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1.
The presented work aims at validating the generalization of the asymptotic distribution model of Boccotti for large wave heights recently proposed by Tayfun [1] to laboratory generated mixed sea states with two-peak spectra. The input wave spectra are modelled as the sum of two JONSWAP spectra describing unidirectional wave systems with different or identical directions of propagation (crossing or following mixed seas). In order to account for the effect of the energetically dominant wave system on the largest observed waves, the Boccotti's parameters were calculated at the absolute minimum of the autocorrelation function which can differ from the first minimum for some cases of mixed seas, such as those dominated by the swell or seas with comparable contribution of the two spectral components. So far the proposed model has been validated elsewhere against samples of large wave heights exceeding the significant wave height in wind seas and in mechanically generated long-crested seas, both characterized by unimodal spectra and strong third-order nonlinearities. The present study demonstrates that it can predict equally well the tail of the distributions for mixed seas, irrespective of the type of the mixed sea, particularly when the third-order statistics is relatively large. Typically, the mixed seas from the considered offshore basin experiment display such conditions as the propagation distance from the wavemaker increases, though this effect is less pronounced for mixed following than for mixed crossing wave conditions. Moreover, the generalized model remains valid irrespective of the sign of the fourth-order sum Λ which is a key parameter of the distribution. Its good predictive ability is quantified here by the root-mean-square errors between observations and theory. 相似文献
2.
Kyoung Kim Powers E. Ritz C. Miksad R. Fischer F. 《Oceanic Engineering, IEEE Journal of》1987,12(4):568-575
A quadratic system model based on Volterra series representation is utilized to model the nonlinear response of moored vessels subjected to random seas. The key idea is to represent the relationship between the incident sea wave (input) and corresponding sway response of the moored vessel (output) with a parallel combination of linear and quadratic transfer functions, and to estimate them by processing actual input and output data. Compared to previous approaches, we take the important step of removing the restriction that the random input must possess Gaussian statistics. The feasibility and validity of the approach is demonstrated by analyzing experimental data taken in model basin tests. We also describe some of the deleterious consequences of assuming Gaussian sea-wave excitation when in fact the excitation is non-Gaussian. 相似文献
3.
本文对海-气边界层波致风机制的相关理论进行了阐述,并利用ERA-40再分析资料给出了太平洋谱峰速度、波龄、波陡等描述涌浪和波致风机制物理量的年际和季节空间分布特征。分析表明:东太平洋赤道地区等海域涌浪速度最大且涌浪由南向北传播明显;太平洋波边界层高度基本呈现出东高西低的分布形势;波致风机制主要发生在赤道热带海域,北半球夏季波致风机制偏强,冬季偏弱,南半球反之;北半球北部海域夏季更易发生波致风机制,赤道附近海域相反;南海为风浪与涌浪组成的混合浪,对其波候等相关研究有必要分开进行讨论。 相似文献
4.
V. G. Bondur V. A. Dulov A. B. Murynin V. Yu. Ignatiev 《Izvestiya Atmospheric and Oceanic Physics》2016,52(6):637-648
A method to register sea-wave spectra using optical aerospace imagery has been developed. The method is based on the use of retrieval operators both in areas of high and low spatial frequencies, including the areas of spectral maximum. The approach to adjust and validate the method developed using sea truth data obtained by string wave recorders has been suggested. This paper presents the results of using the suggested method to study sea-wave spectra using high-resolution satellite imagery for various water areas under different conditions of wave generation. 相似文献
5.
基于星载波谱仪海浪方向谱探测原理，仿真了不同海况、风速下的海浪波谱仪接收信号，并采用周期图法、Welch法、AR模型法以及最小方差法共4种不同的调制谱估计方法反演出海浪谱，比较各种调制谱估计方法的海浪方向谱反演性能。仿真结果表明:对于一定方位向下的一维海浪谱反演，不同调制谱估计方法反演海浪谱性能优劣没有绝对的顺序。对于二维海浪谱反演，在成长中海浪条件下周期图法反演性能最差，其他3种方法的反演性能没有绝对优劣顺序；对于成熟风浪，最小方差法在积分能量误差、有效波高误差两个指标上的反演性能最好，在主波波向、主波波长误差上，周期图法反演性能最差，其他3种方法没有绝对优劣顺序。在涌浪条件下，AR模型法反演性能优于其他3种方法。在不同海况下，随着波谱仪中心入射角的下降，反演性能会下降。基于这些仿真结果，本文推荐最小方差法作为充分成长海浪的海浪方向谱反演的调制谱估计方法，AR模型法作为涌浪海浪方向谱反演的调制谱估计方法。 相似文献
6.
A method of determining sea-wave parameters from frequency characteristics of an RF signal scattered by the sea surface is considered. The method is based on the Doppler frequency shift due to orbital velocity of motion of long sea waves. It is shown that by measuring the frequency shift ofS -band signals scattered by a small (as compared to the sea-wave length) site on the sea surface, one is able to determine both integrated sea-wave parameters (e.g., rms waveheight and mean period) and the space-time structure of energy-carrying sea components. Results of field tests are presented substantiating the efficiency of the method and allowing measurement accuracy to be evaluated. The main systematic errors of the method are discussed. 相似文献
7.
8.
Current specification of the ocean wave environment for the design of offshore platforms does not adequately describe the directional nature of a real seaway. The strong wave frequency dependent nature of the directional behavior of observed seas is often over-simplified for design. A general formulation encompassing a wide range of directional sea models is presented. Parameter values used in some of the more popular directional sea models are examined. Approximate expressions for the two frequency dependent parameters in a modified Longuet-Higgins cosine wave spreading model are presented. A general procedure which allows an engineer to estimate parameters for alternate wave spreading models is discussed. To illustrate this procedure an empirically based modified cosine spreading model is used as the basis to estimate frequency dependent parameters for circular normal and wrapped Gaussian wave spreading models. A comparison of the contours of the various directional sea models and the prediction of the root-mean-square velocity distribution is presented. 相似文献
9.
There is a growing practical interest in the ability to increase the sea states at which marine operations can be safely undertaken by exploiting the quiescent periods that are well known to exist under a wide range of sea conditions. While the actual prediction of quiescent periods at sea for the control of operations is a deterministic process, the long term planning of future maritime tasks that rely on these quiescent periods is a statistical process involving the anticipated quiescence properties of the forecasted sea conditions in the geographical region of interest. It is in principle possible to obtain such data in tabular form either large scale simulation or from field data. However, such simulations are computationally intensive and libraries of appropriate field data are not common. Thus, it is clearly attractive to develop techniques that exploit standard wave spectral models for describing the quiescence statistics directly from such spectra. The present study focuses upon such techniques and is a first step towards the production of a computationally low-cost quiescence prediction tool and compares its efficacy against simulations. Two significant properties emerge for a large class of wave spectral models that encompasses the ubiquitous Neumann and Pierson Moskowitz or Bretschneider forms. Firstly, the auto-correlation function of the wave profile that are required to produce the quiescence property can be obtained analytically in terms of standard special functions. This considerably reduces the computational cost making desktop computer-based planning tools a reality. Secondly, for each class of these parametric spectra, the probability of a given number of consecutive wave heights (normalised to the significant wave heights) less than some critical value is in fact independent of absolute wave height. Thus, for a broad class of practically interesting wave spectra all that is required to obtain the statistical distribution of the quiescent periods is simple rescaling. 相似文献
10.
《Applied Ocean Research》2004,26(1-2):49-60
The influence of longer (swell) on shorter, wind sea waves is examined using an extensive database of directional buoy measurements obtained from a heave-pitch-roll buoy moored in deep water in the South Atlantic. This data set is unique for such an investigation due to the ubiquitous presence of a young swell component propagating closely in direction and frequency with the wind sea, as well as a longer, opposing swell. Our results show, within the statistical limits of the regressions obtained from our analysis when compared to measurements in swell free environments, that there is no obvious influence of swell on wind sea growth. For operational purposes in ocean engineering this means that power-laws from fetch limited situations describing the wind sea growth can be applied in more realistic situations in the open sea when swell is present. 相似文献
11.
The wave climate at the Maui site off the west coast of the North Island and off the east coast of Great Barrier Island to the east of the North Island are examined. This is done by means of average wave spectra derived from a 2‐year database, acquired from Waverider buoy measurements made over 1980 and 1981. The average spectra provide information about the individual sea states which characterise the wave climate, and show that on average the sea state on the east coast is less energetic than it is on the west coast. Further, it is seen that this difference results largely from a dominant and persistent long‐period south‐westerly swell of 12.4 s period which is present at the Maui location but absent from the Great Barrier Island seas. 相似文献
12.
-In this paper, the maximum entropy spectral, the cross-spectral and the frequency response analyses are madeon the basis of the data of monthly mean sea levels at coastal stations in the Bohai Sea during 1965-1986. The results show that the annual fluctuations of the monthly mean sea levels in the Bohai Sea are the results of the coupling response of seasonal variations of the marine hydrometeorological factors. Furthermore, the regression prediction equation is obtained by using the double screening stepwise regression analysis method . Through the prediction test , it is proved that the obtained results are desirable. 相似文献
13.
OSTIA数据在中国近海业务化环流模型中的同化应用 总被引：3，自引：0，他引：3
The prediction of sea surface temperature(SST) is an essential task for an operational ocean circulation model. A sea surface heat flux, an initial temperature field, and boundary conditions directly affect the accuracy of a SST simulation. Here two quick and convenient data assimilation methods are employed to improve the SST simulation in the domain of the Bohai Sea, the Yellow Sea and the East China Sea(BYECS). One is based on a surface net heat flux correction, named as Qcorrection(QC), which nudges the flux correction to the model equation; the other is ensemble optimal interpolation(En OI), which optimizes the model initial field. Based on such two methods, the SST data obtained from the operational SST and sea ice analysis(OSTIA) system are assimilated into an operational circulation model for the coastal seas of China. The results of the simulated SST based on four experiments, in 2011, have been analyzed. By comparing with the OSTIA SST, the domain averaged root mean square error(RMSE) of the four experiments is 1.74, 1.16, 1.30 and 0.91°C, respectively; the improvements of assimilation experiments Exps 2, 3 and 4 are about 33.3%, 25.3%, and 47.7%, respectively.Although both two methods are effective in assimilating the SST, the En OI shows more advantages than the QC,and the best result is achieved when the two methods are combined. Comparing with the observational data from coastal buoy stations, show that assimilating the high-resolution satellite SST products can effectively improve the SST prediction skill in coastal regions. 相似文献
14.
The problem of fatigue damage estimation of ageing jack-up platforms is considered, using theories of random processes. The sea-wave excitations are modelled as stationary, Gaussian random processes, with specified power spectral density function. The loads acting on the structure due to the sea waves is calculated using Morison’s equation and are therefore non-Gaussian whose probabilistic properties are not available in explicit form. Assuming linear structure behaviour, the probabilistic properties of the structure response are determined using theories of random vibrations. The simple peak counting method is adopted for estimating the mean fatigue damage. This requires knowledge of the joint probability density function of the structure response and its first and second time derivatives, at the same time instant. A methodology has been presented for developing analytical expressions for this joint pdf. This requires evaluation of multidimensional integrals. A recently developed computational algorithm is presented to deal with integrals for which derivation of closed form analytical expressions may not be feasible. The methodology proposed in this paper provides an alternative and computationally cheaper technique for estimating the fatigue damage in comparison to the Monte Carlo simulation procedure. Numerical results have been presented for illustration of the proposed methodology. 相似文献
15.
次重力波在近岸水动力运动过程中起到重要作用,深入地了解次重力波对预防其引发的近岸灾害有着重要意义。结合波浪现场观测方法和数值模拟方法研究了斯里兰卡南部海域次重力波特征。短波和自由次重力波通过海浪谱模型WAVEWATCH III模拟,而约束次重力波通过二阶非线性理论模拟,数值模拟结果与现场观测结果对比吻合良好。研究结果表明,斯里兰卡南部海域大部分时间以自由次重力波为主;在强涌浪海况下（短波波高大于2.5 m,周期大于15 s）约束次重力波逐渐逼近自由次重力波甚至占主导地位;斯里兰卡大陆架极其狭窄,对涌浪的能量损耗作用极为有限,使得近岸面对强劲的涌浪及其伴生的次重力波的侵袭,增大了次重力波引发近岸水动力灾害的风险。 相似文献
16.
The paper aims at introducing practical methods for power capture performance enhancement of a heaving wave energy converter in irregular seas. The optimum control solution requires tuning to wave frequency based on wave force information. However, identification of the wave frequency in irregular seas is considered to be a complex and difficult task. This is partly due to technical difficulties in determination of the wave force. Besides, there are no clear guidelines for identification of wave frequency from an irregular sea state based wave force information. In a typical application, one of the available sources of information about the wave properties is the wave elevation record. The proposed approach presents a method for estimation of the wave frequency information from the wave elevation data by using signal processing and filtering techniques. The proposed method uses filters to generate an estimation of wave force information, which is used to identify the local wave frequency by method of a time-series analysis of the data. This wave frequency information is then used in tuning the device. The details of the proposed techniques, the model of the wave energy converter, the simulated sea states and the related simulation results are also presented. 相似文献
17.
We establish a mathematically consistent theory of the pseudo-sound pressure fluctuation in the deep ocean induced by nonlinearly interacting random plane waves on the surface. In the process, a new set of the second-order perturbation equations is derived and power-correlation coefficients between random plane waves are introduced. A phenomenological model is adopted for wind pressure which excites the surface waves consisting of wind-driven sea and swell. By solving the first-order- and the second-order-perturbation equations with this wind pressure as the excitation, we obtain an expression for the pressure fluctuation and its power spectral density in the gravity-wave regime. It is concluded that only the swell part of the surface waves generates the pressure fluctuation and the spectral density is modified by the power correlation coefficient. 相似文献
18.
The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching. 相似文献
19.
海面电磁回波频谱宽度与海浪波高密切相关，可应用频谱宽度进行海浪有效波高反演。本文应用线性滤波法仿真出了海表散射面元在雷达视向上的投影速度，建立了回波谱宽模型，分析了雷达空间分辨率、回波时间序列长度及海洋环境参数等因素对频谱宽度的影响，同时还针对如何在实际观测过程中选择回波时间序列长度、观测方位角等参数进行了讨论。最后还将理论结果与CSIR-X波段雷达实测数据谱宽估计结果进行了比较。结果表明，剔除雷达噪声以及频率泄露的影响后，基于高斯分布标准偏差的谱宽估计方法所得结果与理论结果吻合很好，这从而证明了理论结果的可靠性。本文所得结果对海浪有效波高反演具有一定参考价值。 相似文献
20.
This paper analyses 10 years of wave data from the Mediterranean Spanish (Catalan) coast considering the mean wave climate and storm events from the standpoint of wind-wave momentum transfer and wave prediction. The data, registered by a buoy at about 12 km from the coastline, revealed two main groups of wave storms, with NW and E directions. NW storms correspond to a fetch-limited situation since the intense wind blows from land. Low-pressure centres located over the Mediterranean Sea produce easterly storms. Near the coast the eastern winds from the sea are replaced by NW winds coming from meteorological patterns over northern Spain and south-western France. Wave storms are classified and studied to obtain their main features (including spectral width, wave length, wave age and bimodality) and discussed in terms of wind-wave momentum transfer for operational wave predictions. Observations show a complex coastal wave climate. Fetch-limited storms presented smaller spectral widths while varying wind situations presented larger widths due to the presence of bimodal spectra. These wave features are highly relevant for wind–ocean momentum transfer and, thus, for current and wave predictions. The spectral width proved to be a good indicator of sea complexity and is thus applicable for improved wind drag estimations. A new drag coefficient formulation is proposed, based on existing wind dependent drag expressions, but including also spectral wave properties (a spectral width parameter) that highlights the characteristics of wind-wave generation under pre-existing swell. Such a formulation, once properly validated with field observations, is expected to improve wind-wave predictions. 相似文献