Dear Nazhar,

will try to give an answer that can be applied in any sceintific field.

Assume that we have an object that we want to describe its behavior. This can be done in two methods:

- Either theoretically, or

- Experimentally

The perform the theoretical solution, one has to develop what is called the physical model of the object, then the mathematical models which is system of equations. The solution of these equations can be made:

either analytically by finding a closed form solution and /or numerical solutions.

Normally, the objects are complicated such that there will be only closed form solutions under simplifying assumptions. And therefore such solutions are characterized by their transparency and ease of interpretation and prediction. But they can not describe the behavior of the object under all operating conditions.

Numerical solutions are subjected to much less assumptions and they can describe the performance of the object under wide range of operating condition with acceptable accuracy. But they are more complicated and requires software and hard ware to perform them.

Then comes the experimental characterization of the object which relies on fabricating the object and measuring its performance under real operating condition. This approach is more expensive and time consuming than the previews method.

So, one can use all these methods to reach to real performance of the object as fast as possible with minimum cost.

Best wishes

I agree in toto with Zekry

Thank you both of you for valuable input