OPTIMIZATION DOUBTS


Hi,
I am a new user of hyperworks. I am currently working on topology optimization of inner structure of airfoils and trying to get a good setup of the settings available in the software.I have a few doubts that i couldn't get cleared by reading the hyperworks help:
1. The use of DISCRETE option regarding the value of it and the phases involved with it.
2. How can the OBJ REFERENCE and DESVAR LINK be used in the setup?
3. Usually to avoid computational cost we go from discrete to continuous design variables and that is the general way. Then how can the given option of discrete DVs be fruitful as compared to contnuous DVs ?
4. It is written in the help site that 'DUAL' solver is used where the number of design variables is large compared to the number of constraints applied. It is advised for a general topology optimization problem. In ANSYS generally 'optimality criteria' is used´similar to 'DUAL' but when stress constraint is applied it leads to an increase in the number of constraints thus it is better to prefer a solver with capability to handle large number of constraints like sequential convex programming in ANSYS. So is the same true in hyperworks as well that if I change from a less constraint problem to a large constraint problem I would have to change from 'DUAL' as a solver to other solver? If so then which would be the best?