Radial accelerometer measuring vertical vibration

[PEC MENTOR]

I am working with existing accelerometers attached to the shell of a simply supported cylinder. Accelerometers are oriented radially at +/- 45 degrees from horizontal. There is a forced vibration on the cylinder in the vertical and horizontal directions and the cylinder is also exposed to torsion. I don't know the input forced vibration, only the acceleration and velocity measurements I get from these two accelerometers. My ultimate goal is to calculate the centerline displacement of the cylinder from these two accelerometers so I can apply those loads on an FEA model.
With vertical vibration, the vertical displacement is the accelerometer measurement / cos(45deg). With lateral vibration, the lateral dispacement is the accelerometer measurement / sin(45deg). If I have vertical and lateral vibration and then add torsion how do I calculate the vertical and lateral acceleration or velocity of the cylinder centerline. I think the torsion generates a vertical and lateral displacement at the accelerometer, which adds to the accelerometer measurement from the vertical and lateral vibration . I think I have to subtract the displacements due to torsion from the accelerometer measurement to get the centerline motion. Need help to understand if my approach is correct and how to generate the centerline vibration.

 

[eljose79]

your approach to calculating the centerline displacement of the cylinder from the accelerometers is generally correct. However, there are a few things to consider and clarify.

First, it is important to understand that accelerometers measure acceleration, not displacement. Therefore, the measurements you get from the accelerometers are not directly related to the centerline displacement of the cylinder. To calculate the centerline displacement, you will need to integrate the acceleration measurements over time, which will give you velocity, and then integrate the velocity to get displacement.

Secondly, you are correct that torsion will also generate vertical and lateral displacements at the accelerometers. However, these displacements will not be simply added to the accelerometer measurements from vertical and lateral vibrations. This is because the accelerometers are oriented at +/- 45 degrees from horizontal, so the torsion-induced displacements will need to be resolved into vertical and lateral components before they can be added to the accelerometer measurements.

To generate the centerline vibration, you will need to use the equations you mentioned in your post, but instead of using the accelerometer measurements, you will need to use the integrated acceleration values. This will give you the centerline displacement due to vertical and lateral vibrations. Then, you can add the torsion-induced displacements to get the total centerline displacement.

In summary, your approach is generally correct, but it is important to keep in mind that accelerometers measure acceleration and not displacement. You will need to integrate the acceleration measurements to get displacement and resolve torsion-induced displacements before adding them to the accelerometer measurements. Additionally, it may be helpful to consult with an engineer or expert in structural dynamics to ensure the accuracy of your calculations.