I.-W. Lee, H.-J. Jung, and M.-C. Kim, “Efficient free vibration analysis of large structures with close or ultiple natural frequencies. Part II: Damped structures”, Comp. Assist. Methods Eng. Sci., vol. 6, no. 3-4, pp. 415–424, May 2023, Accessed: Jan. 18, 2026. [Online]. Available: https://cames.ippt.gov.pl/index.php/cames/article/view/1301