# Design of a Spin Test System for Burst Phenomen Considering Nonlinear Rotordynamic Effects
## 2 Materials and Methods  
In this paper, applications for the most appropriate design of the spin test rig, which will not be affected by alternating stresses due to vibration, are presented. The primary objective of this study is to present solutions that minimize vibration effects caused by rotordynamics during the testing of high-speed components, such as those in spin test systems. In this context, the aim is to establish an optimal rotordynamic layout during the preliminary design phase by developing a discrete model in Matlab Simulink that incorporates factors influencing the vibration characteristics. By developing a discrete model based on the equations of motion, the rotordynamic characteristics of high-speed rotating components can be determined during the preliminary design phase. This approach allows for the potential vibration issues that may arise during the detailed design phase to be addressed and mitigated at the preliminary design stage. In this context, a discrete rotor dynamics model was established in MATLAB SIMULINK. The results obtained from this model were compared with those from general axisymmetric and 3D modal analyses. Input data used for calculations, including angular speed, bearing stiffness, and damping ratio, were incorporated into the harmonic analysis. Bearing stiffness values were not treated as constants; instead, nonlinear stiffness behaviors were used in both axial and radial directions. The damping ratio applied in this study was obtained directly from impact tests on the relevant mode. The advantage of conducting tests under vacuum is that aerodynamic damping effects are eliminated, allowing for the direct use of system damping data. Results from both the finite element approach and the 3D MATLAB SIMULINK rotordynamics model were compared with test data. Error rates resulting from these comparisons are presented in the results section. The algorithm for this study is illustrated in Figure 1. To enhance the accuracy of this study, calculations and impact tests were conducted on two distinct test specimens with different moments of inertia and masses. The first test specimen weighs 10 kg, while the second specimen weighs 4 kg. The vacuum chamber in which the tests were conducted is shown in Figure 2, and the details of the test specimens and shaft connections are provided in Figure 3.  
The primary purpose of using the two-dimensional analysis model is to keep the number of mesh elements at a minimum, enabling fast solution time and facilitating the comparison of preliminary Simulink results. However, in two-dimensional analyses, the effects of sections that break axial symmetry on modal analyses are neglected. Therefore, the Simulink results, which are initially validated through two-dimensional analyses, are further verified in the next phase using three-dimensional models. The model created in the Simulink environment is highly effective in determining the bearing stiffness and axial locations. This allows for a rapid execution of rotordynamic layout studies using the discrete model in Simulink. Moreover, the bearing locations and stiffness values can be parametrized within the model to derive the optimal rotordynamic layout. In these studies, the preliminary validations are performed using two-dimensional analyses, assuming axial symmetry. Subsequently, three-dimensional analyses are conducted to account for the effects of sections that disrupt axial symmetry, incorporating them into the rotordynamic calculations. The spin test system consists of three main components: the power transmission system, rotor rig, and vacuumed cabin, as seen in Figure 2. The system specifications are as follows: For the Inconel 718 material used in the test rotor, the maximum temperature is 700 \({}^{\circ}\)C. The maximum rotational speed for the test rotor is 60,000 rpm. The vacuum level should be equal to or less than 50 Pa. The geometric dimensions of the main rotor shaft and bearing positions have been determined through an optimization study.