Friction damping is common in engineering structures for the purpose of energy dissipation and vibration control. Examples of applications are bolted connections and earthquake isolation systems. However, there is a shortage of works that investigate the effects of different contact materials on the energy dissipation performance and friction behaviour of friction dampers, which is valuable knowledge for design optimization. This thesis uses a numerical approach to explore the time response and energy dissipated by friction of the harmonically excited SDOF (single-degree-of-freedom) system with Coulomb friction contact between the sliding mass and a fixed wall. In addition, for the same SDOF system, an experimental investigation of the friction damping performance in terms of friction behaviour and energy dissipation is carried out for (1) steel, (2) rubber and (3) aramid contact materials. The aim is to get a better understanding of how different contact materials affect the performance of friction dampers. Various time scales, excitation frequencies and friction forces are considered. The main findings of this research are: (1) the characterization of the friction behaviour of steel-to-steel, rubber-to-steel and aramid-to-steel contacts; (2) the comparative analysis of the energy dissipation performance of the different contact materials; (3) the assessment of the long-term performance of the different contacts; (4) the comparison between numerical results based on the Coulomb friction model and experimental results. The tests have shown that rubber has the highest energy dissipation capacity and fairly unstable behaviour, steel has the second highest energy dissipation and irregular behaviour and aramid has the lowest energy dissipation performance and very consistent behaviour. Finally, the application of a method that calculates the energy dissipation of friction damping based on direct experimental outputs is an important contribution to the field regarding experimental investigations.

In recent years, there has been a lot of focus on system identification using vibration data instead of building mathematical models based on domain knowledge. The Sparse Identification of Nonlinear Dynamical System (SINDy) is a method that has been a great tool to identify the nonlinear dynamics. Therefore, in this report, the nonlinear systems such as duffing oscillator, Single Degree of Freedom (SDoF) with friction are identified using SINDy algorithm. An impact of noise in the measurement data is studied briefly. The components used in the process of identification are smooth finite difference-based differentiator, Sequential Threshold Least Squares (STLSq) optimizer and custom candidate library. Further, a comparison is made between the numerical models and the models obtained from PySINDy. The Root Mean Squares Errors are calculated for all the cases. It is seen that SINDy is capable of identifying these nonlinearities with good accuracy.

This thesis investigates a novel load alleviation technique known as mini-tabs, small devices placed on the upper surface of wings to reduce lift. Reynolds-Averaged Navier-Stokes (RANS) simulations were conducted to analyze the impact of geometrical properties on mini-tab performance in reducing the load on a wing. The initial simulations focused on a single mini-tab, varying parameters such as height, aspect ratio, chordwise, and spanwise positions. Results indicate that increasing height or aspect ratio leads to decreased lift due to flow deceleration at the leading edge and expansion of the separated flow region downstream of the mini-tab. This will also increase the pressure drag. Increasing the height or aspect ratio also accelerates the flow at the lower surface, further reducing the lift generated by the wing. Placing mini-tabs closer to the wingtip exhibits similar effects on lift reduction as increasing the height of the mini-tabs. This is because the relative height of the mini-tab with the local chord length increases when the mini-tab is positioned closer to the wingtip. A maximum lift reduction is also achieved when the mini-tab is placed at a 60% chordwise position. Subsequent simulations explored the performance of multiple mini-tabs, revealing that orienting them orthogonal to the wind direction may not be optimal due to gap formation between the mini-tabs that energizes the wake downstream of the mini-tabs and reduces the reduction in lift. Conversely, aligning the mini-tabs with the leading edge has a higher efficiency in the reduction of the lift. Overall, the findings suggest that mini-tabs offer a viable method for reducing wing forces and for load alleviation

This thesis investigates a novel load alleviation technique known as mini-tabs, small devices placed on the upper surface of wings to reduce lift. Reynolds-Averaged Navier-Stokes (RANS) simulations were conducted to analyze the impact of geometrical properties on mini-tab performance in reducing the load on a wing. The initial simulations focused on a single mini-tab, varying parameters such as height, aspect ratio, chordwise, and spanwise positions. Results indicate that increasing height or aspect ratio leads to decreased lift due to flow deceleration at the leading edge and expansion of the separated flow region downstream of the mini-tab. This will also increase the pressure drag. Increasing the height or aspect ratio also accelerates the flow at the lower surface, further reducing the lift generated by the wing. Placing mini-tabs closer to the wingtip exhibits similar effects on lift reduction as increasing the height of the mini-tabs. This is because the relative height of the mini-tab with the local chord length increases when the mini-tab is positioned closer to the wingtip. A maximum lift reduction is also achieved when the mini-tab is placed at a 60% chordwise position. Subsequent simulations explored the performance of multiple mini-tabs, revealing that orienting them orthogonal to the wind direction may not be optimal due to gap formation between the mini-tabs that energizes the wake downstream of the mini-tabs and reduces the reduction in lift. Conversely, aligning the mini-tabs with the leading edge has a higher efficiency in the reduction of the lift. Overall, the findings suggest that mini-tabs offer a viable method for reducing wing forces and for load alleviation