Nonlinear vibration absorbers for ropeway roller batteries control

This work investigates a nonlinear passive control strategy designed to reduce the peak accelerations in ropeway roller batteries systems by deploying an array of nonlinearly visco-elastic vibration absorbers. The control effectiveness is compared with that of an equivalent array made of linearly visco-elastic absorbers. A nonlinear parametric model describing the interactions between the different parts of this mechanical multibody system previously developed by the present authors is here extended to include the passive vibration control system aimed to mitigate the acceleration peaks induced by the vehicles transit at different operational speeds. To this aim, a set of linearly visco-elastic vibration absorbers is first optimized through the Differential Evolution (DE) algorithm seeking to minimize the area below the frequency-response curves of the linear equations of motion. Then, a new group of nonlinearly visco-elastic absorbers, that can be largely tuned (i.e., they can exhibit either softening or hardening behaviors), is proposed to mitigate the accelerations induced in the roller by the vehicle transit. These nonlinearly visco-elastic absorbers are optimized by means of the DE algorithm and comparisons with the control achieved by the linear absorbers are carried out to show the higher performance of the proposed nonlinear device. A possible design of the nonlinearly visco-elastic absorber, based on the hysteresis of a wire rope assembly undergoing flexural cycles, is also proposed and discussed

Two-to-one resonant multi-modal dynamics of horizontal/inclined cables. Part I : theoretical formulation and model validation

This paper is first of the two papers dealingwith analytical investigation of resonant multimodal dynamics due to 2:1 internal resonances in the finite-amplitude free vibrations of horizontal/inclined cables. Part I deals with theoretical formulation and validation of the general cable model. Approximate nonlinear partial differential equations of 3-D coupled motion of small sagged cables - which account for both spatio-temporal variation of nonlinear dynamic tension and system asymmetry due to inclined sagged configurations - are presented. A multidimensional Galerkin expansion of the solution ofnonplanar/planar motion is performed, yielding a complete set of system quadratic/cubic coefficients. With the aim of parametrically studying the behavior of horizontal/inclined cables in Part II [25], a second-order asymptotic analysis under planar 2:1 resonance is accomplished by the method of multiple scales. On accounting for higher-order effectsof quadratic/cubic nonlinearities, approximate closed form solutions of nonlinear amplitudes, frequencies and dynamic configurations of resonant nonlinear normal modes reveal the dependence of cable response on resonant/nonresonant modal contributions. Depending on simplifying kinematic modeling and assigned system parameters, approximate horizontal/inclined cable models are thoroughly validated by numerically evaluating statics and non-planar/planar linear/non-linear dynamics against those of the exact model. Moreover, the modal coupling role and contribution of system longitudinal dynamics are discussed for horizontal cables, showing some meaningful effects due to kinematic condensation

Sustainable Modification of Chitosan Binder for Capacitive Electrodes Operating in Aqueous Electrolytes

Biopolymers emerged in recent years as a promising alternative for a more sustainable manufacturing of electrochemical energy storage systems. In fact, for environmentally friendly aqueous systems, fluorinated polymers are usually adopted. For this reason, substituting these polymers with water processable binders could improve the overall environmental impact of the device. In this study, a low – cost and environmentally friendly modification of chitosan binder for self-standing activated carbon electrodes operating in Na ion, aqueous electrochemical double layer capacitors is reported and discussed

Early mandibular canine-lateral incisor transposition: case report

Purpose. The main aim of the present study is to present a case of mandibular transposition between lateral incisor and canine in a paediatric patient. Materials and methods. A fixed multibracket orthodontic treatment was performed by means of a modified welded arch as to correct the transposition and obtaining a class I functional and symmetrical occlusion, also thanks to the early diagnosis of the eruption anomaly. Results. Our case report shows that a satisfactory treatment of mandibular transpositions is obtained when detected at an early stage of the tooth development. Conclusions. The main treatment options to be taken into consideration in case of a mandibular transposition are two: correcting the transposition or aligning it leaving the dental elements in their transposed order; in both cases, the followups show a stable condition, maintained without relapses. Several factors, such as age of the patient, occlusion, aesthetics, patient’s collaboration, periodontal support and duration of treatment have to be considered as to prevent potential damage to dental elements and support appliances. The choice between the two treatment approaches for mandibular lateral incisor/canine transpositions mainly depends on the time the anomaly is detected

Stabilization Environment for Swing Stabilization and MEDEVAC Hoists

This paper presents data related to helicopter sling load stabilization and MEDEVAC (Medical Evacuation) rescues collected by cadets performing research in the field at the United States Military Academy (West Point, NY) and Sapienza University of Rome (Rome, Italy) since 2018. The aim of this paper is to identify engineering constraints in MEDEVAC rescues. Constraints in two typical scenarios are presented. This information can then be included in simulations and models of swing stabilization and hoist control methods. Information is obtained through a literature review and interviews with U.S. Army helicopter pilots and crew chiefs who perform MEDEVAC rescues

The effect of branched carbon nanotubes as reinforcing nano-filler in polymer nanocomposites

This work discusses the mechanical and dissipative properties of nanocomposite materials made of a high-performance thermoplastic polymer (polybutylene terephthalate, PBT) integrated with branched carbon nanotubes (bCNTs) as nanofiller. The storage and loss moduli as well as the loss factor/damping ratio of the nanocomposites are experimentally characterized for increasing bCNT weight fractions (wt% bCNT) upon variations of the input cyclic strain amplitude and of the input frequency, respectively. The trends obtained for the nanocomposites mechanical properties indicate improvements both in storage and loss modulus by increasing the bCNT weight fraction from 0.5% to 2%. The striking differences between the damping capacities exhibited by CNT/polymer and bCNT/polymer nanocomposites are discussed to shed light onto the different underlined mechanics of the nanocomposites. Due to the stick–slip relative sliding motion of the polymer chains with respect to the straight CNTs, CNT/PBT nanocomposites are known to exhibit a peak in the damping vs. strain amplitude curves, past which, the damping capacity shows a monotonically increasing trend due to the conjectured sliding of the polymer crystals. On the other hand, we show for the first time that bCNT/PBT nanocomposites do not exhibit a peak in the damping capacity but rather a plateau after an initial drop at low strains. This behavior is attributed to the much reduced mobility of the branched CNTs and the lack of formation of crystalline structures around the bCNTs

Free propagation of resonant waves in nonlinear dissipative metamaterials

This paper deals with the free propagation problem of resonant and close-to-resonance waves in one-dimensional lattice metamaterials endowed with nonlinearly viscoelastic resonators. The resonators’ constitutive and geometric nonlinearities imply a cubic coupling with the lattice. The analytical treatment of the nonlinear wave propagation equations is carried out via a perturbation approach. In particular, after a suitable reformulation of the problem in the Hamiltonian setting, the approach relies on the well-known resonant normal form techniques from Hamiltonian perturbation theory. It is shown how the constructive features of the Lie Series formalism can be exploited in the explicit computation of the approximations of the invariant manifolds. A discussion of the metamaterial dynamic stability, either in the general or in the weak dissipation case, is presented

DYNAMIC MORPHING of ELASTIC PLATES VIA PRINCIPAL PARAMETRIC RESONANCE

Principal parametric resonances of elastic plates actuated by periodic in-plane stresses effected by embedded piezoelec-tric wires are investigated to describe the morphing scenarios of flexible, ultra-lightweight panels. A mechanical model of elastic plate including geometric nonlinearities and the parametric actuation provided by the piezoelectric wires, is adopted to for-mulate the nonlinear equation of motion. A bifurcation analysis is carried out by means of an asymptotic approach based on the method of multiple scales leading to a comprehensive paramet-ric study on the effect of the wires width on the morphing regions (i.e., parametric instability regions) associated with the princi-pal parametric resonances. The threshold voltages triggering the onset of the principal parametric resonances of the lowest three symmetric modes are also calculated as a function of the wires size so as to determine the voltage requirements for the morphing activation

Nonlinear vibration absorber design: An asymptotic approach

The one-to-one internal resonance occurring in a two-degree-of-freedom (2DOF) system composed by a damped non-linear primary structure coupled with a nonlinear vibration absorber is studied via the method of multiple scales up to higher order (i.e., the first nonlinear order beyond the internal/external resonances). The periodic response predicted by the asymptotic approach is in good agreement with the numerical results obtained via continuation of the periodic solution of the equations of motion. The asymptotic procedure lends itself to manageable sensitivity analyses and thus to versatile optimization by which different optimal tuning criteria for the vibration absorber can possibly be found in semi-closed form.</jats:p