共查询到20条相似文献，搜索用时 31 毫秒
1.
Towed-array history, 1917-2003 总被引：1，自引：0，他引：1
《Oceanic Engineering, IEEE Journal of》2004,29(2):365-373
Towed-array research and development over 86 years is examined from the inventions of Dr. H. C. Hayes during World War I to multiple arrays towed by oil exploration ships in 2003. Time lines of the effort over the years are presented for array applications to military surface ships, submarines, and for oil exploration efforts. Military surface ship towed-array systems from the Hayes electric eel effort to the SQR-14, SURTASS, ETASS, and APL/Johns Hopkins dual towed arrays are reviewed. Submarine towed-array programs from the early 1960s to today are described and a prediction of future towed-array development is presented. 相似文献
2.
The major obstacle to underwater acoustic communication is the interference of multi-path signals due to surface and bottom reflections. High speed acoustic transmission over a shallow water channel characterized by small grazing angles presents formidable difficulties. The reflection losses associated with such small angles are low, causing large amplitudes in multi-path signals. In this paper we propose a simple but effective model for multi-path interference, which is then used to assess the performance of a digital communication system operating in a shallow water channel. The results indicate that transmission rates in excess of 8 kbits/s are possible over a distance of 13 km and channel depth of only 20 meters. Such a system offers improved performance in applications such as data collection from underwater sensors 相似文献
3.
《Ocean Modelling》2001,3(3-4):137-165
The implementation of a system for variational assimilation of data into ocean models is described. The system is modular: the ocean dynamics may be changed by replacing subroutines for the tangent-linear forward model and for the adjoint model. The assimilation is `weak': the ocean dynamics need not be satisfied exactly. An iterative algorithm within the system enables the solution of nonlinear assimilation problems. There is a suite of diagnostics including posterior error statistics, term balances and array assessment. The system has been in development for over a decade, and has been used in conjunction with a variety of oceanic, atmospheric and coupled models, with real data in quantity. The algorithms used in these applications, and the particular scientific assumptions and results, have been reported elsewhere. The emphasis in this article is on the implementation. This is a considerable challenge, both in the scale and complexity of the calculations, over and above those of the underlying ocean model. The vehicle for this presentation is a `toy' model, defined by a single nonlinear equation of motion. Code for real models is available at an anonymous ftp site. Components of the code are matched here in detail to stages of the assimilation algorithm and the diagnostics. Options are given for preconditioning, parallelization, memory management and other performance issues. Resource requirements, from computing speed through preconditioning effort to algebraic derivation, are also discussed in detail. Several applications are reviewed with the emphasis, again, on implementation. 相似文献
4.
Field observations of flows in coastal zone are scarce, but important for understanding the spatial variability of currents. The design of small, low-cost GPS drifters for collecting accurate Lagrangian data in the coastal zone is described. The drifters are intended for using in nearshore environments, lakes and estuaries over timescales of a few minutes up to several hours and are a low-cost alternative for applications which do not require drifter’s sea-going capability. Two field tests of GPS drifters in the south coast of Caspian Sea in Anzali port, Iran, in November 2008 and July 2009 were successful. 相似文献
5.
A Review of Shallow-Water Mapping Systems 总被引：1，自引：0，他引：1
In recent years shallow-water mapping systems have been developing rapidly for various applications of coastal, nearshore, and other shallow-water regions. Some systems can operate in only 0.5 m deep water, while the operating range of some systems is over 600 m depth. This article reviews the characteristics of nine shallow-water mapping systems developed by seven manufacturers. The design and the data collection methods of these systems are different from each other, and each has its advantage. Most of these systems have been tested in the real environment and are in use for various purposes around the world. 相似文献
6.
The littoral drift rose (LDR) concept is presented herein for improvement in understanding of longshore sediment transport and consequent shoreline processes in areas with smooth (gradually varying) offshore bathymetry extending over a coastal region where the deep water wave climate is reasonably uniform. The concept of the littoral drift rose (LDR) is presented and LDRs are shown to provide insight into coastal evolution and shoreline stability (or instability) for a given region having uniform wave climate. This paper reviews earlier documented applications and work using LDRs and provides an interpretation of earlier findings of shoreline stability using LDRs. Previously known but undocumented findings are also discussed herein which show that the wave climate and hence the LDR can be synthesized into an equivalent LDR developed from one wave component of given magnitude and direction. Practical applications using LDRs are presented, which show that the magnitude and direction of littoral drift throughout a region can be interpreted from limited measured, calculated, or observed data on littoral drift at two locations in the region. 相似文献
7.
SERR-1D is a 4th-order finite volume 1D Boussinesq model including wave breaking energy dissipation through extra diffusive-like terms. This model has been primarily conceived to compute wave propagation in coastal areas and has been validated for breaking and non-breaking waves propagating over uneven bathymetries (Cienfuegos et al., 2005, 2006a, b, 2007). The present paper aims at investigating the ability of SERR-1D to simulate challenging fluvial hydraulic applications such as sudden gate operation in open channels generating short waves, dam-break flows and a steady hydraulic jump over a bump. The performance of the absorbing-generating boundary condition implemented in SERR-1D is first analysed in the context of fluvial applications where relatively short waves must be evacuated from the computational domain without producing spurious reflection. Next, by comparing numerical results to analytical and experimental dam-break test cases we show that the model is able to reproduce the overall features of these flows, but that additional care should be paid to the representation of energy dissipation and front speed in order to accurately represent bore dynamics. 相似文献
8.
根据共轭敏感性理论,用共轭模式对1983～1987年北半球从冬到夏的季节急变,包括这5a平均情况及1983年和1987年异常偏早或偏晚的个例进行分析,分别得出这些急变影响最大的初始扰动分布。从年平均的资料来看,在4月前后季节急变所对应的最敏感扰动与海洋的作用有关;而6月前后的季节急变所对应的最敏感扰动与海洋的作用延伸到陆地后受到大地形的影响有关。1983年和1987年的个例分析表明:4月份大陆上出现最敏感扰动中心,造成4月急变偏早或偏晚发生;6月份海洋上出现最敏感扰动中心,造成6月急变的异常;4月急变偏早时6月急变偏晚;4月急变偏晚时6月急变偏早。 相似文献
9.
Hartley变换是一种基于谐函数的实变换,具有Fourier变换的特性,在海洋工程中使用Fourier变换的大部分应用都可以通过Hartley变换实现,并且快速Hartley变换的计算效率是快速Fourier变换的2倍,并易于实现,所以Hartley变换可以在许多应用中代替Fourier变换。详细介绍了Hartley变换在海洋工程领域的应用,包括:波谱分析、波浪分离、PIV(粒子图像测速法)技术和微分方程的Hartley域变换,举例说明了Hartley变换在节约计算空间和提高计算效率上具备的优越性。 相似文献
10.
《Marine Policy》2015
A rejoinder to our recent paper suggests that there has been confusion over our central point. The 85 IUCN Red List Threatened species that the International Game Fish Association issues world records became threatened due to commercial overfishing, not recreational. However, given that they are threatened now, we have concerns about trophy fishing for them, at least in the current form that precludes catch and release. Additionally, while the IGFA claims that an insignificantly low number of record applications for these species have been submitted, many more anglers attempt to catch a large fish than end up submitting record applications. We are grateful for the opportunity to discuss this important issue. 相似文献
11.
The application of Hartley transform to ocean engineering 总被引：1，自引：0，他引：1
The Hartley transform is a real integral transform based on harmonic functions and hassome characteristics similar to the Fourier transform. Most applications in ocean engineering requiring the Fourier transform can also be performed by the Hartley transform. The fast Hartley transform is twice faster and more convenient to handle than the corresponding fast Fourier transform, so it is a real valued alternative to the complex Fourier transform in many applications. The use of the Hartley transform in ocean engineering is presented in detail in this paper, including wave spectral analysis, separation of waves, cross-correlation in PIV technique and expression of equation in the Hartley domain. The examples in the paper show deeply the advantage and efficiency of the Hartley transform over the Fourier transform. 相似文献
12.
The existing numerical models for nearshore waves are briefly introduced, and the third-generation numerical model for shallow water wave, which makes use of the most advanced productions of wave research and has been adapted well to be used in the environment of seacoast, lake and estuary area, is particularly discussed. The applied model realizes the significant wave height distribution at different wind directions. To integrate the model into the coastal area sediment, sudden deposition mechanism, the distribution of average silt content and the change of sediment sudden deposition thickness over time in the nearshore area are simulated. The academic productions can give some theoretical guidance to the applications of sediment sudden deposition mechanism for stormy waves in the coastal area. And the advancing directions of sediment sudden deposition model are prospected. 相似文献
13.
C. F. de Valk 《Coastal Engineering》1999,37(3-4)
HF radar systems are designed to measure spatially variable sea surface currents. A methodology was developed to complement these data with information about the current variability over the water column in a stratified shallow sea. Current profiles were estimated using a diagnostic model driven by surface current measurements from an HF radar system and by sea surface slopes derived from tide gauge data. The structure of the model has a physical basis but its parameters were derived from an analysis of in-situ current profile measurements. Application of the model to HF radar data from the SCAWVEX Rhine outflow experiment showed fair agreement with in-situ current data. As applications, estimation and tidal analysis of current fields are demonstrated. 相似文献
14.
时—频联合分析法及其在海洋资料处理中的应用 总被引：2，自引：0，他引：2
时－频联合信号分析法能描述非稳态信号的频率如何随时间而变化,故它能使我们更好地理解信号的本质。本文简要介绍了这种方法,说明了它的优点,并列举了它在海洋资料处理中应用的一个实例。 相似文献
15.
16.
Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing 总被引：6，自引：0，他引：6
Hans Burchard Peter D. Craig Hans van Haren H.E. Markus Meier Hartmut Prandke Eric D. Skyllingstad David J.S. Welsh Hemantha W. Wijesekera 《Progress in Oceanography》2008,76(4):399-442
In this review paper, state-of-the-art observational and numerical modeling methods for small scale turbulence and mixing with applications to coastal oceans are presented in one context. Unresolved dynamics and remaining problems of field observations and numerical simulations are reviewed on the basis of the approach that modern process-oriented studies should be based on both observations and models. First of all, the basic dynamics of surface and bottom boundary layers as well as intermediate stratified regimes including the interaction of turbulence and internal waves are briefly discussed. Then, an overview is given on just established or recently emerging mechanical, acoustic and optical observational techniques. Microstructure shear probes although developed already in the 1970s have only recently become reliable commercial products. Specifically under surface waves turbulence measurements are difficult due to the necessary decomposition of waves and turbulence. The methods to apply Acoustic Doppler Current Profilers (ADCPs) for estimations of Reynolds stresses, turbulence kinetic energy and dissipation rates are under further development. Finally, applications of well-established turbulence resolving particle image velocimetry (PIV) to the dynamics of the bottom boundary layer are presented. As counterpart to the field methods the state-of-the-art in numerical modeling in coastal seas is presented. This includes the application of the Large Eddy Simulation (LES) method to shallow water Langmuir Circulation (LC) and to stratified flow over a topographic obstacle. Furthermore, statistical turbulence closure methods as well as empirical turbulence parameterizations and their applicability to coastal ocean turbulence and mixing are discussed. Specific problems related to the combined wave-current bottom boundary layer are discussed. Finally, two coastal modeling sensitivity studies are presented as applications, a two-dimensional study of upwelling and downwelling and a three-dimensional study for a marginal sea scenario (Baltic Sea). It is concluded that the discussed methods need further refinements specifically to account for the complex dynamics associated with the presence of surface and internal waves. 相似文献
17.
In the present paper, Miles' (1981) theory is implemented to derive formulae for describing the Bragg scattering of water waves for doubly composite artificial bars with different shapes, spacings, relative bar heights, relative bar footprint and the number of bars. The theory has clear advantage in estimating Bragg reflection coefficient for practical applications concerning coastal problems. Experiments of Bragg reflections over doubly composite rectangular artificial bars have also been performed in a wave flume. Key parameters that may lead to the optimal selection of a doubly composite artificial bar are studied. Theoretical solutions are seen to compare fairly well with the numerical computations and the laboratory experiments. Our simulated results reveal that the Bragg resonance for doubly composite artificial bars effectively increases the bandwidth of the reflection coefficient. 相似文献
18.
The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference finite-volume TVD-type scheme, is coupled with the wave model SWAN in the Nearshore Community Model (NearCoM) system. The new modeling system is named NearCoM-TVD and the purpose of this study is to report the capability and limitation of NearCoM-TVD for several coastal applications. For tidal inlet applications, the model is verified with the semi-analytical solution of Keulegan (1967) for an idealized inlet-bay system. To further evaluate the model performance in predicting nearshore circulation under intense wave–current interaction over complex bathymetry, modeled circulation patterns are validated with measured data during RCEX field experiment (MacMahan et al., 2010). For sediment transport applications, two sediment transport models are applied to predict three sandbar migration events at Duck, NC, during August to October 1994 (Gallagher et al., 1998). The model of Kobayashi et al. (2008) incorporates wave-induced onshore sediment transport rate as a function of the standard deviation of wave-induced horizontal velocities. The modeled beach profile evolution for two offshore events and one onshore event agrees well with the measured data. The second model investigated here combines two published sediment transport models, namely, the total load model driven by currents under the effect of wave stirring (Soulsby, 1997) and the wave-driven sediment transport model due to wave asymmetry/skewness (van Rijn et al., 2011). The model study with limited field data suggests that the parameterization of wave stirring is appropriate during energetic wave conditions. However, during low energy wave conditions, the effect of wave stirring needs to be re-calibrated. 相似文献
19.
In addition to its narrow beamwidth and wide-band capability, the underwater parametric acoustic source has the advantage of maintaining a relatively constant beamwidth over a wide range of difference frequencies. However, for some applications, the beamwidth of the difference frequency is narrower than desired or an adjustable beamwidth is required. This article describes techniques by which the beamwidth at a given difference frequency can be increased and varied over a 3-to-1 range by controlling the input waveform and amplitude to the transducer. The effect of the waveform changes on the harmonic content of the difference-frequency energy is also discussed. 相似文献
20.
Dennis Trizna Lillian Xu 《Oceanic Engineering, IEEE Journal of》2006,31(4):904-918
In this paper, we describe a high-frequency (HF) radar capable of multifrequency operation over the HF band for dual-use application to ship classification and mapping ocean current shear and vector winds. The radar is based on a digital transceiver peripheral component interconnect (PCI) card family that supports antenna arrays of four to 32 elements with a single computer, with larger arrays possible using multiple computers and receiver cards. The radar makes use of broadband loop antennas for receive elements, and a number of different possibilities for transmit antennas, depending on the operating bandwidth desired. An option exists in the choice of monostatic or multistatic operation, the latter providing the ability to use several transmit sites, with all radar echo signal reception and processing conducted at a single master receiver site. As applications for such a multifrequency radar capability, we show measurement and modeling examples of multiple frequency HF radar cross section (RCS) of ships as an approach to ship target classification. Results of using 32 radar frequencies to measure the fine structure in ocean current vertical shear are also shown, providing evidence of one edge of a 1-3-m deep uniform flow masked at the surface by wind-driven current shear in a different direction. Other applications of current-shear measurements, such as vector wind mapping and volumetric current estimation in coastal waters, are also discussed 相似文献