Hypothesis formulation
Are you required to write down a specific, formal hypothesis by your departmental or university dissertation requirements? Much of science is done without this level of formalism. If you are required to do such a thing, it might be better to write something like: 


  Using approach X to model Y will lead to quantifiable improvement in Z.


Where Z is the error in approximation, efficiency of the method, or some other quantifiable measure of the performance of the approach. You probably don't need to know what level of improvement will obtained before you start the work, but you're better off stating a quantifiable improvement in some specific aspect rather than a vague statement that X is better for modeling Y.