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Figures 1 and 2 show stress wave energy plots, called Stress Wave Operating Histories, from sensors placed at the same point on two identical podded drives from sister ships. The drives were operated at comparable power, and the stress wave energy they produced was tracked over time. It is easy to see that the two drives exhibit different levels of stress.
The stress wave energy plot in Figure 1 shows a steady stress wave energy trend that actually decreases over the seven hour period of measurement. The dispersion of values around the trend line is relatively low, and the component appears to be in good operating health. Figure 2, from the sister ship’s drive, shows much higher levels of stress wave energy and an unmistakable upward trend over an eighteen-hour assessment period. In fact, because this data was taken right after the initial sensor installation, the amplification levels had not yet been optimized. The stress wave energy levels from the second drive were clipped at their peak values and even higher than displayed in Figure 2. The higher levels of stress wave energy in Figure 2 are only part of the story. While the plot shows that the drive is clearly less healthy than the one in Figure 1, it is still operating at acceptable levels of stress. Stress Wave Operating Histories, once plotted against health-indicating color zones, allow a ship’s engineers to monitor drive health and accurately predict when it will reach the red zone, the point where catastrophic failure is imminent. Maintenance can then be scheduled at the optimum point, before the occurrence of failure or secondary damage to other components. |
