An intercomparison of GEOSAT, TOPEX and ERS1 measurements of wind speed and wave height

Mean monthly values of altimeter wind speed and wave height are compared with data from NDBC buoys. As a result of these comparisons, corrections are made to the raw data products available from these satellites. Data from the GEOSAT, TOPEX and ERS1 missions corrected in this fashion are used to show that there have been no measurable changes in the global wind and wave climate during the 10 years spanned by these various missions. It is proposed that the corrected values of wind speed and wave height provide the basis for the formation of a long-term global data base which spans the periods of these multiple missions.     

台湾岛邻近海域台风浪模拟分析

本文概略介绍了目前国际上较为先进的第三代近岸海浪数值模式SWAN（SimulationWavesNearshore）及风生浪、底摩擦、白帽耗散、深度诱导波破碎、非线性波－波相互作用等物理过程；在此基础上，以较高的分辨率对袭击台湾岛邻近海域的9015、8616号台风浪过程进行了模拟分析；台风浪高模拟值与实际台风浪资料相符较好，可以为该海域台风浪的模拟提供较好的参考。     

平行激波加速离子的数值研究

伴随耀斑和日冕物质抛射共生的日冕和行星际快激波作为一种粒子加速机制一直是理论研究关注的热点课题.在准平行激波传播条件下,首先建立数值求解一维输运方程的方法,然后探讨加速离子分布与激波和背景等离子参数之间的关系.取扩散系数分别为常数和能量的函数、有限自由逃逸边界的计算结果表明:(1)随着加速时间的增大,高能粒子近似呈双幂律分布,低能端(3～10 MeV)谱指数逐渐从10.2减小到2.4,能谱逐渐变硬,粒子被激波加速后能量逐渐增大;(2)随着激波压缩比从2增大到4,相同时间同一能量范围的粒子能谱谱指数逐渐从3.2减小到2.2,能谱逐渐变硬,表明激波强度的增大使得加速效率增大;(3)上下游逃逸边界由5减小到2后,粒子能谱的谱指数由2.4增大到3.3,粒子的加速效率减小;(4)当粒子注入能量增大时,粒子能谱的谱指数由2.4减小到0.9,加速效率增大;(5)当扩散系数与能量成正比时,粒子能谱指数由2.2增大到4.3,能谱变软.     

Paramètres statistiques de la houle au large de la côte sud-aquitaine

Statistical parameters of waves on the south Aquitaine coast have been determined by comparison of two datasets: in situ local measurements on a short duration and numerical simulation outputs from the WAVEWATCH III model over a period of 6 years and 9 months. Data and simulation results are well correlated in the case of the significant wave height, whereas in the case of the peak periods $(T_{\mathrm{p}})$ and directions $(D_{\mathrm{p}})$, this correlation is lower. This is due respectively to the intrinsic unstable nature of $T_{\mathrm{p}}$ and the narrow distribution of $D_{\mathrm{p}}$. An adjustment of simulation data on measurement is then used to give an evaluation of the wave statistics for the southern fraction of the French Atlantic coast. Eventually, the relationships between the three statistical variables $(H_{\mathrm{s}},T_{\mathrm{p}},D_{\mathrm{p}})$ are analysed in order to determine representative sea states. The classification obtained shows the predominance of swell regimes, distributed on a very narrow angular sector over wind sea regimes. To cite this article: S. Abadie et al., C. R. Geoscience 337 (2005).     

Numerical prediction of green water incidents

Green water loads on moored or sailing ships occur when an incoming wave significantly exceeds the freeboard and water runs onto the deck. In this paper, a Navier–Stokes solver with a free surface capturing scheme (i.e. the VOF model; [Hirt and Nichols, 1981]) is used to numerically model green water loads on a moored FPSO exposed to head sea waves. Two cases are investigated: first, green water on a fixed vessel has been analysed, where resulting waterheight on deck, and impact pressure on a deck mounted structure have been computed. These results have been compared to experimental data obtained by [Greco, 2001] and show very favourable agreement. Second, a full green water incident, including vessel motions has been modelled. In these computations, the vertical motion has been modelled by the use of transfer functions for heave and pitch, but the rotational contribution from the pitch motion has been neglected. The computed water height on deck has been compared to the experimental data obtained by [Buchner, 1995a] and it also shows very good agreement. The modelling in the second case was performed in both 2-D and 3-D with very similar results, which indicates that 3-D effects are not dominant.     

The analysis of tandem hull vessel motion in waves

This paper attempts to provide a better understanding of the hydrodynamic behavior of a tandem hull form in a floating production platform application where high deck payload capacity and low wave induced motions of this vessel are primary design goals. A simplified hydrodynamic analysis and a more representative radiation and diffraction theory based hydrodynamic analysis are used for wave induced forces and motions. The analysis results are compared with model test results to deduce principal features of these special purpose hull configurations. The motion responses in different wave headings evaluated from the complicated diffraction analysis are compared and discussed in some detail.     

CALCULATION OF THE PERFORATED WAVE HEIGHT FOR VERTICAL PERFORATED-PIPE BREAKWATER

在导出作用于管式透空直立式防波堤波浪反射系数之后，本文对由于透空存在而使波浪透入港内的机制进行了分析，考察了影响透射波高的各种因素，确定了堤厚的作用，并依据物理表现寻求具有待定系数的函数表达式，由水动力模型试验数据拟合了函数表达式中的待定系数。本文所得表达式不仅反映了波动的物理机制，而且在数值上达到了令人满意的结果。     

Dynamics of the turbidity maximum in King Sound, tropical Western Australia

King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km². The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m⁻³. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height.     

A distribution function calculation of the H α profiles of SNR filaments

In shocked media of high preshock ionisation, the lack of thermal contact between atoms in the neutral component of the gas can prevent the formation of a thermal equilibrium independent of the ionic component. The behaviour of the neutral gas in such a shock is dominated by the atomic processes driven by the postshock ionic component.A transport equation for the velocity distribution of the neutral gas is explicitly solved under the physical conditions of a 1D ionic shock transition. The resulting distributions are used to calculate predicted H line emission from such a system.     

Simulations of the wardle instability of c-type shock waves

C-type shocks in the partially ionized ISM are modelled by numerical simulations. Under certain conditions the shocks are subject to the Wardle instability, which initially makes the shock front rippled, then in the non-linear stage can produce density variations in both the ion and neutral fluids. A systematic search in the numerically accessible parameter space is done to determine the wave vector k_max and the growth rates _max of the fastest growing modes. The neutral Alfvén number, and the angle _sbetween the shock normal and the upstream magnetic field determine the strength and obliqueness of the shock, as well as the dimensionless parameters of the fastest growing mode. The results confirm and extend Wardle's linear analysis.The non-linear evolution shows saturation of the instability and the formation of high density regions that detach from the shock front with the downstream flow. Numerical difficulties are partially solved by an implicit treatment of the ion-neutral friction terms, but strong shocks still can not be modelled efficiently. A fully implicit method for the ions and the magnetic field is used to model C-type shocks with low fractional ionization and high ion Alfvén speed.