Forced response of shrouded blades with a coupled static/dynamic approach

A coupled static-dynamic method is proposed and applied to bladed disks with shrouds, in order to calculate the nonlinear forced response in presence of friction damping in the frequency domain. The novel approach allows to improve the already existing methods, which require a preliminary static analysi

Determination of periodic response limits among multiple solutions for mechanical systems with wedge dampers

Wedge dampers are commonly used to utilize the frictional behavior in many engineering fields such as vehicle dynamics and turbo-machinery. However, the presence of non- unique contact forces in the damper interfaces creates an uncertainty that provides different dynamic response amplitudes even for the same input parameters. The maximum limits of the variability range always take the core attention in most of the damper design processes. In this paper, determination of an upper and a lower boundary among multiple steady-state solutions is presented by using a numerical approach. The method is specifically suitable for the mechanical systems with wedge dampers modeled by macro-slip frictional contact elements in the joint interfaces. In the approach proposed, a criterion that determines the periodic response boundaries according to the limit tangential force values is utilized. The method is demonstrated by illustrating several case studies on a lumped parameter system which represents a turbo-machinery application with a symmetric wedge damper pressed against two vibrating adjacent blades. A point-to-point 1D friction model with varying normal force is used in both contact sides. A parametric investigation on the variability range and response limits is performed for different damper configurations. Harmonic Balance Method with Newton’s iteration scheme is used in the numerical solution of the governing equations. The results show that a large variability exists for damper geometries where a strong coupling is present between tangential and normal contact forces. The method proposed successfully captures the limits of the variability range in all cases

Paleoenvironmental implications through the study of an Eemian paleosol in northwestern Sardinia (Italy)

The aim of this work is to define the paleoenvironmental changes related to a soil belonging to the studied succession, by means of an in-depth micromorphological study. In particular, the presence of this paleosol is associated to the fast climatic fluctuations that took place between MIS5e and MIS5c

La storia di Marco. L’intervento educativo-didattico per un bambino con autismo

During our discussion, we will deal with the specific details, the behavioral difficulties and the impairments of the Autism Spectrum Disorder. We will do this through a case study regarding the story of a child, a son and a student that we will decide to call Marco. This means that the cognitive investigation will focus on an ideal situation typical of something much bigger that is the world of childhood autism. Under this label, in fact, there are personal conditions that, although they have some common elements among them, they are totally autonomous, difficult to access and, with no doubt, cannot be narrowed down to a single descriptive model. In light of this, by way of example, we intend here to examine the main behavioral characteristics of a subject with a neurodevelopmental disorder, his strengths and elements of weaknesses, focusing on special pedagogy methodologies required to carry out a preliminary analysis of the situation and to set the necessary educational-training interventions.We will try to go in depth, "touching" the experience of Marco's family closely, the stories with doctors and his main famly figures and we will try to get close to the practice of an educationaldidactic intervention at school. At this point, we will also present some aspects and strategies of inclusive teaching will be presented such as observation and evaluation as well as the functional analysis of behavior.Whereas the analysis of Autism Spectrum Disorder usually focuses a review of the impairments at the neuropsychological level and explanatory theories, the aim of this study is, on the opposite, to bring a real story, an experiencet can provide, although not solutions, but at least some practical tips and ideas

Measuring the Performance of Underplatform Dampers for Turbine Blades by Rotating Laser Doppler Vibrometer

Underplatform friction dampers are commonly used to control the vibration level of turbine blades in order to prevent high-cycle fatigue failures. Experimental validation of highly non-linear response predictions obtained from FEM bladed disk models incorporating underplatform dampers models, has proved to be very difficult so as the assessment of the performance of a chosen design. In this paper, the effect of wedgeshaped underplatform dampers on the dynamics of a simple bladed disk under rotating conditions is measured and the effect of the excitation level on the UPDs performances is investigated at different number of the engine order excitation nearby resonance frequencies of the 1st blade bending modes of the system. The measurements are performed with an improved configuration of a rotating test rig, designed with a noncontact magnetic excitation and a non-contact rotating SLDV measurement syste

Smorzatori sotto-pala per turbomacchine: un nuovo metodo basato sul calcolo simultaneo delle forze statiche e dinamiche di contatto

Underplatform dampers are widely used to reduce vibration amplitude of turbine bladed disks by friction. They are metal devices placed under the blade platforms and held in contact with them by the centrifugal force acting during rotation. The common procedure used to calculate the static loads acting on underplatform dampers consists in decoupling the static and the dynamic balance of the damper. A preliminary static analysis of the contact is performed in order to compute the static pressure distribution over the damper/blade interfaces, assuming that it does not change when vibration occurs. In this paper a coupled approach is proposed to solve the static and the dynamic balance equations of the system. Numerical case studies are presented in order to show the capabilities of the method and the improvements with respect to the state of the ar

A novel test rig to study the effect of fretting wear on the forced response dynamics with a friction contact

This paper presents a novel test rig to study the effect of fretting wear and of the contact surface evolution on the forced response of systems with dry friction contact. This rig allows simulating contacts similar to the type of contacts present between the shrouds at the blade tip. Several research groups have been studying how fretting wear affects the dynamic response of mechanical systems, developing numerical prediction tools that consider dry friction contact and nonlinearity. The aim of this work is to experimentally study the evolution of contact interfaces and how this evolution affects the system dynamics. Experimental results will aid to validate the numerical predictions. The test rig developed for this activity is made of a cantilever beam fixed at one end and with a friction contact at the free end. The contact couple is made of two replaceable specimens. The contact is loaded via a lifting mechanism through a screw with fine thread. Fretting wear test was performed at a constant frequency and force amplitude, exciting the beam with an electromagnetic shaker. To emphasize the change of the dynamic response, frequency sweeps were performed at various intervals during the wear test. The full range test with ‘changing preload’ due to progressing wear was performed until a full loss of contact. This paper describes the test rig design, intent, set-up, instrumentation, test plan and results. Results include the frequency response curves for unworn contact, wear profiles at multiple intervals and the effect of wear on the frequency response. Though energy dissipation per cycle is quite small, wear leads to material loss at the contact with a sufficiently large number of cumulative cycles and substantially affects the dynamic response. Results collected in this research activity are of particular importance to validate numerical tool that aim to simulate the dynamic behaviour of systems with dry friction contacts that undergo material loss caused by wear