# Towards Hierarchical Workflows in SysML to Support Virtual Validation of Technical Systems
## 5 Case Study
The activity \"Check if the corresponding solution fulfills the function\" contains and executes the virtual testing workflows. The testing results are compared with the design requirements for verification. Taking the function \"Support rotation with low friction\" as an example, the virtual testing workflow \"Failure Testing\" is created in the SysML package \"Bearing\" at the solution layer. The workflows can be added to the activity \"Check if the corresponding solution fulfills the function\" by dragging and dropping. That is, by performing the virtual testing workflow \"Failure Testing\", the simulation result \"Lifetime\" will be used as a criterion to check whether the solution \"Bearing A\" fulfills the corresponding function. Simulation testing results must be compared to the relevant design requirements to assess whether the function is fulfilled based on the verification. For example, bearing lifetime serves as one criterion, assisting in determining if the chosen solution satisfies the function according to the lifetime calculation. If the simulated lifetime meets or exceeds the required lifetime, the verification results are considered true, indicating a passed verification. Otherwise, the verification fails. Figure 12 shows the validation results of the WT system under different design parameters. The same as the scenario in Section 3, customers expect a higher energy production from the system. Therefore, the calculated AEP value of the original solution \"Wind Turbine A\" is lower than the changed AEP requirement. Therefore, the requirement verification fails. The failed verification result states that the solution \"Wind Turbine A\" does not fulfill the function \"Convert wind energy into electricity\". The \"Wind Turbine  
B\" is designed to meet AEP requirements, while the larger blades and generator result in higher loads on the redesigned rotor and a corresponding increase in loads on the bearings. Therefore, the lifetime of the bearing is lower than the design requirement, and it is also regarded as a verification failure. Bearings have been redesigned in \"Wind Turbine C\". It has been verified to meet not only AEP requirements in the scope of WT, but also lifetime requirements in the scope of bearing. It is worth noting that the virtual testing workflows can be easily adapted when the system context changes. \"Bearing\" is a common solution in WT systems. The solution \"Bearing\" can be used not only in rotor-bearing arrangements, but also in high-speed bearing arrangements. In the reuse process, designers can easily add the corresponding validation workflow, virtual testing workflow, and modular domain model simulation activities into the framework. Due to changes in the system context, the designer might need to change the step information of virtual testing workflows to execute the appropriate domain model. For example, to calculate the lifetime of the bearing of the high-speed bearing arrangement, loads on the bearing can be calculated from a \"Nacelle MBS\" domain model instead of the \"Wind Turbine MBS\" domain model.