Impact of macrozoobenthic structures on near-bed sediment fluxes

Sandy sediments in shallow coastal waters of the Baltic Sea are often characterised by large numbers of biogenic structures which are produced by macrozoobenthos species. A series of experiments was devised to quantify how the interaction of such structures with the near-bed flow regime affects the sediment flux. Most experiments were done with simplified replicates of structures generated by typical species commonly found in the Mecklenburg Bight, starting with solitary structures and regularly-spaced arrays in a range of characteristic population densities, followed by a complex benthic macrofauna community, both artificial and alive. A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a topography scanning laser, was used for high-resolution measurements (2 mm horizontal step size and 0.3 mm vertical resolution) of sand erosion (220 µm median grain size, at 20 cm s^− 1) and fine particle deposition (8 µm grain size, at 5 cm s^− 1). Sediment transport threshold values were measured for each layout. As a rule-of-thumb, both the erosion fluxes and the deposition of suspended matter increased considerably at low population densities (below 2%, expressed as percent of the sediment surface covered, i.e. roughness density RD). Above densities of 4%, erosion almost stopped inside the test arrays, and deposition remained well below the level of unpopulated areas. An attempt to extrapolate these findings to field conditions (using field current velocity data from 2001) showed that the net flux switched from erosion to deposition for densities above 5%. These parameters can now be integrated into a numerical sediment transport model coupling waves, currents, sediment dynamics and biological processes, which is currently under construction at the Baltic Sea Research Institute (IOW), Rostock, Germany.     

Biologically induced differences in erodibility and aggregation of subtidal and intertidal sediments: a possible cause for seasonal changes in sediment deposition

This study was carried out to describe the difference in erodibility and aggregation in a tidal basin including both subtidal and intertidal study sites and to use these results to explain the shifting erosion/deposition cycles at the sites. Erosion thresholds, erosion rates and settling velocities of the eroded material were measured at a mudflat transect and at sediment cores taken from a nearby tidal channel during surveys made in May 2000 and March 2002. Surface samples were analysed for grain-size, chl. a content, faecal pellet content, dry bulk density and organic content. Additionally, surface samples were taken at eight occasions in the period January 2002 to May 2003 from shallow tidal channels in the area. These samples were analysed for mud content and showed that major shifts in sediment distribution occurred in the period. The erodibility of the mudflat was generally high due to pelletization by the mudsnail Hydrobia ulvae but close to the salt marsh much lower erodibility was found, probably due to stabilisation by microphytobenthos. In contrast, the erodibility of the channel bed seemed to be very little influenced by biological activity and the relatively low erodibility found here was caused by physical characteristics of the sediment. The sediment eroded from the mudflat was generally strongly pelletized and showed high settling velocities whereas less aggregation and lower settling velocities were found for the channel bed sediments. Temporal variations of the mudflat stability and hydrodynamics resulted in temporal variations of deposition and erosion and the changing stability at the mudflat is likely to be one of the main reasons for a general transport of fine-grained sediment from the mudflat to the channel in the cold seasons and vice versa during the rest of the year.     

高凝成品油管道蜡沉积速率的室内环管道实验分析

以 5号成品油为例 ,在理论推导的基础上建立了成品油管道蜡沉积的理论模型 ,确定了成品油管道蜡沉积速率与输油温度、输量和运行时间有关。并通过室内管流蜡沉积实验 ,分析了蜡沉积层速率与输油温度、输量和运行时间的关系 ,并逐一分析。运用Sigmaplot软件建立了实验室蜡沉积倾向与各影响因素之间的计算公式 ,为成品油管道的实际操作提供了一定的理论依据。     

南汇边滩细颗粒泥沙动水沉降的实验研究

细颗粒泥沙在盐水中的絮凝沉降是河流泥沙向海输送过程中在河口区发生的重要现象之一。文章根据室内环形水槽实验对南汇边滩泥沙由盐度和含沙量这两种因素在不同的流速条件下的沉降特性进行了研究。该实验结果对该区域实施围垦工程有实际意义。     

模型环道蜡沉积装置测试段流场温度场数值模拟

对模型环道蜡沉积装置测试段流场温度场进行了数值模拟。模拟结果表明 :因为测试段管外壁冷却水的作用 ,近壁处油温会下降 ,越靠近管壁 ,温度下降越多 ;测试段流场发生了畸变 ,近壁处流速减小 ,管中心附近流速增大 ;近壁处油温下降及流场畸变造成管段压降增加。     

利用模型环道研究原油蜡沉积

准确预测出含蜡原油管道中的蜡沉积对节约费用、管线设计以及确保管道安全输送有重要的意义。改造安装了模型环道蜡沉积测试装置。该装置上使用了 2个实验段 :测试段和参比段。通过 2个实验段两端压差的对比可确定出蜡沉积厚度。考虑了贴壁处油温下降及流场畸变对管段压差的影响 ,给出了确定蜡沉积厚度的压差计算方法。实测数据显示该实验装置用于蜡沉积测试是可行的     

沥青含蜡量太赫兹透射谱初步研究

文章针对太赫兹透射谱沥青含蜡量测试原理,介绍了沥青含蜡量理论分析方法,阐述了相应的含蜡量试验流程,并对比分析了沥青含蜡量与延迟性、衰减性的关系以及试验夹具的影响,为建立一种基于太赫兹透射谱的沥青含蜡量测试方法提供依据。     

吹填淤泥自重固结性状研究

结合围海造陆软基处理工程项目,基于以界限孔隙比作为吹填淤泥落淤过程沉积与自重固结的分界点、考虑落淤后发生以自重固结为主的变形,推导吹填淤泥一维自重固结方程并编制有限差分法求解程序,进行初始压缩性、初始渗透性及初始体积分数对吹填淤泥自重固结性状的影响分析,结果表明:初始压缩性和初始渗透性的增加,明显加快颗粒体自重有效应力、体积分数的增长及孔隙比的减小,加速表面沉降及沉降速率的发展;吹填淤泥自身强度的增长、压密程度、孔隙特征和表面沉降对初始体积分数的变化极其敏感,初始体积分数的增加会减缓颗粒体自重有效应力、体积分数和孔隙比的变化,初始体积分数的减小会加速表面沉降与沉降速率的发展.