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In recent years, hydrogels have been introduced as new materials suitable for applications in areas such as biomedical engineering, agriculture, etc. The rate and degree of hydrogel swelling are important parameters that control the diffusion of drugs or solvents inside a polymer network. Therefore, the description of the dynamic swelling process of the hydrogels is very important in applications that require precise control of the absorption of solvents inside the hydrogel structure. To date, most of the numerical models developed for describing the swelling process are based in the finite difference methods. Even though numerical models supported in finite differences can be easily implemented, their use is limited to samples with very simple shapes. In this paper, a new model based on the finite element method is proposed. The diffusion equation is solved in a time-deformable grid. An original procedure is proposed to numerically solve the non-linear algebraic equation system that permits computing a new grid for each time-step. Hydrogel samples of different shapes were prepared in order to conduct experimental tests to validate the numerical proposed model. Numerical results show that the new model is able to describe the mass and shape changes in the hydrogel samples in time. An application of the numerical model to determine the relation between diffusion coefficients and density in Polyacrylamide samples allows verifying the versatility of the model.

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In this paper, the behavior of a tuned mass damper (TMD), to torsionally control a linear structure subjected to seismic excitations, is investigated. The dynamic system is analyzed taking into account lateral-torsional coupling, soil-structure interaction, and the rotational components of the foundation motion. The system model consists of an asymmetrical structure, founded on a soil modeled as a homogeneous semi-space. A stationary stochastic analysis is performed in the time domain, and a double Clough-Penzien filter of broad frequency content is used to define the random process for the X and Y directions. The torsional balance criterion is employed for the optimization of the TMD design parameters. The influence of the plan static eccentricity over optimum TMD parameters' behavior is also addressed, taking into account the fixed base period, flexible period, torsional frequency ratio, and soil type. Compliance with the torsional balance is verified. The results show that the inclusion of the soil rotational component has a notorious influence on the optimum TMD parameters. Moreover, torsionally flexible structures founded on soft and medium soil show significant influence on the torsional balance.Finally, a transitory response analysis is carried out for a 15-story model, subjected to an artificial bidirectional earthquake with a broadband frequency content. The multistory model response validates the results derived from the stochastic analysis.

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