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沙波运动与床沙交换调整 总被引:5,自引:1,他引:4
冲积河流非均匀沙表层床沙粒径组成是影响水流阻力、输沙及河床冲淤的重要因素.表层床沙组成随着冲淤及与深层床沙不断交换而调整变化.本文分析提出沙波运动是床沙交换最基本最普遍的原因,提出了随冲淤及床沙交换床沙调整变化的计算关系.根据作者及其它水槽试验和河流实测沙波资料,文中总结得出了沙波高度、沙波运动速度及周期的新的计算公式,可用于估算床沙活动交换层厚度及交换速度,也可用于其它方面的分析计算. 相似文献
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不同重率轻质沙的床面形态和阻力的试验研究 总被引:2,自引:0,他引:2
本文通过动床水槽试验,研究了白色塑料沙,磺化塑料沙,电木粉三种轻质沙的床面冲淤形态和阻力特性,观察了各种材料床面冲淤形态的发展过程,并分析了各种材料沙波形态参数与水流参数的关系,从理论上分析了沙粒阻力和沙波阻力的影响因素,表明沙粒阻力与颗粒粒径和水面比降有关,沙波阻力与沙波的相对高度和沙波背水面的坡角成正比,而沙波背水面坡角的大小又只与颗粒几何性质有关,本文的试验资料和多家水槽试验资料的比较结果证 相似文献
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本文分析了输移泥沙床沙质中值粒径D50i的变化规律和计算方法,指出由于水流的分选作用,输移泥沙的中径D50i一般较床沙中值粒径D50为细,且相对中值粒径D50i/D50随床沙标准方差σg的增大而减小。还分析了床沙非均匀性对输沙能力的影响,结果在相同的D50条件下,输沙能力随σg的增大而增大。此外,对采用D50i作为床沙代表粒径的输沙能力计算进行了探讨,结果可以大大提高输沙能力的计算精度。研究表明,用于非均匀沙输沙能力计算的床沙代表粒径,不应是一个固定不变的粒径,床沙代表粒径及相应的沙重百分数应随σg的增大而减小,Einstein等建议的D35仅在σg值为1.5左右才适用。 相似文献
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不均匀沙的推移质输移规律的研究 总被引:2,自引:0,他引:2
本文详细地分析了不均匀沙与均匀沙翅动和输移规律的主要不同点。指出:不均匀沙的起动和输移过程又是一个床沙粗化或细化过程,两者互相制约。具有不恒定的特性。使得不均匀沙的起动和输移复杂多变,与同粒径的均匀沙相比较,较细颗粒的动动流速高于均匀沙;较粗颗粒的起动流速又低于均匀沙。这一临界粒径的大小,随不同的床沙而异,床沙越粗、组成越不均匀。粗化作用越大,这临界粒径也越大。 相似文献
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沙波运动与推移质输沙率 总被引:1,自引:0,他引:1
本文依据沙波运动尺度,从沙波运动角度建立了推移质输沙率表达式,该式既能用于均匀沙又能用于非均匀沙的输沙率计算,并经百余组室内外实测资料的验证,同时与其他公式进行了对比,结果表明,在各种强度的输沙情况下都能较好的吻合。 相似文献
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《泥沙研究》2015,(5)
模型沙的选择是推移质动床模型试验中一项关键技术,直接影响推移质运动的相似性和河道冲淤趋势与量级的判断。整理以往的研究成果,结合概化动床模型试验,从起动条件、输沙强度和沙波形态三个方面对比精煤和天然沙这两种典型模型沙的运动特性。研究表明,精煤为代表的轻质沙与天然沙在起动条件和输移强度方面基本类似,都能模拟天然河道中的推移质起动和输移现象,但是在较大水流强度时形成沙波形态后,在波高、波长等几何形态上存在明显差异,对床面阻力的准确模拟有一定影响。因此,遇超过沙波临界条件的较大水流强度时,宜采用天然沙作为动床模型沙模拟推移质运动。该研究成果可为推移质动床模型选沙和设计提供参考依据。 相似文献
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沙波迎流面泥沙起动流速研究 总被引:1,自引:0,他引:1
利用概化沙波模型,研究了不同坡度、粒径及位置情况下的泥沙起动流速,根据实测数据指出沙波泥沙起动流速特征,并分析比较了与平坡起动的差别。通过对泥沙颗粒的受力分析,提出水流冲击力,并利用沙波垂线流速分布公式进行流速换算,建立了沙波泥沙起动流速计算公式。结果表明:在相同水流条件下,因沙波地形影响,迎流面泥沙起动流速值小于平坡;沙波不同位置处的泥沙起动流速非定值,随着水平位置而变化;坡度和粒径对再附点附近泥沙起动流速影响较小。通过验证比较表明,公式计算结果与实测资料基本一致,适用于描述沙波迎流面泥沙起动规律,可反映出沙波坡度和水平位置的影响。 相似文献
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根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。 相似文献
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The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects. 相似文献
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In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment. 相似文献
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简述天湖水电站投运以来各种故障的表现形式,分析其原因,提出了相应的处理方法及措施,并对合理利用国内外设备提出建议。 相似文献
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Various designs of low‐head dams are used to rehabilitate streams or forestall upstream channel incision after channelization. We report on the efficacy of using notched sills and grade control structures (GCS) to restore the fish assemblage in Luxapallila Creek, Mississippi. We tested the null hypotheses that habitat variables and species richness, evenness, and assemblage structure would not differ among: (1) a channelized segment with no modifications; (2) a channelized segment mitigated by the installation of sills and GCS; (3) a segment upstream of the installations and undergoing channel incision; and (4) an unaltered segment. Although habitat variables changed, neither species richness, evenness, nor fish assemblage structure differed between mitigated and channelized segments with both exhibiting less richness and different assemblage structures than the unaltered segment. Lack of differences in species richness between the incised and unaltered segments suggest that the GCS may have halted the negative effects of upstream channel incision before species were extirpated. Conspicuous habitat differences between the altered (channelized and mitigated) and unaltered segments were lack of backwaters and canopy coverage and finer substrates in the altered segments. Our results suggest a more comprehensive rehabilitation strategy is required in Luxapallila Creek. Published in 2003 by John Wiley & Sons, Ltd. 相似文献
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NUMERICAL STUDY OF WAVE EFFECTS ON SURFACE WIND STRESS AND SURFACE MIXING LENGTH BY THREE-DIMENSIONAL CIRCULATION MODELING 总被引:1,自引:0,他引:1
LIANG Bing-chen LI Hua-jun LEE Dong-yong 《水动力学研究与进展(B辑)》2006,18(4):397-404
1. INTRODUCTION Coastal and continental shelf regions are characterized by intensive interaction between wave and current. These regions are of great economic significance to mankind. Therefore, the modeling of wave and current as well as their mutual int… 相似文献