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以结构随机风振响应分析为背景,考察了线性体系在平稳风荷载激励下的随机动力反应,进行了广义密度演化方程与经典随机振动分析的比较.基于物理随机系统研究框架,平稳脉动风荷载模型化为随机Fourier谱.分别以线性单自由度体系和线性多自由度体系为研究对象,比较分析了系统响应的概率密度演化解、理论平稳解和虚拟激励法解答.结果表明,分析系统有限时间内的随机动力反应,概率密度演化方法不仅能够获得渐近平稳段的稳态响应,而且能够反映响应非平稳初始效应的影响,与经典随机振动理论的虚拟激励法解答在均方特征意义上是等价的. 相似文献
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本文研究在海床作水平运动情况下,多个大尺度弹性柱体由于辐射波所引起的水动力荷载及其动力响应。该体系的数学模型考虑了结构与流体的相互作用,同时也考虑了柱体相互之间的水动力干扰作用,以及柱体与地基之间的相互作用。文中逐个分析了上述几种相互作用对水动力荷载的影响。其结果表明,在自由表面处以及当地震激励频率与体系自振频率接近时,各种相互作用对水动力荷载有明显的影响。 相似文献
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结构动力特性决定结构在动力荷载作用下的动力响应,对结构的动力破坏与安全具有重要意义.精确测试结构动力特性参数是其研究的一个重要方面.采用基础激励的方法测试结构动力特性是一种行之有效的方法.通过实验的方法研究了基础激励测试结构动力特性的精度.实验结果表明,结构动力特性参数在实验范围内不受激励幅值大小的影响;基础激励频段范围对结构的振型影响不大,但对频率与阻尼比的影响很大;只要基础激励的频段包含所要测试的结构固有频率,就能精确测试出结构此阶的频率与阻尼比;如基础激励频段不包含所要测试的结构固有频率,则不能精确测试出结构此阶的频率与阻尼比.因此在使用基础激励方法测试结构动力特性时,应使基础激励的频段包含所要测试的结构固有频率. 相似文献
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针对拉索预应力巨型网格结构的参激振动及动力稳定性问题进行了研究。首先建立索-拱简化模型,分析了桁架拱拉索参激振动的诱发机制与特征,并利用ANSYS软件进一步探究了参激振动的影响因素,然后对简谐荷载作用下拉索预应力桁架拱及整体结构的动力稳定性进行了分析。研究表明:当结构振动频率为索基频的2倍左右时,拉索会发生参激振动,振动响应特征与激励幅值、阻尼、拉索初张力、支承方式等相关;拉索预应力桁架拱在水平简谐荷载作用下一般会发生动力失稳破坏,在竖向简谐荷载作用下发生动力强度破坏,拉索预应力巨型网格整体结构在简谐荷载作用下通常发生动力失稳破坏。 相似文献
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本文对有限长充满流体的理想刚塑性园柱壳,在轴对称矩形冲击侧压作用下的塑性动力反应进行了分析。在某些简化假定的前提下,导出了流体对园柱壳塑性动力反应影响的解析解和主要参数之间的关系。经数值计算,流体对园柱壳动力极限荷载和最终位移的影响与不充流体条件下的壳体作了对比,并给出了主要的图线。 相似文献
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运用复模态理论对考虑海洋平台结构与流体相互作用而引起的非经典阻尼问题进行了理论分析。水中耦合阻尼矩阵运用复模态解法,可以不必近似对角化。推导了随机波浪荷载作用下结构各种反应的能量谱密度函数及结构反应的统计特性,得到了结构反应的均方差和峰值的表达式。针对某典型平台在随机波浪荷载作用下动力反应用复模态法进行了计算并与运用实模态方法多重叠代方法的结果进行了比较。 相似文献
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Liu Rongmei 《力学与实践》1979,42(4):442
建立了扁担挑物的动力学模型和动力学方程,并进行了数值求解。扁担挑物时存在三种频率,即重物类似于单摆的振动频率、挑运者的步行频率和扁担-重物系统铅垂方向的振动频率。计算结果表明,为了获得较好的挑担体验,三种频率应该相互协调。当人挑担行走的频率为扁担-重物系统铅垂方向振动频率的70%,$\sim$,80%时,肩部铅垂附加动反力为重物重力的30%左右且与肩部铅垂运动同相,当重物类似于单摆的振动频率为人步行频率的25%,$\sim$,30%时,重物的摆角和肩部受到的水平附加动反力均较小,从而有利于人挑担行走。 相似文献
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以产生相同位移场为基础,将动荷载转化为一系列的等效静荷载,然后将这些等效静荷载作为多个载
荷工况进行有限元优化设计分析. 通过几个算例的验证,表明这种基于动荷载等效转换的算
法能够反映动荷载对结构的动力响应,对具有大规模自由度的结构形状优化问题是有效的. 相似文献
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为了快速准确地识别挖掘机等工程机械的工作载荷谱,基于时域内动应变响应与载荷的关系,提出一种新的工作载荷谱识别方法.首先,采集工作中的挖掘机结构上若干测点工作应变谱;其次建立有限元模型,通过有限元方法计算挖掘机在各种可能外载的单位载荷下的应变;最后,建立实测响应与数值模拟测点单位应变之间的关系,通过时间迭代求解结构响应与载荷间关系的线性方程组得到工作载荷谱.为说明方法的实用性和有效性,通过在结构上选择的7个基底测点的假设应变谱和数值模拟单位应变,获得挖掘机样机的工作载荷谱.文章最后讨论了在本文所提方法基础之上求解结构关键位置疲劳应力的方法. 相似文献
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钢管在海洋油气资源开发中应用广泛,一般依据在位应用时的荷载进行设计,设计理论较为成熟。但在某些安装工况中的拉伸和弯曲荷载与在位荷载具有相同的量级,此时钢管的设计需要考虑安装荷载的影响。本文针对钢管在承受拉伸和弯曲荷载下的抗外压压溃性能开展研究。基于商业软件ABAQUS建立有限元模型,开展钢管压溃实验与带有弯曲荷载下的钢管压溃实验验证有限元模型的正确性,进而利用验证后的数值模型讨论拉伸、弯曲荷载和两者联合作用下对管道抗外压压溃性能的影响。结果表明,弯曲荷载是影响抗压溃性能的重要因素,弯曲荷载的增加都会使极限压溃值显著下降。管道所受拉伸荷载对抗压溃性能有一定的影响,但影响很小,在两者共同作用下极限压溃值随弯曲荷载的增加都出现先增大后减小的现象,而且极值的位置与拉伸荷载的大小和弯曲荷载有关。因此,在抗压溃设计中应重点考虑弯曲荷载对压溃的影响,可忽略拉伸荷载的影响。本文可为海洋管道的安装起到指导作用。 相似文献
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The development of mechanical means of landmine clearing using flail machines requires a good knowledge of load transfer and tool-soil-landmine interaction. Recent research have provided a good understanding of the soil-tool interaction, but load transfer and responses of buried landmines due to loading from the flails remains undefined. Buried landmines act as unsupported buried structures and loads from the flailing motion are considered as impact loading on the soil surface. A 4 degree-of-freedom mechanical model is constructed and corresponding experiments are conducted to better understand the load transfer and dynamic responses of buried structures due to surface impact loading. The model and experiment is limited to a single impact load directly above the structure, and the buried structure is assumed to move only in the vertical direction. Experiments are conducted for various load magnitude and depth of burial for buried structure in two types of soil. The minimum surface impact forces needed to trigger a landmine in prescribed conditions for two different types of soils have been found. This information could be useful in the design optimization of a mine flail. A correction factor to account for nonlinearity in the form of the ratio of Burgers model and Kelvin stiffness and damping constants is introduced. Considering an appropriate correction factor, the response behavior of the model compares well with the experimental results. The model, while simple, is deemed adequate to represent and predict the behavior of a buried landmine in a mine clearing condition - or any other unsupported buried structure - in soil and sand medium subjected to surface impact loads. 相似文献
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The mooring loads on an aquaculture net cage in current and waves are investigated by dedicated model tests and numerical simulations. The main purpose is to investigate which physical effects are dominant for mooring loads, and in this respect, to investigate the validity of different rational hydrodynamic load models. Also structural and numerical aspects are investigated. The model tests are performed to provide benchmark data, while the numerical model is used to study the effect and sensitivity of different load models and parameters.Compared to a realistic aquaculture plant, the total system is simplified to reduce the complexity. The system does, however, include all the four main components of an aquaculture plant: net cage, floater, sinker weights and moorings. The net cage is bottomless, flexible and circular. It is attached to a circular, elastic floater at the top and has 16 sinker weights at the bottom. The system is nearly linearly moored with four crow feet mooring lines.The loads are measured in the four mooring lines. A systematic variation of current only, wave only as well as combined current and wave conditions is carried out. The numerical simulation results are first benchmarked towards the experimental data. The mean loads in general dominate over the dynamic part of the loads in combined current and waves, and they significantly increase in long and steep waves, relative to current only. Next, a sensitivity study is carried out. A rigid floater significantly alters the loads in the mooring lines compared to a realistic, elastic floater. The theoretical model for the wave matters. The mooring loads are rather insensitive to a majority of the parameters and models, in particular: frequency dependent added mass of the floater and nonlinear restoring loads. It seems not to be necessary to represent the net cage with a very fine numerical mesh. 相似文献
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Post-buckling of a cantilever column is examined under a combined load consisting of a tip-concentrated load and a distributed axial load, through dynamic formulation. The formulation of the problem is based on the moment–curvature relationship. The two-point boundary value problem described by the governing equations is dependent on the frequency parameter and the two load parameters. The buckling loads are those loads at which the eigencurve, namely, the load versus frequency curve of the column meets the load axis. A simple and reliable iterative procedure to convert the two-point boundary value problem into an initial value problem is followed and solved the non-linear differential equations utilizing a fourth-order Runge–Kutta integration scheme. To demonstrate the potentiality of the adopted numerical scheme, linear vibration frequencies of truncated, tapered cantilever wedges and cones are determined and compared with the published analytical and test results. Buckling and post-buckling loads of a simply supported stepped column are obtained and compared with the published test results. The loads and deflections of non-uniform cantilever columns are obtained for various slopes at the tip. The interaction of load parameters for a free–free truncated conical column has also been examined. The numerical results indicate that the path represented by the two load parameters turns out to be nearly a straight line. 相似文献
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鸟与叶片的撞击过程是一个复杂的加载过程。为了将其简化,以建立一个简单且合理的鸟撞击载荷模型,需要分析鸟撞击载荷的各种因素对叶片响应的影响。本文通过计算机数值模拟进行上述工作。以矩形悬臂板模拟实际叶片,以冲击载荷模拟鸟撞击载荷,采用有限元法计算悬臂板在冲击载荷下的非线性瞬态响应。从鸟撞击载荷的冲量、时间因索、空间因素三个方面分析了冲量、加载持续时间、力-时间函数、初始冲击压力、加载位置、载荷的空间分布以及载荷类型等七种因素对叶片响应的影响。本文得出的结论为合理简化鸟撞击加载过程及建立鸟撞击载荷模型提供了参考与依据。 相似文献