Horizontal baffles for robust shallow water tuned sloshing dampers

Shallow tuned sloshing dampers (TSDs) experience performance degradation during modest wind events due to the severe excitation of higher order sloshing modes through nonlinear modal coupling. These higher order modes produce a "hardening"-spring type of response, whereby the natural sloshing frequency increases with TSD response amplitude, detuning the device from the primary structure. This study proposes using a horizontal baffle near the centre of the tank to suppress higher order sloshing modes, and thereby improve the robustness of shallow TSDs. This is a simple and effective solution to a problem that has hindered the application of TSDs in many tall buildings. A 6-node finite element model is employed to predict the natural frequencies and mode shapes of the lowest sloshing modes in a rectangular tank with a horizontal baffle. The addition of a modest-sized horizontal baffle at the center of the tank produces a minor (<2%) decrease to the equivalent TSD mass, and the natural frequency of the fundamental sloshing mode. Conversely, the baffle reduces the natural sloshing frequencies of the higher order sloshing modes considerably. Contour plots demonstrate how the equivalent TSD mass, and natural sloshing frequencies of the first four sloshing modes are reduced by horizontal baffles of various sizes and heights above the tank floor. A third-order multimodal model is used to simulate the coupling among the first three sloshing modes. Time series of the sloshing wave heights and sloshing forces show that the horizontal baffle suppresses the excitation of higher order sloshing modes significantly. Similarly, frequency response curves of the wave heights and sloshing forces show that the excitation of higher order harmonics is suppressed, producing a substantial reduction to the "hardening"-spring response behaviour.