# Hybrid Model-Based Analysis of Underground Articulated Vehicles Steering Characteristics
## 3 Validation of Dynamic Model
### Discussion of Field Test Results  
In order to verify the dynamic model, the results of simulation and field test were compared, and the simulation carried out by MATLAB/Simulink. A region with constant longitudinal velocity and different steering maneuvers was selected for analysis in which the velocity was 3.1 km/h. In addition, the simulation input signal of steering was also the same as the signal in the field test, which is shown in Figure 8. According to the steering signal in Figure 8, steering maneuvers with different amplitudes in left and right directions are included, which can cover the different actual operating conditions. Figure 8: Steering signal of test and simulation. Figure 6: The system configuration of the field test. Figure 7: Route of field test. It should be noted that the error of the steering system is always obtained by constant radius steering (0-360 degree), i.e., stable steering, while the experiment was not processed considering the limitations of the field test site. For the field test conditions in this article, different amplitudes and directions were considered that can represent the dynamic characteristics of the hydraulic steering system. The dynamic characteristics of the steering system are particularly important during the dynamic driving process, therefore, we used the consistent dynamic response results to verify the dynamic model. As the most important information of UAVs, the articulation angle was considered first, and the comparison results are shown in Figure 9. According to the comparison results in Figure 9, the response of the articulation angle for the simulation model and test vehicle is the same under different steering maneuvers, including the process and end of steering. Not only is the steering angle during the steering process the same, but also the final steering angle was the same. The Root Mean Square (RMS) of the error is 0.1 degree. In addition, the detailed information shows that some ripples occurred in the field test. Similarly, the simulation results have the same characteristics. The comparison results of the two steering cylinders' displacements are shown in Figure 10. The result of the simulation is the same as the field test results, except for some errors after steering. The maximum error during the comparison region is 0.01 m. The accuracy is high enough to simulate the steering response considering the errors brought about by the installation of sensors. The results of steering cylinder pressure are shown in Figure 11. During the start stage (0-2.5 s), the pressure is 3 MPa in the field test, but the simulation pressure is the atmosphere pressure of 0.1 MPa. This is because the stage is only the start of the simulation and there is no load in the steering system according to the results in Figure 11a,b. The pressure peak values of the simulation and field test  
Figure 10: Comparing results of displacements of steering cylinders. Figure 9: Comparing results of articulation angle. appear at the same time around 15 s and the approximate value is 14 MPa. In addition, the trends and values of pressure are almost identical according to the detailed comparison results in Figure 11c. Firstly, the trends are the same during the steering process. However, the trends are obviously different after steering. The test results show that the pressure fluctuates repeatedly, and the attenuation is not obvious. Although simulation data show the same fluctuation, the attenuation is faster. In addition to the above differences, the system average pressure is almost the same after the fluctuation. As is well known, the attenuation of vibration is directly related to the damping of the system. According to the above results, the main difference between the simulation model and target vehicle is the numerical difference of damping.