## 3 General Discussion  
In an SRM, in addition to electromagnetic noise sources, various other noise sources such as mechanical and aerodynamic ones may also exist. Although all these sources can cause noise and vibration problems in the motor, the most prominent noise source in an SRM is structure-borne noise caused by radial electromagnetic forces [6]. In SRMs, the irregular and non-uniform distributions of flux and force densities in their air gap and near the stator/rotor lead to high levels of torque ripple and vibrations in the motor. In fact, the irregular and non-uniform force and flux distributions, which are already considered undesirable behaviors for the motor, are identified as the main causes of torque ripple and vibrations [32]. In SRMs, the attraction force is divided into two components, tangential and radial, based on the rotor structure. While the tangential force is converted into torque in the motor, the radial force causes unwanted vibrations and acoustic noise [33]. When the appropriate phase in an SRM is excited with direct voltage, the rotating rotor begins to turn in a direction that reduces the reluctance of the magnetic circuit. However, the sudden increase in torque at the point where the stator and rotor poles begin to overlap causes an abrupt tangential movement around the stator. This tangential movement combines with a strong centripetal motion when the stator phase is de-energized very quickly [32]. The radial force generated in RFSRMs contains various harmonic components that cause the vibration of the stator core and, consequently, acoustic noise. Over time, this leads to deformations in the stator core [34]. Similarly, in AFSRMs, an axial electromagnetic force is generated between the stator and rotor due to the axial magnetic flux. This force primarily causes rotor vibrations and negatively impacts the motor's performance [35]. In other words, radial forces that occur in RFSRMs occur as axial forces in AFSRMs. However, due to their disk structure, AFSRMs are not as resilient to these forces as RFSRMs. This  
Figure 2: (**a**) Short pitched AFSRM (**b**) fully pitched AFSRM. also leads to a risk of pole collisions in addition to high vibrations. Furthermore, while in AFSRMs, the bearings are expected to absorb these forces through balls; in RFSMs, the radial forces are balanced by the rotor and stator structures. The axial force \((\mathrm{F})\) in a magnetic system with an air gap can be determined by the ratio of change of the coenergy \((W_{c})\) with respect to the distance \(\left(l_{g}\right)\), as expressed in Equation (9) [20]. Figure 3 illustrates the forces in RFSM and AFSRM structures. \[F=\frac{dW_{c}}{dl_{g}} \tag{9}\]  
When Figure 3a is examined, it can be seen that in electrical machines, the electromagnetic flux follows a path through the stator-air gap rotor to generate the electromagnetic torque. In SRMs, each phase is sequentially excited to align the rotor poles with the excited stator poles, minimizing the reluctance along the flux path. As a result of this alignment process, an electromagnetic force \(F\) is generated, which consists of a tangential force \(F_{t}\) and a radial force \(F_{r}\). The torque obtained from the motor is derived from the tangential component of the electromagnetic force between the stator and rotor. While this situation can cause torsional vibrations in the stator poles and windings, most of the resulting vibrations are due to radial force fluctuations in the radial direction [14]. When examining Figure 3b, similar situations occur in the AFSRM structure. In AFSRMs, which operate on the same principle as RFSMs, the phases are sequentially excited to minimize the reluctance along the flux path. As a result, the rotor poles move to achieve an aligned position with the stator poles. As a result of the alignment process, an electromagnetic force \(F\) is generated, which consists of a tangential force \(F_{t}\) and, an axial force \(F_{a}\), which occur in the axial direction, unlike in RFSMs.