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将无网格点插值法、径向基点插值法、光滑节点插值法用于中心刚体-旋转柔性梁的动力学分析。基于浮动坐标系方法,考虑梁的纵向拉伸变形和横向弯曲变形,并计入横向弯曲变形引起的纵向缩短,即非线性耦合项,运用第二类Lagrange方程推导得到作大范围运动的中心刚体-旋转柔性梁系统的动力学方程。将无网格法的仿真结果与有限元法和假设模态法进行比较分析,表明其作为一种柔性体离散方法在中心刚体-旋转柔性梁的刚柔耦合多体系统动力学的研究中具有可推广性。 相似文献
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大范围运动刚体-柔性梁刚柔耦合动力学分析 总被引:2,自引:1,他引:1
对自由大范围运动情况下刚体-柔性梁系统的刚柔耦合动力学特性进行了研究.考虑系统作平面大范围运动及柔性梁的纵向和横向变形,在纵向变形位移中计及横向弯曲引起的轴向缩短,即耦合变形项.采用假设模态法对柔性梁进行离散,运用拉格朗日方程推导出系统刚柔耦合动力学方程.分大范围运动为转动、平动,平面运动进行了动力学仿真,重点探讨了大范围平动下的刚体-柔性梁系统的刚柔耦合动力学特性.首先研究了系统在外界激励作用下的耦合动力学,其次分析了已知大范围平动对柔性梁小变形运动的影响.结果表明:零次近似模型不能反映大范围平动和柔性梁小变形运动之间的耦合作用;在不同的大范围平动加速度下,柔性梁中既可存在动力刚化效应,也可存在动力柔化效应. 相似文献
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本文论述了杆件结构多刚体-弹簧系统模型的建立及其在平面弯曲情况下动力学方程的推导,文中用此方法对梁动力大变形与非线性材料的动力响应作了数值分析。 相似文献
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由于铰接梁式浮桥的主梁在移动荷载作用下产生弹性变形的同时,还会随着桥脚舟浮箱的运动而运动,其力学特征比较复杂.将每一段铰接梁独立进行研究,同时考虑了刚体运动与弹性变形,在梁振动理论的基础上建立了浮桥的运动方程.在移动集中荷载模型的基础上构建了多轴车辆模型,在势流理论基础上对桥脚舟浮箱进行了时域运动分析,运用假设模态法构... 相似文献
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索-梁耦合系统非线性振动分析 总被引:1,自引:0,他引:1
研究了在惯性参考系中弹性斜拉索与悬臂梁耦合结构的非线性振动问题,利用Hamilton原理建立了索-梁耦合系统的非线性动力学方程,利用Galerkin方法将索-梁耦合系统的非线性运动偏微分方程离散为一组常微分方程,然后利用多尺度法分析研究索-梁耦合动力学系统的非线性振动,用Runge-Kutta法对数学模型进行数值计算,同时探讨了各种参数对索-梁耦合系统非线性振动的影响,并提出对工程有实际意义的结论. 相似文献
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本文在文[1]建立的层合梁理论的基础上,得到了弹性地基上层合梁的动力控制方程,并将此控制方程简化,获得了不考虑剪切变形时的弹性地基上层合梁经典理论的动力控制方程.利用这二种不同的控制方程,文中获得了层合梁自由振动问题的相应的精确解.由这二种不同的结果,讨论了剪切变形对层合梁固有频率的影响. 相似文献
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《Membrane Technology》1991,1991(16):7-9
Although extractions using hollow fibres can be faster and more efficient than those carried out in more conventional equipment, such as mixer/separators, accidental convection through the pores in the fibre walls can compromise these advantages. A way of overcoming this drawback is to fill the walls of the fibres with a gel, such as crosslinked polyvinyl alcohol. The overall mass transfer is unaltered but the convection through the pores is eliminated. 相似文献
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《Materials Today》2002,5(7-8):36-43
The materials issues facing the microelectromechanical systems (MEMS) community can be understood best in terms of the historical context. The field began almost as an afterthought among those engaged in integrated circuit production. These researchers recognized early on that the same processes used in the production of circuits could be re-ordered to make very small mechanical devices. The huge investment made by the electronics community in silicon technologies — and the relative ease with which these techniques could be adapted to device production — made them an obvious resource for early MEMS designers. It is no accident that polycrystalline silicon is the most commonly used structural material.But with the continued expansion of MEMS devices into new areas of application, the limitations of silicon (Si) usefulness became clear. The need to combine electronics and MEMS on the same chip (iMEMS), improve the wear characteristics of moving parts, and achieve a greater mass of moving parts in MEMS inertial sensors have led researchers away from a ‘one-material-fits-all’ approach. Instead the search is on for materials that more directly serve specific ends. The need for biocompatibility in the emerging field of bio-MEMS has added urgency to the quest for new materials, since Si-based materials cannot meet every bio-MEMS need. 相似文献
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前几天妹妹在我的"世界之星"颁奖仪式的照片下留言说:"哥,我没想过你的人生会这么精彩!",是啊,连我自己也从未想过我的人生能如此丰富多彩.
很多设计师是因为喜欢美术或是因为从小便培养的美术基础才选择美术专业,跟别人不同,美术是我不高的文化分数无奈之下的选择,万幸的是当我接触它时,便狂热地爱上了它. 相似文献
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Writing with Fluid: Structuring Hydrogels with Micrometer Precision by AFM in Combination with Nanofluidics
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Nicolas Helfricht Andreas Mark Marina Behr Andreas Bernet Hans‐Werner Schmidt Georg Papastavrou 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(31)
Hydrogels have many applications in biomedical surface modification and tissue engineering. However, the structuring of hydrogels after their formation represents still a major challenge, in particular due to their softness. Here, a novel approach is presented that is based on the combination of atomic force microscopy (AFM) and nanofluidics, also referred to as FluidFM technology. Its applicability is demonstrated for supramolecular hydrogel films that are prepared from low‐molecular weight hydrogelators, such as derivates of 1,3,5‐benzene tricarboxamides (BTAs). BTA films can be dissolved selectively by ejecting alkaline solution through the aperture of a hollow AFM‐cantilever connected to a nanofluidic controller. The AFM‐based force control is essential in preventing mechanical destruction of the hydrogels. The resulting “chemical writing” process is studied in detail and the influence of various parameters, such as applied pressure and time, is validated. It is demonstrated that the achievable structuring precision is primarily limited by diffusion and the aperture dimensions. Recently, various additive techniques have been presented to pattern hydrogels. The here‐presented subtractive approach can not only be applied to structure hydrogels from the large class of reversibly formed gels with superior resolution but would also allow for the selective loading of the hydrogels with active substances or nanoparticles. 相似文献
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Accommodation with higher-order monochromatic aberrations corrected with adaptive optics 总被引:2,自引:0,他引:2
Chen L Kruger PB Hofer H Singer B Williams DR 《Journal of the Optical Society of America. A, Optics, image science, and vision》2006,23(1):1-8
Higher-order monochromatic aberrations in the human eye cause a difference in the appearance of stimuli at distances nearer and farther from best focus that could serve as a signed error signal for accommodation. We explored whether higher-order monochromatic aberrations affect the accommodative response to 0.5 D step changes in vergence in experiments in which these aberrations were either present as they normally are or removed with adaptive optics. Of six subjects, one could not accommodate at all for steps in either condition. One subject clearly required higher-order aberrations to accommodate at all. The remaining four subjects could accommodate in the correct direction even when higher-order aberrations were removed. No subjects improved their accommodation when higher-order aberrations were corrected, indicating that the corresponding decrease in the depth of field of the eye did not improve the accommodative response. These results are consistent with previous findings of large individual differences in the ability to accommodate in impoverished conditions. These results suggest that at least some subjects can use monochromatic higher-order aberrations to guide accommodation. They also show that some subjects can accommodate correctly when higher-order monochromatic aberrations as well as established cues to accommodation are greatly reduced. 相似文献
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Bridge circuits with considerably extended functional capabilities are considered. They enable one, without any change in
configuration, to determine the parameters of RL, RC, and RCL multicomponent two-terminal networks when connected to the same
two leadouts of the bridge circuits.
Translated from Izmeritel’naya Tekhnika, No. 4, pp. 40–45, April, 2009. 相似文献
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Dongoo Lee 《工程优选》2019,51(2):352-367
This article introduces a new routing problem referred to as the vehicle routing problem with vector profits. Given a network composed of nodes (depot/sites) and arcs connecting the nodes, the problem determines routes that depart from the depot, visit sites to collect profits, and return to the depot. There are multiple stakeholders interested in the mission and each site is associated with a vector whose kth element represents the profit value for the kth stakeholder. The objective of the problem is to maximize the profit sum for the least satisfied stakeholder, i.e. the stakeholder with the smallest total profit value. An approach based on linear programming relaxation and column-generation to solve this max–min type routing problem was developed. Two case studies—the planetary surface exploration and the Rome tour cases—were presented to demonstrate the effectiveness of the proposed problem formulation and solution methodology. 相似文献
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S.K. Stephenson 《成像科学杂志》2013,61(2):91-95
An account is given of the construction and uses of home-made film packs suitable for mounting on the fingertips of persons who handle radioactive sources or palpate patients during X-ray fluoroscopic procedures, etc. Various types of film, cut to I cm squares, have been used in these light-tight, waterproof packages. The calibration and interpretation of films exposed to various types and qualities of ionizing radiation are discussed and some examples are given of typical results obtained. 相似文献