共查询到20条相似文献，搜索用时 15 毫秒
1.
《Oceanic Engineering, IEEE Journal of》1996,21(4):537-544
The acoustic spectrum of a transiting aircraft, when received by a hydrophone located beneath the sea surface, changes with time due to the acoustical Doppler effect. The traditional method for analysing signals whose frequency content changes with time is the short-time Fourier transform that selects only a short segment of the signal (or window of data) for spectral analysis at any one time. The short-time Fourier transform requires the frequency content of the signal to be stationary during the analysis window, otherwise the frequency information will be smeared by the transformation. Recently, joint time-frequency distributions, which highlight the temporal localisation of a signal's spectral components, have been used to analyse nonstationary signals whose spectra are time dependent. In this paper, the short-time Fourier transform and the Wigner-Ville time-frequency distribution are applied to time-series data from a hydrophone so that the instantaneous frequency of the propeller blade rate of a turbo-prop aircraft can be estimated at short time intervals during the aircraft's transit over the hydrophone. The variation with time of the estimates of the Doppler-shifted blade rate is then compared with the corresponding temporal variation predicted using a model that assumes the sound propagates from the airborne acoustic source to the subsurface receiver through two distinct isospeed media (air and water) separated by a plane boundary (the air-sea interface). The results for five transits are presented in which the altitude of the aircraft ranged from 350 to 6050 ft with the speed of the aircraft varying from 232 to 245 kn 相似文献
2.
《Oceanic Engineering, IEEE Journal of》2009,34(1):75-82
3.
Passive sonar systems that localize broadband sources of acoustic energy estimate the difference in arrival times (or time delays) of an acoustic wavefront at spatially separated hydrophones, The output amplitudes from a given pair of hydrophones are cross-correlated, and an estimate of the time delay is given by the time lag that maximizes the cross correlation function. Often the time-delay estimates are corrupted by the presence of noise. By replacing each of the omnidirectional hydrophones with an array of hydrophones, and then cross-correlating the beamformed outputs of the arrays, the author shows that the effect of noise on the time-delay estimation process is reduced greatly. Both conventional and adaptive beamforming methods are implemented in the frequency domain and the advantages of array beamforming (prior to cross-correlation) are highlighted using both simulated and real noise-field data. Further improvement in the performance of the broadband cross-correlation processor occurs when various prefiltering algorithms are invoked 相似文献
4.
AbstractIn long baseline (LBL) positioning system, errors due to uncertain sound speed are the major facts to its positioning accuracy. In this study, the problem is solved by setting acoustic signal travels between the target and different hydrophones with different sound speed and using particle swarm optimization algorithm to solve the multi-parameter optimization problem to obtain the sound speeds. Presented simulation results show that the proposed algorithm can effectively improve the positioning accuracy of the LBL system compared to existing algorithms and its computational efficiency is high enough. 相似文献
5.
Badiey M. Yongke Mu Simmen J.A. Forsythe S.E. 《Oceanic Engineering, IEEE Journal of》2000,25(4):492-500
Coherence of broad-band acoustic waves for mid-to-high frequencies (0.6-18 kHz) is obtained for a very shallow-water (15-m-deep) waveguide over a wide band of environmental conditions and for a source-receiver range of 387 m. Temporal behavior is sampled at two different rates: one that resolves at fractions of a second over intermittent periods of 40 s and another that resolves at 10 min over periods of several days. Spatial behavior is sampled in the vertical by hydrophones with spacings of the order of meters. The effect of environmental variability on coherence, in particular, soundspeed fluctuations in the water column and wind-induced modulations of the air-sea interface, is noted as a function of acoustic frequency and ray path. Analysis of the acoustic fluctuations over short time scales more accurately resolves the temporal decorrelation of the received signal due to sea surface waves. The vertical sampling of the received signal permits an analysis of arrival-angle fluctuations. The dependence of coherence on the number of surface bounces is studied by comparing arrivals that have zero, one, two, and three surface bounces 相似文献
6.
Marine cycloidal propulsion system is efficient in maneuvering ships like tugs, ferries, etc. It is capable of vectoring thrust in all direction in a horizontal plane. When used in pair, the system enables a vessel to perform maneuvers like moving sideways, perform rotation about a point, i.e. turning diameter of its own length, etc. In this system, the propeller blades have to change their angle of attack at different angular position of the disc. Due to this reason, the inflow velocity vector to propeller blades changes continuously. The propeller blade oscillates about a vertical axis passing through its body and at the same time rotates about a point. Superposed on these motions is the dynamics of the ship on which the propulsion system is installed. This results in a formidable and challenging hydrodynamics problem. Each of the propeller blade sections could be considered as an aerofoil operating in combined heave and pitch oscillation mode. Due to the constantly varying inflow velocity, the hydrodynamic flow is unsteady. The unsteady hydrodynamic flow is simulated by incorporating the effect of shed vortices at different time instant behind the trailing edge. Due to the kinematics of the problem, the blade is subjected to higher structural deformation and vibration load. The structural deformation and vibration when coupled with the hydrodynamic loading add another level of complexity to the problem. In this paper, the variation of hydrodynamic load on the propeller blade due to steady and unsteady flow is compared. We also model the structural dynamics of the blade and study its effect on the hydrodynamic loading. Finally, we couple the structural dynamics with hydrodynamics loading and study its influence on the propeller blade for different operating regimes. 相似文献
7.
Localizing noise sources in cavitation experiments is an important research subject along with predicting noise levels. A cavitation tunnel propeller noise localization method is presented. Propeller noise measurement experiments were performed in the MOERI cavitation tunnel. To create cavitating conditions, a wake-generating dummy body was devised. In addition, 10 hydrophones were put inside a wing-shaped casing to minimize the unexpected flow inducing noise around the hydrophones. After measuring both of the noises of the rotating propeller behind the dummy body and acoustic signals transmitted by a virtual source, the data were processed via three objective functions based on the ideas of matched field processing and source strength estimation to localize noises on the propeller plane. In this paper, the measured noise analysis and the localization results are presented. Through the experiments and the analysis, it was found that the source localization methods that have been used in shallow water applications could be successfully adapted to the cavitation tunnel experiments. 相似文献
8.
Wilmut M.J. Chapman N.R. Heard G.J. Ebbeson G.R. 《Oceanic Engineering, IEEE Journal of》2007,32(4):940-947
This paper describes a simple approach for inferring the depth and track of a sound source at short ranges by inversion of acoustic field data at a set of sea bottom hydrophones. At short ranges, the acoustic field consists of a dominant Lloyd mirror (LM) signal from the direct and surface-reflected ray paths and a series of bottom-reflected paths that modulate the LM signal. A computationally efficient propagation model based on the method of images is developed to calculate replica fields for the inversion. The matched field inversion method for inferring the source depth and track is demonstrated using data from an experiment carried out in shallow water off the east coast of Canada. The estimated values were in very good agreement with independent measurements taken during the experiment. 相似文献
9.
This paper introduces a novel ESPRIT-based closed form source localization algorithm applicable to arbitrarily spaced three-dimensional arrays of vector hydrophones, whose locations need not be known. Each vector hydrophone consists of two or three identical but orthogonally oriented velocity hydrophones plus one pressure hydrophone, all spatially co-located in a point-like geometry. A velocity hydrophone measures one Cartesian component of the incident sonar wavefield's velocity-vector, whereas a pressure hydrophone measures the acoustic wavefield's pressure. Velocity-hydrophone technology is well established in underwater acoustics and a great variety of commercial models have long been available. ESPRIT is realized herein by exploiting the nonspatial inter-relations among each vector hydrophone's constituent hydrophones, such that ESPRIT's eigenvalues become independent of array geometry. Simulation results verify the efficacy and versatility of this innovative scheme 相似文献
10.
This paper introduces a novel ESPRIT-based closed-form source localization algorithm applicable to arbitrarily spaced three-dimensional arrays of vector hydrophones, whose locations need not be known. Each vector hydrophone consists of two or three identical but orthogonally oriented velocity hydrophones plus one pressure hydrophone, all spatially co-located in a point-like geometry. A velocity hydrophone measures one Cartesian component of the incident sonar wavefield's velocity vector, whereas a pressure hydrophone measures the acoustic wavefield's pressure. Velocity-hydrophone technology is well established in underwater acoustics and a great variety of commercial models have long been available. ESPRIT is realized herein by exploiting the nonspatial interrelations among each vector hydrophone's constituent hydrophones, such that ESPRIT's eigenvalues become independent of array geometry. Simulation results verify the efficacy and versatility of this innovative scheme 相似文献
11.
The understanding and the accurate assessment of propeller loads in realistic operative scenario, both design and off-design conditions, is of paramount importance to design low emission and comfortable ships, fulfilling the requirements of structural integrity of the propulsion system, safety and continuity of operations at sea. To this purpose, a deeper characterization of the propeller functioning, in terms of averaged and fluctuating loads, can be attained by means of the quantification of the single blade loads. In this work, a novel set up that allows to monitor the loads developed by a single blade was implemented on a free running, self propelled maneuvering model with the aim to investigate in details the hydrodynamic interactions between the spatially non-homogeneous and time-variant wake of the hull and the propeller and a complete characterization of its performance. This preliminary work introduces the experimental setup and provides a preliminary overview of the results relative to straight ahead motion. 相似文献
12.
13.
Carey W.M. Doutt J. Evans R.B. Dillman L.M. 《Oceanic Engineering, IEEE Journal of》1995,20(4):321-336
Calibrated acoustic measurements were made under calm sea state conditions on the New Jersey shelf near the AMCOR 6010 borehole, a surveyed area with known geophysical properties. The experiment was conducted in 73 m water with supporting measurements of salinity, temperature, and sound speed. Acoustic measurements were obtained with a vertical array of 24 hydrophones spaced equally at 2.5 m intervals; one of which was near the bottom. A source towed at 1/2 the water depth transmitted one of two sets of four tones spaced between 50 and 600 Hz for each run to ranges of 4 and 26 km. The data were processed with both a Hankel transform and a high resolution Doppler technique to yield horizontal wave-number spectrum at several depths. Results were obtained along both constant and gradually varying depth profiles. Similar modal interference patterns were observed at the lower frequencies. The constant depth-profile radial results were compared to calculations performed with several shallow water acoustic models using geoacoustic profiles derived from geophysical parameters and shear wave inversion methods 相似文献
14.
当船舶在冰区航行时,螺旋桨会与海冰相互碰撞并导致桨叶的变形和损坏,进而影响船舶的航行安全。为研究海冰与螺旋桨的相互作用过程,采用离散元(DEM)—有限元(FEM)耦合方法构建海冰—螺旋桨切削模型。海冰和螺旋桨模型分别采用具有黏结—破碎特性的球体离散单元和8节点六面体有限单元构造。基于该DEM-FEM耦合模型讨论了不同切削深度下,螺旋桨所承受冰载荷的特点和规律;最后,研究了螺旋桨切削海冰过程中进速系数、推力系数、扭矩系数之间的对应关系,并讨论了海冰—螺旋桨相互作用过程中冰压力、Mises应力和变形的分布特点。以上研究可为寒区船舶安全航行和螺旋桨设计提供有益的参考。 相似文献
15.
导管桨的尾流不稳定性在其性能评价中非常重要，不但是其能否提供稳定推力的保证，而且也与螺旋桨的尾流噪声直接相关。为了改善导管桨的尾流，提高尾流稳定性，并优化导管桨的流场脉动，根据座头鲸鳍肢前缘结节的仿生原理，对导管桨叶片的导边进行改进，提出了两种仿生桨型，采用IDDES湍流模型对低进速系数下常规导管桨和仿生叶片导管桨进行数值模拟，探究叶片构型对导管桨性能和尾流不稳定性的影响。计算结果表明，前缘结节可以有效降低叶片受力波动的幅值和叶片所受合力的主频域峰值，具有较大结节的叶片对导管桨尾流有明显的优化作用，在尾流远场中扩大了流动稳定区，延后了尾流处涡破碎的发生，改善了能量谱密度的频域分布。进一步，大前缘结节叶片导管桨应用在低速工况下时，可以大量减少尾流泄涡区域的二次涡产生，这是由于前缘结节提升了相邻涡互感的强度，使得尾流更加稳定，而小结节叶片仿生桨型对导管桨尾流则无明显优化作用。研究方法和成果可为螺旋桨尤其是导管桨尾流不稳定性研究提供参考，不仅验证了前缘结节在导管桨叶片应用的合理性，而且揭示了其优化尾流稳定性的机理。 相似文献
16.
Aperture extension is achieved in this novel ESPRIT-based two-dimensional angle estimation scheme using a uniform rectangular array of vector hydrophones spaced much farther apart than a half-wavelength. A vector hydrophone comprises two or three spatially co-located, orthogonally oriented identical velocity hydrophones (each of which measures one Cartesian component of the underwater acoustical particle velocity vector-field) plus an optional pressure hydrophone. Each incident source's directions-of-arrival are determined from the source's acoustical particle velocity components, which are extracted by decoupling the data covariance matrix's signal-subspace eigenvectors using the lower dimensional eigenvectors obtainable by ESPRIT. These direction-cosine estimates are unambiguous but have high variance; they are used as coarse references to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector-hydrophone spacing exceeds a half-wavelength. In one simulation scenario, the estimation standard deviation decreases with increasing intervector-hydrophone spacing up to 12 wavelengths, effecting a 97% reduction in the estimation standard deviation relative to the half-wavelength case. This proposed scheme and the attendant vector-hydrophone array outperform a uniform half-wavelength spaced pressure-hydrophone array with the same aperture and slightly greater number of component hydrophones by an order of magnitude in estimation standard deviation. Other simulations demonstrate how this proposed method improves underwater acoustic communications link performance. The virtual array interpolation technique would allow this proposed algorithm to be used with irregular array geometries 相似文献
17.
18.
Tattersall J.M. King P.C. Mingrone J.A. Herstein P.D. 《Oceanic Engineering, IEEE Journal of》1992,17(3):227-238
An acoustic transient recording buoy (ATRB) developed to provide improved dynamic range and recording capacity in a reconfigurable manner is described. This digital system can acquire and record up to 16 h of broadband wide dynamic range (≈80 dB) acoustic data from eight hydrophones. A unique feature is the use of two inexpensive video cassette recorders to obtain up to 10 Gb of data storage capacity. The system is self-contained and capable of unattended bottom-moored operation. An experiment designed and conducted using a single ship and this system to obtain simultaneous measurements of sea surface forward scatter, propagation loss, and sea floor interaction is reported. Data obtained demonstrate the utility of this system for ocean acoustic experiments. Explosive charge source levels using direct path measurements agreed with previous measurements. Surface reflected data exhibited a frequency dependence attributed to sea surface swell and roughness 相似文献
19.
Coastal acoustic tomography system and its field application 总被引：3，自引：0，他引：3
Yamoaka H. Kaneko A. Jae-Hun Park Hong Zheng Gohda N. Takano T. Xiao-Hua Zhu Takasugi Y. 《Oceanic Engineering, IEEE Journal of》2002,27(2):283-295
The coastal acoustic tomography system (CATS), composed of five moored acoustic stations, has been constructed to measure current fields. The system is developed with special considerations in mind, including the use of Global Positioning System clock signals in the synchronization of the system clock timing among the multiple acoustic stations, and the use of the differently coded Gold sequences to identify the acoustic signals corresponding to individual stations from a received signal. The CATS was successfully applied to map the structure of strongly nonlinear tidal currents in the coastal sea. In spite of the limited spatial resolution caused by inadequate sound transmission data, the two-dimensional tidal vortices features of growth, translation, and decay processes are reconstructed through an inverse analysis of the acoustic travel time obtained among the station pairs. It is evident that the CATS is a powerful tool for measuring variable current fields generated in the coastal seas 相似文献
20.
Nelson E. Martins Srgio M. Jesus 《Oceanic Engineering, IEEE Journal of》2006,31(3):646-656
A blind estimator of the ocean acoustic channel impulse response envelope is presented. The signal model is characterized by a deterministic multipath channel excited by a highly nonstationary deterministic source signal. The time-frequency (TF) representation of the received signal allows for the separation between the channel and the source signal. The proposed estimator proceeds in two steps: First, the unstable initial arrivals allow for the estimation of the source signal instantaneous frequency (IF) by maximization of the radially Gaussian kernel distribution; then, the Wigner-Ville distribution (WV) is sequentially windowed and integrated, where the window is defined by the previously estimated IF. The integral gives the channel impulse response envelope, which turns to be an approximation to the blind conventional matched filter (MF). The blind channel estimator (CE) is applicable upon the following conditions: that the multipath channel contains at least one dominant arrival well separated from the others, and that the IF of the source signal is a one-to-one function. Results obtained on real data from the INternal TIde Measurements with Acoustic Tomography Experiments (INTIMATE'96), where the acoustic channel was driven by an linear frequency modulation signal, show that the channel's envelope detailed structure could be accurately and consistently recovered, with the correlation of the estimates ranging from 0.796 to 0.973, as compared to the MF result 相似文献