## 4 Experimental Validation
### Comparison of Pressure Drop in Conformity with Impact Energy under Off-State
Because the plastic-viscosity model used in the mathematical modeling is constructed based on the measurement data of the MR viscometer, the error level is generally uniform in the low-stroke velocity interval of 0.5 m/s or less. In other words, the design formula for the general MR damper considering only the major loss may be used within an error range of 15% or less in the application utilized in the experiment under the stroke velocity of 0.5 m/s. The maximum pressure drop and the damping force at the maximum compression velocity are compared between the experimental results and the pressure drop models. The RMS of the maximum pressure drop error and relative error are calculated and compared. For the \(\Delta P_{total}\) model at the stroke velocity of 0.5 m/s, the RMS values for the error and relative error with the experimental data are 15.49 kPa and 4.104%, respectively, and for the \(\Delta P_{maj}\) model they are 54.51 kPa and 14.44%, respectively. Values are 35.13 kPa, 4.997%, 173.1 kPa, and 24.62% in sequence in Figure 7b; 50.79 kPa, 2.412%, 1011 kPa, and 48.01% in sequence in Figure 7d; and 426.6 kPa, 12.41%, 2.032 kPa, and 59.12% in sequence in Figure 7f. Therefore, it is necessary to consider the minor loss as the maximum stroke velocity increases in order to reduce the error. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Dissipated Energy**} & \multicolumn{4}{c}{**Pressure Drop**} \\ \cline{2-10}
**Impact Energy (J)** & \multirow{2}{*}{**Experiment**} & \(\Delta\)**P\(-\)\(\hat{s}\) Model** & **Relative Error** & \multicolumn{2}{c}{**RMS Error**} & \multicolumn{2}{c}{**RMS Relative Error**} \\  & & **(J)** & & **(\%)** & **(kPa)** & \multicolumn{2}{c}{**(\%)**} \\ \cline{3-10}  & & \(\Delta\)**P\({}_{total}\)** & \(\Delta\)**P\({}_{maj}\)** & \(\Delta\)**P\({}_{total}\)** & \(\Delta\)**P\({}_{maj}\)** & \(\Delta\)**P\({}_{total}\)** & \(\Delta\)**P\({}_{maj}\)** & \(\Delta\)**P\({}_{total}\)** & \(\Delta\)**P\({}_{maj}\)** \\ \hline
456.7 & 276.6 & 263.5 & 200.6 & 4.748 & 27.46 & 16.72 & 109.2 & 5.650 & 19.37 \\
937.5 & 737.2 & 672.5 & 406.1 & 8.781 & 44.92 & 70.28 & 419.1 & 13.54 & 28.07 \\
1538 & 1339 & 1149 & 621.2 & 14.18 & 53.61 & 189.5 & 735.8 & 11.66 & 31.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dissipated energy in MR shock absorber for impact energy; RMS values of error for model-based and measured pressure data over stroke velocity range of 0.1 m/s or more. Comparison of Pressure Drop and Landing Efficiency in Conformity with Input Current and Fixed Drop Height  
In this section, the response of the MR shock absorber depending on the input current is analyzed experimentally with the impact energy fixed. The input current is applied 10 s before the drop to exclude a time delay with respect to the input current. The impact energy during touchdown is the same at 1538 J. Figure 8 presents the internal pressure drop of the MR shock absorber in conformity with the input current for the stroke displacement and velocity. As in the case of Figure 7, \(\Delta P_{total}\) and \(\Delta P_{maj}\) on the legend of Figure 8 are the pressure drop calculated for the estimated stroke velocity. 'Experiment' on the legend is the pressure drop measured through the pressure sensors during the drop test. When the impact energy is constant, the pressure drop in all stroke displacement ranges of both the \(\Delta P_{total}\) and \(\Delta P_{maj}\) models increases as the input current increases. As shown in Figure 8a,c,e, the maximum stroke displacement decreases as the input current increases due to the energy dissipated by the additional pressure drop generated by the yield stress. The dissipated energy is calculated in Table 3 for comparison with the input current. As the input current increases, the dissipated energy for the measured data and the \(\Delta P_{total}\) model does not change significantly. Because the impact energy does not change, the potential and kinetic energies do not change, and the dissipated energy also does not.