Design optimization of quarter-car models with passive and semi-active suspensions under random road excitation

A methodology is presented for optimizing the suspension damping and stiffness parameters of nonlinear quarter-car models subjected to random road excitation. The investigation starts with car models involving passive damping with constant or dual-rate characteristics. Then, we also examine car models where the damping coefficient of the suspension is selected so that the resulting system approximates the performance of an active suspension system with sky-hook damping. For the models with semi-active or passive dual-rate dampers, the value of the equivalent suspension damping coefficient is a function of the relative velocity of the sprung mass with respect to the wheel subsystem. As a consequence, the resulting equations of motion are strongly nonlinear. For these models, appropriate methodologies are first employed for obtaining the second moment characteristics of motions resulting from roads with a random profile. This information is next utilized in the definition of a vehicle performance index, which is optimized to yield representative numerical results for the most important suspension parameters. Special attention is paid to investigating the effect of road quality as well as on examining effects related to wheel hop. Finally, a critical comparison is performed between the results obtained for vehicles with passive linear or bilinear suspension dampers and those obtained for cars with semi-active shock absorbers

Parametric identification and fault detection in vehicle models with nonlinear suspension

Systematic methodologies are applied for performing parametric identification and fault detection in nonlinear vehicle systems. The dynamic response of the vehicle models examined is caused by road excitation. In these models, the nonlinearities arise due to the function of the suspension dampers, which assume a different damping coefficient in tension and in compression. This leads to oscillator models with parameter discontinuities. First, emphasis is put on investigating some issues of fundamental importance, by employing a classical two degree of freedom quarter-car model. Since the dominant nonlinearities are due to switches between constant damping coefficients, appropriate methodologies are applied for obtaining exact motions of these models. Moreover, a statistically based methodology is applied for parametric identification and fault detection in vehicle suspensions with nonlinear characteristics, using dynamic test data. This methodology is then extended and applied to more involved and complete vehicle models. The numerical results presented demonstrate that this methodology provides an effective and practical way of detecting the type, location and severity of faults in vehicle suspensions

Multi-objective optimization of quarter car models with passive and semi-active suspensions

A methodology is presented for optimising the suspension damping and stiffness parameters of quarter car models, subjected to road excitation. First, models involving passive damping with constant or dual rate characteristics are considered. Then, models where the damping coefficient of the suspension is selected so that the resulting system approximates the performance of an active suspension system with sky-hook damping are also examined. For all these models, appropriate methodologies are first employed for obtaining the second moment characteristics of motions resulting from roads with random profile. This information is next utilized in the definition of a composite vehicle performance index, which is optimised to yield representative numerical results for the most important suspension parameters. Finally, results obtained by applying a suitable multi-objective optimization methodology are also presented in the form of classical Pareto fronts

Fault detection and optimal sensor location in vehicle suspensions

A statistical system identification methodology is applied for performing parametric identification and fault detection studies in nonlinear vehicle systems. The vehicle nonlinearities arise due to the function of the suspension dampers, which assume a different damping coefficient in tension than in compression. The suspension springs may also possess piecewise linear characteristics. These lead to models with parameter discontinuities. Emphasis is put on investigating issues of unidentifiability arising in the system identification of nonlinear systems and the importance of sensor configuration and excitation characteristics in the reliable estimation of the model parameters. A methodology is proposed for designing the optimal sensor configuration (number and location of sensors) so that the corresponding measured data are most informative about the condition of the vehicle. The effects of excitation characteristics on the quality of the measured data are systematically explored. The effectiveness of the system identification and the optimal sensor configuration design methodologies is confirmed using simulated test data from a classical two-degree-of-freedom quarter-car model as well as from more involved and complete vehicle models, including four-wheel vehicles with flexible body

Computer-aided estimation of acetone, methyl acetate, and chloroform diffusion coefficients in poly(vinyl acetate)

The diffusion coefficients of acetone, methyl acetate, and chloroform in amorphous poly(vinyl acetate) are estimated using the solvent evaporation method. The evaporation process from polymer solutions, cast in the form of thin films, is studied as a numerical experiment. The process is modeled as a coupled heat and mass transfer problem with a moving boundary. Lattice fluid (LF) thermodynamics is used to describe polymer-solvent system volumetric properties and to derive appropriate expressions for solvents' chemical potentials. The resulting nonlinear system of governing equations is solved with the Galerkin finite element method. The estimated diffusion coefficients are in satisfactory agreement with reported data

Polymerisation Kinetics on FT-IR and Colorimetric Changes under UV Irradiation for a Commercial Polycyanoacrylate Adhesive, Addressed to Glass Restoration

This study evaluates a commercial polycyanoacrylate adhesive of medium viscosity regarding its suitability for the restoration of glass objects of cultural heritage in a museum environment (exhibition/storage). Loctite® Super Attak was investigated in terms of (a) its polymerisation rate and degree of conversion, using Infrared Spectroscopy FT-IR by monitoring the change of the C=C peak vs. C=O peak and (b) the alteration of the colour parameters of its films after its submission to UVC irradiation for several time intervals. It was confirmed that within 6 h, a thin-layered adhesive film acquires 80–85% of its polymerization in ambient conditions, while the reaction continues for up to 12–18 h in the conditions examined. The progress of the reaction is slower when the adhesive is in a protected environment. On the other hand, the effect of UVC rays on the glue is destructive and oxidative, provoking a yellow shade/colour from the first hours of exposure. The intensity of the yellowness becomes higher after 6 h of exposure, showing shifts in the absorption peaks of C–O/C=O groups of the initial IR spectrum and the augmentation of –OH absorptions. It was concluded that the adhesive is suitable for glass restoration, especially for instant, rapid, applications, under mild conditions of maintenance and exposure

Polymerization Kinetics of <i>n</i>‑Butyl Methacrylate in the Presence of Graphene Oxide Prepared by Two Different Oxidation Methods with or without Functionalization

Nanocomposite materials based on poly­(butyl methacrylate) and either graphene oxide (GO) or functionalized graphene oxide (F-GO) were produced using the in situ bulk radical polymerization technique. It was found that the Hummers method results in a higher degree of oxidation, compared to the Staudenmaier, whereas F-GO was produced using a silane-modifying agent. Polymerization kinetics were studied both experimentally and theoretically, and it was found that the presence of hydroxyl groups in the surface of GO results in scavenging the primary initiator radicals, thus reducing the initiator efficiency and the reaction rate, whereas the number-average molecular weight of the polymer formed was increased. The presence of F-GO affected the polymerization kinetics in a different way resulting in partially grafted structures. The theoretical study included the addition of a phenomenological transfer to the polymer side-reaction to account for the polymerization occurring at the F-GO surface