排序方式: 共有56条查询结果,搜索用时 15 毫秒
41.
河底裸露的礁石增加水体紊动,有助于鱼卵正常形成,大量存在礁石的河段往往是鱼类栖息和产卵的重要场所。礁石也存在碍航的可能,航道清礁一定程度上影响水体紊动强度,改变鱼类栖息环境。为此,在重要鱼类栖息河段进行航道清礁需充分论证。以紊动动能作为评价水体紊动强度指标,开展西江中游珍稀鱼类保护区河段三维紊流数值模拟,计算并统计航道清礁工程前后水体紊动动能及不同强度的紊流水体体积,分析其变化规律及原因。研究结果表明,断面中紊动动能强度与水深成正相关关系;清礁工程导致河段中弱紊动动能的紊流水体体积增加,强紊动动能的紊流体积减小;底层水体紊动动能的变化量高于表层;强紊动动能水体体积减少的变化率大于弱紊动动能水体体积增加的变化率。 相似文献
42.
43.
连续梁桥利用支点处产生负弯矩来降低跨中的正弯矩,有效地分散了各截面的受力,由此增大了桥梁跨度.鱼腹式连续箱梁桥的边腹板呈流线形状,增加了界面抗弯、抗扭刚度的同时兼具了外形的美观性.现浇连续箱型梁桥的发展使得桥梁能够适应多种截面形式和道路线形设计,但同时增加了结构的复杂性.因此鱼腹式连续梁桥的计算需要经过精密的计算和调整以保证其安全可靠[1-3].通过一个鱼腹式连续箱梁桥实例,应用平面及空间有限元模型,对桥梁结构进行计算及调整优化,确保桥梁纵、横向以及桥面板等构件满足受力和抗裂等要求[41,为类似桥型设计提供参考. 相似文献
44.
目的采用负重游泳、转轮耐力及爬绳耐力实验方法观察腹腔注射生姜水对小鼠运动疲劳的对抗作用。方法 72只小鼠随机分为3个实验项目组,每个实验项目24只小鼠,并随机分为高、低浓度生姜水(100g生姜溶于150mL蒸馏水、100g生姜溶于200mL蒸馏水)实验组及阴性对照组,每组8只。各组小鼠腹腔注射不同剂量生姜水或生理盐水,30min后分别进行各项运动疲劳测试。结果腹腔注射生姜水可显著延长小鼠负重游泳测试的存活时间、转轮耐力时间以及爬绳能力,且高浓度组与低浓度组相比,其效应更为显著。结论生姜水对小鼠有显著的抗运动疲劳作用。 相似文献
45.
The small pelagic fish represents the link between nekton and demersal communities, and they are an important food source for some demersal fish species. In the autumns between 1993 and 2002, 74,869 stomach contents of 25 demersal fish species were analysed during the scientific surveys organized by the Instituto Español de Oceanografía. These species represent the demersal fish community of the southern Bay of Biscay. An important part of their diet (39% by volume) was composed of pelagic fish species (e.g. Engraulis encrasicolus, Gadiculus argenteus, Micromesistius poutassou, Trachurus trachurus, Sardina pilchardus, Scomber scombrus). Among all these prey species, the relevance of M. poutassou and G. argenteus stood out because of their high abundance both in the diets and during the scientific surveys. The relevance of pelagic fish as prey increased with predator size, reaching more than 60% of the diet by volume in the length range 25–29 cm. However, fish predators larger than 50 cm depended less on pelagic fish (33%), since they were also able to feed on other sources such as megafaunal invertebrates, mainly cephalopods. The pelagic fish resource was primarily exploited by 12 demersal fish species, with Merluccius merluccius and Zeus faber being the main ones feeding on small pelagics, which was related to the vertical movement of predators and prey through the water column. Survey abundance indices were used as indicators of prey abundance in the ecosystem, both for biomass and number. There was evidence for density-dependant feeding by predators on E. encrasicolus, G. argenteus and T. trachurus, while the main discrepancies between abundance in the stomachs and in the surveys were due to differential availability of prey length classes in the environment. Small prey species and individuals were exploited by most demersal fish while large prey species were less accessible to predators. 相似文献
46.
47.
港口系泊系统的设计关系到船舶停靠的安全问题,是船舶与海洋工程研究的热点之一,以往的研究中,对于动荷载的考虑较少。在动荷载的基础上研究港口系泊系统的设计,首先,分析了港口系泊系统主要组成的钢管、钢桶、重物球、电焊锚链和抗拖移锚的受力情况;然后,基于物体受力平衡方程以及悬链线模型建立了系统受力模型,采用遗传算法进行数值模拟求解;最后,通过MATLAB编程得出了在不同情况下钢桶、钢管的倾斜角度、锚链形状、浮标的吃水深度和游动区域,并讨论了各影响因素对系泊系统组成部分的影响程度。 相似文献
48.
考虑到半潜船海上运输超宽悬垂货物过程中可能发生波浪砰击,提出利用波浪势流理论及超宽悬垂货物海运过程中砰击控制条件的数值模拟方法,以半潜式“海上渔场”载运为例,利用OCTOPUS软件建立计算模型,模拟海运过程中不同海况、航行吃水及航速情况下,船舶横摇、纵摇、垂荡、“海上渔场”砰击发生概率及砰击载荷的变化情况,“海上渔场”海运过程砰击数值模拟结果与工程实际数据十分吻合,验证了数值模拟方法的合理、可行。 相似文献
49.
基站覆盖优化问题是移动通信网络优化的核心问题.针对网络节点严重冗余,基站之间相互干扰的情况,提出了一个移动通信网络基站最优覆盖模型,并利用人工鱼群算法对移动通信网络基站覆盖优化问题进行求解,得到了最优设计方案.最后选取某城市核心区域对模型与算法进行了验证,仿真结果表明:本文提出的方法提高了移动通信网络基站的覆盖率,减少了节点冗余,从而达到减少网络建设成本,提高网络规划效率和准确度的网络优化目的. 相似文献
50.