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This paper characterizes two semi-active control algorithms through strategy analysis and parametric simulation study. A brief literature review discloses two kinds of semi-active controls: non-model based skyhook-like control policy (or skyhook variations), and model-based clipped semi-active control strategies. Both can be formulated as a bi-state control algorithm. In this paper, the no-jerk skyhook control policy is chosen to represent bi-state strategies, while a nonlinear adaptive semi-active control algorithm without need of clipping control signals is selected for comparison study. Then the studied MR suspension and its model setup are presented. In the paper we explain dynamic analysis approach and controller tuning for this simulation study. While analytic analysis of strategies is based on linear base-excited vibration systems by using transmissibility plots, simulation study adopts sine-sweep excitations so that comparison of transient dynamics could be stressed out and simultaneously the vibration isolation capability compared in the frequency domain by directly observing the time domain data. In addition, one pure-tone excitation case is simulated to explain higher harmonics inherent with bi-state skyhook controls. From the simulation study, the effectiveness of both semi-active controls can be observed for vibration isolation. In addition, the adaptability of both selected controls is compared regarding plant variations and different excitation profiles, both of which are typical in vehicle suspension systems. Finally the characteristics of these two semi-active controls are summarized from the simulation findings. [ABSTRACT FROM AUTHOR]

The primary purpose of this study is to investigate the dynamic characteristics of semi-active groundhook tuned vibration absorbers (TVAs), using closed-form equivalent models of such systems. Closed-form, equivalent models of groundhook TVAs are developed and compared analytically with those for passive TVAs. Additionally, closed-form solutions of groundhook equivalent TVA models are obtained and are used for a parametric study to evaluate the dynamic characteristics of such systems as various parameters change. The numerical results are compared with passive TVAs which have been studied extensively in the past. The results indicate tat groundhook TVAs, with off-state damping levels within a critical value, are capable of lowering the magnitude of resonant peaks without increasing vibration. In contrast, increasing damping in passive TVAs results in a reduction in the amplitude of resonant peaks, at the expense of increased vibrations at the tuned frequency. The results further indicate that increasing the mass ratio between the TVA and the structure increases the effectiveness of groundhook TVAs, in a manner much similar to passive TVAs. However, increasing off-state damping decreases the effectiveness of groundhook TVAs. [ABSTRACT FROM AUTHOR]

An optimality criteria algorithm is presented for three-dimentional truss structure optimization with multiple constraints on its natural frequencies. Both nodal coordinates and element cross-sectional areas, which are quite different in their natures, are treated simultaneously in a unified design space for structural weight minimization. First the optimality criterion is developed for a single constraint based on differentiation of the Lagrangian function. It states that, at the optimum, all of the variables should have equal efficiencies. Then, the global sensitivity numbers are introduced to solve multiple constraints of frequencies, avoiding computation of the Lagrange multipliers. Finally, upon the sensitivity analysis, the most efficient variables are identified and modified in priority. The optimal solution is achieved gradually from the initial design with a minimum weight increment. Four typical trusses are used to demonstrate the feasibility and validity of the proposed method. [ABSTRACT FROM AUTHOR]