浅海遥感图片海底研究

利用海洋水色进行浅海水深反演,国内外已经提出了很多方法,并建立了各种模型。在他们的反演系统中,无一例外的要运用不同的水下测试仪器进行某些信息的提取,利用提取的信息确定参数,从而完成水深反演。在脱离任何水下测试仪器的情况下,仅通过卫星图片或航空图片提取浅海水深信息,利用海洋水色变化的基本原理,讨论了辐照度与波长以及水深的关系,模拟了浅海水下地形,并通过三维立体形式演示海底地貌。以遥感图片和数码照片为例,分别模拟了所拍摄地区的浅海海底概貌。结果表明,此方法具有一定的可行性,可以进行更深层次的研究,并可应用于航海安全保证、大陆架遥感测绘和环境检测等多个领域。     

基于通道型光电倍增管的电弧放电检测

针对电气设备接触不良或质量缺陷引起的电弧放电现象对用电设备安全运行的影响,本文分析了电弧的产生机理及检测方法.依据紫外光强辐射特点,设计了基于通道型光电倍增管的检测系统.通过实验,对放电弧光进行捕获,作为判断电弧放电程度依据,实现对电气设备的有效保护和控制.实验表明,该系统灵敏度高,线性度好,能实现微弱紫外光探测在线监测.     

采用混合模型数值模拟从深海到浅海内波的传播

在南海东沙岛附近, 从MODIS遥感图像发现内波传播是从深海经陆架坡再到浅海, 由于深海和浅海环境条件的差异以及传播模型的适用条件不同, 因此 不能采用同一模型模拟内波的传播, 需用两种模型来分别模拟内波在深海和浅海中的传播. 采用差分法, 首先用非线性薛定谔方程模拟了深海内波的传播, 然后用EKdV方程模拟了内波在浅海中的继续传播. 模拟结果与实际的MODIS遥感内波图像相符合, 并与应用单一模型模拟结果相比, 混合模型模拟该海区的内波传播更接近遥感实测, 表明了混合模型的合理性.     

采用混合模型数值模拟从深海到浅海内波的传播

在南海东沙岛附近, 从MODIS遥感图像发现内波传播是从深海经陆架坡再到浅海, 由于深海和浅海环境条件的差异以及传播模型的适用条件不同, 因此 不能采用同一模型模拟内波的传播, 需用两种模型来分别模拟内波在深海和浅海中的传播. 采用差分法, 首先用非线性薛定谔方程模拟了深海内波的传播, 然后用EKdV方程模拟了内波在浅海中的继续传播. 模拟结果与实际的MODIS遥感内波图像相符合, 并与应用单一模型模拟结果相比, 混合模型模拟该海区的内波传播更接近遥感实测, 表明了混合模型的合理性.     

Micro-layers of polystyrene film preventing metal oxidation: implications in cultural heritage conservation

Protection of surfaces directly exposed to the detrimental action of degradative agents (i.e. oxygen, air pollutants and bacteria) is one of the most important challenges in the field of conservation of works of art. Metallic objects are subjected to specific surface corrosion phenomena that, over the years, make mandatory the research of innovative materials that should avoid the direct contact between the metal surface and the weathering agents. In this paper, the set-up, characterisation and application of a new reversible material for preserving metal artefacts are reported. Micro-layers constituted of low-adhesive polystyrene (PS) films obtained from recycling waste packaging materials made of expanded PS were studied. The morphology and thickness of PS films were characterised by optical, atomic force and scanning electron microscopy (SEM). A further check on thickness was carried out by means of visible spectrophotometry doping the films with a hydrophobic dye. Thermal properties of the PS micro-layers were studied by means of differential scanning calorimetry coupled with optical microscopy. Permeability of the PS films to water vapour was also determined. The potential of the low-adhesive PS films, that enabled an easy removal in case of film deterioration, for preventing metal oxidation was investigated on brass specimens by simulating standard artificial corrosion programmes. Morphological and chemical (coupling the energy-dispersive X-rays spectrometry to SEM measurements) analyses carried out on these metal samples showed promising results in terms of surface protection against corrosion.     

Phänomenologie und Energiebilanz von Lichtbogenkatoden bei niedrigen Drücken und hohen Stromstärken

The behaviour of an arc cathode in a coaxial gas stream is investigated experimentally in a pressure and current range of 15 to 120 mms Hg and 400 to 1000 A, respectively. Argon and hydrogen are used as ambient test gases. Particular phenomena occurring during the short instationary ignition period are described. Stationary operation characterized by a diffused cathode attachment covering a relatively large area is more closely studied. Measurements of the extension of the arc attachment and the distribution of the cathode temperature are made and evaluated quantitatively. Average current densities in the attachment are presented, as functions of pressure and current, by empirical expressions. Using a quasi-onedimensional approach, an interior energy balance of the cathode is set up and heat entering the cathode in the attachment region is calculated. Finally, under further simplifying assumptions, the cathode drop voltage and the fraction of current carried by ions are estimated and the so-called Richardson constant is determined assuming electron emission according to the Richardson-Schottky-equation. All data discussed depends — in general, strongly — on ambient pressure and current, and the type of gas has a substantial qualitative and quantitative influence.     

X-ray photoelectron spectroscopy for surface film analysis in corrosion research

Surface films on metals and alloys often protect them from reaction with the environment, and hence a knowledge of their protective properties and composition could be invaluable for predicting their corrosion behaviour. XPS (x-ray photoelectron spectroscopy) could provide a quantitative analysis of the chemical composition, the nature of valence states and elemental distribution within the surface films. The present paper reviews the potential of this technique in corrosion studies. A brief review of the work done on the passivation of iron and iron-chromium alloys and on the inhibition studies on copper base alloys has been given. A few examples of investigations carried out at authors’ laboratory are also included. An attempt has been made to establish a correlation between the compositions of the films formed and corrosion behaviour of carbon steel in 10.5 pH lithium hydroxide solution and of Cu-Ni alloys and sacrificial Al-Zn-Sn alloys in synthetic sea-water.     

CCD接力测量船体变形研究

在舰船上,不少设备需要导航仪器提供姿态信息,船体变形会引起设备之间的姿态传递误差,导致设备效用降低。为了修正误差,获得精确的设备姿态测量结果,需要一套测量装置对船体变形进行测量。基于CCD的船体变形测量具有非接触性、精度高的优点。但当测量的两设备安装基座之间光路不能通视时,需要采用接力测量方法。阐述了CCD接力测量船体变形方法的原理和模型,并进行了模拟试验。试验结果表明,CCD接力测量船体变形方法可以高精度测量设备之间的相对姿态变化量。     

深海表面层声速剖面变化对声传播的影响

在我国部分海域，表面声速常常在较短的时间内从弱正梯度变为弱负梯度，这将对表面附近的声传播产生巨大影响。本文通过数值模拟的方法，讨论了表面层声速梯度变化对声传播的影响，同时解释了某次海上实验出现的异常现象：在同一地点同一航向，前后两天海况相同，水文相差不大，第一天的实验可以在50km之外接收到信号，而第二天只能在30km处才能收到信号。     

Acoustic propagation from a spiral wave front source in an ocean environment

A spiral wave front source generates a pressure field that has a phase that depends linearly on the azimuthal angle at which it is measured. This differs from a point source that has a phase that is constant with direction. The spiral wave front source has been developed for use in navigation; however, very little work has been done to model this source in an ocean environment. To this end, the spiral wave front analogue of the acoustic point source is developed and is shown to be related to the point source through a simple transformation. This makes it possible to transform the point source solution in a particular ocean environment into the solution for a spiral source in the same environment. Applications of this transformation are presented for a spiral source near the ocean surface and seafloor as well as for the more general case of propagation in a horizontally stratified waveguide.     

岛礁海域海洋环境噪声垂直分布和垂直指向性

依据岛礁海域复杂海底地形、海试期间航船分布和实测风速数据,应用射线声传播理论,建立岛礁海域海洋环境噪声三维模型。在海试岛礁海域深海声道条件下,采用射线3D算法,仿真计算了32元垂直测量阵所处265~885 m负声速梯度深度范围内1 kHz风关和50 Hz远处航船海洋环境噪声级垂直分布,以及50 Hz航船海洋环境噪声垂直指向性,并与实测分析进行比较。结果表明,仿真结果与海试实测数据一致性良好。在本例海底起伏、接收点周边存在众多岛礁和海底山的三维环境中,1 kHz风关海洋环境噪声级随深度分布较近于均匀;西南方向较远处航道区海域海底较平坦,航道区至接收阵为缓斜坡海底,50 Hz远处航船海洋环境噪声级随深度有所增加,其噪声垂直指向性无明显水平凹槽。文中建立的岛礁海域海洋环境噪声三维模型,可较好地表征本例岛礁复杂地形海底起伏海域的风关和航船海洋环境噪声级的垂直分布、及航船环境噪声的垂直指向性,实测和仿真的岛礁海域海洋环境噪声相关数据,可供实际应用及相关研究参考。      

Vortex Flows Induced by Electric Arc

In this paper a mathematical model of the stationary electric arc is made on the basis of solution of radiation gas dynamics two-dimensional equations. Numerical analysis of electric arc with small length, depending on current force, distance between electrodes, electrode behaviour and geometry, type and expenditure amount of plasma forming gas, is carried out. It is shown that under some definite conditions electric arc induces toroidal gas vortexes playing an important part in the process of heat and mass transfer in electric arc plasma.     

卷积神经网络主动目标方位估计

复杂海洋环境中信道的传输特性、时空变化、频散效应等一定程度上制约了主动声呐目标方位估计的性能。该文引入卷积神经网络(CNN),提出了适用于主动声呐中目标方位的高精度估计方法。仿真声场环境为浅海负梯度,主动发射信号为具有多普勒不变性质的双曲调频信号,水平线列阵作为接收装置,目标按仿真路线运动。该文利用Kraken进行声场数据仿真,并对接收的信号在频域做均匀加权常规波束形成,进而进行卷积神经网络的模型训练和测试。数值仿真研究表明,该文所用方法可以有效估计目标波达方向,对信噪比具有一定的鲁棒性。     

热流传感器传热特性电弧风洞实验及数值模拟

高超声速飞行器面临剧烈的气动加热环境, 电弧风洞是飞行器防热材料地面考核筛选的主力设备。热流密度是电弧风洞重要的模拟参数之一, 需要进行准确有效的测量。针对电弧风洞气流环境特点, 开展传统塞式量热计和新型同轴热电偶的对比测热试验, 并采用数值模拟对两种热流传感器的传热特性进行了分析。在电弧风洞平板自由射流试验热流密度分布在0~1 100 kW/m2范围内, 同轴热电偶的热流密度测试试验结果相对塞式量热计偏低10%~15%。数值模拟结果表明, 塞式量热计本身结构热物性参数不匹配会导致热流密度测量数值偏高至少10%, 而同轴热电偶测量数值偏高最大仅为2.19%, 相对塞式量热计具备更高的测量精度。同时, 电弧风洞中不同材质热流密度测试模型使用同轴热电偶进行测热试验时, 需要在同轴热电偶同模型之间增加适当厚度的不锈钢套以满足传感器周围环境的热匹配。      

Spatial coherences of the sound pressure and the particle velocity in underwater ambient noise

The spatial coherences were investigated between the sound pressure and the three orthogonal components of the particle velocity in underwater ambient noise. Based on the ray theory, integral expression was derived for the spatial coherence matrix of the sound pressure and the particle velocity in a stratified ocean with dipole noise sources homogenously distributed on the surface. The integrand includes a multiplying factor of the vertical directivity of the noise intensity, and the layered ocean environment affects the spatial coherences via this directivity factor. For a shallow water environment and a semi-infinite homogenous medium, the coherence calculation results were given. It was showed that the sound speed profile and the sea bottom could not be neglected in determining the spatial coherences of the ambient noise vector field.     

Surface characterisation and electrochemical behaviour of porous titanium dioxide coated 316L stainless steel for orthopaedic applications

Porous titanium dioxide was coated on surgical grade 316L stainless steel (SS) and its role on the corrosion protection and enhanced biocompatibility of the materials was studied. X-ray diffraction analysis (XRD), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were carried out to characterise the surface morphology and also to understand the structure of the as synthesised coating on the substrates. The corrosion behaviour of titanium dioxide coated samples in simulated body fluid was evaluated using polarisation and impedance spectroscopy studies. The results reveal that the titanium dioxide coated 316L SS exhibit a higher corrosion resistance than the uncoated 316L SS. The titanium dioxide coated surface is porous, uniform and also it acts as a barrier layer to metallic substrate and the porous titanium dioxide coating induces the formation of hydroxyapatite layer on the metal surface.     

Interactions between chloride and cement-paste materials

The durability of cement-based materials with respect to exterior aggressions is one of the current priorities in civil engineering. Depending on their use, the cement-based materials can be exposed to different types of aggressive environments. For instance, damages to concrete structures in contact with a saline environment (sea water on bridges, deicing salts on roads, etc.) are of utmost importance. Upon exposure to saline water, Cl- ions penetrate into the structures and subsequently lead to reinforcement corrosion. Chloride attack is often combined with other aggressive influences such as temperature (e.g., freezing) or the ingress of other ions (e.g., sulfates in sea water). We therefore aim to explore the effect of sodium chloride (NaCl) on the structural chemistry of cement paste. Existing studies about reinforcement corrosion by chloride have focused on the penetration of Cl- ions and the comparison between "free" ions (water-soluble ions) and bound ones. However, little is known about the fixation mechanisms, the localization of Cl in the cement matrix and the structural interaction between Cl and the silicate and aluminate hydrate phases present in cement paste. We present here results of a multinuclear nuclear magnetic resonance study on the fixation of chloride in the hydration products and the characterization of new phases potentially appearing due to chloride ingress.     

Field measurements of sonic boom penetration into the ocean

Six sonic booms, generated by F-4 aircraft under steady flight at a range of altitudes (610-6100 m) and Mach numbers (1.07-1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30-50 m, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.     

Influence of chromate, molybdate and tungstate on pit formation in chloride medium

It has been characterized and evaluated the 2024-T351 and 7050-T7451 aluminum alloys pitting corrosion in naturally aerated chloride aqueous solutions containing chromate, molybdate and tungstate. It has been carried out electrochemical and non-electrochemical immersion corrosion tests accompanied by surface metallography analysis using an optical microscopy. Chromate for the two alloys and in molybdate for 7050 has corrosion inhibiting effects, whereas tungstate promotes the pitting corrosion for these alloys. Quantitative surface analysis upon the alloys after immersion has indicated that pits are predominantly conical or quasi-conical and irregular. In general, pits have been wider than deep and the widest have been also the deepest. Despite inhibitor presence, when pits have been nucleated, they grow with the same intensity.     

Spectroscopic Approach to the Analysis of High Current Arcs in SF6

Spectroscopic observations were carried out on transient free-burning arcs drawn by separating copper/tungsten electrodes in SF6 gas. The peak value of the arc current was varied up to 60 kA. A new optical method was developed to measure temperature and pressure profiles of the arc taking the magnetic pinch force into account. The arc voltage calculated from the obtained temperature and pressure profiles agreed well with electrical measurements. The results made it clear that the composition of the arc changes significantly at the critical instantaneous current of 10 kA. Above 10 kA the arc is composed of the electrode vapor, while it contains SF6 gas below 10 kA.