Editorial Proc IMechE Part C: J Mechanical Engineering Science 2021, Vol. 0(0) 1–3 © The Author(s) 2021 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/09544062211058605 journals.sagepub.com/home/pic “Nonlinear Dynamics of Mechanical Systems” dedicated to 75th birthday and 52 years scientific contribution of Prof. Katica R. (Stevanovic) Hedrih Fotios Georgiades 1 , Andjelka Hedrih 2 and Ivana Atanasovska 2 The work on this Special Issue (SI) started in 2019 and it is dedicated to the 75th birthday and to 52 years of scientific work of Professor Katica R. (Stevanovi´ c) Hedrih. The SI mostly contains invited papers that were presented in the form of abstracts at the international Symposium “Non- linear Dynamics – Scientific work of Prof. dr Katica (Stevanovi´ c) Hedrih” that was held in the Mathematical Institute of the Serbian Academy of Sciences and Arts (MI SANU), Belgrade, September 4th - 6th 2019. As mentioned in the Tribute of Professor Hedrih [Hedrih and Georgiades], her contribution is mainly in nonlinear dynamics, hence the title of the SI. It might be misleading since this SI includes articles with linear analysis from other fields too. Apologies to the readers, since Prof. Hedrih is a quite beloved person, a very popular scientist, and respected by scientists from many other fields of science (like the- oretical and applied mechanics, mathematical physics and history of mechanics), a compromise had to be done and the contribution of all scientists is considered. The articles on this SI fall in one of the following categories: structural mechanics, multiphysics problems with structural me- chanics, fluid dynamics and thermodynamics. Dynamic analysis, [Awrejcewicz et al, Georgiades, Hedrih, Jiang et al, Kurpa and Shmatko, Mohajed et al, Nesic et al] 1–7 modeling, [Dwaikat et al 2021a, Dwaikat et al 2021b, Spitas et al, Hammami et al, Kevac et al, Mirtaheri and Zohoor, Trajkovi´ c-Milenkovi´ c et al] 8–14 control, and stability [Carboni et al, Lazarevic et al, Manevich] 14–16 are the three subcategories of structural mechanics. Considering, whereas is possible, alphabetical order in the analysis of the articles for each subcategory a summary is following. In Awrejcewicz et al. 2 the principal component analysis is used in analyzing dynamics of several elastic continua, like straight beams in Winkler foundation and spherical shells. More precisely the principal component analysis used to describe the dynamics in noise signals and the results were compared with Wavelet and also with Em- pirical Mode Decomposition with Hilbert Transform spectra. Georgiades proved a theorem that the perpetual points in linear mechanical dissipative systems are asso- ciated with rigid body modes. Hedrih’ s 4 review article is a summary of some of her work in 52 years of contribution to science. Highlighting the performed nonlinear dynamic analysis of hybrid systems with the stochastic stability of vibration modes of sandwich panels, transversal vibrations of axially moving double belt system, fractional type hybrid system dynamics applied in multideformable bodies cou- pled by fractional derivatives type continues layers, and a new model of dislocations in elastic continua. Jiang et al based on a nonlinearity quantification of the complexity of the trajectories with nonlinearity measures a method for nonlinear system identification method is shown, and in rotor bearing system is applied. Buckling and free of force dynamic analyses of functionally graded sandwich plates and shallow shells using the R-functions in Kurpa and Shmatko 6 with good agreement with the literature results is shown. Mohajed et al. 1 with nonlinear dynamic analysis showed the existence of a particular type of modal inter- actions with a self-adeptness of an attachment to narrow or broadband targeted energy transfers in low or high fre- quencies. Super-harmonic resonance of a nanobeam with geometric nonlinearities rested on a fractional visco- Paternak foundation in 7 with multiple scale analysis is shown. There are three articles [Dwaikat et al 2021a, Dwaikat et al 2021b, and Spitas et al] 8–10 in modelling by the same authors that are falling on the same topic to be discussed. Modifying the viscous damping model to exhibits weak dependency on frequency Spitas et al. 10 proposed the single degree of freedom time-domain model for elastic hysteretic damping. Free and forced vibration responses under both harmonic and nonharmonic periodic excitations were evaluated and model compared with the viscous, Collar ’ s and Reid’ s models. The model is further developed in a nonlinear elastic hysteresis model for multi-degree of freedom systems in Dwaikat et al 2021a 8 for quantification of damping and the results are in good agreement with the reported in the literature. The computational procedure for solving the multi-degree of freedom systems with this elastic hysteresis model and the adoption of finite ele- ment formulation by Dwaikat et al 2021b 9 is elaborated. Hammami et al. 11 developed a nonlinear planetary gear 1 Centre of Perpetual Mechanics & Centre for Nonlinear Systems, Chennai Institute of Technology, Chennai, India 2 Mathematical Institute of the Serbian Academy of Sciences and Arts, Belgrade, Serbia Corresponding author: Fotios Georgiades, Centre of Perpetual Mechanics & Centre for Nonlinear Systems, Chennai Institute of Technology, Chennai, India. Email: fotiosgeorgiades@citchennai.net