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1.
In conventional beamforming systems, the use of aperiodic arrays is a powerful way to obtain high resolution employing few elements and avoiding the presence of grating lobes. The optimized design of such arrays is a required task in order to control the side-lobe level and distribution. In this paper, an optimization method aimed at designing aperiodic linear sparse arrays with great flexibility is proposed. Simulated annealing, which is a stochastic optimization methodology, has been utilized to synthesize the positions and the weight coefficients of the elements of a linear array in order to minimize the peak of the sidelobes and to obtain a beam pattern that meets given requirements. An important novelty is the fact that the latter goal can be achieved in parallel to the minimization of both the number of elements and the spatial aperture, resulting in a “global” optimization of the array characteristics. The great freedom that simulated annealing allows in defining the energy function to be minimized is the main reason for the notable versatility and the good results of the proposed method. Such results show an improvement in the array characteristics and performances over those reported in the literature 相似文献
2.
In this study, a moored array optimization tool (MAOT) was developed and applied to the South China Sea (SCS) with a focus on three-dimensional temperature and salinity observations. Application of the MAOT involves two steps: (1) deriving a set of optimal arrays that are independent of each other for different variables at different depths based on an empirical orthogonal function method, and (2) consolidating these arrays using a K-center clustering algorithm. Compared with the assumed initial array consisting of 17 mooring sites located on a 3°×3° horizontal grid, the consolidated array improved the observing ability for three-dimensional temperature and salinity in the SCS with optimization efficiencies of 19.03% and 21.38%, respectively. Experiments with an increased number of moored sites showed that the most cost-effective option is a total of 20 moorings, improving the observing ability with optimization efficiencies up to 26.54% for temperature and 27.25% for salinity. The design of an objective array relies on the ocean phenomenon of interest and its spatial and temporal scales. In this study, we focus on basin-scale variations in temperature and salinity in the SCS, and thus our consolidated array may not well resolve mesoscale processes. The MAOT can be extended to include other variables and multi-scale variability and can be applied to other regions. 相似文献
3.
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
4.
An array of ring radiators which generates a symmetric search-light-type narrow beam with greatly reduced sidelobes is proposed. Such a narrow beam can find several applications related to acoustic remote sensing, telemetry, and specialized sonars. A design procedure which benefits from design techniques developed for linear arrays is detailed. The developed methodology requires only simple matrix operation and does not involve nonlinear optimization. The results indicate that radiation patterns with arbitrary sidelobe suppression can be achieved 相似文献
5.
《Oceanic Engineering, IEEE Journal of》2008,33(2):224-231
6.
随着超大型海洋结构物的设计和研究日益受到重视,研究多物体之间的流体动力干扰特性显得十分必要。用波动源在截面周线上分布的方法,就垂直桩柱间三维流体动力干扰对波浪力的影响进行了系统的研究,不仅可得到单行柱列的流体动力干扰力学机理的新特性,而且对多行桩柱阵列的研究也取得了若干新的发现：多行柱柱阵列的遮蔽作用强于单行的;无论是单行还是多行柱列,其流体动力干扰特性存在一个十分敏感的来波频域,在此区域内,力的幅值会大大超过其他频域的受力,而且桩柱阵列与交错阵列的力学特性也有所不同。这对超大型海洋结构物的设计有着重要的指导意义。 相似文献
7.
This paper examines the effectiveness of horizontal line arrays (HLAs) for matched-field inversion (MFI) by quantifying geoacoustic information content for a variety of experiment and array factors, including array length and number of sensors, source range and bearing, source-frequency content, and signal-to-noise ratio (SNR). Emphasis is on bottom-moored arrays, while towed arrays are also considered, and a comparison with vertical line array (VLA) performance is made. The geoacoustic information content is quantified in terms of marginal posterior probability distributions (PPDs) for model parameters estimated using a fast Gibbs sampler approach to Bayesian inversion. This produces an absolute, quantitative estimate of the geoacoustic parameter uncertainties which can be directly compared for various experiment and array factors. 相似文献
8.
A comparison of methods for the calculation of the hydrodynamic characteristics of arrays of wave power devices is presented. In particular, the plane-wave approximation and an exact multiple scattering formulation have been used to compute exciting wave forces, hydrodynamic coefficients and q factors for arrays of interacting wave power devices. The results obtained are compared with each other, and accuracy aspects of the computations are stressed and critically assessed. 相似文献
9.
An anchor design for instrument arrays was developed for use in the very soft muddy sediments adjacent to the Mississippi Delta. Because of low sediment shear strengths and high sensitivities combined with large dynamic loadings due to strong currents, problems in successful deployments and recoveries were anticipated. A total of six deployments were attempted; four were sediment trap arrays and two were current meter/transmissometer arrays. All six deployments and recoveries were successful. The array design presented herein is a safe, easy and cost effective method for deploying instrument arrays in areas where soft bottoms and strong currents are a consideration. 相似文献
10.
The majority of optimal shading methods for arrays of irregularly spaced or noncoplanar elements rely on numerical optimizations and iterative techniques to compute the desired weighting function because analytic solutions generally do not exist. Optimality is meant here in the Dolph-Chebyshev sense to provide the narrowest mainlobe width for a given sidelobe level. We present a simple and efficient technique to compute real shading coefficients for nonuniform-line, curved-line, and noncoplanar arrays by resampling the optimal Dolph-Chebyshev window computed for a uniform line or plane array of equivalent aperture at the element position of the irregular array. Computer simulation examples of narrowband plane-wave beamforming with irregular arrays, in which phase compensation is achieved by projecting the elements on a line or plane tangent to the array, show peak sidelobe levels close to those obtainable for optimally shaded uniform arrays of equal aperture sizes and numbers of elements, where the differences depend upon the spacing variations and numbers of elements. This resampling technique is applied to seafloor acoustic backscatter data collected at sea with the 68-kHz Toroidal Volume Search Sonar to highlight a tradeoff between peak and outer sidelobe levels and illustrate the requirement for element pattern when processing data from irregular arrays 相似文献
11.
Modern radio positioning systems often use multiple-antenna arrays or corner reflector arrays in order to increase the system range. A theoretical investigation of the movement of the antenna phase center on these arrays is carried out, and the resulting distance error is presented for several array configurations. 相似文献
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13.
The interaction of regular waves with arrays of bottom-mounted circular cylinders is considered. This subject has been thoroughly investigated in the recent past, but most of the time under the assumption of regular and spatially periodic arrangements. Unlike these authors, we consider here arrays of unevenly spaced cylinders, displaced randomly from a regular array according to a disorder parameter. Focus is put on two effects of this spacing irregularity: reduction of peak forces associated to trapped mode phenomena, and regularization of the transmission coefficient for waves propagating through the arrays. 相似文献
14.
《Oceanic Engineering, IEEE Journal of》2008,33(2):210-214
15.
Analysis of swath bathymetry sonar accuracy 总被引：2，自引：0，他引：2
The practical limitations of many bottom mapping sonars lie in their ability to accurately estimate the angle of arrival. This paper addresses the accuracy of angle estimation when employed to determine the location of an extended target such as the bottom. A Gaussian model is assumed for the bottom backscatter and the corresponding Cramer-Rao lower bound for the variance of the angle estimate is determined for multi-element linear arrays. The paper focuses on determining the performance of high-resolution swath bathymetry sonars and, therefore, concentrates on the ability to determine bottom location with short pulses. Two error mechanisms, footprint shift and uncorrelated noise, are identified as important contributors to measurement errors. The two-element interferometric sonar configuration is investigated in detail. It is shown through the use of probability distributions, the Cramer-Rao bound, and simulation that it is difficult to get a good estimate of performance through simulation alone. Performance enhancement through pre-estimation and post-estimation averaging of multiple snapshots and changes in performance with pulse length and pulse rise time are also considered. Bottom estimation performance employing multi-element arrays is compared and contrasted with that of the two-element interferometric array. It is determined that there is little benefit associated with the multi-element array in terms of angle estimation performance alone. However, when other considerations such as angle ambiguities, multiple angles of arrival, and physical shortcomings associated with practical arrays are taken into account, the multi-element array is favored. 相似文献
16.
An approach for the design of line arrays which synthesizes array factors having desired attributes is developed. This approach draws upon, clarifies, and expands earlier developments in nonuniformly positioned line-array design. A new array with important characteristics, called the square-root design, is derived. The approach is also applied to formulation and evaluation of design tradeoff studies. Specific examples are given for exponential and square-root arrays. 相似文献
17.
Most of the research on model-based geoacoustic inversion techniques has concentrated on data collected using moored vertical receiver arrays. However, there are many advantages to considering geoacoustic inversion using a towed horizontal array. Towed arrays are easily deployed from a moving platform; this mobility makes them well suited for surveying large areas for sea-bed properties. Further, if a model-based geoacoustic inversion scheme uses both a towed source and array, the separation between the two can be kept short, which reduces the requirement for range-dependent modeling. Range-independent modeling is used for inverting all the horizontal array data considered in this paper. Using the Inversion Techniques Workshop Benchmark Test Cases, the performance of a horizontal (simulated towed) and vertical arrays are compared and found to be very similar. However, it will be shown that, for Benchmark Test Case 3, where the bathymetry is flat and a hidden bottom intrusion exists, a towed horizontal array is ideal for determining the range-dependent sea-bed properties. The practical advantages of using a towed array are clear and the purpose of this paper is to show that the performance is similar (and in some cases better) than using moored vertical arrays. 相似文献
18.
C.Z. Wang 《Ocean Engineering》2010,37(4):400-417
Fully nonlinear interactions between water waves and vertical cylinder arrays in a numerical tank are studied based on a finite element method (FEM). The three-dimensional (3D) mesh is constructed through an extension of a 2D Delaunay surface grid along the vertical line. The velocity potential is obtained by solving a linear matrix system of FEM, and a difference scheme is then used to calculate the velocity on the free surface to track its movement. Waves and hydrodynamic forces are obtained for both bottom mounted and truncated cylinders. The simulations have provided many results to show the nature of mutual interference between cylinders in arrays and its effects on waves and forces at the nearly trapped mode frequency. The effect of the tank wall on waves and forces has been investigated, and the nonlinear features of waves and forces have also been discussed. 相似文献
19.
Traditionally, matched-field processing (MFP) has been used to localize low-frequency sources (e.g., <300 Hz) from their acoustic signals received on long vertical arrays. However, some sources emit acoustic signals of much higher frequency. Applying MFP to signals in the mid-frequency range (e.g., 1-4 kHz) is a very challenging problem because MFP's sensitivity to environmental parameter mismatch becomes more severe with increasing frequency. Robust MFP techniques are required to process signals in the mid-frequency range. As a practical issue, short vertical arrays are more convenient to work with than are long vertical arrays; they are easier to deploy and are less prone to large amounts of deformation. However, short vertical arrays undersample the water column, which can result in severely degraded MFP performance. In this paper, we present experimental data results for this nonconventional paradigm. Using the environmentally robust broad-band L/sub /spl infin//-norm estimator, MFP results are given using shallow-water experimental data. This data consisted of broad-band signals in the 3-4-kHz band collected on an eight-element 2.13-m vertical array. These results serve to demonstrate that good localization performance can be attained for this difficult problem. Guidelines on the appropriate use of ray and normal-mode propagation models are also presented. 相似文献
20.
The three-dimensional scattering of cnoidal waves by cylinder arrays are studied numerically by using the generalized Boussinesq equations. The boundary-fitted coordinate transformation and a dual-grid technique are used to simplify the finite-difference computation. Also, a set of open boundary conditions and an incident cnoidal wave are incorporated for time-domain simulation. The free-surface elevation and hydrodynamic forces on each cylinder are calculated to illustrate the evolution of nonlinear waves and their interactions with large cylinder arrays. Comparisons are made between the present nonlinear wave loads and those obtained from linear diffraction theory. The sheltering role played by the neighboring cylinders and the feature of wave interference are discussed. 相似文献