# Experimental Verification of a Compressor Drive Simulation Model to Minimize Dangerous Vibrations
## 4 Comparison of Experimental and Simulation Models  
The comparison of the experimental model in the laboratory with the simulation model was mainly aimed at determining the position of the critical revolutions based on the waveform of the effective value of the dynamic component of the _RMS_\(M_{D}\) load torque. The comparison of the experimental and simulation model results is shown in Figures 28-33, where the waveforms of the effective values of the dynamic component  
Figure 27: Frequency analysis using a Hamming window at \(n\) = 500 min\({}^{-1}\) and one cylinder out of operation. Figure 25: Effective value of the dynamic component of the load torque _RMS_\(M_{D}\) of the pneumatic flexible coupling at pressure 700 kPa vs. the engine revolutions \(n\) with the cylinder out of operation. Figure 26: Frequency analysis using a Hamming window at \(n\) = 500 min\({}^{-1}\) at steady operation. of the load torque \(RMS\)\(M_{D}\) as a function of the steady-state and dropped single cylinder revolutions at pressures of 700, 500, and 300 kPa, respectively, are compared. Figure 30: Comparison of the characteristics at steady operation of a piston compressor—pressure in the elastic element of the coupling \(p_{S}=500\) kPa. Figure 28: Comparison of the characteristics at steady operation of a piston compressor—pressure in the elastic element of the coupling \(p_{S}=700\) kPa. Figure 29: Comparison of the characteristics at one cylinder out of operation of a piston compressor—pressure in the elastic element of the coupling \(p_{S}=700\) kPa. Table 9 shows the values of the natural circular frequencies obtained from the solution of the simulation model and the realization of the experimental measurements for the steady-state operation at pressure \(p_{S}\) = 700 kPa, \(p_{S}\) = 500 kPa, and \(p_{S}\) = 300 kPa in the elastic element of the coupling. Accuracy in terms of the meaning of correspondence between the calculated and experimentally determined critical revolutions is determined as the ratio of experimentally determined revolutions to the revolutions determined by calculation. The sign (\(+\)) in the column indicates an increase, and the sign (\(-\)) indicates a decrease in the value of the critical revolutions determined experimentally compared to the value of the critical revolutions determined by calculation. Figure 31: Comparison of the characteristics at one cylinder out of operation of a piston compressor— pressure in the elastic element of the coupling \(p_{S}\) = 500 kPa. Figure 32: Comparison of the characteristics at steady operation of a piston compressor—pressure in the elastic element of the coupling \(p_{S}\) = 300 kPa. In general, the difference between the results can be caused by a number of different factors and their combination:  
* Incomplete information on the input parameters, i.e., torsional shaft stiffness and mass moments of inertia. * The method used to determine the natural frequencies and mode shapes of oscillations;
* Tooth clearance in the gearbox. * The effect of frequency on the stiffness of the flexible coupling. * Influence of the value of the mean torque and amplitude on the equivalent torsional stiffness of the flexible coupling (non-linearity of the loading characteristic of the coupling);
* Torsional vibration in the gearbox. * Tongues clearance in individual flanges. * Ambient temperature not included in the calculation. * Temperature of elastic elements not included in the simulation model. * Location of the torque meter. * Insufficient heat dissipation from the piston compressor in operating mode. * Maintaining and regulating constant pressure by a throttle valve at the outlet of the pressure tank. * Operating revolutions close to the resonance from the main harmonic component in steady (even) operation. Because the decrease in accuracy presented in Table 9 corresponds very well with the decrease in coupling stiffness due to temperature, it can be stated that the main cause of the decreasing agreement of the results is precisely this phenomenon.