## 4 Results and Discussion
mulation treats rotor perturbation motions about static equilibrium positions as bounded limit-cycle oscillations, enabling the derivation of dynamic pressure components and the determination of rotor critical mass, equivalent lubricant film stiffness and damping coefficients, maximum permissible rotor mass, and whirl frequency limits, which collectively establish conditions for stable equilibrium recovery and sustained operational performance. Alternative parameter identification methods employ nonlinear analytical approaches, rotor center vibrational response monitoring or experimental signal analysis techniques. Figure 13 demonstrates the influence of texture geometry and depth variation on the critical mass of the rotor within two angular sectors (270-300\({}^{\circ}\) and 300-330\({}^{\circ}\)) of two-lobe bearings. Results reveal that surface texturing in the 300-330\({}^{\circ}\) region fails to enhance system stability with increasing dimple depth in noncircular journal bearings. Rather, surface modifications generally degrade stability until reaching a critical penetration threshold, beyond which the destabilizing effect stabilizes. However, when surface textures are implemented in the 270-300\({}^{\circ}\) angular region (Figure 13), the system's dynamic stability initially declines relative to untextured bearings until reaching a threshold depth. Beyond this depth, stability improves temporarily before decreasing again after exceeding a second critical depth value. This behavior reveals that in two-lobe journal bearings, surface texturing within the 270-300\({}^{\circ}\) sector produces a characteristic stability pattern featuring sequential descending, ascending, and descending phases compared to non-textured configurations. Furthermore, the analysis demonstrates that two-lobe journal bearings with properly positioned cubic textures offer superior dynamic stability enhancement compared to cylindrical and semi-ellipsoidal geometries when optimal texture parameters are maintained. Analysis of the results reveals that optimal dimensionless depths for maximizing rotor critical mass differ significantly by texture geometry. Cubic and cylindrical textures achieve peak effectiveness within the 0.4-0.5 dimensionless depth range, while semi-ellipsoidal configurations positioned in the 270-300\({}^{\circ}\) circumferential zone require substantially greater penetration depths to reach comparable performance levels. Figure 13: The effect of the geometric shape of surface textures on the critical mass of the rotor in two-lobe bearings as a function of texture depth. Figure 14 presents how different surface texture geometries (cubic, cylindrical, and semi-ellipsoidal) influence the whirl frequency ratio--a critical dynamic stability parameter--across varying penetration depths in two distinct circumferential regions of a two-lobe journal bearing. An elevated whirling frequency at constant axial rotational velocity indicates intensified orbital motion of the rotor center about its equilibrium position, demonstrating the system's heightened propensity for dynamic instability escalation. This condition progressively leads to critical operational states characterized by surface contact phenomena and accelerated wear mechanisms. The data in Figure 14 show reduced stability in textured rotor-bearing systems compared to non-textured configurations when surface modifications are implemented within the 300-330\({}^{\circ}\) circumferential range. This destabilization intensifies with greater texture penetration depths, correlating with elevated whirl frequency ratios in the bearing clearance. For textures positioned in the 270-300\({}^{\circ}\) sector, system stability initially decreases, then recovers with increasing texture depth. The analysis further reveals that cubic textures exert the strongest influence on stability modification, enhancing the stable operational range while amplifying instability in critical regimes, followed sequentially by cylindrical and semi-ellipsoidal geometries.