This paper introduces a high-fidelity, nonlinear dynamic modeling and intelligent analysis framework for assessing the dynamic response of onshore wind turbines. A 13-degree-of-freedom (DOF) multibody model is established using Euler-Lagrange formalism, integrating coupled rigid and flexible body dynamics across the tower, blades, rotor, nacelle, and drivetrain. The tower and blades are modeled as Euler-Bernoulli beams capable of capturing both bending and torsional deformation, with aerodynamic loads computed via an enhanced blade element momentum (BEM) approach. To ensure predictive accuracy under complex loading conditions, an intelligent analysis algorithm is developed for selection and validation of vibration mode functions based on structural response convergence. Numerical simulations, implemented symbolically in MATLAB ®, are validated against the widely recognized OpenFAST code. Results indicate that the proposed model effectively captures nonlinear and coupled dynamic turbine behavior, achieving relative errors within 3.5% in key response metrics. The framework offers a reliable tool for structural dynamic assessment and establishes a foundation for future applications in optimization and control of large-scale wind energy systems.