共查询到20条相似文献,搜索用时 375 毫秒
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Floating structures oscillate in waves, where these wave-induced motions may be critical for various marine operations. An important consideration is thereby given to the sea states at the planning and operating stages for an offshore project. The most important information extracted from a sea state is the directional wave spectrum, indicating wave direction, significant wave height, and wave spectrum peak period. Among several available methods of measuring and estimating the directional wave spectrum, the wave buoy analogy technique based on vessel motion responses is an in situ and almost real-time solution without extra costs of devices. If the forms of the wave spectra are not predefined in the estimation, the method is called a nonparametric approach. Its most remarkable advantage is the flexible form, but the smoothness should be regulated. After the discrete Fourier transform has been applied to the measured vessel motions, smoothing is necessary. However, this process results in disturbed vessel cross-spectra and a lowpass characteristic of the windowing function. This paper presents a nonparametric approach for directional wave spectrum estimation based on vessel motion responses. It introduces novel smoothness constraints using Bézier surface and includes a more robust estimate using L1 optimization. Both techniques are applied to the wave buoy analogy for the first time. Numerical simulations are conducted to verify the proposed algorithm. 相似文献
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To ensure hull structural strength of container ships in association with their increase in size, it is very important to grasp the hull stress histories all over the hull structure in actual sea state. However, ordinary hull stress monitoring systems are insufficient for this purpose because of the small number of stress sensors actually practicable. Therefore, in this paper, we discuss an approach to reproduce the hull stress responses which are not measured based on the estimated wave spectrum from the limited measurement data. To achieve this, we introduce a new model to estimate directional wave spectra based on measured ship stress responses and ship response functions, and further we estimate other ship responses using the model. To model an arbitrarily shaped directional wave distribution, the 360° direction is discretized into 36 directions of 10-degree intervals instead of using a directional distribution function, and in each direction, the wave spectrum is represented using the Ochi (3P) spectrum with three parameters (average wave period, significant wave height, and kurtosis). The authors discuss the evaluation results based on two stress response combinations, and a comparison is made between the sea state estimates made by the proposed method and the ocean wave hindcast database (JWA). Furthermore, by comparing the significant values and the spectra of the measured response of the ship with the estimated response based on both the estimated sea state by the proposed method and the hindcast sea state, the accuracies of the proposed method and the hindcast method are discussed in terms of ship stress estimation at non-instrumented locations. 相似文献
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Michio Ueno Hideki Miyazaki Harukuni Taguchi Yasushi Kitagawa Yoshiaki Tsukada 《Journal of Marine Science and Technology》2013,18(2):192-202
A model scale experiment at a new basin reproduced a phenomenon occurring for a fast ferry; large roll motion and subsequent cargo shift in a quartering sea. Wave generators surrounding the whole periphery of the basin realized a designated directional sea. A carriage system tracked a free-running model ship and a movable weight simulated the cargo shift. Measuring the directional wave field in the basin confirmed the all-around wave generator successfully reproduced the intended wave field that was estimated for the location and the time of the incident. The encounter wave spectrum analyzed using measured data agree well with the theoretically predicted one. The reproduced ship motion, triggered by a small concentrating wave, tells how the ship responded in the successive large quartering waves and the validity of the procedure to reproduce the incident. Repeated measurements of the model ship’s extreme motion confirm a high repeatability of the experiment. 相似文献
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深海极限波浪运动特性的简便算法(英文) 总被引:1,自引:0,他引:1
本文基于五阶Stokes规则波理论,提出了一种快速求解深海极限波浪运动特性的数学模型.研究中,按照上跨零点和下跨零点的方法由计算或实测的极限波浪波面时间历程确定包含极限波峰或波谷的相邻两个周期的平均值为五阶Stokes规则波的波浪周期,然后根据极限波峰或波谷值反推确定波浪入射波幅.通过与已有的数值结果和实验数据对比,验证了本文所建立的数值模型可以快速准确的计算出极限波浪下的速度场,相比其他模型,更适合于工程应用. 相似文献
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《Marine Structures》2000,13(4-5):331-347
The irrotational Green–Naghdi model for nonlinear wave propagation in deep water is developed to simulate the irregular sea surface of a given directional wave spectrum. The model is derived from Hamilton's principle with a depthwise approximation to the flow field. The nonlinear boundary conditions are exactly satisfied on the actual free surface, and the continuity equation is satisfied exactly within the fluid domain. The ‘level’ of approximation in the depthwise direction is optimally chosen to simulate a given wave spectrum accurately with minimum computational effort. Several numerical techniques also are introduced to cut the computational cost further. Numerical results for two-dimensional nonlinear waves are presented. 相似文献
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基于Greenberg方法推导了含有阻抗边界条件的浅水Green函数,利用边界元法研究了含阻抗的三维海洋波导与散射体相互作用的问题.分析了海底阻抗对声波与结构体相互作用时的散射特性影响,数值分析表明:含有阻抗边界条件的浅海目标的散射特性与理想海底明显不同,海底阻抗对水平断面以及垂直断面的散射场都有一定的影响,目标距离海底越近,场点散射声压受海底边界条件的影响越大;阻抗越大,散射声压越大.指向性的分布对受海底阻抗的大小比较敏感.分析浅海声散射时,海底阻抗的影响不可忽视. 相似文献
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基于可靠度理论,进行了允许越浪条件下海堤越浪量的可靠度分析,建立了允许越浪条件下海堤越浪量的极限状态方程。以青岛某斜坡式海堤为例,将有效波高和谱峰周期作为基本随机变量进行越浪量可靠度分析。首先对有效波高和谱峰周期进行Log-normal、Gumbel分布拟合,根据拟合结果,二者均采用Log-normal分布,然后采用Monte Carlo模拟计算了该海堤越浪量的可靠性指标。计算结果表明:进行允许越浪条件下海堤越浪量的可靠度分析是可行的,并且海堤越浪量的可靠性指标概率意义明确,比允许越浪量标准更合理。 相似文献
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基于谱的海浪模拟与谱估计 总被引:1,自引:0,他引:1
针对掠海飞行器系统仿真的需要,研究了海浪仿真方法。选取P—M谱作为海浪谱,通过海况确定波谱参数,在波谱仿真带宽内采用频率等分法对其进行分割,根据Longuest—Higgins海浪模拟模型进行仿真,得出了海浪时域波形。并采用Welch法进行波谱估计,从波谱能量度量,仿真精确度达到了99.22%。 相似文献
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本文主要研究在非线性混合海况(即风浪和涌浪组合海况)下,以NREL 5MW_Baseline Monopile近海风机为研究对象,对其塔筒底部(基线)所受到的剪力和弯矩载荷的动力响应进行仿真。在近海风机的时域仿真中,选用了Ochi-Hubble六参数波浪谱,并编制了该谱的程序嵌入到FAST中进行编译。计算过程中,共进行了20次10 min的仿真分析。对于得到的短期载荷,给出了波高程,塔筒底部首尾向剪力和弯矩在线性与非线性不规则波作用下的时程曲线对比图。采用分块最大值法对每一次的短期载荷提取极值,并基于20次仿真所得的极值,给出了塔筒底部首尾向剪力与弯矩在线性与非线性不规则波作用下的超越概率曲线对比图。研究表明,在非线性混合海况下进行近海风机塔筒底部载荷的动力响应研究,计算结果对工程实际应用具有指导意义。 相似文献
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[Objective]To investigate ship motion and load responses in realistic 3D waves and overcome the limitations of the traditional 2D wave assumption, this paper develops a method for predicting ship motion and load responses in short-crested waves. [Method]The long- and short-term responses of ship motion and load in long- and short-crested waves are numerically predicted using the spectral analysis and statistical probability methods, respectively. The influence of directional function on ship response is also numerically analyzed. Moreover, tank model tests and a large-scale model sea trial are comparatively conducted to validate the difference between ship response and statistics in long- and short-crested irregular waves. [Results]The results show that when navigating against the waves in the same sea condition, the long-crested wave assumption overestimates the statistical mean value of ship load response, but underestimates extreme load in real seas. For long-crested waves, the ship motion and acceleration power spectrum is concentrated around a certain frequency band. [Conclusion]Ship motion and load responses in realistic 3D waves are significantly different from those in 2D long-crested waves. The directional function of short-crested waves also has a significant effect on ship motion and load responses. © 2023 The Author(s). 相似文献
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《Marine Structures》2006,19(1):33-69
In general, two main concepts can be applied to estimate the on-site directional wave spectrum on the basis of ship response measurements: (1) a parametric method which assumes the wave spectrum to be composed by parameterised wave spectra; or (2) a non-parametric method where the directional wave spectrum is found directly as the values in a completely discretised frequency-directional domain without a priori assumptions on the spectrum. The paper outlines the theory of these two concepts, and it is shown how to deal with the speed-of-advance problem for operating ships. In addition, the methods include an equivalence of energy in the governing equations and, as regards the parametric concept, a frequency-dependent spreading of the waves is introduced.The paper includes an extensive analysis of full-scale measurements for which the directional wave spectra are estimated by the two ship response-based methods. Hence, comparisons are made between these estimates and, moreover, the agreement with the corresponding directional wave spectra produced by the wave radar system WAVEX is studied. The agreement between the two methods is reasonable, as well is the agreement between the results of these methods and those of WAVEX. It is difficult to propose one of the ship response-based methods in favour of the other, since they perform equally well. 相似文献