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1.
E.R. Jefferys 《Applied Ocean Research》1984,6(1):31-39
Classical frequency and time domain models of a single degree of freedom wave power device are presented. In the time domain, a convolution integral is conventionally used to represent the fluid dynamic radiation force, characterised by added mass and damping in the frequency domain. This integral is replaced by an approximate ordinary differential equation (ODE) model which is faster and more convenient in simulations. A time domain model of the fluid dynamics of an oscillating water column (OWC) device is derived to illustrate the technique. Digital simulations of the OWC are used to compare the accuracy of the classical and ODE models. The simulation of the ODE model runs about six times as fast as the classical model based on convolution, yet characterises the fluid dynamics accurately. 相似文献
2.
Comparison of sound speed and attenuation measured in a sandy sediment to predictions based on the Biot theory of porous media 总被引：2，自引：0，他引：2
Williams K.L. Jackson D.R. Thorsos E.I. Dajun Tang Schock S.G. 《Oceanic Engineering, IEEE Journal of》2002,27(3):413-428
During the sediment acoustics experiment in 1999 (SAX99), several researchers measured sound speed and attenuation. Together, the measurements span the frequency range of about 125 Hz-400 kHz. The data are unique both for the frequency range spanned at a common location, and for the extensive environmental characterization that was carried out as part of SAX99. Environmental measurements were sufficient to determine or bound the values of almost all the sediment and pore water physical property input parameters of the Biot poroelastic model for sediment. However, the measurement uncertainties for some of the parameters result in significant uncertainties for Biot-model predictions. Here, measured sound-speed and attenuation results are compared to the frequency dependence predicted by Biot theory and a simpler "effective density" fluid model derived from Biot theory. Model/data comparisons are shown where the uncertainty in Biot predictions due to the measurement uncertainties for values of each input parameter are quantified. A final set of parameter values, for use in other modeling applications e.g., in modeling backscattering (Williams et al., 2002) are given, that optimize the fit of the Biot and effective density fluid models to the sound-speed dispersion and attenuation measured during SAX99. The results indicate that the variation of sound speed with frequency is fairly well modeled by Biot theory but the variation of attenuation with frequency deviates from Biot theory predictions for homogeneous sediment as frequency increases. This deviation may be due to scattering from volume heterogeneity. Another possibility for this deviation is shearing at grain contacts hypothesized by Buckingham; comparisons are also made with this model. 相似文献
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近海海上风电场水下噪声传播模型适用性研究 总被引：1，自引：0，他引：1
通过现场采集近海海上风电场工程区运营期风机水下噪声和背景噪声数据,计算了噪声信号的倍频带声压级,功率谱级和峰值声压级,确定了海上风电场水下噪声总声源级为148.3 d B,以此开展近海海上风电工程风机水下噪声频域特性、功率密度谱特性等研究。在此基础上使用Kraken简正波模型和Bellhop射线模型对风电场运营期风机水下噪声在水平与垂直方向上的传播进行模拟,模拟了噪声在不同频带内的衰减程度,结果显示模型模拟结果在不同频率下的衰减趋势有着很大差异,产生了明显的多途干涉现象,通过实测数据对建立的噪声传播模型进行验证,发现Kraken简正波模型在500 Hz以下,Bellhop射线模型在500 Hz以上适合模拟实际水下噪声传播情形,同时海区本身背景噪声的存在会对预测的准确性产生影响。这些结论可用于进一步对近海海上风电场水下噪声传播的研究。 相似文献
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1 .IntroductionRecently, more and more importance is attached to the development of offshore oil and gas alloverthe world and many submarine pipelines have been laid.Submarine pipelines are the lifeline ofthe transportation of offshore oil and gas .Submar… 相似文献
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The acoustic properties of seafloor sediments are of great importance in geoacoustic modeling, detecting, and oceanic engineering. The methods based on the first arrival cycle are investigated to calculate sound speed and attenuation of sediment more precisely in in situ measurements. The comparison of different data analysis methods based on the first arrival cycle approach for in situ measurement results in the following conclusions: (1) the calculated methods can help find the effective cycles and reduce the errors in calculating sound speed and attenuation; (2) using this approach, the point judgment method-based data analysis has the same effectiveness as the cross-correlation method-based data analysis in calculating group sound speed and has the same effectiveness in calculating attenuation in the time domain as the spectrum analysis method-based data analysis has in calculating attenuation in frequency domain; and (3) measurement in water can help not only calibrate the transmitting distance but also can calculate the time delay for the sound speed and the attenuation loss in the transmitting process. Finally, theoretical calculation was used to calculate the measured results, indicating a good agreement, which supports that first arrival cycle-based calculated methods can be used to analyze the measured data and the effective density fluid model can be used to analyze more acoustic properties and invert several physical properties in this experiment. 相似文献
7.
A numerical model based on the mild-slope equation is applied to reproduce the propagation of small-amplitude transient waves. The model makes use of the Fourier Transform to convert the time-dependent hyperbolic equation into a set of elliptic equations in the frequency domain. The results of two available experimental studies on tsunamis generated by landslides are used to validate the model, which appears to be able of carefully reproducing the effects of the frequency dispersion. An example application of tsunamis propagating around the Stromboli island is also presented to show the applicability of the present approach to real life scenarios. It is finally discussed how this model could be applied as support to a tsunami early warning system. 相似文献
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A remote sediment classification technique based on attenuation measurements from Chirp sub-bottom profiler data is described. This differs from previously published work in that attenuation measurements are obtained for each stratigraphic unit within a complex, thinly interbedded sedimentary sequence. Compressional wave attenuation measurements are obtained for a wide variety of lithologies, including muds, silts, sands, clayey sands, silty clays and gravel lags, with grain sizes ranging from 8 Phi to -4 Phi. In addition, attenuation measurements from sub-bottom profiler data were calibrated against laboratory acoustic measurements of vibracores and seabed samples from corresponding geographic locations, under simulated in-situ conditions using a Pulse Tube method. We adapt an instantaneous frequency matching method using a causal attenuation filter to model the decay of the Chirp transmitted waveform. From this modelling, a relationship between t* (a causal attenuation operator) and change in instantaneous frequency is established. The Hilbert transform is used to extract instantaneous frequency information from Chirp seismic, which is used to derive attenuation information for selected individual stratigraphic layers imaged by the sub-bottom profiler. This paper draws attention to the limitations in comparing attenuation measurements derived from Chirp sub-bottom profiler data against previously published literature on experimental attenuation measurements, which are limited by the wide variance of these data, and the difficulty in finding a meaningful best fit to these data. This demonstrates the importance of calibrating remote sediment classification observations using complimentary acoustic analysis of seabed samples to generate a site-specific geoacoustic database. A positive correlation between laboratory and sub-bottom profiler attenuation measurements was obtained, with a correlation coefficient of 0.885. Poorly sorted gravels with a mixed lithic and biogenic pebble component are characterised by very high attenuation with values of Q from 4 to 19. These sediments are considerably coarser-grained than those typically described in previously published experimental studies. 相似文献
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地震波在穿过含油气储层时,由于受油气流体的黏滞性和内摩擦力影响,在频率上会表现为高频衰减快、低频衰减慢的特征,在频谱上就表现为整体能量向低频移动,使得低频能量相对增强。同时,前人大量研究表明流体黏度越大,黏滞性越强,对地震波的吸收衰减效果越明显。在所研究的YP地区,油气运移到浅部成藏,经历了大量的生物降解作用,原油具有比重大、黏度大的特性。利用频率域的吸收衰减技术在研究区这种特性的油层进行了识别,最终实验结果与已钻井结果吻合度较好,预测井也与实钻井相吻合,验证了该技术在该区应用的可行性。 相似文献
10.
A method for estimating the physical and acoustic properties of the sea bed using chirp sonar data 总被引：2，自引：0，他引：2
This paper proposes a method, based on the Biot model, for estimating the physical and acoustic properties of surficial ocean sediments from normal incidence reflection data acquired by a chirp sonar. The inversion method estimates sediment porosity from reflection coefficient measurements and, using the estimated porosity and the measured change in fast wave attenuation with frequency, estimates the permeability of the top sediment layer. The spectral ratio of echoes from the interface at the base of the upper sediment layer and from the sediment-water interface provides a measure of the change in attenuation with frequency. Given the porosity and permeability estimates, the Kozeny-Carman equation provides the mean grain size and the inversion method yields the acoustic properties of top sediment layer. The inversion technique is tested using chirp sonar data collected at the 1999 Sediment Acoustics Experiment (SAX-99) site. Remote estimates of porosity, grain size, and permeability agree with direct measurements of those properties. 相似文献
11.
Shallow-water transmission loss measurements taken in 1988 and 1993 along the same cross slope track on the New Jersey shelf are examined for the frequency interval 50-1000 Hz. Computed results, using a geoacoustic model based on a linear frequency dependence of the sediment volume attenuation, showed less loss than the measured data at the higher frequencies. A two stage, least squares procedure, is developed as a means of quantitatively examining the differences between the measured and computed results. The procedure focuses on the frequency dependence of the sediment volume attenuation and allows the comparison between measurements and computations to be formulated as a statistical test of hypothesis. A geoacoustic model, using a nonlinear frequency dependency and reasonable uncertainty for the sediment volume attenuation, provides a good fit to the data 相似文献
12.
Zhaohui Peng Ji-Xun Zhou Dahl P.H. Renhe Zhang 《Oceanic Engineering, IEEE Journal of》2004,29(4):1038-1045
As a part of the Asian Seas International Acoustic Experiment (ASIAEX) in the East China Sea, sound propagation signals from wideband explosive sources were measured using a 32-element vertical line array. Measurements were made as a function of range in two perpendicular tracks. Sea-bed geoacoustic parameters based on a fluid half-space geoacoustic model (sound speed, density, and attenuation) are inverted from the sound propagation in the frequency range 100-500 Hz. The sea-bed sound speed and density were first derived from mode arrival time differences which were obtained using a spatial mode filtering technique. Sea-bed acoustic attenuation was subsequently estimated by comparing measured transmission loss with model results. 相似文献
13.
Clément (2013) derived a second order ordinary differential equation (ODE) satisfied by the free-surface Green function in the frequency domain. Since then, similar ODEs for the gradient of the Green function have been developed. Unfortunately, all these ODEs degenerate at zero frequency. Therefore, it is not possible to initialize the numerical solution of these ODEs from this zero frequency. Alternative methods based on the shifting of the initial condition to frequencies strictly greater than zero have then been developed.The present paper describes an alternative approach to address this issue. It involves a new function which is the solution of a modified ODE which can be solved from the zero frequency.Finally, comparisons with evaluations of the Green function using the classical direct integration method are provided. They show that the new ODE can provide accurate estimates of the Green function. 相似文献
14.
浅海水下地形的SAR遥感仿真研究 总被引：2，自引：0，他引：2
结合连续性方程和布拉格后向散射模型,在准一维简化浅海水下地形情况下,建立了浅海水下地形SAR海面相对后向散射强度仿真模型,将浅海水下地形区域的SAR海面后向散射强度的相对变化与大尺度背景流场、海面风场和雷达系统参数等联系起来.海上实验和研究结果表明,浅海水下地形的SAR成像主要由通过受水下地形影响的海表层流场对海表面风引起的微尺度波的水动力调制而获取浅海水下地形信息,其中潮流与水下地形的相互作用过程改变海表层流场,变化的海表层流与海表面微尺度波之间的相互作用改变海表面波的空间分布,雷达波与海表面波之间的相互作用决定雷达海面后向散射强度.因此SAR图像中浅海水下地形或水深信息量的多少不仅与海表层流场和海面风速有关,而且与雷达工作波段、雷达波束入射角和极化方式也密切相关.认为由水下地形变化引起的缓慢变化的表层流场中海表面定常微尺度波谱能量密度的变化满足波作用量谱平衡方程;而在波数空间中,海表面微尺度波谱的成长过程也可以用波数谱平衡方程描述,在此基础上,得出了海表面波高频谱(毛细-重力波)形式的解析表达式.众所周知,浅海水下地形信息是由于水下地形影响下SAR海面后向散射强度与背景海面后向散射强度的相对差异而在SAR图像上的呈现,从而在建立浅海水下地形SAR海面相对后向散射强度仿真模型的基础上,仿真计算了浅海水下地形SAR海面相对后向散射强度相对于海表层流场、海面风场等海况参数和SAR工作波段、SAR波束入射角、极化方式等雷达系统参数的数值仿真结果,分析得到了有关浅海水下地形SAR海面相对后向散射强度的特征和SAR浅海水下地形遥感的最佳海况参数与最佳雷达系统参数,为研究和开展SAR浅海水下地形遥感研究提供了有价值的参考. 相似文献
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采用弹性基础梁模型,模拟钢悬链线立管(steel catenary riser,SCR)与海床土的相互作用,推导了弹性基础梁模型的有限元公式,基于该模型编制了钢悬链式立管的动力分析程序,在此基础上,分析了在浮体运动及环境载荷作用下,钢悬链线立管触地点区域的动力响应特征,并与弹簧支撑模型进行了比较。研究表明,弹性基础梁模型对单元长度的敏感性较低,可采用较长的单元,从而减少计算量。 相似文献
16.
海洋立管复模态动力特性分析 总被引：1，自引：0，他引：1
考虑阻尼的影响,研究海洋立管的动力特性。通过分析管内流体及管外海洋环境荷载的共同作用,建立海洋立管涡激振动偏微分方程,进而得到立管动力特性方程,用复模态分析法求解动力特性方程得到立管考虑阻尼的自振频率。算例计算表明:考虑阻尼的立管自振频率略小于不考虑阻尼的立管自振频率;立管的自振频率随着内流流速的增加而减小,但内流流速不大时,影响较小;管道长度对立管的自振频率影响较大。 相似文献
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文章基于长乐海滩前滨剖面的实测波浪数据, 通过统计分析以及谱分析的方法, 探讨了潮汐过程中长乐海滩波浪参数及耗能过程的变化规律。结果表明, 观测期间内波浪以混合浪为主, 各测点谱型较宽, 存在多峰振荡现象。向岸传播过程中, 波能耗散的形式为窄频域向宽频域转变, 能量分布趋于分散, 高频波能减小, 低频波能反而有所上升, 波浪破碎后生成长重力波。破波带内的能量衰减与波浪传播距离具有良好的相关性, 破碎波能在破波带内大约衰减了98.3%。潮汐水位对波浪具有明显的调制作用。入射波能随潮汐水位的增加而有所增加, 且水位越高, 入射波能分布越分散。破波带内的有效波高和潮汐水位具有显著的正相关关系。潮汐过程中固定测点的波谱变化与波浪沿剖面的波谱变化具有明显的相似性。 相似文献
18.
二维各向异性介质中三分量波动方程有限元法模拟 总被引：1，自引：0，他引：1
利用六面体单元和三线性插值函数 ,推导出在任意弹性各向异性介质中三维三分量波动方程所满足的有限元方程 ,同时给出也适用于矩形单元和双线性插值的二维三分量各向异性介质中的波动方程模拟的一般性公式 ,最后讨论两个数值模拟的结果。 相似文献
19.
Sirilath J. DeSilva Ronald B. Guenther Robert T. Hudspeth 《Applied Ocean Research》1996,18(6):293-302
Oscillatory, two dimensional free-surface, irrotational flows of an incompressible fluid are treated numerically. Rather than basing the treatment on perturbation expansions, the unknown fluid domain bounded by a free surface is mapped onto a rectangular domain. This has the effect of exchanging a boundary value problem for a linear, constant coefficient Laplace equation having nonlinear boundary conditions into a nonlinear elliptic equation specified on the known rectangular domain. In the known transformed domain, compatibility conditions at the corners are derived, the boundary value problem is solved and the results are transformed back to the original domain. 相似文献