Parametric study of the wave-induced residual liquefaction around an embedded pipeline

Wave-induced liquefaction in a porous seabed around submarine pipeline may cause catastrophic consequences such as large horizontal displacements of pipelines on the seabed, sinking or floatation of buried pipelines. Most previous studies in relation to the wave and seabed interactions with embedded pipeline dealt with the wave-induced instaneous seabed response and possible resulting momentary liquefaction (where the soil is liquefied instantaneously during the passage of a wave trough), using theory of poro-elasticity. Studies for the interactions between a buried pipeline and a soil undergoing build-up of pore pressure and residual liquefaction have been comparatively rare. In this paper, this complicated process was investigated by using a new developed integrated numerical model with RANS (Reynolds averaged Navier–Stokes) equations used for governing the incompressible flow in the wave field and Biot consolidation equations used for linking the solid–pore fluid interactions in a porous seabed with embedded pipeline. Regarding the wave-induced residual soil response, a two-dimensional poro-elastoplastic solution with the new definition of the source term was developed, where the pre-consolidation analysis of seabed foundation under gravitational forces including the body forces of a pipeline was incorporated. The proposed numerical model was verified with laboratory experiment to demonstrate its accuracy and effectiveness. The numerical results indicate that residual liquefaction is more likely to occur in the vicinity of the pipeline compared to that in the far-field. The inclusion of body forces of a pipeline in the pre-consolidation analysis of seabed foundation significantly affects the potential for residual liquefaction in the vicinity of the pipeline, especially for a shallow-embedded case. Parametric studies reveal that the gradients of maximum liquefaction depth with various wave and soil characteristics become steeper as pipeline burial depth decreases.     

日照计测量误差探讨

通过对聚焦式日照计、暗筒式日照计与直射表测日照 ,进行对比观测与测试。得出聚焦式日照计阈值为 1 2 0 W· m- 2左右 ,WMO定为 IRSR(暂定标准日照计 )是正确的。暗筒式日照计记录比它偏少 5 %左右 ,主要差在日出、日落时段 ,基本满足业务使用。直射表做为检定日照阈值的标准器 ,如用做日照的传感器 ,必须克服其跟踪太阳的偏差 ,否则准确度很难达到要求。     

Live benthic foraminiferal faunas off Cape Blanc, NW-Africa: Community structure and microhabitats

Live (Rose-Vengal stained) benthic foraminifera were studied along a transect across the main area of organic matter deposition in the Cape Blanc upwelling region. The faunal analyses suggest that at the shallowest station (1200 m) the benthic ecosystem is permanently influenced by the upwelling, whereas at the deepest stations (3010 and 2530 m depth) the ocean bottom is subject to significant organic influxes only in summer. The vertical zonation of foraminiferal species in the sediment shows a close correspondence with the depth distribution of oxic respiration, nitrate and sulphate reduction. It is suggested that this linkage is caused by the presence of various stocks of anaerobic and sulphate- and nitrate-reducing bacteria. Deep infaunal foraminiferal species are thought to feed selectively, either on the bacterial stocks or on nutritious particles produced by bacterial degradation of more refractory organic matter. As such, foraminiferal microhabitats are only indirectly controlled by pore water oxygen concentrations.     

半潜式平台气隙数值预报

气隙预报是半潜平台设计过程中要考虑的关键问题之一.以一座250 m水深半潜式钻井平台为例,对其在5种海况下的气隙响应进行了数值计算,并与相应的模型试验相比较.从比较结果可以看出,一阶数值计算和Stokes二阶统计修正的结果均低估了相对波面升高的极值,且波陡越大,低估越严重.但是,它可以较好地预报危险点的位置,因此,可以用来在进行模型试验之前确定探针的布置位置和试验浪向.     

深水中极限波峰下速度场快速算法

基于五阶斯托克斯规则波理论,提出了一种快速求解深水极限波峰下速度场的数学模型.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的相邻两个周期的平均值为五阶斯托克斯规则波的波浪周期,然后根据极限波峰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,验证了所建立的数值模型可以快速准确的计算出极限波峰下的速度场,相比其他模型,更适合于工程应用.