共查询到20条相似文献，搜索用时 15 毫秒
1.
An array of elliptic ring radiators is proposed which generates a fan-type beam with controllable sidelobe levels. Such an array has applications in specialized acoustic systems such as sidescan sonars, sonars for fish finding and stock assessment, obstacle avoidance systems, and others. Two possible approaches to the design are presented. One approach utilizes a mapping which transforms a radiation pattern generated by a circular ring array to that of an elliptic ring array. This approach takes advantage of methodologies developed for the design of circular ring arrays. The other approach uses the concept of an equivalent linear array. This approach benefits from existing design techniques developed for linear arrays. It requires only simple matrix operations and does not involve any optimization. The design examples presented demonstrate that a fan-type beam with sidelobes suppressed to more than 40 dB in all possible directions is achievable 相似文献
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1 .IntroductionNowadays tremendous efforts have been devotedtothe analysis of randomseismic responses .Forexample ,American PetroleumInstitute (API) has declared that the analysis of randomseismic re-sponsesis a useful tool for safety inspection. Owing to the complexity of platformand randomness ofload,it is difficult to carry out the randomresponse analysis of a jacket platform. The conventionalrandomvibration methods ,such as square root of the sumof squares (SRSS) and complete quadratic… 相似文献
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A computer model to simulate the formation of underwater images has been developed. The model incorporates the inherent and apparent properties of the propagation of light in water. An image is approximated as a linear superposition of several image components. The model has been used to simulate the relative advantages of different camera/light configurations. The results indicate that extremely large gains in image contrast can be obtained by careful design of beam patterns and the manipulation of camera and light locations. The performance of range-gated systems is explored, and it is demonstrated that these systems are presently power limited. In order to obtain better quality images at larger distances, an imaging configuration which consists of scanning an incoherent light beam across the field of view of a camera is proposed. The incoherent light-scanning system is shown to have advantages over both conventional imaging techniques and range-gated methods 相似文献
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The possibility of determining the near-surface wind speed from aircraft measurements of the mean density of reflected pulses is considered. The method of sounding with a narrow continuous laser beam is discussed and its potential exhibited.Translated by V. Puchkin. 相似文献
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以浮式两级缓冲防撞系统为研究对象,介绍其工作原理,利用动力学分析软件LS-DYNA构建了碰撞模型并进行了仿真计算,依据仿真结果完成了以阻尼索组与浮体结构构型为主要内容的防撞系统设计。研究确定了阻尼索组的布置位置、材料及数量,为浮体内部结构构型设计了7种比选方案,分别对5 000 t船舶撞击浮体前梁和侧梁的动态过程进行了仿真分析,对比了不同方案及不同板梁厚度下的接触力。研究结果表明:浮体内部构造若选用板梁厚度12 mm的方案6设计,则碰撞发生时浮体前梁和侧梁分别可以稳定地提供10.4 MN和7.9 MN的均值力,以及11.5 MN和8.9 MN的峰值力,设计浮体能够满足整体刚度要求,防撞系统符合双保护原则。防撞系统及浮体结构构型设计为下一步全面开展船舶撞击防撞系统后的动力学响应分析奠定了基础。 相似文献
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A basic formalism is developed to treat the vertical spatial coherence of backscatter from wind-generated microbubbles beneath the ocean surface. This formalism treats signals multiply scattered by the sea surface and the subsurface scatterers, as well as absorption in the bubble layer. Approximate solutions are obtained for the case of narrow beamwidth sources and are applied to study the influence of measurement system and environmental parameters on coherence. Using bubble densities derived from acoustic backscatter data, the coherence is found to depend strongly on source frequency and beam pattern. The primary environmental effect is due to the increase in both bubble density and penetration depth below the surface that occurs with increasing windspeed. At high wind speeds, the vertical coherence is sufficiently dependent on the scatterer depth distribution to provide a viable means of studying this phenomenon. 相似文献
7.
报道采用 1 - 3压电复合材料设计低旁瓣换能器的方法 ,可使单个换能器获得低于 -2 5d B的旁瓣级从而显著优化波束。该方法以 1 - 3压电复合材料为换能材料 ,在设计过程中通过控制换能器的辐射面的形状来对换能器实现窗函数加权 ,达到控制波束的目的。本文举例阐述设计方法 ,所提供的实验数据证明了本方法的工程可行性 ,并与国外同类典型产品进行性能比较 相似文献
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A gamma-ray transmission method is discussed for measuring the water content of marine sediment samples during consolidation testing. This method permits obtaining consolidation curves for sediment cores while still in the core liner, thereby eliminating several sources of sample disturbance. A narrow beam of gamma-rays is passed through the sample to a detector and counting equipment. The attenuation of this beam is a function of the sample density and hence water content or void-ratio. Equations are developed for calculating water content from gamma-counts. The results of experiments are presented confirming the validity of these equations. 相似文献
10.
A. G. Luchinin 《Izvestiya Atmospheric and Oceanic Physics》2012,48(6):663-671
The main effects accompanying the propagation of an initially narrow complex modulated light beam in sea water are studied. Sea water, with respect to modulation waves, is shown to be similar to a medium with frequency dispersion with respect to electromagnetic waves; in the medium, the effects of the time focusing of a wave packet are possible. Based on the self-similar small-angle solution to the equation of radiation transfer, we estimate spatial-temporal characteristics of pulse-signal amplitude modulated by a complex signal. We propose a scheme for constructing underwater LIDAR using a complex modulated illumination beam and the processing of a received echo signal. The processing allows the separation of the modulated component and its matched filtration. Values of possible delays and broadening of the separated echo signal caused by dispersion properties of sea water are estimated. 相似文献
11.
Discrete Element with Flexible Connector for Dynamic Analysis of 3-D Beam Structures 总被引：1，自引：1，他引：1
Combined multi-body dynamics with structural dynamics,a new discrete element with flexibleconnector,which is applicable for 3-D beam structures,is developed in this paper.Both the generalizedelastic coefficient matrix of the flexible connector and the mass matrix of discrete element may be off-diag-onal in a general case.The zero-length rigid element is introduced to simulate the node at which multiple el-ements are jointed together.It may also be effective when the axes of adjacent elements are not in the sameline.The examples for eigenvalue calculation show that the model is successful.It can be extended to thegeometric nonlinear response analysis. 相似文献
12.
High-resolution Echo-sounding and Detection of Embedded Archaeological Objects with Nonlinear Sub-bottom Profilers 总被引：3，自引：0，他引：3
Sub-bottom profilers based on nonlinear acoustics offer many advantages especially for detecting and locating embedded objects
in shallow waters. They have a narrow beam in spite of small transducers and virtually no side lobes. It is possible to realize
mobile low-frequent sub-bottom profilers, which transmit very short sound pulses. Excellent vertical as well as horizontal
resolutions at reasonable penetrations are proven benefits of using this technique. In this paper some technical aspects are
discussed and a new experimental nonlinear scanning sub-bottom profiler system is described. Results from a field trial in
archaeological prospection are shown to illustrate the successful application in practice. 相似文献
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V.I. BeenaV.Anantha Subramanian 《Ocean Engineering》2003,30(9):1077-1106
This paper reports seakeeping studies performed on a parametrically varied set of SWATH hull forms. The SWATH form, because of its de-linked nature of design affords many variations of the underwater hull geometry without affecting overall deck length and beam. For a given displacement, the hull form can be varied in terms of length, basic section shape, maximum area of cross section of under water hull and strut water plane shape. Using these variants, a parametric family of hull forms has been generated employing Chebychev polynomial scheme for representing sectional area distribution and using a bi-quintic B-spline based surface definition scheme. Not all designs offer optimal performance in a given sea state. A twin-hull motion analysis program SEDOS has been used to study the motions and other dynamic effects. Setting criteria for operability, these dynamic effects have been quantified into a single value namely, operability index. The approach here fulfils an investigation at the design stage in order to tap the full advantage of the SWATH form. The study brings out a methodology for assessment of the SWATH at the design stage highlighting interesting results related to section shapes and sectional area distribution. Thus, combining a newly developed interactive surface generation scheme with an analysis package, a rapid assessment tool is offered for new design. 相似文献
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The moored three-float line absorber WEC M4 has been developed to optimise power capture through experiments and linear diffraction modelling. With the progression down wave from small to medium to large floats, the device heads naturally into the wave direction. The bow and mid floats are rigidly connected by a beam and a beam from the stern float is connected to the hinge point above the mid float for power take off (PTO). Increasing the bow to mid float spacing to be more than 50% greater than the mid to stern float spacing has been found to improve power capture. To increase power capture further and potentially reduce electricity generation cost the number of mid floats and stern floats is increased while maintaining a single bow float for mooring connection. The bow and mid floats still form a rigid body while the stern floats may respond independently. A time domain linear diffraction model based on Cummins method has been applied to configurations of 121, 123, 132, 133, and 134 floats where the numbers indicate the number of floats: bow, mid, stern. This shows how power capture is increased while response remains similar. We only consider uni-directional (long-crested) waves with narrow band width typical of swell. By considering scatter diagrams for various offshore sites capacities may range from 3.7 MW to 17.3 MW for the eight float system with a capacity factor of 1/3 while the cost of electricity assuming capital cost to be a fixed multiple of steel cost is reduced from that for the three-float system. 相似文献
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This paper applies the narrow band Internet of things communication technology to develop a wireless network equipment and communication system, which can quickly set up a network with a radius of 100 km on water surface. A disposable micro buoy based on narrow-band Internet of things and Beidou positioning function is also developed and used to collect surface hydrodynamic data online. In addition, a web-based public service platform is designed for the analysis and visualization of the data collected by buoys. Combined with the satellite remote sensing data, the study carries a series of marine experiments and studies such as sediment deposition tracking and garbage floating tracking. 相似文献
17.
High-frequency (HF) radars based on ground-wave propagation are used for remotely sensing ocean surface currents and gravity waves. For some 20 years a number of systems have been developed taking advantage of improved electronics and computer techniques. However, the performance of these systems are limited by physical constraints, which are due to HF wave propagation and scattering as well as to the technical design of the measuring system. Attenuation of the HF ground-wave is strongly dependent on the radio frequency and sea-water conductivity. Experimental data confirm the predicted decrease of propagation range with decreasing conductivity. HF radar systems use different methods of spatial resolution both in range and azimuth. Range resolution by means of short pulses and frequency-modulated chirps is compared, as well as azimuthal resolution by means of beam forming and direction finding (phase comparison). The emphasis is placed on recent developments. 相似文献
18.
南海东沙海域的陆坡台地区, 浅表断裂及生物礁发育众多, 浅层新生界多为碳酸盐岩层, 中深层的中生界内部构造复杂, 断裂较多, 常规单船窄方位地震剖面显示中深层反射品质较差。利用双船可以设计灵活的观测系统, 形成双方位角地震探测方式, 对于地下同一反射点的照明, 可以获得比窄方位角探测更好的效果, 也可以改善高速屏蔽层下方、高陡倾角斜层等区域的成像质量。文章通过重点技术的攻关研发, 进行了单源激发、双缆接收的双方位角采集试验, 成功实现该方法在南海海域中深层地震勘探中的应用。 相似文献
19.
辛几何算法是专门针对动力学过程设计的算法,以提高动力学问题求解的精度与效率。高斯束偏移过程中的运动学与动力学射线追踪,从物理上讲是一个动力学过程,可以利用辛几何算法对其进行优化。本文将基于辛几何算法的运动学射线追踪引入高斯束叠前深度偏移中,并在推导了动力学射线追踪方程组的辛差分格式基础上,实现了基于辛几何算法的高斯束叠前深度偏移。模型实验表明,基于辛几何算法的运动学射线追踪,其效率与精度相比常规算法都具有一定优势,而基于辛几何算法的高斯束叠前深度偏移方法能够对复杂构造模型精确成像。 相似文献
20.
周向变刚度环肋圆柱壳应力分析研究 总被引：1，自引：0，他引：1
采用大曲率梁理论和弹性基础梁带理论,建立潜艇特殊舱段结构的力学模型。利用能量法求出肋位处耐压船体壳板中面周向应力。建立环肋圆柱壳微分方程并根据边界条件求解,得到周向变刚度环肋圆柱壳应力计算方法。通过理论分析和模型试验验证了本计算方法。 相似文献