# Shape Finding Panel

Form:  Modify Undeformed Geometry

The Analysis > Shape Finding panel has two subcommands:  Modify Geometry and Reset Geometry.

• Modify Geometry command. After at least one analysis has been run, use the Analyze > Shape Finding > Modify Geometry command to access the Modify Undeformed Geometry form. That form allows modification of the undeformed geometry of the structure to achieve a desired deformed shape. The original undeformed geometry of the structure (geometry when the structure was first defined) is assumed to be the target for the deformed geometry of the structure under a user-specified load case.

• Revise Original Join Coordinates by Subtracting Displacements Obtained from this Case option. When this option is selected, use the Load Case drop-down list to select the load case for which the geometry is to be modified. Use the Scale Factor for Displacement edit box to specify a factor for scaling the displacements of the points defining the deformed geometry of the structure. For the specified load case, the modified undeformed geometry of a point in the structure is calculated as follows:

xn = xc + sf * [xo - (xc + dx)]

yn = yc + sf * [yo - (yc + dy)]

zn = zc + sf * [zo - (zc + dz)]

where,

(xn, yn, zn) = new undeformed coordinates of the point

(xc, yc, zc) = current undeformed coordinates of the point

(xo, yo, zo) = original undeformed coordinates of the point (target deformed coordinates)

dx = current x displacement of point under the specified load case

dy = current y displacement of point under the specified load case

dz = current z displacement of point under the specified load case

sf = user-specified scale factor (default value is 1)

and the terms in the square brackets are the errors in deformed geometry for the current geometry

Several iterations may need to be performed to achieve the target for the deformed shape. For each iteration, run the analysis, and check the deformed shape to evaluate if it is satisfactory. If not, click the Analyze > Shape Finding > Modify Geometry command again and adjust the scale factor if needed to improve convergence. Use a scale factor greater than 1 if the convergence toward the target shape is too slow; use a scale factor less than 1 if the geometry is overshooting the target shape. Click the OK button to modify the geometry, then re-run the analysis and check the results.

If the change in geometry significantly changes the load-carrying mechanism, convergence may be difficult. For example, a flexible flat slab may be changed to a domed shape that is much stiffer. Be aware that some structures cannot have their shapes determined using this procedure, such as cables and membranes, whose shape is completely determined by the shape of the loading.

• Reset Geometry command. Use this option to restore the original geometry.