FEA is well known as an analysis method using a computation solver. In recent years, the utilization of specialized computation solvers for FEA in the development process is not unusual. Furthermore, large scale analyses exceeding a million elements or analyses that have multiple cases are being used more frequently. However, this was not the case a quarter of a century ago due to the limitations and cost of the computation solver performance.
Therefore, how did FEA enter into the development process as a design tool at that time?
The simple answer is years of intuition and experience. However, the magnetic circuit method has been used systematically as the primary method to analyze the magnetic characteristics of electromechanical machines. The magnetic circuit method is a universal analysis method that is used widely even today, but, it was the only analysis method available at the time because the computation solvers were not as sophisticated as they are today.
The magnetic circuit method is a method to estimate the magnetic flux produced in the magnetic pathways of the magnetic circuit by replacing the core, coils, and magnets making up a machine with a magnetic circuit composed of the source of magnetomotive force and magnetic resistance. An example of a magnetic circuit overlayed on a motor is indicated in Fig. 1. This method can be calculated by hand without a computation solver because large scale calculation is not required for a simple magnetic circuit. The electromagnetic attractive force between the stator and mover obtained using the simple magnetic circuit method for the solenoid value shown in Fig. 2 is indicated in Fig. 3. In Fig. 3, the calculation results using FEA are compared to the simple magnetic circuit method to show the similarity of the results regardless of which method is used.
Fig. 1. Magnetic circuit of a motor
There are also software based on the magnetic circuit method. Results can be obtained instantly because an analysis can be performed using very few calculation resources.
Therefore, the magnetic circuit method was widely used in the design process before FEA become a standard tool (before FEA).
Then why has analysis using FEA become necessary and widely adopted in the development process?
Fig. 2. Model of a solenoid valve using the magnetic circuit method
Fig. 3. Attractive force characteristics obtained using
the magnetic circuit method in Fig. 2