This study presents analytical and experimental approaches to identify packing factors for polydisperse granular materials that maximize structural strength. The findings indicate that structural strength depends not only on the packing density but also on the particle-size distribution. A higher percentage of large particles correlates with greater structural strength, even for packings with identical density values. Therefore, this study proposes that the criterion for optimal packing should prioritize the maximum structural strength instead of the maximum packing density. This criterion is derived from proposed coordination numbers for polydisperse granular materials, which account for both the compaction degree and the proportion of particles of varying sizes. Physical experiments were conducted to measure the densities of packings with different particle-size distributions, and the experimental results were compared with analytical simulations using the discrete-element method. These comparisons indicate qualitative agreement between experimental and analytical data.

The air gap in a generator, defined as the space between the rotor and stator, is a critical factor that significantly influences electromagnetic induction and overall machine performance. The size and uniformity of the air gap affect magnetic flux distribution, electromotive force, losses, vibration, and noise characteristics. Any eccentricity or non-uniformity in the air gap can cause electromagnetic force imbalances, leading to increased mechanical vibrations and noise, which may reduce the machine’s lifespan. Therefore, optimal air gap design is essential for maximizing generation efficiency and ensuring durability. This requires precise control of the air gap dimensions and shape through detailed electromagnetic analysis and experimental validation. This study presents an electromagnetic force analysis conducted to optimize the air gap design of a 30 kW-class high-speed (15,000 rpm) AC generator. Based on both simulation results and experimental validation, the air gap was optimized to improve power generation efficiency and enhance product durability. As a result, a rational design and testing methodology for military AC generators is proposed.