共查询到20条相似文献，搜索用时 15 毫秒
1.
The band structures of flexural waves in a phononic crystal thin plate with straight, bending or branching linear defects are theoretically investigated using the supercell technique based on the improved plane wave expansion method. We show the existence of an absolute band gap of the perfect phononic crystal and linear defect modes inside the gap caused by localization of flexural waves at or near the defects. The displacement distributions show that flexural waves can transmit well along the straight linear defect created by removing one row of cylinders from the perfect phononic crystals for almost all the frequencies falling in the band gap, which indicates that this structure can act as a high efficiency waveguide. However, for bending or branching linear defects, there exist both guided and localized modes, and therefore the phononic crystals could be served as waveguides or filters. 相似文献
2.
Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test.The results show that the times of an elastic wave propa-gating from one end to the other in a specimen to attain stress equilibrium,is related to input wave-forms and relative mechanical impedance between the specimen and the input/output bars.Here-into,with the increae of the relative impedance,the times decreases under rectangular input waves loading,while it increases under half-sine input wave loading.The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the rela-tive mechanical impedance.However,the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance,and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance.In gen-eral,the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test,and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance. 相似文献
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An array of rigid piles used as a screening barrier for plane shear （S） waves is investigated in a homogeneous unbounded space. The dynamic poroelastic theory of Biot is employed, under the assumption of an incompressible solid grain. Using Fourier-Bessel series, the problem of multiple scattering is solved by imposing continuity conditions and equilibrium conditions at the soil-pile interfaces with the translational addition theorem. A parametric analysis is conducted to investigate the influence of the permeability of poroelastic soil, separation between piles, number of piles and frequency of incident waves on screening effectiveness of the barrier, and the results are compared with those in an elastic soil medium. Computed results show that the intrinsic permeability of the soil medium displays an apparent effect on the screening of plane S waves. 相似文献
5.
WU Yi-jie LENG Hong-bin ZHAO Zhang-rong CHEN Jun-hua 《浙江大学学报(A卷英文版)》2006,7(12):2073-2078
INTRODUCTION With the development of engine power and ro- tational speed, the load of pin hole of piston is more and more heavy. By analyzing the load of common cylindrical pin hole, the load of each part of the pin hole is asymmetric when the engine is working. The stress of inner side is the most and that of the outer side is the least. So, to improve engine performance, people reduce the stress concentration of the inner side of the pin hole by changing the geometric shape and improve … 相似文献
6.
基于超磁致伸缩材料的非圆曲面形活塞销孔加工新型机构 总被引：2，自引：0，他引：2
To bear more loads for heavy truck pistons, the shape of heavy truck piston pinhole is often designed as noncylinder form. Current methods cannot meet the needs for precision machining on non-cylinder piston pinhole （NCPPH）. A novel mechanism based on giant magnetostrictive materials （GMM） is presented. New models are established for the servo mechanism, GMM, and magnetizing force of the control solenoid to characterize the relationship between the control current of the solenoid and the displacement of the giant magnetostrictive actuator （GMA）. Experiments show that the novel mechanism can meet the needs to perform fine machining on NCPPH effectively. 相似文献
7.
钟浩浩 《江西电力职业技术学院学报》2012,(1):28-30
针对差压变送器测量凝汽器水位存在的缺点进行原因分析,提出采用了导波雷达液位变送器的改进措施,解决了长期以来差压变送器测量凝汽器水位波动大的问题。 相似文献
8.
To improve localization accuracy, the spherical microphone arrays are used to capture high-order wavefield information. For
the far field sound sources, the array signal model is constructed based on plane wave decomposition. The spatial spectrum
function is calculated by minimum variance distortionless response (MVDR) to scan the three-dimensional space. The peak values
of the spectrum function correspond to the directions of multiple sound sources. A diagonal loading method is adopted to solve
the ill-conditioned cross spectrum matrix of the received signals. The loading level depends on the alleviation of the ill-condition
of the matrix and the accuracy of the inverse calculation. Compared with plane wave decomposition method, our proposed localization
algorithm can acquire high spatial resolution and better estimation for multiple sound source directions, especially in low
signal to noise ratio (SNR). 相似文献
9.
This study presents a new method to solve the difficult problem of precise machining a non-cylinder pinhole of a piston using embedded giant magnetostrictive material （GMM） in the component. We propose the finite element model of GMM smart component in electric, magnetic, and mechanical fields by step computation to optimize the design of GMM smart component. The proposed model is implemented by using COMSOL multi-physics V3.2a. The effects of the smart component on the deformation and the system resonance frequencies are studied. The results calculated by the model are in excellent agreement （relative errors are below 10%） with the experimental values. 相似文献
10.
A 3D multi-time scale discrete element method-computational fluid dynamic (DEM-CFD) coupling approach was applied to investigate the filtration of micron-sized particles by different types of fiber arrays. Both the pressure drop and the filtration efficiency were examined to indicate the filtration performance of the fiber arrays. Fibers that were uniformly arrayed in a parallel or staggered manner were compared. Results showed that the staggered array showed a better performance than the parallel array in terms of both pressure drop and filtration efficiency. Further, we compared the performance of different staggered arrays, i.e. a regular case, one densified in the front layers and another densified in the back layers. The front densified array was found to enter the clogging and cake filtration stage in the shortest time, leading to the highest filtration efficiency, but the highest pressure drop. The back densified array still achieved a much higher filtration efficiency, despite a much lower pressure drop comparable to that of the regular array. The results suggest that the two kinds of densified arrays may be suited for different purposes, e.g. baghouse filters or breathing masks. 相似文献
11.
基于大型铁磁材料的磁致伸缩特性是电力设备发生电磁振动的主要因素,提出了一种适用于普通实验室环境的硅钢片磁致伸缩测量系统,设计了能产生外加磁场的螺线管用来激励硅钢片发生形变,运用陶瓷发热片和温度传感器对硅钢片温度进行调节和控制。基于高精度应变电阻片实现对硅钢片形变的测定,通过理论仿真和实验研究,该装置能准确测量饱和状态和不同温度下的磁致伸缩率。为电磁测量实验及电磁振动分析提供了可靠依据。 相似文献
12.
Cher Ping Lim Sungsup Ra Brian Chin Tianchong Wang 《Educational Media International》2020,57(2):87-111
ABSTRACT Information and Communication Technologies (ICT) have had significant impacts on many sectors in today’s knowledge economy. In developing and emerging countries, ICT have enhanced equity, quality, and efficiency in the education sector. However, the adoption of ICT in the South Asian countries’ education sector has not been at scale and its impacts have been limited. There are several gaps and issues that are hindering the wider adoption of ICT and limiting its impacts in the education sector. Through the case studies of the adoption of ICT for education in Bangladesh and Nepal, this paper examines the gaps and issues to be addressed in order to better leverage ICT to enhance education equity, quality, and efficiency. This discussion is guided by the ICT in the education framework that has been developed by the authors, and could provide insights into the state of ICT in education and offer strategies to better leverage ICT for the education sector of other countries in South Asia and the region. 相似文献
13.
Reliability of substation protection system based on IEC61850 总被引：1，自引：0，他引：1
Although the new technology of protection and automation system of substation based on IEC61850 standard has developed rapidly in China, reliability measures depending on this technology need to be further research＇ed. By taking advantage of convenient information sharing, two kinds of new schemes, shared backup protection unit （SBPU） and signal backup （SB）, have been proposed to solve the failure problem of protective devices and current/voltage transducers respectively, and the working principle of these two schemes are also described. Furthermore, the key technologies of on-line diagnosis of protective devices＇ failure and on-line status diagnosis of optical or electronic current/voltage transducers to realize the two schemes are proposed. 相似文献
14.
杨应崧 《泰州职业技术学院学报》2012,12(5):1-5
近年来,高职院校正按照教育部＂逐步形成以学校为核心、教育行政部门为引导、社会参与的教学质量保障体系＂的要求,积极开展研究和探索。文章拟就建设高职院校人才培养质量保障体系的重要意义;建设现状,成效与问题;高职院校人才培养质量保障体系建设基本思路等问题谈一些个人的意见,以期引起建设院校的关注,并引发进一步的思考与探讨。 相似文献
15.
张诚 《教学研究(河北)》2006,29(3):238-240
语言学习策略对提高学习者的学习效率具有极其明显的作用。本文探讨了语言学习策略的内涵、分类及其影响因素,并指出大学英语教学应在学习策略研究的指导下进行。 相似文献
16.
Nicole Mockler 《Cambridge Journal of Education》2013,43(3):273-289
Large-scale school/university partnerships for the enhancement of teacher professionalism and teacher professional learning have been part of the teacher development landscape in Australia for the past two decades. This paper takes a historical perspective on Australian school/university partnerships through detailing three national projects over a 15-year period, arguing that regimes of increased compliance and accountability that have characterised education policy in Australia over the past decade in particular, have impacted upon the way that school/university partnerships for professional learning have been conceptualised and framed. The kinds of transformative and emancipatory approaches described and advocated by scholars such as Stenhouse, and Carr and Kemmis, in the 1980s, which visibly guided earlier iterations of national projects, are largely absent from their successors. Increasingly, projects have been guided by instrumentalist approaches that emphasise efficiency, such that university-based partners are positioned more as ‘providers’ of professional development than learning partners, and relationships are conceived of as short-term and funding-dependent. Finally, the paper explores the capacity of school/university partnerships to overcome this trajectory, meeting the accountability demands of the current age of compliance while also working into the more transformative domain of teacher development. It suggests conditions under which such partnerships might flourish and concludes with a challenge to both school- and university-based practitioners to reclaim this generative edge in their partnership work, regardless of the policy framework within which it is enacted. 相似文献
17.
TANG Zhi-feng LV Fu-zai XIANG Zhan-qin 《浙江大学学报(A卷英文版)》2007,8(7):1059-1064
This paper presents two numerical realization of Preisach model by Density Function Method (DFM) and F Function Method (FFM) for a giant magnetostrictive actuator (GMA). Experiment and simulation showed that FFM is better than DFM for predicting precision of hysteresis loops. Lagrange bilinear interpolation algorithm is used in Preisach numerical realization to enhance prediction performance. A set of hysteresis loops and higher order reversal curves are predicted and experimentally verified. The good agreement between the measured and predicted curves shows that the classical Preisach model is effective for modelling the quasi-static hysteresis of the GMA. 相似文献
18.
Giant magnetostrictive actuators （GMAs） often work in a close-loop feedback system. This system needs independent sensors which may be difficult to be fixed, besides, excessive sensors may cause more unpredicted problems in a large system. This paper aims to develop a self-sensing GMA. An observer based on piezomagnetic equations is constructed to estimate the stress and strain of the magnetostrictive material. The observer based self-sensing approach depends on the facts that the magnetic field is controllable and that the magnetic induction is measurable. Aiming at the nonlinear hysteresis in magnetization, a hysteresis compensation observer based on Preisach model is developed. Experiment verified the availability of the observer approach, and the hysteresis compensation observer has higher tracking precision than linear observer for dynamic force sensing. 相似文献
19.
该文通过在多值遗传算法中引入模式基因来引导种群的搜索方向,算法在运行过程中不断搜索基因的各种组合,是一种有导向性的组合,模式基因的提取和利用加强了基因组合的导向性,有效提高算法的搜索效率。仿真实验表明了改算法的有效性。 相似文献
20.
用通用有限元软件分析了夹心式超声换能器的纵向和径向耦合振动特性与其尺寸的关系,在此基础上,提出了有耦合振动时换能器的设计原则,并利用“等效声速”法给出了耦合振动换能器的设计方法。最后对理论结果进行了实验验证。 相似文献