共查询到20条相似文献，搜索用时 29 毫秒
1.
Gerstoft P. Hodgkiss W.S. Kuperman W.A. Heechun Song Siderius M. Nielsen P.L. 《Oceanic Engineering, IEEE Journal of》2003,28(1):44-54
During maneuvering, towed array beamforming degrades if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. It is experimentally demonstrated that adaptive beamforming is feasible on a turning array, provided that array shape is estimated. The array shape can be inferred solely from the coordinates of the tow vessel's Global Positioning System (GPS) without any instrumentation in the array. Based on estimated array shape from the GPS, both the conventional beamformer and the white noise constrained (WNC) adaptive beamformer are shown to track the source well during a turn. When calculating the weight vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies. The proposed algorithms have been tested on real data with the tow-vessel making 45/spl deg/ turns with a 500-m curvature radius. While turning, the improvement in performance over the assumption of a straight array geometry was up to 5 dB for the conventional beamformer and considerably larger for the WNC adaptive beamformer. 相似文献
2.
Turbulent wall pressure data acquired during tests of a full-scale experimental towed array over a range of tow speeds in straight tows and turns is presented. The experimental towed array contained a linear array of sensors mounted at the fluid–solid interface to measure the spectra of the wall pressure fluctuations due to the cylindrical turbulent boundary layer. The physics are dominated by the growth of a thick, high Reynolds number turbulent boundary layer at arc length Reynolds numbers as high as 9×108. The measured wavenumber-frequency spectra, autospectra, cross-spectral decay and convection velocities are presented. A well-defined convective ridge exists in the wavenumber-frequency spectra obtained during straight tows and turns. Turns give rise to a complicated fluid–structure interaction problem, but do not lead to the separation of the turbulent boundary layer. As the array moves through a turn, flow-induced vibrations of the array are shown to dominate the spectra at low frequencies, with more rapid decay in the measured coherence occurring at higher frequencies. The use of tow speed as a velocity scale is shown to collapse autospectra and convection velocities. 相似文献
3.
Reverberation rejection with a dual-line towed array 总被引：1，自引：0，他引：1
Low-frequency bottom reverberation from explosive sources was measured with a dual-line horizontal towed array during a 1991 system engineering trial. The receiver's parallel line arrays were processed coherently in order to unambiguously resolve the reverberation field in azimuth. Initial beamforming that assumed a straight-and-parallel array configuration led to poor or erroneous ambiguity resolution, suggesting the system was deformed significantly from the assumed shape. In the absence of reliable shape measurement data, the array shape was deduced acoustically using tow ship signals and the direct blast of an explosive source. The estimated shape was then used in a shape-compensated beamformer to produce azimuthally unambiguous estimates of the reverberation field. Backlobe rejection of more than 20 dB was attained for both direct blast and distant reverberation energy 相似文献
4.
In July 2000, an array of instruments called acoustic extensometers was deployed at the Cleft segment of the southern Juan de Fuca Ridge, a seafloor observatory site selected by the National Science Foundation RIDGE Program. These instruments are designed to precisely measure horizontal deformation across the axis of a mid-ocean ridge in order to detect and quantify seafloor spreading events. The instruments were deployed in semipermanent seafloor benchmarks in a linear array that is 1.2-km long and spans the floor of the axial valley. The instruments make daily measurements of distance to their neighbors in the array by recording the round trip travel time of 100-kHz acoustic pulses, and simultaneous temperature measurements are used to correct the ranges for sound speed variations. The instruments are expected to have lifetimes of at least five years. In addition, precise pressure measurements have been made at each benchmark with a remotely operated vehicle in order to monitor for vertical deformation across the array. Preliminary results show that the resolution of the acoustic measurements is ±1-2 cm and that no abrupt deformation events occurred during the first year 相似文献
5.
van Ballegooijen E.C. van Mierlo G.W.M. van Schooneveld C. van der Zalm P.P.M. Parsons A.T. Field N.H. 《Oceanic Engineering, IEEE Journal of》1989,14(4):375-383
A practical method is described for the three-dimensional determination of the position, shape, and attitude of a hydrophone array towed from a surface vessel. It provides successive snapshots of the array configuration with a maximum rate of about three per minute. The method is intended as an alternative to the use of fixed test ranges and provides results suitable for validating computer models of array motion. It uses the travel-time differences of impulsive waves measured across the array. The waves are generated by two explosive charges dropped from consorts. Results of a typical experiment are presented as an illustrative example. The array position relative to the tow ship is obtained to within an accuracy of a few metres 相似文献
6.
拖曳线列阵声纳中隔振模块研究 总被引：6，自引：0，他引：6
介绍了作为隔振模块研究依据的拖缆抖动特性的试验研究结果及隔振模块理论分析方法 ,给出了隔振模块有关参数变化对隔振量影响的理论值 ,提供了隔振模块隔振量试验方法 ,某隔振模块隔振量的测量结果以及装与不装隔振模块情况下 ,声阵的拖曳噪声声压谱级的测量结果 相似文献
7.
设计了一种拉线机构驱动的仿鱼型自主巡游机器人,阐述了其机械结构、电路系统及控制算法的设计方案,同时开展开敞水域试验对其游动性能进行研究。研究表明,在直行及转弯试验中,当摆尾频率相同时,随着尾鳍摆动幅度的增加,机器鱼的游动速度上升;当尾鳍摆动幅度相同时,随着摆尾频率的增加,机器鱼游动速度先升后降,且在0.60 Hz附近时达到峰值;在目标角度转向试验中,当摆尾频率及目标角度相同时,随着尾鳍摆动幅度的增加,机器鱼的角度响应时间逐渐减小;当尾鳍摆动幅度及目标角度相同时,随着摆尾频率的增加,角度响应时间先降后升;当摆尾频率及摆动幅度相同时,目标角度的增加会使得角度响应时间呈上升趋势。研究成果验证了该机器鱼平台的可靠性,为将来进一步理论研究及实际应用提供了一定的参考。 相似文献
8.
《Oceanic Engineering, IEEE Journal of》2008,33(2):215-223
9.
Sutat Weesakul Thamnoon Rasmeemasmuang Somruthai Tasaduak Chanon Thaicharoen 《Coastal Engineering》2010
A numerical model is developed to compute the shoreline planform in a crenulate bay beach. The new model combines polar and Cartesian coordinates and can be used effectively to compute a hooked zone shoreline in the lee of upcoast headland. The model is calibrated using laboratory data with an incident wave angle ranging from 25° to 60°. The results of calibration and verification suggest that the ratio of the sediment transport parameters by wave and longshore current in this model is close to unity, and the computed shoreline planforms for the hooked and unhooked zones are in good agreement with the ones measured, especially when a bay is close to static equilibrium. In addition, the bay shape calculated by the present model is similar to that given by the well-known empirical parabolic equation for a bay in static equilibrium. The process of bay shape development from a straight beach to a static equilibrium bay is studied using laboratory experiments and the present numerical model. The temporal variations in the computed longshore sediment transport at different locations within a bay beach are analyzed. From this the decrease in the sediment transport becomes apparent while a bay beach changes its shape from straight toward a state of equilibrium. Based on this experience, it may be concluded that the present numerical model can produce a temporal change in the shoreline planform of a crenulate bay beach from a transition state to static equilibrium subject to seasonal wave action. 相似文献
10.
Underwater acoustic transient signals are generated mechanically at known positions along a wharf. These signals are received by a wide aperture planar array of four underwater acoustic sensors, whose positions relative to the wharf are unknown. A method is described that enables the positions of the sensors to be estimated from accurate differential time-of-arrival measurements (with 0.1 /spl mu/s precision) as the signal wavefronts traverse the array. A comparison of the estimated positions with the nominal positions of the first three sensors, which form a 20-m-wide aperture horizontal line array, reveals a 2-cm displacement of the middle sensor from the line array axis. This slight bowing of the line array results in overranging (bias error of 3%) when the wavefront curvature method is used with the nominal collinear sensor positions to locate a static source of active sonar transmissions at a range of 59.2 m. The use of the spherical intersection method coupled with the estimated sensor positions of the line array provides an order of magnitude improvement in the range estimate (within 0.3% of the actual value). However, systematic ranging errors are observed when the sound propagation medium becomes nonstationary. Next, the differences in the arrival times of the direct path and boundary-reflected path signals at the middle sensor of the wide aperture line array are estimated using the differential phase residue of the analytic signal at the sensor output. These multipath delays are used to estimate the range and depth of the source. Although the average value of the multipath range estimates is within 0.5% of the actual value, the variance of the range estimates is 50 times larger when compared with the results of the spherical intersection and wavefront curvature methods. The multipath delay data are also processed to provide a reliable estimate of the temporal variation in the water depth enabling the tidal variation to be observed. 相似文献
11.
A simple, low cost, deep-towed system for high-resolution reflection seismic profiling is described. It consists of a vertical array with two hydrophones having a separation of 2.2 m and rigidly mounted onto streamlined tow bodies. Improvement of the signal-to-noise ratio is attained by simple stacking of the hydrophone outputs after signal conditioning and travel time corrections. The suppression of side echoes and surface reflections is achieved by an analog procedure which in effect improves the directional characteristics of the array. A circuit for automatic gain control is included to enhance weak signals as well as to suppress ringing.Results in Kiel Bay and over the crest of the Jan Mayen Ridge (northern Atlantic) suggest that this simple vertical array may supplement air gun systems better than conventional, surface pinger-type equipment.Institute of Geophysics 相似文献
12.
为了研究潮流能水轮机尾流场的变化规律,本文在水平轴水轮机现有理论基础上,采用计算流体力学技术建立了数值模型,计算了水轮机的功率特性,进行了网格独立性验证,比较了模型中旋转区域不同对结果的影响。仿真结果与试验结果进行了对比分析,验证了数值模型的有效性。研究了全工况下尾流场速度衰减随尖速比和距离变化的规律,结果显示在小尖速比下尾流场速度恢复情况相对大尖速比下较好;靠近水轮机轮毂中心线位置处,衰减相对较大。研究建议水轮机在同等功率表现下尽量选择在小尖速比下工作,水轮机组在实际排列时避免采用成列布置,水轮机设计阶段应综合考虑功率特性和尾流场衰减。本文研究内容可以为潮流能水轮机的研究以及阵列式应用提供参考。 相似文献
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Swedish fish stocking policy constitutes an example of the disparate challenges associated with adaptive management theory and the realization thereof. The vast substantial and institutional uncertainties of the policy subsystem have previously been identified as variables that complicate the realization of adaptive policy making. The aim of this paper is to address and tentatively explain differences in regards to how these uncertainties are handled. What regional variances in Swedish fish stocking policy can be distinguished and how can these variations be explained? The empirical analysis shows that Swedish fish stocking policy consists of a wide array of different regional policies. These regional variations are explained by differences in existing implementation resources, policy beliefs and readings of formal regulations. Policy makers can decrease these divergences in two ways; they can either change formal regulations or influence available implementation resources. Both management approaches might have positive as well as negative effects on the subsystem's adaptability. 相似文献
15.
The dynamic behavior of a towed cable system that results from the tow ship changing course from a straight-tow trajectory to one involving steady circular turning at a constant radius is examined. For large-radius ship turns, the vehicle trajectory and vehicle depth assumed, monotonically and exponentially, the large-radius steady-state turning solution of Chapman [Chapman, D.A., 1984. The towed cable behavior during ship turning manoeuvers. Ocean Engineering 11, 327–361]. For small-radius ship turns, the vehicle trajectory initially followed a corkscrew pattern with the vehicle depth oscillating about and eventually decaying to the steady-state turning solution of Chapman (1984). The change between monotonic and oscillatory behavior in the time history of the vehicle depth was well defined and offered an alternate measure to Chapman's (1984) critical radius for the transition point between large-radius and small-radius behavior. For steady circular turning in the presence of current, there was no longer a steady-state turning solution. Instead, the vehicle depth oscillated with amplitude that was a function of the ship-turning radius and the ship speed. The dynamics of a single 360° turn and a 180° U-turn are discussed in terms of the transients of the steady turning maneuver. For a single 360° large-radius ship turn, the behavior was marked by the vehicle dropping to the steady-state turning depth predicted by Chapman (1984) and then rising back to the initial, straight-tow equilibrium depth once the turn was completed. For small ship-turning radius, the vehicle dropped to a depth corresponding to the first trough of the oscillatory time series of the steady turning maneuver before returning to the straight-tow equilibrium depth once the turn was completed. For some ship-turning radii, this resulted in a maximum vehicle depth that was greater than the steady-state turning depth. For a 180° turn and ship-turning radius less than the length of the tow cable, the vehicle never reached the steady-state turning depth. 相似文献
16.
《Oceanic Engineering, IEEE Journal of》2008,33(2):182-197
17.
文章介绍了在时间常数测量装置中所涉及到的几个控制问题 ,系统采用由计算机为上位机和以可编程序控制器 (PL C)为下位机构成的两级控制模式。在上位微机中使用 VB5 .0编程语言设计了微机软仪表面板风格的监控程序 ,通过 RS2 32通讯接口将上位微机操作指令送至 PL C完成控制过程。本文还介绍了传感器运动速度的控制和测量 ,传感器穿越阶越界面的运动控制以及高速数据采集系统。 相似文献
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Accurate propeller shaft speed controllers can be designed by using nonlinear control theory and feedback from the axial water velocity in the propeller disc. In this paper, an output feedback controller is derived, reconstructing the axial flow velocity from vehicle speed measurements, using a three-state model of propeller shaft speed, forward (surge) speed of the vehicle, and the axial flow velocity. Lyapunov stability theory is used to prove that a nonlinear observer combined with an output feedback integral controller provide exponential stability. The output feedback controller compensates for variations in thrust due to time variations in advance speed. This is a major problem when applying conventional vehicle-propeller control systems. The proposed controller is simulated for an underwater vehicle equipped with a single propeller. The simulations demonstrate that the axial water velocity can be estimated with good accuracy. In addition, the output feedback integral controller shows superior performance and robustness compared to a conventional shaft speed controller 相似文献
20.
The location of the hydrophones on a towed underwater acoustic array as a function of time (array element localization) is needed for signal processing. Methods to perform this localization using least squares polynomial fitting to data from depth sensors, heading sensors, and sensors detecting a ping from a single source are discussed. Arc distance along the array is used as the independent parameter so that all solutions are constrained to be space curves. Examples of application to real data are presented, and techniques to discriminate against bad sensor data are discussed 相似文献