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rotor dynamic analysis of the steam turbine rotor

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rotor dynamics analysis of the Steam turbine rotor

Initial data

Rotor drawing and weights description document 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 reqired.
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 diagrams) was obtained (Figure 2).

Critical speeds were calculated using complex modal solution and there are following conclusions:

  • ther 1st critical speed achived at 2200 rpm;
  • the second critical speed is out of operating range

Modeshape animation of the rotor is presented in Figure 4.

Figure 2. Campbell diagrams.

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. Excitation force is proportional to square of rotational speed.

Obtained vibration magnitutes do not exceed allowable values for all operatiing 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 @1st critical speed.