Explanation:

In a hydrodynamic journal bearing, the stable operating condition is achieved when a sufficient oil film is present between the bearing surfaces to separate them and prevent metal-to-metal contact. When the bearing encounters higher magnitude loads, the oil film may become insufficient, leading to increased friction and potential damage to the bearing surfaces.

To restore stable operating conditions in such a situation, the oil viscosity needs to be increased. Here's why:

1. Importance of oil viscosity:
- Oil viscosity is a measure of its resistance to flow. Higher viscosity oils offer greater resistance to flow, while lower viscosity oils flow more easily.
- In a hydrodynamic journal bearing, the oil film's thickness directly depends on the oil viscosity. Thicker oil films provide better separation between the bearing surfaces, reducing friction and wear.
- When the load on the bearing increases, the oil film is subjected to higher pressures and shear forces. Higher viscosity oils can withstand these forces better, maintaining a thicker and more stable oil film.

2. Effects of increasing oil viscosity:
- Increasing the oil viscosity helps to maintain a thicker oil film, which prevents metal-to-metal contact and reduces friction. This improves the bearing's ability to handle higher loads.
- Higher viscosity oils also exhibit better damping properties, which can help absorb vibrations and shocks caused by the higher magnitude loads. This further enhances the bearing's stability and performance.

3. Considerations:
- While increasing oil viscosity can improve the stability of the hydrodynamic journal bearing, it is essential to ensure that the viscosity increase does not exceed the bearing's design limits. Excessive viscosity can lead to increased power losses, reduced heat dissipation, and potential damage to the bearing surfaces.
- Therefore, the selection of the appropriate oil viscosity should be based on the bearing's design parameters, operating conditions, and load requirements.

In conclusion, to restore stable operating conditions in a hydrodynamic journal bearing when it encounters higher magnitude loads, the oil viscosity should be increased. This increase in viscosity helps to maintain a thicker oil film, which improves separation between the bearing surfaces, reduces friction, and enhances the bearing's ability to handle higher loads.