共查询到20条相似文献,搜索用时 15 毫秒
1.
针对抽水蓄能电站水泵水轮机运行过程中出现的振动问题,从产生共振的条件出发,分析了转轮叶片和活动导叶形成的叶栅组合的动静干涉机理。根据转轮对水力激振模式的动态响应,研究了不同叶栅组合方式对水力激振力的影响。建立流固耦合数学模型,对转轮、活动导叶、顶盖及底环等过流部件的动态特性进行了有限元分析,以7/20的叶栅组合为例,阐述了流体激发结构共振的可能性。为了避免过流部件发生共振以及由此产生的疲劳裂纹或断裂等事故,提出了最佳叶栅组合的选择原则、降低无叶区压力脉动的方法以及提高结构固有频率和降低局部应力集中系数的具体措施。 相似文献
2.
A.E.P. Veldman 《Journal of Engineering Mathematics》2001,39(1):189-206
The paper presents a personal view on the history of viscous-inviscid interaction methods, a history closely related to the evolution of the method of matched asymptotic expansions. The main challenge in solving Prandtl's boundary-layer equations has been to overcome the singularity at a point of steady flow separation. Stewartson's triple-deck theory has inspired a solution to this challenge, and thereby it paved the way for industrial use of viscous-inviscid interaction methods. 相似文献
3.
Shigeo Horiuchi Marco Cantoni Masaya Uchida Tadamasa Tsuruta Yoshio Matsui 《Bulletin of Materials Science》1999,22(3):227-231
Quantized magnetic flux lines (vortices) in a Nb foil were directly observed in different magnetic fields up to 200 G by a
cryo-Lorentz electron microscope. The interaction of vortices with dislocations in the specimen was examined and clarified;
edge-on dislocations weakly pin individual vortices at magnetic fields below 100 G. In higher magnetic fields the formation
of a regular hexagonal vortex lattice started preferentially at in-plane dislocations. At 200 G the Abrikosov vortex lattice
was formed with small domains, whose centre included the dislocations, showing their important role on the formation of the
vortex lattice. For a NbTi foil no clear image of vortices could be seen, because the surface was rough due to the formation
of fine grains and precipitates. 相似文献
4.
It is experimentally demonstrated on a series of one-stage superconducting cables, composed from multifilamentary superconducting wires, that the coupling current losses being induced in the wire and in the cable matrix, contain interaction loss terms directly proportional to the wire twist pitch Iw. This proves partly their theoretically expected lc.lw-dependence. Different twisting directions in a one or multistage superconducting cable increase the ac losses and should be avoided. The magnitude of the effect can become important. 相似文献
5.
We simulate and analyse an Airy pulse coupled with a dark soliton in a single-mode fibre by solving the non-linear Schrödinger equation (NLSE). Simulations show that the group velocity parameter β22 has a huge impact on the interaction between the Airy pulse and the dark soliton. At some values of β22, a bright soliton arises from the Airy pulse. The intensity of the bright soliton reaches a maximum when β22 takes a certain value. Meanwhile, the transmission distance and the primary energy of the Airy pulse are affected by the different values of β22. However, when the Airy pulse propagates in a linear medium, varying the value of β22 has only a slight impact on the interaction, and no bright soliton detaches from the Airy pulse. In brief, the dispersion effect has a large impact on the interaction of Airy pulses and dark solitons in a non-linear medium; however, dispersion has a lesser impact on interactions in a linear medium. 相似文献
6.
The mechanistic–empirical pavement design guide (MEPDG) uses mechanistic–empirical models by analysing the impacts of traffic, climate, materials and pavement structure to predict performances of pavement. The MEPDG software uses a three-level hierarchical input to predict performance in terms of terminal International Roughness Index, permanent deformation, total cracking (reflective and alligator), asphalt concrete (AC) thermal fracture, AC bottom-up fatigue cracking and AC top-down fatigue cracking. However, these inputs with different levels of accuracy may have significant impact on performance prediction. This study focuses on the sensitivity of the inputs of MEPDG distresses to identify the effect of the accuracy level of inputs based on experimental design. A local sensitivity analysis is carried out to identify the main effect of inputs considering them as independent variables. Interaction effects are also analysed based on random combination of the inputs. Sensitive input variables and their combinations are evaluated through a multiple regression analysis for respective distresses. 相似文献
7.
W. Lin A. L. Graham M. S. Ingber J. R. Abbott J. W. Leggoe 《Computational Mechanics》2005,36(4):307-319
The hydrodynamic interaction between two particles suspended in shear flows is fundamental to the macroscopic characterization of suspension flows. Although such interaction in quiescent or linear shear flow is well understood, studies on that in a nonlinear shear field are rare. In this study, the hydrodynamic interaction between two neutrally-buoyant smooth spheres moving at negligible Reynolds numbers in an unbounded plane Poiseuille flow has been calculated by three-dimensional boundary element method (BEM) simulations. The BEM results have been compared with the analytical results obtained with the method-of-reflection (MoR) approximations. The BEM simulations have been found to provide satisfactory predictions if the number of elements on the spheres are more than 200, whereas the MoR approximations provide satisfactory predictions only when the minimum separation between the spheres is relatively large although this MoR method has the advantage to easily calculate the hydrodynamic interaction between two spheres freely moving at negligible Reynolds numbers in unbounded quadratic flow by solving ordinary differential equations. Furthermore, it is found that there is a preferential cross-streamline migration of the center-of-gravity of the sphere-pair in the plane of shear in plane Poiseuille flow which does not arise in simple shear flow. This migration is always directed towards low shear regions when the sphere having larger translational velocity approaches the other sphere, and reverses towards high shear regions when the faster sphere leads the other sphere in the plane of shear. There is also a cross-streamline migration of the center-of-gravity of the sphere-pair in the plane of vorticity, but this migration does not have a preferential direction. These migrations are symmetric about the point where the spheres are at the minimum separation, and are only significant when the hydrodynamic interaction of the spheres is strong. These results show that the migration of the center-of-gravity of the sphere-pair can be attributed to the nonlinearity of the shear field, which agrees with the MoR approximations. The hydrodynamic interaction between the two spheres has been quantified under various conditions by the BEM simulations for both identical and disparate spheres. 相似文献
8.
We consider an infinite chain of particles with nearest neighbour (NN) and next to nearest neighbour (NNN) being coupled by nonlinear springs. To mimic the Lennard–Jones potential, the NN and NNN springs act against each other. We prove that in contrast to the NN interaction case, there are supersonic periodic solutions. 相似文献
9.
研究热环境中输送微流体的微尺度管道流固耦合振动问题。根据线性热弹性理论建立系统振动控制方程,并利用复模态法对其进行求解,得到了系统的固有频率和屈曲失稳临界流速,讨论了温度变化、微尺度效应及管道壁厚对系统振动特性的影响。研究结果表明:提高环境温度会降低系统的固有频率和临界流速;管道和流体的微尺度效应分别会使临界流速升高和降低,但微流体的这种影响会随着温度的升高而逐渐减弱并最终消失;管壁较薄(外径接近微尺度特征尺寸)时,壁厚的变化对固有频率的影响很大,而管壁较厚时,温度变化对固有频率的影响更为明显。 相似文献
10.
In light of the disadvantages of celebrity spokespersons and the prevalence of brand anthropomorphism, the branding strategy of having an animated spokescharacter (ASC) is gaining popularity. Based on social information processing theory and parasocial interaction relationship (PSR) theory, this study explored the characteristics of brand animated spoke scharacters regarding whether and how they generate advertising effects. In an empirical study involving 292 participants concerning two animated spokescharacters (“Tuniu” and “Three Squirrels”), we obtained the following findings: (1) The characteristics of ASCs (likeability, expertise, and congruence) are positively related to parasocial interaction relationships (PSRs) and advertisement effects; (2) PSRs fully mediate the relationship among likeability and ASC congruence and advertisement effects but partially mediate between ASC expertise and advertisement effects; and (3) adult playfulness moderates the effect of ASC likeability on advertisement effectiveness. This research expands the study of the effects of ASCs on advertising and enriches our understanding of the positive associations of ASCs. 相似文献
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12.
载体炭与Pt催化剂之间的相互作用及其引起的尺寸效应(英文) 总被引:1,自引:0,他引:1
通过乙二醇还原,在VulcanXC-72炭黑上负载了三种具有不同平均粒径(1.7nm,3.0nm和5.0nm)的Pt催化剂。利用透射电子显微镜,研究了载体炭黑表面的微孔与Pt催化剂之间的几何相互作用。结果表明:尺寸较小的Pt颗粒(平均粒径为1.7nm)通常被包含在载体表面的微孔中,表现为被一薄碳层所覆盖并嵌入炭黑基体。而尺寸较大的Pt颗粒(平均粒径为3.0nm和5.0nm)则不存在这种现象,往往显示出裸露的清洁表面。这种与载体表面微孔的不同相互作用引起了Pt颗粒在电化学活性比表面上的反常尺寸效应,进而影响了其催化甲醇氧化的质量比活性。 相似文献
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15.
《Optical Materials》2014,36(12):2496-2501
We introduce a figure of merit for the photon spin-to-orbital angular momentum conversion via electrooptic (EO) Pockels effect in single crystals. Relations for the effective EO coefficients are derived for different symmetry groups. We show that Bi12TiO20 crystals reveal the highest figure of merit among well studied crystalline EO materials. The efficiency of the spin-to-orbital angular momentum conversion is measured experimentally for a number of single crystals. 相似文献
16.
为了分析A11VO190恒功率轴向柱塞泵滑靴副的摩擦特性,建立了剩余压紧力滑靴的数学模型.在考虑由热膨胀引起的热楔力和由阶梯结构引起的动压效应的基础上,根据空间力系平衡原理,利用软件Matlab计算滑靴在排油区的动态特性,得到滑靴在斜盘不同位置的油膜厚度.在此基础上推导出滑靴副摩擦功率损失和泄漏功率损失的计算公式,并对比不同负载压力和主轴转速对油膜厚度和功率损失的影响.结果表明:负载压力增大,油膜厚度减小,功率损失增加;转速增大,油膜厚度增大,功率损失也随之增加. 相似文献
17.
采用实验和数值模拟两种方法对长宽比为3∶1的矩形柱尾流进行了稳定性研究.实验发现当雷诺数接近临界值时,未加扰动的矩形柱尾流呈二维定常状态.当在柱体上游一定位置和下游靠近柱体的位置上沿垂直于来流方向施加一个宽度很小的短时脉冲射流扰动以后,扰动随时间放大,并出现旋涡脱落现象,并且这种扰动激发的旋涡脱落可以持续很长时间,不会衰减.而在下游较远处施加同样的扰动时,扰动将会衰减,不能激发出持续的旋涡脱落.数值模拟再现了上述实验结果,并且表明,当扰动强度(脉冲射流出口速度)较小时,不会出现持续的规则旋涡脱落,只有当扰动强度达到一定阈值时,旋涡脱落才能被激发. 相似文献
18.
V. A. Bazhenov O. S. Pogorelova T. G. Postnikova S. N. Goncharenko 《Strength of Materials》2009,41(4):392-398
We consider different methods of modeling impact in vibroimpact systems by contact interaction force which can be regarded
as elastic force as well as force corresponding to the Hertz law and with the help of the boundary condition method by using
the coefficient of restitution. Comparison of the results of the modeling by means of these methods is performed, and recommendations
for their application are proposed.
Translated from Problemy Prochnosti, No. 4, pp. 69–77, July–August, 2009. 相似文献
19.
两种立方型状态方程相平衡推算中相互作用系数的研究进展 总被引:4,自引:0,他引:4
混合制冷剂工质的相互作用系数是混合工质汽液相平衡性质计算中所需的一个重要参数.对两种立方型状态方程混合规则中相互作用系数的研究进展做了回顾,评述了以天然气组分混合物为对象的实验工作中相互作用系数kij的回归方法,关联数值和关联式,寻找提高汽液相平衡推算精度的途径,研究和探索更加精确的预测模型. 相似文献
20.
The emergent patterns of collective motion are thought to arise from application of individual-level rules that govern how individuals adjust their velocity as a function of the relative position and behaviours of their neighbours. Empirical studies have sought to determine such rules of interaction applied by ‘average’ individuals by aggregating data from multiple individuals across multiple trajectory sets. In reality, some individuals within a group may interact differently from others, and such individual differences can have an effect on overall group movement. However, comparisons of rules of interaction used by individuals in different contexts have been largely qualitative. Here we introduce a set of randomization methods designed to determine statistical differences in the rules of interaction between individuals. We apply these methods to a case study of leaders and followers in pairs of freely exploring eastern mosquitofish (Gambusia holbrooki). We find that each of the randomization methods is reliable in terms of: repeatability of p-values, consistency in identification of significant differences and similarity between distributions of randomization-based test statistics. We observe convergence of the distributions of randomization-based test statistics across repeat calculations, and resolution of any ambiguities regarding significant differences as the number of randomization iterations increases. 相似文献