Session: 07-09-01: Vibrations of Continuous Systems

Paper Number: 113857

113857 - Complex Dynamic Phenomena in Circular Cylindrical Shells 

Shell structures are common components are in Mechanical, Aerospace and Civil Engineering. Such structures allow to design highly efficient lightweight systems: drones, electric vehicles, deployable space systems. Such high efficiency is not costless, shells present several drawbacks: propensity to instability and resonances, sensitivity to imperfections, sensitivity to the presence of a fluid structure. In many applications, such as pipes and heater exchangers, the environmental temperature across the shell thickness can be different; this likely produces strong temperature gradients that influence the dynamic behavior. Applications of shells with fluid structure interaction (FSI) is important in engineering but also in medical science and in bio-engineering, examples are: wings and panel flutter, galloping of cables, blood circulation and related diseases, e.g. the human aorta, where the fluid is non-Newtonian. The interaction with fluids can cause a dramatic change in the dynamic response of a vibrating elastic system: instabilities, change the natural frequencies and mode shapes. It is to note that many fluids of common use are non-Newtonian: blood, blood plasma, toothpaste, starch suspensions, corn starch, paint, melted butter, shampoo. In real applications structures are often excited by non-deterministic dynamic forcing: turbulent flows, gravel roads, rockets or jet thrust. In many applications, complicating factors such as temperature variability strongly influence the material properties. When shell-like structures are subjected to strong random excitations and exposed to high thermal gradients, the dynamics can be characterized by strong nonlinearity, which leads to the rise of unexpected phenomena that cannot be predicted by standard design tools. In general, when a linear system is excited by a random force the response is random; however, in some particular conditions, like internal or parametric resonances, the presence of nonlinearities in the system can give rise to unexpected phenomena, for example the synchronization that induces an almost harmonic response. 

In this work we present the results a series of experiments on the subject of shell nonlinear dynamics with and without fluid interaction, with thermal effects, subjected to harmonic or random excitations. The effect of extreme thermal conditions, and high thermal gradients across the thickness of the shell is studied: a test setup has been developed to perform tests in controlled environment, in order to investigate unstable states. Empty and a fluid-filled shells are considered. Both Newtonian and non-Newtonian (dilatant) fluids are considered, in particular dilatant fluids. 

The results show a strong non-linear response due to the coupling between the fluid and structure and the shaker-structure interaction that leads to a very interesting dynamic scenario.

In the case of harmonic excitation, the dynamic scenario is analyzed by means of time histories, spectra, phase portraits and Poincaré maps. The experiments show the onset of complex dynamics: subharmonic and quasiperiodic responses, Chaos.

In the case of high-energy random excitation a synchronicity phenomenon was detected for particular thermal and loading conditions: a severe transfer of energy from a broadband excitation to almost harmonic response is experimentally observed; energy transfer to low frequencies was observed as well. 

Presenting Author: Francesco Pellicano Università di Modena e Reggio Emilia

Presenting Author Biography: Francesco Pellicano is Aeronautical Engineer and Ph.D. in Theoretical and Applied Mechanics, he is currently Full Professor, Head of the Centre Intermech MoRe and was committee president of 2 BsC and 2 MsC programmes. He was coordinator of EU Regional projects: METaGEAR (Gears, Materials, Robotics), INDGEAR (condition monitoring) and HPGA Fortissimo (applications of high performance computing); he was coordinator of several international and national projects. He published 2 Books, more than 70 Journal papers and more than 100 conference papers. Bibliometry: h-index 34, more than 3000 citations. His research activities are: fluid-structure interaction, gear stress and vibration modelling and testing; nonlinear vibrations of structures; vibration control; shell dynamics and stability; thermal effects, vibration of carbon nanotubes; non-smooth dynamics; Chaos; devices for Parkinson disease mitigation.

Authors:

Francesco Pellicano Università di Modena e Reggio Emilia
Giovanni Iarriccio University of Modena and Reggio Emilia
Antonio Zippo University of Modena and Reggio Emilia