## 4 Results
### Optimization of the Damping Effect Control Parameters
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**It.** & \multicolumn{2}{c}{**B\({}_{1}\)**} & \multicolumn{2}{c}{**B\({}_{2}\)**} & \multicolumn{2}{c}{**B\({}_{3}\)**} & \multicolumn{2}{c}{**B\({}_{4}\)**} & \multicolumn{2}{c}{**C**} \\ \hline  & **T [s]** & **R** & **T [s]** & **R** & **T [s]** & **R** & **T [s]** & **R** & **T [s]** & **R** \\  & **\(\Delta\)T [s]** & **[\(\upmu\)m]** & \(\Delta\)T [s]** & **[\(\upmu\)m]** & \(\Delta\)T [s]** & **[\(\upmu\)m]** & \(\Delta\)T [s]** & **[\(\upmu\)m]** \\ \hline \multirow{2}{*}{1} & 10.5 & \multirow{2}{*}{575.7} & 10.9 & \multirow{2}{*}{453.3} & 10.9 & \multirow{2}{*}{453.3} & 10.5 & \multirow{2}{*}{398.8} & 10.7 & \multirow{2}{*}{408.4} \\  & 0.2 & & 0.2 & & 0.6 & & 0.6 & & 0.4 & \\ \hline \multirow{2}{*}{2} & 10.3 & \multirow{2}{*}{395.5} & 10.7 & \multirow{2}{*}{408.4} & 10.7 & \multirow{2}{*}{423.9} & 10.3 & \multirow{2}{*}{398.4} & 10.5 & \multirow{2}{*}{394.8} \\  & 0.4 & & 0.4 & & 0.8 & & 0.8 & & 0.6 & \\ \hline \multirow{2}{*}{3} & 10.4 & \multirow{2}{*}{427.8} & 10.6 & \multirow{2}{*}{401.7} & 10.6 & \multirow{2}{*}{404.2} & 10.4 & \multirow{2}{*}{398.8} & 10.5 & \multirow{2}{*}{394.8} \\  & 0.5 & & 0.5 & & 0.7 & & 0.7 & & 0.6 & \\ \hline \multirow{2}{*}{4} & 10.45 & \multirow{2}{*}{405.0} & 10.55 & \multirow{2}{*}{399.0} & 10.55 & \multirow{2}{*}{400.5} & 10.45 & \multirow{2}{*}{397.0} & 10.5 & \multirow{2}{*}{394.8} \\  & 0.55 & & 0.55 & & 0.65 & & 0.65 & & 0.6 & \\ \hline \multirow{2}{*}{5} & 10.475 & \multirow{2}{*}{399.5} & 10.525 & \multirow{2}{*}{397.0} & 10.525 & \multirow{2}{*}{398.3} & 10.475 & \multirow{2}{*}{395.7} & 10.5 & \multirow{2}{*}{394.8} \\  & 0.575 & & 0.575 & & 0.625 & & 0.625 & & 0.6 & \\ \hline \multirow{2}{*}{6} & 10.4875 & \multirow{2}{*}{396.7} & 10.5125 & \multirow{2}{*}{396.0} & 10.5125 & \multirow{2}{*}{396.8} & 10.4875 & \multirow{2}{*}{395.0} & 10.5 & \multirow{2}{*}{394.8} \\  & 0.5875 & & 0.5875 & & 0.6125 & & 0.6125 & & 0.6 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Iteration process. Figure 14: Time history of the disc center radial displacement (optimized damping). Even if the differences in the maximum amplitude of the disc vibration are very small, it is evident that the phase shift of the excitation effect induced by the disc unbalance has influence on efficiency of the control process. If adequate means of measurements are to be used, it is possible to choose the case (reference case) when the optimum vibration amplitude is minimum and to find the displacements and velocities of the disc vibration (reference kinematic parameters) at the moment when the rotor starts to accelerate and the angular speed (reference angular speed) at the moment when the current decrease begins. Then, in a general case for arbitrary value of the phase shift, if (i) the acceleration starts at the moment when the rotor kinematic parameters (displacements and velocities) are equal to the reference ones, (ii) the current decrease begins when the rotor angular velocity reaches the reference value, and (iii) duration of the current decrease is the same as in the reference case, then the magnitude of the maximum radial displacement of the disc center will be optimal and the same as in the reference case. Figure 16 shows the time histories of displacements of the disc center in the horizontal and vertical directions referred to the case (reference case) when the maximum vibration amplitude of 394 \(\upmu\)m is minimum from all investigated cases (Table 2). The corresponding phase shift of the excitation effect is 5/3 \(\times\)\(\pi\) rad (300\({}^{\circ}\)). The reference values of the displacements in the horizontal and vertical directions, the reference value of the angular speed of the rotor rotation, and duration of the current decrease are \(-\)19.11 \(\upmu\)m, \(-\)156.09 \(\upmu\)m, 170.2 rad/s, and 0.6375 s, respectively. The same analysis was performed for the arbitrary chosen phase shift of 1/2 \(\times\)\(\pi\) rad (90\({}^{\circ}\)).