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Many engineering problems can be solved using a linear approximation. In the Finite Element Analysis (FEA) the set of equations, describing the structural behaviour is then linear K d = F (1.1) In this matrix equation, K is the stiffness matrix of the structure, d is the nodal displacements vector and F is the external nodal force vector. Characteristics of linear problems is that the displacements are proportional to the loads, the stiffness of the structure is independent on the value of the load level. Though behaviour of real structures is nonlinear, e.g. displacements are not proportional to the loads; nonlinearities are usually unimportant and may be neglected in most practical problems.
This third of three volumes from the inaugural NODYCON, held at the University of Rome, in February of 2019, presents papers devoted to New Trends in Nonlinear Dynamics. The collection features both well-established streams of research as well as novel areas and emerging fields of investigation. Topics in Volume III include NEMS/MEMS and nanomaterials: multi-sensors, actuators exploiting nonlinear working principles; adaptive, multifunctional, and meta material structures; nanocomposite structures (e.g., carbon nanotube/polymer composites, composites with functionalized nanoparticles); 0D,1D,2D,3D nanostructures; biomechanics applications, DNA modeling, walking dynamics, heart dynamics, neurodynamics, capsule robots, jellyfish-like robots, nanorobots; cryptography based on chaotic maps; ecosystem dynamics, social media dynamics (user behavior dynamics in multi-messages social hotspots, prediction models), financial engineering, complexity in engineering; and network dynamics (multi-agent systems, leader-follower dynamics, swarm dynamics, biological networks dynamics).
Nonlinear dynamics of transverse bending vibrations in a cantilever beam with an edge crack is studied by means of nonlinear system identification (NSI) technique, which is based on close correspondence between analytical and empirical slow flows. A cantilever beam without crack (or a healthy beam) is considered as a reference for underlying linear behaviors. Numerical study by finite element analysis (FEA) and experimental modal analysis (EMA) are performed as compared to analytical modal information by Euler beam theory. A saw-cut slit with two different depths is created at different locations along the beam span to model an edge crack (and it is named a damaged beam). By means of FEA and EMA with referenced to the healthy beam, fundamental nonlinear behaviors such as softening nonlinearity due to the edge crack and energy transfers from a certain mode to another through nonlinear modal interactions (or internal resonances) can be observed under different loading levels and crack depths. Such nonlinear modal interactions can also be evidenced by the modal assurance criterion, where significant correlations between non-likewise modes can be exhibited at off-diagonal locations. Finally, the NSI technique is employed to investigate the experimentally observed nonlinear dynamics of the damaged beam. Through empirical mode decomposition method, intrinsic mode functions (IMFs) of each measured data are obtained, which are monocomponent to analytically calculate respective instantaneous frequencies. Nonlinear interaction models (NIMs) are derived from the IMFs, and are validated and verified accordingly. The NIMs obtained are sets of linear second-order ordinary differential equations (or called intrinsic modal oscillators), whose nonhomogeneous terms include nonlinear modal interactions, and they can be utilized to establish a data-driven yet physics-based reduced-order model. Softening nonlinearity and energy transfers between specific modes are verified with the NIMs. Future work consist on performing the NSI on more crack locations. To create an analytical model in order to describe the nonlinear model of the system where the nonlinear model contains a nonlinear homogeneous solution instead of a nonlinear nonhomogeneous solution.
Dynamics with friction: Modeling, analysis and experiments, part II. ch. 1. Interaction of vibration and friction at dry sliding contacts / Daniel P. Hess -- ch. 2. Vibrations and friction-induced instability in discs / John E. Mottershead -- ch. 3. Dynamics of flexible links in kinematic chains / Dan B. Marghitu and Ardeshir Guran -- ch. 4. Solitons, chaos and modal interactions in periodic structures / M.A. Davies and F.C. Moon -- ch. 5. Analysis and modeling of an experimental frictionally excited beam / R.V. Kappagantu and B.F. Feeny -- ch. 6. Transient waves in linear viscoelastic media / Francesco Mainardi -- ch. 7. Dynamic stability and nonlinear parametric vibrations of rectangular plates / G.L. Ostiguy -- ch. 8. Friction modelling and dynamic computation / J.P. Meijaard -- ch. 9. Damping through use of passive and semi-active dry friction forces / Aldo A. Ferri