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401.
Low-frequency waves in the surf and swash zones on various beach slopes are discussed using numerical simulations. Simulated surface elevations of both primary waves and low-frequency waves across the surf zone were first compared with experimental data and good agreement found. Low-frequency wave characteristics are then discussed in terms of their physical nature and their relationship to the primary wave field on a series of sea bottom slopes. Unlike primary waves, low-frequency wave energy increases towards the shoreline. Low-frequency waves in the surf and swash are a function of incident waves and the sea bottom slope and hence the saturation level of the surf zone. Wave energy on a gently sloping beach is dominated by low-frequency waves while primary waves play a significant role on a steep beach. Low-frequency wave radiation from the surf zone on a given beach depends on primary wave frequency and beach slope. However, a very poor correlation was found between surf similarity parameter and low-frequency wave radiation. 相似文献
402.
403.
Robb Eric S. Moss Joseph A. Caliendo Loren R. Anderson 《Soil Dynamics and Earthquake Engineering》1998,17(7-8):519-523
In certain regions of the world, designing deep foundations to withstand seismic loading is a reality. Seismic loading of structures and foundations reaches its most critical state as a cyclic lateral force. The response of soils and foundations to repetitive lateral forces is highly complex, relegating most design methods to be based upon overly conservative rules-of-thumb. The primary objective of this research was to analyze the mechanics of seismic loading on pile groups in clay soils. To achieve this a model testing facility was constructed to house a fully instrumented 1×5 model pile group that was subjected to cyclic lateral loading. An empirically based method for pile group design is suggested based upon the results generated from model pile group testing. 相似文献
404.
Yan Tongzhen Li Yun ’an Faculty of Environmental Science Geotechnique China University of Geosciences Wuhan Zhong Yufang Faculty of Earth Sciences China University of Geosciences Wuhan 《中国地质大学学报(英文版)》1998,9(2)
INTRODUCTIONLandslidehasbeenregardedasoneofthegeologicalhaz-ardswhichtrendstodescendenvironmentalqualityandde-stroysecologicb... 相似文献
405.
大华北新构造运动和地震活动“成片迁移”的成因探讨 总被引:5,自引:0,他引:5
基于板块间的作用及有关物理参数,分别组构了大华北第Ⅲ(1484-1739年)、第Ⅳ(1815年至今)地震活动期的动力边界和厚度非均匀的“薄板”模型,采用有限元法,并根据地壳屈曲的研究,作了屈曲变形计算.所得屈曲图象与大华北新生代隆起、凹陷分布的基本特征一致,也与近30年来大华北垂直形变速率的分布特怔吻合.不同期高变形梯度区不同,7级以上地震均分布在这种区内.由此得出了新构造运动和地震“成片迁移”的力学机制. 相似文献
406.
本文详细推导了附有限制条件的条件分组平差的计算公式和精度评定公式,并由此引出其它各种分组平差——附有未知参数的条件分组平差,无参数的条件分组平差,附有限制条件的间接分组平差和序贯平差——的计算公式和精度评定公式。 相似文献
407.
Radar data from three experiments are analysed. Scatter characteristics of 50 cm wind-generated waves have been investigated
with a C-band radar in a large wind-wave tank. Evidence of wave groups in sea clutter from the west coast of Scotland in the
Sound of Sleat is also presented. The spectrum of the waves in the sound is narrow-banded and the waves are young, like the
wind-wave spectrum in the laboratory. Clutter measurements, collected on the English south coast at Portland, of more ocean-like
waves with broad band spectra also suggest the presence of wave groups. Evidence of the presence of wave groups is demonstrated
in range-time images, as well as in the Fourier domain. Some ad hoc processing schemes, the normalised variance and binary
threshold techniques, were successfully applied to enhance the appearance of the wave groups. The wind waves change frequency
with fetch in the wave tank and the downshifting process is investigated using range-frequency maps of the radar data. The
waves appear to change frequency in discrete steps that are associated with wave breaking events. The difference in wave period
before and after breaking could be measured, and a wave crest was shown to be lost to compensate for the change in period,
as expected. Some downshifting could also be measured in the Sound of Sleat. The ratio of wave group frequency and wave frequency
is inaccordance with Benjamin-Fier sideband instability theory, as it is for the data measured at Portland.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
408.
409.
峨眉地幔柱与峨眉地裂运动有何关系?它对中上扬子区二叠纪天然气藏有何影响?研究地幔柱和地裂运动对塔里木盆地油气勘探和开拓新的油气资源有何意义?这些均是复杂而有挑战性的问题。在多年研究峨眉地裂运动基础上,利用前人对峨眉地幔柱的研究成果,探讨扬子板块西北缘拗拉槽群形成与峨眉地幔柱关系,以及峨眉地幔柱产生的热力作用对烃源岩转化和优质储层的影响。对比塔里木盆地和四川盆地构造演化史,建议塔里木盆地油气勘探加强地幔柱和地裂运动对油气成藏条件影响的研究,同时开展地幔柱对2个盆地无机成因油气资源的探索,争取发现新的油气资源。 相似文献
410.
In this paper we explore the impacts of the training programmes offered to lone mothers with young children on the Government's 'New Deal for Lone Parents' in one local labour market: West London. Our research suggests that regulatory workfare policies are (re)producing and reinforcing gendered inequalities in the labour market by encouraging lone mothers to undertake training in feminised occupational areas such as childcare. We will argue that in a local economy such as West London where more childcare workers are desperately needed to enable other more highly skilled workers to take up employment opportunities, such training programmes may be doing little more than exacerbating the already gendered and class-based polarisation of the labour market – embedding low-skilled, poorly qualified lone mothers into low-paid jobs. 相似文献