Papers by Keyword: Rotordynamics

Abstract: A numerical code for calculation of leakage flowand rotordynamic coefficients of labyrinth seals has beendeveloped. The code is based on the solution of Reynolds-averagedNavier-Stokes equations combined with a two-equation turbulencemodel. The numerical solution is achieved with finite volume methodand the rotordynamic coefficients are evaluated from severalsimulations with different rotor precessions. The solution iscompared to single control volume based bulk flow method[Williams, 1998] and to the experimental results for look-throughlabyrinth seal [Schettel, 2004].

Abstract: Unbalance of rotors is one of the principal causes of their lateral vibration. A technological solution frequently used to its suppression consists in placing damping devices to the rotor supports. To achieve their optimum performance their damping effect must be controllable. This is offered by squeeze film dampers utilizing the magnetorheological phenomenon to control the damping force. In mathematical models magnetorheological oils are usually represented by Bingham or Herschel-Bulkley theoretical materials. Here the magnetorheological oil is modeled by bilinear material with the yielding shear stress depending on magnetic induction. Its flow curve is continuous which contributes to reducing nonlinear character of the motion equations. The new mathematical model was applied to investigate several operating regimes of rotating machines.

Abstract: Reliability of rotating machinery is determined to a considerable degree by the bearing units. For several applications the requirements in rotation speed, bearing load and maximal vibration level are so extreme that neither rolling-element bearings nor fluid-film bearings could provide necessary performance characteristics during all regimes of operation. Hybrid bearings, which are a combination of rolling-element and fluid-film bearings, can improve performance characteristics and reliability of the rotor-bearing systems. The aim of this work is to analyze the advantages and disadvantages of the hybrid bearings. Known real applications of hybrid bearings are discussed. Analysis shows that depending on the application different hybrid bearing types could improve dynamic characteristics and life time of the bearing unit, increase load capacity and DN limit of the rolling-element bearing.

Abstract: In this paper the effects of rotordynamics under the aspect of the choice of shape functions are discussed. For this purpose a rotor system which consists of a slim shaft and two rigid disks is modeled using the Projection Equation. The shaft is assumed as an elastic Euler-Bernoulli beam, supported by two bearings modeled as radial spring systems. The rotor is driven by a permanent-magnet synchronous motor whose torque is transmitted with a spur gear pair next to one of the bearings. A Ritz approach is used to separate the elastic displacements in position and time, thereby different shape functions are evaluated. Approximated eigenfunctions are computed and used as shape functions as well. For validation, the eigenfrequencies are compared with semi-analytical ones, calculated with the Transfer-Matrix-Method and experimental results. The insights obtained from this work should make it easier to choose the appropriate shape functions for such problems.

Abstract: In this paper, a two-node beam element (as a simplified modeling approach) has been presented to investigate the vibration characteristic of rotor system with a complicated geometry. The decline of stiffness near the region of discontinuity is investigated on the basis of stain energy, and the conclusion is applied to the 2-node beam element analysis. In addition, the bending critical speeds and corresponding mode shapes of an integral rotor of 1000MW turbine have been investigated as an example. Verification results show that the simplified modeling approach by this 2-node beam element meets the accuracy requirement.

Abstract: Over the years various techniques have been developed to extract information on the dynamic state of the rotating machinery. This paper introduces a new method based on the phase data of the shaft rotation angle. Usually the phase data is omitted and only the frequency components of the vibration spectrum are taken into consideration. However, the transverse shaft crack has a specific angular location about the shaft axis. Therefore, it is supposed that by measuring the vibration response of the rotor deflected by an additional constant force applied perpendicularly to the shaft axis at different angular locations, different vibration signatures can be obtained. Such signatures can then be used to detect the crack. The method utilizes also the coupling phenomenon between the lateral/torsional vibrations of the cracked rotor, since the shaft is additionally excited by an external harmonic torque. The computer simulation study is based on the uncracked and cracked rotor models obtained by using the finite element (FE) approach. The results of the numerical analysis demonstrate the potential of the suggested method for the effective shaft crack detection.

Abstract: An industrial turbo engine is modeled and meshed in ANSYS using solid elements. A rotordynamic analysis of the selected parts of the turbo engine is performed. For the unbalance response prediction, a novel method for modeling unbalance in 3D solid rotor model is presented and validated using a simple rotor model. In order to reduce the model order degree, transfer functions of the casing and bearings are generated and incorporated into the rotor-bearing system to account for the influence of elastic support stiffness on the rotor system. Modal and unbalance response analysis is performed on the 3D solid finite element rotor-bearing model using the unbalance modeling method presented in this paper. The results obtained from modal and unbalance analysis are compared and discussed.

Abstract: With the rotor structure ofturbopump, using a one-dimensional finite element method, considering the mass of shaft, gyroscopic effect and influence of shearing deformation,establishedtheone-dimensional rotor dynamics finite element model, calculated its six rank of the critical speed, and compared the gyroscopic effect and mass of shaft to the influence of the critical speed turbopump, and the results show that, considering the mass of shaft there is a slight decrease of critical speed value, and gyroscopic effect on critical speed calculation has a significant effect, therefore, gyroscopic effect must be considered in the design of turbopumps.

Abstract: According to magnetic suspension motorized spindle system, high speed motorized spindle system based on bearingless induction motor is presented in this paper. The prototype of high speed motorized spindle system with bearingless induction motor is studied and analyzed by using finite element analysis software Ansoft/Maxwell and Riccati transfer matrix method, and compared with high speed motorized spindle system supported by Active Magnetic Bearing (AMB). The results show that high speed motorized spindle system with bearingless induction motor has distinct advantage of simple and compact structure, which is easier to realize high speed and extra-high speed operation.

Abstract: Centrifugal compressors are widely used to compressor gas in many different processes within the petroleum and chemical industry. Two vibration types of concern in industrial compressors are synchronous and subsynchronous vibration. The latter, more troubling type of vibration, occurs when non-conservative whirling forces(Cross-coupling) act to excite a lateral natural frequency, which lies below the running speed(subsynchronous vibration). In this paper, more attention is paid to impellers from a rotordynamic standpoint and a synthesis gas compress in ammonia plant is analyzed in order to diagnosis the root cause of vibration fault using the best available resources for seals and bearing. Logarithmic decrement predictions for the full rotor model consisting of all the stages and seals are conducted under different bearing structure. On this basis, a resolvent to improve the rotordynamic stability is presented. The field application result indicates that this method is effective.