This survey provides an insight into the modeling and testing of uniaxial friction dampers. The focus is on attenuating the linear relative movement along planar surfaces for frequencies between 10 Hz and 1 kHz. An overview of the different approaches seen in the literature concerning friction damping is provided. Examples and evaluation of such dampers excited over a wide range of frequencies are presented. The information required to develop models of friction dampers is covered. To that end, different modeling approaches are presented for dry friction. Dynamic friction models with an internal state are covered, and their advantages are described. Other modeling approaches are reported for complete systems with friction dampers. Both numerical and analytical models are covered. Experimental configurations from a selection of authors are also included. Finally, a series of suggestions for the numerical modeling and experimental testing of a friction damper are given.
Due to imperfect surface profiles, heavy vehicles moving at high speed on flexible pavement structures oscillate in the vertical axis. This phenomenon induces dynamic loads, which oscillate at lower and higher values than the average load associated with static load considered with most pavement analysis and design applications. Higher loads applied to flexible pavements are likely to significantly reduce pavement service life. A new multibody dynamic truck model was used to study heavy vehicle wheel load for various pavement profiles of varying international roughness index (IRI). The modelled heavy vehicle wheel load response were used to calculate the dynamic load coefficient, and a relationship with IRI was proposed. On the basis of this relationship, the evolving pavement surface profile, and thus evolving IRI, was used to determine the evolution of dynamic loading with pavement life. A comparison of pavement service life for the classical static loading and for dynamic loading was made for three highway flexible pavement structures. When dynamic loads are considered, it was found that the pavement service life reduction may be reduced of about 29 and 20% for bottom-up fatigue cracking and structural rutting failure criteria
In this work, four key design parameters of cycloidal rotors, namely the airfoil section, number of blades, chord-to-radius ratio, and pitching axis location, are addressed. The four parameters, which have a strong effect on rotor aerodynamic efficiency, are analyzed with an analytical model and a numerical approach. The numerical method, which is based on a finite-volume discretization of two-dimensional unsteady Reynolds averaged Navier-Stokes equations on a multiple sliding mesh, is proposed and validated against experimental data. A parametric analysis is then carried out considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering conditions. Results demonstrate that the airfoil thickness significantly affects the rotor performance; such a result is partly in contrast with previous findings for small-scale and microscale configurations. Moreover, it will be shown that increasing the number of blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius will demonstrate that values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with microscale cyclogyros, the generated thrust increases as the pitching axis is located away from the leading edge, up to 35% of chord length. Furthermore, the shortcomings of using simplified analytical tools in the prediction of thrust and power in nonideal flow conditions are discussed
A multibody tractor-trailer model specialised in measuring the impact of road surface quality on the efficiency of transport was developed. It was calibrated and validated using a coastdown tests experimental campaign. The model was then used within an extensive profile study that linked specific profiles to their impact on energy consumption, vehicle wear, driver and passenger health, and safety. Two hundred and seventy 1 km long profiles were tested with the multibody vehicle travelling at 100 km/h. It allowed to identify trends in the relationships between various profile rating criteria and the impacts aforementioned. The criteria consist of 19 indices observed on a quarter car model operating on longitudinal road profiles. They yield accurate predictions of profile impacts. For the operating conditions considered, the long wavelengths have a strong effect on health, medium wavelengths on safety, and short to medium wavelengths on energy consumption.
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