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J. Comput. Nonlinear Dynam. 2017;13(3):031001-031001-14. doi:10.1115/1.4038445.

Nonlinear dynamics, control, and stability analysis of dry friction damped system under state feedback control with time delay are investigated. The dry friction damped system is harmonically excited, and the nonlinearities in the equation of motion arise due to nonlinear damping and spring force. In this paper, a frequency domain-based method, viz., incremental harmonic balance method along with arc-length continuation technique (IHBC) is first employed to identify the primary responses which may be present in such system. The IHBC is then reformulated in a manner to treat the dry friction damped system under state feedback control with time delay and is applied to obtain control of responses in an efficient and systematic way. The stability of uncontrolled responses is obtained by Floquet's theory using Hsu' scheme, and the stability of the controlled responses is obtained by applying a semidiscretization method for delay differential equation (DDE).

Commentary by Dr. Valentin Fuster
J. Comput. Nonlinear Dynam. 2017;13(3):031002-031002-12. doi:10.1115/1.4038508.

In this paper, the dynamic response of a spatial four-bar mechanism with a spherical clearance joint with flexible socket is investigated. Previous research treats the socket as a whole rigid part and neglects the flexibility of the socket. In order to better describe the influence of the spherical clearance joint, a rigid-flexible coupling model of a four-bar mechanism is established, in which the socket of the spherical clearance joint is treated as flexible body. The dynamic responses of this spatial mechanism are discussed for the mechanism with a flexible socket and the case with traditional rigid socket. Furthermore, the effects of clearance size and driving speed are also separately discussed. The results demonstrated that the dynamic response of mechanism is affected by the clearance joint. The socket flexibility can relieve the undesired effects of the clearance on the responses of the mechanism with clearance. The flexible socket acts as a suspension for the mechanism with clearance joint.

Commentary by Dr. Valentin Fuster

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