what this iso<current value mean...In hyper mesh tutorial help 'design concept for a structural c_clip' the value given as 0.3..how one can say this number is right value that give optimal material for over all stiffness and max displacement (i;e:required displacement)..
thank you.

The iso value when you are post processing topology optimization results, represents the element density values between 0 and 1. sp when you use the value 0.3 you are specifying display of elements that have density more than 0.3 to 1.0
Use this tool to get a better look at the material layout and the load paths from OptiStruct.
This is more of a visualisation tool, the density threshold matters when you are extracting the geometry, say in OSSmooth,
see image below
<?xml version="1.0" encoding="UTF-8"?>