共查询到20条相似文献,搜索用时 140 毫秒
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对饱和砂土在冲击载荷下发现的变形和流动效应进行了落锤模拟实验研究,发现砂土骨架出现纵向排水通道和横向断裂等现象,对可能影响这些现象的主要因素进行了对比的实验,对上述实验现象进行了初步的解释. 相似文献
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圆板振子超谐分岔和混沌运动的实验研究 总被引:9,自引:0,他引:9
设计了非线性圆板混沌实验振动台,就轴对称圆板在简谐载荷作用下的非线性动力学行为进行了较为系统的实验研究,理论分析和数值计算,对基础作简谐运动,周边固支圆板,进行了实验。通过测量时间-中心挠度的加速度曲线,进行快速傅立叶变换(FFT)分析,实验发现了对称破缺,超谐分岔,调幅调相等复杂现象;对基础作简谐运动,周边固支,中心加质量块的圆板,进行了实验,通过测量时间-周边应变曲线,进行FFT分析,实验发现了混沌,对称破缺和恢复及超谐分岔等复杂动力学行为。 相似文献
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以超声振动原理模拟滑动轴承的气蚀磨损 总被引:2,自引:1,他引:1
采用超声振动原理建立了滑动轴承气蚀磨损模拟试验装置,并用该试验装置研究了滑动轴承气蚀磨损现象,通过分析比较大量实验研究结果,发现了一些新的气蚀现象,并对滑动轴承气蚀机理进行了分析。 相似文献
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分别用RANS-SA方法和DES方法对NACA0012翼端梢涡进行模拟计算,分析了梢涡区域网格局部加密对梢涡计算结果的影响,并与实验结果进行了对比.相比于RANS-SA方法,DES方法在梢涡流场计算中具有更好的适用性,能够得到更准确的流动信息和更精细的涡结构;另外,网格局部加密对脉动量的计算影响很大.通过对脉动量的分析发现,在近尾缘处,几股涡的融合产生了比较强烈的脉动,随着梢涡的逐渐稳定,脉动量也逐渐减小;现有的实验结果显示在偏下游处会产生梢涡的振荡现象,使统计脉动量增大,而本文计算中未发现该现象. 相似文献
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均匀来流中横向振动圆柱近迹涡结构的数值模拟 总被引:1,自引:0,他引:1
从涡量流函数形式的N-S方程出发,在不同的振动频率、振幅及Re数下数值研究了均匀来流中横向振动圆柱粘性统流的涡脱泻现象。着重探讨了近迹复杂的涡结构及其非定常演化过程,以及它们对物体受力特性的影响,并首次成功地模拟了近年来实验研究中所发现的一些重要的流动现象,如相位“开关”现象(phase switch phenomena)及复杂涡结构(complex vortex structure),等等。通过数值模拟,不仅能够再现实验研究中所发现的一些重要的流动现象,还可进一步预示某些新的流动现象,使数值计算起到与实验研究相辅相成的作用。 相似文献
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微裂纹串级连接及临界破坏 总被引:1,自引:0,他引:1
对一铝合金材料层裂过程的实验研究发现,当损伤累积到一定程度时,受损材料的残余强度突然丧失,表现出临界破坏现象。层裂表面具有分形特征,其分形断面的形成归因于大量微裂纹的串级连接。据此提出了一重正化群弱面模型,并对损伤演化后期的临界破坏现象进行了初步的分析和探讨。 相似文献
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PBX材料蠕变性能的云纹干涉法实验研究 总被引:5,自引:0,他引:5
本文利用云纹干涉法对PBX材料蠕变行为进行了研究。实验中采用圆盘试件进行压缩实验。利用圆盘对径受压实验间接拉伸的特点,测量了PBX材料的拉伸蠕变及蠕变恢复曲线,同时也得到了圆盘部分区域压缩蠕变及蠕变恢复曲线。实验中,观察到蠕变的阶段上升现象,这一现象不同于一般的纯的高聚物的蠕变变形。并针对这一蠕变现象利用破坏力学理论进行了初步分析。文中的实验现象及实验数据将为PBX材料蠕变破坏变形的进一步的理论分析提供科学依据。 相似文献
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Laboratory study on cracks in saturated sands 总被引:1,自引:0,他引:1
It has been reported[1] that when a loosely packed column of saturated sand in a vertical cylindrical container is shock loaded axially by dropping
to the floor, large horizontal cracks initiate, grow and eventually fade away in the sand as it settles under gravity. This
paper shows that a similar phenomenon can also be observed when shock loading is replaced by forcing water to percolate upward
through the sand column. It is believed that our result sheds further light on the physics of formation of these cracks.
The project supported by the National Natural Science Foundation of China (19832010) and by the Chinese Academy of Sciences
(KJ952-S1-202) 相似文献
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On the mechanism of the formation of horizontal cracks in a vertical column of saturated sand 总被引:3,自引:0,他引:3
Extended horizontal cracks have been observed experimentally in a vertical column of saturated sand when a flow of water is
forced to percolate upward through it. This paper provides a theory for this phenomenon. It will be shown that the presence
of inhomogeneity in permeability along the length of the column is essential for such cracks to develop. It will also be shown
that small initial inhomogeneity may be magnified through the transport of the finer component of the sand by percolation.
Under certain conditions liquefaction takes place at a section of the sand column causing a crack to initiate and grow there.
This theory is found to be in good qualitative agreement with the experimental findings.
The project supported by the National Natural Science Foundation of China (19832010) 相似文献
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In order to investigate the influence of the vertical vibration loading on the liquefaction of saturated sand, one dimensional
model for the saturated sand with a vertical vibration is presented based on the two phase continuous media theory. The development
of the liquefaction and the liquefaction region are analyzed. It is shown that the vertical vibration loading could induce
liquefaction. The rate of the liquefaction increases with the increase of the initial limit strain or initial porosity or
amplitude and frequency of loading, and increases with the decrease of the permeability or initial modulus. It is shown also
that there is a phase lag in the sand column. When the sand permeability distribution is non-uniform, the pore pressure and
the strain will rise sharply where the permeability is the smallest, and fracture might be induced. With the development of
liquefaction, the strength of the soil foundation becomes smaller and smaller. In the limiting case, landslides or debris
flows could occur.
The project supported by the National Natural Science Foundation of China (40025103, 10202024) 相似文献
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首先引入状态向量,将直角坐标系下横观各向同性饱和土的Biot波动方程转化为一组状态方程,然后基于双重Fourier变换,求解了状态方程,得到传递矩阵.进而利用传递矩阵,并结合饱和地基的边界条件、排水条件及层间接触和连续条件,求解了横观各向同性饱和层状地基的稳态动力响应问题. 相似文献
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《International Journal of Solids and Structures》2002,39(13-14):3523-3541
The ideal case of an infinite horizontal, homogeneous oedometrically consolidated saturated loose sand stratum, sheared in displacement controlled conditions is numerically analysed. The phenomenon of the stratum liquefaction, which is due to both the material mechanical instability and the water presence within pores, is discussed. The numerical results have been obtained by means of a spatial one dimension finite difference numerical code within which both the local and the non-local versions of the same elasto-viscoplastic constitutive model are implemented. Both pore water and shear strain wave propagation within the soil layer is described. 相似文献
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Albert Gyr 《Flow, Turbulence and Combustion》1998,60(3):235-255
A turbulent flow at modest Reynolds numbers (26,000–32,000, as defined in the text) over flat erodible sandy beds was investigated. The beds were composed of sand grains of uniform size with a diameter smaller than the viscous sublayer of the flow. When a modest sand transport (1.2 × 10-3–8.5 × 10-3 g/s·cm) was present, the near-wall coherent structures of the flow produced a bed form with a streaky longitudinal pattern. This pattern had a lateral spacing of about 100 viscous units and had less drag than a flat wall.The mechanism causing the drag reduction is due to a low-frequency riblet pattern which allows the flow to sustain higher wall shear stresses without additional erosion. That means during the riblet regime the sediment transport remains quasi-constant.The formation of the sand streaks as well as the drag reducing mechanism are discussed. 相似文献
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用于吸力式基础离心机模拟的动力加载设备 总被引:1,自引:0,他引:1
吸力式桶形基础广泛地应用于海洋油气开发的海洋平台。在冬季,渤海冰排会对平台产生强烈的冲击,引起振动。本文介绍了一套用于土工离心机实验的动力加载设备,并介绍了该套设备在模拟吸力式桶形基础在受到等效动冰载作用下的响应的实验研究情况及实验结果。结杲表明,当载荷幅值超过一个临界值时,地基上部会发生软化甚至液化。超孔隙水压从土体上部到下部,从桶形基础壁面到远处逐渐减小。在动载荷作用下,桶形基础和临近土体会发生大的沉降。桶形基础尺寸越小,动载荷响应越大。 相似文献
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The formation mechanism of “water film” (or crack) in saturated sand is analyzed theoretically and numerically. The theoretical analysis shows that there will be no stable “water film” in the saturated sand if the strength of the skeleton is zero and no positions are choked. It is shown by numerical simulation that stable water films initiate and grow if the choking state keeps unchanged once the fluid velocities decrease to zero in the liquefied sand column. The developments of “water film” based on the model presented in this paper are compared with experimental results.The project supported by the National Natural Science Foundation of China (40025103 and 10202024) and Key Laboratory of Mountain Hazards and Surface Process, Chinese Academy of Sciences. The English text was polished by Keren Wang. 相似文献