Hypothesis formulation Can hypothesis for doctoral dissertation be formulated as "to demonstrate that approach X can be used effeciently/successfully to model Y"? 

I'm trying to use novel approach X that has been rarely used in my field to model Y in my country where X has not been used at all. 

The problem is I don't have anything to compare it with Y to validate my results. I can only compare Y with Z which has been modeled using different approach and aggregates several other factors that are not the subject of my research. They are not directly comparable but both Y and Z should have similar trend. Nevertheless, I will compare these two to check external validity of my results.

In addition, there are some previous predictions about Y which I will also use for testing/proving validity of my results.
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.