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50 6.0 WHEEL AND RAIL PROFILES Wheel and rail profile shapes can have a significant effect on vehicle dynamics and ride quality. Both wheel and rail profiles were measured. Rail profiles were taken on tangent and curved track. Profiles were also taken in places a track maintenance issue was identified by DART. Figure 43 shows both wheel and rail profiles. This information was used for input to the NUCARS simulations. Figure 44 shows the wheel on a curved rail profile. The wheel and rail profiles are very conformal, which is a normal wear condition that may lead to high contact stresses. Figure 43. Wheel Profile Contacting Tangent Rail Profile Figure 44. Wheel Profile Contacting Curved Rail Profile 7.0 NUCARS MODELING A NUCARS model was built to represent the DART SLRV, using design data updated by the measured characteristics. The model includes a detailed representation of the articulation between the carbodies and a full nonlinear representation of the air suspension, including the effects of damping due to air flow in the orifices between the reservoirs and air bags.7,8 7 Oda, N. and S Nishimura. 1970. âVibration of Air Suspension Bogies and Their Design.â Bulletin of the JSME Vol. 13, No. 55. The measured track geometry was used as input to the model. 8 Berg, Mats. 1999. âA Three-Dimensional Airspring Model with Friction and Orifice Damping.â Vehicle System Dynamics Supplement 33, pp. 528-539.
51 A simulation of the same conditions as the ride quality test was done to determine if the model accurately predicted the vehicle performance. Figure 45 shows a plot of the actual test data and modeling results for the section of track between Cedars and 8th Figure 46 shows the vertical accelerations of the test and the model. The model accurately predicted the trend of the acceleration, but under predicted the amplitude. & Corinth stations. The plot shows data collected on the leading end of the vehicle. The accelerometer was placed on the floor under the operatorâs seat. In the NUCARS model, representative wheel and rail profiles were used. The NUCARS model predicted the same general trend as the actual ride quality data. The model showed the yaw response subsided more quickly than the test data. The model also under predicted the lateral acceleration amplitude in this area. Figure 47 shows the frequency content of the model and test data where yaw response/hunting occurred. Both the model and the test had a response at 1 Hz. This is a result of the 1 Hz frequency content in the lateral alignment. However, the model did not have the frequency response of 1.63 Hz. The difference between the model and the test data may be due to a number of issues that will require further investigation. In the model, representative rail profiles were used in the curve and tangent. Wheel/rail interface issues may contribute to the response seen in the test. It will be necessary to use different rail profiles to determine the effect of the wheel/rail interface. In the carbody resonance test, the u-shaped yaw mode was not excited. It is evident in the ride quality test that it was excited. It will be important to review the model and update the parameters to assure the correct frequency can be simulated in the eigenvalue analysis. Figure 45. Measured Lateral Accelerations Compared to Predicted Lateral Accelerations
52 Figure 46. Measured Vertical Accelerations Compared with Predicted Vertical Accelerations Figure 47. Measured Frequency Content Compared with Predicted Frequency Content
