Eddy Current Damping: A Concept Study for Steam Turbine Blading

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Jacob Laborenz ◽  
Christian Siewert ◽  
Lars Panning ◽  
Jörg Wallaschek ◽  
Christoph Gerber ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Eddy Current ◽  
Theoretical Models ◽  
Forced Response ◽  
Resonance Frequencies ◽  
Different Types ◽  
Stationary Test ◽  
Eddy Current Damping ◽  
Fatigue Failures ◽  
Turbine Blading

In gas and steam turbine applications a common approach to prevent the blades from high cycle fatigue failures due to high vibration amplitudes is the usage of friction damping elements. Besides the intended amplitude reduction this procedure also features some possibly unwanted side effects like a shift in resonance frequencies due to stiffening effects caused by the contact. Thus, as an alternative an eddy current based noncontacting damping concept for the application in turbomachinery is investigated. In this paper two different types of eddy current dampers are considered. Theoretical models for both are established by applying electromagnetic-mechanical theory. The theoretical models are compared with forced response measurements that are performed at a stationary test rig.

Eddy Current Damping: A Concept Study for Steam Turbine Blading

2009 ◽  
Author(s):  
Jacob Laborenz ◽  
Christian Siewert ◽  
Lars Panning ◽  
Jo¨rg Wallaschek ◽  
Christoph Gerber ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Eddy Current ◽  
Theoretical Models ◽  
Forced Response ◽  
Resonance Frequencies ◽  
Different Types ◽  
Stationary Test ◽  
Eddy Current Damping ◽  
Fatigue Failures ◽  
Turbine Blading

In gas and steam turbine applications a common approach to prevent the blades from high cycle fatigue failures due to high vibration amplitudes is the usage of friction damping elements. Besides the intended amplitude reduction this procedure also features some possibly unwanted side effects like a shift in resonance frequencies due to stiffening effects caused by the contact. Thus, as an alternative an eddy current based non-contacting damping concept for the application in turbo machinery is investigated. In this paper two different types of eddy current dampers are considered. Theoretical models for both are established by applying electromagnetic-mechanical theory. The theoretical models are compared to forced response measurements that are performed at a stationary test rig.

Long Arc Shrouding—A Reliability Improvement for Untuned Steam Turbine Blading

1981 ◽  
Vol 103 (3) ◽  
pp. 522-527 ◽  
Author(s):  
R. J. Ortolano ◽  
J. A. La Rosa ◽  
W. P. Welch
Keyword(s):  
Steam Turbine ◽  
Arc Length ◽  
Variable Speed ◽  
Butt Welding ◽  
Reliability Improvement ◽  
Fatigue Failures ◽  
Short Arc ◽  
Turbine Blading ◽  
Turbine Exhaust

An approach to the design and modification of untuned variable speed steam turbine exhaust blading has been found to be highly successful in eliminating fatigue failures due to the first tangential in-phase mode resonance. The approach consists of butt-welding the shrouds on the short arc blade groups to form a substantially longer arc length. The result is a significant reduction in vibratory stress at resonant speeds. Because of the ease with which the approach can be implemented in the field, backfitting is highly attractive to turbine operators. Availability benefits to the marine, utility, petrochemical, refining, industrial and commercial fields are anticipated.

Eddy Current Damper for Turbine Blading: Electromagnetic Finite Element Analysis and Measurement Results

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Jacob Laborenz ◽  
Malte Krack ◽  
Lars Panning ◽  
Jörg Wallaschek ◽  
Markus Denk ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Eddy Current ◽  
Dynamic Performance ◽  
Forced Response ◽  
Element Analysis ◽  
Transient Electromagnetic ◽  
Eddy Current Damper ◽  
Mechanical Damping ◽  
Turbine Blading

In the dynamics of turbomachinery, the mechanical damping of the blading has been the focus of research for the last decades to improve the dynamic performance in terms of high cycle fatigue issues. In addition, an increased mechanical damping can produce a higher flutter safety margin such that stable operation conditions are achievable in a bigger range. Hence, novel damping techniques are considered besides the well known friction based damping devices. In this paper, an extended analysis of the eddy current based damping device for a last stage steam turbine blading presented in GT2009-59593 is conducted. A transient electromagnetic finite element analysis of the eddy current damper is performed, and the resulting damping forces are compared to their analytical solution. Parameter studies are carried out, and equivalent damping factors are calculated. Furthermore, for the validation of the finite element model, a test rig was built that allows for the direct measurement of damping forces when forcing a sinusoidal relative motion. Forced response measurements and simulations are used to demonstrate its dynamic performance and predictability.

Multiharmonic Forced Response Analysis of a Turbine Blading Coupled by Nonlinear Contact Forces

2009 ◽  
Author(s):  
Christian Siewert ◽  
Lars Panning ◽  
Jo¨rg Wallaschek ◽  
Christoph Richter
Keyword(s):  
Frequency Domain ◽  
Steam Turbine ◽  
Equations Of Motion ◽  
Forced Vibrations ◽  
Forced Response ◽  
Contact Forces ◽  
Dynamic Loads ◽  
Turbine Stage ◽  
Nonlinear Equations Of Motion ◽  
Turbine Blading

The rotor blades of a low pressure (LP) steam turbine stage are subjected to high static and dynamic loads during operation. The static loads are mainly due to the centrifugal force and thermal strains, whereas the dynamic loads are caused by fluctuating gas forces resulting in forced vibrations of the blades. The forced vibrations can lead to high cycle fatigue (HCF) failures causing substantial damage and high maintenance effort. Thus, one of the main tasks in the design of LP steam turbine blading is the vibration amplitude reduction in order to avoid high dynamic stresses that could damage the blading. The vibration amplitudes of the blades in a LP steam turbine stage can be reduced significantly to a reasonable amount if adjacent blades are coupled by shroud contacts that reinforce the blading, see Fig. 1. Furthermore, in the case of blade vibrations, relative displacements between neighboring blades occur in the contacts and friction forces are generated that provide additional damping to the structure due to the energy dissipation caused by micro- and macroslip effects. Therefore, the coupling of the blades increases the overall mechanical damping. A three-dimensional structural dynamics model including an appropriate spatial contact model is necessary to predict the contact forces generated by the shroud contacts and to describe the vibrational behavior of the blading with sufficient accuracy. To compute the nonlinear forced vibrations of the coupled blading, the nonlinear equations of motion are solved in the frequency domain owing to the high computational efficiency of this approach. The transformation of the nonlinear equations of motion into the frequency domain can be carried out by representing the steady-state displacement in terms of its harmonic components. After that transformation, the nonlinear forced response is computed as a function of the excitation frequency in the frequency domain.

Eddy Current Damper for Turbine Blading: Electromagnetic Finite Element Analysis and Measurement Results

2011 ◽  
Author(s):  
Jacob Laborenz ◽  
Malte Krack ◽  
Lars Panning ◽  
Jo¨rg Wallaschek ◽  
Markus Denk ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Eddy Current ◽  
Dynamic Performance ◽  
Forced Response ◽  
Element Analysis ◽  
Transient Electromagnetic ◽  
Eddy Current Damper ◽  
Mechanical Damping ◽  
Turbine Blading

In the dynamics of turbomachinery the mechanical damping of the blading is in the focus of research for the last decades to improve the dynamic performance in terms of high cycle fatigue issues. Besides that an increased mechanical damping can produce a higher flutter safety margin such that stable operation conditions are achievable in a bigger range. Hence, novel damping techniques are considered besides the well known friction based damping devices. In this paper an extended analysis of the eddy current based damping device for a last stage steam turbine blading presented in GT2009-59593 is conducted. A transient electromagnetic finite element analysis of the eddy current damper is performed and the resulting damping forces are compared to their analytical solution. Parameter studies are carried out and equivalent damping factors are calculated. Furthermore, for the validation of the finite element model a test rig was built which allows for the direct measurement of damping forces when forcing a sinusoidal relative motion. Forced response measurements and simulations are used to demonstrate its dynamic performance and predictability.

Prediction of High Cycle Fatigue Life of Steam Turbine Blading Based on Unsteady CFD and FEM Forced Response Calculation

2007 ◽  
Author(s):  
Tomas Misek ◽  
Antonin Tetiva ◽  
Lubos Prchlik ◽  
Karel Duchek
Keyword(s):  
Fatigue Life ◽  
Steam Turbine ◽  
High Cycle Fatigue ◽  
Forced Response ◽  
Life Assessment ◽  
Scale Model ◽  
Cycle Fatigue ◽  
Blade Root ◽  
Resonance Frequencies ◽  
Root Attachment

This paper presents the high cycle fatigue life prediction of a shrouded packet blade row for a large high pressure steam turbine. The fatigue life assessment was based on a loosely coupled CFD and FEM calculations supported by the direct cyclic mechanical testing of a full scale model of the blade root attachment. In the first stage, potentially dangerous vibration modes were identified from the linear finite element analyses and verified by testing. Aerodynamic forces acting on rotating blades were obtained from an unsteady sliding mesh CFD calculation based on a viscous unsteady compressible turbulent flow. A forced vibration analysis was then performed for critical resonance frequencies close to nozzle passing frequency considering only the inherent material damping. The calculated alternating stress in the blade root attachment was used to estimate the safety against the high cycle fatigue failure. Fatigue life was evaluated for current and new design of stationary vanes. In the new design the number of vanes was increased and their full 3D shape was optimized. Both changes reduced the excitation forces by more then an order of magnitude. The final evaluation showed that the vibratory stresses for the new design were well below the actual fatigue limit of the blade root attachment.

Impact of Mistuning on the Vibration Behaviour of the Last Stage in a Model Three Stage Low Pressure Steam Turbine

2011 ◽  
Author(s):  
Christoph Heinz ◽  
Markus Schatz ◽  
Michael V. Casey ◽  
Heinrich Stu¨er
Keyword(s):  
Steam Turbine ◽  
Amplitude Distribution ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Scale Model ◽  
Resonance Frequencies ◽  
Pressure Steam ◽  
Last Stage ◽  
Operating Points

The last stages of a low-pressure steam turbine, with long freestanding blades, may experience forced response excitation during resonance crossing at start-up and shut-down and this can be responsible for blade failure. This paper presents an experimental investigation of the circumferential blade amplitude distribution at different operating conditions and for different mistuning configurations in a scale model of a state-of-the-art low pressure steam turbine. Five configurations are investigated; two with different intentionally mistuned frequency arrangements, where the blades are placed alternately in different high-low configurations and three randomly mistuned systems. For the randomly mistuned systems the standard deviation of the resonance frequencies of the last stage blades is varied. The maximum blade amplitude and the circumferential blade amplitude distribution of each mistuning configuration are compared at different operating points and at a repeatable rotational speed gradient. The behaviour of the blade amplitude distribution at different operating conditions shows that the vibration levels depend on both the mistuning configuration and the operating points.

scholarly journals Topological Network Properties of Fractal-Like Metallic Nanoparticle Patterns and Their Effects on Optical Resonances

2018 ◽  
Vol 8 (8) ◽  
pp. 1310
Author(s):  
Naoya Kihara ◽  
Osamu Sakai
Keyword(s):  
Unit Length ◽  
Theoretical Models ◽  
Topological Properties ◽  
Metallic Nanoparticle ◽  
Diffusion Limited Aggregation ◽  
Complex Network Theory ◽  
Geometrical Properties ◽  
Optical Resonances ◽  
Resonance Frequencies ◽  
Network Topologies

Fractal-like nanoparticle two-dimensional patterns forming in diffusion-limited aggregation show variant spatial patterns. However, they have invariant statistical properties in their network topologies, even though their formation is completely in self-assembled processes. One of the outputs from these topological properties is optical resonances at invariant frequencies, which is a required feature of a metamaterial alternative. Fractal-like metallic patterns studied here in both experiments and theoretical models exhibit similar resonance frequencies in the infrared-ray range, and they depend on the unit length of nanoparticles composing arbitrary fractal-like structures. The scheme of analysis applied here using complex network theory does not only reveal the topological properties of the nanoparticle network, but points out their optical and possibly other physical potentials arising from their geometrical properties.

Forced Response Variation of Aerodynamically and Structurally Mistuned Turbo-Machinery Rotors

2006 ◽  
Author(s):  
I. Sladojevic´ ◽  
E. P. Petrov ◽  
M. Imregun ◽  
A. I. Sayma
Keyword(s):  
Three Dimensional ◽  
Forced Response ◽  
Navier Stokes ◽  
Fe Model ◽  
Frequency Shifts ◽  
Aero Engine ◽  
Different Types ◽  
Aerodynamic Parameters ◽  
Reynolds Averaged Navier Stokes ◽  
Response Variation

The paper presents the results of a study looking into changes in the forced response levels of bladed disc assemblies subject to both structural and aerodynamic mistuning. A whole annulus FE model, representative of a civil aero-engine fan with 26 blades was used in the calculations. The forced response of all blades of 1000 random mistuned patterns was calculated. The aerodynamic parameters, frequency shifts and damping, were calculated using a three-dimensional Reynolds-averaged Navier-Stokes aero-elasticity code. They were randomly varied for each mistuning pattern, with the assumption that the system would remain stable, i.e. flutter would not occur due to aerodynamic mistuning. The results show the variation of the forced response with different types of mistuning, with structural mistuning only, with aerodynamic mistuning only and with both structural and aerodynamic mistuning.

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