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81.
82.
目的利用频域子结构方法(FBSM,FRF Based Sub-structuring Method)对结构的力学环境进行准确高效地预示。方法分别对处理子结构间为刚性连接和弹性连接两种问题的FBSM进行理论推导。为了验证FBSM的正确性,设计连接为刚性连接和弹性连接两种算例结构,并将FBSM对算例结构频响函数的计算结果与有限元方法(FEM,Finite Element Method)的对应计算结果进行对比。其中,弹性连接利用空间梁单元进行等效,并将该等效方法与利用六自由度标量弹簧的等效方法进行对比。结果对于刚性连接和弹性连接两种情况,FBSM对频响函数的计算结果均与FEM的对应计算结果吻合程度良好。此外,空间梁单元的结点刚度矩阵为非对角阵,与六自由度标量弹簧相比,可更为准确地等效工程实际中的弹性连接。结论FBSM可对结构的力学环境进行准确高效的预示,且在处理具有弹性连接结构的力学环境预示问题时,可采用空间梁单元等效弹性连接。 相似文献
83.
Summary. Predation is a pervasive selective agent highly variable in space and time. Due to the costs associated with antipredator
responses, prey would be at a selective advantage if they respond to predation threats with an intensitfy matching the threat
posed by the predator. Many aquatic organisms have been shown to use chemical alarm cues present in the water to assess the
level of risk in their environment. This includes mosquito larvae which show antipredator responses to conspecific alarm cues.
In this study, we investigated the nature of the responses of larval mosquitoes Culex restuans to those cues. In our initial observations, we showed pond/population differences in the response intensity of C. restuans to alarm cues. In experiment 1, we showed that the response intensity to alarm cues could be increased by increasing the
background level of risk in the mosquitoes’ environment (by adding salamander predators) and once turned on, the response
intensity to alarm cues was likely maintained for the remainder of the mosquitoes’ aquatic life. In experiments 2 and 3, we
investigated if the increase in response intensity to alarm cues was directly correlated with the level of background risk
in the mosquitoes’ environment. When given increasing levels of background risk, mosquito larvae subsequently showed a graded
response to conspecific alarm cues. This series of experiments demonstrates that the response intensity of larval mosquitoes
to a standard concentration of alarm cues is not fixed, but rather dependent on the background level of risk in the environment.
An understanding of the background level of risk is particularly important for comparing antipredator responses of prey between
habitats. 相似文献
84.
全球环境变化对农作物影响的研究进展 总被引:14,自引:2,他引:14
从CO2浓度升高、CO2浓度与温度升高以及CO2浓度与水分变化的协同作用、CO2浓度升高与环境盐胁迫的协同作用和作物产量预测模拟及其适应对策4个方面总结了近年来国内外关于农业生产对全球环境变化的响应与适应及其变化趋势的研究进展,指出目前人类关于农业生产对未来全球环境变化响应机理的理解与预测很有限,提出中国未来需要拟加强的研究领域.参38 相似文献
85.
86.
Use of Water Clarity to Monitor the Effects of Climate Change and other Stressors on Oligotrophic Lakes 总被引:6,自引:0,他引:6
We present evidence from studies oflakes in Killarney Park, Ontario, Canada that waterclarity is a key variable for monitoring theeffects of climate change, high UV exposure andacidification. In small oligotrophic lakes, thesestressors affect water clarity primarily byaltering the concentration of DOC in lake water. Clear lakes (<2 mg L-1 DOC) proved to be highlysensitive indicators of stressors, exhibiting largethermal and optical responses to small changes inDOC. Extremely clear (<0.5 mg L-1 DOC) acidic lakesshowed the effects of climate change and solarbleaching in recent decades. These lakes becamemuch clearer even though they were slowlyrecovering from acidification. 相似文献
87.
目的利用特殊设计夹具来模仿PCB板的典型插入式固定方式,通过响应面法对安装有PBGA的菊花链PCB板有限元模型进行修正。方法有限元模型经过三次响应面修正,每一个修正阶段都计算仿真前三阶频率与相对应的模态试验结果相对比,建立两个目标函数,并利用多目标遗传算法来缩小仿真分析与模态试验结果。结果有限元模型得到了有效的改善。结论响应面法可以从实际出发来提升有限元模型准确度。 相似文献
88.
A diverse range of response options was evaluated in terms of their utility for sustaining ecosystem services in the UK. Robustness of response options was investigated by applying a ‘stress-testing’ method which evaluated expected performance against combined scenarios of socioeconomic and climate change. Based upon stakeholder feedback, a reference scenario representing current trends in climate and socioeconomic drivers (‘business-as-usual’) was used as a dynamic baseline against which to compare results of other scenarios. The robustness of response options was evaluated by their utility in different environmental and social contexts as represented by the scenarios, and linked to their adaptability to adjust to changing conditions. Key findings demonstrate that adaptability becomes increasingly valuable as the magnitude and rate of future change diverges from current trends. Stress-testing also revealed that individual responses in isolation are unlikely to be robust meaning there are advantages from integrating cohesive combinations (bundles) of response options to maximise their individual strengths and compensate for weaknesses. This identifies a role for both top-down and bottom-up responses, including regulation, spatial targeting, incentives and partnership initiatives, and their use in combination through integrated assessment and planning consistent with the adoption of an Ecosystem Approach. Stress-testing approaches can have an important role in future-proofing policy appraisals but important knowledge gaps remain, especially for cultural and supporting ecosystem services. Finally, barriers and enablers to the implementation of more integrated long-term adaptive responses were identified drawing on the ‘4 Is’ (Institutions, Information, Incentives, Identity) conceptual framework. This highlighted the crucial but usually understated role of identity in promoting ownership and uptake of responses. 相似文献
89.
为获得大跨度刚构桥在多维多点地震激励下的响应特征,基于功率谱模型合成了满足给定相关函数的多维多点人工地震波。采用有限元软件SAP2000分别在线性与非线性领域对某大跨度刚构桥进行计算分析,研究刚构桥在多维多点地震下的响应特点。结果表明,多点激励下刚构桥主梁的横向弯矩往往较一致激励下的大;考虑非线性特性后,刚构桥在三向地震作用下的响应并不等于单向地震响应的简单叠加,且刚构桥的墩顶比墩底部位更易形成塑性铰,建议在实际工程中重视刚构桥墩顶部位的延性设计。 相似文献
90.
连续钢构桥成桥荷载试验实施方案研究 总被引:1,自引:0,他引:1
王静 《中国安全生产科学技术》2011,7(8):93-97
新建连续钢构桥的质量是保证桥梁安全运营的关键,因此,成桥后通过荷载试验对桥梁质量进行评定以评判桥梁的质量,确保桥梁安全运营,防止安全事故发生就显得至关重要。本文对连续钢构桥成桥荷载试验实施方案进行研究,确定了此类桥梁的试验内容、提出了静载试验方案的加荷原则、控制截面、试验工况和测点布置原则以及动载试验方案的测试内容和脉冲试验、跑车试验、跳车试验、刹车试验的试验方法。运用这些原则和方法能够对新建桥梁的质量进行详细鉴定,以检验设计理论以及施工质量,为即将投入使用的桥梁的运营、养护提供依据。 相似文献