Check the units of the geometry, the material properties, loadings etc to ensure that they are consistent. |
Check all material properties to ensure that the magnitudes of the moduli, thicknesses etc are correct. |
Check the boundary conditions to ensure that they are representative of the physical support conditions and that they are sufficient to restrict the rigid body motion of the structure. |
Check that adjacent elements are consistent i.e. that each edge of an element is connected to a full edge of other elements and that corner nodes of elements are only connected to corner nodes of other elements, not midside nodes. This is especially important in regions of the mesh that have been locally refined. |
Check that the number of degrees of freedom on elements connected to one another is compatible. For example you should not connect a beam to a QUAD4 plate as the beam element has 6 degrees of freedom and the plate only 5 at each node. Of course this rule can be broken by the experienced analyst if adequate precautions are taken. Carefully check the mesh to ensure that all connected nodes are properly zipped. This can also be checked very effectively in the output display by plotting the mesh with a large displacement scale. |
Check that all the plate elements have their normal Z and preferably their local XY axis systems pointing in the same direction. The Z normal axis is particularly important. As an example consider a model of a pressure vessel. If some of the elements have their normal pointing outward and others pointing inward and we plot a contour of say the +Z surface stresses, we will get a picture showing the stresses on the outer surface of part of the structure and the inner surface of the rest. If some of the elements have the incorrect orientation it is a simple matter to correct this using the flip option in the graphical editor. The orientation of elements can be checked by setting the Type option in the graphical editor or output display to Orientation and redrawing (F3). |
Similarly check the orientation of any beam elements. This is best done by displaying the section of the beam (again from the Type option) however if your model does not use standard section beam properties then you will have to do this by displaying the reference nodes of the beams (set the NREF button to (active). The reference node of the beam and hence the beam local axis system should be checked against the beam local axis system assumed in the input data for I11, I22 etc. |
Check that the singularities (suppressed drilling freedoms) listed are consistent with the types of elements in the model and the boundary conditions applied. |
Check the summation of the forces produced by the solver. Does this equal the applied loads. Note that there may be some minor difference here if some loads are applied to nodes that have fixed boundary conditions since the load applied to these nodes is not included in the summation. Generally though, the forces and moments listed, must be in equilibrium with the applied loads including forces, moments, pressures, inertia loads etc. |
Check for warning messages. Ensure that you understand all warning messages and the implications of these on the results. Typical warnings are for warped elements, elements with acute internal angles etc. You can use the View ASCII File module to search for warning messages. |
Check that the sum of the reactions equals the applied loads. |
Check the displacements at the supports or symmetry conditions to ensure that the boundary conditions have worked correctly (i.e. that the displacements are zero in the correct directions). |
At a few locations where the stresses can be calculated using simple equations, do a 'back of the envelope calculation' to verify the output stresses. Again using the example of a pressure vessel, the stresses can be calculated approximately from the classic PR/2T type calculations for hoop and axial stress. Ensure that the stresses are within a few percent of these. Obviously these simple equations cannot calculate the stresses at the ends of the vessel where the stress state is more complex due to bending etc, but this is the reason we use finite elements. |
Similarly check the magnitude of the displacements at some point where the results are easily checked by a simple calculation. Just because the stresses are correct does not necessarily guarantee that the deflections are also correct. If the modulus is out by a factor of 1000, say, then the deflections would be wrong but in a linear static analysis the stresses would be correct. |
Check the deflected shape of the structure and ensure that this is consistent with the stiffness and geometry of the structure, the loads and boundary conditions. |
6.24 | 20.4 | |
TREE @ A | 4.60 | 20.5 |
TREE @ B | 1.60 | 15.2 |
Structure suited to the GEOM sorting.
Minimum RAM for InCore Solve = ???
Structures suited to TREE sorting.
Memory Usage | Amount |
---|---|
Conventional memory not used by STRAUS because STRND6 runs in protected mode | 1 MB |
SMARTDRV.EXE (if loaded) | Up to 2 MB |
Program space for loading the STRAUS solver and its associated memory requirements (stack space, etc.) | Up to 1 MB |
Amount of memory actually available to the STRAUS solver | Remaining 4 MB |
V is equal to the square root of 2as
Establish the loading input ie. magnitude, period and shape of load vs time curve. |
Establish the frequency range of interest ie. check which modes of the structure will contribute to the response when the loading is applied. |
For each of the frequencies of interest, f, construct a simple single degree of freedom model such that the simple model has a fundamental frequency equal to f (f= square root of k/m). Normally this model would be a mass on a spring (beam element). If the spectral curve for an acceleration response is being determined the loading will be applied as an acceleration. |
For each of the models carry out a full time history transient solution with the loading defined by a load vs time table. The loading in all cases should be the input established in step 1. From the transient response analysis determine the peak acceleration response. This is the spectral acceleration required by STRAUS. |
The spectral value used in the above method is the ratio between this calculated spectral acceleration and the applied peak acceleration. |
Plot a graph of spectral acceleration or spectral value vs the frequency of the structure and fit a curve through this. This is the spectral curve. |