In this article you will learn how to set up a constraint based on a summation of responses. In this case, the constraint is based on the sum of the x and y force components through a CBUSH element. This process can be generalized to other operations for creating constraints from a combination of responses.

Note: If you are having trouble finding any of these solver cards, remember that you can use CTRL + F and search for the card name (DRESP2, DEQATN, etc.).

1. Setup the responses for Fx and Fy as usual:

 

2. Setup a DRESP2 definition. The DRESP2 card identifies the function definition and inputs(responses).

In response list, we refer to the responses Force_x and Force_y.

OPTION A: Use built-in functions

This definition shown above uses this built-in SUM function on the DRESP2 card, but there is a full list of built-in functions:

OPTION B: Define custom equation with DEQATN

If you want to add your own function outside of those defined above, you would have to setup DEQATN and specify ‘dequation’ in the function entry on the DRESP2 card.

 

The order in which the responses are fed into the equation are determined by the order they are listed in the DRESP2 card. You can check this by card editing (right click > card edit).

In this case, response ID 5 would be variable “a” and response ID 6 would be variable “b” in the function definition.

3. Reference this DRESP2 response to set a constraint on the summation:

 

4. Run optimization.