Nonlinear geometrically free vibration analysis of two beams coupled by double spring‐mass. - Hassa, Mustapha; Adri, Ahmed; El Khouddar, Yassine; Outassafte, Omar; El Hantati, Issam; Echouai, Brahim; Benamar, Rhali (ZAMM -- Journal of Applied Mathematics & Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2025)