Wave run-up on slender circular cylindrical foundations for offshore wind turbines in nonlinear random waves     

Dag Myrhaug  Lars Erik Holmedal 《Coastal Engineering》2010

A practical method for estimating the wave run-up height on a slender circular cylindrical foundation for wind turbines in nonlinear random waves is provided. The approach is based on the velocity stagnation head theory and Stokes second order wave theory by assuming the basic harmonic wave motion to be a stationary Gaussian narrow-band random process. Comparisons are made with measurements by De Vos et al. (2007), and some of the highest wave run-up events that were predicted agree with those measured.  相似文献   

基于VAP方法的多普勒雷达风场反演研究     

周鑫  刘艳 《成都信息工程学院学报》2007,22(3):338-342

采用VAP(Velocity Azimuth Processing)方法反演多普勒雷达风矢量场,在利用各个距离圈径向速度随方位角分布的廓线推算风向和风速的设计中,要求基数据速度资料中没有明显的脉动.介绍了在多普勒天气雷达风场反演设计中,直接将方格法的速度资料处理过程融入到方格法风场反演的过程中,利用距离方格内保持中尺度特性的特点,不改变原始资料的同时保证风场反演的正确性.  相似文献   

风浪对海-气界面动量通量估计的影响   总被引：1，自引：0，他引：1  

赵栋梁  李明明  马昕 《中国海洋大学学报(自然科学版)》2008,38(6)

利用实验室和有代表性的外海观测数据综合分析表明,海面粗糙度对波龄的依赖性与是否将实验室和外海数据一起考虑有关,而风应力拖曳系数与此无关,且随波龄增大而减小.利用Toba-3/2指数律和风浪成长关系的分析表明,风应力拖曳系数为常数或随波龄的增大而增大,与上述结果定性上相矛盾,说明风浪对风应力拖曳系数影响问题需要进一步研究.  相似文献   

Obliquity evolution of extrasolar terrestrial planets     

Keiko Atobe 《Icarus》2007,188(1):1-17

We have investigated the obliquity evolution of terrestrial planets in habitable zones (at ∼1 AU) in extrasolar planetary systems, due to tidal interactions with their satellite and host star with wide varieties of satellite-to-planet mass ratio (m/Mp) and initial obliquity (γ₀), through numerical calculations and analytical arguments. The obliquity, the angle between planetary spin axis and its orbit normal, of a terrestrial planet is one of the key factors in determining the planetary surface environments. A recent scenario of terrestrial planet accretion implies that giant impacts of Mars-sized or larger bodies determine the planetary spin and form satellites. Since the giant impacts would be isotropic, tilted spins (sinγ₀∼1) are more likely to be produced than straight ones (sinγ₀∼0). The ratio m/Mp is dependent on the impact parameters and impactors' mass. However, most of previous studies on tidal evolution of the planet-satellite systems have focused on a particular case of the Earth-Moon systems in which m/Mp?0.0125 and γ₀∼10° or the two-body planar problem in which γ₀=0° and stellar torque is neglected. We numerically integrated the evolution of planetary spin and a satellite orbit with various m/Mp (from 0.0025 to 0.05) and γ₀ (from 0° to 180°), taking into account the stellar torques and precessional motions of the spin and the orbit. We start with the spin axis that almost coincides with the satellite orbit normal, assuming that the spin and the satellite are formed by one dominant impact. With initially straight spins, the evolution is similar to that of the Earth-Moon system. The satellite monotonically recedes from the planet until synchronous state between the spin period and the satellite orbital period is realized. The obliquity gradually increases initially but it starts decreasing down to zero as approaching the synchronous state. However, we have found that the evolution with initially tiled spins is completely different. The satellite's orbit migrates outward with almost constant obliquity until the orbit reaches the critical radius ∼10-20 planetary radii, but then the migration is reversed to inward one. At the reversal, the obliquity starts oscillation with large amplitude. The oscillation gradually ceases and the obliquity is reduced to ∼0° during the inward migration. The satellite eventually falls onto the planetary surface or it is captured at the synchronous state at several planetary radii. We found that the character change of precession about total angular momentum vector into that about the planetary orbit normal is responsible for the oscillation with large amplitude and the reversal of migration. With the results of numerical integration and analytical arguments, we divided the m/Mp-γ₀ space into the regions of the qualitatively different evolution. The peculiar tidal evolution with initially tiled spins give deep insights into dynamics of extrasolar planet-satellite systems and discussions of surface environments of the planets.  相似文献   

Non-Stationary Rayleigh-Taylor Instabilities in Pulsar Wind Interaction with a Supernova Shell     

X. Ribeyre  L. Hallo  V. T. Tikhonchuk  S. Bouquet  J. Sanz 《Astrophysics and Space Science》2007,307(1-3):169-172

The Rayleigh-Taylor instability (RTI) plays an important role in the dynamics of several astronomical objects, in particular, in the supernovae (SN) evolution. In the present paper we examine the dynamics of a shell (representing a type II SN remnant) blown-up by a wind emitted by a central pulsar. The shell is accelerated by the pulsar wind and its inner surface experiences the RTI. We develop an analytical approach by using a specific transformation into the coordinate frame co-moving with the SN ejecta. We first derive a non-stationary spherically symmetric solution describing an expansion of a gas shell under the pressure of a central source (pulsar). Then, we analyze its 3D stability with respect to a small perturbation on the inner shell surface. The dispersion relation is derived in the co-moving reference frame. The growth rate of the perturbation is found and its temporal evolution is discussed. We compare our result with the previous published studies and apply it to the Crab nebula evolution.  相似文献   

The cause for the north-south orientation of the crustal dichotomy and the equatorial location of Tharsis on Mars     

James H. Roberts  Shijie Zhong 《Icarus》2007,190(1):24-31

The crustal dichotomy and the Tharsis rise are the most prominent topographic features on Mars. The dichotomy is largely an expression of different crustal thicknesses in the northern and southern hemispheres, while Tharsis is centered near the equator at the dichotomy boundary. However, the cause for the orientation of the dichotomy and the equatorial location of Tharsis remains poorly understood. Here we show that the crustal thickness variations associated with the dichotomy may have driven true polar wander, establishing the north-south orientation of the dichotomy very early in martian history. Such a reorientation that placed the dichotomy boundary near the equator would also have constrained the Tharsis region on the dichotomy boundary to have originated near the equator. We present a scenario for the early generation and subsequent reorientation of the hemispheric dichotomy, although the reorientation is independent of the formation mechanism. Our results also have implications for the sharply different remanent magnetizations between the two hemispheres.  相似文献   

基于四种再分析资料的1988-2015年中国近海月均风速特征评估   总被引：1，自引：0，他引：1  

王国松  王喜冬  王慧  侯敏  李琰  范文静  刘玉龙 《海洋学报(英文版)》2020,39(1):83-90

This study investigates the long-term changes of monthly sea surface wind speeds over the China seas from 1988 to 2015. The 10-meter wind speeds products from four major global reanalysis datasets with high resolution are used: Cross-Calibrated Multi-Platform data set(CCMP), NCEP climate forecast system reanalysis data set(CFSR),ERA-interim reanalysis data set(ERA-int) and Japanese 55-year reanalysis data set(JRA55). The monthly sea surface wind speeds of four major reanalysis data sets have been investigated through comparisons with the longterm and homogeneous observation wind speeds data recorded at ten stations. The results reveal that(1) the wind speeds bias of CCMP, CFSR, ERA-int and JRA55 are 0.91 m/s, 1.22 m/s, 0.62 m/s and 0.22 m/s, respectively.The wind speeds RMSE of CCMP, CFSR, ERA-int and JRA55 are 1.38 m/s, 1.59 m/s, 1.01 m/s and 0.96 m/s,respectively;(2) JRA55 and ERA-int provides a realistic representation of monthly wind speeds, while CCMP and CFSR tend to overestimate observed wind speeds. And all the four data sets tend to underestimate observed wind speeds in Bohai Sea and Yellow Sea;(3) Comparing the annual wind speeds trends between observation and the four data sets at ten stations for 1988-1997, 1988–2007 and 1988–2015, the result show that ERA-int is superior to represent homogeneity monthly wind speeds over the China seaes.  相似文献   

小麦玉米田耕作模式的防风蚀效果   总被引：2，自引：0，他引：2  

杨彩红  冯福学  柴强  耿艳香  伏星舟 《中国沙漠》2019,39(4):9-15

通过风洞实验，在5个风速下对6种耕作方式下农田土壤风蚀速率、0~20 cm风沙流结构进行了模拟研究。结果表明：保护性耕作土壤风蚀速率较传统耕作平均降低20%~40%；保护性耕作和传统耕作条件下土壤风蚀速率均随风速的增大呈幂函数递增，但在传统耕作条件下递增较快；风速14 m·s^-1是荒漠绿洲农田土壤风蚀加剧转折点，当风速>14 m·s^-1时保护性耕作下风蚀速率较传统耕作明显降低；0~20 cm内，传统耕作和保护性耕作下输沙率与高度分别呈线性和指数关系，保护性耕作下0~4 cm输沙量和输沙量百分比（Q_0~4/Q_0~20）均低于传统耕作。  相似文献   

荒漠草原区风力发电场建设前后的植被变化     

马松尧  陈龙  滕泽宇  丁爱军  何子豪 《中国沙漠》2019,39(2):186-192

调查了甘肃景泰荒漠草原区一处风电场基础设施建设和运行对植被的影响。结果表明：荒漠草原区百兆瓦级风力发电场建设造成直接植被生产力损失量为6.79 g·m^-2·a^-1，间接植被生产力损失量为91.43 g·m^-2·a^-1。随着扰动程度增加，物种丰富度降低，均匀度减小。在工程运行后，经历近10 a的自然恢复，核心扰动区虽然物种单一，但植被生产力是次级扰动区的两倍以上，为间接扰动区和未扰动区的50%和33%左右；而间接扰动区植被生产力仅为未扰动区的50%。总体上，风电工程扰动对区域植被的影响，不仅在于建设期对局地群落植被生产力的完全丧失，更重要的是在运行期间对周边大面积间接影响区群落植被生产力的大幅度降低，而且这种影响是长期和持续性的。  相似文献   

Theoretical expressions for soil particle detachment rate due to saltation bombardment in wind erosion   总被引：1，自引：0，他引：1  

XuYang Liu  WenXiao Ning  ZhenTing Wang 《寒旱区科学》2020,12(4):234-241

Saltation bombardment is a dominate dust emission mechanism in wind erosion. For loose surfaces, splash entrainment has been well understood theoretically. However, the mass loss predictions of cohesive soils are generally empirical in most wind erosion models. In this study, the soil particle detachment of a bare, smooth, dry, and uncrusted soil surface caused by saltation bombardment is modeled by means of classical mechanics. It is shown that detachment rate can be analytically expressed in terms of the kinetic energy or mass flux of saltating grains and several common mechanical parameters of soils, including Poisson's ratio, Young's modulus, cohesion and friction angle. The novel expressions can describe dust emission rate from cohesive surfaces and are helpful to quantify the anti-erodibility of soil. It is proposed that the mechanical properties of soils should be appropriately included in physically-based wind erosion models.  相似文献