Evolution of Tuned Mass Dampers: From Structural Vibration Control to Aeroelastic Applications in Flexible Aircraft Wings - A Review

Structural Vibration Control of Offshore Wind Turbines Using Tuned Mass Damper Inerter in OpenFAST: Implementation, Validation, and Illustration

The tuned mass damper inerter (TMDI) is a passive vibration absorber that suppresses structural vibrations by leveraging the inertance property of inerter devices. Previous studies have demonstrated TMDI effectiveness in wind turbines, but relied on simplified structural models. To date, no study has implemented multi-directional TMDIs within aero-hydro-servo-elastic tools such as OpenFAST to enable independent vibration control across multiple turbine components, including the tower, blades, and substructure. This paper addresses this gap by implementing the TMDI in OpenFAST. The governing equations of motion are derived and implemented within the Structural Control (StC) Module, supporting arbitrary TMDI connectivity and independent multi-directional configurations across turbine components. Verification against independent numerical models confirms the implementation's accuracy across all supported configurations. An application study examines the IEA 15MW reference wind turbine equipped with a tower-top TMDI under combined wind-wave loading. Optimal tuning is performed using a simplified two-degree-of-freedom model, with modal properties extracted from an OpenSeesPy finite element model of the IEA 15MW. Results show that TMDIs with secondary mass up to 100 times smaller than a conventional TMD achieve matching or superior vibration suppression in the fore-aft and side-side directions, in terms of peak and standard deviation of tower-top displacement and acceleration. Notably, TMDI stroke is markedly reduced compared to the TMD, better suiting the spatially constrained wind turbine environment. These results support the practical merit of lightweight TMDIs for wind turbine vibration control, with the OpenFAST implementation enabling performance-driven design under realistic loading conditions.

Model predictive gust load alleviation for a flexible wing considering system limitations

Future aircraft with increasingly flexible high aspect ratio wings are more vulnerable to gust and turbulence encounters. Active control technologies are therefore required to mitigate the effects of atmospheric disturbances and reduce structural sizing loads. However, the achievable load alleviation performance is constrained by system limitations such as time delays, parasitic dynamics, actuator limits, and sensor noise. In this context, model predictive control systems offer strong potential, as they can address these limitations. This paper presents the design and evaluation of such a model predictive gust load alleviation controller for a flexible test wing. The aeroelastic simulation model is based on a modal description of the structural dynamics and aerodynamic strip theory, with its parameters identified from ground vibration and wind tunnel tests. A Kalman filter is designed to estimate structural loads and non-measurable quantities including generalized structural coordinates and wind disturbances from highly noisy wind tunnel measurements. Preview information of upcoming gusts is provided to the controller, enabling feedforward control to compensate for time delays. The formulation can account for actuator limits and maximum allowable loads, ensuring effective operation within the system boundaries. To reduce the computational effort of the controller, Laguerre functions and an efficient soft output constraint formulation are employed. The resulting control system is evaluated in virtual wind tunnel tests based on the identified model with gust encounters of varying frequency. Further, the effects of degraded actuator limits and failure cases are investigated. Particular emphasis is placed on encounters with short and load-critical gusts, where the controller achieves good load alleviation performance despite restrictive system limitations.

Robust Optimization of Multiple Tuned Mass Dampers for the Offshore Monopile-Supported Wind Turbine

Offshore wind turbine (OWT) towers are continuously subjected to highly variable wind-wave excitations, where structural parameter uncertainties arising from manufacturing tolerances and material heterogeneity may significantly degrade vibration control performance. Conventional tuned mass dampers (TMDs), particularly single-TMD configurations, are highly sensitive to detuning effects and thus lack robustness under uncertain operating conditions. This study proposes a robust optimization framework for vibration mitigation of offshore wind turbine towers using multiple tuned mass dampers (MTMDs). Structural parameter uncertainties in total mass and stiffness are explicitly considered through Latin hypercube sampling (LHS), enabling a sample-based evaluation of control performance. Inverse Element Exchange Method with Multi-level Programming (MulIEEM) is applied to determine the optimal distribution of damping coefficient, mass, and for the TMDs. Three objective functions are investigated, including minimization of the sample mean, sample standard deviation, and single-sample response, allowing a systematic assessment of vibration reduction effectiveness and robustness. Stochastic wind and wave loads are synthesized using the Kaimal wind spectrum and JONSWAP wave spectrum, while structural uncertainties are represented through Latin Hypercube Sampling (LHS). The statistical characteristics of the displacement responses across all samples are used to evaluate robustness and provide an indirect measure of sensitivity to uncertainty-induced detuning effects. Three objective functions are investigated, including minimization of the sample mean, sample standard deviation, and single-sample response, allowing a systematic assessment of vibration reduction effectiveness and robustness, defined herein as reduced sensitivity to structural uncertainties. Numerical results demonstrate that the proposed MulIEEM-based MTMD designs significantly reduce both the mean and variability of tower displacement responses across a wide range of wind speeds. Furthermore, single-sample-based optimization is shown to achieve a favorable balance between control effectiveness and computational efficiency. The proposed framework provides a practical and robust design strategy for vibration control of offshore wind turbine towers under structural uncertainty.

Wind Tunnel Investigation of Spoileron Effectiveness on a Low-Aspect-Ratio Swept Wing with Reflex Airfoils

Politecnico di Milano is undergoing the design of a highly swept, low-aspect-ratio radio-controlled aircraft with reflex airfoils. This model is necessary to expand the automated flight-testing activities conducted inside the university, adding to the flying models a more unconventional one to verify the flight-testing technique implemented. Plain-type spoilerons were investigated as primary roll control devices and compared with conventional aerodynamic predictions and wind-tunnel data. The experimental tests assessed performance across spanwise and chordwise positions, angles of attack, and spoileron geometric variations. A normalized control effectiveness parameter, accounting for moment coefficient, spoileron surface area, and moment arm, was introduced to compare configurations. Results show consistent peak performance at intermediate incidence and highlight distinct degradation patterns near stall. Spanwise variations primarily affect roll authority, while yaw response remains weakly sensitive. Geometric analysis indicates span increases are more efficient than chord increases for equivalent performance, reducing actuator loads and aerodynamic penalties.

Review of Semi-Active Shock Absorption Mechanisms in Landing Systems

Effective shock absorption is essential for maintaining stability during landing events. Aerospace systems traditionally rely on oleo-pneumatic struts, while robotic platforms utilize lightweight compliant joints for impact mitigation. Recent advances have shifted attention toward adaptive solutions, including magnetorheological and electrorheological dampers, which can adjust their damping characteristics in real time through sensor feedback and control algorithms. By integrating established mechanical design principles with advanced materials and intelligent control strategies, modern landing systems can achieve improved energy dissipation and enhanced performance under variable and unpredictable conditions. This work evaluates the transition from passive to adaptive shock absorption technologies by examining landing dynamics, the mechanical architectures of conventional and semi-active systems, and the control strategies that enable adaptive damping. The findings indicate that, although passive systems offer reliability and simplicity, they lack the adaptability required for highly variable environments, while semi-active systems provide enhanced performance through real-time modulation enabled by advanced control algorithms. However, challenges related to power requirements, system complexity, material durability, and long-term reliability continue to limit widespread implementation of adaptive technologies. Overall, this review highlights the limitations of passive designs, evaluates the tradeoffs between MR and ER damping technologies, examines the evolution of semi-active control strategies, and identifies the key technical barriers that must be addressed before adaptive shock absorption systems achieve broader operational adoption.

ANALYTICAL INVESTIGATION OF THE CRITICAL FLUTTER SPEED FOR A TRANSPORT AIRCRAFT HIGH-ASPECT-RATIO WING