Measuring the torsional natural frequency of an aeroelastic circular cylinder using accelerometers is a feasible approach. To do this, you'll need to follow a specific procedure that involves exciting the cylinder, measuring its response, and analyzing the data. Here's a step-by-step guide:

1. Instrumentation:

• First, make sure you have the necessary equipment, including the accelerometer (PCB Model 352C65 or similar), data acquisition system, and a way to securely mount the accelerometer to the cylinder.

2. Mounting the Accelerometer:

• Mount the accelerometer to the cylinder at the location where you want to measure the torsional motion. Ensure that it is securely attached and properly aligned with the axis of rotation.

3. Excitation:

• To measure the torsional natural frequency, you need to excite the cylinder's torsional motion. This can be done by applying a known torque or moment to the cylinder. You can use a torsional motor or a controlled mechanical excitation system for this purpose.

4. Data Acquisition:

• Connect the accelerometer to a data acquisition system capable of recording the accelerometer's output signals. Ensure that the data acquisition system is properly calibrated.

5. Excitation and Data Collection:

• Start the excitation system and apply a sinusoidal or harmonic excitation to the cylinder at a range of frequencies. Sweep through a range of frequencies that you expect the torsional natural frequency to be within.

6. Measure the Response:

• Record the accelerometer's output signals as you sweep through the frequency range. The accelerometer will measure the acceleration response of the cylinder to the excitation.

7. Frequency Analysis:

• Analyze the recorded data using a Fourier Transform or a similar frequency analysis technique to convert the time-domain signals into the frequency domain.
• Look for peaks in the frequency spectrum. The peak corresponding to the highest amplitude will indicate the torsional natural frequency of the cylinder.

8. Data Interpretation:

• The frequency at which you observe the peak in the spectrum represents the torsional natural frequency of the cylinder.

9. Validation and Repeatability:

• Perform multiple measurements and ensure repeatability to obtain a more accurate estimate of the torsional natural frequency.
• Validate your results by comparing them with analytical or numerical predictions if available.

10. Post-Processing:

• Depending on your specific research or engineering application, you may need to perform further data processing and analysis to obtain additional insights into the cylinder's behavior, such as damping ratios and mode shapes.

Remember that the accuracy of your measurement will depend on various factors, including the quality of your instrumentation, the excitation system's control, and the accuracy of your data analysis techniques. Additionally, it's important to ensure the safety of the experimental setup and adhere to any safety guidelines relevant to your specific testing environment.