This article presents a novel fixed-time safe-by-design control for uncertain active vehicle suspension systems (AVSSs) with matched/unmatched disturbances, high energy consumption, input saturations, and asymmetric time-varying constraints on both displacement/velocity. Several asymmetric time-varying barrier Lyapunov functions are carefully constructed to deal with displacement/velocity constraints under the fixed-time convergence framework. Furthermore, a new fixed-time auxiliary state system is proposed to compensate for the saturation effect. It is then rigorously demonstrated that the convergence time is independent of initial state conditions and both the displacement/velocity are always restricted within the asymmetric time-varying ranges. Importantly, by employing beneficial nonlinearities of a bioinspired X-shaped reference model, the burden of high control energy cost can be relaxed compared with traditional controllers. As far as we know, this should be the first attempt to achieve a fixed-time safe-by-design control for AVSSs, which simultaneously considers practical issues including meeting the safety requirements for input saturations and displacement/velocity, achieving fixed-time convergence, maintaining energy efficiency, and rejecting matched/unmatched disturbances. Experimental testing results validate the effectiveness, advantage, and feasibility of the proposed control algorithm, compared to other existing methods.

In this study, a rail dynamic vibration absorber with negative stiffness is developed to reduce the vibration transmission and radiated noise from the rail components of a ballasted track. The compound models of the ballasted track system with and without the proposed dynamic vibration absorber and a traditional dynamic vibration absorber are constructed. A parametric study is performed to evaluate the effects of the design parameters of the proposed dynamic vibration absorber on the vibration and noise reduction of the track system in terms of the point receptance, the decay rate of rail vibration along the track, and the vibration energy level of the rail. Compared with the traditional dynamic vibration absorber, the proposed counterpart can work effectively over a broad frequency range around resonance. The efficiency of the dynamic vibration absorber can be improved by adjusting the design values of the active mass and damping coefficient. A comparison with the traditional dynamic vibration absorber shows that the vibration and noise suppression capability of the proposed one can be enhanced by increasing the value of the stiffness ratio. However, different from the traditional dynamic vibration absorber, the design parameters of the proposed one can also affect the decay rate and vibration energy at low-frequency regions. A discrete track with the proposed dynamic vibration absorber, which is arranged in continuous or discrete distribution along the rail, is illustrated to study the influences of the rail components on the decay rate and vibration energy level of rails. These calculated results could provide a theoretical basis for the design of the proposed dynamic vibration absorber in controlling the vibration and radiated noise from rails.

The dynamic performance of an integrated quasi-zero stiffness (IQZS) isolator which is constructed by a single elastic structure is investigated in this study. This prototype exhibits the characteristics of the best simplicity, high reliability, and without friction by using the minimum number of elements. For completeness, the static properties of the IQZS isolator are provided at first. And then, the dynamic behavior is analyzed and the frequency response under harmonic excitation is derived by using an equivalent mechanical model. Frequency response curves (FRCs) under force excitation condition are obtained by using the harmonic balance method (HBM). Moreover, the dynamic performance of the nonlinear isolator supporting a lumped mass is investigated, and the vibration isolation performance is evaluated by utilizing force transmissibility and comparing with an equivalent linear system with the same design parameter setting. It can be concluded that the effective isolation range of the nonlinear isolator is broader than the linear counterpart. The effects of system parameters on the transmissibility are also examined. At last, the comparison between the analytical and experimental results under force excitation shows that the analytical model of the IQZS isolator is accurate in terms of force transmissibility. The calculation results may provide a theoretical basis for designing this class of IQZS isolator in engineering practice.