Lin, Yun-HsiYun-HsiLinChai, Jeng-DaJeng-DaChai2025-08-052025-08-052024-12-17https://scholars.lib.ntu.edu.tw/handle/123456789/730982In this work, we investigate the transition from regular dynamics to chaotic behavior in a one-dimensional quartic anharmonic classical oscillator driven by a time-dependent external square-wave force. Owing to energy conservation, the motion of an undriven quartic anharmonic oscillator is regular, periodic, and stable. For a driven quartic anharmonic oscillator, the equations of motion cannot be solved analytically due to the presence of an anharmonic term in the potential energy function. Using the fourth-order Runge–Kutta method to numerically solve the equations of motion for the driven quartic anharmonic oscillator, we find that the oscillator motion under the influence of a sufficiently small driving force remains regular, while by gradually increasing the driving force, a series of nonlinear resonances can occur, grow, overlap, and ultimately disappear due to the emergence of chaos.chaosnonlinear resonancesquartic anharmonic classical oscillatorssquare-wave forces[SDGs]SDG7journal article10.3390/computation12120246