电瓷瓷套磨削过程中芯轴模态分析

采用ANSYS有限元软件分析了有预应力作用情况下,电瓷瓷套磨削过程中的动力学问题,分别建立起无瓷套芯轴和有瓷套芯轴两种情况下的有限元模型。对比分析了有、无瓷套两种情况下芯轴的前几阶固有频率和振型等相关动力学问题。得出结论:无瓷套时芯轴临界转速远高于车床常用转速,故无瓷套时只要芯轴装配合理不用考虑芯轴的共振问题;有瓷套时芯轴临界转速接近车床常用转速,故加工较小尺寸且较轻的瓷套时车床主轴转速不得高于30rad/s,转速区间选用15-30rad/s较为合适;而加工尺寸较大且较重的瓷套时车床主轴转速不得高于15rad/s,转速区间选用6-15rad/s较为合适;带瓷套芯轴旋转时,橡胶圈对结构振动影响很大,振型主要表现为橡胶圈的伸缩和弯曲变形,扭转变形较小。     

Drag force control of flow over wavy cylinders at low reynolds number

Three-dimensional numerical simulations on the laminar flow around a circular cylinder with different diameter along the spanwise leading to a type of sinusoidal waviness, named wavy cylinder are performed at low Reynolds number. A series of wavy cylinders with different combinations of spanwise wavelength and wave amplitude are conducted at a Reynolds number of 100. The optimal range of wavelength and the effect of wave amplitude are obtained. The results show that the 3-D free shear layers from the cylinder are more difficult to roll up to vortex and hence the wake formation lengths of some typical wavy cylinders are larger than that of the circular cylinder and in some cases the free shear layers even do not roll up into vortex behind the cylinder. The mean drag coefficients of the typical wavy cylinders are less than that of a corresponding circular cylinder with the same mean diameter; also the fluctuating lift coefficients are reduced. The reduction of mean drag coefficient and fluctuating lift coefficient of wavy cylinder increases with the value of wavy amplitude. Furthermore, a typical wavy cylinder model at Re=150 is also simulated and found that the control of flow induced vibration by modifing the spanwise wavelength of cylinder has a relationship with the variation of Reynolds number.     

液压缸非线性约束下的轧机辊系振动行为

以四辊板带轧机为例,分析液压压下缸及弯辊缸在轧机辊系振动时表现出的分段弹性力和摩擦力两种非线性约束,建立液压缸非线性约束作用下的轧机辊系振动模型,并采用平均法求得振动系统的幅频响应。通过比较两种非线性作用下辊系振动速度和振动幅值的仿真曲线,研究辊系受分段弹性力和摩擦力影响时的行为特性。取不同分段弹性力和摩擦力,仿真分析两种非线性因素分别对轧机辊系幅频特性的影响规律。结果表明,轧机辊系振动速度受分段弹性力大小影响,系统不稳定频率区域随分段弹性力增大而变宽;摩擦力较小时,对辊系振动行为影响表现为阻尼特性,较大时,摩擦力的非线性成为影响辊系振动行为的主要特性。该结论为轧机辊系振动控制提供了理论参考。     

一种旋转振动圆柱获取能量的参数化研究

提出一种旋转振动圆柱从潮流能中主动获取能量的方法。基于Fluent软件的用户自定义函数求解旋转振动圆柱升力,采用动网格技术对一定速度下的旋转振动圆柱获取潮流能进行数值模拟研究。参照相关试验结果,进行数值模拟结果确认,得到的最大升力系数幅值与平均阻力系数幅值与试验结果基本吻合。分析相位差、振幅比及转动幅值对旋转振动圆柱获能效率的影响。结果表明,同振幅比、同转动幅值的旋转振动圆柱,能量利用率都是随着相位差先逐渐增大后减小;同相位差、同转动振幅的旋转振动圆柱,在有效获能范围,其振幅比越大则能量利用率越高;同相位差、同振幅比的旋转振动圆柱,随着转动幅值的增加,其能量利用率先逐渐增加后减小;当相位差为243°,转动幅值为3,振幅比为2.0时,能量利用率最高。     

状态热图在AGC伺服缸早期振动辨识中的应用

通过对轧制自动厚度控制系统(automated gauge control,简称AGC)伺服缸分别模拟3个阶段的保载和振动加载下所收集到的声发射信号,依托前期研究,探索基于状态热图的AGC伺服缸早期振动的辨识方法。通过在迁安沪久660mm轧机的AGC伺服缸上模拟保载和早期振动状态,采集声发射信号,对所采集信号的累计概率分布进行分析,选取可表征伺服缸加载状态变化的声发射特征。基于对所选特征进行组合并施加一定的值域约束和逻辑运算条件,构建了AGC伺服缸保载和早期振动的声发射热图。对状态热图的分析结果显示,AGC伺服缸在同等加载状态下的振动和保载状态可较好地通过此类状态热图予以呈现,为AGC伺服缸的早期振动状态提供一种快速、便捷的可视化辨识方案。     

Simultaneous two-axis vibration measurement of a nonmetallic cylinder by electromagnetic induction and metallic foil loops

This work presents a method based on electromagnetic induction for the simultaneous non-contact measurement of two-axis lateral vibrations of a nonmetallic cylinder. The suggested method employs two pairs of hollow metallic loops, four pairs of permanent magnets and two solenoids. When the cylinder vibrates, eddy currents are generated in the metallic loops due to electromagnetic induction. The current in one pair of loop is induced by the lateral vibration in one direction, while the other by the lateral vibration in the perpendicular direction. The induced currents can be sensed through the remotely installed solenoids. While the proposed technique can be useful for the vibration measurement in hot or insulated cylinders, for which a contact type sensor is hardly applicable, the present study is focused on its underlying measurement mechanism and fundamental experiments. To this end, two-axis vibrations and frequency response functions of a thin nonmetallic cylinder were measured simultaneously by the proposed sensor. They were compared with those extracted by using commercial accelerometers to check the working performance of the proposed measurement technique. The effects of some parameters in the proposed technique, such as the length of the loop, were also investigated.     

Numerical simulation of vortex-induced vibration of a square cylinder

Vortex-induced vibration (VIV) of a square cylinder in a cross flow is examined numerically. Both the rigid and elastic cases are simulated at a low Reynolds number of 100. The approach solves the unsteady flow field using a finite element method with a deforming grid to accommodate the moving cylinders. As for the cylinder motions, a two-degree-of-freedom structural dynamics model is invoked. Fluid-structure interactions are resolved through iteration at the same time step. The calculated results for the case of rigid cylinder indicated that the non-dimensional vortex shedding frequency (or the Strouhal frequency) of a square cylinder at rest is 0.13, which is in good agreement with the published results. For the elastic case, with the change of the cylinder’s natural frequency, “lock-in” and “beat” phenomena were successfully captured. The phenomena of resonance and galloping can also be indicated.     

串列三圆柱绕流的时均压力分布与气动力

运用刚性模型测压风洞试验方法对单圆柱、不同间距串列双圆柱和串列三圆柱绕流的时均压力分布与气动力进行了研究。首先,进行单圆柱模型和不同间距串列双圆柱模型的绕流试验,试验的雷诺数为3.4×104;其次,通过与单圆柱进行对比,讨论了气动干扰对串列三圆柱时均压力分布与时均阻力的影响规律;最后,通过与串列双圆柱进行对比,讨论了圆柱的数量对干扰规律的影响。试验结果发现,串列三圆柱的绕流存在两个完全不同的流态,其切换的临界间距(L/D)cr在3.5～4.0之间,两个流态下的时均压力分布与时均阻力存在明显的差异。本研究可对实际工程中串列圆柱结构的风荷载取值提供参考。     

薄壁筒件内孔车削振动建模与分析

分析了车削薄壁筒件内孔表面时影响振动的主要因素,以切削加工中工件过渡表面的法线方向为建模方向,重点考虑车削加工中动态切削力的影响,依据振动基本理论建立了薄壁筒件动态车削过程的振动模型方程,通过对方程的数值分析探讨加工过程中的振动问题。分析结果表明:切削用量三要素对动态切削力的影响起主导作用,进而对切削振动产生较大影响。刀具主偏角对动态切削力也有一定影响,车削产生的振动与主偏角之间是非线性的关系。这些结论为薄壁筒件加工中的振动研究提供有益的参考。     

两种串列方柱气动性能的试验研究

针对两种布置形式（水平布置和对角布置）的串列双方柱,通过同步测压风洞试验,在雷诺数为Re = 8.0×104、间距比为P/B = 1.75 ~ 5.00（其中P为方柱中心间距、B为方柱边长）条件下,得到了两种布置形式串列双方柱的表面风压,重点研究了对角串列双方柱的气动力、风压分布、Strouhal数等气动性能随方柱间距的变化规律,并与水平串列双方柱进行比较。水平串列双方柱的气动力在P/B = 3.00 ~ 3.50时会发生跳跃现象,下游方柱的平均阻力由负值突变为正值,而对角下游方柱平均阻力系数则均为负值。结果表明：当P/B<3.00时,对角串列双方柱的平均和脉动气动力系数、最大平均负压强度和脉动风压系数均大于水平串列双方柱,而当P/B > 3.00时则情况相反;对角串列双方柱的Strouhal数明显小于相同间距下的水平串列双方柱,且在P/B <3.00时对角串列双方柱的升力功率谱出现了多个峰值。     

活塞导向长度对油气悬架减振性能的影响

烛式油气悬架兼有主销的作用,所以通常具有2°～5°的安装内倾角,内倾角会造成油气缸承受横向力的作用,从而增大缸筒和活塞之间的摩擦力.摩擦力增大会影响油气缸的减振性和车辆乘坐舒适性,严重时会造成油气缸"摩擦锁死"现象,使油气缸失去减振能力.以某矿用自卸车的烛式油气悬架为研究对象,通过理论分析了缸筒和活塞之间摩擦力的影响因...     

Multivariate statistical analysis strategy for multiple misfire detection in internal combustion engines

This paper proposes a multivariate statistical analysis approach to processing the instantaneous engine speed signal for the purpose of locating multiple misfire events in internal combustion engines. The state of each cylinder is described with a characteristic vector extracted from the instantaneous engine speed signal following a three-step procedure. These characteristic vectors are considered as the values of various procedure parameters of an engine cycle. Therefore, determination of occurrence of misfire events and identification of misfiring cylinders can be accomplished by a principal component analysis (PCA) based pattern recognition methodology. The proposed algorithm can be implemented easily in practice because the threshold can be defined adaptively without the information of operating conditions. Besides, the effect of torsional vibration on the engine speed waveform is interpreted as the presence of super powerful cylinder, which is also isolated by the algorithm. The misfiring cylinder and the super powerful cylinder are often adjacent in the firing sequence, thus missing detections and false alarms can be avoided effectively by checking the relationship between the cylinders.     

The temperature distribution due to frictional heat generated between a stationary cylinder and a rotating cylinder

An analytical model has been developed to find the distribution of heat between two cylinders placed at right angles to one another. One cylinder is stationary and the other rotates at high speed. The model assumes that the contact width is very small compared with the overall dimensions of the cylinders. The heat conduction problem has been solved for both the rotating and the stationary cylinder, the average temperature over the contact area has been determined and the heat distribution between them obtained by matching the average temperatures. Allowance has been made for surface heat transfer from both bodies.     

Numerical solution of flow past two circular cylinders in different arrangement rotating in various directions

The combined effects of different rotation types and the Reynolds number on the flow past two rotating circular cylinders about their axes in different arrangement (Side-by-side and tandem) were considered at a range of 520 ≤ Re ≤ 1570 and 0 ≤ ω ≤ 4 (ω is the rotational speed) at one gap spacing of L/D = 2 for a side-by-side arrangement, ω = 0, 2000 ≤ Re ≤ 21000 and L/D = 2 and 4/3 for tandem arrangement (L and D are the distance between the centers of two cylinders and the cylinder diameter, respectively). The results show that the variation of both rotation speed and Reynolds number have an important role in changing the pattern of vortex shedding. As the rotational speed further increases, the separation phenomenon in the boundary layers disappears at the attachment rotational speed. Regardless of Reynolds number, as ω increases, the lift decreases for up and down cylinders while the drag decreases for up cylinder and increases for down cylinder. Quantitative information is highlighted about the flow variables such as the pressure coefficient the Stanton number, the skin friction factor and wall viscous coefficient of the cylinders.     

The free vibrations of a thin circular finite rotating cylinder

The natural frequencies of a finite circular thin cylinder are obtained by employing an exponential matrix expansion of the so-called “fundamental matrix”. It is shown that the method is general enough and able to handle any system of linear differential equations of constant coefficients together with arbitrary boundary conditions. Results are given for rotating cylinders with clamped and free edges. The vibration frequencies of a stationary finite cylinder, previously obtained by other methods of solution, are used as a check on the present method with the special case of zero spinning velocity.     

二级剪叉式液压升降机液压缸布置方式研究

分析了二级剪叉式液压升降机的三种主要布置方式,以及液压缸倾斜布置时的三种液压缸安装位置方案。对于其中的一种方案,应用虚位移原理计算求解液压缸推力,并以液压缸推力最小为目标建立优化设计数学模型,通过MATLAB软件得到液压缸推力最小时的液压缸安装位置。通过研究液压缸布置方式,提高了二级剪叉式液压升降机的设计效率和传动质量。     

Experimental identification of fluid-induced force in labyrinth seals

The seal force is an important factor in turbomachineries. Therefore, the current paper puts forward an expanded seal force identification model. A seal test rig consisting of several sets of seals was prepared. Using the double-plane unbalance force identification theory in rotordynamics, the distributed seal force in the cylinder became equivalent to two selected planes. Considering the complex cylinder vibration with increasing rotating speed and inlet pressure, the cylinder was regarded as a vibration system with 4 degrees of freedom. The 4×4 impedance matrix was tested at the two selected planes using a shaker in two orthogonal directions. The equivalent seal force can be obtained by multiplying the impedance matrix with the measured change in the cylinder vibration. In the seal rig, tests were performed on the influence of inlet pressure, rotating speed, eccentricity ratio, rotor vibration, and clearance. The seal force increases almost linearly with the increasing inlet pressure, eccentricity ratio, and vibration amplitude. Furthermore, the seal force is strongly sensitive to the change in clearance between the cylinder and the rotating rotor. The phase difference between the seal force and the vibration influences the work done. If the phase difference is nearly 90°, then the work is at maximum. Moreover, the seal force applies positive force on the cylinder and negative force on the rotor.     

汽缸开裂的临界裂纹尺寸分析

汽缸在打压时开裂现象时有发生,通过对汽缸材料的常规力学性能和断裂力学特性的试验研究以及对汽缸工作状态下的受力的有限元方向,用断裂力学方法可以计算汽缸不同位置的临界裂纹尺寸,为汽缸的无损检验提供参考。     

Horizontal cylinder-in-cylinder buckling under compression and torsion: Review and application to composite drill pipe

Available analytical results and experiments on the structural behavior of constrained horizontal cylinders subjected to axial compression, torsion, and gravitational loads are reviewed. Such configurations are of interest to the oil-drilling field and provide static design expressions for steel tubulars. The buckling problem is similar to restrained railroad tracks and submerged/underwater pipelines under thermal expansion. Due to outer cylinder constraint and gravitational loads, analysis has shown that long cylinders initiate buckling at loads significantly higher than classical Euler buckling loads. For these constrained long cylinders, buckling initiates in a sinusoidal mode that snakes along the lower surface of the constraining cylinder. Classic analytical expressions hold that as the axial load increases, the cylinder achieves an overall helically buckled state in which the buckled cylinder forms a helix spiraling around the inner surface of the constraining cylinder. Torsion is shown to have little effect on either buckling load but controls the sense/direction of the helical buckling. Little experimental data exist on constrained cylinder buckling, and it is unclear how the initiating sinusoidal mode transitions to the helical mode. Implications of the buckling progression for composite cylinder applications are described including the finding that composites perform poorly relative to steel on the metric of buckling due to lower density and axial stiffness; composites perform well on the metric of lock-up length when friction is considered. Based on this review and findings for composite cylinders, recommendations are made for further work.     

斜置方柱气动力特性试验研究

土木工程结构中有很多方形断面的细长结构,常常受到斜向风作用,其风荷载可以简化为斜置方柱的气动力,与垂直风向作用不同,目前尚没有明确的气动力估算方法。针对此问题,采用刚性节段模型测压风洞试验,分析了风偏角对方柱的静态气动力特性的影响规律。结果表明:采用传统风速分解法仅可以有效地估计在分离点之前的风压,并不适用于斜置方柱完整气动力的估算;由于背风面风压的减弱,斜置方柱的平均和脉动气动力系数小于垂直方柱的对应值;斜置方柱的旋涡脱落频率小,强度弱,频带宽。因此,采用垂直方柱的平均气动力作为方柱抗风设计的平均风荷载是偏于安全的,但是由于旋涡脱落频率及带宽的变化,斜置方柱的风致振动与垂直方柱会有明显的差别。