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dynamic analysis of the steam turbine rotor

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dynamics analysis of the Steam turbine rotor

Initial data

Rotor drawings and weights description documents were used as an intitial data.

Rotor finite lement model (FEM) is presented in Figure 1.

Pad sliding bearings and support stiffness/damping were taken into acount using CBEAR and CBUSH elements respectively.

Rotor length is about 8 meters; weight - is approximately 21 tonn.

Introduction

Steam turbine rotor is one of the most critical and expensive assembly.

Usually a turbine rotor is a subject of dynamic unbalance excitation. And because of that rotor dynamics analysis of steam turbine rotor is required.
FEA Engineering was asked to perform rotor dynamic analysis for 21-tonn tubine rotor and analyze occured results.

Figure 1. Finite element model of the steam turbine rotor

Critical speeds results

At the first stage of dynamic analysis critical speeds of the rotor (Campbell diagram) were obtained (Figure 2).

Critical speeds were calculated using complex modal solution and the following data was obtained:

  • ther 1st critical speed obtained 2200 rpm;
  • the second critical speed was out of operating range.

Modeshape animation of the rotor is presented in Figure 4.

Figure 2. Campbell diagram

Figure 3. Rotor vibrations

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Frequency response results due to rotor unbalance

At the second stage frequency response analysis was performed.

Dynamic unbalance was used as a dynamic excitation.

Obtained vibration magnitudes aren't exceed allowable values for all operating speeds according to standard API 612.

Rotor vibration diagram can be seen in Figure 3.

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Figure 4. Deformed modeshape of the rotor's 1st critical speed