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结合某水电工程,在1:150双曲拱坝水弹性振动整体模型上进行了“动荷载-拱坝-地基”耦联系统中拱坝的实验模态分析,测定了拱坝泄洪时坝体的动力响应,成果表明,该拱坝在校核水位中表孔联合泄洪时,坝体动力响应比较微弱,不致危及到大坝安全。 相似文献
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对深孔弧形闸门水弹性模型进行了模态测试和分析,其分析结果与数值模态分析结果进行对比,较准确地找出 了结构的模态参数,对模型设计的问题作了论述。对闸门在各种工况下的振动响应进行试验,获得了系统的动荷载与闸门的振动参数,结果表明:闸门在0.6-0.7开度时,出现了强迫振动。 相似文献
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对风洞中弹性圆柱腔壳的流激振动及声进行了研究。对腔口流体自持振荡和腔内声振荡的压力及壳的振动加速度作了测量和谱分析,并对三者之间的相互影响进行了综合研究。研究结果表明,一般情况下,流体自持振荡对腔壳振动影响不大,但是,当自持振荡与腔内驻声发生耦合并形成共振时,对壳体的振动可产生重要的影响。此外,文中还给出了流激壳体各阶模振动的加速度均方根随流速的变化曲线。均方根值随流速大约是2.4次方线性关系。但 相似文献
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高水头船闸输水廊道反弧门水弹性振动试验研究 总被引:2,自引:1,他引:1
本文简要介绍水弹性振动模型试验的相似准则,用近似满足水弹性相似准则的有机玻璃模型对-高水头船闸反弧形阀门进行流激振动试验研究.试验表明阀门的振动是随机振动,不仅有质量振动而且有结构振动,有若干阶模态被激发参与振动。在开门和关门过程中,阀门面板脉动压力和阀门振动是不大的,与葛洲坝船闸类似阀门间歇开启的振动水平相当。由于常压模型不能正确模拟空化现象,对于廊道内可能产生的空泡溃灭所引起的阀门振动尚需通过减压模型进行研究。 相似文献
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该文通过实验和数值计算相结合的方法,对弹性水翼非定常空化流激振动特性进行了研究。实验中,采用高速摄像机获取云状空化不同发展阶段的流动发展规律,应用激光测振仪测量弹性水翼的流激振动特性,通过同步测量技术获取水翼振动特性数据并结合空穴形态图对其进行分析,同时在实验结果基础上加入数值计算部分对流激振动特性进行进一步的说明。研究结果表明:云状空穴的发展为一个准周期过程,包括附着型空穴的生长、空穴的脉动以及空穴的脱落三个阶段;弹性水翼的振动主要受空穴发展过程的影响,因此流激振动特性呈现出周期性的变化过程,且弹性水翼振动主导频率为空穴脱落频率;在不同的空穴发展阶段,表现出不同流激振动特性,并且在空穴脉动和空泡脱落阶段水翼振动较为剧烈。 相似文献
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基于某型号卫星抑制动量轮扰动的需求,本文提出了一种新型的采用弹性平面索网对动量轮进行振动抑制的隔振结构,将扰动源动量轮组件与承力筒基础隔离,以减小传递到承力筒处的扰动能量,保证安装在承力筒上的敏感载荷正常工作。本文利用实验验证了该结构的隔振性能并且研究了附属部件的对隔振效果的影响。在对索网结构进行分析时,发现其具有非线性特性,为研究其响应,建立了索网结构非线性振动的一维等效模型,研究了其在受到简谐扰动力时的非线性振动特性;并且通过改变索网结构网格的疏密程度和预紧力等参数,研究其对索网振动特性的影响,从而指导结构的设计和参数优化。 相似文献
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本文以船体薄壁梁理论和二维流体直接边界元方法为基础,建立一个用于薄壁梁型船舶结构在水上运动的流固耦合作用的计算模型,将流体对结构的作用处理为集束的附加质量阵,迭加到结构的一致质量阵之中,用迭代的方法求得船体在水上运动的湿固有频率和模态,进而得到了其动力响应。 相似文献
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模态参数的准确辨识是对在线结构进行损伤诊断和状态监测的难点和核心之一。以二滩高拱坝原型测试为背景,结合随机子空间算法与改进的稳定图对泄流激励下的拱坝模态参数进行辨识,并实现对高坝振动状态的长期在线监测,为结构的安全评估提供依据。针对时域法所面临的模型定阶困难和噪声干扰以及由它们所引起的虚假模态辨识与剔除问题,利用改进的稳定图方法对模态参数进行更为精确辨识,并与ERA算法的识别结果进行对比。研究表明,该方法具有良好的品质与较高的计算精度,具有良好的工程应用前景。 相似文献
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根据高拱坝泄流结构自身的工作特点,为准确辨识环境激励下的结构模态参数特征,提出了一种基于改进的HHT-RDT算法的高拱坝泄流结构工作模态识别方法。以某高拱坝原型振动响应测试资料为基础,利用改进的小波阈值-EMD算法对原始信号进行降噪预处理,滤除干扰噪声的同时保留有效特征信息;采用HHT-RDT算法识别高拱坝泄流结构的工作模态参数,运用带通滤波对振动响应信号的EMD过程进行控制得到结构的各阶模态分量,利用RDT法提取各阶模态分量的自由衰减信息,识别出高拱坝泄流结构系统的固有频率及阻尼比。工程实例表明,该方法避免了复杂系统定阶过程,有效提高结构振动响应工作模态识别精度,为辨识高拱坝泄流结构的工作模态参数提供捷径。 相似文献
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Single-walled carbon nanotubes (SWNTs) were synthesized by a novel method. The dc arc discharge in H2-Ar gas atmosphere with Fe3O4 as catalyst was used. The morphology and structures of the as-prepared SWNTs were characterized by SEM, HRTEM and Raman spectroscopy techniques. The results indicated that this new catalyst could be used to produce SWNTs with high purity and yield in large scale. The purity and yield of the SWNTs synthesized from these new catalysts were affected by the mixture buffer gas. Based on the overall ease and low-cost advantages of these new catalysts, these results suggest a potential opportunity for cost-effective and commercial production of SWNTs. 相似文献
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目前,高拱坝的抗震安全性分析中仅考虑单独主震的作用,而忽略地震中可能伴随发生的多次余震,对高拱坝在主余震序列作用下的动力响应规律尚缺乏充分认识。以大岗山拱坝为例,建立了综合考虑坝体损伤非线性、横缝开合以及半无限地基辐射阻尼效应的拱坝-库水-地基有限元分析模型,并基于耐震时程法(ETA)构建主震-ETA余震序列进行高拱坝非线性动力分析。研究结果表明:ETA的计算结果与增量动力分析法(IDA)具有可比性;高拱坝的极限抗震能力在主震受损情况下将发生损失,且随主震强度增大而损失增加。最后,基于主震-ETA余震序列计算结果给出了大岗山拱坝的极限抗震能力损失曲线。 相似文献
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Although post-equating (PE) has proven to be an acceptable method in the scaling and equating of items and forms, there are times when the turn-around period for equating and converting raw scores to scale scores is so small that PE cannot be undertaken within the prescribed time frame. In such cases, pre-equating (PrE) could be considered as an acceptable alternative. Assessing the feasibility of using item calibrations from the item bank (as in PrE) is conditioned on the equivalency of the calibrations and the errors associated with it vis a vis the results obtained via PE. This paper creates item banks over three periods of item introduction into the banks and uses the Rasch model in examining data with respect to the recovery of item parameters, the measurement error, and the effect cut-points have on examinee placement in both the PrE and PE situations. Results indicate that PrE is a viable solution to PE provided the stability of the item calibrations are enhanced by using large sample sizes (perhaps as large as full-population) in populating the item bank. 相似文献
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盘管式冷冻柜因结构限制,在蒸发器盘管设计要求较长的情况下,会直接造成蒸发温度下降,压缩机吸气压力降低,最终导致压缩终点排气温度升高。针对压缩机排气温度过高问题进行理论分析,并进行验证,提出最终解决方案,从而对该制冷系统进行优化设计。 相似文献
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Ju-Suk Byun Jinho Lee Chang-Duk Jeon Jinho Mok 《International Journal of Refrigeration》2006,29(6):1034
This study investigated the pressure drop and heat transfer characteristics of heat exchanger according to the arrangement of fins as well as fin configuration by the similitude experiments with the finned-tube geometry scaled as large as four times. Colburn j factor, Fanning friction factor, f, and goodness factors are compared to each other to estimate performance of each case for four different kinds of fins, which are louver, double side slit, single side slit and plain fin. Results show that heat transfer would be altered by fin arrangement and that friction loss is more affected by fin configurations than by the fin arrangements. In particular, heat transfer depends more on the shape of front row than that of rear row. The heat transfer rate of combined fin arrangement increases a lot more under the same pressure drop than that of conventional fin arrangement. This indicates that the heat exchanger of higher efficiency would be designed by the proper combination of fins of different shapes. 相似文献
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针对高拱坝施工过程具有很强的复杂性和随机性的特征,提出将系统集成理论应用于高拱坝施工实时控制中,设计了高拱坝施工实时控制系统集成框架,从数据信息集成、应用功能集成、技术方法集成和监控指标集成4个方面详细论述了系统集成的实现过程,并研制开发了网络平台下的高拱坝施工实时控制系统。工程应用实例表明,基于系统集成理论构建的高拱坝施工实时控制系统能对高拱坝施工过程实现动态的集成控制与分析,有效地提高了大坝建设管理水平。 相似文献
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In the present article, large amplitude vibration analysis of multilayered graphene sheets is presented and the effect of small length scale is investigated. Using the Hamilton’s principle, the coupled nonlinear partial differential equations of motion are obtained based on the von Karman geometrical model and Eringen theory of nonlocal continuum. The solutions of free nonlinear vibration, based on the harmonic balance method, are found for graphene sheets with three different boundary conditions. For numerical results single, double and triple layered graphene sheets with both armchair and zigzag geometries are considered. The results obtained herein are compared with those available in the literature for linear vibration of multilayered graphene sheets and an excellent agreement is seen. Also, the effects of number of layers, geometric properties and small scale parameter on nonlinear behavior of graphene sheet are discussed in details. 相似文献