# Prof. Yu's Research Group in the Cloud

## Forum

### VABS Beam Coordinate System

1. I have a question regarding the VABS beam coordinate system.

To quote the 2021 VABS manual, "First, VABS uses a right hand system, the beam coordinate system, denoted as x1; x2 and x3, with x1 as the beam axis and x2 and x3 as the local Cartesian coordinates of the cross section, see Figure 1 for a beam with an arbitrary cross section. Usually, for rotor blades, x1 is along the direction of the span and points to the tip, x2 is along the direction of the trailing edge to the leading-edge of the airfoil and points to the direction of the leading edge, and x3 points upward so that x1; x2; x3 form a right-hand system."

However when I define an airfoil in a similar manner to PreVABS example "airfoil", with the normalized coordinates of the leading edge at 0,0, trailing edge at 1,0, my eventual VABS coordinate system is not that described in the manual. Rather I have x1 along the direction of the span and points towards the root, x2 along the direction of the the trailing edge to the leading edge of the airfoil and points to the direction of the trailing edge, and x3 pointing upward so that x1; x2; x3 form a right-hand system

I have delivered a set of VABS properties to a rotordynamics engineer on my team, and requested that the VABS models be modified such that the coordinate system is the same as what is used in RCAS, which is the same as what is described in the VABS manual (x1 towards tip, x2 towards leading edge, x3 up).

How would  you recommend modifiying the VABS file to achieve this? Is the only way to invert the normalized coordinates of the airfoil so that the leading edge is at 0,0 and the trailing edge is at -1,0? Or is there an easier/better way?

1. If you are using the prevabs with version lower than 1.5, then you need to manually change the airfoil data file to flip it.

A recent update of prevabs can make this easier. You can flip the airfoil through an option in the input file. Another benefit is that you do not need to label the airfoil points anymore.

The code can be downloaded here: https://github.com/wenbinyugroup/ivabs/releases. PreVABS is now released together with an integrated tool iVABS. An example is also attached to show how to use this new feature.

1. Thanks Su, I appreciate the help.

Is it possible to keep getting preVABS installations for versions 1.5 and beyond that are not integrated with iVABS? I currently don't have the need for the integrated Dakota/RCAS iVABS functionality, but I definitely would like to have the latest and greatest version of preVABS.

Thanks!