## 4 Results and Discussions
### PVEH Performance  
The frequency, force and displacement value for each wind speed and the load resistance applied is used to obtain the voltage and power performance when the model is under the influence of vortex induced vibration through experimental and simulation. The range of frequency used in both experiment and simulation is from 20 to 100 Hz which is within the frequency range of the first natural frequency. The second natural frequency of 480 Hz is far away and required higher wind velocity  
Figure 19: Deflection contour of model (**a**) 19 m/s isometric (**b**) 25 m/s isometric (**c**) 19 m/s top (**d**) 25 m/s top.  
that is hardly achievable in applications even with forced wind devices. In order to obtain the highest power output for each individual wind speed, the optimum resistance load is obtained from impedance analyzer as shown in Figure 20. For higher wind speeds, (i.e., higher vibrating frequency) the resultant optimum resistant load decreases until a local minimum at-resonant frequency, however after passing that point the resistance increases to a local maximum before going down again. The voltage generated by the PVEH plate in respective cases is then obtained through both electromechanical FSI simulation and experimental procedures. A graph of both wind speed and vibrational frequency against voltage is plotted in Figure 21a,b indicates that the pattern of both experimental and simulated result has the highest voltage generated is at 19 m/s, (i.e., 75.758 Hz). The result from experimental is 10.85 V or equivalent to 7.758 V lower than the results generated from simulation which is 18.608 V.  
Figure 21: _Cont._  
Figure 20: Graph of Optimal Resistance against Frequency obtained from Impedance Analyzer.  
Implementing Equation (19), and combining both the optimal load resistance and voltage results obtained above, the optimum output power at each wind speed is generated. By plotting output power against wind speed or frequency as shown in Figure 22, the highest optimum power generated in simulation is recorded at 12.038 mW at wind speed of 19 m/s, (i.e., 75.758 Hz) due to matched vortex frequency and natural frequency. The experimental results show a higher output power of 15.584 mW, with an increment of 22.7%.  
Figure 21: Voltage against (**a**) wind speed (**b**) frequency.  
Figure 22: _Cont._  
Normalized power--also known as the average power per unit volume--and acceleration at each respective frequency is computed from the optimum power value above and is shown in Figure 23. The experimental result shows that the maximum normalized power is recorded at a value of 13.439 mW/cm\({}^{3}\)g\({}^{2}\) under the wind speed of 19 m/s, (i.e., 75.758 Hz) while the simulated result shows the highest normalized power of 10.595 mW/cm\({}^{3}\)g\({}^{2}\) at same wind speed of 19 m/s, which gives a difference of 21.16% between experiment and simulation.  
Figure 23: Cont.  
Figure 22: Optimum power against (**a**) wind speed (**b**) frequency.  
The difference in output voltage, output power and normalized power results between experiment and simulation is probably due to the variation in modeling and the definition of the boundary conditions of the coupled bluff splitter body and PVEH plate in the simulation environment. As the model in simulation is modeled using a designated condition, while during experimental studies slight changes such as bonding of piezoelectric material and brass being ignored, the clamping of the structural model and resulting vibrational pattern have caused differences in data. The modal analysis result in Section 4.1 also discussed the difference between 2 models in which the actual PVEH plate has a higher natural frequency of 80 Hz. This has an effect on the difference in output power obtained between simulation and experimental results.