**7. Results**

The search of the optimal combination of the Kp and Kspring parameter values for the maximization of the power generated by the harvester system through the implementation of a JADE algorithm has been proposed in Section 6. The results obtained for each one of the analyzed scenarios are represented in Tables 4 and 5 for *D* = 10 mm and *D* = 20 mm, respectively. The last column of each table represents the increment of the power ΔPower (%) generated by the U-shape underwater energy harvester with respect to the traditional underwater harvester based on a cylindrical oscillating body.

**Table 4.** Results of the JADE optimization algorithm for the cylinder and U-shaped oscillating bodies with *D* = 10 mm.


**Table 5.** Results of the JADE optimization algorithm for the cylinder and U-shaped oscillating bodies with *D* = 20 mm.


The power generated by the harvesting system is considerably improved with the application of the proposed U-shaped geometry, especially for cases at higher Reynolds numbers, as observed in Tables 4 and 5. In general, the power achieved by the U-shaped geometry is larger than the cylinder for both diameters considered. However, for the lowest Reynolds number studied, Re = 3000 and *D* = 10 mm, the power achieved by the U-shaped based harvester is lower than the one obtained by the cylinder. The largest power output is achieved at Re = 12,000 and *D* = 10 mm for both geometries. The cylinder oscillating body reaches a power of 1848.3 μW, and the U-shape geometry gets the maximum power with a value of 5321.7 μW, as shown in Table 4. Nevertheless, it must be taken into account that the water velocity associated at this high Reynolds number is difficult to obtain in the water pipes considered in this study from 2 to 5 inches of diameter. A graphical comparison of the optimal power generated by the analyzed four different harvester geometries for different Reynolds number values is presented in Figure 7. The present U-shaped harvester with an oscillating body size of *D* = 10 mm generates up to 5.2 mW at Re = 12,000. This result shows a significant improvement from the literature; please see the model presented on a review on mechanisms for piezoelectric-based energy harvesters for an underwater harvester [17], which is able to produce merely 0.9 mW at the same Re number.

**Figure 7.** Comparison of the optimal power generated by the proposed four different energy harvesting system geometries.

Similarly, a comparison of the optimal values of the Kp and Kspring parameters for each one of the four analyzed harvester geometries and for different Reynolds number values is presented in Figure 8.

**Figure 8.** Comparison of the optimal values of the Kp and Kspring parameters for the proposed four different energy harvesting system geometries.

There are slight differences in the optimal value of the Kp and Kspring parameters, especially for the geometries with *D* = 10 mm. This could be translated in a non-optimal performance of the system and in a reduction in the power generation of the harvesting system, with its subsequent decrease of energy yield. These increased power generation of the harvesting system and the differences in the optimal values of the Kp and Kspring parameters prove the correct performance of the proposed harvester geometry and the JADE optimization algorithm presented in this paper.
