Actual engineering processes can be simulated and analyzed in virtual environments by using Computer Aided Design (CAD) methods. The CAD is presented by geometrical parameter as Non-Uniform Rational B-Splines (NURBS), B-spline and T-splines. Stress and strain of produced parts can also be simulated in virtual environments by using the CAD models in order to be analyzed and controlled. The Finite Element Method (FEM) is a very common analysis method in order to analyze CAD models. Efficiency of FEM is under influence of many parameters such as approximation, polynomial based geometry, mesh generation and mesh refinement process, sliding contact and flows about aerodynamic shapes. The isogeometric analysis is introduced to eliminate the analysis costs related to geometry clean-up, defeaturing and mesh generation. The integrated numerical simulation in the part designing is development and implementation of the next generation design and simulation methods based on isogeometric analysis. Polynomial splines over hierarchical T-meshes (PHT-splines) will be employed to construct exact geometric models. PHT-splines will be extended to RHT-spline (Rational spline over Hierarchical T-meshes) as rational spline in order to capture a wider class of geometries. So, a general framework of unifying preprocessing as well as designing using isogemetric analysis can be provided in order to improve efficiency of produced parts.