Rotordynamic coefficients in staggered labyrinth seals

In this paper, the flow properties of staggered labyrinth seals are investigated. Leakage flowrates and pressure distributions are calculated for this seal. Then the dynamic stiffness and damping coefficients are calculated. The results are compared to the results of the some other papers.     

Leakage from labyrinth seals under stationary and rotating conditions

Although the leakage flow through labyrinth seals under stationary conditions has been examined by many investigators a reliable prediction of the effect of various labyrinth parameters on leakage rate has not been reported so far. The theoretical models for the seals proposed in most of the previous literature provided results with considerable differences and contradictions in some cases. The structure of the laminar incompressible flow and the performance of a number of seals of various shapes for both stationary and rotating conditions are investigated in this paper. The theoretical treatment is based on the formulation of three-dimensional axisymmetric momentum and continuity equations for labyrinth shapes having small height to radius ratio as is always the case in turbomachinery, rotodynamic pumps and many hydraulic devices. It is found in this paper that shaft rotation is only beneficial for the up-the-step seal, has no effect on grooved shaft and grooved casing seals and has an adverse effect on the down-the-step seal. It is also found that the use of a smaller clearance size at the entrance makes some improvement in the performance of the grooved shaft and down-the-step seals depending on the value of the height to width ratio of the seal.     

带阻尼套筒的篦齿封严结构模态计算方法研究

这里采用波传播技术对带阻尼套筒的篦齿封严结构进行了振动特性的计算分析,通过建立接触面刚度矩阵来模拟阻尼套筒对篦齿封严结构固有振动特性的影响,对各参数进行无量纲处理,使所得结论具有通用性效果。     

Neural network and CFD-based optimisation of square cavity and curved cavity static labyrinth seals

The pressure drop characteristics for leakage of water through circular grooved, square cavity and curved cavity static labyrinth seals are investigated. A semi-theoretical model employing two new terms named virtual cavity velocity and vortex loss coefficient, to determine the pressure drop across the seal is presented. Five different square cavity labyrinth seals (SCLS) were subjected to flow visualisation tests to observe the leakage flow patterns. Computational fluid dynamic (CFD) analysis was done using Fluent commercial code. The values of the vortex loss coefficient for the SCLS at turbulent flow conditions were obtained experimentally. Using the data pool, an artificial neural network (ANN) simulation model was employed to identify the optimal SCLS configuration. Based on the insights gained, two different curved cavity labyrinth seal (CCLS) geometries were developed and optimised using parametric CFD analysis. They were visualisation tested and experimentally found to have higher pressure drops and vortex loss coefficients as compared to the SCLS configurations. The studies show that the enhanced performance is due to the presence of multiple recirculation zones within their cavities, which dissipate higher amount of leakage flow momentum.     

Analysis of contact force and thermal behaviour of lip seals

Using the Mooney-Rivlin model, the contact force and thermal behaviour of a radial lip seal are studied numerically and experimentally as a function of the interference. The numerical and experimental results on the static contact forces show good correspondence with and without the garter spring. The FEM calculated results indicate that increased interference may increase the eracking of seal material due to the maximum contact stresses close to the contacting area of the seal lip and produce local separation between the seal lip and the shaft. Also a coupled thermal-mechanical analysis method will be a useful tool to predict the contact behaviour of rubber lip seals for small values of the interference.     

Experimental and numerical evaluation of contact pressure in pneumatic seals

An experimental procedure is presented for measuring contact pressure between a pneumatic seal and its counterface. Measurements were performed using pressure-sensitive films, for which a suited calibration procedure was developed, also taking into account humidity influence. Having validated the experimental procedure on a lip seal rectilinear specimen, tests were carried out on commercial piston seals. Results were compared with those coming from numerical simulations performed using a finite-elements analysis.     

An improved dynamic milling force coefficients identification method considering edge force

The identification of the dynamic coefficients is the key to realize accurate simulation of dynamic milling process. To enlarge the scope of dynamic simulation without ignoring edge force, an improved method is presented to calculate milling force coefficients. In this method, linear approximation of average milling force is integrated with multiple linear regressions by supposing that milling force coefficients are time invariant for small variation of feed rate. Therefore, both the shear coefficients and the edge coefficients can be calculated simultaneously. A comparison of simulated milling force with and without the edge force is illustrated and the result shows that the accuracy is higher if the edge force coefficients are considered. This method casts new light on fast and accurate simulation of the dynamic milling force in real industrial environment.     

An experimental identification model of rotordynamic coefficients of seals using unbalanced synchronous excitation method

This study presents an improved impedance method based on unbalanced synchronous excitation to identify the rotordynamic coefficients of labyrinth seals. The rotordynamic coefficient test is implemented near the cylinder resonance frequency to enlarge the influence of seal force. The force generated by the rotor unbalance is used to provide synchronous frequency excitation for the rotordynamic coefficient test. Four unique equations are set up under two sets of different rotor unbalance conditions to obtain four unknown complex rotordynamic coefficients. The factors that influence the rotordynamic coefficients of seals, namely, unbalance mass, inlet/outlet pressure ratio, and rotating speed, are considered. The dynamic coefficients are minimally affected by different rotor unbalances. The direct items are nearly equal with same signs, whereas the cross-coupled items are nearly equal with opposite signs. All coefficients increase with increasing inlet/outlet pressure ratio and rotating speed. The direct stiffness coefficients increase more quickly than the cross-coupled items. In addition, the effect stiffness and effect damping coefficients are analyzed; results indicate that both coefficients increase with increasing rotating speed.     

先导式套筒调节阀的流体激振原因及处理

论述了先导式套筒调节阀产生流体激振的各种原因,提出了相应的处理方法。     

Experimental force response of a grooved squeeze film damper

The effects of a circumferential feeding groove on the dynamic force response of a squeeze film damper are determined experimentally. Open end and sealed damper configurations are tested for different groove depths, Journal orbit radii, whirl frequency and fluid viscosity conditions. Significant levels of dynamic pressures are measured at the groove in dampers with groove depth-to-clearance ratios equal to 5 and 10. These pressures affect considerably the dynamic forces of the dampers tested. Large tangential (damping) forces are produced at the circumferential groove which contribute significantly to the damping characteristics of the test articles. For uncavitated lubricant conditions, radial forces of substantial magnitude are determined at the groove and at the thin film land where the squeeze film Reynolds numbers are typically less than 1.     

Experimental on-line identification of an electromechanical system

Identification of electromechanical systems operating in open-loop or closed-loop conditions has long been of prime interest in industrial applications. This paper presents experimental on-line identification of an electromechanical system represented by a digital input/output model. The paper also bridges the theory and practice gap for applied researchers. Studies are carried out by formulating the mathematical model using differential equations and experimental discrete-time identification using on-line plant input-output data. A recursive least-squares method is used to estimate the unknown parameters of the system. Discrete-time data for the parameter identification are obtained experimentally from a setup constructed in the laboratory. A root-mean-square error criterion is used for model validation. Results are presented which show variations in parameters of the electromechanical system. It is demonstrated that identified model output and actual system output match. All tests are performed with no previous results from finite element simulations.     

氧化锆陶瓷侧铣切削力实验研究

在五坐标加工中心上采用硬质合金刀具对氧化锆陶瓷进行了侧铣实验.基于Matlab软件对采集到的切削力信号进行了时域、频域和小波包分析.研究了进给速度、切削宽度、主轴转速的变化对切削力的影响.实验结果表明:切削力随切削宽度的变化而变化,且近似成正比例关系;随进给速度的增加切削力不成比例增大;切削力在主轴转速低于4000 r/min前提下随转速的提高略有减小.     

Experimental and theoretical investigation on the sealing performance of the combined seals for reciprocating rod

Sealing performance of the combined seals at supply oil pressure of 40MPa was experimentally and theoretically investigated. An experimental setup of combined seals for reciprocating piston rods was established in Shanghai Jiao Tong University. Two combined seals were chosen for studies, e.g. C-shape and T-shape (Fig. 1). A theoretical model based on one-dimensional Reynolds equation was made for obtaining the oil film distribution between the rod and the combined seals. Finite element method was used to calculate the contact pressure between the rod and the combined seals. The sealing performance of combined seals was analyzed in terms of the contact pressure, the back-pumping ability, the fluid transport and the net leakage under the conditions of varying the inlet pressure, the frequency of the pressure and the velocity of the rod. The experimental results demonstrated that the velocity of the rod significantly influences the sealing performance of the combined seals. Furthermore, the theoretical analysis on the influence of the rod velocity on the fluid transport was in good agreement to the experimental measurements.     

航空发动机篦齿封严特性数值分析

为了解航空发动机空气系统中封严篦齿的流动及封严情况,采用数值模拟方法对二维蓖齿封严特性进行研究.使用商业软件FLUENT6.3对直通型蓖齿齿数N为3、5、7、9,间隙比t/c为0.5、1、2时不用工况下进行计算,得出各种情况下流量系数随压比变化关系.主要结论为:流量系数随压比的增加而增大;齿数N越多,封严效果越好;缝隙越小,间隙比t/c越大,封严效果越好.同时比较了齿数N为3时的直通型与非直通型封严效果,得出非直通型封严效果更好.     

Influence analysis of secondary O-ring seals in dynamic behavior of spiral groove gas face seals

The current research on secondary O-ring seals used in mechanical seals has begun to focus on their dynamic properties. However, detailed analysis of the dynamic properties of O-ring seals in spiral groove gas face seals is lacking. In particular a transient study and a difference analysis of steady-state and transient performance are imperative. In this paper, a case study is performed to gauge the effect of secondary O-ring seals on the dynamic behavior (steady-state performance and transient performance) of face seals. A numerical finite element method (FEM) model is developed for the dynamic analysis of spiral groove gas face seals with a flexibly mounted stator in the axial and angular modes. The rotor tilt angle, static stator tilt angle and O-ring damping are selected to investigate the effect of O-ring seals on face seals during stable running operation. The results show that the angular factor can be ignored to save time in the simulation under small damping or undamped conditions. However, large O-ring damping has an enormous effect on the angular phase difference of mated rings, affecting the steady-state performance of face seals and largely increasing the possibility of face contact that reduces the service life of face seals. A pressure drop fluctuation is carried out to analyze the effect of O-ring seals on the transient performance of face seals. The results show that face seals could remain stable without support stiffness and O-ring damping during normal stable operation but may enter a large-leakage state when confronting instantaneous fluctuations. The oscillation-amplitude shortening effect of O-ring damping on the axial mode is much greater than that on the angular modes and O-ring damping prefers to cater for axial motion at the cost of angular motion. This research proposes a detailed dynamic-property study of O-ring seals in spiral groove gas face seals, to assist in the design of face seals.     

Elastohydrodynamics of lip seals

A numerical elastohydrodynamic analysis of a rotary lip seal with microundulations reveals that the undulation pattern plays a central role in the operation of the seal. The undulations hydrodynamically generate elevated pressures within the lubricating film, providing load support, and deform in such a manner as to produce reverse pumping. The reverse pumping counteracts the flow induced by the sealed pressure, and thereby prevents leakage through the seal.

1 See p. 25 for the nomenclature.

     

全向凝视型多目标识别实验研究

针对目前大视场凝视红外多目标处理技术的急需,提出了基于红外鱼眼全向凝视型多目标识别数据处理系统和威胁水平排列算法。给出了全向凝视型多目标识别系统组成、硬件电路和算法实现方法,通过采集序列红外图像,实现不同目标在航路、距离、方向、速度等参数的提取。综合目标运动速度、加速度、方向等因素,对多目标威胁等级排序。通过半实物仿真红外多目标源的配合实验,证明了识别系统的可行性和处理精度。     

Experimental dynamic identification of backlash using skeleton methods

In this paper, we present a practical application of non-linear system identification, namely to a mechanical system with a backlash component, based on the skeleton curve reconstruction technique. In the case presented, the identification procedure employs the instantaneous amplitude and frequency of the input and the output of the base motion system under certain forced excitation.Hilbert transform analysis is a well-known method to extract these instantaneous characteristics; however, it is strictly exact only if the signal is weakly damped. A time–frequency representation technique, the Wavelet transform analysis, is therefore introduced to overcome this problem. The instantaneous characteristics in the signals can be obtained from the ridges and skeletons of the Wavelet transform. We apply both methods to the case study and compare the results, showing that the Wavelet-based extraction is generally more accurate than the Hilbert-analysis-based method. We show further that it is possible to obtain good non-linear identification results using either of the methods.     

Structural damage identification of a cantilever beam using excitation force level control

Most studies in damage identification so far have concentrated on comparing modal parameters of a structure with an open crack with those of an intact structure. In this study, a new damage identification method for beam-like structures with a fatigue crack is proposed, which does not require comparative measurement on an intact structure but several measurements at different level of excitation forces on the cracked structure. The idea comes from the fact that dynamic behavior of a structure with a fatigue crack changes with the level of the excitation force. In other words, a beam with a real fatigue crack would behave as an intact beam at low excitation forces due to the crack closure. The 2nd spatial derivatives of frequency response functions along the longitudinal direction of a beam are used as the sensitive indicator of crack existence. Then, weighting function is employed in the averaging process in frequency domain to account for the modal participation of the differences between the dynamic behavior of beam with a fatigue crack at the low excitation and one at the high excitation. Subsequently, a damage index is defined such that the location and level of the crack may be identified. Finally, it is shown that damage identification method using the proposed damage index is very successful through experiment and finite element analysis.