The adiabatic sea surface cooling in the Gulf of Trieste due to the ?Bora? wind blowing: an analytical model

Summary A two-dimensional, analytical model is formulated to describe the adiabatic evolution of the nearshore sea temperature field, for shallow basins, in the presence of wind. The model is compared with experimental data of sea surface temperature, taken in the Gulf of Trieste, in the presence of ?Bora? wind.

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Riassunto Viene formulato un modello analitico bidimensionale per l'evoluzione adiabatica del campo di temperatura del mare sottocosta, valido per bacini poco profondi, in presenza di vento. Il modello è confrontato con dati sperimentali di temperatura superficiale del mare, assunti nel Golfo di Trieste, in presenza di vento di bora.

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Резюме Формируется двумерная, аналитическая модель для описания адиабатической эволюции температурного поля поверхности моря для неглубоких бассейнов в присутствии ветра. Модель сравнивается с экспериментальными данными для температуры поверхности моря, полученными в заливе Триеста в присутствии ветра ?Бора?.

     

Elements for a comparison between the Tyrrhenian and Ligurian coastal currents during spring

Summary Hydrological and current measurements effected along the western Italian coasts permit to compare the main dynamical peculiarities of the coastal circulation of the Ligurian and Tyrrhenian basins, evidencing in particular their different response to atmospheric fluctuations. While the Ligurian currents show a great energy that depends essentially on the large-scale circulation, the Tyrrhenian shelf dynamics is characterized by a low thermohaline driven velocity, largely influenced by the local wind. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell' Atmosfera e dell'Oceano, Rome, June 19–22, 1984.     

海洋环境噪声研究发展概述及应用前景

海洋环境噪声是海洋声场的背景场,通常被当作干扰项。在传统的水声学和海洋声学中,对海洋环境噪声的研究目的大多是为了降低或抑制环境噪声对水下设备的干扰,提高水下设备的性能和作用距离。目前,许多国家纷纷投入力量,开展海洋环境噪声数据获取、分析及噪声场建模工作。从另一个角度考虑,海洋环境噪声是海洋中永恒存在的声场,包含了水体及海底海面等环境特性信息。因此,可利用海洋环境噪声来研究海洋环境物理特性,通过低代价换取丰富的海洋声学信息。若能对海洋环境噪声的宽频带和任意时间存在的特性加以利用,则可以从海洋环境噪声中提取出相关的海洋环境参数。     

A finite-element method using dispersion reduced spline elements for room acoustics simulation

This paper presents a finite element method (FEM) using hexahedral 27-node spline acoustic elements (Spl27) with low numerical dispersion for room acoustics simulation in both the frequency and time domains, especially at higher frequencies. Dispersion error analysis in one dimension is performed to increase the accuracy of FEM using Spl27 by modifying the numerical integration points of element stiffness and mass matrices. The basic accuracy and efficiency of the FEM using the improved Spl27, which uses modified integration points, are presented through numerical experiments using benchmark problems in both the frequency and time domains, revealing that FEM using the improved Spl27 in both domains provides more accurate results than the conventional method does, and with fewer degrees of freedom. Moreover, the effectiveness of FEM using the improved Spl27 over that using hexahedral 27-node Lagrange elements is shown for time domain analysis of the sound field in a practical sized room.     

Dynamic forces on agglomerated particles caused by high-intensity ultrasound

In this paper the acoustic forces on particles and agglomerates caused by high-intensity ultrasound in gaseous atmosphere are derived by means of computational fluid dynamics (CFD). Sound induced forces cause an oscillating stress scenario where the primary particles of an agglomerate are alternatingly pressed together and torn apart with the frequency of the applied wave. A comparison of the calculated acoustic forces with respect to the inter particle adhesion forces from Van-der-Waals and liquid bridge interactions reveals that the separation forces may reach the same order of magnitude for 80 μm sized SiO₂-particles. Hence, with finite probability acoustically agitated gases may de-agglomerate/disperse solid agglomerate structures. This effect is confirmed by dispersion experiments in an acoustic particle levitation setup.     

Information for Contributors

正1 Chinese Journal of Acoustics is the publication of the Acoustical Society of China and The Institute of Acoustics,Chinese Academy of Sciences,to promote the international understanding and collaboration in the field of acoustics.It publishes original works in all branches of acoustics in China.Contributions from invited guests and friends overseas are also solicited.2 Contributed papers submitted for publication in the Journal should be original,unpub-     

宽视场大相对孔径高光谱成像仪光学系统设计

宽视场大相对孔径高光谱成像仪已成为航空海洋水色遥感等领域的应用需求。根据宽视场和大相对孔径的研究目标,采用离轴Schwarzschild望远成像系统和改进型Dyson光谱成像系统匹配的结构型式,设计了一个视场为40°、相对孔径为1/1.8、工作波段为0.35~1.05μm的航空遥感高光谱成像仪光学系统。基于像差理论,分析了改进型Dyson光谱成像系统球差校正原理,运用光学设计软件Zemax对高光谱成像仪光学系统进行了光线追迹和优化,并对设计结果进行了分析。分析结果表明,设计的光学系统在各个波长的光学传递函数均不小于0.82,谱线弯曲和谱带弯曲均小于像元尺寸的5%。这便于光谱和辐射定标,完全满足设计指标要求,且系统体积小、重量轻,适合于航空遥感应用。     

Multi-crack imaging using nonclassical nonlinear acoustic method

Solid materials with cracks exhibit the nonclassical nonlinear acoustical behavior. The micro-defects in solid materials can be detected by nonlinear elastic wave spectroscopy （NEWS） method with a time-reversal （TR） mirror. While defects lie in viscoelastic solid material with different distances from one another, the nonlinear and hysteretic stress-strain relation is established with Preisach-Mayergoyz （PM） model in crack zone. Pulse inversion （PI） and TR methods are used in numerical simulation and defect locations can be determined from images obtained by the maximum value. Since false-positive defects might appear and degrade the imaging when the defects are located quite closely, the maximum value imaging with a time window is introduced to analyze how defects affect each other and how the fake one occurs. Furthermore, NEWS-TR- NEWS method is put forward to improve NEWS-TR scheme, with another forward propagation （NEWS） added to the existing phases （NEWS and TR）. In the added phase, scanner locations are determined by locations of all defects imaged in previous phases, so that whether an imaged defect is real can be deduced. NEWS-TR-NEWS method is proved to be effective to distinguish real defects from the false-positive ones. Moreover, it is also helpful to detect the crack that is weaker than others during imaging procedure.     

光学窗口表面憎水改性工艺研究

海洋环境下使用的光学窗口常因海水等附着而影响其光学性能。从固体-液体界面理论入手,分析了光学窗口的表面能对海：水附着特性的影响,开发了一种外场环境下可以实施的光学窗口表面憎水改性工艺。该工艺采用一种含有氟烃基硅烷的活性物质掺杂于SiO2溶胶中,通过涂擦和低温固化方式,在光学窗口表面形成纳米憎水膜,该憎水膜可使SiO2表面能由30mJ／m^2降至5mJ／m^2以下,水接触角由47°增加至105°以上。试验研究了改性后光学窗口的盐水接触角、光学透过率及耐候性,结果表明,用于改性的憎水膜海洋环境使用寿命大于6个月。通过定期对光学表面实施憎水改性保养可以显著减少海水附着。     

Remote acoustic cloaks

Due to the correspondence of the acoustic equations to Maxwell??s equations of one polarization in two dimensions, we exploit theoretically the acoustic counterpart of the recently proposed remote invisibility cloak. The cloak consists of a circular cylindrical core with designed bulk moduli, and an ??anti-object?? embedded inside a shell with anisotropic mass densities. The material parameters of the cloaking shells are obtained by using the coordinate transformation method. The essence of the new design of cloaks relies on the ability that the cloaked object is no longer deafened by the cloaking shell, which is verified by both the far-field and near-field full-wave finite-element simulations in two dimensions.