四孔差分像运动测量大气相干长度的方法研究

 介绍了最新研制的基于四孔差分像运动法到达角起伏测量仪，利用该仪器测量的4个方向（两组正交方向）上的到达角起伏方差，从而推算出大气相干长度。在近地面水平路径的实验中发现，不同方向上的测量结果获得的大气相干长度值有一定的差别。测量结果表明：大气湍流存在一定的各向异性，在实际应用中应考虑这个因素；在一些应用场景下，大气相干长度应根据至少一组正交方向的测量结果来分析确定。     

融合K-means和熵权法的高鲁棒性大气边界层高度估计方法

针对常用激光雷达边界层高度估计方法在云层或悬浮气溶胶层等复杂大气结构下会产生误判的问题，提出一种融合K-means和熵权法的高鲁棒性大气边界层高度估计方法。选取美国大气辐射测量项目南部大平原站点的微脉冲激光雷达数据，将K-means算法和熵权法应用于多种条件下的边界层高度估计，从初始参数选取和距离计算两个方面提升基于聚类分析的边界层高度的估计性能。实验结果表明：与常用激光雷达边界层高度估计方法相比，所提方法具有较强的抗干扰能力，能更好地追踪复杂大气结构下的边界层高度日变化过程；在晴朗无云天气和复杂大气结构下，其边界层高度的估计值与无线电探空仪边界层高度的测量值基本一致，相关系数分别为0.9718和0.9175。所提方法具有较高的鲁棒性，可以可靠地估计多种条件下的大气边界层高度。     

激光雷达探测北京城区夏季大气边界层

为了研究北京城区夏季大气边界层结构变化特征及大气边界层内气溶胶消光特性,2004年8月利用便携式米散射激光雷达对北京城区夏季大气边界层进行了系统观测。反演了观测站上空大气气溶胶的消光特性垂直分布以及大气边界层的高度。分析了气象条件和人类活动对大气边界层结构的影响。观测数据表明： 北京城区夏季大气边界层有明显的日变化特征,早晚比较低,日间有一个从低变高再变低的过程,中午前后达到最高。结合气象参数对测量数据进行的统计分析表明：北京城区夏季大气边界层高度相对稳定,多分布在1.8km以下,平均值为0.68km;大气边界层内存在浓度较高的气溶胶粒子,平均光学厚度（3km以内）在0.30左右。     

海面大气边界层中聚焦光束漂移各向异性的实验研究

 利用位置敏感型光电倍增管（PSPMT），设计了测量聚焦光束漂移的实验装置。该装置在80 mm的有效探测面内实现了2维位置信号的直接探测，空间分辨率可达1 mm，明显优于四象限探测器和阵列探测器，最高采样频率可达80 kHz，且动态范围很大，优于一般的成像器件。在近海岸海面上5 m处的大气边界层中进行了距离为1 000 m的聚焦激光传输实验。测量结果表明：聚焦光斑的质心漂移具有各向异性，水平方向光斑漂移幅度一般介于5.61 mm和14.83 mm之间，垂直方向光斑漂移幅度介于3.54 mm和7.3 mm之间，两者之比的平均值为1.69；水平方向和垂直方向的光斑漂移功率谱密度（PSD）在低频段也存在差异，垂直方向光斑漂移的PSD比水平方向光斑漂移的PSD下降速率更快。     

北京城区大气边界层的激光雷达观测

激光雷达是边界层大气气溶胶和云的一个高效探测工具。利用MPL激光雷达测量出的数据反演出了测站地域上空大气边界层气溶胶消光系数的垂直分布,利用气溶胶消光系数的垂直分布可决定测站上空的大气边界层高度。测量数据表明:大气边界层内气溶胶的含量较为稳定,有明显的气溶胶多层结构。     

热带气旋大气边界层风洞模拟

在风洞中正确复现大气边界层特性是保证风洞实验结果准确度的必要条件。本文利用三角形尖劈和粗糙元配合对风洞内热带气旋大气边界层模拟进行了研究,生成了较好反映热带气旋风特性的大气边界层,平均速度和湍流强度廓线与设计值吻合较好,同时提出了用于热带气旋大气边界层内的风力机模型的设计要求。     

复杂地形风场绕流数值模拟方法

与一般的工业问题相比,风电场近地面的流动总是充分发展的湍流边界层流动.为了把已广泛应用于工业问题分析的CFD软件包FINE/TURBO和带有壁面函数的k-ε湍流模型用于复杂地形地貌风电场大气流动的数值模拟,本文首先以平板地形为几何模型,探索湍流模型及壁面函数模型中的一些参数对模拟沿流动方向均匀大气边界层的影响.然后采用...     

激光云高仪对那曲地区大气边界层高度的探测分析

2014年7月至8月在第三次青藏高原大气科学试验的支持下,分析了夏季那曲地区大气边界层高度日变化特征.采用激光云高仪通过后向散射信号梯度法求得大气边界层高度,将云顶高度判定为边界层高度时,那曲地区对流边界层高度最高可达3800m,在夜间稳定边界层情况下,最低只有40m.采用无线电探空仪数据,利用位温梯度法、相对湿度梯度法求得大气边界层高度.利用云高仪与探空仪同步实验40天得到的有效数据,对后向散射信号梯度法与位温梯度法得到的大气边界层高度的相关性进行分析,相关系数达0.78,标准偏差为738.84m.对8组较为异常量据的再分析发现云高仪在晴空探测大气时信噪比存在一定的不足.对比早、晚测量结果可知,那曲地区大气边界层高度日变化大,是由于该地区地处内陆海拔较高,夏季日照辐射相对平原地区较强,对流和气温强烈的日变化引起大气层结日变化较大.     

利用湍流廓线获得斜程大气相干长度的实验研究

 用两种方法获得有限高度斜程大气相干长度。一种方法用安置在测量铁塔上的温度脉动仪以及多普勒声雷达测量了大气边界层下部折射率结构常数廓线，用以计算有限高度球面波斜程大气相干长度；另一种方法用系留气球搭载一个点光源，在地面用差分光学系统接收球面波到达角起伏法测量了实时斜程大气相干长度。对实验结果进行了比较和分析，二者都反映了实际大气斜程相干长度的时间变化特点。两种方法结果的相关性比较好，因此两种方法都可以在大气光学传输研究中应用。最后在实验的基础上对湍流廓线计算球面波斜程大气相干长度作了讨论。     

Mie散射激光雷达研究大气边界层特性

基于Mie散射大气激光雷达,应用Klett算法对回波信号进行了反演,得到大气消光系数和后向散射系数。然后,通过对大气后向散射系数曲线进行拟合得到大气边界层混合层高度以及卷夹层厚度等特征参数。对比雷达实测数据与探空气球所测数据,证明二者存在较好相关性。基于实测数据讨论了四川盆地大气边界层特性对气候的影响。     

Sidelobe suppression in volume holographic optical correlators by use of speckle modulation

By use of speckle modulation on the object beam of a volume holographic optical correlation system, we show that the sidelobes of the correlation patterns along the vertical direction, as well as those along the horizontal direction, are well suppressed. A theoretical explanation and experimental results are presented and discussed.     

类氖锗X射线激光光学特性研究

本工作测量了类氖锗3s-3p X射线激光的23.2nm和23.6nm两条强激光跃迁线水平方向和垂直方向的空间分布,当靶长20mm时,X射线激光水平方向束发散角约为12mrad,主束指向偏离线状等离子体轴线约8mrad;垂直方向束发散角约为22mrad,本工作还采用钼/硅多层膜平面反射镜,对X射线激光进行正反射,获得了X射线激光双程放大的光学特性。 关键词：     

On the weakly damped vibrations of a vertical beam with a tip-mass

In this paper the wind-induced, horizontal vibrations of a weakly damped vertical Euler-Bernoulli beam with and without a tip-mass will be studied. The damping is assumed to be boundary damping and global Kelvin-Voigt damping. The boundary damping is assumed to be proportional to the velocity of the beam at the top. The horizontal vibrations of the beam can be described by an initial-boundary value problem. In this paper, the multiple-timescales perturbation method will be applied to construct approximations of the solutions of the problem. Also it will be shown that a combination of boundary damping and Kelvin-Voigt damping can be used to damp the wind-induced vibrations of a vertical beam with tip-mass uniformly.     

光折变晶体LiNbO_3:Fe中的特殊散射现象

用柱面透镜把经针孔滤波器扩束的激光束沿某一个方向聚焦成细丝状(或长条状),细丝状光束垂直入射到LiNbO_3:Fe晶体上,在远场位置观察散射光.我们发现光散射的方向与晶体的c轴方向不一致,不仅沿着晶体的c轴方向有散射光出现,沿光束的条形方向也出现很强的散射光.     

Transmission beam pattern and echolocation signals of a harbor porpoise (Phocoena phocoena)

The transmission beam pattern of an echolocating harbor porpoise (Phocoena phocoena) was measured in both the vertical and horizontal planes. An array of seven Brüel and Kjaer 8103 hydrophones connected to an amplifier-line driver module was used to measure the beam patterns. The porpoise was trained to station in a hoop and echolocate a cylindrical target located at a range between 7 and 9 m while the array was located 2 m in front of the hoop. The 3-dB beamwidth in both the vertical and horizontal planes was the same at approximately 16 degrees and the beam was pointed toward the forward direction. The individual hydrophones in both the vertical and horizontal arrays measured signal waveforms that were similar throughout the 40-degree span of the array. The porpoise emitted signals with intervals that were 20 to 35 ms longer than the round trip travel time between the animal and the target. The average source level, peak frequency, and bandwidth were 157 dB, 128 kHz, and 16 kHz, respectively.     

Heat and mass transfer characteristics during rapid solidification of Fe-Cu peritectic alloys

The viscose flow and microstructure formation of Fe-Cu peritectic alloy melts are investigated by analyzing the velocity and temperature fields during rapid solidification, which is verified by rapid quenching experiments. It is found that a large temperature gradient exists along the vertical direction of melt puddle, whereas there is no obvious temperature variation in the tangent direction of roller surface. After being sprayed from a nozzle, the alloy melt changes the magnitude and direction of its flow and velocity rapidly at a height of about 180 μm. The horizontal flow velocity increases rapidly, but the vertical flow velocity decreases sharply. A thermal boundary layer with 160–300 μm in height and a momentum boundary layer with 160–240 μm in thickness are formed at the bottom of melt puddle, and the Reynolds number Re is in the range of 870 to 1070 in the boundary layer. With the increase of Re number, the cooling rate increases linearly and the thickness of thermal boundary layer increases monotonically. The thickness of momentum boundary layer decreases slowly at first, then rises slightly and decreases sharply. If Re < 1024, the liquid flow has remarkable effects on the microstructure formation due to dominant momentum transfer. The separated liquid phase is likely to form a fiber-like microstructure. If Re>1024, the heat transfer becomes dominating and the liquid phase flow is suppressed, which results in the formation of fine and uniform equiaxed microstructures. Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105)     

Echolocation transmitting beam of the Atlantic bottlenose dolphin

The transmitting beam patterns of echolocation signals emitted by an Atlantic bottlenose dolphin Tursiops truncatus were measured in the vertical and horizontal planes with an array of seven hydrophones. Particular emphasis was placed on accurately verifying the animal's position on a bite-plate/tail-rest stationing device using underwater video monitoring equipment. The major axis of the vertical beam was directed at an angle of 5 degrees above the plane defined by the animal's lips. This angle was 15 degrees lower than previously measured. The vertical beam measurements indicate that the major axis of the transmitting beam is aligned with the major axis of the receiving beam. The horizontal beam was directed forward. The directivity index of 26.5 dB calculated from the beam pattern measured in both planes agreed well with previous calculation of 25.4 dB.     

激光大气闪烁的高频谱特性

 采用三波长闪烁仪进行了大气边界层的光传输实验，结果表明：在相同的传播条件下，非平面波激光大气闪烁功率谱的高频部分与波长存在着一定的关系，功率谱无标度区间的斜率即标度指数是一个与湍流强度、波长等因素有关的函数，在满足弱起伏的条件下，标度指数一般与波长呈负相关，波长愈长则标度指数愈小，频谱下降的趋势愈快；波长愈短则标度指数愈大，频谱下降的趋势愈慢。