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Journal of Vibration Testing and System Dynamics 5(2) (2021) 113--120 | DOI:10.5890/JVTSD.2021.06.001

Carmen Chicone, Z. C. Feng

Department of Mathematics, University of Missouri, Columbia, MO 65211, USA Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA

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Abstract

Many control systems incorporate input from actuators. The actuators can be represented as force or displacement input. When an actuator is modeled as a displacement input, there are many practical applications for which the displacement is not smooth and its time derivative, i.e. the velocity, is not continuous everywhere. Numerical study for such displacement input becomes tedious since the state variables experience a finite jump at the time of acceleration singularity. Although the acceleration singularity can be avoided if the actuator dynamics is modeled by a force input, such an approach increases the order of the overall system. To preserve the simplicity of the displacement input of the actuators, we propose transforms of state variables so that only the velocity of the displacement input appears explicitly in the equations of the dynamical system. In short, we introduce transforms that reduce the order of time derivatives of the input. This approach simplifies the numerical solutions for non-smooth displacement input. Moreover, when the transform is applied to a parametrically excited pendulum, the stabilizing effect of the parametric excitation is shown explicitly.

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