Wind Turbines

Aerodynamic model of 5‐MW National Renewable Energy Laboratory (NREL) wind turbine    Schematic representation of the outer bracing magnetorheological (MR) damper configuration with a lever mechanism connection for displacement amplification to enhance the performance of the dampers

 

 Wind turbine modeling flowchart.   Modeling of MDOF wind turbine.

 

The increased demand in energy and the need for sustainable and renewable sources of electricity in hazardous environments with a significantly growing population yields the installation of more wind turbines in these areas. The technological development in material and construction methods has led to the building of taller and more flexible wind turbines, with inherent low structural damping. Installing modern wind turbines in offshore harsh environments or seismic prone areas can cause an increment in the probability of failure due to excessive vibrations. We evaluate the performance of onshore and offshore wind turbines under multiple hazards, including wind, wave, earthquake, and mass and aerodynamic imbalances for both parked and operating conditions. The Lagrangian approach is employed to model the wind turbine considering the blade/tower coupling. To reduce the vibrations induced by multihazard loads, external smart dampers are used and a novel energy‐based probabilistic approach is employed to tune the semiactive controllers. The results show the effectiveness of the approach for the design of semiactive controllers in vibration mitigation of a wind turbine subjected to multiple hazards.

 

 

High-Rise Buildings

 

tall buildings subjected to multidirectional wind loadsa framework for the calculation of the dynamic response and internal loads

 

Proposed configuration of the MR dampers with bracing system: (a) bracings with dampers between adjacent floors for shear buildings; (b) outer bracings with dampers for cantilever and slender buildings; (c) damping unit consisting of a viscous damper, helical spring, and a lever mechanism for drift amplification across the damper.

In the past few decades, high-rise buildings have received a renewed interest in many city business locations, where land is scarce, as per their economics, sustainability, and other benefits. Taller and taller towers are being built everywhere in the world. However, the increased frequency of multihazard disasters makes it challenging to balance between resilient and sustainable construction. Accordingly, it is essential to understand the behavior of such structures under multihazard loadings, to apply such knowledge to design. Earthquake loads excite higher modes that produce lower inter-story drift, compared to wind loads, but higher accelerations that occur for a shorter time. Wind-induced accelerations may have comfort and serviceability concerns, while excessive inter-story drifts can cause safety issues. High-rise and slender buildings designed for wind may be safe under moderate earthquake loads, regarding the main force resisting system. Nevertheless, nonstructural components may present a significant percentage of loss exposure of buildings to earthquakes due to higher floor acceleration.

To alleviate these issues, fluid viscous dampers are employed under both wind and earthquake loads. The optimum number and location of dampers are selected based on modal drifts and targeted values of the response. Displacement, acceleration, inter-story drift ratio, shear force, and base bending moment are considered along with other concise sets of system-level performance criteria that are easily understood by decision-makers and/or stakeholders of diverse technical backgrounds. Placement of viscous dampers with a lever mechanism shows that higher reductions in responses can be achieved with smaller damping devices. Stiffness uncertainty and damper failure are considered to check the robustness of the mitigation system. Viscous dampers are a viable solution for vibration attenuation in high-rise buildings susceptible to wind and earthquake loads, which permits the minimization of structural and nonstructural damage by counteracting multi-hazard forces in real-time. Viscous dampers show their potential to enhance the dynamic performance of buildings under multiple hazards and can directly promote community resiliency.

Selected Publications