Experimental Modal Analysis
Florence – test bench
High vibration levels were recorded on the probe SV-2H on the steam turbine front journal bearing, when rotational speed approached the maximum value (1xRev component at about 176 Hz).
Aim of the test was to determine if any resonance frequency of the basement could be excited by the steam turbine at maximum speed so that it could justify the high vibration level recorded.
Eventually, some modifications of the structure could be suggested by the experimental results.
SINT Technology suggested to carry out an experimental modal analysis (impulse method) in order to verify the structural response of the system and, if necessary, to make some modifications on the structure in order to move up or down the resonant frequency.
The experimental modal analysis carried out on the plinth No.1 showed a natural frequencies at 172Hz, that is a value near to the 1xRev component with the steam turbine running at maximum speed.
The experimental modal analysis carried out on the plinth No.1 showed a natural frequencies at about 172Hz, that is a value near to the 1xRev component with the steam turbine running at maximum speed.
Considering the corresponding modal shape, some modifications were implemented in order to move the frequency (increasing the stiffness).
After these modifications, the amplitude of the response of the structure at that frequency widely decreased as shown in Figure 8; therefore the modifications have been effective for moving the resonance away from that condition.
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