基于传递矩阵与有限元法对陶瓷电主轴转子动态特性的分析

目的求解170SD30-SY无内圈陶瓷电主轴转子的固有频率,分析转子动态特性.方法利用Prohl传递矩阵法、有限元法对陶瓷电主轴转子进行了固有频率的计算和仿真分析,并绘制位移与频率、刚度与频率曲线,对陶瓷电主轴转子动态特性进行分析.结果通过Prohl传递矩阵法求解的结果与有限元仿真结果对比,固有频率误差最大为12%,有限元分析得出转子前四阶振型,主轴前端振动范围及刚度与固有频率的变化趋势,从而便于研究预紧与振动之间的关系.结论通过计算与仿真验证,证实两种方法的可行性及有限元法便于求解分析,得出陶瓷电主轴的固有频率高于普通钢轴,增加刚度有利于固有频率的提高,为陶瓷电主轴转子的动态特性分析提供充分依据.     

高速气浮电主轴转子系统不平衡响应分析

针对高速气浮电主轴转速高,动力学行为复杂,对不平衡激励敏感的特点,基于推广的拉格朗日方程,建立了高速电主轴转子气体轴承系统的动力学数学模型,获得了自由振动微分方程与强迫振动微分方程。在分析气浮电主轴系统残余不平衡质量产生的惯性离心力及不平衡磁拉力的作用机理的基础上,利用有限元方法,对某最高工作转速为250000 r／min 的高速气浮电主轴转子系统进行了不平衡激励的谐响应分析,揭示了运行于超临界模式的高速气浮电主轴在不平衡激励下的动力学行为,为实际工程应用中的高速气浮电主轴转子系统的优化设计、振动控制等提供了理论依据。     

高速电主轴在切削过程中的振动分析与研究

针对高速电主轴在高速切削过程中主轴轴端的振动问题,文中通过建立主轴轴端在受高速切削力的条件下的拉刀—主轴—轴承双转子系统振动动力学模型,并对电主轴的固有频率与振型进行有限元分析,模拟主轴在切削力的作用下的响应,最后通过测试电主轴的振动量完成对振动分析结果的验证。结果表明:总切削力在垂直于假定工作平面方向上的分力对主轴振动的影响最大,实现了对主轴振动的更有效的分析方法。该方法对提高主轴加工精度有一定的指导作用。     

基于磁流变阻尼器的磁悬浮转子系统的振动特性研究

磁悬浮转子系统刚度、阻尼可调范围小,振动抑制能力差,限制了磁悬浮轴承的推广使用,基于磁流变效应的磁流变装置可以对自身的刚度、阻尼进行快速、可控的调节。本文以磁流变技术和磁悬浮技术为基础,对基于磁流变阻尼器的磁悬浮转子系统的机械结构进行了设计与研究,提出了一种新的结构方案,并将该结构简化为有限元模型,借助ANSYSWORKBENCH与MATLAB软件对该结构的减振特性进行了仿真分析,验证了该结构的可行性,可以通过调整阻尼器刚度、阻尼来改变转子临界转速附近的振幅,有效帮助转子系统跨越临界转速。     

利用磁悬浮技术提高动平衡精度及平台设计

在现有的磁悬浮技术和动平衡原理的基础上,对常规的机械式动平衡仪进行改进,提出了利用磁悬浮技术对动不平衡质量进行不停机自动切除的方案.即在不停机的情况下,采用激光加工器对不平衡质量进行自动切除,使转子由不平衡到平衡.分析转子的动平衡特性和磁悬浮的振动特性,建立振动方程,对工作平台的结构进行分析设计.该方法与传统的在停机情况下对不平衡质量进行切除相比,提高了动平衡的精度和系统的效率.     

数控机床高速电主轴动态性能测试与分析

电主轴的性能尤其是动态性能直接影响着主轴运转的稳定性及高速加工的加工精度和生产效率,也决定着高速数控机床的整体发展水平。通过分析数控机床高速电主轴动态性能的主要影响因素,搭建了电主轴动态性能测试试验平台,完成了电主轴在1 000~15 000 rpm转速范围内的振动信号采集与处理,实现了电主轴的动态性能测试与分析,并据此提出了提高电主轴动态性能的有效措施。     

柔性转子系统动力特性分析及实验研究

为了研究高速柔性转子系统工作时发生共振的可能性、工作状态的安全性及改善柔性转子系统振动过大的优化方法,采用有限元分析软件ANSYS,针对支承方案为1-0-1的双盘柔性转子系统,通过参数化建模的方法,建立动力学模型并进行模态分析、谐响应分析以及加速情况下的瞬态响应分析,得到该柔性转子系统的固有频率、临界转速、振型以及跨一阶临界转速时的转盘振幅和支承处的支反力,并在高速柔性模拟转子实验器上进行了瞬态实验。结果表明:理论分析与实验结果相符,转子系统有限元模型分析结果能正确反映实际转子系统的真实动力特性。研究对认识复杂转子系统的全工况动力特性以及柔性转子系统减振优化设计均具有积极意义。     

磁悬浮轴承系统不平衡振动控制的方法

针对磁悬浮磨床电主轴系统中存在的同步振动问题 ,通过计算机仿真和实验 ,研究了 2种处理方法 :力自由控制和开环前馈控制。在力自由控制中 ,控制环节对同频振动分量不加以响应。在开环前馈控制中 ,由不同于主控制器的前馈控制环节对同频振动分量进行处理 ,其结果叠加到主控制器的输出中。计算机仿真和实际的实验结果均表明 ,这2种方法对提高系统性能具有明显的效果。该研究对于磁悬浮轴承系统不平衡振动的控制具有重要意义。     

考虑基础激励输入的柔性磁悬浮控制系统

设计了基于全状态反馈的考虑轨道板振动的柔性磁悬浮控制算法,并与传统的不考虑轨道板振动的刚性控制算法进行比较。分析了轨道板刚度对磁悬浮系统稳定性的影响,探究了存在轨道基础激励时不同控制算法下的磁悬浮系统响应。结果表明:不考虑轨道板振动的刚性控制器对轨道板刚度的要求很高,并且对轨道基础激励敏感,极易造成振荡和失稳;考虑轨道板振动的柔性控制算法对轨道板刚度要求低,在基础激励作用下稳定性仍旧能够满足要求。     

基于非线性支承的磁悬浮双转子系统碰摩特性研究

采用Lankarani-Nikravesh模型,建立了磁悬浮双转子系统的定点碰摩动力学模型,并将磁悬浮轴承的非线性支承力模型融入动力学模型中,研究了非线性支承下磁悬浮双转子系统定点碰摩特性和各参数对系统定点碰摩响应的影响。结果表明,磁悬浮轴承的非线性支承特性对双转子系统的碰摩特性会造成较大影响,且系统碰摩对外加负载更加敏感;当负载较大时,非线性支承下磁悬浮双转子系统的碰摩更加剧烈;此外,合理选择比例系数和较大的微分系数可有效降低系统的碰摩程度。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the