constant stiffness. In [1, 2] Sawalhi and Randall combined the gear model with a bearing model, which has the capacity to model faults. This resulted in a 34 DOF model (Fig.4) . Figure 4: 34 DOF Dynamic Model of the gear test rig. (Vertical direction y aligned with the line of action of the gears) [1] The 34 DOF in the LPM included a 5 DOF bearing model (Fig. 5). The translational degrees of freedom were considered both along the Line of Action (LoA) and perpendicular to it. The casing model considered was a simple one and contained only two modal frequencies from hundreds available. This still gave a valid simulation of the gearbox for the purpose of studying its behavior for a spalled bearing (envelope signal for demodulation of a high frequency resonance) and also in studying the different interactions that exist in the system by comparing simulations with real measurements, for a variety of localized and extended faults in both gears and bearings [1, 2]. It was noticed however that localized faults gave better results than extended faults when compared to the experimental ones. More details about the LPM model and the bearing model can be found in [1]. Figure 5: Five degree of freedom bearing-pedestal model [1] 402
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