## 4 Analysis of Experimental Results
### Load Characteristic Analysis
Regarding ice-water-propeller interaction at atmospheric pressure, Figures 7 and 8b depict that there was no ice-propeller milling action during \(t=0\)-0.52 s. However, owing to the combined influence of propeller rotation in water and the blockage effect and proximity effect of ice, the thrust and torque of the propeller changed to approximately \(-500\) N and 15 N\(\cdot\)m, respectively. During gradual ice-propeller milling (\(t=0.52\)-1.08 s), with an increase in time, propeller thrust exhibited a gradually decreasing trend, which was different from the change trend of propeller axial force in air. The main reason was that the directions of the hydrodynamic load and ice milling load on the propeller were different. During ice-propeller milling in air, the back of the blade was compressed by the ice, which produced a positive axial force, as shown in Figure 7. During ice-propeller milling in water, a negative thrust was generated owing to the pressure difference between the face and back of the blade [31], as shown in Figure 7, and the direction of the propeller thrust during the blockage stage. The distributions of the axial force of the ice milling load and thrust of the hydrodynamic load in the propeller blade section are shown in Figure 9. Propeller thrust loss was caused by the combined action of two loads. However, with the passage of time, the propeller torque presented a gradually increasing trend, which indicates that the effects of water and ice on the propeller torque are the same, that is; the presence of water increases the torque of the propeller mixed load. In \(t=1.08\)-3.51 s, the mixed load on the propeller has a stable periodic change, but the propeller thrust is alternatively positive and negative; the negative thrust is the main component, whereas propeller torque is all positive. Figure 9: Load distribution diagram for the four blade sections of the propeller. Regarding ice-water-propeller interaction under the decompression condition (\(\sigma\) = 0.33), shown in Figure 7, it can be concluded that during the entire blockage and milling stage, the variation trend of the mixed load on the propeller with time is similar to that under atmospheric pressure, with the difference that the range of fluctuation of the hydrodynamic load on the propeller is larger in the blockage stage. In the milling stage, the range of fluctuation of the propeller thrust increased in the positive direction and decreased in the negative direction, which indicated that the occurrence of cavitation on the blade surface decreased the thrust of the hydrodynamic load on the propeller [15]. Moreover, the peak value of the propeller torque decreased. The main reason for this decrease was that the back of the blade was covered by cavitation and the drag-lift ratio of the blade increased, which deteriorated hydrodynamic performances of the blade section and consequently that of the propeller. In addition, Figure 8c clearly shows the change in the cavitation shape on the blade surface during ice-water-propeller interaction under the decompression condition. An investigation based on Figure 8c reveals that when there is no milling action between the ice and propeller, the tip vortices near the wake of the propeller in the blocked area do not show spiral characteristics but are disturbed. The tip vortex is sucked onto the previous blade when it enters the blocked area. This is because this area has a significantly lower pressure [22; 32; 33], which results in a sharp explosion of the tip vortices. The sheet cavitation on the blade surface is evident when the blade exits from the blocked region; the sheet cavitation collapses rapidly with the rotation of the blade, and the tip vortex cavitation can only be observed near the tip of the blade. It is verified that the conditions for the formation of sheet cavitation are more severe than those for the tip vortex cavitation, and it is evident that the blockage effect of ice on the blade results in the formation of sheet cavitation.