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Author Topic: How do I model General Orthogrids?  (Read 21195 times)

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How do I model General Orthogrids?
« on: May 05, 2008, 03:46:06 PM »
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"I am doing a grid stiffened panel optimization in HS-Std. My concept is simple orthogrid (0,90 ribs) panel. My thickness variables top face, 0 and 90 webs are bunch of laminates with different thickness, based on layups with orthotropic material. HS allows me to enter material and thickness for top face and 0 degree web. However it does not allow me to enter material (laminate) and thickness variable to 90 degree web. How to overcome this? Second, 90 degree spacing variable is shown as depended variable. How 90 degree spacing is related to other (0, degree spacing) variables?"


For the materials and thicknesses of the 90 web, HyperSizer only allows  unique materials for the 0 web and then uses these same materials for the 90 and angle webs as well.  If you are sizing using continuous variable (i.e. min/max and #permutations), then you can independently size the 90 web thickness separately from the 0 web.  You should be able to click on the 90 web thickness variable and enter min, max and number of permutations for the 90 web variable.

If you are using laminates, and you want a different layup for the 0 and 90 web, you must use a concept called a “HyperLaminate”.  This was originally designed for doing ply drop-offs for example to have a different layup in the web and flange of a stiffened panel.  However, it works for your situation as well.  To use a HyperLaminate, open up a laminate and go to “Select” and choose “Hyper Definition”.  You will then see three columns of checkboxes appear in columns for L2, L3 and L4.  For a grid stiffened panel, L2 represents the 90 web, L3 represents the 0 web, and L4 represents the angle web (if you use one).  If you want a ply represented in the 0 web, you would turn on the checkbox of that ply in the L3 column. For a ply that is included in the 90 web, turn on that ply checkbox in the L2 column.  Using these checkboxes, you can include any number of plies in each web.

For your second question,  the orthogrid concept is a subset of a larger set of panel concepts called “grid stiffened” which includes orthogrid, isogrid, general grid, etc.  The variables on the variables tab are generic to cover any of the possible concepts.  For example, the facesheet thickness variable is the same for an isogrid as for an orthogrid.    For the 90 spacing, if you think about it, there is a relationship between the  0 spacing, the 90 spacing and the angle, theta.  The relationship is tan(theta) = (0 spacing) / (90 spacing).  So we cannot allow the user to specify all three of these values.  At the time this was done, our thinking was that the more common panel concept would be the isogrid or general grid concept where the angle would be the more important variable.  We might want to re-think this as in recent years, the orthogrid seems to be more important.  Anyway, in the software today, you control the spacing of the 90 ribs by controlling the spacing of the 0 ribs and the angle and then let the 90 spacing be dependent on the other two.  For example, lets say you want 0 spacing = 3 inches and 90 spacing = 6 inches.  To get this, enter the angle theta = arctan (0 spacing / 90 spacing)  = arctan(3 / 6) = 26.57 degrees.