Comparison of Two Widely-Used Frequency-Time Domain Contact Models for the Vibration Simulation of Shrouded Turbine Blades

2014 ◽  
Author(s):  
Anna Herzog ◽  
Malte Krack ◽  
Lars Panning-von Scheidt ◽  
Jörg Wallaschek
Keyword(s):  
Coulomb Friction ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Special Focus ◽  
Friction Contact ◽  
Numerical Convergence ◽  
Bladed Disk ◽  
Contact Models ◽  
Coulomb Friction Law ◽  
Vibration Simulation

Friction damping is often used in turbomachinery to reduce the vibration amplitudes of turbine blades in operation. Different approaches can be used to simulate the friction contact in the design process. For nonlinear steady state simulations, the Multi-Harmonic Balance Method (MHBM) is often used in combination with an Alternating Frequency Time (AFT) Method. The friction contact can be modeled by introducing normal and tangential stiffnesses and a Coulomb friction law. However, it is difficult to identify these contact stiffnesses experimentally. Alternatively, a formulation with Dynamic Lagrangians can be chosen. This contact model can be formulated without the need for contact stiffnesses. Both widely-used approaches are applied to a model bladed disk with nonlinear shroud contact and compared with a special focus on the predicted vibrational behaviour, numerical convergence, and their sensitivity towards changes in the input parameters.

Modeling Complex Contact Conditions and Their Effect on Blade Dynamics

2020 ◽  
Author(s):  
Chiara Gastaldi ◽  
Johann Gross ◽  
Maren Scheel ◽  
Teresa M. Berruti ◽  
Malte Krack
Keyword(s):  
Contact Pressure ◽  
Harmonic Balance Method ◽  
Structural Vibrations ◽  
Bladed Disks ◽  
Contact Conditions ◽  
Softening Behavior ◽  
Contact Models ◽  
Coulomb Friction Law ◽  
Fatigue Failures ◽  
Laboratory Demonstrator

Abstract Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels. An unexpected hardening behavior was observed on the frequency response functions of two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator, however its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the Multi-Harmonic Balance Method (MHBM) in combination with the Alternating Frequency Time (AFT) Method.

Modeling Complex Contact Conditions and Their Effect on Blade Dynamics

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Chiara Gastaldi ◽  
Johann Gross ◽  
Maren Scheel ◽  
Teresa M. Berruti ◽  
Malte Krack
Keyword(s):  
Contact Pressure ◽  
Coulomb Friction ◽  
Structural Vibrations ◽  
Bladed Disks ◽  
Contact Conditions ◽  
Softening Behavior ◽  
Contact Models ◽  
Coulomb Friction Law ◽  
Fatigue Failures ◽  
Laboratory Demonstrator

Abstract Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels. An unexpected hardening behavior was observed on the frequency response functions (FRFs) of a two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator; however, its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady-state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the multiharmonic balance method in combination with the alternating frequency time method.

A Contact Model for Nonlinear Forced Response Prediction of Turbine Blades: Calculation Techniques and Experimental Comparison

2008 ◽  
Author(s):  
Christian M. Firrone ◽  
Marco Allara ◽  
Muzio M. Gola
Keyword(s):  
Normal Load ◽  
Contact Stiffness ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Contact Forces ◽  
Contact Model ◽  
Experimental Comparison ◽  
Normal Contact ◽  
Contact Models

Dry friction damping produced by sliding surfaces is commonly used to reduce vibration amplitude of blade arrays in turbo-machinery. The dynamic behavior of turbine components is significantly affected by the forces acting at their contact interfaces. In order to perform accurate dynamic analysis of these components, contact models must be included in the numerical solvers. This paper presents a novel approach to compute the contact stiffness of cylindrical contacts, analytical and based on the continuous contact mechanics. This is done in order to overcome the known difficulties in simultaneously adjusting the values of both tangential and normal contact stiffness experimentally. Monotonic loading curves and hysteresis cycles of contact forces vs. relative displacement are evaluated as a function of the main contact parameters (i.e. the contact geometry, the material properties and the contact normal load). The new contact model is compared with other contact models already presented in literature in order to show advantages and limitations. The contact model is integrated in a numerical solver, based on the Harmonic Balance Method (HBM), for the calculation of the forced response of turbine components with friction contacts, in particular underplatform dampers. Results from the nonlinear numerical simulations are compared with those from validation experiments.

An Adaptive Tuned Mass Damper Using Friction Bars

2013 ◽  
Author(s):  
Marcus Neubauer ◽  
Jörg Wallaschek
Keyword(s):  
Dry Friction ◽  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Tuned Mass Damper ◽  
Special Focus ◽  
System Behavior ◽  
Friction Contact ◽  
Friction Forces ◽  
Damping Behavior ◽  
Mass Damper

This publication presents a novel realization of a Tuned Mass Damper (TMD) using friction bars. Because of the friction forces in the contact, they dissipate energy similar to a dry friction contact. Because of the nonlinear, amplitude depending damping behavior, it is possible to have the pure absorbing effect combined with broadband damping, which cannot be achieved by the classical, viscousely damped TMD. Special focus is layed on the modeling aspects. The friction contact is modeled using the Harmonic Balance method, and with help of the replacement parameters the system behavior is studied.

Some Consequences of Coulomb Friction in Modeling Longitudinal Traction

1990 ◽  
Vol 18 (1) ◽  
pp. 13-65 ◽  
Author(s):  
W. W. Klingbeil ◽  
H. W. H. Witt
Keyword(s):  
Shear Force ◽  
Coulomb Friction ◽  
Interfacial Shear ◽  
Force Generation ◽  
Behavior Patterns ◽  
Inflation Pressure ◽  
Friction Law ◽  
The Coefficient Of Friction ◽  
Coulomb Friction Law ◽  
Perfect Adhesion

Abstract A three-component model for a belted radial tire, previously developed by the authors for free rolling without slip, is generalized to include longitudinal forces and deformations associated with driving and braking. Surface tractions at the tire-road interface are governed by a Coulomb friction law in which the coefficient of friction is assumed to be constant. After a brief review of the model, the mechanism of interfacial shear force generation is delineated and explored under traction with perfect adhesion. Addition of the friction law then leads to the inception of slide zones, which propagate through the footprint with increasing severity of maneuvers. Different behavior patterns under driving and braking are emphasized, with comparisons being given of sliding displacements, sliding velocities, and frictional work at the tire-road interface. As a further application of the model, the effect of friction coefficient and of test variables such as load, deflection, and inflation pressure on braking stiffness are computed and compared to analogous predictions on the braking spring rate.

The elastic contact influences on passive walking gaits

Robotica ◽  
2010 ◽  
Vol 29 (5) ◽  
pp. 787-796 ◽  
Author(s):  
Feng Qi ◽  
Tianshu Wang ◽  
Junfeng Li
Keyword(s):  
Coulomb Friction ◽  
Dynamic Models ◽  
Contact Stiffness ◽  
Contact Forces ◽  
Hertz Contact ◽  
Walking Gait ◽  
Routes To Chaos ◽  
Coulomb Friction Law ◽  
Contact Parameters ◽  
Passive Model

SUMMARYThis paper presents a new planar passive dynamic model with contact between the feet and the ground. The Hertz contact law and the approximate Coulomb friction law were introduced into this human-like model. In contrast to McGeer's passive dynamic models, contact stiffness, contact damping, and coefficients of friction were added to characterize the walking model. Through numerical simulation, stable period-one gait and period-two gait cycles were found, and the contact forces were derived from the results. After investigating the effects of the contact parameters on walking gaits, we found that changes in contact stiffness led to changes in the global characteristics of the walking gait, but not in contact damping. The coefficients of friction related to whether the model could walk or not. For the simulation of the routes to chaos, we found that a small contact stiffness value will lead to a delayed point of bifurcation, meaning that a less rigid surface is easier for a passive model to walk on. The effects of contact damping and friction coefficients on routes to chaos were quite small.

The Effect of Non-Uniform Aerodynamic Loading on the Blade Responses

2007 ◽  
Author(s):  
Abdelgadir M. Mahmoud ◽  
Mohd S. Leong
Keyword(s):  
Turbine Blades ◽  
Forced Response ◽  
Flow Section ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Bladed Disk ◽  
Aerodynamic Loading ◽  
Bladed Disk Assembly ◽  
Flow Generator ◽  
Inlet Flow Distortion

Turbine blades are always subjected to severe aerodynamic loading. The aerodynamic loading is uniform and Of harmonic nature. The harmonic nature depends on the rotor speed and number of nozzles (vanes counts). This harmonic loading is the main sources responsible for blade excitation. In some circumstances, the aerodynamic loading is not uniform and varies circumferentially. This paper discussed the effect of the non-uniform aerodynamic loading on the blade vibrational responses. The work involved the experimental study of forced response amplitude of model blades due to inlet flow distortion in the presence of airflow. This controlled inlet flow distortion therefore represents a nearly realistic environment involving rotating blades in the presence of airflow. A test rig was fabricated consisting of a rotating bladed disk assembly, an inlet flow section (where flow could be controlled or distorted in an incremental manner), flow conditioning module and an aerodynamic flow generator (air suction module with an intake fan) for investigations under laboratory conditions. Tests were undertaken for a combination of different air-flow velocities and blade rotational speeds. The experimental results showed that when the blades were subjected to unsteady aerodynamic loading, the responses of the blades increased and new frequencies were excited. The magnitude of the responses and the responses that corresponding to these new excited frequencies increased with the increase in the airflow velocity. Moreover, as the flow velocity increased the number of the newly excited frequency increased.

scholarly journals Thermomechanical Couplings in Aircraft Tire Rolling/Sliding Modeling

2011 ◽  
Vol 274 ◽  
pp. 81-90 ◽  
Author(s):  
Ange Kongo Kondé ◽  
Iulian Rosu ◽  
F. Lebon ◽  
L. Seguin ◽  
Olivier Brardo ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Thermal Effects ◽  
Coulomb Friction ◽  
Large Deformations ◽  
Element Model ◽  
Slip Angle ◽  
Tire Model ◽  
Vertical Load ◽  
Coulomb Friction Law ◽  
Lateral Friction

This paper presents a finite element model for the simulation of aircraft tire rolling. Large deformations, material incompressibility, heterogeneities of the material, unilateral contact with Coulomb friction law are taken into account. The numerical model will allow estimating the forces in the contact patch - even in critical and extreme conditions for the aircraft safety and security. We show the influence of loading parameters (vertical load, velocity, inflating pressure) and slip angle on the Self Aligning torque and on the lateral friction coefficient. A friction coefficient law corresponding to Chichinadze model is considered to take into account thermal effects in the aircraft tire model behaviour.

scholarly journals Dry Friction Interblade Damping by 3D FEM Modelling of Bladed Disk: HPC Calculations Compared with Experiment

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Luděk Pešek ◽  
Pavel Šnábl ◽  
Vítězslav Bula
Keyword(s):  
Finite Element Method ◽  
Dry Friction ◽  
Computational Time ◽  
Friction Contact ◽  
3D Fem ◽  
3D Finite Element ◽  
Bladed Disk ◽  
3D Finite Element Method ◽  
Good Agreement ◽  
Damping Estimation

Interblade contacts and damping evaluation of the turbine bladed wheel with prestressed dry friction contacts are solved by the 3D finite element method with the surface-to-surface dry friction contact model. This makes it possible to model the space relative motions of contact pairs that occur during blade vibrations. To experimentally validate the model, a physical model of the bladed wheel with tie-boss couplings was built and tested. HPC computation with a proposed strategy was used to lower the computational time of the nonlinear solution of the wheel resonant attenuation used for damping estimation. Comparison of experimental and numerical results of damping estimation yields a very good agreement.

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