Browsing by Author "Ladipo, Ismail Ladele"

Dynamic Vibration Absorbers (DV A) are passive devices that attenuate vibration at a single resonance frequency. However, to use the DVA for the reduction of vibration in multi degrees of freedom (MDOF) systems which have more than one resonance frequency requires modification of the DV A. These modifications are accomplished by using active control strategy on the DV A. This transforms the DV A into an Active Dynamic Vibration Absorber (ADVA). Various actuator systems have been used for the transformations of DV A into ADV A. These include Proof Mass Actuators (PMA), Piezoelectric Absorbers and Smart spring Absorbers. Limitations in the ADVA design and their control strategy which always affect their performance include friction force, energy requirement and complexity of design. In this research, a less complex design of an Active Dynamic Vibration Absorber (ADV A) and its controller is proposed. The ADVA adaptively tunes to attenuate vibration of the broadband resonance frequencies of MDOF system with minimum limitations. This study includes the mathematical modeling and experimental verifications of the resonance frequencies of the three degrees of freedom (3DOF) system on which the ADV A was implemented. Based on the broadband resonance frequencies of the 3DOF system, a prototype ADV A has been developed. The ADV A uses a proportional-integral-derivative {PID) controller to change its stiftb.ess adaptively to reduce vibration. The optimal location of the ADV A on the MDOF system was also identified. Experimental results show that the ADVA was able to reduce the vibration of the MDOF system at all the modes. Due to the properties of the ADVA spring material used in this study, vibration attenuation at the first mode was limited to SdB. For further research, a spring material with a lower modulus of rigidity is suggested to improve the performance of the ADV A.

Passive, semi-active and active mounts have been used to isolate vibration in engines. However, due to changes in materials used for engine construction, there is a need to improve the performance of engine mounts. These improvements require sophisticated computation software, experimentation difficulties and cost. On the other hand, smart materials applications in engineering is growing but with lesser research on the analysis of models used for simulating behaviors of these smart materials. With proper analysis of mathematical models, isolation of engine vibrations can be improved in modern vehicles using smart materials. One of such smart materials is Magnetorheological Elastomer (MRE). Usually, dynamic responses of visco-elastic materials are observed using phenomenological experiments which include creep, stress relaxation and rheological models. The simulations of these dynamic responses and characterization of engine mounts using Magnetorheological Elastomers (MREs) are limited in literature. These have contributed largely to the absence of commercial MRE mounts albeit their characteristics and performance in theory. The aim is to develop characteristics equation for MREs and simulate its behavior as MRE mount. In this research, the comparison between the Standard Linear Solid (SLS) model and the MRE model reveals the mechanical properties of MREs. These mechanical properties are utilized in the simulation of dynamic behaviors of MRE mount. Sensitivity Analysis (SA) is then used to determine the importance of the parameters which contribute to the performance of MRE mount. The SA reveals that that magnetic field input is more important than characteristic constituents stiffness of MREs. With this knowledge, MRE mount is controlled to reduce low frequency and high frequency vibration in half car model. It is shown by using different vibration measurement criteria, that there is significant reduction of vibration by using MRE mount. The results obtained when the Passive rubber mount was replaced with MRE mount shows 27% reduction in vibration in low frequency and 25% reduction in vibration in high frequency. The performance of the MRE in nonlinear model is however less promising as shown in the simulation results and further studies are needed. The values identified in this study can be useful in the subsequent design of MRE mounts in engine mount systems.