Search

A slender footbridge can suffer from a large vibration under vertical human-induced excitation. To improve its serviceability, a tuned mass damper (TMD) has a wide application. However, considering the randomness and synchronization of crowd-induced excitation and the effect of crowd-structure interaction (CSI), the control robustness of a passive TMD needs to be improved. To achieve a better performance, a semi-active TMD (STMD) with variable mass and damping (VMD-STMD) is presented in this paper, which can not only adjust the own mass and frequency in real time to adapt to the dynamic characteristics of the footbridge through the water pump and electromagnetic valve, but also adjust its damping to improve the effect of energy dissipation through changing the eddy current damping. The proposed VMD-STMD can maximize the absorption of structural kinetic energy and dissipate. The working mechanism and control algorithm of VMD-STMD are introduced first, and then, a Euler-Bernoulli simply supported beam is studied. To highlight the best control effect and robustness of VMD-STMD, an optimized passive TMD, variable mass STMD (VM-STMD) and variable damping STMD (VD-STMD) are compared, 100 calculations of them based on crowd probabilistic models are proposed. The influence of CSI is investigated and different crowd density and synergy rate are discussed in detail. Through the maximum, mean and standard deviation of the three comfort evaluation indexes of the 100 groups of acceleration, the control effect and robustness of different TMDs are analyzed. Results show that structural dynamic responses and TMD's performance vary greatly due to the randomness of CSI. In general, VMD-STMD has the best control effect, and its standard deviation is also the smallest, indicating the best control robustness. ● A semi-active tuned mass damper (STMD) with variable mass and damping and its control algorithm are proposed. ● The randomness and synchronization of crowd and the crowd-structure interaction effect are investigated. ● STMDs with different control strategies are compared based on multiple calculations according to crowd probabilistic models. ● Combined variable mass and damping STMD has the best control effect and robustness. [ABSTRACT FROM AUTHOR]

• The collision between a spar-type floating offshore wind turbine (FOWT) and ship is numerically investigated by the nonlinear finite element (FEM) method. • Model verification of finite element model is performed for both FOWT and ship. • The collision forces, displacements and accelerations of FOWT with different impact velocities are obtained. • The incurred structural damage of FOWT and ship with different impact velocities is evaluated. • The energy conversion ratio between FOWT and ship subjected to collision is obtained. This paper investigated the dynamic responses and the incurred structural damage of a 5 MW spar-type floating offshore wind turbine (FOWT) and a ship when they collide. Ansys/LS-DYNA was used to establish the finite element models (FEMs) of the FOWT and the ship and to subsequently conduct the collision analysis. The global dynamics of the FOWT are captured well by the FEM comparing with FAST code and a simplified 8-degree of freedom (8-DOF) model established in MATLAB. The validity of the ship FEM was guaranteed by the fact that the model outputs agree well with empirical formulas. A series of simulations were then carried out using the FEMs to analyze the impact forces, displacements, accelerations, damages and energy dissipation during the ship collision for various impact velocities. The results show that the peak collision force, peak spar platform displacement and peak tower top displacement increase almost linearly with the initial velocity of the ship. The maximum tower top acceleration during the collision consistently exceeds 0.2 g, severely affecting the normal operation of the FOWT. The collision causes dents on the spar platform rather than the collapse of the whole wind turbine. After the collision, the initial kinetic energy of the ship is mainly transformed into the plastic deformation energy of the FOWT and the energy dissipated in the water. In addition, assuming a rigid ship bow results in accurate FOWT dynamic responses but fails to provide a good evaluation of the spar platform deformation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modeling of rubberized concrete-filled steel tubular columns under cyclic bending. • Dynamic explicit analyses with kinetic energy control of short columns using ABAQUS. • Influence of rubberized concrete (RuC) on columns' energy dissipation capacity (ΔE) • Lower brittleness of RuC is offset by its lower strength, reducing (ΔE) of columns. • RuC with increased strength is shown to potentially increase ΔE of columns. In this paper, the mechanical behaviour of short rubberized concrete-filled steel tubular (RuCFST) columns with square cross-section under combined cyclic bending and (monotonic) compression is studied numerically. For this purpose, dynamic explicit analyses with kinetic energy control (for the quasi-static behavior to be obtained) using the commercial finite element modelling package ABAQUS were performed. Firstly, a brief introduction and literature review on the topic is made. Then, the numerical models are described in detail with emphasis on the modelling of the materials (natural aggregate concrete (NAC), rubberized concrete (RuC) and steel) under cyclic loading. An in-depth presentation of the numerical results is made afterwards. It includes firstly a verification of the models by comparison of the numerical results with their experimental counterparts, the latter previously obtained by the authors. Secondly, a numerical study on the effectiveness of RuC on the energy dissipation capacity of CFST columns under lateral cyclic loading is performed. It is concluded that the models yield similar results regarding stiffness, maximum loads, load–displacement curves and failure modes as those obtained experimentally, with RuC leading to a moderate reduction (of up to 2%) of the strength of the columns. Regarding the energy dissipation capacity of the columns, it is concluded that RuC generally leads to a reduction of this property (of circa 2.5% per each 5% of rubber aggregates replacement). The lower strength and stiffness of the RuC mixes designed for this study compared to NAC are found to generally offset the benefit of their lower brittleness in increasing the energy dissipation capacity of the columns. [ABSTRACT FROM AUTHOR]