## 5 Experimental Tests
### Time Domain Performance Evaluation
#### 5.2.1 Random Road Profile  
The objective of this time domain experimental test was to ascertain the effectiveness of the proposed controllers in reducing the seat vertical acceleration when the virtual vehicle was subject  
Figure 12: Measured seat acceleration transmissibilities of the passive and active systems. to random road inputs at a range of vehicle forward speeds. To this end, a random road profile was generated with five different vehicle speeds (20, 40, 60, 80, and 100 km/h) over a time period of 12 s as shown in Figure 13. To avoid extremely large MAST acceleration inputs at high frequency that could damage the active seat suspension the road roughness was set as \(\Phi(\Omega_{0})=40\times 10^{-6}\) m\({}^{3}\). The measured seat acceleration and seat suspension travel time responses of the active seat suspension with the proposed controllers (A1 to A5), as well as the demand control force are shown in Figures 14-18 parts (a), (b), and (d). It can be clearly observed that all of the proposed controllers perform better than the passive suspension in reducing the seat vertical acceleration with a reasonable seat suspension travel and demand control force. Moreover, the power spectrum densities (PSD) of the active seat suspension using the different proposed controllers (A1 to A5) are compared with the passive seat suspension in Figures 14c, 15c, 16c, 17c and 18c. Generally, the active seat suspension utilising any of these proposed controllers has lower PSD when compared with the passive system over a wide frequency range, especially in the range of 4-8 Hz where humans are most sensitive. However, at a low frequency below 4 Hz, the active seat suspension performs less well, especially controllers A1 and A2 that only use the vehicle suspension feedforward signals. The SEAT factors of the passive and active seat suspensions at a range of vehicle speeds are shown in Figure 19. It can be clearly seen that all the proposed active controllers have SEAT factor values less than the passive, regardless of the vehicle speed. Specifically, the active seat, when using controller A4, provides the best improvement in the SEAT factor, followed by the controller A3, with a percentage improvement of at least 25% at all vehicle speeds, when compared with the passive system. The frequency-weighted RMS seat acceleration is also presented in Figure 19. It is notable that all the proposed active seat suspension controllers provide superior lower frequency-weighted RMS seat acceleration when compared with the passive seat suspension, across the range of vehicle speeds. In addition, at intermediate and high vehicle speeds the passive seat system exceeds the \"not uncomfortable\" range in terms of ride comfort level according to Table 2. In summary, these results prove the capability and the robustness of the active seat suspensions using the controllers A4 and A3. Figure 20 presents the frequency-weighted RMS acceleration of the active and passive seat suspensions with respect to the daily threshold limit values (TLVs), as suggested by ISO-2361-1, over the range of vehicle speeds. It can be seen that the active seat suspension, employing any of the proposed controllers, performs better than the passive system, especially over the human body sensitivity frequency range in which the passive system exceeds the 16 h working daily exposure limit. This indicates that, in a practical application, the active seat suspensions provide a less tiring and potentially safer working environment for drivers working long hours. Figure 13: Random road profile at a vehicle speed of 60 km/h. Figure 16: Time responses and PSD of the passive system and active seat suspension with controller A3. (**a**) Seat acceleration; (**b**) Seat suspension travel; (**c**) PSD of the seat acceleration; (**d**) Output control force. Figure 14: Time responses and PSD of the passive system and active seat suspension with controller A1. (**a**) Seat acceleration; (**b**) Seat suspension travel; (**c**) PSD of the seat acceleration; (**d**) Output control force.