Methods are presented for parameter identification of an annular gas seal on a flexiblerotortest rig. Dynamic loads are applied by magnetic bearings (MBs) that support therotor. MB forces are measured using fiber-optic strain gauges that are bonded to thepoles of the MBs. In addition to force and position measurements, a finite element (FE)rotor model is required for the identification algorithms. The FE rotor model matchesfree-free characteristics of the test rotor. The addition of smooth air seals to the systemintroduces stiffness and damping terms for identification that are representative ofreaction forces in turbomachines. Tests are performed to experimentally determine sealstiffness and damping coefficients for different running speeds and preswirl conditions.Stiffness and damping coefficients are determined using a frequency domainidentification method. This method uses an iterative approach to minimize errorbetween theoretical and experimental transfer functions. Several time domainapproaches are also considered; however, these approaches do not produce valididentification results. Stiffness coefficients are measured using static test results and anMB current and position based model. Test results produce seal coefficients with lowuncertainties for the frequency domain identification method. Static test uncertaintiesare an order of magnitude larger, and time domain attempts fail to produce sealIn addition to the primary identification research, an investigation of the relationshipsbetween MB force, strain, and magnetic field is conducted. The magnetic field of anMB is modeled using commercial FE software. The magnetic field model is used topredict strain measurements for quasi-static test conditions. The strain predictions arecompared with experimental strain measurements. Strain predictions agree withexperimental measurements, although strain is typically over-predicted.coefficient measurements.
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