Inside the laboratory, there are two workgroups centred around some unifying theme.

The workgroup focused on nonlinear wave dynamics is composed of Andrus Salupere, Jüri Engelbrecht, Arkadi Berezovski, Dmitri Kartofelev, Kert Tamm, Tanel Peets, Mart Ratas and Martin Lints. Most of the members of the group are currently involved in the project PRG1227 “Modelling of nonlinear wave processes in advanced materials” while Mart Ratas is also involved in COVSG22 “Monte-Carlo analysis of the spreading rate of a virus as a function of human mobility and social distancing” and Martin Lints is currently primarily focused on PRG737 “Quantitative imaging methods and efficient signal processing algorithms for ultrasonic nondestructive evaluation”.

The workgroup focused on reinforced composites and meta-materials is composed of Heiko Hermann and his PhD students Oksana Goidyk and Mark Heinštein. Heiko Hermann is currently focused on project COVSG22 “Monte-Carlo analysis of the spreading rate of a virus as a function of human mobility and social distancing”.

Recent and current research projects

PRG1227 “Modelling of nonlinear wave processes in advanced materials (1.01.2021−31.12.2025)”, Andrus Salupere, Tallinn University of Technology, School of Science, Department of Cybernetics.

The project is focused on modelling nonlinear wave processes in advanced materials. It is well known that no general analytical methods exist for the solution of nonlinear wave equations. Each specific case has to be treated individually. Problems under consideration include analysis of wave processes in axons, sound generation in string instruments, wave control using modulated metamaterials. All the problems are unified through mathematical modelling: similar methods are used to study different phenomena. The models, that will be created, focus on wave dynamics in biological and metamaterials, structural damping of vibrations, wave dispersion, energy transformation or dissipation. Problem formulations and solution methods are based on the thermodynamically consistent continuum mechanics framework. Mathematical modelling is a beneficial approach in gaining a better understanding of the underlying physical processes from different viewpoints and for performing in silico experiments.

IUT33-24 “Wave propagation in complex media and applications (1.01.2015−31.12.2020)”, Andrus Salupere, Tallinn University of Technology, Institute of Cybernetics at TUT, Tallinn University of Technology, School of Science, Department of Cybernetics.

The research topic is focused on wave propagation in complex media and corresponding applications. On the one hand, the topic includes direct problems where the goal is to analyse how waves of different types emerge, propagate and interact in materials which properties and characteristic parameters are known. Here the main attention is paid to the interaction between deformation waves and the internal structure of the material. On the other hand, the aim is to solve inverse problems, in order to determine properties of materials, the existence of defects or residual stresses, etc making use of quantities measured from physical experiments (eg speed of waves, the extent of phase shifts, the transformation of the polarisation etc.). The results can be applied for nondestructive testing of materials, for monitoring production during exploitation, in medicine, etc Further studies are related to the development of functionally graded materials, metamaterials, or smart materials having self-monitoring capability

PUT1146 “Rheology of short fibre reinforced cementitious composites and influence on fracture behaviour (1.01.2016−31.12.2019)”, Heiko Herrmann, Tallinn University of Technology, Institute of Cybernetics at TUT, Tallinn University of Technology, School of Science, Department of Cybernetics.

Within this project, the influence of the rheology on the spatial and orientational distribution of short fibres in short fibre reinforced cementitious composites were investigated numerically and experimentally. The orientation distribution of the fibres defines material symmetry and is important for material properties. The dependence of the material properties on the fibre orientation was investigated. Further, software for the analysis of fibre distributions from CT images was developed. The software makes the analysis easier. Also, software for the visualization of orientation distribution fields will be developed.

PUT434 “Wave energy redistribution in solids with microstructure (1.01.2014−31.12.2017)”, Arkadi Berezovski, Tallinn University of Technology , School of Science, Department of Cybernetics, Tallinn University of Technology , Institute of Cybernetics at TUT.

Wave energy redistribution in solids is concerned with applications in many fields such as impact mitigation, crashworthiness, sound control, earthquake mitigation. To achieve the desired energy redistribution, the knowledge of how the microstructure of a solid influences wave shape and speed is necessary. The main objectives of the project are the theoretical understanding of wave processes in microstructured solids and the development of computational tools which will predict quantitatively wave fields including these in time-dependent phononic crystals with desired functionality. The dual internal variables approach will be applied to the description of microstructure influence on wave propagation in solids. A finite volume numerical approach will be used for the development of computational algorithms for wave propagation in microstructured solids. The concept of dynamic materials will be applied for the modelling of wave management in time-dependent phononic crystals.

“Center of Excellence (TK)” project TK124 – “Centre for Nonlinear Studies – CENS (1.01.2011−31.12.2015)”, Jüri Engelbrecht, Tallinn University of Technology, Institute of Cybernetics at TUT, University of Tartu, Faculty of Science and Technology (old), Institute of Physics, University of Tartu.

CENS was the Estonian hub for knowledge, research and training in nonlinear phenomena such as solitons, coherence, chaos, etc., that need specific tools for their analysis and control. CENS carryed out analytic and experimental research of top quality targeted at making progress in the analysis, synthesis and control of nonlinear processes, with a special focus on the training of young scientists. The key research areas were nonlinear wave motion in solids, fluids and optical media, nonlinear dynamics in soft matter physics and heart energetics, and nonlinear control theory. Synergy was reached via joint progress in the modelling and analysis of different systems and intense internal, national and international transfer of knowledge and experience, especially through collaboration with industry, developing innovative applications in Estonian and EU priority areas (material science, medicine, environment), and regular events for the general public and specific stakeholders