## 3 Results and Discussion
### Stress Distributions in Every Layer of the FRP Composite Risers  
For each case, there were two significant times, when the maximum displacement occurred and the maximum stresses occurred. Comparing the stresses in the FRP composite layers at these two time points, the maximum stresses in every lamina of FRP composite risers (risers 2 and 3) were obtained and the factor of safety (FS) are presented in Figures 13-15. Here, the factor of safety was defined as allowable strength/stress. In composite riser design, the factor of safety was utilised to verify the stress failure. In this paper, the maximum stress failure criterion [47] considered failures in the fiber direction, transverse  
Figure 12: Maximum von Mises stresses of the risers (**a**) riser 1 at 72.6 s with 0.36 m/s, (**b**) riser 2 at 30.6 s with 0.36 m/s, (**c**) riser 3 at 24.6 s with 0.36 m/s, (**d**) riser 1 at 71.0 s with 1.22 m/s, (**e**) riser 2 at 52.6 s with 1.22 m/s, (**f**) riser 3 at 68.0 s with 1.22 m/s, (**g**) riser 1 at 46.6 s with 2.13 m/s, (**h**) riser 2 at 39.8 s with 2.13 m/s, (**i**) riser 3 at 54.4 s with 2.13 m/s. direction and in-plane shear separately for all composite layers. The minimum FS required was 1.53 for composite layers and 1.68 for titanium liner [46]. For cases with velocity of 0.36 m/s for riser 2, the maximum von Mises stress in the titanium liner is 3 MPa and FS = 293. Figure (a)a,b, respectively, show the minimum FSs in the fiber and transverse directions for all the layers of riser 2. Here, it was noted that for the riser geometry with only orthotropic reinforcements (riser 2), the shear stresses in all layers were small enough to be neglected. The minimum FS in the fiber direction was 493 (layer 20 in Figure (a)a) while that in the transverse direction is 168 (layers 21 in Figure (b)b). It is evident that, for riser 2 with 0.36 m/s, the in-plane transverse stresses were the most critical stresses and they were far away from the failure stresses. For cases with velocity of 0.36 m/s for riser 3, the maximum von Mises stress in the titanium liner was 5.2 MPa and FS = 169. Figure (c)c-e, respectively, show the minimum FSs in the fiber, transverse and shear directions for all the layers of riser 3. The minimum FS in the fiber direction were 304 (layer 3 in Figure (c)c), 73.7 (layer 17 in Figure (d)d in the transverse direction and 273 in shear direction (layer 13 in Figure (e)e). It was evident that, for riser 3 with 0.36 m/s, the in-plane transverse stresses were the most critical stresses and much smaller than those in riser 2. They were, however, far away from the failure stresses. Comparing the FS (s) in riser 2 and riser 3, it was obvious that the tailor-designed composite riser 3 could take advantage of the fiber strength more efficiently. Figure 13: _Cont._  
For cases with velocity of 1.22 m/s for riser 2, the maximum von Mises stress in the titanium liner was 11.2 MPa and FS = 78. Figure 14a,b, respectively, show the minimum FSs in the fiber and transverse directions for all the layers of riser 2. Here, it was noted that for the riser geometry with only orthotropic reinforcements (riser 2), the shear stresses in all layers were small enough to be neglected. The minimum FS in the fiber direction was 120 (layer 20 in Figure 14a) while that in the transverse direction was 43.7 (layers 21 in Figure 14b). It was evident that, for riser 2 with 1.22 m/s, the in-plane transverse stresses were the most critical stresses and they were far away from the failure stresses. For cases with velocity of 1.22 m/s for riser 3, the maximum von Mises stress in the titanium liner was 22.4 MPa and FS = 39. Figure 14c-e, respectively, show the minimum FSs in the fiber, transverse and shear directions for all the layers of riser 3. The minimum FS in the fiber direction were 71.4 (layer 3 in Figure 14c), 24.2 (layers 17 in Figure 14d) in the transverse direction and 60.3 in the shear direction (layer 13 in Figure 14e).