小掠角下波束折射声场的数值计算

文章针对小掠角下的波束折射声场进行了数值计算,一般将远场的有指向性的球面波视为平面波束,除截取3dB带宽外不再考虑指向性问题,此处,对折射声场进行了更为准确地计算,给出了理论推导和数值计算的结果,并与相关试验进行了定性对比。通过研究,考虑指向性的球面波束（这也是实际情况）的声中心会在折射之前在界面上发声水平位移。同时,指向性对折射声场也有不小的影响。最后,对相关问题提出了建议。     

高频宽波束球冠形换能器研究

通过解析法以及有限元法分析,设计制作了一种球冠形复合材料换能器,在频率为300kHz时的水平及垂直指向性均大于46°,其制作工艺简单、成本不高。     

回波图像混响抑制方法研究

针对二维图像声呐近程混响干扰严重,无法分辨目标亮点的问题,基于混响信号自动增益控制(AGC)的基本原理,对时间增益控制电路进行改进,实现了混响背景平稳化。回波图像仿真结果表明,此方法能较好改善回波图像质量,有利于对目标的定位与识别。     

圆柱阵主动声纳混响抑制方法研究

圆柱阵主动声纳混响的强非均匀性,会降低空时自适应处理的性能。对圆柱阵主动声纳混响的空时二维分布特性以及混响数据的非均匀性进行分析,在此基础上研究了基于修正的角度-多普勒补偿(Modified Angle-Doppler Compensation,MADC)和导数更新技术(Derivative Based Updating,DBU)的降维自适应处理方法在圆柱阵声纳混响抑制中的应用。仿真结果表明:这两项技术可降低混响的非均匀程度,对运动中的圆柱阵主动声纳有较好的混响抑制效果,其性能更接近最优处理。     

钢筋混凝土板裂缝开展角的计算方法

本文研究了钢筋混凝土板固定角（α２）、裂缝开展角（α＇）、转动角（α）和钢筋角（αｓ）之间的关系,建立了钢筋混凝土板的平衡方程、协调方程以及钢筋和混凝土的本构方程,提出了钢筋混凝土板裂缝开展角的计算方法．通过两块板的计算结果与试验结果的比较,本文提出ｒ计算方法的可靠性得到了验证．     

有风攻角的棱柱体驰振计算方法研究

基于准定常理论,推导了有风攻角的横风向驰振临界风速以及振幅计算公式。采用H形柱开展风洞试验,发现:关于驰振临界风速,在较小的风攻角下本文方法计算结果和Den-Hartog公式计算结果很接近,而在较大的风攻角之下两者相差较大,说明Den-Hartog公式无法应用于较大风攻角的驰振计算;关于驰振振幅,理论计算结果和试验非常吻合,证实了该计算方法的正确性。     

电磁混响室内的场均匀性与均方根时延展宽波动性研究

在评定电磁混响室内的场均匀性基础上,进一步测试了机械搅拌桨的扰动以及不同接收天线位置对所模拟复杂无线信道的均方根时延展宽波动性的影响。证明了该新建电磁混响室的场均匀性指标优于2.5 dB,且定量评价了均方根时延展宽波动范围。对两类指标差异性的分析则进一步明确了场均匀性与均方根时延展宽波动性在不同应用中的作用。     

用有限多途声线计算浅海混响衰减规律的研究

以射线声学理论为基础,推导出典型海洋环境下各类多途声线的海底混响平均强度计算式,在数值计算的基础上,分析比较各类多途声线海底混响的相对大小以及它们对总混响的贡献,以确定用射线线声学方法计算海底混响时,最有效的多途声线数.     

预白化与小波变换联合的混响抑制方法研究

针对主动声呐在强混响背景下匹配滤波器检测性能不理想的问题,提出了将预白化与小波变换联合处理方法.首先将混响预白化处理,然后通过小波变换将混响和回波信号分解到不同的尺度空间下,在尺度空间进行阈值量化处理,对有用的信号成分进行数据重构,最后利用重构的数据进行匹配滤波处理,使得混响被有效抑制,改善检测性能.仿真和试验数据处理...     

轨道车辆车钩垂向最大摆角计算方法

针对传统的车钩最大摆角计算方法的不足,提出了基于含故障的车辆动力学模型的车钩垂向最大摆角计算方法。依据该方法,对某型地铁连挂车辆开展了悬挂故障下的车钩垂向最大摆角分析,研究了关键参数对车钩最大摆角的影响规律。结果表明,新方法相比传统计算法可以充分考虑车体柔性、故障冲击下各悬挂变形等因素,在单个钢簧断裂和单个空簧失气工况下,新方法的最大摆角计算结果相比理论计算法分别偏大1.2%和10.2%。此外,钢簧断裂的下降量每增加5 mm,车钩摆角增大约0.086°,空簧失气的下降量每增加5 mm,车钩摆角增大约0.173°;车体垂向变形每增加1 mm,车钩摆角均增大约0.05°。     

Propagation through the ocean's surface at shallow angles with a laser beam

Propagation through the ocean's surface at shallow angles with a laser has been successfully demonstrated experimentally in the ocean. A 6-mJ multipulse laser at a depth of 1.5 m in water with an attenuation coefficient of approximately 3.3 m(-1) was easily detected 600 m away on a sunlit day at an angle of 1 degree to the ocean's surface. The measured efficiency was 3.6 x 10(-2) (J/J)/sr (joules received per receiver steradian per joule transmitted). Statistical ray trace analysis and physical tank modeling produced equivalent efficiencies.     

基于回传射线矩阵法的含裂缝智能梁的动态特性

基于压电阻抗（EMI）技术和回传射线矩阵法（RMM）对含裂缝智能梁进行了振动特性研究,提出了修正的理论模型,使得压电阻抗信号能与结构裂缝的各物理参数定量地联系起来。采用Timoshenko梁理论描述了含裂缝梁的弯曲振动特性。结构裂缝模拟为具有一定刚度的转动弹簧。对于黏贴有压电片的结构元件,把它作为压电片－粘结剂－主体梁这一耦合结构系统加以考察。最后推导出包含了结构裂缝信息的压电阻抗的解析表达式。基于该模型,与实验数据以及其它研究结果进行了对比分析。最后,考察了各物理参数对压电阻抗信号的影响。 .     

Effects of a butterfly scale microstructure on the iridescent color observed at different angles

Multilayer thin-film structures in butterfly wing scales produce a colorful iridescence from reflected sunlight. Because of optical phenomena, changes in the angle of incidence of light and the viewing angle of an observer result in shifts in the color of butterfly wings. Colors ranging from green to purple, which are due to nonplanar specular reflection, can be observed on Papilio blumei iridescent scales. This refers to a phenomenon in which the curved surface patterns in the thin-film structure cause the specular component of the reflected light to be directed at various angles while affecting the spectral reflectivity at the same time by changing the optical path length through the structure. We determined the spectral reflectivities of P. blumei iridescent scales numerically by using models of a butterfly scale microstructure and experimentally by using a microscale-reflectance spectrometer. The numerical models accurately predict the shifts in spectral reflectivity observed experimentally.     

Dependence on the sample width of signals from a near-field optical microscope

We numerically investigated signals from a scanning near-field optical microscope (NOM) for samples of various sizes by using the finite-difference time-domain method. Under the usual conditions that apply to detection, the signal intensity depends on the width of the sample, even though the sample will be wider than the wavelength, which is much larger than the aperture, i.e., the lateral resolution of the NOM. This is an obstacle to measuring the local optical constant of samples by means of obtaining the signal intensity. When waves propagating in all directions are collected, this dependence on the sample width is reduced. The whole angle detection is important for observing the distribution of the optical constants.     

Influence of the shock wave pressure gradient in α-Fe irradiated by a high-power ion beam on the occurence of a microhardness maximum at large depths

The defect structure and microhardness of α-Fe irradiated by a high-power pulsed beam have been studied using positron annihilation, transmission electron spectroscopy, and a nanoindenter, and results are presented. It is shown that in α-Fe exposed to a high-power pulsed beam, the pressure gradient and depth of formation of the shock wave front influence the formation and location of the dislocation density maximum and the microhardness maximum in the modified layer. Pis’ma Zh. Tekh. Fiz. 24, 47–53 (February 12, 1998)     

大跨度梁式渡槽改进拟三维流固耦合模型的三维模拟效果分析

针对作者提出的大跨度梁式渡槽改进拟三维流固耦合模型,分析了该模型的三维模拟效果。分析结果显示,采用大跨度梁式渡槽的改进拟三维流固耦合模型不仅能很好地反映出三维耦合效应,而且可以有效降低计算成本,大大提高了计算效率。因此,改进拟三维流固耦合模型可以用于大型梁式渡槽多跨联合的复杂三维动力流固耦合分析计算。     

Theory of the acoustic radiation force exerted on a sphere by standing and quasistanding zero-order Bessel beam tweezers of variable half-cone angles

A rigorous theory is developed to predict the radiation force (RF) exerted on a sphere immersed in an ideal fluid by a standing or quasistanding zero-order Bessel beam of different half-cone angles. A standing or a quasistanding acoustic field is the result of counter propagating 2 equal or unequal amplitude zero-order Bessel beams, respectively, along the same axis. Each Bessel beam is characterized by its halfcone angle β_l;l = 1, 2 of its plane wave components, such that β_l = 0 represents a plane wave. Analytical expressions of RF are derived for a homogeneous viscoelastic sphere chosen as an example. RF calculations for a polyethylene sphere immersed in water are performed. Particularly, the half-cone angle dependency on the RF is analyzed for standing and quasistanding waves. Changing the half-cone angle is equivalent to changing the beamwidth. Potential applications include particle manipulation in microfluidic lab-on-chips as well as in reduced gravity environments.     

Research on the formation mechanism of big data technology cooperation networks: empirical evidence from China

Scientometrics - The purpose of the present paper is to investigate the formation mechanism of big data technology cooperation networks by considering the combined effect of three key factors,...     

Application of the Kirchhoff method to the problem of wave diffraction on a ribbon at small sliding incidence angles

A new approach to the problem of electromagnetic wave diffraction on a conducting ribbon at small sliding incidence angles is developed within the framework of the Fresnel-Kirchhoff method. The wave diffraction in this system has been theoretically and experimentally studied using the proposed method. The experimental data agree with the results of theoretical analysis.