Numerical methods are established tools for the design of stirring systems. CFD describes flow conditions in the reactors and provides information on the process result. Dynamic loads of components due to the agitator flow can therefore be predicted reliably. They serve as input for the calculation of stresses and deformations using FEM. Especially turbulent flows induce dynamic loads that excite internals and bring them to resonance. Such conditions can be predicted by the modal analysis. The described tools contribute to the reliable design and efficiency of production.