方法

拼接异常是光谱在红蓝两端拼接区域表现出的光谱连续性差的一种现象。在LAMOST的光谱处理中,仪器的稳定性、观测条件以及获得的响应函数等问题都是造成拼接异常的原因。光谱拼接是否正常对于光谱发布等后续工作的质量有重要影响。提出一种拼接异常光谱的自动检测方法,有效地提高了工作效率。该研究可以为LAMOST数据提供一个自动的标记,来评价拼接质量,也可以为用户提供一个使用数据时的选择。该方法首先将待测光谱进行流量归一化、去除钠线等预处理,并将其分为红蓝两端;然后对红蓝两端分别进行拟合;最后对两条拟合曲线,选取一系列等波长间隔的点,计算在这些点处的流量差值,得到所有流量差值的均值,标准差,并且计算两条曲线积分面积的差值;基于上述统计量,提出了一个判断光谱是否异常及其异常程度的评价函数。大量的实验证明,该方法具有良好的拼接异常光谱检测效果。     

一种骨小管中液体流动产生的流量及切应力模型

骨组织受力变形后其内部液体就会流动,同时在其微观结构——骨单元壁中扩散,并进一步产生一系列与骨液流动相关的物理效应,如流体剪切应力、流动电位等,这些物理效应被细胞感知并做出破骨或成骨等反应,来使骨适应外部载荷环境.鉴于骨组织产生的内部液体流动很难实验测定,理论模拟是目前的主要研究手段.基于骨单元的多孔弹性性质建立了骨小管内部液体的流动模型,该模型将骨单元所受的外部载荷与骨小管内部液体的压力、流速、流量和切应力联系起来,并进一步可以研究其力传导与力电传导机制.骨小管模型的建立分别基于中空和考虑哈弗液体的骨单元模型,并考虑了骨单元外壁的弹性约束和刚性位移约束两种边界条件.最终得到骨单元在外部轴向载荷作用下,骨小管内部液体的流量及流体切应力的解析解.结果表明:骨小管中的液体流量与流体切应力都正比于应变载荷幅值和频率,并由载荷的应变率决定.因此应变率可以作为控制流量和流体切应力的一种生理载荷因素.流量随着骨小管半径的增大而非线性增大,而流体切应力则随着骨小管半径的增大而线性增大.此外,在相同的载荷下,含哈弗液体的骨单元的模型中,骨小管中液体的流量和切应力均大于中空骨单元模型.     

梯形薄壁堰流量规律数值模拟研究

旨在用数值模拟方法推求计算梯型薄壁堰堰流的简化公式。通过推求梯型薄壁堰堰流的基本理论公式,并求解气液两相流时均方程,辅以RNG k-ε湍流模型模拟了5种不同堰顶水头下梯形薄壁堰的过流能力。用SIMPLE算法对模拟体系中的压力与速度的耦合进行求解,同时用VOF法对自由水面的流动变化信息进行捕捉;进而通过最小二乘法的拟合得到模拟的流量值随堰顶水头变化的简化计算式,采用此公式计算了梯形薄壁堰在不同堰顶水头时的过流流量,与所推基本理论公式的计算值相比结果基本一致,可为实际工程中流量的控制和测量提供参考。     

一种新型光纤Bragg光栅流量传感器的仿真与实验研究

为了克服传统单个光纤布喇格光栅传感器对温度交叉敏感的问题,设计制作了一种基于双光纤布喇格光栅的以阻流件和弹性体为换能元件的流量传感器.该流量传感器采用弹性伞状结构体作为流量传感器的换能元件,用硅胶树脂封装双光纤光栅的弹性伞状结构体,起到了温度补偿的作用且提高了应变测量灵敏度.用有限元优化传感器结构,在1~20m/s的流速下利用ANSYS对传感器结构和传感器周围的流体场进行模拟分析,并计算了传感器的灵敏度,实验证明了硅胶树脂作为封装材料的优越性.进行了砝码干校法模拟实验,完成传感器封装前后的性能测试,通过提取该传感器的反射谱信号特征值,得到封装前后传感器的载荷响应灵敏度分别为:1.71nm/kg,0.103nm/kg.表明该流量传感器结构简单、安装方便、具有较好的线性度和灵敏度.     

Flow characterization and dilution effects of N_2 and CO_2 on premixed CH_4/air flames in a swirl-stabilized combustor

Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goal is to provide a systematic assessment on combustion characteristics in diluted regimes for its application to environmentally-friendly approaches such as biogas combustion and exhanst-gas recirculation technology. Two main diluting species, N2 and CO2, are tested at various dilution rates. The results obtained by means of optical diagnostics show that five main flame regimes can be observed for Nz-diluted flames by changing excess air and dilution rate. CO2-diluted flames follow the same pattern evolution except that all the domains are shifted to lower excess air. Both N2 and CO2 dilution affect the lean blow- out （LBO） limits negatively. This behavior can be counter-balanced by reactant preheating which is able to broaden the flammability domain of the diluted flames. Flame reactivity is degraded by increasing dilution rate. Meanwhile, flames are thickened in the presence of both diluting species. NOx emissions are significantly reduced with dilution and proved to be relevant to flame stability diagrams： slight augmentation in NOx emission profiles is related to transitional flame states where instability occurs. Although dilution results in increase in CO emissions at certain levels, optimal dilution rates can still be proposed to achieve an ideal compromise.     

风力机风轮振动特性研究

针对风轮的轴向窜动效应和陀螺效应振动特性,采用流固耦合分析原理进行模态数值模拟及风力机实际运行状态下的试验验证.结论发现:轴向窜动效应振动的触发源于塔架弹性,气动载荷和离心力对该类振动频率的变化基本没有影响;陀螺效应振动的触发源于同一时刻不同叶片表面气动压力的不对称,气动载荷中的周向力是导致该类振动频率发生变化的主要原因,轴向力则对其振动频率的变化没有影响,离心力对该类振动频率的变化影响不大,且近似成线性.相关研究成果,可能为很多风力机在远短于设计寿命期内频繁发生叶根损伤和断裂、变速箱齿轮严重磨损、发电机主轴变形等一些困扰学界的问题提供新的分析思路和答案.     

周期射流冲击下导流板流动换热特性数值研究

本文对被动隔热导流板在周期射流冲击环境下的流场特性及热响应特性进行三维数值研究,分析了射流喷管与导流板间距、导流板水平倾角及轴向倾角三个参数的影响规律。研究结果表明射流空气冲击到导流板后90%的气流被向上侧及前后两侧偏导,导流板的水平倾角越大则气流向上侧偏导能力越弱,轴向倾角的存在可实现对气流前后侧导流流量的分配。导流板耐热层温度在进入第四个射流周期后呈现稳定周期波动,射流冲击距离越小、导流板水平倾角越大则其板面温度水平越高。     

贝雷砂岩射孔孔道流动效应正交计算分析

对射孔孔道流动效应进行了量纲分析,建立了轴向和径向流量与影响流量因素间的工程表达式。综合考虑影响流动效应的主要因素和取值范围,设计了数值模拟计算工况的正交计算方案,并利用ANSYS/FLOTRAN流体程序进行了带损伤区贝雷砂岩流量数值模拟研究,获得了各个计算方案的径向流量和轴向流量,用以确定出流量公式的系数。最终确定的流量公式表明,各要素对流量影响的重要顺序依次为固有渗透率、损害区厚度、孔深、渗透率剩余百分数和孔径。     

A qualitative study on the pulsatile flow phenomenon in a dense fly ash pneumatic conveyor

Understanding of the dynamic particulate flow structures within a dense gas-fly ash pneumatic conveyor must be improved in order to better aid its design guidance.The complex pulsatile movement of the gas-fly ash mixture dominates the flow performance within the pipeline,and historically,non-invasive measurement devices such as the electrical capacitance tomography（ECT） were often used to sufficiently capture the flow dynamics.However,inadequate studies have been conducted on the pulsatile flow phenomenon,which directly relate to the gas-fly ash two-phase flow performance.This paper aims to investigate the pulsatile flows using an ECT device.Initially,pulsatile flow patterns under various experimental conditions were obtained through ECT.Pulses within a flow were then characterised into pulse growth and decay segments,which represent the superficial fluidisation and deaeration processes during conveying.Subsequently,structural and statistical analyses were performed on the pulse growth and decay segments.Results suggested that the increasing air mass flow rate led to the decrease of the superficial fluidisation/deaeration magnitude,however,the increase of the superficial fluidisation/deaeration durations.Also,the air mass flow rate was indicated as the dominant factor in determining the pulsing statistical parameters.This research provides fundamental insights for further modelling the dense fly ash pneumatic flows.