# Performance Prediction of Composite Marine Propeller in Non-Cavitating and Cavitating Flow
## 2 Methodology and Results
### Coupled CFD-FEM FSI Analysis
#### 2.4.1 Non-Cavitating Flow  
The pitch distributions of models 1 and 5 in a non-cavitating flow, which vary as the blade rotates at specific radial positions (\(r/R\) = 0.630, 0.729, 0.816, 0.918, 0.965), are shown in Figures 8 and 9, respectively. Deformed pitch distributions were compared with the fixed pitch values of a rigid (pre-deformed) propeller at specific radial positions. For model 1, pitch distributions at all radial positions increased compared to the rigid propeller. Additionally, the pitch difference between the rigid and model 1 propellers was prominent at the tip of the propeller. Conversely, for model 5, the pitch distributions at all radial positions decreased compared to the original value. It appears that the stacking angle was closely related to the direction of deformation.  
Additionally, the elastic bending-twisting coupling effect of orthotropic composites especially affected the change of pitch [22]. The influence of wake was insignificant because  
Figure 8: Pitch distribution changes of model 1 in the non-cavitating flow: (**a**) pitch distribution change according to the blade position, (**b**) radial chart of pitch distribution of composite propeller.  
Figure 9: Pitch distribution changes of model 5 in the non-cavitating flow: (**a**) pitch distribution change according to the blade position, (**b**) radial chart of pitch distribution of composite propeller.  
the submerged body was symmetrical [23], as shown in the radial charts in Figures 7 and 8. However, appendages as shown in the right picture in Figure 1, including a conning tower and 4 control planes, had an effect on the local deformation according to the blade position in the radial direction.  
The Ffowcs Williams-Hawkings (FW-H) model is used here, which is the generalized form of [PERSON]'s acoustic analogy [24; 25; 26]. The pressure fluctuations in the near field around the propeller were calculated in STAR-CCM+. The SPL at a specific position (receiver point) was compared for rigid and composite propellers and calculated by integrating the fluctuating pressure received from the propeller blade, defined as an impermeable surface. Farassat 1A is an integral form of the FW-H equation that omits the volume source term [25].  
The total acoustic pressure (\(P\)) can be expressed as:  
\[P=P_{T}(x,t)+P_{L}(x,t) \tag{4}\]  
where \(x\), \(t\), \(P_{T}\), and \(P_{L}\) are the position and time of the receiver, thickness noise, and loading noise term, respectively. In this study, the position of the receiver point (1.0, 1.1, \(-\)0.43) was based on the center of the propeller (0, 0, 0).  
The sound pressure levels of rigid and composite propellers in the non-cavitating flow were compared, as shown in Figures 10 and 11. Although the composite propellers (models 1 and 5) were deformed in opposite directions, the noise characteristics of rigid and composite propellers did not demonstrate significant differences in the non-cavitating flow based on the first blade passing frequency (BPF). Additionally, the deformation of the composite propeller itself did not significantly affect the underwater noise characteristics.