## 3 Results and Discussion  
Figure 6 presents both measured and simulated pitch angles of the assembly movement for the driving speeds of 10 km h\({}^{-1}\) and 12 km h\({}^{-1}\). Three different cases are highlighted, i.e., when the MR damper was supplied with 0.3 A, 0.5 A, and 0.7 A. For the same current input levels applied on the MR damper, i.e., 0.3 A, 0.5 A, and 0.7 A, both measured and simulated damper forces for the driving speeds of 10 km h\({}^{-1}\) and 12 km h\({}^{-1}\) are shown in Figure 7.  
The results of the correlation, in terms of the RMSE, RMSD and correlation coefficient, which were calculated using Equations (9)-(11), respectively, are given in Table 1.  
The analyses of the RMSE percentage and RMSD showed good agreement between the simulated and the measured outputs. The average values of the RMSE and the RMSD for the pitch angle at the speed of 10 km h\({}^{-1}\) were equal to around 10% and 0.4 deg, respectively. These figures were below 8% and around 0.5 deg for the speed of 12 km h\({}^{-1}\). Based on the above a high correlation coefficient was  
Figure 5: The measured vertical forces at the speed of (**a**–**c**) 10 km h\({}^{-1}\) and (**d**–**f**) 12 km h\({}^{-1}\), when the MR damper was supplied with 0.3 A, 0.5 A, and 0.7 A.  
determined with an average value of 0.96 and 0.97 for the traveling speed of 10 km h\({}^{-1}\) and 12 km h\({}^{-1}\), respectively. The correlation analyses of the damper forces indicated slightly different results, in terms of a higher RMSE percentage and RMSD value, and smaller correlation coefficient compared to the ones resulted from the pitch angles. The average value of the RMSE percentage was 15% and 13% for the operation speed of 10 km h\({}^{-1}\) and 12 km h\({}^{-1}\), respectively. The average of the RMSD, indicated a value of 1.2 N at the speed of 10 km h\({}^{-1}\) and 1.3 N at the speed of 12 km h\({}^{-1}\). Consequently, the higher error resulted in a lower correlation coefficient with an average value of around 0.7 and 0.69 for these speeds. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Speed**} & \multicolumn{6}{c}{**10 km h\({}^{-1}\)**} & \multicolumn{6}{c}{**12 km h\({}^{-1}\)**} \\ \hline
**Parameter** & \multicolumn{2}{c}{**Pitch**} & \multicolumn{6}{c}{**Force**} & \multicolumn{6}{c}{**Pitch**} & \multicolumn{6}{c}{**Force**} \\ \hline Current [A] & 0.3 & 0.5 & 0.7 & 0.3 & 0.5 & 0.7 & 0.3 & 0.5 & 0.7 & 0.3 & 0.5 & 0.7 \\ RMSE [\%] & 11.8 & 8.6 & 9.6 & 12.3 & 14.8 & 16.2 & 6.9 & 6.7 & 7.1 & 11.2 & 13.6 & 13.7 \\ RMSD & 0.35 & 0.52 & 0.34 & 0.98 & 1.03 & 1.69 & 0.60 & 0.49 & 0.35 & 1.52 & 0.98 & 1.38 \\ CorrCoef & 0.95 & 0.987 & 0.97 & 0.72 & 0.67 & 0.73 & 0.984 & 0.97 & 0.964 & 0.65 & 0.72 & 0.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Root-mean-squared-error (RMSE) in percentage, root-mean-squared-deviation (RMSD) and correlation coefficient. Figure 6: The measured and simulated pitch angle of the assembly movements at the speed of (**a–c**) 10 km h\({}^{-1}\) and (**d–f**) 12 km h\({}^{-1}\), when the MR damper was supplied with 0.3 A, 0.5 A and 0.7 A. Since the correlation analyses in the time domain indicated lower agreement between the measured and the simulated damper forces, a correlation was carried out based on the coherence analyses in the frequency domain (Equation (12)). Figures 8 and 9 present the frequency content of the measured and the simulated damper forces, for the traveling speed of 10 km h\({}^{-1}\) and 12 km h\({}^{-1}\), respectively, together with the corresponding coherence, with current inputs of 0.3 A, 0.5 A, and 0.7 A applied on the MR damper. Despite the fact that there was a wide range of wavelengths of the damper forces in the time domain, which resulted in lower correlation, the analyses of their frequency content showed good agreement according to the resulted coherence values. The resulting coherence values were above 0.96 at the speed of 10 km h\({}^{-1}\) for all the current inputs applied on the MR damper.