Switching tenses from past to present within a paragraph in a research paper
In a paper, actions taken are typically in the past, while goals, interpretations, and conclusions are still valid in the present.

Thus, the juxtaposition of tenses in your example is entirely reasonable: the creation took place in the past, while the goal remains the same in the present.  You could also, if you wished, place the goal in past by tying it to the creation, e.g.


  Our goal in creating this model was to allow the ...