Q: I am trying to use the VABS program, however when I drag the data file into the executable file, the window disappears and no output is created.
A: Some file (or a *.ech file) will be generated in the folder and it will tell you the error message. Most possibly VABS cannot recognize the file you just dragged into. The safest way is to use the Command line and run VABSIII inputfile_name.
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Q: How to interpret VABS results?
A: VABS results are given with respect to the coordinate system the user chooses to create the mesh. The origin of the coordinate system and the orientation of the axes will affect the VABS calculated results.
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Q: Can VABS provide the values with respect to neutral axes and principal bending axes?
A: VABS can calculate the location of neutral axes and orientation of principal bending axes and shear center locations. You can transform the calculated sectional properties into any coordinate system you like. The formulas to transform the 6x6 mass and stiffness matrices are given in our wind turbine tools assessment paper. If you really think it is more convenient to compute it within VABS, please let us know and we can add this functionality into the code.
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Q: Are there any interfaces between VABS and ANSYS, and some other FEA preprocessors?
A: The interface between VABS and ANSYS has been developed under the sponsorship of Rotor Industry Technology Association at Georgia Tech. You might also want to ask on the google group to see whether other VABS users already developed the interfaces you need. If you have other specific FEA package and want to interface with VABS, please let us know and we can try to accomondate the need.
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Q: What are the use of *.v0, *.V1s, *.V1 files?
A: These three files are intermediate files and only used by VABS. They store the warping functions corresponding to each node for difference corrections according to an optimized numbering scheme. A 4X4 Stiffness matrix are also output at the end of *.v0 and *.V1 files. A 6X6 flexibility matrix is output at the end of *.V1s file. They are not supposed to be used by common users. If you want the warping of the section, it is better to use the VABS recovery option.
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Q: Regarding the recovery, how do I get displacement and direction cosine matrix terms required for classical beam theory and how do I get other derivative terms required as an input for Timoshenko theory and what are they? I only have forces and moment in three directions.
A: If you are interested to recover the 3D displacements over the cross section, you need to get the 1D displacement and direction cosine matrix term of the reference axis from the 1D beam analysis. For their definitions, please refer to our paper in Journal of American Helicopter Society. For Timoshenko beam, f_i and m_i are the distributed 1D applied load and inertial loads as defined in Hodges 1990's paper (Mixed formulation of moving beams). Because they are known as functions of x_1, the beam axis, you should be able to get the derivatives.
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Q: How to obtain the nodal ply angles for each element?
A: If the ply are not very curved, the nodal ply angles can just be the element ply angles. The element ply angles is the same as the ply where the element is. Regarding convention, you can read conventions.ppt. The nodal ply angle is the slope of the ply at the location given by the nodal coordinates. If you know the mathematical representation of the curve, you can calculate it by hand. If you have an arbitrary curve create using a CAD software, you should be able to write some macros to ask the software to calculate the value for you.
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Q: According to VABS manual, shear correction factors can be calculated for isotropic sections. Can it be for composite sections?
A: Shear correction factor has a clear definition for isotropic materials. However, for composite beams, it is recommended to use the shear stiffness from the stiffness matrix directly. If there is indeed such a need, you need to calculate some other value for transverse stiffness and let it divided by the value from VABS.
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Q: Is it possible to extract bending, axial or torsional stiffness values from the stiffness matrix? And the last one, could you verify that in VABS unit system that is used does not affect the results? When we use slug for mass and feet for length and lbf for force, we get the related values in terms of them, do not we?
A: It is in principle possible to extract individual stiffness terms, usually just the diagonal terms. However, you will lose the couplings between the different deformation modes. It should be fairly easy to generalize your beam analysis code to take VABS fully populated stiffness matrix as inputs. ANSYS already made their changes. Also, you can use GEBT, a general-purpose beam analysis code designed to be completely compatible with VABS. Regarding units, as long as you're consistent with the units, the stiffness matrix should be consistent in that set of units.
------------------------------------------------------------------------Q: How to let the computer run a large number of VABS analyses for many cross-sections.
A: Name all your cross-section input files with an extension *.vab, put them in the same folder as the VABS executable. Then use a batch file containing "for %%f in (*.vab) do VABSIII %%f" to run all the analyses.
------------------------------------------------------------------------Q: Why the stress recovered by VABS is very different from the analytical formulas for simple isotropic beams?
A: VABS's original recovery was based on geometrical nonlinear analysis. If you have significant deformation such as a strain significantly larger than 0.5%, then the nonlinear effect will become significant. While your analytical formulas are usually for linear beam theory. For a fair comparison, you need to set the recovery flag to be 2 instead. This option is available since VABS 3.2.4.