Radial dampers impact on shaft vibration at resonance

Gustavsson, Rolf; Nässelqvist, Mattias; Österud, J.

doi:10.1088/1755-1315/240/2/022011

Cited by 4 publications

(2 citation statements)

References 4 publications

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“…Each supporting structure consists of an eight-shoe TPJB and a bracket with a stiffness of 500 MN/m and no damping (Nässelqvist et al, 2012). Note that TPJBs installed in Swedish hydropower units consist of eight pads or more (Gustavsson et al, 2019). The technical specification of the test rig is presented in Table 1.…”

Section: Rotor Descriptionmentioning

confidence: 99%

Simplified Transformation Matrices of Journal Bearings in Vertical Application

Benti

Aidanpää

Gustavsson

2023

Preprint

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Section: Rotor Descriptionmentioning

confidence: 99%

Simplified Transformation Matrices of Journal Bearings in Vertical Application

Benti

Aidanpää

Gustavsson

2023

Preprint

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“…Later, Gustavsson et al [13] and Keto-Tokio et al [14] calculated the added mass by means of acoustic structural simulations and a method derived from Theodorsen's unsteady thin airfoil theory. The added mass was found to significantly influence the natural frequencies of a rotor [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

On the Added Modal Coefficients of a Rotating Submerged Cylinder Induced by a Whirling Motion—Part 1: Experimental Investigation

Roig,

Sánchez-Botello,

Jou

et al. 2023

JMSE

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The operation of submerged rotating machines, such as marine current or tidal turbines, can present deleterious fluid phenomena that may provoke extreme structural vibrations. To predict their dynamic responses, it is necessary to know the added modal coefficients of their runners under a whirling motion. For that purpose, a bespoke test rig was designed to investigate the added modal coefficients of a submerged cylinder, which could rotate at different speeds both in air and completely submerged in water inside a cylindrical tank. First, the modes of vibration were experimentally measured by exciting the cylinder with a push-release method during steady tests or with ramps in rotating speed during transient tests. The calculated natural frequencies and damping ratios were then used in a mathematical model of the dynamic system to calculate the added modal coefficients. During steady tests, the natural frequencies and damping ratios of the whirling modes changed significantly as a function of the rotating speed. Additionally, a whirling mode was observed to change its direction at a given rotating speed. During transient tests, rotating speed ramps with high accelerations were found to present lower lock-in amplitude and frequencies. Moreover, fast downward ramps presented lock-in amplitudes four times higher than fast upward ramps. Consequently, the added modal coefficients changed accordingly as a function of the rotating speed, ramp acceleration, and ramp direction. For these reasons, it was confirmed that the modal responses of submerged rotating bodies must be calculated for each operational rotating speed, even at low velocities, and for each transient event in order to precisely predict their vibration behaviors.

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Procedure to minimize rotor vibrations from flow-induced excitations in Kaplan turbines

Jonsson

Nässelqvist

Mulu

et al. 2022

IOP Conf. Ser.: Earth Environ. Sci.

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The flow pattern in the draft tube is commonly considered when investigating rotor vibration problems, especially for Francis turbines. However, phenomenon in the vaneless space for Kaplan turbines have been shown to induce rotor vibrations when operating in non-standard conditions such as speed no load (SNL). These flow disturbances develop in the vaneless space at small guide vane openings and high swirls. Depending on the number of flow disturbances and runner blades they can excite transversal, axial or torsional vibrations. In the case of transversal excitation they can in some cases cause resonance problems if the frequency is close to a natural frequency of the rotating structure. Recently it was observed that the excitation causes severe resonance in the rotating structure on a refurbished turbine when operated at SNL. The present paper presents frequency analysis of the flow-induced excitations coupled to the shaft vibrations on an old and a refurbished Kaplan turbine. To investigate the causes of the resonance problem, measurements have been performed on both the model and prototype turbine and on a twin unit with the old runner design. The measurements on the prototypes consist of pressure, shaft bending moment, and vibrations. Pressure and radial forces were measured on the model. The result shows the dependence of the runner blade opening on the transversal excitation and the frequency of the flow disturbances. The rotordynamic analysis showed the same phenomena with forward and backward precession. The results agree well between the model and prototype when measured data are normalized by the runner rotational frequency. It is proposed, when refurbishing a unit, to use measured pressures, shaft bending moment and vibrations on the prototype before the refurbishment and the new model turbine to identify critical excitation frequencies for the new prototype turbine, i.e., use the information from the tests to set rotordynamic requirements for the new prototype unit.

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Radial dampers impact on shaft vibration at resonance

Cited by 4 publications

References 4 publications

Simplified Transformation Matrices of Journal Bearings in Vertical Application

Simplified Transformation Matrices of Journal Bearings in Vertical Application

On the Added Modal Coefficients of a Rotating Submerged Cylinder Induced by a Whirling Motion—Part 1: Experimental Investigation

Procedure to minimize rotor vibrations from flow-induced excitations in Kaplan turbines

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