A computer model for forecasting ocean wave parameters at specific sites around the the New Zealand coast

An applications model for forecasting frequency‐directional wave spectra at any appropriately specified site is described. There are two stages to the calculations. Firstly, a spectrum is calculated based on results at nearby gridpoints from an ocean wave prediction model. This is then adjusted to make the spectrum consistent with the local wind history. Verifications of the model are made at sites off Cape Egmont and Great Barrier Island, North Island, New Zealand. These give encouraging results for the shape of the frequency spectrum, with reasonable skill evident in the energetic parts of the spectrum. The significant wave heights also agree well, with the model estimates explaining two thirds of the measured variance.     

嵊泗地区风浪分布及其时间变化分析

通过对嵊泗地区实测波浪资料的分析,探讨了嵊泗地区的风浪分布形式。并且依据1992年12月至2002年8月的TOPEX卫星高度计资料给出了本地区长期有效波高的时间变化,为该地区海洋减灾防灾和工程设计提供了科学依据。     

一种加装稳定翼的海上风电负压桶型基础研究

针对海上风电负压桶型基础,以提高桶基水平承载性能和降低结构动力响应为目的,提出了一种加装稳定翼的负压桶型基础型式。通过在桶身设置一组稳定翼,使得桶周土抗力得以充分利用。以单立柱负压桶基为例,建立桶土全实体有限元模型,进行了静力分析和包括模态分析、瞬态分析、谱分析在内的动力分析。结果表明:稳定翼的设置增强了桶基水平承载性能;水平位移和动力响应显著减小;结构低阶固有频率略有提高。     

利用浅水地形及其SAR影像确定海面风向的一种方法

利用浅水地形的SAR影像以及基于浅水地形SAR仿真模型计算得到的仿真SAR影像,基于仿真SAR影像与真实SAR影像之间的相关性提出了一种确定海面风向的方法——最大相关系数法.以南沙双子礁海域为例,利用最大相关系数法确定出了一幅RADARSAT SAR影像成像时刻的海面风向,通过对结果的比较分析可以看出对于包含浅水地形的SAR影像应用该方法探测海面风向是可行的.     

Dynamic Analysis of A 5-MW Tripod Offshore Wind Turbine by Considering Fluid–Structure Interaction

Fixed offshore wind turbines usually have large underwater supporting structures. The fluid influences the dynamic characteristics of the structure system. The dynamic model of a 5-MW tripod offshore wind turbine considering the pile–soil system and fluid structure interaction (FSI) is established, and the structural modes in air and in water are obtained by use of ANSYS. By comparing low-order natural frequencies and mode shapes, the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed. On basis of the above work, seismic responses under excitation by El-Centro waves are calculated by the time-history analysis method. The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water. The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.     

Uncertainty Analysis of Wind-Wave Predictions in Lake Michigan

With all the improvement in wave and hydrodynamics numerical models, the question rises in our mind that how the accuracy of the forcing functions and their input can affect the results. In this paper, a commonly used numerical third-generation wave model, SWAN is applied to predict waves in Lake Michigan. Wind data are analyzed to determine wind variation frequency over Lake Michigan. Wave predictions uncertainty due to wind local effects are compared during a period where wind has a fairly constant speed and direction over the northern and southern basins. The study shows that despite model calibration in Lake Michigan area, the model deficiency arises from ignoring wind effects in small scales. Wave prediction also emphasizes that small scale turbulence in meteorological forces can increase prediction errors by 38%. Wave frequency and coherence analysis show that both models can predict the wave variation time scale with the same accuracy. Insufficient number of meteorological stations can result in neglecting local wind effects and discrepancies in current predictions. The uncertainty of wave numerical models due to input uncertainties and model principals should be taken into account for design risk factors.     

Changes in storminess and surges in western France during the last century

French meteorological data provide some information on wind direction since 1890. Since 1951, wind speed and direction have been digitised every three hours in many stations. The Brest tide gauge has recorded hourly sea levels since 1860, thus enabling hourly surges to be calculated and studied. This set of data has been organised into a data base and analysed in order to recognize evolution and trends. Strong winds are increasing in frequency in the western part of Brittany and decreasing in Normandy and Pays de Loire. Surges associated with these winds do present a slight decreasing trend. A more precise analysis allows to distinguish between southerly winds, which are slightly decreasing, and strong winds from other directions, which display a more or less important increase in frequency. The analysis shows trends that may be linked to the global circulation pattern, and that result in a new spatial distribution of winds on western France.     

Influence of wavelength on the parameterization of drag coefficient and surface roughness

Surface waves are the roughness element of the ocean surface, the air-sea interaction processes are influenced by the wave conditions. The dynamic influence of surface waves decays exponentially with distance from the air-water interface. The relevant length scale characterizing the decay rate is the wavelength. The parameterization of drag coefficient and surface roughness can be significantly improved by using wavelength as the reference length scale of atmospheric measurements. The wavelength scaling of drag coefficient and dynamic roughness also receives support from theoretical studies of wind and wave coupling.     

Diagnostic calculation of the upper-layer circulation in the South China Sea during the winter of 1998

On the basis of hydrographic data obtained in November 28 to December 27, 1998 cruise, the calculation of the circulation in the South China Sea (SCS) is made by using the P-vector method, in combination with SSH data from TOPEX/ERS-2 analysis. For study of the dynamical mechanism, which causes the pattern of winter circulation in the SCS, the diagnostic model (Yuan et al., 1982; Yuan and Su, 1992) is used to simulate numerically the winter circulation in the SCS. The following results have been obtained.(1) The main characteristics of the circulation systems in the central SCS are as follows: A coastal southward jet in winter is present at the western boundary near the coast of Vietnam; there is a stronger cyclonic circulation with a larger horizontal scale east of this coastal southward jet and west of 114°E; there is a weaker anti-cyclonic circulation in the central part of eastern SCS; there is a stronger and northeastward flow opposing the northeasterly monsoon between above a stronger cyclonic circulation and a weaker anti-cyclonic circulation.(2) The circulation systems in the northern SCS are as follows: 1)There is a cyclonic circulation system northwest of Luzon, and it has three centers of the cold water; 2) There is an anti-cyclonic eddy. Its center is located near(20°N, 116°40' E); 3)There is a warm and anti-cyclonic circulation south of Hainan Island; 4) There is a northeastward flow, the South China Sea Warm Current, in winter off Guangdong coast in the northern SCS.(3) In the southem SCS there is an anti-cyclonic circulation, and also there is a smaller scale cold water and cyclonic eddy.(4) The above pattern of winter circulation in the SCS agrees qualitatively with the horizontal distribution of temperature at 200 m level.(5) The dynamical mechanism which produces the above basic pattern of winter circulation is because of the following two causes: 1) The joint effect of the baroclinity and relief (JEBAR) is an essential dynamical cause; 2) The interaction between the wind stress and bottom topographic (IBWT) under the strong northeasterly monsoon is the next important dynamical mechanism.(6) Comparing the hydrographic structure and the horizontal distribution of velocity with the SSH data from TOPEX/ERS-2 analysis in the SCS during December of 1998, it is found that they agree qualitatively.