圆筒型鱼礁体纵横布设间距下的水动力特性研究          下载免费PDF全文

胡聪  毛海英  王开睿 《海洋科学进展》2022,40(1):154-164

应用计算流体力学(Computational Fluid Dynamics,CFD)软件数值计算了圆筒型人工鱼礁体在不同纵向和横向布设间距下的水动力特性,实测了圆筒型人工鱼礁体在纵向布设间距1.0L和2.0L (L为礁体长度)下的流场及受力特性,验证了物理模型实验中各个测点的流速值和阻力值,计算值与实验值吻合较好.研究...  相似文献   

基于泥沙流变特性的吸力式沉箱减阻技术     

钟丹  张民曦  俞梅欣  李小军  喻国良 《海洋工程》2022,40(6):31-40

针对吸力式沉箱在黏性底床中沉贯安装的减阻问题,基于黏性泥沙的流变特性,开展了一系列不同振动荷载作用下的室内沉贯模型试验,分析了振动荷载对吸力式沉箱沉贯过程的影响和沉贯减阻效果。试验结果表明：在压力沉贯阶段或吸力沉贯阶段施加高频振动荷载,均能促使吸力式沉箱侧壁周围的土体发生流化,有效降低沉箱的沉贯阻力;减阻效果与振动频率和沉箱的长径比有关,与振动频率成正比,与沉箱的长径比成反比;存在一个临界频率,当振动频率大于该频率后,沉贯阻力随频率的减小不明显;施加高频振动荷载有助于减小吸力沉贯阶段沉箱内的土塞高度,促进沉箱沉贯到位。研究成果可为黏性泥沙流变减阻技术在吸力式沉箱中的应用提供理论依据和技术参考。  相似文献   

南海水下生产系统防沉板基础裙板贯入模拟试验与入泥阻力计算     

谭红莹 《海洋工程》2019,37(6):140-145

防沉板基础裙板入泥阻力计算和长度设计是海洋工程水下生产系统基础设计的关键,基于南海番禺和荔湾地区水下防沉板基础裙板贯入模拟试验,验证了Lunne和Eide等建立的裙板入泥阻力经验计算方法对南海水下生产系统防沉板裙板设计的可靠性,确定了南海地区裙板入泥的端部阻力系数(0.320～0.360)和侧摩阻力系数(0.008～0.014 5),为南海水下生产系统防沉板基础裙板入泥阻力计算和裙板长度设计提供了依据,确保了南海地区水下生产系统的顺利安装。在工程地质调查时,既可以进行土壤钻孔取样并与已开展裙板贯入模拟试验的番禺和荔湾地区土壤组成和粒度对比,也可开展静力触探试验或裙板贯入模拟试验,得到裙板入泥的端部阻力系数和侧摩阻力系数。  相似文献   

Hydraulic properties affected by litter and stem cover under overland flow     

Lin Ding  Suhua Fu  Hui Zhao 《水文研究》2021,35(3):e14088

Vegetation stems and litter cover have different effects on sediment transport capacity under the same experimental conditions, which in essence, may be due to differences in their hydraulic properties, but the availability of comparative studies is limited. This study aimed to compare the hydraulic properties affected by litter and stem cover, compare differences in the drag forces exerted by litter and stems on overland flow, and develop new Manning's n and flow velocity equations for litter cover. Two series of flume experiments were conducted with the same slope gradients (8.8%, 17.6%, 26.8%) and flow discharge rates (0.5, 1.0 × 10⁻³ m³ s⁻¹). Artificial Gramineae stems with a 0%–30% cover level and Pinus tabulaeformis litter with a 0%–70% cover level were used in series 1 and series 2, respectively. The flow velocity and depth were measured. The results showed that the Froude number and flow velocity affected by stem cover were much lower than those affected by litter cover, while the opposite trend was observed in the relative magnitude of the Reynolds number, flow depth and shear stress. The form resistance caused by stems was 22–57 times greater than that caused by litter for the same cover level, which suggests that stem cover contributes more than litter cover to increasing the flow resistance and reducing the flow's ability for sediment detachment and transport. Two new equations for calculating Manning's n and flow velocity under the influence of litter cover were developed, with R² and NSE values of 0.96. The results of this study contribute to revealing the mechanisms of the differences of the effects of stem and litter cover on soil erosion.  相似文献   

黑方台地区崩塌灾害发育类型和发育机制分析          下载免费PDF全文

韩剑波  杨飞 《山东国土资源》2018,34(3)

以甘肃省永靖县黑方台地区实地调查为基础,通过野外勘察黄土崩塌变形破坏特征及总结地质现象,并结合数据统计分析进行研究,得出黑方台地区崩塌地质灾害的分布特点,并且发现凸型和阶梯型坡面更容易发生崩塌灾害。崩塌发育因素可分为2方面,一方面是自然因素,包括地形地貌,地层构造和水文地质条件;另一方面是人为因素,主要是人类工程活动。天然条件下,斜坡在自重或其他因素作用下,后缘黄土垂直节理或裂隙受拉张作用力开始破裂,并向深部扩展,随着水流下渗,逐渐形成贯通面,潜在崩塌体中心外移,最终形成崩塌。黑方台地区崩塌灾害按崩塌物质成分分为黄土崩塌和基岩崩塌2类,按崩塌发生的主控因素分为自然型崩塌、人为型崩塌和人为—自然复合型崩塌3类,而大量的节理裂隙发育是发生崩塌灾害的内在因素。通过野外调查,根据动力形成机制分析,在自然因素和人为因素影响下,将黑方台地区崩塌形成方式分为4种,并阐述其发育机制。  相似文献   

Public Intellectualism as Assemblage     

Hilda E. Kurtz 《The Professional geographer》2019,71(1):179-183

This article responds to Alderman and Inwood's call for geographers to engage in public intellectualism. Geographers have long been underrepresented among the ranks of public intellectuals, even as the discipline has fostered many and diverse traditions of robust critical explanation. The lens of assemblage theory on civic engagement efforts in Athens, Georgia, offers insight into how a democratically inclined public intellectualism might be temporarily achieved.  相似文献   

Evaluation of state indices in predicting the cyclic and monotonic strength of sands with different fines contents     

《Soil Dynamics and Earthquake Engineering》2014

State parameter, ψ, has been widely used to combine the influence of void ratio, e, and stress level, p′, on the soils behavior. Stress ratio, R_s, and modified state parameter, ψ_m, have also been proposed for the same purpose. This paper aims to evaluate and compare the different state indices in combining the effect of fines content, density and stress level for five different types of sands, by processing a large number of previously published experimental data. The use of the recently established concept of equivalent interparticle void ratio, e^⁎, in definition of the state indices is also evaluated. The results indicate that the influence of fines presence, in addition to the e and p′, on the behavior is favorably reflected by the state indices. Unique correlations were derived between the cyclic or monotonic strength and each of the state indices, independent of the fines content. The correlations, for all the different types of soils, fell into limited types of common formulations. ψ and R_s worked generally better than ψ_m, whether defined in terms of e or e^⁎. The extension of straight part of critical state line was found to be an appropriate reference line for calculating R_s used in conjunction with e or e^⁎.  相似文献   

Wet surface resistance of forest canopy in monsoon Asia: Implications for eddy‐covariance measurement of evapotranspiration          下载免费PDF全文

J. Hong  K. Takagi  T. Ohta  Y. Kodama 《水文研究》2014,28(1):37-42

During the Asian monsoon period, intense precipitation commonly occurs for an extended period in accompaniment with a reduction in solar radiation. This suggests that wet surface evapotranspiration is an important contributor to the total evapotranspiration. Therefore, investigating evapotranspiration over a wet canopy surface is critical to achieve a better understanding of water and energy cycles in Asia. In this study, we estimated surface resistances under wet conditions in a mixed forest influenced by the East Asian monsoon system. We showed that the surface resistance had a non‐negligible magnitude of about 30 sm^?1 even under wet conditions. We also found that the ratio between the actual and potential evapotranspiration depended on the friction velocity regardless of the time of day. Our analyses suggest that this dependency is tightly related to the underestimation of turbulent fluxes by the eddy‐covariance system under wet surface conditions. Together, our findings suggest that the wet surface resistance, although small, should be considered in simulating evapotranspiration because the forest ecosystem is strongly coupled to the overlying atmosphere. This could significantly improve the shortcomings of evapotranspiration measurement and modeling in Asian forest canopies influenced by the monsoon system. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Towards quantifying the negative feedback regulation of peatland evaporation to drought          下载免费PDF全文

Nicholas Kettridge  J. M. Waddington 《水文研究》2014,28(11):3728-3740

The frequency and intensity of drought is projected to increase within the boreal region under future climatic conditions. Peatlands are widely considered to regulate water loss under drought conditions, increasing surface resistance (r_s) and reducing evaporative losses. This maintains peat moisture content, increasing the resilience of these globally important carbon stores. However, the magnitude and form of this important negative feedback response remains uncertain. To address this, we monitored the response of r_s to drought within four peat cores under controlled meteorological conditions. When the water‐table was dropped to a depth of 0.30 m and the humidity reduced to ≤40%, a step shift in r_s from ~50 s m^‐1 up to 1000 s m^‐1 was observed within burned and unburned peat, which virtually shuts down evaporation, limiting water loss. We show that measured near‐surface tension cannot be used to directly calculate this transition in peat surface resistance. However, empirical relationships that account for strong vertical variations in tension through the near‐surface and/or disequilibrium between pore air and near‐surface pore water pressure provide the potential to incorporate this negative feedback response into peatland ecohydrological models. Further observations are necessary to examine this response under dynamic atmospheric conditions. We suggest that the link between surface temperature and evaporation provides potential to further examine this feedback in either burned peatlands or peatlands with a low vascular vegetation cover. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Characterizing ephemeral streams in a southern Ontario watershed using electrical resistance sensors          下载免费PDF全文

Sarah E. Peirce  John B. Lindsay 《水文研究》2015,29(1):103-111

Ephemeral streams are small headwater streams that only experience streamflow in response to a precipitation event. Due to their highly complex and dynamic spatial and temporal nature, ephemeral streams have been difficult to monitor and are in general poorly understood. This research implemented an extensive network of electrical resistance sensors to monitor three ephemeral streams within the same small headwater catchment in Southern Ontario, Canada. The results suggest that the most common patterns of network expansion and contraction in the studied streams are incomplete coalescence and disintegration, respectively. Binary logistic regression analysis of the primary controls on ephemeral streamflow showed only weak Nagelkerke R² values, suggesting that there are more complex processes at work in these ephemeral streams. A comparison of all three streams suggests that even ephemeral streams within the same subwatershed may experience differences in network expansion and contraction and may be dominated by different spatial and temporal controls. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献