## 3 Vibration Measurement and Analysis
### Operational Deflection Shape (ODS)  
In contrast to EMA, ODS operates by animating the dynamic behavior of the measurement system and does not apply a corrected input (force, N). Instead, it receives and analyzes the responses via the input values derived from the operating conditions of the system. This technique visualizes and evaluates dynamic rigidity. Before conducting the ODS actual vehicle test, the following are needed to analyze the vibration phenomenon of the sunroof while driving: the driving conditions, including the condition of the sunroof; the irregularity of the driving surface; and the speed at which the vehicle is being driven. As the mode shape and clear natural frequency of the sunroof were analyzed in the fully open state during the EMA actual vehicle test, the aim was to replicate those conditions during the ODS actual vehicle test. This was to enable a more precise comparison of the test data. Second, the input value of the vibration transmitted to the sunroof system via the vehicle body is negligible when driving on a general asphalt road because of the roughness of the driving surface. Consequently, the driving vibration characteristics of the sunroof system may not be displayed clearly. Therefore, an uneven road surface was chosen to conduct the test. In conclusion, considering the conditions above of a fully open sunroof and a rough road surface, driving at high velocities under such circumstances endangers the safety and condition of the vehicle and its occupant and constitutes a standard driving condition. If this is not the case, the driving disturbance of the sunroof is determined by maintaining a constant speed of 30, 40, or 50 km/h. Nine accelerometers affixed to the sunroof glass were used to identify a vibration that accurately represents the sunroof vibration and to determine the natural frequency by measuring driving vibration originating from the sunroof glass during vehicle operation. Regarding the representative vibration, the objective was to identify a location where the sunroof glass exhibited a distinct natural frequency with a significant vibration magnitude owing to the vibrations that transpire during vehicle operation. The amplitude in the Z-direction of the accelerometer affixed to the sunroof glass was assessed to verify this, as shown in Figure 11. The comparison of the vibration sizes (amplitude (RMS)) of the G:5 and G:25 sensors affixed to both ends of the sunroof showed that the former had the largest vibration size. Furthermore, the natural frequency characteristics of the two sensors exhibited a resemblance. Subsequent analysis was undertaken using the G:25 accelerometer, which demonstrated a greater vibration magnitude, as the representative accelerometer for sunroof vibration. First, an analysis of the vibration characteristics of the G:25 accelerometer under driving conditions at a speed of 30 km/h confirmed that the major vibrations occurred at 12.5 Hz, 17.1 Hz, 21.0 Hz, 26.9 Hz, and 29.6 Hz. Second, at 40 km/h, an analysis of the vibration characteristics of the G:25 accelerometer under these driving conditions confirmed that the major vibrations occurred at 15.6 Hz, 22.9 Hz, 27.0 Hz, and 28.9 Hz. Lastly, at  
Figure 10: EMA mode shape of the full open sunroof: (**a**) Mode #1 (15.7 Hz), (**b**) Mode #2 (22.2 Hz), (**c**) Mode #3 (28.5 Hz). The verification of the sunroof glass via EMA revealed the primary vibration frequencies of the data collected while driving at a constant speed of 40 km/h: 15.6 Hz, 22.9 Hz, 27.0 Hz, and 28.9 Hz. This conclusion was reached after comparing the vibration characteristics of the representative accelerometers according to driving speed. The natural frequency band showed the highest degree of similarity to the natural frequencies of 15.724 Hz, 22.245 Hz, and 28.501 Hz.