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柔性基础上的干摩擦隔振系统 总被引:6,自引:3,他引:3
本文运用增量谐波子衡(IHB)法研究了安装于柔性基础上的含有三次非线性粘性阻尼双线性滞迟隔振系统,考察了基础柔性对隔振性能的重要影响作用,为这类干摩擦隔振系统在工程上的实际应用提供了理论依据。 相似文献
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针对目前复杂柔性隔振系统的数学模型与实际隔振系统之间存在的差异,将阻抗/导纳方法和矩阵传递法相结合,建立包括被隔离设备、多个电磁式主被动一体隔振器和柔性基础在内的复杂柔性耦合系统的状态空间模型。将相对于名义模型中隔振系统参数的变化量以虚拟回路增益的方式引入模型,建立具有参数摄动的隔振系统数学模型。在此基础上,通过矩阵变换的形式,推导出反映模态频率不确定的参数摄动的隔振系统模型,直观反映系统模态阻尼和模态频率的变化,为下一步复杂柔性耦合隔振系统的鲁棒控制器的设计提供依据。 相似文献
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针对复杂隔振系统———单层隔振和多层隔振的混合式系统的求解策略进行了详细的理论分析,给出了 深度优先的结构化建模方法。在此基础上,将隔振系统的结构化分析方法和软件设计中的OO(Object Oriented)思想相 结合,提出了复杂柔性隔振系统面向对象的功率流求解策略。 相似文献
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为定量分析中间构架柔性对内燃动力包双层隔振系统隔振特性的影响规律,指导双层隔振系统的优化设计,建立中间构架的有限元模型并进行模态计算,通过与试验模态对比,验证有限元模型的正确性。在Adams中建立考虑中间构架柔性的刚柔耦合系统动力学模型以及将中间构架视为刚体的多刚体系统动力学模型。通过自由振动和扫频分析,得到中间构架柔性对双层隔振系统隔振特性的影响规律。研究结果表明中间构架柔性会使系统固有频率及主模态方向解耦度减小,并使系统幅值响应出现"移频"、"增频"现象,其中低频段以"移频"为主,高频段以"增频"为主,中频段二者同时出现。相关结论可为隔振设计以及耦合振动的有效控制提供动力学方面的参考。 相似文献
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Supersonic flow over cylindrical afterbodies with base bleed 总被引:1,自引:0,他引:1
J. Sahu 《Computational Mechanics》1987,2(3):176-184
Computations of supersonic flow over two cylindrical afterbodies have been made using a thin-layer Navier-Stokes base flow code. The capability to compute the base flow with base bleed at supersonic speeds has been developed and used to show the effect of mass injection on the base pressure or base drag. Solutions have been obtained for a projectile and a missile configuration having cylindrical afterbodies. Numerical results show the effect of base bleed on the near wake flow field. The rise in base pressure or reduction in base drag has been clearly predicted for various mass injection rates and comparison with experimental data shows generally good agreement. 相似文献
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在浮筏系统中的基座和下层隔振器间增加阻抗变换器,以改变基座的阻抗特性,改变从激励到壳体的传递特性,使整个系统中与激励频率相近、并和舱段壳体振动相关的固有频率和激励频率错开。首先将经典的两单自由度系统的刚性基础用弹性基础取代,并在隔振系统和壳体之间插入可变阻抗的基座,通过改变基座的阻抗特性,改变传入到基座和壳体的功率流的频率特性。在此基础上,进一步针对复杂浮筏系统,研究基座阻抗的变化在各个频率段对传入基座功率流的影响,并对阻抗变换器参数进行优化。为浮筏系统中弹性基座的参数设计提供理论依据。 相似文献
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A single-stage production-inventory system produces parts in a make-to-stock mode, and unsatisfied demand is backordered. The system operates under a so-called base stock with WIP cap replenishment policy, which works as follows. Whenever the Work-In-Process (WIP) plus finished goods inventory falls below a specified level, called base stock, a replenishment order for the production of a new part is issued. If the WIP inventory is below a different specified level, called WIP cap, the order goes through and a new part is released for production; otherwise, the order is put on hold until the WIP inventory drops below the WIP cap. First, it is shown that the optimal base stock that minimizes the long-run, average, inventory holding cost for a given minimum customer service level, is a non-increasing function of the WIP cap that reaches a minimum value, called minimum optimal base stock, at a finite WIP cap value, called critical WIP cap. Then, it is shown that the optimal WIP cap is less than or equal to the critical WIP cap and therefore the optima! base stock is greater than or equal to the minimum optimal base stock. More interestingly, however, it is conjectured that the optimal WIP cap is in fact exactly equal to the critical WIP cap and therefore the optimal base stock is exactly equal to the minimum optimal base stock. The minimum optimal base stock is none other than the optimal base slock of the same system operating under a classical base stock policy (with no WIP cap). Finally, the optimal parameters of a system operating under a base stock with WIP cap policy are related to the optimal parameter of the same system operating under a make-to-stock CONWIP policy. 相似文献
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Inverted base pavements are flexible pavement structures built by placing a top quality compacted granular aggregate base between a rigid cement-treated base and a thin-asphalt surface layer. The proximity of the granular base to the load makes its behaviour critical to the pavement response. Three-dimensional finite-element simulations are conducted to assess the mechanical performance of different inverted base pavement structures, with emphasis placed on pavements that feature thin-asphalt surface layers. A nonlinear constitutive model captures the anisotropic stress-dependent stiffness of the granular base. Results show that the stress distribution within inverted base pavements is markedly different from that of conventional pavements due to the stiffness contrast between successive layers. Thin-asphalt layers deform more uniformly and experience lower tension than thick layers. However, in the presence of combined shear and vertical contact loads, the benefits of a membrane response in thin asphalt concrete layers may be overwhelmed by the increased tensile strain at the load edge. The transition from beam to membrane asphalt response depends on the relative stiffness between the asphalt layer and the aggregate base. In most cases, the transition takes place at an asphalt layer thickness between 25 mm and 50 mm. 相似文献
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The behavior of a freestanding block subjected to base excitation is a nonlinear problem. In the past, many researchers have analyzed freestanding blocks subjected to base excitation and reported their findings. However, still more understanding is required to understand excitation frequency effects on the stability of a freestanding block. Detailed experiments and numerical analysis were performed on a parallelepiped blockhaving an aspect ratio of four, for different values of coefficient of friction and base amplitudes. It was observed that base excitation frequency has a predominant role on the motion and hence the stability of a freestanding block. Contrary to the present understanding of the subject, it was observed that initiation of any mode of motion (like sliding, rocking) from rest depends not only on the parameters like amplitude of base excitation,coefficient of friction and aspect ratio, but also on the base excitation frequency. A freestanding system initially at rest shall remain in rest until excited by a base excitation frequency below a particular value.We numerically determined the value of this frequency (termed as cutoff frequency) for different values of coefficient of friction (0.1–1) and base amplitude (0.1–1 g) for a constant aspect ratio of four of a parallelepiped block with square base. Using data generated from numerical analysis, a three-dimensional diagram named as initiation criteria diagram was developed that identifies various regions corresponding to sliding, rocking, slide–rock and rest (no motion) phase for a freestanding block subjected to base excitation. A novel finding was the presence of a region of no motion above a frequency value for any given combination of parameters. The ratio ofthe amplitude of acceleration obtained at the top of the block to the amplitude of applied base acceleration (amplification factor) was calculated for different experimental cases. The dependence of the amplification factor on the base excitation frequency was also studied. Hence, it was concluded that the base excitation frequency plays an important role in determining the stability of a freestanding rigid block. 相似文献
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基于线性混合小波基的图像去噪 总被引:2,自引:0,他引:2
单小波基由于时频特性难以与复杂的图像特征相匹配,限制了小波闽值算法在图像去噪效果上的进一步提高.提出了一种基于线性混合小波基的图像去噪方法,将多个不同特性的正交小波基进行线性混合构成一个新的小波基,用该混合小波基对图像进行分解后再通过阈值处理实现去噪.调节混合系数,可使混合小波基的时频特性与图像特征相匹配,从而提高小波阈值去噪效果.实验结果表明,该方法去噪效果优于参与混合的各单小波基去噪效果,其峰值信噪比(PSNR)最大可提高3.5 dB. 相似文献
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Ali Zokaei-Ashtiani Cesar Tirado Cesar Carrasco Soheil Nazarian 《International Journal of Pavement Engineering》2016,17(10):861-869
The magnitude of stresses induced in jointed concrete slabs due to thermal loads is influenced by the stiffness of the underlying foundation layers (base, sub-base and subgrade). The layer that most significantly affects the Portland cement concrete (PCC) slab responses is the base. Field observations have demonstrated the increase in reflecting cracking of PCC slabs placed over relatively stiff base layers. To predict thermo-mechanical responses of jointed PCC slabs accurately, appropriate idealisation of foundation layers in finite element (FE) analysis is required. Several modelling methods have been proposed to idealise the effect of the base layer. These methods differ in the structural contribution assigned to the base layer in the pavement concrete system. Four approaches for modelling the base layer in FE analysis of jointed concrete pavements are presented in this paper. The first and second approaches involve modelling the base as a plate separate from the other foundation layer(s). In the third and fourth approaches, the base layer is modelled as part of a Winkler or Vlasov foundation, respectively. A series of parametric studies are carried out to evaluate the capability and feasibility of each modelling approach proposed in this study in reflecting the effect of the base course rigidity on the PCC slab responses under thermal loads. 相似文献
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提出隔震结构的地震损伤模型,并采用概率密度演化理论分析隔震结构地震损伤指数的概率统计特征,为隔震结构性态目标的量化提供依据。考虑隔震支座的压剪相关性和拉压性能的差异,给出隔震层的损伤指数模型,再利用Park-Ang损伤指数描述上部结构的损伤状况,建立隔震体系的损伤指数模型;将隔震结构简化为双质点模型,采用Bouc-Wen模型和刚度退化的Bouc-Wen模型分别描述隔震层与上部楼层的滞变特性,建立隔震结构的状态方程,应用四阶龙格-库塔方法迭代求解求解出隔震结构的位移反应和滞变耗能,进而求解隔震结构的损伤指数;建立隔震结构损伤指数的概率密度演化方程,求解损伤指数的统计特征和概率密度函数,然后根据极值分布理论计算损伤指数超过不同性能水准的可靠度。本研究为以可靠度为理论基础的隔震结构损伤分析提供了可借鉴的方法。 相似文献
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孟广萱 《中国计量学院学报》2004,15(4):304-306,313
介绍了一种圆锥螺纹塞规基面上中径的测量方法.应用量针和万能测长仪测得距基面一定截面上的中径d2,然后在万能工具显微镜上测得此截面距离基面的距离,以此求得基面上的中径d基. 相似文献